Author name code: benz ADS astronomy entries on 2022-09-14 author:"Benz, Arnold O." ------------------------------------------------------------------------ Title: Peculiar Radio-X-Ray Relationship in Active Stars Authors: Vedantham, H. K.; Callingham, J. R.; Shimwell, T. W.; Benz, A. O.; Hajduk, M.; Ray, T. P.; Tasse, C.; Drabent, A. Bibcode: 2022ApJ...926L..30V Altcode: 2022arXiv220112203V The empirical relationship between the nonthermal 5 GHz radio luminosity and the soft X-ray luminosity of active stellar coronae, canonically called the Güdel-Benz relationship, has been a cornerstone of stellar radio astronomy, as it explicitly ties the radio emission to the coronal heating mechanisms. The relationship extends from microflares on the Sun to the coronae of the most active stars suggesting that active coronae are heated by a flare-like process. The relationship is thought to originate from a consistent partition of the available flare energy into relativistic charges, which emit in the radio-band via the incoherent gyrosynchrotron mechanism, and heating of the bulk coronal plasma, which emits in the X-ray band via the Bremsstrahlung mechanism. Consequently, coherent emission from stellar and substellar objects is not expected to adhere to this empirical relationship, as it is observed in ultracool dwarf stars and brown dwarfs. Here we report a population of radio-detected chromospherically active stars that surprisingly follow the Güdel-Benz relationship despite their radio emission being classified as coherent emission by virtue of its high circularly polarized fraction and high brightness temperature. Our results prompt a reexamination of the physics behind the Güdel-Benz relationship, its implication for the mechanism of coronal heating and particle acceleration in active stars, and the phenomenological connection between solar and stellar flares. Title: STIX X-ray microflare observations during the Solar Orbiter commissioning phase Authors: Battaglia, Andrea Francesco; Saqri, Jonas; Massa, Paolo; Perracchione, Emma; Dickson, Ewan C. M.; Xiao, Hualin; Veronig, Astrid M.; Warmuth, Alexander; Battaglia, Marina; Hurford, Gordon J.; Meuris, Aline; Limousin, Olivier; Etesi, László; Maloney, Shane A.; Schwartz, Richard A.; Kuhar, Matej; Schuller, Frederic; Senthamizh Pavai, Valliappan; Musset, Sophie; Ryan, Daniel F.; Kleint, Lucia; Piana, Michele; Massone, Anna Maria; Benvenuto, Federico; Sylwester, Janusz; Litwicka, Michalina; Stȩślicki, Marek; Mrozek, Tomasz; Vilmer, Nicole; Fárník, František; Kašparová, Jana; Mann, Gottfried; Gallagher, Peter T.; Dennis, Brian R.; Csillaghy, André; Benz, Arnold O.; Krucker, Säm Bibcode: 2021A&A...656A...4B Altcode: 2021arXiv210610058B Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is the hard X-ray instrument onboard Solar Orbiter designed to observe solar flares over a broad range of flare sizes.
Aims: We report the first STIX observations of solar microflares recorded during the instrument commissioning phase in order to investigate the STIX performance at its detection limit.
Methods: STIX uses hard X-ray imaging spectroscopy in the range between 4-150 keV to diagnose the hottest flare plasma and related nonthermal electrons. This first result paper focuses on the temporal and spectral evolution of STIX microflares occuring in the Active Region (AR) AR12765 in June 2020, and compares the STIX measurements with Earth-orbiting observatories such as the X-ray Sensor of the Geostationary Operational Environmental Satellite (GOES/XRS), the Atmospheric Imaging Assembly of the Solar Dynamics Observatory, and the X-ray Telescope of the Hinode mission.
Results: For the observed microflares of the GOES A and B class, the STIX peak time at lowest energies is located in the impulsive phase of the flares, well before the GOES peak time. Such a behavior can either be explained by the higher sensitivity of STIX to higher temperatures compared to GOES, or due to the existence of a nonthermal component reaching down to low energies. The interpretation is inconclusive due to limited counting statistics for all but the largest flare in our sample. For this largest flare, the low-energy peak time is clearly due to thermal emission, and the nonthermal component seen at higher energies occurs even earlier. This suggests that the classic thermal explanation might also be favored for the majority of the smaller flares. In combination with EUV and soft X-ray observations, STIX corroborates earlier findings that an isothermal assumption is of limited validity. Future diagnostic efforts should focus on multi-wavelength studies to derive differential emission measure distributions over a wide range of temperatures to accurately describe the energetics of solar flares.
Conclusions: Commissioning observations confirm that STIX is working as designed. As a rule of thumb, STIX detects flares as small as the GOES A class. For flares above the GOES B class, detailed spectral and imaging analyses can be performed. Title: Ion Acceleration and the Development of a Power-law Energy Spectrum in Magnetic Reconnection Authors: Che, H.; Zank, G. P.; Benz, A. O. Bibcode: 2021ApJ...921..135C Altcode: How charged particles are accelerated efficiently and form a power-law energy spectrum in magnetic reconnection is a problem that is not well understood. In a previous paper, it was shown that the electron Kelvin-Helmholtz instability (EKHI) in force-free magnetic reconnection generates fast-expanding vortices that can accelerate electrons in a few tens of ion gyroperiods (less than 1 ms in the solar corona) to form a power-law energy distribution. In this paper, we present a particle-in-cell (PIC) simulation study of ion acceleration in force-free magnetic reconnection in the presence of the EKHI-induced turbulence. We find that ions are not significantly accelerated by the EKHI-induced stochastic electric field until the magnetic vortices expand to sizes comparable to the ion gyroradius. The Alfvén waves generated by the EKHI couple with the magnetic vortices, leading to resonance between the ions inside the magnetic vortices and Alfvén waves and enhanced ion heating. The induced Alfvén wave resonance results in a broken power-law energy spectrum with a breakpoint at $\sim {m}_{i}{v}_{A}^{2}$ , where vA is the Alfvén velocity. We show that the process that forms the nonthermal tail is a second-order Fermi mechanism and the mean spectral index is α = (1 + 4a2D/R)/2, where D is the spatial scale of the inductive electric field, R is that of vortices, and a = Bg/B0, with ratio of guide field Bg and asymptotic B0. Title: ALMA small-scale features in the quiet Sun and active regions Authors: Brajša, R.; Skokić, I.; Sudar, D.; Benz, A. O.; Krucker, S.; Ludwig, H. -G.; Saar, S. H.; Selhorst, C. L. Bibcode: 2021A&A...651A...6B Altcode: 2021arXiv210503644B
Aims: The main aim of the present analysis is to decipher (i) the small-scale bright features in solar images of the quiet Sun and active regions obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and (ii) the ALMA correspondence of various known chromospheric structures visible in the Hα images of the Sun.
Methods: Small-scale ALMA bright features in the quiet Sun region were analyzed using single-dish ALMA observations (1.21 mm, 248 GHz) and in an active region using interferometric ALMA measurements (3 mm, 100 GHz). With the single-dish observations, a full-disk solar image is produced, while interferometric measurements enable the high-resolution reconstruction of part of the solar disk, including the active region. The selected quiet Sun and active regions are compared with the Hα (core and wing sum), EUV, and soft X-ray images and with the magnetograms.
Results: In the quiet Sun region, enhanced emission seen in the ALMA is almost always associated with a strong line-of-sight magnetic field. Four coronal bright points were identified, while other small-scale ALMA bright features are most likely associated with magnetic network elements and plages. In the active region, in 14 small-scale ALMA bright features randomly selected and compared with other images, we found five good candidates for coronal bright points, two for plages, and five for fibrils. Two unclear cases remain: a fibril or a jet, and a coronal bright point or a plage. A comparison of the Hα core image and the 3 mm ALMA image of the analyzed active region showed that the sunspot appears dark in both images (with a local ALMA radiation enhancement in sunspot umbra), the four plage areas are bright in both images and dark small Hα filaments are clearly recognized as dark structures of the same shape also in ALMA. Title: Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy Authors: van Dishoeck, E. F.; Kristensen, L. E.; Mottram, J. C.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.; Baudry, A.; Benedettini, M.; Bjerkeli, P.; Blake, G. A.; Braine, J.; Bruderer, S.; Cabrit, S.; Cernicharo, J.; Choi, Y.; Coutens, A.; de Graauw, Th.; Dominik, C.; Fedele, D.; Fich, M.; Fuente, A.; Furuya, K.; Goicoechea, J. R.; Harsono, D.; Helmich, F. P.; Herczeg, G. J.; Jacq, T.; Karska, A.; Kaufman, M.; Keto, E.; Lamberts, T.; Larsson, B.; Leurini, S.; Lis, D. C.; Melnick, G.; Neufeld, D.; Pagani, L.; Persson, M.; Shipman, R.; Taquet, V.; van Kempen, T. A.; Walsh, C.; Wampfler, S. F.; Yıldız, U.; WISH Team Bibcode: 2021A&A...648A..24V Altcode: 2021arXiv210202225V Context. Water is a key molecule in the physics and chemistry of star and planet formation, but it is difficult to observe from Earth. The Herschel Space Observatory provided unprecedented sensitivity as well as spatial and spectral resolution to study water. The Water In Star-forming regions with Herschel (WISH) key program was designed to observe water in a wide range of environments and provide a legacy data set to address its physics and chemistry.
Aims: The aim of WISH is to determine which physical components are traced by the gas-phase water lines observed with Herschel and to quantify the excitation conditions and water abundances in each of these components. This then provides insight into how and where the bulk of the water is formed in space and how it is transported from clouds to disks, and ultimately comets and planets.
Methods: Data and results from WISH are summarized together with those from related open time programs. WISH targeted ~80 sources along the two axes of luminosity and evolutionary stage: from low- to high-mass protostars (luminosities from <1 to > 105 L⊙) and from pre-stellar cores to protoplanetary disks. Lines of H2O and its isotopologs, HDO, OH, CO, and [O I], were observed with the HIFI and PACS instruments, complemented by other chemically-related molecules that are probes of ultraviolet, X-ray, or grain chemistry. The analysis consists of coupling the physical structure of the sources with simple chemical networks and using non-LTE radiative transfer calculations to directly compare models and observations.
Results: Most of the far-infrared water emission observed with Herschel in star-forming regions originates from warm outflowing and shocked gas at a high density and temperature (> 105 cm−3, 300-1000 K, v ~ 25 km s−1), heated by kinetic energy dissipation. This gas is not probed by single-dish low-J CO lines, but only by CO lines with Jup > 14. The emission is compact, with at least two different types of velocity components seen. Water is a significant, but not dominant, coolant of warm gas in the earliest protostellar stages. The warm gas water abundance is universally low: orders of magnitude below the H2O/H2 abundance of 4 × 10−4 expected if all volatile oxygen is locked in water. In cold pre-stellar cores and outer protostellar envelopes, the water abundance structure is uniquely probed on scales much smaller than the beam through velocity-resolved line profiles. The inferred gaseous water abundance decreases with depth into the cloud with an enhanced layer at the edge due to photodesorption of water ice. All of these conclusions hold irrespective of protostellar luminosity. For low-mass protostars, a constant gaseous HDO/H2O ratio of ~0.025 with position into the cold envelope is found. This value is representative of the outermost photodesorbed ice layers and cold gas-phase chemistry, and much higher than that of bulk ice. In contrast, the gas-phase NH3 abundance stays constant as a function of position in low-mass pre- and protostellar cores. Water abundances in the inner hot cores are high, but with variations from 5 × 10−6 to a few × 10−4 for low- and high-mass sources. Water vapor emission from both young and mature disks is weak.
Conclusions: The main chemical pathways of water at each of the star-formation stages have been identified and quantified. Low warm water abundances can be explained with shock models that include UV radiation to dissociate water and modify the shock structure. UV fields up to 102−103 times the general interstellar radiation field are inferred in the outflow cavity walls on scales of the Herschel beam from various hydrides. Both high temperature chemistry and ice sputtering contribute to the gaseous water abundance at low velocities, with only gas-phase (re-)formation producing water at high velocities. Combined analyses of water gas and ice show that up to 50% of the oxygen budget may be missing. In cold clouds, an elegant solution is that this apparently missing oxygen is locked up in larger μm-sized grains that do not contribute to infrared ice absorption. The fact that even warm outflows and hot cores do not show H2O at full oxygen abundance points to an unidentified refractory component, which is also found in diffuse clouds. The weak water vapor emission from disks indicates that water ice is locked up in larger pebbles early on in the embedded Class I stage and that these pebbles have settled and drifted inward by the Class II stage. Water is transported from clouds to disks mostly as ice, with no evidence for strong accretion shocks. Even at abundances that are somewhat lower than expected, many oceans of water are likely present in planet-forming regions. Based on the lessons for galactic protostars, the low-J H2O line emission (Eup < 300 K) observed in extragalactic sources is inferred to be predominantly collisionally excited and to originate mostly from compact regions of current star formation activity. Recommendations for future mid- to far-infrared missions are made. Title: The Formation of Electron Outflow Jets with Power-law Energy Distribution in Guide-field Magnetic Reconnection Authors: Che, H.; Zank, G. P.; Benz, A. O.; Tang, B.; Crawford, C. Bibcode: 2021ApJ...908...72C Altcode: Observationally, electron beams with power-law energy spectra are commonly associated with solar flares. Previous studies have found that during magnetic reconnection with a guide field Bg larger than 0.1 times the asymptotic field B0, electron beams are unable to develop due to the strong deflection caused by the guide field. Using particle-in-cell simulations we show that in force-free reconnection, the development of an electron Kelvin-Helmholz instability can suppress the Hall effect and produce a flute-like outflow exhaust, in which both electrons and ions are nearly frozen-in with the magnetic field. The coupling of a continuously growing electron velocity shear and E × B drift drive the electrons out of magnetic vortices and results in collimated jets with a power-law energy spectrum in the elongated exhaust. The spatial density of electron jets is comparable to the background and is highly inhomogeneous, signifying on asymmetric density structure in guide field reconnection. Title: Electron Acceleration and the Development of Power-Law Energy Spectra in Magnetic Reconnection with A Force-free Current Sheet Authors: Che, Haihong; Benz, Arnold; Tang, Bofeng; Crawford, Chris Bibcode: 2021APS..GECM13007C Altcode: Extensive observations have discovered that a huge number of energetic electrons with energy up to MeV (~0.9c and Lorentz factor ~2) are produced during solar flares. These very mild relativistic energetic electrons demonstrate two-stage power-law spectral evolutions. What mechanism efficiently accelerates non-relativistic particles to a power-law has been a long-standing `` injection problem'' in particle acceleration theory since Fermi first proposed his famous Fermi-acceleration model in 1949. In this talk, I will discuss why particle acceleration in solar flares is an ``injection problem'' and what problems are with the previous and current widely invoked models. I will present a new acceleration mechanism in magnetic reconnection. I will show how the velocity shear stored naturally in force-free currents drives an electron Kevin-helmholtz instability (EKHI) during magnetic reconnection and efficiently acceleration electrons to a power-law energy spectrum via a two-stage soft-hard-hard evolution. Finally, I will discuss the potentially broad application of this mechanism in solar physics and how the complexity of solar flares may impact the further development of this model.

NASA Heliophysics Career award No. 80NSSC19K1106NSF EPSCoR RII-Track-1 Cooperative Agreement OIA1655280NSF Grant PHY-1707247. Title: The Spectrometer/Telescope for Imaging X-rays (STIX) Authors: Krucker, Säm; Hurford, G. J.; Grimm, O.; Kögl, S.; Gröbelbauer, H. -P.; Etesi, L.; Casadei, D.; Csillaghy, A.; Benz, A. O.; Arnold, N. G.; Molendini, F.; Orleanski, P.; Schori, D.; Xiao, H.; Kuhar, M.; Hochmuth, N.; Felix, S.; Schramka, F.; Marcin, S.; Kobler, S.; Iseli, L.; Dreier, M.; Wiehl, H. J.; Kleint, L.; Battaglia, M.; Lastufka, E.; Sathiapal, H.; Lapadula, K.; Bednarzik, M.; Birrer, G.; Stutz, St.; Wild, Ch.; Marone, F.; Skup, K. R.; Cichocki, A.; Ber, K.; Rutkowski, K.; Bujwan, W.; Juchnikowski, G.; Winkler, M.; Darmetko, M.; Michalska, M.; Seweryn, K.; Białek, A.; Osica, P.; Sylwester, J.; Kowalinski, M.; Ścisłowski, D.; Siarkowski, M.; Stęślicki, M.; Mrozek, T.; Podgórski, P.; Meuris, A.; Limousin, O.; Gevin, O.; Le Mer, I.; Brun, S.; Strugarek, A.; Vilmer, N.; Musset, S.; Maksimović, M.; Fárník, F.; Kozáček, Z.; Kašparová, J.; Mann, G.; Önel, H.; Warmuth, A.; Rendtel, J.; Anderson, J.; Bauer, S.; Dionies, F.; Paschke, J.; Plüschke, D.; Woche, M.; Schuller, F.; Veronig, A. M.; Dickson, E. C. M.; Gallagher, P. T.; Maloney, S. A.; Bloomfield, D. S.; Piana, M.; Massone, A. M.; Benvenuto, F.; Massa, P.; Schwartz, R. A.; Dennis, B. R.; van Beek, H. F.; Rodríguez-Pacheco, J.; Lin, R. P. Bibcode: 2020A&A...642A..15K Altcode:
Aims: The Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter is a hard X-ray imaging spectrometer, which covers the energy range from 4 to 150 keV. STIX observes hard X-ray bremsstrahlung emissions from solar flares and therefore provides diagnostics of the hottest (⪆10 MK) flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons.
Methods: To accomplish this, STIX applies an indirect bigrid Fourier imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated CdTe detectors to provide information on angular scales from 7 to 180 arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of STIX has intrinsically low telemetry and it is therefore well-suited to the limited resources available to the Solar Orbiter payload. To further reduce the downlinked data volume, STIX data are binned on board into 32 selectable energy bins and dynamically-adjusted time bins with a typical duration of 1 s during flares.
Results: Through hard X-ray diagnostics, STIX provides critical information for understanding the acceleration of electrons at the Sun and their transport into interplanetary space and for determining the magnetic connection of Solar Orbiter back to the Sun. In this way, STIX serves to link Solar Orbiter's remote and in-situ measurements. Title: Centre-to-Limb Brightness Variations from the Atacama Large Millimeter-Submillimeter Array (ALMA) Full-Disk Solar Images Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O. Bibcode: 2019SoPh..294..163S Altcode: Science Verification (SV) data of solar observations with the Atacama Large Millimeter-submillimeter Array (ALMA) telescope have been released to the scientific community. Understanding the centre-to-limb brightness function is necessary to compare features in full-disk images. Our goals are to find the empirical centre-to-limb brightness functions in two available spectral bands and create flattened images with centre-to-limb brightness variations removed. We used a second-order polynomial fit of the cosine of incidence angle to data points as a function of radial distance to the centre of the solar disk. The method also includes iterative removal of outliers based on the inter-quartile range. Fitting functions for all available images proved to describe the data adequately with comparatively small errors in the fitting coefficients. In both bands we found brightening towards the limb, which is a consequence of the increase in electron temperature with radial distance in this region of the solar atmosphere. This study found that the brightness temperature [Tb] of an active region has about 180 K difference between estimates with and without the limb brightening at radial distance ≈0.75 R⊙ in Band 6. We also made flattened images with limb brightening removed. The limb-brightening effect in ALMA images is significant enough (of the order of 10% for Band 3 and about 15% in Band 6) that it cannot be neglected in further analyses. Since the effect of the side lobes was not included in this study, these values probably represent the lower limit of the limb brightening. The shape of the limb-brightening function can also be used to constrain electron densities and temperatures in various layers of the solar atmosphere. Title: Centre to limb brightness variations from ALMA full disk solar images Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O. Bibcode: 2019arXiv190908952S Altcode: Science Verification (SV) data of solar observations with Atacama Large Millimeter-submillimeter Array (ALMA) telescope were released to the scientific community. Understanding the centre to limb brightness function is necessary to compare features in full disk images. Our goals are to find the empirical centre to limb brightness functions in two available spectral bands and create flattened images with centre to limb brightness variations removed. We used second-order polynomial fit of the cosine of incidence angle to data points as a function of radial distance to the centre of the solar disk. The method also includes iterative removal of outliers based on the interquartile range. Fitting functions for all available images proved to adequately describe the data with comparatively small errors in the fitting coefficients. In both bands we found brightening towards the limb which is a consequence of increase in electron temperatures with radial distance in this region of the solar atmosphere. This study found that the $T_{b}$ of an active region has about 180 K difference between with and without the limb brightening at radial distance $\approx$0.75$R_{\odot}$ in Band 6. We also made flattened images with limb brightening removed. The limb brightening effect in ALMA images is significant enough (of the order of 10% for Band 3 and about 15% in Band 6) that it can not be neglected in further analyses. Since the effect of the side lobes was not included in this study, these values probably represent the lower limit of the limb brightening. The shape of the limb brightening function can also be used to constrain electron densities and temperatures in various layers of the solar atmosphere. Title: Observations of the solar chromosphere with ALMA and comparison with theoretical models Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.; Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.; Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L. Bibcode: 2018csss.confE..37B Altcode: 2018arXiv181207293B In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysisis to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere andcorona. The study has an observational and a modeling part. In the observational part full-disc solar images are analyzed.Based on a modied FAL atmospheric model, radiation models for various observed solar structures are developed. Finally, theobservational and modeling results are compared and discussed. Title: First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta, M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.; Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y. Bibcode: 2018A&A...613A..17B Altcode: 2017arXiv171106130B Context. Various solar features can be seen in emission or absorption on maps of the Sun in the millimetre and submillimetre wavelength range. The recently installed Atacama Large Millimetre/submillimetre Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA, the first important step is to compare solar ALMA maps with simultaneous images of the Sun recorded in other spectral ranges.
Aims: The first aim of the present work is to identify different structures in the solar atmosphere seen in the optical, infrared, and EUV parts of the spectrum (quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points) in a full-disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and to compare them with the corresponding quiet Sun level.
Methods: A full-disc solar image at 1.21 mm obtained on December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and compared with full-disc solar images from the same day in Hα line, in He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the calibrated ALMA image.
Results: Positions of the quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points are identified in the ALMA image. At the wavelength of 1.21 mm, active regions appear as bright areas (but sunspots are dark), while prominences on the disc and coronal holes are not discernible from the quiet Sun background, despite having slightly less intensity than surrounding quiet Sun regions. Magnetic inversion lines appear as large, elongated dark structures and coronal bright points correspond to ALMA bright points.
Conclusions: These observational results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of coronal bright points represents the most important new result. By comparing ALMA and other maps, it was found that the ALMA image was oriented properly and that the procedure of overlaying the ALMA image with other images is accurate at the 5 arcsec level. The potential of ALMA for physics of the solar chromosphere is emphasised. Title: Order out of Randomness: Self-Organization Processes in Astrophysics Authors: Aschwanden, Markus J.; Scholkmann, Felix; Béthune, William; Schmutz, Werner; Abramenko, Valentina; Cheung, Mark C. M.; Müller, Daniel; Benz, Arnold; Chernov, Guennadi; Kritsuk, Alexei G.; Scargle, Jeffrey D.; Melatos, Andrew; Wagoner, Robert V.; Trimble, Virginia; Green, William H. Bibcode: 2018SSRv..214...55A Altcode: 2017arXiv170803394A Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous " order out of randomness", during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type. Title: Erratum: Correction to: Observations of a Radio-Quiet Solar Preflare Authors: Benz, Arnold O.; Battaglia, Marina; Güdel, Manuel Bibcode: 2018SoPh..293...32B Altcode: Correction to: Solar Physhttps://doi.org/10.1007/s11207-017-1175-3 Title: A comparison of solar ALMA observations and model based predictions of the brightness temperature Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar, D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.; Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R. Bibcode: 2018CEAB...42....1B Altcode: The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in the wavelength range from 0.3 mm to 10 mm with an unprecedented spatial, temporal and spectral resolution. The first aim of the present work is to identify different structures in the solar atmosphere (quiet Sun, active regions, filaments on the disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign. It is compared with full disc solar images from the same day in the Hα line (Cerro Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm, 21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun areas, active regions, filaments on the disc, and coronal holes are identified in the ALMA image. To interpret solar observations with ALMA it is important to compare the measured and calculated intensities of various solar structures. So, the second aim of this work is to calculate the intensity (brightness temperature) for those structures (quiet Sun, active regions, filaments on the disc, and coronal holes) for a broad wavelength range (from 0.3 mm to 10 mm), closely related to that of the ALMA, and to compare the results with available ALMA observations. Thermal bremsstrahlung is the dominant radiation mechanism for explanation of the observed phenomena. A procedure for calculating the brightness temperature for a given wavelength and model atmosphere, which integrates the radiative transfer equation for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm active regions appear as bright areas, while filaments on the disc and coronal holes are not discernible from the quiet Sun background. The models generally agree with the observed results: Active regions are bright primarily due to higher densities, filaments can appear bright, dark or not at all and coronal holes cannot be easily identified. Title: Flare Observations Authors: Benz, Arnold O. Bibcode: 2017LRSP...14....2B Altcode: Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays beyond 1 GeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, SOHO, and more recently Hinode and SDO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections, electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting magnetic reconnection as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's ionosphere. Flare scenarios have slowly converged over the past decades, but every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Title: Observations of a Radio-Quiet Solar Preflare Authors: Benz, Arnold O.; Battaglia, Marina; Güdel, Manuel Bibcode: 2017SoPh..292..151B Altcode: 2017arXiv170906417B The preflare phase of the flare SOL2011-08-09T03:52 is unique in its long duration, in that it was covered by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph, and because it showed three well-developed soft X-ray (SXR) peaks. No hard X-rays (HXR) are observed in the preflare phase. Here we report that no associated radio emission at 17 GHz was found either, despite the higher sensitivity of the radio instrument. The ratio between the SXR peaks and the upper limit of the radio peaks is higher by more than one order of magnitude than the ratio in regular flares. The result suggests that the ratio between acceleration and heating in the preflare phase was different than in regular flares. Acceleration to relativistic energies, if any, occurred with lower efficiency. Title: Identification of features in solar ALMA images and comparison with solar atmospheric models Authors: Skokić, I.; Brajša, R.; Sudar, D.; Kuhar, M.; Benz, A. O. Bibcode: 2017simi.conf..121S Altcode: Various solar features were identified in the full-disc single-dish ALMA images taken at wavelength of 1.2 and 2.8 mm and compared with Hα, Ca II K and EUV images and magnetograms. Assuming thermal bremsstrahlung as the dominant radiation mechanism, several models were constructed to calculate the brightness temperature of various solar features (quiet and active solar regions, filaments and coronal holes) in a wavelength range from 0.3 to 10 mm. It is found that model predictions are in a qualitative agreement with ALMA images where active regions appear brighter, while filaments and coronal holes are not discernible from the quiet Sun level. It is also found that in ALMA images regions around magnetic neutral lines appear darker than the quiet Sun. Models predict a critical frequency below which filaments should appear in absorption and above it in emission. Title: A comparison of solar ALMA maps with solar images obtained at other wavelengths Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold; Kuhar, Matej; White, Stephen M. Bibcode: 2017SPD....4820403B Altcode: We use recently released Commissioning and Science Verification data of the Sun from the observing campaigns perfomed with the ALMA radio telescope in December 2014 and in December 2015. The dataset consists of calibrated maps of the Sun recorded in ALMA observing band 3 (corresponding to a wavelength of 3 mm) and band 6 (1.2 mm) which show both bright and dark areas and a background of highly structured pattern. Solar ALMA maps are compared with images in EUV (SDO/AIA), H-alpha (NISP, Cerro Tololo) and He 1083 nm (NSO/SOLIS), as well as with magnetograms (SDO/HMI) recorded at times closest to the ALMA observations. With a special software the images are overlapped and a correspondence of identified structures is checked in both ways. The visibility of active regions, sunspots, inversion lines of global magnetic field, prominences on the disc, coronal holes and coronal bright points is investigated in ALMA images at mm wavelengths. Single-dish ALMA images of the Sun reveal large-scale structures in the solar atmosphere, while high resolution interferometric images are used to analyse the fine-scale chromospheric structure. The intensities (the brightness temperatures) of identified structures were determined and compared with selected model-based predictions. Title: Hydride Ions, HCO+ and Ionizing Irradiation in Star Forming Region Authors: Benz, Arnold O.; Bruderer, Simon; van Dishoeck, Ewine Bibcode: 2016AAS...22830803B Altcode: Hydrides are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides, such as CH+ and OH+ and also HCO+ affect the chemistry of molecules such as water. They also provide complementary information on irradiation by far UV (FUV) or X-rays and gas temperature.We explore hydrides of the most abundant heavier elements in an observational survey covering star forming regions with different mass and evolutionary state. Twelve YSOs were observed with HIFI on Herschel in 6 spectral settings providing fully velocity-resolved line profiles. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 Ls to 2 105 Ls.The targeted lines of CH+, OH+, H2O+, and C+ are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. For the low-mass YSOs the column density ratios of CH+/OH+ can be reproduced by simple chemical models implying an FUV flux of 2 - 400 times the ISRF at the location of the molecules. In two high-mass objects, the UV flux is 20 - 200 times the ISRF derived from absorption lines, and 300 - 600 ISRF using emission lines. Upper limits for the X-ray luminosity can be derived from H3O+ observations for some low-mass objects.If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 Ls, is required. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.The ion molecules are proposed to form in FUV irradiated cavity walls that are shocked by the disk wind. The shock region is turbulent, broadening the lines to some 1 - 12 km/s. It is driven by the outward motion of the wind to blue shifts of 0 to -10 km/s. The blue-shifted H2O emission line (Kristensen et al. 2013) may be related but not coincident with the CH+ and OH+ emitting region. Title: Water in star-forming regions with Herschel (WISH). VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass young stellar objects Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Melchior, M.; Wampfler, S. F.; van der Tak, F.; Goicoechea, J. R.; Indriolo, N.; Kristensen, L. E.; Lis, D. C.; Mottram, J. C.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Tafalla, M.; Visser, R.; Wyrowski, F. Bibcode: 2016A&A...590A.105B Altcode: 2016arXiv160308721B Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH+ and OH+ (and also HCO+), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature.
Aims: We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds.
Methods: Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L⊙ to 2 × 105 L⊙.
Results: The targeted lines of CH+, OH+, H2O+, C+, and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH+, and HCO+. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high-mass objects, the UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600 ISRF using emission lines. Upper limits for the X-ray luminosity can be derived from H3O+ observations for some low-mass objects.
Conclusions: If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 L⊙, is required. There is no molecular evidence for X-ray induced chemistry in the low-mass objects on the observed scales of a few 1000 AU. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.

Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA. Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: ALMA Observations of the Sun in Cycle 4 and Beyond Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.; Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.; Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson, M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.; Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov, V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões, P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig, A.; White, S.; Yagoubov, P.; Zaqarashvili, T. Bibcode: 2016arXiv160100587W Altcode: This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that a large number of scientifically highly interesting observations could be made already with the still limited solar observing modes foreseen for Cycle 4 and that ALMA has the potential to make important contributions to answering long-standing scientific questions in solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and the Commissioning and Science Verification campaign in December 2015 in sight, several of the SSALMON Expert Teams composed strategic documents in which they outlined potential solar observations that could be feasible given the anticipated technical capabilities in Cycle 4. These documents have been combined and supplemented with an analysis, resulting in recommendations for solar observing with ALMA in Cycle 4. In addition, the detailed science cases also demonstrate the scientific priorities of the solar physics community and which capabilities are wanted for the next observing cycles. The work on this White Paper effort was coordinated in close cooperation with the two international solar ALMA development studies led by T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be further updated until the beginning of Cycle 4 in October 2016. In particular, we plan to adjust the technical capabilities of the solar observing modes once finally decided and to further demonstrate the feasibility and scientific potential of the included science cases by means of numerical simulations of the solar atmosphere and corresponding simulated ALMA observations. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu, B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.; Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.; Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier, A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M. Bibcode: 2015AdSpR..56.2679W Altcode: 2015arXiv150205601W The Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) was initiated in 2014 in connection with two ALMA development studies. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new tool, which can also observe the Sun at high spatial, temporal, and spectral resolution. The international SSALMONetwork aims at co-ordinating the further development of solar observing modes for ALMA and at promoting scientific opportunities for solar physics with particular focus on numerical simulations, which can provide important constraints for the observing modes and can aid the interpretation of future observations. The radiation detected by ALMA originates mostly in the solar chromosphere - a complex and dynamic layer between the photosphere and corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Potential targets include active regions, prominences, quiet Sun regions, flares. Here, we give a brief overview over the network and potential science cases for future solar observations with ALMA. Title: Signatures of Accelerated Electrons in Solar and Stellar Flares Authors: Benz, Arnold O. Bibcode: 2015IAUGA..2254709B Altcode: Flares energize electrons (and ions) to supra-thermal energies. In most cases the final distribution in momentum or energy space is non-Maxwellian. The non-thermal part of the energy can be the source for various emissions, including hard X-rays, synchrotron radiation and coherent radio emission. Such non-thermal emissions may contain information on the acceleration process. Several acceleration scenarios have been proposed: electric DC field, stochastic, and shock acceleration. There is observational evidence for all three scenarios. The new data come from SDO, X-ray (RHESSI), radio observations (Nobeyama, VLA and e-Callisto). Solar energetic particles are an additional channel of information.Tiny solar microflares and huge stellar flares in binary systems (RS CVns) and dMe dwarfs differ by more than 10 orders of magnitude in released energy. Yet the relation between peak luminosity in thermal (soft) X-ray and non-thermal synchrotron (radio) emission is surprisingly constant. This observational fact indicates that flare acceleration scales with energy release over a large range. Electron acceleration in flares seems to be a universal process. The constraint on simultaneous thermal X-rays and non-thermal (radio) synchrotron emission seems to select on particular kind of flare. In this subset, there seems to be only one type of acceleration.Yet, small deviations are noted: Small solar flares are softer in hard X-rays. Solar nanoflares are relatively weak in synchrotron emission. The recently noted case of radio-poor preflares will also be presented. The deviations suggest that the acceleration is less efficient in small flares and in the early phase of flares. Larger deviations are reported occasionally for solar flares and more often from stellar flares, where either thermal or non-thermal emission seems to be missing completely.The location of the acceleration in solar flares remains disputed. Observations suggesting acceleration in the soft X-ray top-tops, above top-tops and near the loop footpoints are presented. Whereas reconnection is well understood in MHD, acceleration of electrons (and ions) is not. Title: Formation, Excitation and Destruction of CH+ under the Influence of Water and Irradiation in Star Forming Regions Authors: Benz, Arnold O.; Simon, Bruderer; van Dishoeck, Ewine Bibcode: 2015IAUGA..2255589B Altcode: Simple ionized hydrides were observed for the first time with Herschel/HIFI towards young star-forming objects of low to high mass. Of particular interest is CH+, a fundamental precursor molecule for carbon hydrides. Gaseous H2O reduces the abundance of C and C+, the starting products of CH+. The abundances of H2O and CH+ cannot be enhanced at the same place. Strong irradiation by FUV or X-rays reduces H2O, and CH+ gets more abundant. Thus CH+ signals high irradiation, but low H2O abundance.CH+ was observed to be enhanced in most objects to an abundance of typically 10-10 relative to hydrogen. This suggests an internal source of irradiation. The observed ratio of CH+/OH+ is consistent with irradiation by far UV as expected from chemical modelling. For low-mass objects the required FUV flux is between 1 - 200 times the ISRF at the location of the molecules. If the FUV flux originates at the central protostar, an FUV luminosity up to 1.5 Lsun is required. The UV flux in two high-mass objects is 30 and 90 times the ISRF using absorption lines, and of the order of 500 ISRF using emission lines. It is smaller than the unattenuated flux expected from the central object(s). The observed CH+/OH+ ratio, and other ratios such as OH+/H2O+ and CH+/C+, can only be modelled for low molecular hydrogen densities.The targeted lines of CH+, OH+, H2O+, and C+ are detected mostly in blue-shifted absorption. They are proposed to origin in FUV irradiated cavity walls that are shocked by the disk wind. The shock region is turbulent, broadening the lines to some 1 - 12 km/s. It is driven by the outward motion of the wind to blue shifts of 0 to -10 km/s. The blue-shifted H2O emission line (Kristensen et al. 2013) may be related but not coincident with the CH+ emitting region. Title: Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate Authors: Indriolo, Nick; Neufeld, D. A.; Gerin, M.; Schilke, P.; Benz, A. O.; Winkel, B.; Menten, K. M.; Chambers, E. T.; Black, John H.; Bruderer, S.; Falgarone, E.; Godard, B.; Goicoechea, J. R.; Gupta, H.; Lis, D. C.; Ossenkopf, V.; Persson, C. M.; Sonnentrucker, P.; van der Tak, F. F. S.; van Dishoeck, E. F.; Wolfire, Mark G.; Wyrowski, F. Bibcode: 2015ApJ...800...40I Altcode: 2014arXiv1412.1106I In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = -15.75 (ζH = 1.78 × 10-16 s-1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H_3^+ observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Water in star-forming regions with Herschel (WISH) (Corrigendum). V. The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.; Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.; Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F. Bibcode: 2015A&A...574C...3M Altcode: Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Water in star-forming regions with Herschel (WISH). V. The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.; Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.; Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F. Bibcode: 2014A&A...572A..21M Altcode: 2014arXiv1409.5704M Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow.
Aims: We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources.
Methods: We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components.
Results: Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H2 densities of order 105 - 108 cm-3 and H2O column densities of order 1016 - 1018 cm-2. H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU.
Conclusions: Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgReduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A21 Title: VizieR Online Data Catalog: H2O spectra of 29 nearby Class 0/I protostars (Mottram+, Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.; Bruderer, S.; San Jose-Garcia, I.; Karska, A.; Visser, R.; Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F. Bibcode: 2014yCat..35720021M Altcode: 2014yCat..35729021M This sample was the target of a series of observations of gas-phase water transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel between March 2010 and October 2011. Three of the Class I sources (IRAS3A, RCrA-IRS5A and HH100-IRS) were only observed in the 557GHz H2O 110-101 line, which was presented for all sources by Kristensen et al. (2012A&A...542A...8K). All other sources were observed in between four and seven H216O transitions and between one and four H218O transitions. Additional data from two OT2 programmes, OT2rvisser2 and OT2evandish4, are also included to augment the WISH data.

(2 data files). Title: Short-duration Radio Bursts with Apparent Extragalactic Dispersion Authors: Saint-Hilaire, P.; Benz, A. O.; Monstein, C. Bibcode: 2014ApJ...795...19S Altcode: 2014arXiv1402.0664S We present the results of the longest yet undertaken search for apparently extragalactic radio bursts at the Bleien Radio Observatory covering 21,000 hr (898 days). The data were searched for events of less than 50 ms FWHM duration showing a ν-2 drift in the spectrogram characteristic of the delay of radio waves in plasma. We have found five cases suggesting dispersion measures between 350 and 400 cm-3 pc while searching in the range of 75-2000 cm-3 pc. Four of the five events occurred between 10:27 and 11:24 a.m. local civil time. The only exception occurred at night with the full Moon in the beam. It was an event that poorly fits plasma dispersion, but had the characteristics of a solar Type III burst. However, we were not able to confirm that it was a lunar reflection. All events were observed with a log-periodic dipole within 6800 hr, but none with a more directional horn antenna observing the rest of the time. These properties suggest a terrestrial origin of the "peryton" type reported before. However, the cause of these events remains ambiguous. Title: Herschel HIFI Observations of O2 toward Orion: Special Conditions for Shock Enhanced Emission Authors: Chen, Jo-Hsin; Goldsmith, Paul F.; Viti, Serena; Snell, Ronald; Lis, Dariusz C.; Benz, Arnold; Bergin, Edwin; Black, John; Caselli, Paola; Encrenaz, Pierre; Falgarone, Edith; Goicoechea, Javier R.; Hjalmarson, Åke; Hollenbach, David; Kaufman, Michael; Melnick, Gary; Neufeld, David; Pagani, Laurent; van der Tak, Floris; van Dishoeck, Ewine; Yıldız, Umut A. Bibcode: 2014ApJ...793..111C Altcode: 2014arXiv1408.1962C We report observations of molecular oxygen (O2) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km s-1 with line widths ~3 km s-1 however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O2 emission is sime9'' (6 × 1016 cm) in size, and is located close to the H 2 Peak 1 position (where vibrationally excited H2 emission peaks), and not at Peak A, 23'' away. The peak O2 column density is sime1.1 × 1018 cm-2. The line velocity is close to that of the 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line of sight. The enhanced O2 abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C shock through a clump with preshock density 2 × 104 cm-3, if a reasonable flux of UV radiation is present. The postshock O2 can explain the emission from the source if its line-of-sight dimension is sime10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O2 emission has not been detected in the cores of other massive star-forming molecular clouds. Title: Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation Authors: Wang, K. -S.; Bourke, T. L.; Hogerheijde, M. R.; van der Tak, F. F. S.; Benz, A. O.; Megeath, S. T.; Wilson, T. L. Bibcode: 2013A&A...558A..69W Altcode: 2013arXiv1308.5151W Context. Two competing models describe the formation of massive stars in objects like the Orion Trapezium. In the turbulent core accretion model, the resulting stellar masses are directly related to the mass distribution of the cloud condensations. In the competitive accretion model, the gravitational potential of the protocluster captures gas from the surrounding cloud for which the individual cluster members compete.
Aims: With high resolution submillimeter observations of the structure, kinematics, and chemistry of the proto-Trapezium cluster W3 IRS5, we aim to determine which mode of star formation dominates.
Methods: We present 354 GHz Submillimeter Array observations at resolutions of 1″-3″ (1800-5400 AU) of W3 IRS5. The dust continuum traces the compact source structure and masses of the individual cores, while molecular lines of CS, SO, SO2, HCN, H2CS, HNCO, and CH3OH (and isotopologues) reveal the gas kinematics, density, and temperature.
Results: The observations show five emission peaks (SMM1-5). SMM1 and SMM2 contain massive embedded stars (~20 M⊙); SMM3-5 are starless or contain low-mass stars (<8 M⊙). The inferred densities are high, ≥107 cm-3, but the core masses are small, 0.2-0.6 M⊙. The detected molecular emission reveals four different chemical zones. Abundant (X ~ few 10-7 to 10-6) SO and SO2 are associated with SMM1 and SMM2, indicating active sulfur chemistry. A low abundance (5 × 10-8) of CH3OH concentrated on SMM3/4 suggest the presence of a hot core that is only just turning on, possibly by external feedback from SMM1/2. The gas kinematics are complex with contributions from a near pole-on outflow traced by CS, SO, and HCN; rotation in SO2, and a jet in vibrationally excited HCN.
Conclusions: The proto-Trapezium cluster W3 IRS5 is an ideal test case to discriminate between models of massive star formation. Either the massive stars accrete locally from their local cores; in this case the small core masses imply that W3 IRS5 is at the very end stages (1000 yr) of infall and accretion, or the stars are accreting from the global collapse of a massive, cluster forming core. We find that the observed masses, densities and line widths observed toward W3 IRS 5 and the surrounding cluster forming core are consistent with the competitive accretion of gas at rates of Ṁ ~ 10-4M⊙ yr-1 by the massive young forming stars. Future mapping of the gas kinematics from large to small scales will determine whether large-scale gas inflow occurs and how the cluster members compete to accrete this material. Title: Neutral and Ionized Hydrides in Star-Forming Regions. Observations with Herschel/HIFI Authors: Benz, Arnold O.; Bruderer, Simon; van Dishoeck, Ewine F.; Stäuber, Pascal; Wampfler, Susanne F. Bibcode: 2013JPCA..117.9840B Altcode: 2013arXiv1308.5556B The cosmic abundance of hydrides depends critically on high-energy UV, X-ray, and particle irradiation. Here we study hydrides in star-forming regions where irradiation by the young stellar object can be substantial, and density and temperature can be much enhanced over interstellar values. Lines of OH, CH, NH, and SH and their ions OH+, CH+, NH+, SH+, H2O+, and H3O+ were observed in star-forming regions by the HIFI spectrometer onboard the Herschel Space Observatory. Molecular column densities are derived from observed ground-state lines, models, or rotational diagrams. We report here on two prototypical high-mass regions, AFGL 2591 and W3 IRS5, and compare them to chemical calculations by making assumptions on the high-energy irradiation. A model assuming no ionizing protostellar emission is compared with (i) a model assuming strong protostellar X-ray emission and (ii) a two-dimensional (2D) model including emission in the far UV (FUV, 6-13.6 eV), irradiating the outflow walls that separate the outflowing gas and infalling envelope material. We confirm that the effect of FUV in two-dimensional models with enlarged irradiated surfaces is clearly noticeable. A molecule that is very sensitive to FUV irradiation is CH+, enhanced in abundance by more than 5 orders of magnitude. The HIFI observations of CH+ lines agree with the two-dimensional FUV model by Bruderer et al., which computes abundances, non-LTE excitation, and line radiative transfer.20 It is concluded that CH+ is a good FUV tracer in star-forming regions. The effect of potential X-ray irradiation is not excluded but cannot be demonstrated by the present data. Title: Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using Herschel-HIFI Authors: Kristensen, L. E.; van Dishoeck, E. F.; Benz, A. O.; Bruderer, S.; Visser, R.; Wampfler, S. F. Bibcode: 2013A&A...557A..23K Altcode: 2013arXiv1307.1710K
Aims: Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin.
Methods: A velocity component with an offset of ~10 km s-1 detected in spectra of the H2O 110-101 557 GHz transition towards six low-mass protostars in the "Water in star-forming regions with Herschel" (WISH) programme is also seen in higher-excited H2O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+, OH) where the same component is uniquely detected.
Results: The velocity component is detected in all six targeted H2O transitions (Eup ~ 50-250 K), as well as in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n ~ 5 × 106-108 cm-3) and hot (T ~ 750 K) gas. The H2O and CO column densities are ≳1016 and 1018 cm-2, respectively, implying a low H2O abundance of ~10-2 with respect to CO. The high column densities of ions such as OH+ and CH+ (both ≳1013 cm-2) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with Trot ~ 700 K is identified as arising in the same component and traces the part of the shock where H2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Water in star-forming regions with Herschel (WISH). IV. A survey of low-J H2O line profiles toward high-mass protostars Authors: van der Tak, F. F. S.; Chavarría, L.; Herpin, F.; Wyrowski, F.; Walmsley, C. M.; van Dishoeck, E. F.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Hogerheijde, M. R.; Johnstone, D.; Kristensen, L. E.; Liseau, R.; Nisini, B.; Tafalla, M. Bibcode: 2013A&A...554A..83V Altcode: 2013arXiv1304.2949V Context. Water is a key constituent of star-forming matter, but the origin of its line emission and absorption during high-mass star formation is not well understood.
Aims: We study the velocity profiles of low-excitation H2O lines toward 19 high-mass star-forming regions and search for trends with luminosity, mass, and evolutionary stage.
Methods: We decompose high-resolution Herschel-HIFI line spectra near 990, 1110 and 1670 GHz into three distinct physical components. Dense cores (protostellar envelopes) are usually seen as narrow absorptions in the H2O 1113 and 1669 GHz ground-state lines, the H2O 987 GHz excited-state line, and the H218O 1102 GHz ground-state line. In a few sources, the envelopes appear in emission in some or all studied lines, indicating higher temperatures or densities. Broader features due to outflows are usually seen in absorption in the H2O 1113 and 1669 GHz lines, in 987 GHz emission, and not seen in H218O, indicating a lower column density and a higher excitation temperature than the envelope component. A few outflows are detected in H218O, indicating higher column densities of shocked gas. In addition, the H2O 1113 and 1669 GHz spectra show narrow absorptions by foreground clouds along the line of sight. The lack of corresponding features in the 987 GHz and H218O lines indicates a low column density and a low excitation temperature for these clouds, although their derived H2O ortho/para ratios are close to 3.
Results: The intensity of the ground state lines of H2O at 1113 and 1669 GHz does not show significant trends with source luminosity, envelope mass, or evolutionary state. In contrast, the flux in the excited-state 987 GHz line appears correlated with luminosity and the H218O line flux appears correlated with the envelope mass. Furthermore, appearance of the envelope in absorption in the 987 GHz and H218O lines seems to be a sign of an early evolutionary stage, as probed by the mid-infrared brightness and the Lbol/Menv ratio of the source.
Conclusions: The ground state transitions of H2O trace the outer parts of the envelopes, so that the effects of star formation are mostly noticeable in the outflow wings. These lines are heavily affected by absorption, so that line ratios of H2O involving the ground states must be treated with caution, especially if multiple clouds are superposed as in the extragalactic case. The isotopic H218O line appears to trace the mass of the protostellar envelope, indicating that the average H2O abundance in high-mass protostellar envelopes does not change much with time. The excited state line at 987 GHz increases in flux with luminosity and appears to be a good tracer of the mean weighted dust temperature of the source, which may explain why it is readily seen in distant galaxies.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org Title: OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS Authors: Wampfler, S. F.; Bruderer, S.; Karska, A.; Herczeg, G. J.; van Dishoeck, E. F.; Kristensen, L. E.; Goicoechea, J. R.; Benz, A. O.; Doty, S. D.; McCoey, C.; Baudry, A.; Giannini, T.; Larsson, B. Bibcode: 2013A&A...552A..56W Altcode: 2012arXiv1212.5033W Context. The OH radical is a key species in the water chemistry network of star-forming regions, because its presence is tightly related to the formation and destruction of water. Previous studies of the OH far-infrared emission from low- and intermediate-mass protostars suggest that the OH emission mainly originates from shocked gas and not from the quiescent protostellar envelopes.
Aims: We aim to study the excitation of OH in embedded low- and intermediate-mass protostars, determine the influence of source parameters on the strength of the emission, investigate the spatial extent of the OH emission, and further constrain its origin.
Methods: This paper presents OH observations from 23 low- and intermediate-mass young stellar objects obtained with the PACS integral field spectrometer on-board Herschel in the context of the "Water In Star-forming regions with Herschel" (WISH) key program. Radiative transfer codes are used to model the OH excitation.
Results: Most low-mass sources have compact OH emission (≲5000 AU scale), whereas the OH lines in most intermediate-mass sources are extended over the whole 47.″0 × 47.″0 PACS detector field-of-view (≳20 000 AU). The strength of the OH emission is correlated with various source properties such as the bolometric luminosity and the envelope mass, but also with the [OI] and H2O emission. Rotational diagrams for sources with many OH lines show that the level populations of OH can be approximated by a Boltzmann distribution with an excitation temperature at around 70 K. Radiative transfer models of spherically symmetric envelopes cannot reproduce the OH emission fluxes nor their broad line widths, strongly suggesting an outflow origin. Slab excitation models indicate that the observed excitation temperature can either be reached if the OH molecules are exposed to a strong far-infrared continuum radiation field or if the gas temperature and density are sufficiently high. Using realistic source parameters and radiation fields, it is shown for the case of Ser SMM1 that radiative pumping plays an important role in transitions arising from upper level energies higher than 300 K. The compact emission in the low-mass sources and the required presence of a strong radiation field and/or a high density to excite the OH molecules points toward an origin in shocks in the inner envelope close to the protostar.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are only available in electronic form at http://www.aanda.org Title: Water in star-forming regions with Herschel (WISH). III. Far-infrared cooling lines in low-mass young stellar objects Authors: Karska, A.; Herczeg, G. J.; van Dishoeck, E. F.; Wampfler, S. F.; Kristensen, L. E.; Goicoechea, J. R.; Visser, R.; Nisini, B.; San José-García, I.; Bruderer, S.; Śniady, P.; Doty, S.; Fedele, D.; Yıldız, U. A.; Benz, A. O.; Bergin, E.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Jørgensen, J. K.; Liseau, R.; Tafalla, M.; van der Tak, F.; Wyrowski, F. Bibcode: 2013A&A...552A.141K Altcode: 2013arXiv1301.4821K Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope. Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages. Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H2O, OH, and atomic lines. For four targets the spectra span the entire 55-200 μm region. The PACS field-of-view covers ~47" with the resolution of 9.4". Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H2O 818-707 63.3 μm line (Eu/kB = 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up to J = 49 - 48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ~350 K and ~700 K. H2O has typical excitation temperatures of ~150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on &≥10,000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The H2O line fluxes correlate strongly with those of the high-J CO lines, both for the full array and for the central position, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH fluxes and not with [O I] fluxes. In contrast, [O I] and OH often peak together at the central position. Conclusions. The PACS data probe at least two physical components. The H2O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.

Appendices A-J are available in electronic form at http://www.aanda.org Title: Observing the Sun with ALMA Authors: Benz, A. O.; Brajsa, R.; Shimojo, M.; Karlicky, M.; Testi, L. Bibcode: 2012IAUSS...6E.205B Altcode: The Atacama Large Millimeter Array (ALMA) is in the commissioning phase for solar observations. A filter reduces the solar radiation to a level suitable for solar observations. First observations with one antenna have mapped the Sun by scanning. The results look promising. The image of the quiet chromosphere shows large spatial variations in emissivity. Interferometry is much more demanding and not yet achieved. The current state and problems will be summarized. It is clear that solar ALMA observations will take more developing time, but will eventually be possible. The goal is subarcsecond resolution of the quiet and active submillimeter continuum radiation originating in the chromosphere and possibly in the flaring corona. A limiting factor will be the temporal variability of the solar emission. Title: Spectrometer Telescope for Imaging X-rays (STIX) Authors: Benz, A. O.; Gallagher, P.; Veronig, A.; Grimm, O.; Sylwester, J.; Orleanski, P.; Arnold, N.; Bednarzik, M.; Farnik, F.; Hurford, G.; Krucker, S.; Limousin, O.; Mann, G.; Vilmer, N. Bibcode: 2012IAUSS...6E.509B Altcode: The Solar Orbiter Mission has been confirmed within ESA's M-class Cosmic Vision plan. Launch date is January 2017 into an orbit that reaches nearly one quarter AU in the perihelion. STIX is one of the 10 instruments selected for close cooperation. STIX applies a Fourier-imaging technique using shading tungsten grids. A total of 32 pixelized CdTe detectors will permit high resolution imaging spectroscopy. The design has passed ESA's Preliminary Design Review and will be finalized by the end of 2012. The instrument specification will be presented and its scientific potential discussed. Title: The spectrometer telescope for imaging x-rays on board the Solar Orbiter mission Authors: Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.; Orleanski, P.; Gröbelbauer, H. -P.; Klober, S.; Iseli, L.; Wiehl, H. J.; Csillaghy, A.; Etesi, L.; Hochmuth, N.; Battaglia, M.; Bednarzik, M.; Resanovic, R.; Grimm, O.; Viertel, G.; Commichau, V.; Meuris, A.; Limousin, O.; Brun, S.; Vilmer, N.; Skup, K. R.; Graczyk, R.; Stolarski, M.; Michalska, M.; Nowosielski, W.; Cichocki, A.; Mosdorf, M.; Seweryn, K.; Przepiórka, A.; Sylwester, J.; Kowalinski, M.; Mrozek, T.; Podgorski, P.; Mann, G.; Aurass, H.; Popow, E.; Onel, H.; Dionies, F.; Bauer, S.; Rendtel, J.; Warmuth, A.; Woche, M.; Plüschke, D.; Bittner, W.; Paschke, J.; Wolker, D.; Van Beek, H. F.; Farnik, F.; Kasparova, J.; Veronig, A. M.; Kienreich, I. W.; Gallagher, P. T.; Bloomfield, D. S.; Piana, M.; Massone, A. M.; Dennis, B. R.; Schwarz, R. A.; Lin, R. P. Bibcode: 2012SPIE.8443E..3LB Altcode: The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, a confirmed Mclass mission of the European Space Agency (ESA) within the Cosmic Vision program scheduled to be launched in 2017. STIX applies a Fourier-imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 to 150 keV. The status of the instrument reviewed in this paper is based on the design that passed the Preliminary Design Review (PDR) in early 2012. Particular emphasis is given to the first light of the detector system called Caliste-SO. Title: Remnant Gas in Evolved Circumstellar Disks: Herschel PACS Observations of 10-100 Myr Old Disk Systems Authors: Geers, Vincent C.; Gorti, Uma; Meyer, Michael R.; Mamajek, Eric; Benz, Arnold O.; Hollenbach, David Bibcode: 2012ApJ...755....8G Altcode: 2012arXiv1206.1044G We present Herschel PACS spectroscopy of the [O I] 63 μm gas line for three circumstellar disk systems showing signs of significant disk evolution and/or planet formation: HR 8799, HD 377, and RX J1852.3-3700. [O I] is undetected toward HR 8799 and HD 377 with 3σ upper limits of 6.8 × 10-18 W m-2 and 9.9 × 10-18 W m-2, respectively. We find an [O I] detection for RX J1852.3-3700 at (12.3 ± 1.8) × 10-18 W m-2. We use thermo-chemical disk models to model the gas emission, using constraints on the [O I] 63 μm and ancillary data to derive gas mass upper limits and constrain gas-to-dust ratios. For HD 377 and HR 8799, we find 3σ upper limits on the gas mass of 0.1-20 M ⊕. For RX J1852.3-3700, we find two distinct disk scenarios that could explain the detection of [O I] 63 μm and CO(2-1) upper limits reported in the literature: (1) a large disk with gas co-located with the dust (16-500 AU), resulting in a large tenuous disk with ~16 M ⊕ of gas, or (2) an optically thick gas disk, truncated at ~70 AU, with a gas mass of 150 M ⊕. We discuss the implications of these results for the formation and evolution of planets in these three systems.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Submillimeter line emission from LMC 30 Doradus: The impact of a starburst on a low-metallicity environment Authors: Pineda, J. L.; Mizuno, N.; Röllig, M.; Stutzki, J.; Kramer, C.; Klein, U.; Rubio, M.; Kawamura, A.; Minamidani, T.; Benz, A.; Burton, M.; Fukui, Y.; Koo, B. -C.; Onishi, T. Bibcode: 2012A&A...544A..84P Altcode: 2012arXiv1206.4051P Context. The 30 Dor region in the Large Magellanic Cloud (LMC) is the most vigorous star-forming region in the Local Group. Star formation in this region is taking place in low-metallicity molecular gas that is exposed to an extreme far-ultraviolet (FUV) radiation field powered by the massive compact star cluster R136. 30 Dor is therefore ideally suited to study the conditions in which stars formed at earlier cosmological times.
Aims: Observations of (sub)mm and far-infrared (FIR) spectral lines of the main carbon-carrying species, CO, [C i] and [C ii], which originate in the surface layers of molecular clouds illuminated by the FUV radiation of young stars, can be used to constrain the physical and chemical state of the star-forming ISM.
Methods: We used the NANTEN2 telescope to obtain high-angular resolution observations of the 12CO J = 4 → 3, J = 7 → 6, and 13CO J = 4 → 3 rotational lines and [C i] 3P1- 3P0 and 3P2- 3P1 fine-structure submillimeter transitions in 30 Dor-10, the brightest CO and FIR-emitting cloud at the center of the 30 Dor region. We derived the physical and chemical properties of the low-metallicity molecular gas using an excitation/radiative transfer code and found a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. We compared the derived properties with those in the N159W region, which is exposed to a more moderate far-ultraviolet radiation field compared with 30 Dor-10, but has similar metallicity. We also combined our CO detections with previously observed low-J CO transitions to derive the CO spectral-line energy distribution in 30 Dor-10 and N159W.
Results: The separate excitation analysis of the submm CO lines and the neutral carbon fine structure lines shows that the mid-J CO and [C i]-emitting gas in the 30 Dor-10 region has a temperature of about 160 K and a H2 density of about 104 cm-3. We find that the molecular gas in 30 Dor-10 is warmer and has a lower beam filling factor compared to that of N159W, which might be a result of the effect of a strong FUV radiation field heating and disrupting the low-metallicity molecular gas. We use a clumpy PDR model (including the [C ii] line intensity reported in the literature) to constrain the FUV intensity to about χ0 ≈ 3100 and an average total H density of the clump ensemble of about 105 cm-3 in 30 Dor-10. Title: Water in star-forming regions with Herschel (WISH). II. Evolution of 557 GHz 110-101 emission in low-mass protostars Authors: Kristensen, L. E.; van Dishoeck, E. F.; Bergin, E. A.; Visser, R.; Yıldız, U. A.; San Jose-Garcia, I.; Jørgensen, J. K.; Herczeg, G. J.; Johnstone, D.; Wampfler, S. F.; Benz, A. O.; Bruderer, S.; Cabrit, S.; Caselli, P.; Doty, S. D.; Harsono, D.; Herpin, F.; Hogerheijde, M. R.; Karska, A.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F.; Wyrowski, F. Bibcode: 2012A&A...542A...8K Altcode: 2012arXiv1204.0009K Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published.
Aims: The first systematic survey of spectrally resolved water emission in 29 low-mass (L < 40 L⊙) protostellar objects is presented. The sources cover a range of luminosities and evolutionary states. The aim is to characterise the line profiles to distinguish physical components in the beam and examine how water emission changes with protostellar evolution.
Methods: H2O was observed in the ground-state 110-101 transition at 557 GHz (Eup/kB ~ 60 K) as single-point observations with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel in 29 deeply embedded Class 0 and I low-mass protostars. Complementary far-IR and sub-mm continuum data (including PACS data from our programme) are used to constrain the spectral energy distribution (SED) of each source. H2O intensities are compared to inferred envelope properties, e.g., mass and density, outflow properties and CO 3-2 emission.
Results: H2O emission is detected in all objects except one (TMC1A). The line profiles are complex and consist of several kinematic components tracing different physical regions in each system. In particular, the profiles are typically dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows, not in the quiescent envelope. Several sources show multiple shock components appearing in either emission or absorption, thus constraining the internal geometry of the system. Furthermore, the components include inverse P-Cygni profiles in seven sources (six Class 0, one Class I) indicative of infalling envelopes, and regular P-Cygni profiles in four sources (three Class I, one Class 0) indicative of expanding envelopes. Molecular "bullets" moving at ≳50 km s-1 with respect to the source are detected in four Class 0 sources; three of these sources were not known to harbour bullets previously. In the outflow, the H2O/CO abundance ratio as a function of velocity is nearly the same for all line wings, increasing from 10-3 at low velocities (<5 km s-1) to ≳10-1 at high velocities (>10 km s-1). The water abundance in the outer cold envelope is low, ≳10-10. The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org Title: Multi-line detection of O2 toward ρ Ophuichi A Authors: Liseau, R.; Goldsmith, P. F.; Larsson, B.; Pagani, L.; Bergman, P.; Le Bourlot, J.; Bell, T. A.; Benz, A. O.; Bergin, E. A.; Bjerkeli, P.; Black, J. H.; Bruderer, S.; Caselli, P.; Caux, E.; Chen, J. -H.; de Luca, M.; Encrenaz, P.; Falgarone, E.; Gerin, M.; Goicoechea, J. R.; Hjalmarson, Å.; Hollenbach, D. J.; Justtanont, K.; Kaufman, M. J.; Le Petit, F.; Li, D.; Lis, D. C.; Melnick, G. J.; Nagy, Z.; Olofsson, A. O. H.; Olofsson, G.; Roueff, E.; Sandqvist, Aa.; Snell, R. L.; van der Tak, F. F. S.; van Dishoeck, E. F.; Vastel, C.; Viti, S.; Yıldız, U. A. Bibcode: 2012A&A...541A..73L Altcode: 2012arXiv1202.5637L Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium.
Aims: Only toward ρ Oph A did Odin detect a very weak line of O2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O2 emission and pinpoint its origin.
Methods: We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O2 spectra toward selected positions in the ρ Oph A core. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models.
Results: The NJ = 33 - 12 line at 487.2 GHz is clearly detected toward all three observed positions in the ρ Oph A core. In addition, an oversampled map of the 54-34 transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O2 emitting gas appears to vary quite substantially, with warm gas ( ≳ 50 K) being adjacent to a much colder region, of temperatures lower than 30 K.
Conclusions: The exploited models predict that the O2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O2) = 3 to ≳ 6 × 1015 cm-2. Beam-averaged O2 abundances are about 5 × 10-8 relative to H2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire ρ Oph A core. We speculate that one of the reasons for the generally very low detection rate of O2 is the short period of time during which O2 molecules are reasonably abundant in molecular clouds.

Based on observations with Herschel-HIFI. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Instrument data processing unit for spectrometer/telescope for imaging x-rays (STIX) Authors: Skup, Konrad R.; Cichocki, A.; Graczyk, R.; Michalska, M.; Mosdorf, M.; Nowosielski, W.; Orleański, P.; Przepiórka, A.; Seweryn, K.; Stolarski, M.; Winkler, M.; Sylwester, J.; Kowalinski, M.; Mrozek, T.; Podgorski, P.; Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.; Önel, H.; Meuris, A.; Limousin, O.; Grimm, O. Bibcode: 2012SPIE.8454E..0KS Altcode: The Spectrometer/Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, an M-class mission of the European Space Agency (ESA) scheduled to be launch in 2017. STIX applies a Fourier-imaging technique using a set of tungsten grids in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 to 150 keV. These detectors are source of data collected and analyzed in real-time by Instrument Data Processing Unit (IDPU). Besides the data processing the IDPU controls and manages other STIX's subsystems: ASICs and ADCs associated with detectors, Aspect System, Attenuator, PSU and HK. The instrument reviewed in this paper is based on the design that passed the Instrument Preliminary Design Review (IPDR) in early 2012 and Software Preliminary Design Review (SW PDR) in middle of 2012. Particular emphasis is given to the IDPU and low level software called Basic SW (BSW). Title: Herschel Observations of Interstellar Chloronium Authors: Neufeld, David A.; Roueff, Evelyne; Snell, Ronald L.; Lis, Dariusz; Benz, Arnold O.; Bruderer, Simon; Black, John H.; De Luca, Massimo; Gerin, Maryvonne; Goldsmith, Paul F.; Gupta, Harshal; Indriolo, Nick; Le Bourlot, Jacques; Le Petit, Franck; Larsson, Bengt; Melnick, Gary J.; Menten, Karl M.; Monje, Raquel; Nagy, Zsófia; Phillips, Thomas G.; Sandqvist, Aage; Sonnentrucker, Paule; van der Tak, Floris; Wolfire, Mark G. Bibcode: 2012ApJ...748...37N Altcode: 2012arXiv1201.2941N Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight lines to the bright submillimeter continuum sources Sgr A (+50 km s-1 cloud) and W31C. Both the para-H35 2Cl+ and para-H37 2Cl+ isotopologues were detected, through observations of their 111-000 transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio (OPR) of 3, the observed optical depths imply that chloronium accounts for ~4%-12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed OPR of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ~2 × 1013 cm-2 and ~1.2 × 1013 cm-2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H35 2Cl+ line strengths toward H2 Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor ~10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Location of Decimetric Pulsations in Solar Flares Authors: Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole Bibcode: 2012esrs.book...57B Altcode: This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30 - 240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source. Title: The Radio-X-ray Relation in Cool Stars: Are We Headed Toward a Divorce? Authors: Forbrich, J.; Wolk, S. J.; Güdel, M.; Benz, A.; Osten, R.; Linsky, J. L.; McLean, M.; Loinard, L.; Berger, E. Bibcode: 2011ASPC..448..455F Altcode: 2011csss...16..455F; 2010arXiv1012.1626F This splinter session was devoted to reviewing our current knowledge of correlated X-ray and radio emission from cool stars in order to prepare for new large radio observatories such as the EVLA. A key interest was to discuss why the X-ray and radio luminosities of some cool stars are in clear breach of a correlation that holds for other active stars, the so-called Güdel-Benz relation. This article summarizes the contributions whereas the actual presentations can be accessed on the splinter website. Title: Location of Decimetric Pulsations in Solar Flares Authors: Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole Bibcode: 2011SoPh..273..363B Altcode: 2011SoPh..tmp..166B; 2011arXiv1103.5353B; 2011SoPh..tmp..235B; 2011SoPh..tmp...88B This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30 - 240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source. Title: WISHes coming true: water in low-mass star-forming regions with Herschel Authors: Kristensen, L. E.; Visser, R.; van Dishoeck, E. F.; Yıldız, U. A.; Herczeg, G. J.; Doty, S.; Jørgensen, J. K.; van Kempen, T. A.; Brinch, C.; Wampfler, S.; Bruderer, S.; Benz, A. O. Bibcode: 2011EAS....52..177K Altcode: Water is a key molecule for tracing physical and chemical processes in star-forming regions. The key program "Water in star-forming regions with Herschel" is observing several water transitions towards low-mass protostars with HIFI. Results regarding the 557 GHz transition of water are reported here showing that the line is surprisingly broad, and consists of several different velocity components. The bulk of the emission comes from shocks, where the abundance is increased by several orders of magnitude to ~10-4. The abundance of water in the outer envelope is determined to ~10-8, whereas only an upper limit of 10-5 is derived for the inner, warm envelope. Title: The WADI key project: New insights to photon-dominated regions from Herschel observations Authors: Ossenkopf, V.; Röllig, M.; Kramer, C.; Okada, Y.; Fuente, A.; Akyilmaz Yabaci, M.; Benz, A. O.; Berné, O.; Boulanger, F.; Bruderer, S.; Dedes, C.; France, K.; Gerin, M.; Goicoechea, J. R.; Gusdorf, A.; Güsten, R.; Harris, A.; Joblin, C.; Klein, T.; Latter, W.; Le Petit, F.; Lord, S.; Martin, P. G.; Pilleri, P.; Martin-Pintado, J.; Mookerjea, B.; Neufeld, D. A.; Phillips, T.; Rizzo, R.; Simon, R.; Stutzki, J.; van der Tak, F. F. S.; Teyssier, D.; Yorke, H. Bibcode: 2011EAS....52..181O Altcode: Within the Herschel key project "The Warm And Dense ISM" (WADI) we systematically observe a number of prominent photon-dominated regions (PDRs) to measure the impact of varying UV fields on the energy balance, the chemical and dynamical structure of heated molecular clouds. Title: Tracing FUV Radiation in the Embedded Phase of Star Formation Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Stäuber, P.; Wampfler, S. F.; Dedes, C. Bibcode: 2011EAS....52..239B Altcode: Molecules containing one or a few hydrogen atoms and a heavier atom (hydrides) have been predicted to trace FUV radiation. In some chemical models, FUV emission by the central object or protostar of a star forming region greatly enhances some of the hydride abundances. Two massive regions, W3 IRS5 and AFGL 2591, have been observed in hydride lines by HIFI onboard the Herschel Space Observatory. We use published results as well as new observations of CH+ towards W3 IRS5. Molecular column densities are derived from ground state absorption lines, radiative transfer modeling or rotational diagrams. Models assuming no internal FUV are compared with two-dimensional models including FUV irradiation of outflow walls. We confirm that the effect of FUV is clearly noticeable and greatly improves the fit. The most sensitive molecules to FUV irradiation are CH+ and OH+, enhanced in abundance by many orders of magnitude. Modeling in addition also full line radiative transfer, Bruderer et al. (2010b) achieve good agreement of a two-dimensional FUV model with observations of CH+ in AFGL 2591. It is concluded that CH+ and OH+ are good FUV tracers in star-forming regions. Title: High-resolution Imaging of Solar Flare Ribbons and Its Implication on the Thick-target Beam Model Authors: Krucker, Säm; Hudson, H. S.; Jeffrey, N. L. S.; Battaglia, M.; Kontar, E. P.; Benz, A. O.; Csillaghy, A.; Lin, R. P. Bibcode: 2011ApJ...739...96K Altcode: We report on high-resolution optical and hard X-ray observations of solar flare ribbons seen during the GOES X6.5 class white-light flare of 2006 December 6. The data consist of imaging observations at 430 nm (the Fraunhofer G band) taken by the Hinode Solar Optical Telescope with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The two sets of data show closely similar ribbon structures, strongly suggesting that the flare emissions in white light and in hard X-rays have physically linked emission mechanisms. While the source structure along the ribbons is resolved at both wavelengths (length ~ 30''), only the G-band observations resolve the width of the ribbon, with values between ~0farcs5 and ~1farcs8. The unresolved hard X-ray observations reveal an even narrower ribbon in hard X-rays (the main footpoint has a width perpendicular to the ribbon of <1farcs1 compared to the G-band width of ~1farcs8) suggesting that the hard X-ray emission comes from the sharp leading edge of the G-band ribbon. Applying the thick-target beam model, the derived energy deposition rate is >5 × 1012 erg s-1 cm-2 provided by an electron flux of 1 × 1020 electrons s-1 cm-2 above 18 keV. This requires that the beam density of electrons above 18 keV be at least 1 × 1010 cm-3. Even if field lines converge toward the chromospheric footpoints, the required beam in the corona has too high a density to be described as a dilute tail population on top of a Maxwellian core. We discuss this issue and others associated with this extreme event, which poses serious questions to the standard thick target beam interpretation of solar flares. Title: Recent Advances in Understanding Particle Acceleration Processes in Solar Flares Authors: Zharkova, V. V.; Arzner, K.; Benz, A. O.; Browning, P.; Dauphin, C.; Emslie, A. G.; Fletcher, L.; Kontar, E. P.; Mann, G.; Onofri, M.; Petrosian, V.; Turkmani, R.; Vilmer, N.; Vlahos, L. Bibcode: 2011SSRv..159..357Z Altcode: 2011SSRv..tmp..156Z; 2011SSRv..tmp..249Z; 2011SSRv..tmp..232Z; 2011arXiv1110.2359Z; 2011SSRv..tmp..278Z We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered. Title: The Relationship Between Solar Radio and Hard X-ray Emission Authors: White, S. M.; Benz, A. O.; Christe, S.; Fárník, F.; Kundu, M. R.; Mann, G.; Ning, Z.; Raulin, J. -P.; Silva-Válio, A. V. R.; Saint-Hilaire, P.; Vilmer, N.; Warmuth, A. Bibcode: 2011SSRv..159..225W Altcode: 2011SSRv..tmp..263W; 2011SSRv..tmp..244W; 2011SSRv..tmp..164W; 2011arXiv1109.6629W; 2011SSRv..tmp...88W This review discusses the complementary relationship between radio and hard X-ray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive. Title: Herschel Measurements of Molecular Oxygen in Orion Authors: Goldsmith, Paul F.; Liseau, René; Bell, Tom A.; Black, John H.; Chen, Jo-Hsin; Hollenbach, David; Kaufman, Michael J.; Li, Di; Lis, Dariusz C.; Melnick, Gary; Neufeld, David; Pagani, Laurent; Snell, Ronald; Benz, Arnold O.; Bergin, Edwin; Bruderer, Simon; Caselli, Paola; Caux, Emmanuel; Encrenaz, Pierre; Falgarone, Edith; Gerin, Maryvonne; Goicoechea, Javier R.; Hjalmarson, Åke; Larsson, Bengt; Le Bourlot, Jacques; Le Petit, Franck; De Luca, Massimo; Nagy, Zsofia; Roueff, Evelyne; Sandqvist, Aage; van der Tak, Floris; van Dishoeck, Ewine F.; Vastel, Charlotte; Viti, Serena; Yıldız, Umut Bibcode: 2011ApJ...737...96G Altcode: 2011arXiv1108.0441G We report observations of three rotational transitions of molecular oxygen (O2) in emission from the H2 Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s-1 to 12 km s-1 and widths of 3 km s-1. The beam-averaged column density is N(O2) = 6.5 × 1016 cm-2, and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19''), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O2 relative to H2 is (0.3-7.3) × 10-6. The unusual velocity suggests an association with a ~5'' diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 M sun and the dust temperature is >=150 K. Our preferred explanation of the enhanced O2 abundance is that dust grains in this region are sufficiently warm (T >= 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O2. For this small source, the line ratios require a temperature >=180 K. The inferred O2 column density sime5 × 1018 cm-2 can be produced in Peak A, having N(H2) ~= 4 × 1024 cm-2. An alternative mechanism is a low-velocity (10-15 km s-1) C-shock, which can produce N(O2) up to 1017 cm-2.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: First hyperfine resolved far-infrared OH spectrum from a star-forming region Authors: Wampfler, S. F.; Bruderer, S.; Kristensen, L. E.; Chavarría, L.; Bergin, E. A.; Benz, A. O.; van Dishoeck, E. F.; Herczeg, G. J.; van der Tak, F. F. S.; Goicoechea, J. R.; Doty, S. D.; Herpin, F. Bibcode: 2011A&A...531L..16W Altcode: 2011arXiv1105.5026W OH is an important molecule in the H2O chemistry and the cooling budget of star-forming regions. The goal of the Herschel key program "Water In Star-forming regions with Herschel" (WISH) is to study H2O and related species during protostellar evolution. Our aim in this Letter is to assess the origin of the OH emission from star-forming regions and constrain the properties of the emitting gas. High-resolution observations of the OH {^2Π1/2 J = 3/2-1/2 } triplet at 1837.8 GHz (163.1 μm) towards the high-mass star-forming region W3 IRS 5 with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel reveal the first hyperfine velocity-resolved OH far-infrared spectrum of a star-forming region. The line profile of the OH emission shows two components: a narrow component (FWHM ≈ 4-5 km s-1) with partially resolved hyperfine structure resides on top of a broad (FWHM ≈ 30 km s-1) component. The narrow emission agrees well with results from radiative transfer calculations of a spherical envelope model for W3 IRS 5 with a constant OH abundance of xOH ≈ 8 × 10-9. Comparison with H2O yields OH/H2O abundance ratios of around 10-3 for T ≳ 100 K and around unity for T ≲ 100 K, consistent with the current picture of the dense cloud chemistry with freeze-out and photodesorption. The broad component is attributed to outflow emission. An abundance ratio of OH/H2O ≳ 0.028 in the outflow is derived from comparison with results of water line modeling. This ratio can be explained by a fast J-type shock or a slower UV-irradiated C-type shock.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org Title: Tracing X-ray and FUV Radiation in the Embedded Phase of Star Formation Authors: Benz, A. O.; Bruderer, S.; Wampfler, S. F.; Dedes, C.; van Dishoeck, E. F. Bibcode: 2011IAUS..280P..91B Altcode: 2011arXiv1101.1746B Molecules containing one (or a few) hydrogen atoms and one heavier atom (hydrides) are predicted to trace ionizing FUV radiation. In some chemical models, FUV emission by the central object or protostar of a star forming region greatly enhances the abundance of some hydrides. Two massive regions, W3 IRS5 and AFGL 2591, have been observed in hydride lines by HIFI onboard the Herschel Space Observatory. They both have Ultra Compact HII regions, indicating the presence of FUV. We derive molecular column densities from ground state absorption lines, radiative transfer modeling and/or rotational diagrams. Models assuming no internal FUV are compared with two-dimensional models including FUV irradiation of outflow walls. The most sensitive molecules to FUV irradiation are CH^+, OH^+, SH^+, and NH^+. They are enhanced in abundance by many orders of magnitude. We confirm that the effect of FUV is clearly noticeable and greatly improves the fit of observations with theory (see figure). Modeling in addition also full line radiative transfer, we report good agreement of a two-dimensional FUV model with line observations of CH^+ in AFGL 2591. It is concluded that CH^+ and OH^+ are good and abundant FUV tracers in star-forming regions. Having confirmed the tracer molecules in cases with known FUV radiation, we search for that radiation in cases where FUV irradiation is questionable, such as younger stellar objects and lower mass objects. We report the results of new Herschel observations of CH^+, OH^+, and CH in 5 massive YSOs of different age, in 6 low-mass objects of class 0 and I, and an intermediate-mass source. The observations are compared with chemical and radiative transfer models. For nearby low-mass YSOs, we discuss also the possibility to indentify protostellar X-ray irradiation. The conclusion is that high-energy irradiation has started in all objects observed, thus at a very early phase of star formation. Its impact on star and planet formation needs to be investigated. Title: Studying cooling mechanisms in the massive star forming region IRAS 12326-6245 Authors: Dedes, C.; Herpin, F.; Chavarria, L.; Wampfler, S.; Wyrowski, F.; van der Tak, F.; Benz, A.; Bruderer, D.; Polehampton, E.; Melchior, M. Bibcode: 2011IAUS..280P.149D Altcode: The strong feedback processes of massive stars influence the surrounding ISM both locally and on large scales. An important question to be answered is the one of cooling and heating in massive star forming regions. There, heating is provided mostly by far-UV (FUV) and infra-red radiation. Cooling is mostly provided by emission in the fine structure lines of [CII] and [OI]. There are, however, molecular lines such as CO, OH and H_2O which can become significant coolants in the dense, embedded regions. To understand the heating and cooling balance, one has to consider the contributions of various radiative and dynamical processes such as FUV radiation, shocks, and the PDRs where the radiation impinges on the molecular material. The tracers of these processes can be observed in the far-infrared, a wavelength range that is now accessible at unprecedented high spectral and spatial resolution with the Herschel Space Observatory. Our approved 3 hour Herschel GT project was designed to cover all the major coolants in one massive star forming region, IRAS 12326-6245. H_2O and [CII] were obtained at high spectral resolution with HIFI, [OI] and OH lines will be observed with PACS and the CO ladder with SPIRE. This luminous, massive, region, located at 4.4 kpc, contains a hot core inside a ∼ 1600M⊙ dust envelope and has one of the most massive outflows observed (Dedes et al. 2011). In this contribution, we will present first results of the radiative transfer modeling of the continuum emission, the H_2O lines modeling, and the derivation of physical conditions of the gas obtained from CH_3OH, 13CO and C18O lines. Despite its apparent simplicity in the ground based CO line profiles, Herschel observations of the source show a complicated velocity structure in the water lines, with many lines contributing to absorption from foreground clouds. High spectral resolution measurements from CH^+ and H_2O^+ are used to assign the velocity components to the source and foreground material. Title: First hyperfine structure resolved OH FIR spectrum of a star-forming region Authors: Wampfler, S. F.; Bruderer, S.; Kristensen, L. E.; Bergin, E. A.; Benz, A. O.; van Dishoeck, E. F.; Herczeg, G. J.; van der Tak, F. F. S.; Goicoechea, J. R.; Doty, S. D.; Herpin, F. Bibcode: 2011IAUS..280P.380W Altcode: Embedded protostars interact with their natal cloud through shocks and irradiation. The ambient interstellar medium warms up, allowing icy grain mantles to evaporate and making different chemical routes in the gas phase available. Water then becomes one of the most abundant molecular species in the gas phase. The Herschel key program `Water in Star-Forming Regions with Herschel (WISH)' studies the excitation and chemistry of water around protostars. Hydroxyl (OH) is of the cornerstone species in the water chemistry network, because it is closely linked to both the formation and destruction of water through the OH + H2 leftrightarrow H2O + H reactions and photodissociation processes. This poster presents the first OH observation with resolved hyperfine structure at 163 μm of a star-forming region obtained using HIFI on Herschel. The OH triplet from the high-mass star-forming region W3 IRS5 is in emission, with the line profile revealing a narrow component on top of a broad feature. The broad component is attributed to outflow emission based on comparison with molecular lines of other species, whereas the narrow component is in agreement with radiative transfer results for a spherically symmetric envelope model. The resolved hyperfine structure allows us to constrain the excitation temperature and the OH column density in our models simultaneously. The derived OH/H2O ratios in the envelope are consistent with the current picture of the water chemistry. In the outer envelope (T < 100 K), where OH and H2O are released into the gas phase by photodesorption from the ice mantles of dust grains, we find a ratio of about unity. Laboratory work by Öberg et al. (2009) demonstrated that similar amounts of OH and water are released with an expected OH/H2O ratio of 0.5-1. This ratio is also in agreement with the theoretical work by Andersson & van Dishoeck (2008). In the inner envelope (T > 100 K), water is efficiently formed from OH and the OH/H2O ratio is therefore expected to drop significantly, which is consistent with the derived value of the order of 10-4. For the outflow, a lower limit of OH/H2O > 0.025 is obtained and can be explained with either a fast J-type shock or a slower UV irradiated C-type shock. Title: Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results Authors: van Dishoeck, E. F.; Kristensen, L. E.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Cernicharo, J.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Shipman, R.; Tafalla, M.; van der Tak, F.; Wyrowski, F.; Aikawa, Y.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Brinch, C.; Bruderer, S.; Chavarría, L.; Codella, C.; Daniel, F.; de Graauw, Th.; Deul, E.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Dubernet, M. L.; Encrenaz, P.; Feuchtgruber, H.; Fich, M.; Frieswijk, W.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; Helmich, F. P.; Herczeg, G. J.; Jacq, T.; Jørgensen, J. K.; Karska, A.; Kaufman, M. J.; Keto, E.; Larsson, B.; Lefloch, B.; Lis, D.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld, D.; Olberg, M.; Pagani, L.; Panić, O.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Salter, D.; Santiago-García, J.; Saraceno, P.; Stäuber, P.; van Kempen, T. A.; Visser, R.; Viti, S.; Walmsley, M.; Wampfler, S. F.; Yıldız, U. A. Bibcode: 2011PASP..123..138V Altcode: 2010arXiv1012.4570V Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities—from low (< 1 L⊙) to high (>105 L⊙)—and a wide range of evolutionary stages—from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of H2O, H218O and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, 13CO, and C18O are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of the energy budget indicate that H2O is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks. Title: Heating of the quiet solar corona from measurements of the FET/TESIS instrument on-board the KORONAS-FOTON satellite Authors: Rybák, J.; Gömöry, P.; Benz, A.; Bogachev, P.; Brajša, R. Bibcode: 2010nspm.conf..107R Altcode: The paper presents the first results of the observations of time evolution of the quiet solar corona brightenings obtained due to very rapid photography of the corona with full-disk EUV telescopes of the FET/TESIS instrument onboard the KORONA FOTON satellite. The measurements were performed simultaneously in the emission of the Fe IX / X 17.1 and Fe VIII 13.1 spectral lines with 10 second temporal cadence and spatial scale of 1.7 arc seconds within one hour. This test observation, carried out on 15 July 2009, was analyzed in order to determine whether this type of observation can be used to identify individual microevents in the solar corona heating that are above the tresholds of spatial and temporal resolutions of the observations of non-active regions in the solar atmosphere. For this purpose, a simple method was used involving cross-correlation of the plasma emission time evolution at different temperatures, each time from observations of identical elements. The results obtained are confronted with the expected observable manifestations of the corona heating via nanoflares. TESIS is a set of instruments for the Sun photography developed in the Lebedev Physics Institute of the Russian Academy of Sciences that was launched into orbit in January 2009. Title: Star-forming Dense Cloud Cores in the TeV Gamma-ray SNR RX J1713.7-3946 Authors: Sano, H.; Sato, J.; Horachi, H.; Moribe, N.; Yamamoto, H.; Hayakawa, T.; Torii, K.; Kawamura, A.; Okuda, T.; Mizuno, N.; Onishi, T.; Maezawa, H.; Inoue, T.; Inutsuka, S.; Tanaka, T.; Matsumoto, H.; Mizuno, A.; Ogawa, H.; Stutzki, J.; Bertoldi, F.; Anderl, S.; Bronfman, L.; Koo, B. -C.; Burton, M. G.; Benz, A. O.; Fukui, Y. Bibcode: 2010ApJ...724...59S Altcode: 2010arXiv1005.3409S RX J1713.7-3946 is one of the TeV γ-ray supernova remnants (SNRs) emitting synchrotron X-rays. The SNR is associated with molecular gas located at ~1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C, and D, in the SNR in the 12CO(J = 2-1) and 13CO(J = 2-1) transitions at an angular resolution of 90''. The most intense core in 13CO, peak C, was also mapped in the 12CO(J = 4-3) transition at an angular resolution of 38''. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source, and has a steep gradient with a r -2.2±0.4 variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X-rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X-rays are physically associated with the molecular gas. We present a scenario where the densest molecular core, peak C, survived the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since the shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to enhanced synchrotron X-rays around dense cores. Title: Herschel/HIFI detections of hydrides towards AFGL 2591. Envelope emission versus tenuous cloud absorption Authors: Bruderer, S.; Benz, A. O.; van Dishoeck, E. F.; Melchior, M.; Doty, S. D.; van der Tak, F.; Stäuber, P.; Wampfler, S. F.; Dedes, C.; Yıldız, U. A.; Pagani, L.; Giannini, T.; de Graauw, Th.; Whyborn, N.; Teyssier, D.; Jellema, W.; Shipman, R.; Schieder, R.; Honingh, N.; Caux, E.; Bächtold, W.; Csillaghy, A.; Monstein, C.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Goicoechea, J. R.; Helmich, F.; Herczeg, G. J.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Johnstone, D.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van Kempen, T. A.; Visser, R.; Wyrowski, F. Bibcode: 2010A&A...521L..44B Altcode: 2010arXiv1007.3408B The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+ and SH+ have not been detected. All molecules except for CH and CH+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P = 3/22,- - 1/21,+ ) and CH+(J = 1-0, J = 2-1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH+ emission stems from the envelope. The observed abundance and excitation of CH and CH+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Apppendices and Table 1 (pages 6 to 7) are only available in electronic form at http://www.aanda.org Title: The origin of the [C II] emission in the S140 photon-dominated regions. New insights from HIFI Authors: Dedes, C.; Röllig, M.; Mookerjea, B.; Okada, Y.; Ossenkopf, V.; Bruderer, S.; Benz, A. O.; Melchior, M.; Kramer, C.; Gerin, M.; Güsten, R.; Akyilmaz, M.; Berne, O.; Boulanger, F.; de Lange, G.; Dubbeldam, L.; France, K.; Fuente, A.; Goicoechea, J. R.; Harris, A.; Huisman, R.; Jellema, W.; Joblin, C.; Klein, T.; Le Petit, F.; Lord, S.; Martin, P.; Martin-Pintado, J.; Neufeld, D. A.; Philipp, S.; Phillips, T.; Pilleri, P.; Rizzo, J. R.; Salez, M.; Schieder, R.; Simon, R.; Siebertz, O.; Stutzki, J.; van der Tak, F.; Teyssier, D.; Yorke, H. Bibcode: 2010A&A...521L..24D Altcode: 2010arXiv1007.4957D Using Herschel's HIFI instrument, we observe C ii along a cut through S140, as well as high-J transitions of CO and HCO+ at two positions on the cut, corresponding to the externally irradiated ionization front and the embedded massive star-forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-τ model for photon-dominated regions (PDRs). We derive the physical conditions in S140 and in particular the origin of C ii emission around IRS1. We identify three distinct regions of C ii emission from the cut, one close to the embedded source IRS1, one associated with the ionization front, and one further into the cloud. The line emission can be understood in terms of a clumpy model of PDRs. At the position of IRS1, we identify at least two distinct components contributing to the [C ii] emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the C ii peak at IRS1 coinciding with shocked H2 emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be reproduced well by a single-component KOSMA-τ model. Thus, it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity that has allowed us to uncover an additional hot gas component in the S140 region.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Acknowledgements and appendices (pages 5 to 7) are only available in electronic form at http://www.aanda.org Title: Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Stäuber, P.; Wampfler, S. F.; Melchior, M.; Dedes, C.; Wyrowski, F.; Doty, S. D.; van der Tak, F.; Bächtold, W.; Csillaghy, A.; Megej, A.; Monstein, C.; Soldati, M.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dieleman, P.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Jellema, W.; Johnstone, D.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Ossenkopf, V.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Schieder, R.; Shipman, R.; Stutzki, J.; Tafalla, M.; Tielens, A. G. G. M.; van Kempen, T. A.; Visser, R.; Yıldız, U. A. Bibcode: 2010A&A...521L..35B Altcode: 2010arXiv1007.3370B Context. Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays.
Aims: We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation.
Methods: W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (≃2500 s) in 8 spectral regions.
Results: The target lines including CH, NH, H3O+, and the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J = 1-0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds.
Conclusions: The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.

Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.Appendix (page 5) is only available in electronic form at http://www.aanda.org Title: Water vapor toward starless cores: The Herschel view Authors: Caselli, P.; Keto, E.; Pagani, L.; Aikawa, Y.; Yıldız, U. A.; van der Tak, F. F. S.; Tafalla, M.; Bergin, E. A.; Nisini, B.; Codella, C.; van Dishoeck, E. F.; Bachiller, R.; Baudry, A.; Benedettini, M.; Benz, A. O.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Bruderer, S.; Cernicharo, J.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Gaier, T.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Herpin, F.; Hogerheijde, M. R.; Jackson, B.; Jacq, T.; Javadi, H.; Johnstone, D.; Jørgensen, J. K.; Kester, D.; Kristensen, L. E.; Laauwen, W.; Larsson, B.; Lis, D.; Liseau, R.; Luinge, W.; Marseille, M.; McCoey, C.; Megej, A.; Melnick, G.; Neufeld, D.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Siegel, P.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Wyrowski, F. Bibcode: 2010A&A...521L..29C Altcode: 2010arXiv1007.1248C
Aims: Previous studies by the satellites SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7 × 10-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation.
Methods: High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with the Heterodyne Instrument for the Far Infrared onboard Herschel toward two starless cores: Barnard 68 (hereafter B68), a Bok globule, and LDN 1544 (L1544), a prestellar core embedded in the Taurus molecular cloud complex. Detailed radiative transfer and chemical codes were used to analyze the data.
Results: The RMS in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s-1. The continuum level is 3.5 ± 0.2 mK in B68 and 11.4 ± 0.4 mK in L1544. No significant feature is detected in B68 and the 3σ upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5 × 1013 cm-2, or a fractional abundance x(o-H2O) < 1.3 × 10-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5σ level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8 ± 4) × 1012 cm-2. The corresponding fractional abundance is x(o-H2O) ≃ 5 × 10-9 at radii >7000 AU and ≃2 × 10-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ≃10-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible.
Conclusions: Herschel has provided the first measurement of water vapor in dark regions. Column densities of o-H2O are low, but prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) appear to be very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds and oxygen chemistry in the earliest stages of star formation.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Herschel/HIFI spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2 Authors: Johnstone, D.; Fich, M.; McCoey, C.; van Kempen, T. A.; Fuente, A.; Kristensen, L. E.; Cernicharo, J.; Caselli, P.; Visser, R.; Plume, R.; Herczeg, G. J.; van Dishoeck, E. F.; Wampfler, S.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Benz, A. O.; Bjerkeli, P.; Blake, G.; Bontemps, S.; Braine, J.; Bruderer, S.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Jørgensen, J. K.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van der Tak, F.; Wyrowski, F.; Yıldız, U. A.; Caux, E.; Honingh, N.; Jellema, W.; Schieder, R.; Teyssier, D.; Whyborn, N. Bibcode: 2010A&A...521L..41J Altcode: 2010arXiv1008.1254J Herschel/HIFI observations of water from the intermediate mass protostar NGC 7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four H216O and two H218O lines, were observed and all but one H218O line were detected. The four H216O lines discussed here share a similar morphology: a narrower, ≈6 km s-1, component centered slightly redward of the systemic velocity of NGC 7129 FIRS 2 and a much broader, ≈25 km s-1 component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H2O is constrained to ≈10-7 for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H2O/CO relative abundance is found to be ≈0.2, appears to be tracing the same energetic region that produces strong CO emission at high J.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Appendix (page 6) is only available in electronic form at http://www.aanda.org Title: Herschel/HIFI discovery of interstellar chloronium (H2Cl+) Authors: Lis, D. C.; Pearson, J. C.; Neufeld, D. A.; Schilke, P.; Müller, H. S. P.; Gupta, H.; Bell, T. A.; Comito, C.; Phillips, T. G.; Bergin, E. A.; Ceccarelli, C.; Goldsmith, P. F.; Blake, G. A.; Bacmann, A.; Baudry, A.; Benedettini, M.; Benz, A.; Black, J.; Boogert, A.; Bottinelli, S.; Cabrit, S.; Caselli, P.; Castets, A.; Caux, E.; Cernicharo, J.; Codella, C.; Coutens, A.; Crimier, N.; Crockett, N. R.; Daniel, F.; Demyk, K.; Dominic, C.; Dubernet, M. -L.; Emprechtinger, M.; Encrenaz, P.; Falgarone, E.; Fuente, A.; Gerin, M.; Giesen, T. F.; Goicoechea, J. R.; Helmich, F.; Hennebelle, P.; Henning, Th.; Herbst, E.; Hily-Blant, P.; Hjalmarson, Å.; Hollenbach, D.; Jack, T.; Joblin, C.; Johnstone, D.; Kahane, C.; Kama, M.; Kaufman, M.; Klotz, A.; Langer, W. D.; Larsson, B.; Le Bourlot, J.; Lefloch, B.; Le Petit, F.; Li, D.; Liseau, R.; Lord, S. D.; Lorenzani, A.; Maret, S.; Martin, P. G.; Melnick, G. J.; Menten, K. M.; Morris, P.; Murphy, J. A.; Nagy, Z.; Nisini, B.; Ossenkopf, V.; Pacheco, S.; Pagani, L.; Parise, B.; Pérault, M.; Plume, R.; Qin, S. -L.; Roueff, E.; Salez, M.; Sandqvist, A.; Saraceno, P.; Schlemmer, S.; Schuster, K.; Snell, R.; Stutzki, J.; Tielens, A.; Trappe, N.; van der Tak, F. F. S.; van der Wiel, M. H. D.; van Dishoeck, E.; Vastel, C.; Viti, S.; Wakelam, V.; Walters, A.; Wang, S.; Wyrowski, F.; Yorke, H. W.; Yu, S.; Zmuidzinas, J.; Delorme, Y.; Desbat, J. -P.; Güsten, R.; Krieg, J. -M.; Delforge, B. Bibcode: 2010A&A...521L...9L Altcode: 2010arXiv1007.1461L We report the first detection of chloronium, H2Cl+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory. The 212-101 lines of ortho-H_235Cl+ and ortho-H_237Cl+ are detected in absorption towards NGC 6334I, and the 111-000 transition of para-H_235Cl+ is detected in absorption towards NGC 6334I and Sgr B2(S). The H2Cl+ column densities are compared to those of the chemically-related species HCl. The derived HCl/H2Cl+ column density ratios, ~1-10, are within the range predicted by models of diffuse and dense photon dominated regions (PDRs). However, the observed H2Cl+ column densities, in excess of 1013 cm-2, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Table 1 and acknowledgments (page 5) are only available in electronic form at http://www.aanda.org Title: Water abundances in high-mass protostellar envelopes: Herschel observations with HIFI Authors: Marseille, M. G.; van der Tak, F. F. S.; Herpin, F.; Wyrowski, F.; Chavarría, L.; Pietropaoli, B.; Baudry, A.; Bontemps, S.; Cernicharo, J.; Jacq, T.; Frieswijk, W.; Shipman, R.; van Dishoeck, E. F.; Bachiller, R.; Benedettini, M.; Benz, A. O.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Braine, J.; Bruderer, S.; Caselli, P.; Caux, E.; Codella, C.; Daniel, F.; Dieleman, P.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Gaier, T.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Hogerheijde, M. R.; Jackson, B.; Javadi, H.; Jellema, W.; Johnstone, D.; Jørgensen, J. K.; Kester, D.; Kristensen, L. E.; Larsson, B.; Laauwen, W.; Lis, D.; Liseau, R.; Luinge, W.; McCoey, C.; Megej, A.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Roelfsema, P.; Santiago-García, J.; Saraceno, P.; Siegel, P.; Stutzki, J.; Tafalla, M.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Yıldız, U. A. Bibcode: 2010A&A...521L..32M Altcode: 2010arXiv1007.4119M
Aims: We derive the dense core structure and the water abundance in four massive star-forming regions in the hope of understanding the earliest stages of massive star formation.
Methods: We present Herschel/HIFI observations of the para-H2O 111-000 and 202-111 and the para-H_218O 111-000 transitions. The envelope contribution to the line profiles is separated from contributions by outflows and foreground clouds. The envelope contribution is modeled with Monte-Carlo radiative transfer codes for dust and molecular lines (MC3D and RATRAN), and the water abundance and the turbulent velocity width as free parameters.
Results: While the outflows are mostly seen in emission in high-J lines, envelopes are seen in absorption in ground-state lines, which are almost saturated. The derived water abundances range from 5×10-10 to 4×10-8 in the outer envelopes. We detect cold clouds surrounding the protostar envelope, thanks to the very high quality of the Herschel/HIFI data and the unique ability of water to probe them. Several foreground clouds are also detected along the line of sight.
Conclusions: The low H2O abundances in massive dense cores are in accordance with the expectation that high densities and low temperatures lead to freeze-out of water on dust grains. The spread in abundance values is not clearly linked to physical properties of the sources.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation of NASA.Appendix (pages 6 to 7) is only available in electronic form at http://www.aanda.org Title: Herschel observations in the ultracompact HII region Mon R2. Water in dense photon-dominated regions (PDRs) Authors: Fuente, A.; Berné, O.; Cernicharo, J.; Rizzo, J. R.; González-García, M.; Goicoechea, J. R.; Pilleri, P.; Ossenkopf, V.; Gerin, M.; Güsten, R.; Akyilmaz, M.; Benz, A. O.; Boulanger, F.; Bruderer, S.; Dedes, C.; France, K.; García-Burillo, S.; Harris, A.; Joblin, C.; Klein, T.; Kramer, C.; Le Petit, F.; Lord, S. D.; Martin, P. G.; Martín-Pintado, J.; Mookerjea, B.; Neufeld, D. A.; Okada, Y.; Pety, J.; Phillips, T. G.; Röllig, M.; Simon, R.; Stutzki, J.; van der Tak, F.; Teyssier, D.; Usero, A.; Yorke, H.; Schuster, K.; Melchior, M.; Lorenzani, A.; Szczerba, R.; Fich, M.; McCoey, C.; Pearson, J.; Dieleman, P. Bibcode: 2010A&A...521L..23F Altcode: 2010arXiv1007.1523F Context. Monoceros R2, at a distance of 830 pc, is the only ultracompact H ii region (UC H ii) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. Therefore, it is an excellent laboratory to study the chemistry in extreme PDRs (G0 > 105 in units of Habing field, n > 106 cm-3).
Aims: Our ultimate goal is to probe the physical and chemical conditions in the PDR around the UC H ii Mon R2.
Methods: HIFI observations of the abundant compounds 13CO, C18O, o-H218O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The modeling of the lines has been done with the Meudon PDR code and the non-local radiative transfer model described by Cernicharo et al.
Results: The 13CO, C18O, o-H_218O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n = 5 × 106 cm-3, N(H2)> 1022 cm-2) layer of molecular gas around the H ii region. Based on our o-H_218O observations, we estimate an o-H2O abundance of ≈2 × 10-8. This is the average ortho-water abundance in the PDR. Additional H_218O and/or water lines are required to derive the water abundance profile. A lower density envelope (n ~ 105 cm-3, N(H2) = 2-5 × 1022 cm-2) is responsible for the absorption in the NH 1_1→ 0_2 line. The emission of the CH ground state triplet is coming from both regions with a complex and self-absorbed profile in the main component. The radiative transfer modeling shows that the 13CO and HCO+ line profiles are consistent with an expansion of the molecular gas with a velocity law, ve = 0.5 × (r/Rout)-1 km s-1, although the expansion velocity is poorly constrained by the observations presented here.
Conclusions: We determine an ortho-water abundance of ≈2 × 10-8 in Mon R2. Because shocks are unimportant in this region and our estimate is based on H_218O observations that avoids opacity problems, this is probably the most accurate estimate of the water abundance in PDRs thus far.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figures 1 and 4 (page 5) are only available in electronic form at http://www.aanda.org Title: Herschel/HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region Authors: Yıldız, U. A.; van Dishoeck, E. F.; Kristensen, L. E.; Visser, R.; Jørgensen, J. K.; Herczeg, G. J.; van Kempen, T. A.; Hogerheijde, M. R.; Doty, S. D.; Benz, A. O.; Bruderer, S.; Wampfler, S. F.; Deul, E.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Jacq, T.; Johnstone, D.; Larsson, B.; Lis, D.; Liseau, R.; Liu, F. -C.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; Tielens, A. G. G. M.; van der Tak, F.; Wyrowski, F.; Dieleman, P.; Jellema, W.; Ossenkopf, V.; Schieder, R.; Stutzki, J. Bibcode: 2010A&A...521L..40Y Altcode: 2010arXiv1008.0867Y Herschel/HIFI observations of high-J lines (up to Ju = 10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are complemented by ground-based observations of lower-J CO and isotopologue lines. The 12CO 10-9 profiles are dominated by broad (FWHM 25-30 km s-1) emission. Radiative transfer models are used to constrain the temperature of this shocked gas to 100-200 K. Several CO and 13CO line profiles also reveal a medium-broad component (FWHM5-10 km s-1), seen prominently in H2O lines. Column densities for both components are presented, providing a reference for determining abundances of other molecules in the same gas. The narrow C18O 9-8 lines probe the warmer part of the quiescent envelope. Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices and acknowledgements (pages 5 to 7) are only available in electronic form at http://www.aanda.org Title: Herschel observations of the hydroxyl radical (OH) in young stellar objects Authors: Wampfler, S. F.; Herczeg, G. J.; Bruderer, S.; Benz, A. O.; van Dishoeck, E. F.; Kristensen, L. E.; Visser, R.; Doty, S. D.; Melchior, M.; van Kempen, T. A.; Yıldız, U. A.; Dedes, C.; Goicoechea, J. R.; Baudry, A.; Melnick, G.; Bachiller, R.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; de Graauw, Th.; Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Johnstone, D.; Jørgensen, J. K.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.; Roelfsema, P.; Jellema, W.; Dieleman, P.; Caux, E.; Stutzki, J. Bibcode: 2010A&A...521L..36W Altcode: 2010arXiv1007.2198W
Aims: “Water In Star-forming regions with Herschel” (WISH) is a Herschel key program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature (T ⪆ 250 K) chemistry connects OH and H2O through the OH + H2 Leftrightarrow H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O through H2O + γUV Rightarrow OH + H.
Methods: High-resolution spectroscopy of the 163.12 μm triplet of OH towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory. The low- and intermediate-mass protostars HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) on Herschel in four transitions of OH and two [O i] lines.
Results: The OH transitions at 79, 84, 119, and 163 μm and [O i] emission at 63 and 145 μm were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 μm was detected in absorption. With HIFI, the 163.12 μm was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM ⪆ 11 km s-1) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [O i] flux and the bolometric luminosity, as found in our sample. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices (page 6) are only available in electronic form at http://www.aanda.org Title: Water in massive star-forming regions: HIFI observations of W3 IRS5 Authors: Chavarría, L.; Herpin, F.; Jacq, T.; Braine, J.; Bontemps, S.; Baudry, A.; Marseille, M.; van der Tak, F.; Pietropaoli, B.; Wyrowski, F.; Shipman, R.; Frieswijk, W.; van Dishoeck, E. F.; Cernicharo, J.; Bachiller, R.; Benedettini, M.; Benz, A. O.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bruderer, S.; Caselli, P.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Hartogh, P.; Helmich, F.; Herczeg, G. J.; Hogerheijde, M. R.; Johnstone, D.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.; Lis, D.; Liseau, R.; McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Stutzki, J.; Szczerba, R.; Tafalla, M.; Tielens, A.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Willem, J.; Yıldız, U. A. Bibcode: 2010A&A...521L..37C Altcode: 2010arXiv1007.3986C We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-H_217O 110-101, p-H_218O 111-000, p-H2O 202-111, p-H2O 111-000, o-H2O 221-212, and o-H2O 212-101 lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H2O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H2O 111-000 and o-H2O 212-101 lines show absorption from the cold material (T ~ 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T ≳ 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10-4) is needed to reproduce the o-H_217O 110-101 and p-H_218O 111-000 spectra in our models. We estimate water abundances of 10-8 to 10-9 in the outer parts of the envelope (T ≲ 100 K). The possibility of two protostellar objects contributing to the emission is discussed.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk Authors: Bergin, E. A.; Hogerheijde, M. R.; Brinch, C.; Fogel, J.; Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Bell, T. A.; Blake, G. A.; Cernicharo, J.; Dominik, C.; Lis, D.; Melnick, G.; Neufeld, D.; Panić, O.; Pearson, J. C.; Bachiller, R.; Baudry, A.; Benedettini, M.; Benz, A. O.; Bjerkeli, P.; Bontemps, S.; Braine, J.; Bruderer, S.; Caselli, P.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Herpin, F.; Jacq, T.; Johnstone, D.; Jørgensen, J. K.; Larsson, B.; Liseau, R.; Marseille, M.; McCoey, C.; Nisini, B.; Olberg, M.; Parise, B.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Wyrowski, F.; van der Tak, F.; Jellema, W.; Tielens, A. G. G. M.; Hartogh, P.; Stützki, J.; Szczerba, R. Bibcode: 2010A&A...521L..33B Altcode: 2010arXiv1007.2129B We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3σ levels in 0.5 km s-1 channels of 4.2 mK for the 110-101 line and 12.6 mK for the 111-000 line. We report a very tentative detection, however, of the 110-101 line in the wide band spectrometer, with a strength of Tmb = 2.7 mK, a width of 5.6 km s-1 and an integrated intensity of 16.0 mK km s-1. The latter constitutes a 6σ detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with participation important from NASA. Title: Gas morphology and energetics at the surface of PDRs: New insights with Herschel observations of NGC 7023 Authors: Joblin, C.; Pilleri, P.; Montillaud, J.; Fuente, A.; Gerin, M.; Berné, O.; Ossenkopf, V.; Le Bourlot, J.; Teyssier, D.; Goicoechea, J. R.; Le Petit, F.; Röllig, M.; Akyilmaz, M.; Benz, A. O.; Boulanger, F.; Bruderer, S.; Dedes, C.; France, K.; Güsten, R.; Harris, A.; Klein, T.; Kramer, C.; Lord, S. D.; Martin, P. G.; Martin-Pintado, J.; Mookerjea, B.; Okada, Y.; Phillips, T. G.; Rizzo, J. R.; Simon, R.; Stutzki, J.; van der Tak, F.; Yorke, H. W.; Steinmetz, E.; Jarchow, C.; Hartogh, P.; Honingh, C. E.; Siebertz, O.; Caux, E.; Colin, B. Bibcode: 2010A&A...521L..25J Altcode: 2010arXiv1008.1315J Context. We investigate the physics and chemistry of the gas and dust in dense photon-dominated regions (PDRs), along with their dependence on the illuminating UV field.
Aims: Using Herschel/HIFI observations, we study the gas energetics in NGC 7023 in relation to the morphology of this nebula. NGC 7023 is the prototype of a PDR illuminated by a B2V star and is one of the key targets of Herschel.
Methods: Our approach consists in determining the energetics of the region by combining the information carried by the mid-IR spectrum (extinction by classical grains, emission from very small dust particles) with that of the main gas coolant lines. In this letter, we discuss more specifically the intensity and line profile of the 158 μm (1901 GHz) [C ii] line measured by HIFI and provide information on the emitting gas.
Results: We show that both the [C ii] emission and the mid-IR emission from polycyclic aromatic hydrocarbons (PAHs) arise from the regions located in the transition zone between atomic and molecular gas. Using the Meudon PDR code and a simple transfer model, we find good agreement between the calculated and observed [C ii] intensities.
Conclusions: HIFI observations of NGC 7023 provide the opportunity to constrain the energetics at the surface of PDRs. Future work will include analysis of the main coolant line [O i] and use of a new PDR model that includes PAH-related species.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Herschel spectral surveys of star-forming regions. Overview of the 555-636 GHz range Authors: Ceccarelli, C.; Bacmann, A.; Boogert, A.; Caux, E.; Dominik, C.; Lefloch, B.; Lis, D.; Schilke, P.; van der Tak, F.; Caselli, P.; Cernicharo, J.; Codella, C.; Comito, C.; Fuente, A.; Baudry, A.; Bell, T.; Benedettini, M.; Bergin, E. A.; Blake, G. A.; Bottinelli, S.; Cabrit, S.; Castets, A.; Coutens, A.; Crimier, N.; Demyk, K.; Encrenaz, P.; Falgarone, E.; Gerin, M.; Goldsmith, P. F.; Helmich, F.; Hennebelle, P.; Henning, T.; Herbst, E.; Hily-Blant, P.; Jacq, T.; Kahane, C.; Kama, M.; Klotz, A.; Langer, W.; Lord, S.; Lorenzani, A.; Maret, S.; Melnick, G.; Neufeld, D.; Nisini, B.; Pacheco, S.; Pagani, L.; Parise, B.; Pearson, J.; Phillips, T.; Salez, M.; Saraceno, P.; Schuster, K.; Tielens, X.; van der Wiel, M. H. D.; Vastel, C.; Viti, S.; Wakelam, V.; Walters, A.; Wyrowski, F.; Yorke, H.; Liseau, R.; Olberg, M.; Szczerba, R.; Benz, A. O.; Melchior, M. Bibcode: 2010A&A...521L..22C Altcode: High resolution line spectra of star-forming regions are mines of information: they provide unique clues to reconstruct the chemical, dynamical, and physical structure of the observed source. We present the first results from the Herschel key project “Chemical HErschel Surveys of Star forming regions”, CHESS. We report and discuss observations towards five CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20 and 2 × 105 L_⊙: L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The observations were obtained with the heterodyne spectrometer HIFI on board Herschel, with a spectral resolution of 1 MHz. They cover the frequency range 555-636 GHz, a range largely unexplored before the launch of the Herschel satellite. A comparison of the five spectra highlights spectacular differences in the five sources, for example in the density of methanol lines, or the presence/absence of lines from S-bearing molecules or deuterated species. We discuss how these differences can be attributed to the different star-forming mass or evolutionary status.

Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.Figures [see full textsee full text]-[see full textsee full text] and Tables 3, 4 (pages 6 to 8) are only available in electronic form at http://www.aanda.org Title: First detection of ND in the solar-mass protostar IRAS16293-2422 Authors: Bacmann, A.; Caux, E.; Hily-Blant, P.; Parise, B.; Pagani, L.; Bottinelli, S.; Maret, S.; Vastel, C.; Ceccarelli, C.; Cernicharo, J.; Henning, T.; Castets, A.; Coutens, A.; Bergin, E. A.; Blake, G. A.; Crimier, N.; Demyk, K.; Dominik, C.; Gerin, M.; Hennebelle, P.; Kahane, C.; Klotz, A.; Melnick, G.; Schilke, P.; Wakelam, V.; Walters, A.; Baudry, A.; Bell, T.; Benedettini, M.; Boogert, A.; Cabrit, S.; Caselli, P.; Codella, C.; Comito, C.; Encrenaz, P.; Falgarone, E.; Fuente, A.; Goldsmith, P. F.; Helmich, F.; Herbst, E.; Jacq, T.; Kama, M.; Langer, W.; Lefloch, B.; Lis, D.; Lord, S.; Lorenzani, A.; Neufeld, D.; Nisini, B.; Pacheco, S.; Pearson, J.; Phillips, T.; Salez, M.; Saraceno, P.; Schuster, K.; Tielens, X.; van der Tak, F. F. S.; van der Wiel, M. H. D.; Viti, S.; Wyrowski, F.; Yorke, H.; Faure, A.; Benz, A.; Coeur-Joly, O.; Cros, A.; Güsten, R.; Ravera, L. Bibcode: 2010A&A...521L..42B Altcode: 2010arXiv1007.4691B Context. In the past decade, much progress has been made in characterising the processes leading to the enhanced deuterium fractionation observed in the ISM and in particular in the cold, dense parts of star forming regions such as protostellar envelopes. Very high molecular D/H ratios have been found for saturated molecules and ions. However, little is known about the deuterium fractionation in radicals, even though simple radicals often represent an intermediate stage in the formation of more complex, saturated molecules. The imidogen radical NH is such an intermediate species for the ammonia synthesis in the gas phase. Many of these light molecules however have their fundamental transitions in the submillimetre domain and their detection is hampered by the opacity of the atmosphere at these wavelengths. Herschel/HIFI represents a unique opportunity to study the deuteration and formation mechanisms of species not observable from the ground.
Aims: We searched here for the deuterated radical ND in order to determine the deuterium fractionation of imidogen and constrain the deuteration mechanism of this species.
Methods: We observed the solar-mass Class 0 protostar IRAS16293-2422 with the heterodyne instrument HIFI in Bands 1a (480-560 GHz), 3b (858-961 GHz), and 4a (949-1061 GHz) as part of the Herschel key programme CHESS (Chemical HErschel Survey of Star forming regions).
Results: The deuterated form of the imidogen radical ND was detected and securely identified with 2 hyperfine component groups of its fundamental transition (N = 0-1) at 522.1 and 546.2 GHz, in absorption against the continuum background emitted from the nascent protostar. The 3 groups of hyperfine components of its hydrogenated counterpart NH were also detected in absorption. The absorption arises from the cold envelope, where many deuterated species have been shown to be abundant. The estimated column densities are ~2 × 1014 cm-2 for NH and ~ 1.3 × 1014 cm-2 for ND. We derive a very high deuterium fractionation with an [ND]/[NH] ratio of between 30 and 100%.
Conclusions: The deuterium fractionation of imidogen is of the same order of magnitude as that in other molecules, which suggests that an efficient deuterium fractionation mechanism is at play. We discuss two possible formation pathways for ND, by means of either the reaction of N+ with HD, or deuteron/proton exchange with NH.

Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA. Title: Variations in H2O+/H2O ratios toward massive star-forming regions Authors: Wyrowski, F.; van der Tak, F.; Herpin, F.; Baudry, A.; Bontemps, S.; Chavarria, L.; Frieswijk, W.; Jacq, T.; Marseille, M.; Shipman, R.; van Dishoeck, E. F.; Benz, A. O.; Caselli, P.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Bachiller, R.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G.; Braine, J.; Bruderer, S.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.; Lis, D.; McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago, J.; Saraceno, P.; Tafalla, M.; van Kempen, T. A.; Visser, R.; Wampfler, S.; Yıldız, U. A.; Black, J. H.; Falgarone, E.; Gerin, M.; Roelfsema, P.; Dieleman, P.; Beintema, D.; de Jonge, A.; Whyborn, N.; Stutzki, J.; Ossenkopf, V. Bibcode: 2010A&A...521L..34W Altcode: 2010arXiv1007.4370W Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+. Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2O+ are found in the range of 1012 to a few 1013 cm-2. The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: A high-resolution line survey of IRC +10216 with Herschel/HIFI. First results: Detection of warm silicon dicarbide (SiC{_2}) Authors: Cernicharo, J.; Waters, L. B. F. M.; Decin, L.; Encrenaz, P.; Tielens, A. G. G. M.; Agúndez, M.; De Beck, E.; Müller, H. S. P.; Goicoechea, J. R.; Barlow, M. J.; Benz, A.; Crimier, N.; Daniel, F.; di Giorgio, A. M.; Fich, M.; Gaier, T.; García-Lario, P.; de Koter, A.; Khouri, T.; Liseau, R.; Lombaert, R.; Erickson, N.; Pardo, J. R.; Pearson, J. C.; Shipman, R.; Sánchez Contreras, C.; Teyssier, D. Bibcode: 2010A&A...521L...8C Altcode: 2010arXiv1008.1199C We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901 GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5-636.5 GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC2). We identified 55 SiC2 transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC2 is produced in the inner dust formation zone, with an abundance of ~ 2 × 10-7 relative to molecular hydrogen. These SiC2 lines have been observed for the first time in space and have been used to derive an SiC2 rotational temperature of ~204 K and a source-averaged column density of ~ 6.4 × 1015 cm-2. Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC2.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix (pages 6, 7) is only available in electronic form at http://www.aanda.org Title: Water in low-mass star-forming regions with Herschel . HIFI spectroscopy of NGC 1333 Authors: Kristensen, L. E.; Visser, R.; van Dishoeck, E. F.; Yıldız, U. A.; Doty, S. D.; Herczeg, G. J.; Liu, F. -C.; Parise, B.; Jørgensen, J. K.; van Kempen, T. A.; Brinch, C.; Wampfler, S. F.; Bruderer, S.; Benz, A. O.; Hogerheijde, M. R.; Deul, E.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E. A.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; de Graauw, Th.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; Helmich, F.; Herpin, F.; Jacq, T.; Johnstone, D.; Kaufman, M. J.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; Tielens, A. G. G. M.; van der Tak, F.; Wyrowski, F.; Beintema, D.; de Jonge, A.; Dieleman, P.; Ossenkopf, V.; Roelfsema, P.; Stutzki, J.; Whyborn, N. Bibcode: 2010A&A...521L..30K Altcode: 2010arXiv1007.3031K “Water In Star-forming regions with Herschel” (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC 1333 in several H_216O, H_218O, and CO transitions. Line profiles are resolved for five H_216O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km s-1), medium-broad (~5-10 km s-1), and narrow (<5 km s-1) components. The H_218O emission is only detected in broad 110-101 lines (>20 km s-1), indicating that its physical origin is the same as for the broad H_216O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (⪉1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line profiles are compared to CO line profiles to constrain the H2O abundance as a function of velocity within these shocked regions. The H2O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H2O abundances of ~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 2 and 3 (page 6) are only available in electronic form at http://www.aanda.org Title: Physical Processes in Magnetically Driven Flares on the Sun, Stars, and Young Stellar Objects Authors: Benz, Arnold O.; Güdel, Manuel Bibcode: 2010ARA&A..48..241B Altcode: The first flare on the Sun was observed exactly 150 years ago. During most of the long history, only secondary effects have been noticed, so flares remained a riddle. Now the primary flare products, high-energy electrons and ions, can be spatially resolved in hard X-rays (HXRs) and gamma rays on the Sun. Soft X-rays (SXRs) are observed from most stars, including young stellar objects. Structure and bulk motions of the corona are imaged on the Sun in high temperature lines and are inferred from line shifts in stellar coronae. Magnetic reconnection is the trigger for reorganization of the magnetic field into a lower energy configuration. A large fraction of the energy is converted into nonthermal particles that transport the energy to higher density gas, heating it to SXR-emitting temperatures. Flares on young stars are several orders of magnitude more luminous and more frequent; they significantly ionize protoplanetary disks and planetary ionospheres. Title: Multidimensional Chemical Modeling of Young Stellar Objects. III. The Influence of Geometry on the Abundance and Excitation of Diatomic Hydrides Authors: Bruderer, S.; Benz, A. O.; Stäuber, P.; Doty, S. D. Bibcode: 2010ApJ...720.1432B Altcode: The Herschel Space Observatory enables observations in the far-infrared at high spectral and spatial resolution. A particular class of molecules will be directly observable: light diatomic hydrides and their ions (CH, OH, SH, NH, CH+, OH+, SH+, NH+). These simple constituents are important both for the chemical evolution of the region and as tracers of high-energy radiation. If outflows of a forming star erode cavities in the envelope, protostellar far-UV (FUV; 6 < E γ < 13.6 eV) radiation may escape through such low-density regions. Depending on the shape of the cavity, the FUV radiation then irradiates the quiescent envelope in the walls along the outflow. The chemical composition in these outflow walls is altered by photoreactions and heating via FUV photons in a manner similar to photo-dominated regions. In this work, we study the effect of cavity shapes, outflow density, and of a disk with the two-dimensional chemical model of a high-mass young stellar object introduced in the second paper in this series. The model has been extended with a self-consistent calculation of the dust temperature and a multi-zone escape probability method for the calculation of the molecular excitation and the prediction of line fluxes. We find that the shape of the cavity is particularly important in the innermost part of the envelope, where the dust temperatures are high enough (gsim100 K) for water ice to evaporate. If the cavity shape allows FUV radiation to penetrate this hot-core region, the abundance of FUV-destroyed species (e.g., water) is decreased. On larger scales, the shape of the cavity is less important for the chemistry in the outflow wall. In particular, diatomic hydrides and their ions CH+, OH+, and NH+ are enhanced by many orders of magnitude in the outflow walls due to the combination of high gas temperatures and rapid photodissociation of more saturated species. The enhancement of these diatomic hydrides is sufficient for a detection using the HIFI and PACS instruments on board Herschel. The effect of X-ray ionization on the chemistry is found to be small, due to the much larger luminosity in FUV bands compared to X-rays. Title: Water cooling of shocks in protostellar outflows. Herschel-PACS map of L1157 Authors: Nisini, B.; Benedettini, M.; Codella, C.; Giannini, T.; Liseau, R.; Neufeld, D.; Tafalla, M.; van Dishoeck, E. F.; Bachiller, R.; Baudry, A.; Benz, A. O.; Bergin, E.; Bjerkeli, P.; Blake, G.; Bontemps, S.; Braine, J.; Bruderer, S.; Caselli, P.; Cernicharo, J.; Daniel, F.; Encrenaz, P.; di Giorgio, A. M.; Dominik, C.; Doty, S.; Fich, M.; Fuente, A.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G.; Herpin, F.; Hogerheijde, M.; Jacq, T.; Johnstone, D.; Jørgensen, J.; Kaufman, M.; Kristensen, L.; Larsson, B.; Lis, D.; Marseille, M.; McCoey, C.; Melnick, G.; Olberg, M.; Parise, B.; Pearson, J.; Plume, R.; Risacher, C.; Santiago, J.; Saraceno, P.; Shipman, R.; van Kempen, T. A.; Visser, R.; Viti, S.; Wampfler, S.; Wyrowski, F.; van der Tak, F.; Yıldız, U. A.; Delforge, B.; Desbat, J.; Hatch, W. A.; Péron, I.; Schieder, R.; Stern, J. A.; Teyssier, D.; Whyborn, N. Bibcode: 2010A&A...518L.120N Altcode: 2010arXiv1005.4517N Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H2O emission with a spatial resolution comparable to ground based mm/sub-mm observations.
Aims: In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 μm transition obtained toward the young outflow L1157.
Methods: The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H2O abundance and total cooling.
Results: Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 μm emission is spatially correlated with emission from H2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10-4. This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H2O cooling is ~10-1 L_⊙, about 40% of the cooling due to H2 and 23% of the total energy released in shocks along the L1157 outflow.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important partecipation from NASA. Title: HIFI observations of warm gas in DR21: Shock versus radiative heating Authors: Ossenkopf, V.; Röllig, M.; Simon, R.; Schneider, N.; Okada, Y.; Stutzki, J.; Gerin, M.; Akyilmaz, M.; Beintema, D.; Benz, A. O.; Berne, O.; Boulanger, F.; Bumble, B.; Coeur-Joly, O.; Dedes, C.; Diez-Gonzalez, M. C.; France, K.; Fuente, A.; Gallego, J. D.; Goicoechea, J. R.; Güsten, R.; Harris, A.; Higgins, R.; Jackson, B.; Jarchow, C.; Joblin, C.; Klein, T.; Kramer, C.; Lord, S.; Martin, P.; Martin-Pintado, J.; Mookerjea, B.; Neufeld, D. A.; Phillips, T.; Rizzo, J. R.; van der Tak, F. F. S.; Teyssier, D.; Yorke, H. Bibcode: 2010A&A...518L..79O Altcode: 2010arXiv1005.2517O Context. The molecular gas in the DR21 massive star formation region is known to be affected by the strong UV field from the central star cluster and by a fast outflow creating a bright shock. The relative contribution of both heating mechanisms is the matter of a long debate.
Aims: By better sampling the excitation ladder of various tracers we provide a quantitative distinction between the different heating mechanisms.
Methods: HIFI observations of mid-J transitions of CO and HCO+ isotopes allow us to bridge the gap in excitation energies between observations from the ground, characterizing the cooler gas, and existing ISO LWS spectra, constraining the properties of the hot gas. Comparing the detailed line profiles allows to identify the physical structure of the different components.
Results: In spite of the known shock-excitation of H2 and the clearly visible strong outflow, we find that the emission of all lines up to ⪆2 THz can be explained by purely radiative heating of the material. However, the new Herschel/HIFI observations reveal two types of excitation conditions. We find hot and dense clumps close to the central cluster, probably dynamically affected by the outflow, and a more widespread distribution of cooler, but nevertheless dense, molecular clumps.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Water abundance variations around high-mass protostars: HIFI observations of the DR21 region Authors: van der Tak, F. F. S.; Marseille, M. G.; Herpin, F.; Wyrowski, F.; Baudry, A.; Bontemps, S.; Braine, J.; Doty, S.; Frieswijk, W.; Melnick, G.; Shipman, R.; van Dishoeck, E. F.; Benz, A. O.; Caselli, P.; Hogerheijde, M.; Johnstone, D.; Liseau, R.; Bachiller, R.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G.; Bruderer, S.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J.; de Graauw, Th.; Helmich, F.; Herczeg, G.; Jørgensen, J.; Kristensen, L.; Larsson, B.; Lis, D.; McCoey, C.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J.; Plume, R.; Risacher, C.; Santiago, J.; Saraceno, P.; Tafalla, M.; van Kempen, T.; Visser, R.; Wampfler, S.; Yıldız, U.; Ravera, L.; Roelfsema, P.; Siebertz, O.; Teyssier, D. Bibcode: 2010A&A...518L.107V Altcode: 2010arXiv1005.2903V Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known.
Aims: We study the distribution of dust continuum and H2O and 13CO line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H ii region.
Methods: Herschel-HIFI spectra near 1100 GHz show narrow 13CO 10-9 emission and H2O 111-000 absorption from the dense core and broad emission from the outflow in both lines. The H2O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines.
Results: The dust continuum emission is extended over 36” FWHM, while the 13CO and H2O lines are confined to ≈24” or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of ~2×10-10 for H2O and ~8×10-7 for 13CO in the dense core, and higher H2O abundances of ~4×10-9 in the foreground cloud and ~7×10-7 in the outflow.
Conclusions: The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Origin of the hot gas in low-mass protostars. Herschel-PACS spectroscopy of HH 46 Authors: van Kempen, T. A.; Kristensen, L. E.; Herczeg, G. J.; Visser, R.; van Dishoeck, E. F.; Wampfler, S. F.; Bruderer, S.; Benz, A. O.; Doty, S. D.; Brinch, C.; Hogerheijde, M. R.; Jørgensen, J. K.; Tafalla, M.; Neufeld, D.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E. A.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Jacq, T.; Johnstone, D.; Kaufman, M. J.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; van der Tak, F.; Wyrowski, F.; Yıldız, U. A.; Ciechanowicz, M.; Dubbeldam, L.; Glenz, S.; Huisman, R.; Lin, R. H.; Morris, P.; Murphy, J. A.; Trappe, N. Bibcode: 2010A&A...518L.121V Altcode: 2010arXiv1005.2031V
Aims: “Water In Star-forming regions with Herschel” (WISH) is a Herschel key programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and related species.
Methods: The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory to measure emission in H2O, CO, OH, [O i], and [C ii] lines located between 63 and 186 μm. The excitation and spatial distribution of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible.
Results: Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition, [O i] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km s-1 in both the red- and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [O i] emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 × 10-2 L_⊙, with 60-80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Table 2 is only available in electronic form at http//www.aanda.org Title: Herschel-PACS spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2 Authors: Fich, M.; Johnstone, D.; van Kempen, T. A.; McCoey, C.; Fuente, A.; Caselli, P.; Kristensen, L. E.; Plume, R.; Cernicharo, J.; Herczeg, G. J.; van Dishoeck, E. F.; Wampfler, S.; Gaufre, P.; Gill, J. J.; Javadi, H.; Justen, M.; Laauwen, W.; Luinge, W.; Ossenkopf, V.; Pearson, J.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Benz, A. O.; Bjerkeli, P.; Blake, G.; Bontemps, S.; Braine, J.; Bruderer, S.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Jørgensen, J. K.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Risacher, C.; Santiago, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van der Tak, F.; Visser, R.; Wyrowski, F.; Yıldız, U. A. Bibcode: 2010A&A...518L..86F Altcode: 2010arXiv1006.0210F
Aims: We present preliminary results of the first Herschel spectroscopic observations of NGC 7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope.
Methods: The PACS instrument was used in line spectroscopy mode (R = 1000-5000) with 15 spectral bands between 63 and 185 μm. This provided good detections of 26 spectral lines seen in emission, including lines of H2O, CO, OH, O I, and C II.
Results: Most of the detected lines, particularly those of H2O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines.
Conclusions: It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 3 is only available in electronic form at http://www.aanda.org Title: HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd) Authors: Hartogh, P.; Crovisier, J.; de Val-Borro, M.; Bockelée-Morvan, D.; Biver, N.; Lis, D. C.; Moreno, R.; Jarchow, C.; Rengel, M.; Emprechtinger, M.; Szutowicz, S.; Banaszkiewicz, M.; Bensch, F.; Blecka, M. I.; Cavalié, T.; Encrenaz, T.; Jehin, E.; Küppers, M.; Lara, L. -M.; Lellouch, E.; Swinyard, B. M.; Vandenbussche, B.; Bergin, E. A.; Blake, G. A.; Blommaert, J. A. D. L.; Cernicharo, J.; Decin, L.; Encrenaz, P.; de Graauw, T.; Hutsemekers, D.; Kidger, M.; Manfroid, J.; Medvedev, A. S.; Naylor, D. A.; Schieder, R.; Thomas, N.; Waelkens, C.; Roelfsema, P. R.; Dieleman, P.; Güsten, R.; Klein, T.; Kasemann, C.; Caris, M.; Olberg, M.; Benz, A. O. Bibcode: 2010A&A...518L.150H Altcode: 2010arXiv1005.2969H High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres. We present observations of several rotational ortho- and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 212-101 (1669 GHz) ortho and 111-000 (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 110-101 at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7-2.8 × 1028 s-1 over the range rh = 1.83-1.85 AU.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 5 is only available in electronic form at http://www.aanda.org Title: Detection of interstellar oxidaniumyl: Abundant H2O+ towards the star-forming regions DR21, Sgr B2, and NGC6334 Authors: Ossenkopf, V.; Müller, H. S. P.; Lis, D. C.; Schilke, P.; Bell, T. A.; Bruderer, S.; Bergin, E.; Ceccarelli, C.; Comito, C.; Stutzki, J.; Bacman, A.; Baudry, A.; Benz, A. O.; Benedettini, M.; Berne, O.; Blake, G.; Boogert, A.; Bottinelli, S.; Boulanger, F.; Cabrit, S.; Caselli, P.; Caux, E.; Cernicharo, J.; Codella, C.; Coutens, A.; Crimier, N.; Crockett, N. R.; Daniel, F.; Demyk, K.; Dieleman, P.; Dominik, C.; Dubernet, M. L.; Emprechtinger, M.; Encrenaz, P.; Falgarone, E.; France, K.; Fuente, A.; Gerin, M.; Giesen, T. F.; di Giorgio, A. M.; Goicoechea, J. R.; Goldsmith, P. F.; Güsten, R.; Harris, A.; Helmich, F.; Herbst, E.; Hily-Blant, P.; Jacobs, K.; Jacq, T.; Joblin, Ch.; Johnstone, D.; Kahane, C.; Kama, M.; Klein, T.; Klotz, A.; Kramer, C.; Langer, W.; Lefloch, B.; Leinz, C.; Lorenzani, A.; Lord, S. D.; Maret, S.; Martin, P. G.; Martin-Pintado, J.; McCoey, C.; Melchior, M.; Melnick, G. J.; Menten, K. M.; Mookerjea, B.; Morris, P.; Murphy, J. A.; Neufeld, D. A.; Nisini, B.; Pacheco, S.; Pagani, L.; Parise, B.; Pearson, J. C.; Pérault, M.; Phillips, T. G.; Plume, R.; Quin, S. -L.; Rizzo, R.; Röllig, M.; Salez, M.; Saraceno, P.; Schlemmer, S.; Simon, R.; Schuster, K.; van der Tak, F. F. S.; Tielens, A. G. G. M.; Teyssier, D.; Trappe, N.; Vastel, C.; Viti, S.; Wakelam, V.; Walters, A.; Wang, S.; Whyborn, N.; van der Wiel, M.; Yorke, H. W.; Yu, S.; Zmuidzinas, J. Bibcode: 2010A&A...518L.111O Altcode: 2010arXiv1005.2521O
Aims: We identify a prominent absorption feature at 1115 GHz, detected in first HIFI spectra towards high-mass star-forming regions, and interpret its astrophysical origin.
Methods: The characteristic hyperfine pattern of the H2O+ ground-state rotational transition, and the lack of other known low-energy transitions in this frequency range, identifies the feature as H2O+ absorption against the dust continuum background and allows us to derive the velocity profile of the absorbing gas. By comparing this velocity profile with velocity profiles of other tracers in the DR21 star-forming region, we constrain the frequency of the transition and the conditions for its formation.
Results: In DR21, the velocity distribution of H2O+ matches that of the [C ii] line at 158 μm and of OH cm-wave absorption, both stemming from the hot and dense clump surfaces facing the H ii-region and dynamically affected by the blister outflow. Diffuse foreground gas dominates the absorption towards Sgr B2. The integrated intensity of the absorption line allows us to derive lower limits to the H2O+ column density of 7.2 × 1012 cm-2 in NGC 6334, 2.3 × 1013 cm-2 in DR21, and 1.1 × 1015 cm-2 in Sgr B2.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI) Authors: de Graauw, Th.; Helmich, F. P.; Phillips, T. G.; Stutzki, J.; Caux, E.; Whyborn, N. D.; Dieleman, P.; Roelfsema, P. R.; Aarts, H.; Assendorp, R.; Bachiller, R.; Baechtold, W.; Barcia, A.; Beintema, D. A.; Belitsky, V.; Benz, A. O.; Bieber, R.; Boogert, A.; Borys, C.; Bumble, B.; Caïs, P.; Caris, M.; Cerulli-Irelli, P.; Chattopadhyay, G.; Cherednichenko, S.; Ciechanowicz, M.; Coeur-Joly, O.; Comito, C.; Cros, A.; de Jonge, A.; de Lange, G.; Delforges, B.; Delorme, Y.; den Boggende, T.; Desbat, J. -M.; Diez-González, C.; di Giorgio, A. M.; Dubbeldam, L.; Edwards, K.; Eggens, M.; Erickson, N.; Evers, J.; Fich, M.; Finn, T.; Franke, B.; Gaier, T.; Gal, C.; Gao, J. R.; Gallego, J. -D.; Gauffre, S.; Gill, J. J.; Glenz, S.; Golstein, H.; Goulooze, H.; Gunsing, T.; Güsten, R.; Hartogh, P.; Hatch, W. A.; Higgins, R.; Honingh, E. C.; Huisman, R.; Jackson, B. D.; Jacobs, H.; Jacobs, K.; Jarchow, C.; Javadi, H.; Jellema, W.; Justen, M.; Karpov, A.; Kasemann, C.; Kawamura, J.; Keizer, G.; Kester, D.; Klapwijk, T. M.; Klein, Th.; Kollberg, E.; Kooi, J.; Kooiman, P. -P.; Kopf, B.; Krause, M.; Krieg, J. -M.; Kramer, C.; Kruizenga, B.; Kuhn, T.; Laauwen, W.; Lai, R.; Larsson, B.; Leduc, H. G.; Leinz, C.; Lin, R. H.; Liseau, R.; Liu, G. S.; Loose, A.; López-Fernandez, I.; Lord, S.; Luinge, W.; Marston, A.; Martín-Pintado, J.; Maestrini, A.; Maiwald, F. W.; McCoey, C.; Mehdi, I.; Megej, A.; Melchior, M.; Meinsma, L.; Merkel, H.; Michalska, M.; Monstein, C.; Moratschke, D.; Morris, P.; Muller, H.; Murphy, J. A.; Naber, A.; Natale, E.; Nowosielski, W.; Nuzzolo, F.; Olberg, M.; Olbrich, M.; Orfei, R.; Orleanski, P.; Ossenkopf, V.; Peacock, T.; Pearson, J. C.; Peron, I.; Phillip-May, S.; Piazzo, L.; Planesas, P.; Rataj, M.; Ravera, L.; Risacher, C.; Salez, M.; Samoska, L. A.; Saraceno, P.; Schieder, R.; Schlecht, E.; Schlöder, F.; Schmülling, F.; Schultz, M.; Schuster, K.; Siebertz, O.; Smit, H.; Szczerba, R.; Shipman, R.; Steinmetz, E.; Stern, J. A.; Stokroos, M.; Teipen, R.; Teyssier, D.; Tils, T.; Trappe, N.; van Baaren, C.; van Leeuwen, B. -J.; van de Stadt, H.; Visser, H.; Wildeman, K. J.; Wafelbakker, C. K.; Ward, J. S.; Wesselius, P.; Wild, W.; Wulff, S.; Wunsch, H. -J.; Tielens, X.; Zaal, P.; Zirath, H.; Zmuidzinas, J.; Zwart, F. Bibcode: 2010A&A...518L...6D Altcode:
Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009.
Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1.
Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Multidimensional Chemical Modeling. III. Abundance and excitation of diatomic hydrides Authors: Bruderer, Simon; Benz, Arnold O.; Stäuber, P.; Doty, Steven D. Bibcode: 2010arXiv1007.3261B Altcode: The Herschel Space Observatory opens the sky for observations in the far infrared at high spectral and spatial resolution. A particular class of molecules will be directly observable; light diatomic hydrides and their ions (CH, OH, SH, NH, CH+, OH+, SH+, NH+). These simple constituents are important both for the chemical evolution of the region and as tracers of high-energy radiation. If outflows of a forming star erode cavities in the envelope, protostellar far UV (FUV; 6 < E_gamma < 13.6 eV) radiation may escape through such low-density regions. Depending on the shape of the cavity, the FUV radiation then irradiates the quiescent envelope in the walls along the outflow. The chemical composition in these outflow walls is altered by photoreactions and heating via FUV photons in a manner similar to photo dominated regions (PDRs). In this work, we study the effect of cavity shapes, outflow density, and of a disk with the two-dimensional chemical model of a high-mass young stellar object introduced in the second paper in this series. We find that the shape of the cavity is particularly important in the innermost part of the envelope, where the dust temperatures are high enough (> 100 K) for water ice to evaporate. If the cavity shape allows FUV radiation to penetrate this hot-core region, the abundance of FUV destroyed species (e.g. water) is decreased. In particular, diatomic hydrides and their ions CH$+, OH+ and NH+ are enhanced by many orders of magnitude in the outflow walls due to the combination of high gas temperatures and rapid photodissociation of more saturated species. The enhancement of these diatomic hydrides is sufficient for a detection using the HIFI and PACS instruments onboard Herschel. The effect of X-ray ionization on the chemistry is found to be small, due to the much larger luminosity in FUV bands compared to X-rays. Title: Strong CH+ J = 1-0 emission and absorption in DR21 Authors: Falgarone, E.; Ossenkopf, V.; Gerin, M.; Lesaffre, P.; Godard, B.; Pearson, J.; Cabrit, S.; Joblin, Ch.; Benz, A. O.; Boulanger, F.; Fuente, A.; Güsten, R.; Harris, A.; Klein, T.; Kramer, C.; Lord, S.; Martin, P.; Martin-Pintado, J.; Neufeld, D.; Phillips, T. G.; Röllig, M.; Simon, R.; Stutzki, J.; van der Tak, F.; Teyssier, D.; Yorke, H.; Erickson, N.; Fich, M.; Jellema, W.; Marston, A.; Risacher, C.; Salez, M.; Schmülling, F. Bibcode: 2010A&A...518L.118F Altcode: 2010arXiv1007.1420F We report the first detection of the ground-state rotational transition of the methylidyne cation CH+ towards the massive star-forming region DR 21 with the HIFI instrument onboard the Herschel satellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR 21 molecular ridge and foreground gas. These observations allow us to determine a 12CH+J = 1-0 line frequency of ν = 835 137 ± 3 MHz, in good agreement with a recent experimental determination. We estimate the CH+ column density to be a few 1013 cm-2 in the gas seen in emission, and >1014 cm-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+] /[H] > 1.2 × 10-8. We show that the CH+ column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: Temperature and Density in the Foot Points of the Molecular Loops in the Galactic Center; Analysis of Multi-J Transitions of 12CO (J = 1--0, 3--2, 4--3, 7--6), 13CO (J = 1--0), and C18O (J = 1--0) Authors: Torii, Kazufumi; Kudo, Natsuko; Fujishita, Motosuji; Kawase, Tokuichi; Okuda, Takeshi; Yamamoto, Hiroaki; Kawamura, Akiko; Mizuno, Norikazu; Onishi, Toshikazu; Machida, Mami; Takahashi, Kunio; Nozawa, Satoshi; Matsumoto, Ryoji; Ott, Jürgen; Tanaka, Kunihiko; Yamaguchi, Nobuyuki; Ezawa, Hajime; Stutzki, Jürgen; Bertoldi, Frank; Koo, Bon-Chul; Bronfman, Leonardo; Burton, Michael; Benz, Arnold O.; Ogawa, Hideo; Fukui, Yasuo Bibcode: 2010PASJ...62..675T Altcode: 2009arXiv0909.2073T <A >Fukui et al.(2006)</A> (<A >Fukui et al.(2006)</A>, Science, 314, 106) discovered two molecular loops in the Galactic center, and argued that the foot points of the molecular loops, two bright spots at both loop ends, represent gas accumulated by the falling motion along the loops, subsequent to magnetic flotation by the Parker instability. We have carried out sensitive CO observations of the foot points toward l = 356° at a few pc resolution in the six rotational transitions of CO: 12CO (J = 1--0, 3--2, 4--3, 7--6), 13CO (J = 1--0), and C18O (J = 1--0). A high-resolution image of 12CO (J = 3--2) has revealed the detailed distribution of the high-excitation gas, including U shapes, the outer boundary of which shows sharp intensity jumps accompanying strong velocity gradients. An analysis of the multi-J CO transitions shows that the temperature is in the range from 30 to 100 K and the density is around 103-104cm-3, confirming that the foot points have high temperature and density, although there is no prominent radiative heating source, such as high-mass stars in or around the loops. We argue that the high temperature is likely due to shock heating under the C-shock condition caused by magnetic flotation. We made a comparison of the gas distribution with theoretical numerical simulations, and note that the U shape is consistent with numerical simulations. We also find that the region of highest temperature of ∼100 K or higher inside the U shape corresponds to the spur having an upward flow, additionally heated up either by magnetic reconnection or bouncing in the interaction with the narrow neck at the bottom of the U shape. We note that these new findings further reinforce the magnetic floatation interpretation. Title: Observing Solar Hard X-rays from Heliospheric Orbits Authors: Hurford, Gordon J.; Benz, A.; Dennis, B.; Krucker, S.; Limousin, O.; Lin, R.; Vilmer, N. Bibcode: 2010AAS...21640416H Altcode: 2010BAAS...41Q.902H The coming decade provides two opportunities to acquire a different observational perspective on solar hard x-ray emission. Both ESA's Solar Orbiter and NASA's Solar Probe Plus missions will be in heliocentric orbits with perihelia of 0.28 au and 0.05 au respectively. This poster indicates the unique scientific advantages of hard x-ray imaging/spectroscopy observations from such platforms.

These advantages stem from three factors: First, in combination with other payload elements, the hard x-rays provide the ability to observationally link accelerated electrons at the Sun to radio observations of the propagating electrons and to direct observations of in situ electrons. Second, the substantial gain in sensitivity afforded by close-in vantage points enables exploration of the origin of non-flare associated SEP events to be studied and the character of quiescent active-region heating and electron acceleration to be evaluated. Third, the different observational perspectives provided by the heliocentric orbits compared to low-Earth orbits enable improved separation of coronal and footpoint sources as well as measurements of the isotropy of the x-ray emission.

Despite the limited payload resources (mass, power, telemetry) afforded by such missions, scientifically effective hard x-ray imaging spectroscopy from 5 keV to 150 keV is still feasible. The Spectrometer/Telescope for Imaging X-rays (STIX), accepted as part of the Solar Orbiter payload, combines high spectral resolution ( 1 keV FWHM at 10 keV) with spatial resolution as good as 1500 km, and can efficiently encode the data for several hundred optimized images per hour within a modest telemetry allocation and 4 kg / 4 watt budget. The X-ray Imaging Spectrometer (XIS) proposed for Solar Probe Plus, views the Sun through its thermal shield. It also features high spectral resolution from 6 to 150 keV and spatial resolution of 1500 km at perihelion. The poster describes the imaging principles and current configurations of both instruments. Title: GT1_abenz_1: Completing the OH ladder for HH 46 Authors: Benz, A. Bibcode: 2010hers.prop..586B Altcode: First results from PACS observations towards the low-mass protostar HH 46 show surprisingly bright OH lines. The hydroxyl radical OH plays important roles in the water and oxygen chemistry of star-forming regions and their cooling. Furthermore, the hydroxyl-to-water line ratios are interesting tracers for ionizing radiation. We propose a nearly complete observation of the OH ladder in low-mass star formation for the first time. Four OH transitions in the class I object HH 46 were detected by PACS. We propose complementary observations towards the source in PACS line spectroscopy mode at 53, 56, 65, 71, 96, 115 and 135 micron. We gain insight in the origin and formation of OH from the PACS spatial information. The completeness of the OH ladder allows a reliable determination of the OH abundance and thus constrains water chemistry and cooling contribution more precisely. In addition, we propose HIFI observations of the OH transition at 163.4 micron to resolve the three hyperfine components for the first time. This will allow to determine optical depths of OH and test the hypothesis of asymmetries between the two closely spaced triplets, as the second triplet will be observed within the HIFI priority science program.

Note: This proposal is submitted under the Swiss part of the HIFI guaranteed time program; HIFI PI: Frank Helmich, HIFI Swiss Lead CoI: Arnold O. Benz Title: Warm and Dense Molecular Gas in the N 159 Region: 12CO J = 4-3 and 13CO J = 3-2 Observations with NANTEN2 and ASTE Authors: Mizuno, Yoji; Kawamura, Akiko; Onishi, Toshikazu; Minamidani, Tetsuhiro; Muller, Erik; Yamamoto, Hiroaki; Hayakawa, Takahiro; Mizuno, Norikazu; Mizuno, Akira; Stutzki, Jürgen; Pineda, Jorge L.; Klein, Uli; Bertoldi, Frank; Koo, Bon-Chul; Rubio, Monica; Burton, Michael; Benz, Arnold; Ezawa, Hajime; Yamaguchi, Nobuyuki; Kohno, Kotaro; Hasegawa, Tetsuo; Tatematsu, Ken'ichi; Ikeda, Masafumi; Ott, Jürgen; Wong, Tony; Hughes, Annie; Meixner, Margaret; Indebetouw, Remy; Gordon, Karl D.; Whitney, Barbara; Bernard, Jean-Philippe; Fukui, Yasuo Bibcode: 2010PASJ...62...51M Altcode: 2009arXiv0910.0309M New 12CO J=4-3 and 13CO J=3-2 observations of the N159 region in the Large Magellanic Cloud have been made. The 12CO J=4-3 distribution is separated into three clumps. These new measurements toward the three clumps are used in coupled calculations of molecular rotational excitation and line radiation transfer, along with other transitions of the 12CO as well as the isotope transitions of 13CO. The temperatures and densities are determined to be ~70-80K and ~3x10^3 cm-3 in N159W and N159E and ~30K and ~1.6x10^3 cm-3 in N159S. These results are compared with the star formation activity. The N159E clump is associated with embedded cluster(s) as observed at 24 micron and the derived high temperature is explained as due to the heating by these sources. The N159E clump is likely responsible for a dark lane in a large HII region by the dust extinction. The N159W clump is associated with embedded clusters mainly toward the eastern edge of the clump only. These clusters show offsets of 20"-40" from the 12CO J=4-3 peak and are probably responsible for heating indicated by the derived high temperature. The N159W clump exhibits no sign of star formation toward the 12CO J=4-3 peak position and its western region. We suggest that the N159W peak represents a pre-star-cluster core of ~105M_sol which deserves further detailed studies. Note that recent star formation took place between N159W and N159E as indicated by several star clusters and HII regions, while the natal molecular gas toward the stars have already been dissipated by the ionization and stellar winds of the OB stars. The N159S clump shows little sign of star formation as is consistent with the lower temperature and somewhat lower density. The N159S clump is also a candidate for future star formation. Title: Initial results from the Herschel Oxygen Project Authors: Goldsmith, Paul; Encrenaz, Pierre; Liseau, R.; Bell, T. A.; Bergin, T.; Black, J.; Benz, A.; Caselli, P.; Caux, E.; Falgarone, E.; Gerin, M.; Goicoechea, J. R.; Hjalmarson, A.; Hollenbach, D.; Kaufman, M.; Larsson, B.; Le Bourlot, J.; Le Petit, F.; Li, D.; Lis, D.; Melnick, G.; Neufeld, D.; Pagani, L.; Roueff, E.; Sandqvist, A.; Snell, R.; Vastel, C.; van Dishoeck, E.; Viti, S.; van der Tak, F. Bibcode: 2010cosp...38.2480G Altcode: 2010cosp.meet.2480G Initial Results from the Herschel Oxygen Project (HOP) Oxygen is the third most abundant element in the cosmos, but can be found in many forms. In the gas phase, oxygen can be ionized, atomic, or in molecular form, and it is also incorporated into grains. The molecular form is expected to dominate in cold, well-shielded regions, and in such molecular clouds, oxygen can be found in key species including carbon monoxide and water. Gas phase chemistry models predict molecular oxygen (O2) to be almost as abundant as CO. A number of searches for rotational transitions of O2 have been carried out. These include ground-based searches for the isotopologue 16O18O and searches for 16O2 in galaxies with red shift sufficient to move the line away from terrestrial atmospheric absorption. Searches for Galactic 16O2 carried out with the SWAS and Odin spacecraft have yielded upper limits on the abundance of molecular oxygen typically 1 to 2 orders of magnitude below those predicted by gas-phase models. There has been a statistical detection of O2 in one source, again at a low abundance. A variety of new models have been proposed to explain this low abundance, which involve grain surface and photo effects. To address this important problem in astro-chemistry and molecular cloud structure, we have developed the Open Time Key Project HOP (Herschel Oxygen Project), which exploits the high angular resolution and sensitivity of the HIFI instrument on Herschel to observe 3 rotational transitions of O2 in a broad sample of molecular clouds. We report on the status of HOP and present early results available from Priority Science Phase and Science Definition Phase observations. Title: High Spectral Resolution Observation of Decimetric Radio Spikes Emitted by Solar Flares - First Results of the Phoenix-3 Spectrometer Authors: Benz, Arnold O.; Monstein, Christian; Beverland, Michael; Meyer, Hansueli; Stuber, Bruno Bibcode: 2009SoPh..260..375B Altcode: 2009arXiv0909.4137B A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1 - 5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1 - 5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350 - 850 MHz. Spike bandwidths are found to have a power - law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential. Title: Correlation between decimetric radio emission and hard X-rays in solar flares Authors: Dabrowski, B. P.; Benz, A. O. Bibcode: 2009A&A...504..565D Altcode: 2009A&A...504..565B Aims: The emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate in accelerated, non-thermal particles. On the other hand, non-thermal hard X-rays are also understood to be products of this acceleration. Do radio emission and hard X-ray signatures originate from the same acceleration process? A strong correlation between the light curves in the radio and HXR ranges may help answer this question.
Methods: The delay between the radio and hard X-ray emission was determined by cross-correlation. The time profiles of X-ray and radio emission include a wide range of energies and frequencies. Thus, correlation is not simply a yes/no question, but must be systematically searched for in various ranges. The high spectral resolution of RHESSI ensured that it was possible to carefully choose the energy range, excluding thermal emission. The broad bandwidth of Phoenix-2 allowed the selection of any emission in the full decimetre range. The energy range and duration in hard X-rays, and the frequency range in radio spectrograms were chosen to optimize the correlation. The cross-correlation coefficient was then analyzed by a Gaussian fitting method.
Results: The measured delays have a distribution of FWHM 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from such a Gaussian fitting method. The mean delay for pulsations was found to be -1.4± 0.9 s (minus indicates that hard X-ray emission comes first), and for narrowband spikes to -2.5±2.5 s. There are broad wings in the distribution, which we interpret as chance coincidences. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence, and position on the disk. However, we find an increase in the delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux. This was not the case for pulsations.
Conclusions: In contrast to previous reports, the average delays for all pulsations and all spike groups are consistent with zero. Thus, correlated decimetric pulsations and spikes are, on average, concomitant with non-thermal X-rays. Title: Evidence of warm and dense material along the outflow of a high-mass YSO Authors: Bruderer, S.; Benz, A. O.; Bourke, T. L.; Doty, S. D. Bibcode: 2009A&A...503L..13B Altcode: Context: Outflow cavities in envelopes of young stellar objects (YSOs) have been predicted to allow far-UV (FUV) photons to escape far from the central source, with significant observable effects, especially if the protostar is a forming high-mass star suspected of emitting a copious amount of FUV radiation. Indirect evidence of this picture has been provided by models and unresolved single-dish observations, but direct high-resolution data are necessary for confirmation. Previous chemical modeling has suggested that CS and HCN are good probes of the local FUV field, so make good target species.
Aims: We directly probe the physical conditions of the material in the outflow walls to test this prediction.
Methods: Interferometric observations of the CS(7-6) and HCN(4-3) rotational lines in the high-mass star-forming region AFGL 2591 are carried out in the compact and extended configuration of the SubMillimeter Array (SMA). The velocity structure was analyzed, and integrated maps compared to K-band near-IR observations. A chemical model predicts abundances of CS and HCN for a gas under protostellar X-ray and FUV irradiation, and was used in conjunction with the data to distinguish between physical scenarios.
Results: CS and HCN emission was found in spatial coincidence in extended sources displaced up to 7 arcsec from the position of the young star. Their line widths are small, excluding major shocks. Chemical model calculations predict an enhanced abundance of the two molecules in warm, dense, and FUV irradiated gas. Hot dust observed between the molecular emission and the outflow accounts for the necessary attenuation to prevent photodissociation of the molecules.
Conclusions: The SMA data suggest that the outflow walls are heated and chemically altered by the FUV emission of the central high-mass object, providing the best direct evidence yet of large-scale direct irradiation of outflow walls.

Appendix is only available in electronic form at http://www.aanda.org Title: Chemical Modeling of Young Stellar Objects. I. Method and Benchmarks Authors: Bruderer, S.; Doty, S. D.; Benz, A. O. Bibcode: 2009ApJS..183..179B Altcode: 2009arXiv0906.0584B Upcoming facilities such as the Herschel Space Observatory or Atacama Large Millimeter Array will deliver a wealth of molecular line observations of young stellar objects (YSOs). Based on line fluxes, chemical abundances can then be estimated by radiative transfer calculations. To derive physical properties from abundances, the chemical network needs to be modeled and fitted to the observations. This modeling process is however computationally exceedingly demanding, particularly if in addition to density and temperature, far-UV (FUV) irradiation, X-rays, and multi-dimensional geometry have to be considered. We develop a fast tool, suitable for various applications of chemical modeling in YSOs. A grid of the chemical composition of the gas having a density, temperature, FUV irradiation and X-ray flux is pre-calculated as a function of time. A specific interpolation approach is developed to reduce the database to a feasible size. Published models of AFGL 2591 are used to verify the accuracy of the method. A second benchmark test is carried out for FUV sensitive molecules. The novel method for chemical modeling is more than 250,000 times faster than direct modeling and agrees within a mean factor of 1.35. The tool is distributed for public use. Main applications are (1) fitting physical parameters to observed molecular line fluxes and (2) deriving chemical abundances for two- and three-dimensional models. They will be presented in two future publications of this series. In the course of developing the method, the chemical evolution is explored: we find that X-ray chemistry in envelopes of YSOs can be reproduced by means of an enhanced cosmic-ray ionization rate with deviations less than 25%, having the observational consequence that molecular tracers for X-rays are hard to distinguish from cosmic-ray ionization tracers. We provide the detailed prescription to implement this total ionization rate approach in any chemical model. We further find that the abundance of CH+ in low-density gas with high ionization can be enhanced by the recombination of doubly ionized carbon (C++) and suggest a new value for the initial abundance of the main sulfur carrier in the hot core. Title: Multidimensional Chemical Modeling of Young Stellar Objects. II. Irradiated Outflow Walls in a High-Mass Star-Forming Region Authors: Bruderer, S.; Benz, A. O.; Doty, S. D.; van Dishoeck, E. F.; Bourke, T. L. Bibcode: 2009ApJ...700..872B Altcode: 2009arXiv0906.0588B Observations of the high-mass star-forming region AFGL 2591 reveal a large abundance of CO+, a molecule known to be enhanced by far-ultraviolet (FUV) and X-ray irradiation. In chemical models assuming a spherically symmetric envelope, the volume of gas irradiated by protostellar FUV radiation is very small due to the high extinction by dust. The abundance of CO+ is thus underpredicted by orders of magnitude. In a more realistic model, FUV photons can escape through an outflow region and irradiate gas at the border to the envelope. Thus, we introduce the first two-dimensional axisymmetric chemical model of the envelope of a high-mass star-forming region to explain the CO+ observations as a prototypical FUV tracer. The model assumes an axisymmetric power-law density structure with a cavity due to the outflow. The local FUV flux is calculated by a Monte Carlo radiative transfer code taking scattering on dust into account. A grid of precalculated chemical abundances, introduced in the first part of this series of papers, is used to quickly interpolate chemical abundances. This approach allows us to calculate the temperature structure of the FUV-heated outflow walls self-consistently with the chemistry. Synthetic maps of the line flux are calculated using a raytracer code. Single-dish and interferometric observations are simulated and the model results are compared to published and new JCMT and Submillimeter Array (SMA) observations. The two-dimensional model of AFGL 2591 is able to reproduce the JCMT single-dish observations and also explains the nondetection by the SMA. We conclude that the observed CO+ line flux and its narrow width can be interpreted by emission from the warm and dense outflow walls irradiated by protostellar FUV radiation. Title: Do solar decimetric spikes originate in coronal X-ray sources? Authors: Battaglia, M.; Benz, A. O. Bibcode: 2009A&A...499L..33B Altcode: 2009arXiv0904.4146B Context: In the standard solar flare scenario, a large number of particles are accelerated in the corona. Nonthermal electrons emit both X-rays and radio waves. Thus, correlated signatures of the acceleration process are predicted at both wavelengths, coinciding either close to the footpoints of a magnetic loop or near the coronal X-ray source.
Aims: We attempt to study the spatial connection between coronal X-ray emission and decimetric radio spikes to determine the site and geometry of the acceleration process.
Methods: The positions of radio-spike sources and coronal X-ray sources are determined and analyzed in a well-observed limb event. Radio spikes are identified in observations from the Phoenix-2 spectrometer. Data from the Nançay radioheliograph are used to determine the position of the radio spikes. RHESSI images in soft and hard X-ray wavelengths are used to determine the X-ray flare geometry. Those observations are complemented by images from GOES/SXI.
Results: We find that the radio emission originates at altitudes much higher than the coronal X-ray source, having an offset from the coronal X-ray source amounting to 90´´ and to 113´´ and 131´´ from the two footpoints, averaged over time and frequency.
Conclusions: Decimetric spikes do not originate from coronal X-ray flare sources contrary to previous expectations. However, the observations suggest a causal link between the coronal X-ray source, related to the major energy release site, and simultaneous activity in the higher corona. Title: Observations of conduction driven evaporation in the early rise phase of solar flares Authors: Battaglia, M.; Fletcher, L.; Benz, A. O. Bibcode: 2009A&A...498..891B Altcode: 2009arXiv0903.2754B Context: The classical flare picture features a beam of electrons, which were accelerated in a site in the corona, hitting the chromosphere. The electrons are stopped in the dense chromospheric plasma, emitting bremsstrahlung in hard X-rays. The ambient material is heated by the deposited energy and expands into the magnetic flare loops, a process termed chromospheric evaporation. In this view hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from the hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture.
Aims: For the first time, the pre-flare phase of such solar flares is studied in detail. The aim is to understand the early rise phase of these events. We want to explain the time evolution of the observed emission by means of alternative energy transport mechanisms such as heat conduction.
Methods: RHESSI events displaying pronounced pre-flare emission were analyzed in imaging and spectroscopy. The time evolution of images and full sun spectra was investigated and compared to the theoretical expectations from conduction driven chromospheric evaporation.
Results: The pre-flare phase is characterized by purely thermal emission from a coronal source with increasing emission measure and density. After this earliest phase, a small non-thermal tail to higher energies appears in the spectra, becoming more and more pronounced. However, images still only display one X-ray source, implying that this non-thermal emission is coronal. The increase of emission measure and density indicates that material is added to the coronal region. The most plausible origin is evaporated material from the chromosphere. Energy provided by a heat flux is capable of driving chromospheric evaporation. We show that the often used classical Spitzer treatment of the conductive flux is not applicable. The conductive flux is saturated. During the preflare-phase, the temperature of the coronal source remains constant or increases. Continuous heating in the corona is necessary to explain this observation.
Conclusions: The observations of the pre-flare phase of four solar flares are consistent with chromospheric evaporation driven by a saturated heat flux. Additionally, continuous heating in the corona is necessary to sustain the observed temperature. Title: A World-Wide Net of Solar Radio Spectrometers: e-CALLISTO Authors: Benz, A. O.; Monstein, C.; Meyer, H.; Manoharan, P. K.; Ramesh, R.; Altyntsev, A.; Lara, A.; Paez, J.; Cho, K. -S. Bibcode: 2009EM&P..104..277B Altcode: 2009EM&P..tmp....2B Radio spectrometers of the CALLISTO type to observe solar flares have been distributed to nine locations around the globe. The instruments observe automatically, their data is collected every day via internet and stored in a central data base. A public web-interface exists through which data can be browsed and retrieved. The nine instruments form a network called e-CALLISTO. It is still growing in the number of stations, as redundancy is desirable for full 24 h coverage of the solar radio emission in the meter and low decimeter band. The e-CALLISTO system has already proven to be a valuable new tool for monitoring solar activity and for space weather research. Title: Millimetron—a large Russian-European submillimeter space observatory Authors: Wild, Wolfgang; Kardashev, Nikolay S.; Likhachev, S. F.; Babakin, N. G.; Arkhipov, V. Y.; Vinogradov, I. S.; Andreyanov, V. V.; Fedorchuk, S. D.; Myshonkova, N. V.; Alexsandrov, Y. A.; Novokov, I. D.; Goltsman, G. N.; Cherepaschuk, A. M.; Shustov, B. M.; Vystavkin, A. N.; Koshelets, V. P.; Vdovin, V. F.; de Graauw, Th.; Helmich, F.; Vd Tak, F.; Shipman, R.; Baryshev, A.; Gao, J. R.; Khosropanah, P.; Roelfsema, P.; Barthel, P.; Spaans, M.; Mendez, M.; Klapwijk, T.; Israel, F.; Hogerheijde, M.; Vd Werf, P.; Cernicharo, J.; Martin-Pintado, J.; Planesas, P.; Gallego, J. D.; Beaudin, G.; Krieg, J. M.; Gerin, M.; Pagani, L.; Saraceno, P.; di Giorgio, A. M.; Cerulli, R.; Orfei, R.; Spinoglio, L.; Piazzo, L.; Liseau, R.; Belitsky, V.; Cherednichenko, S.; Poglitsch, A.; Raab, W.; Guesten, R.; Klein, B.; Stutzki, J.; Honingh, N.; Benz, A.; Murphy, A.; Trappe, N.; Räisänen, A. Bibcode: 2009ExA....23..221W Altcode: 2008ExA...tmp...17W Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution. Title: A Venus Flagship Mission: Report of the Venus Science and Technology Definition Team Authors: Bullock, M. A.; Senske, D. A.; Balint, T. S.; Benz, A.; Campbell, B. A.; Chassefiere, E.; Colaprete, A.; Cutts, J. A.; Glaze, L.; Gorevan, S.; Grinspoon, D. H.; Hall, J.; Hashimoto, G. L.; Head, J. W.; Hunter, G.; Johnson, N.; Kerzhanovich, V. V.; Kiefer, W. S.; Kolawa, E. A.; Kremic, T.; Kwok, J.; Limaye, S. S.; Mackwell, S. J.; Marov, M. Y.; Ocampo, A.; Schubert, G.; Stofan, E. R.; Svedhem, H.; Titov, D. V.; Treiman, A. H. Bibcode: 2009LPI....40.2410B Altcode: The Venus STDT has defined the goals, objectives, mission architecture, science investigations and payload for a Flagship-class mission to Venus. The mission puts advanced exploration capabilities in orbit, in the atmosphere, and on the surface. Title: Construction of AN E-Callisto Station in Korea Authors: Bong, Su-Chan; Kim, Yeon-Han; Roh, Hee-Seon; Cho, Kyung-Suk; Park, Young-Deuk; Choi, Seong-Hwan; Baek, Ji-Hye; Monstein, Christian; Benz, Arnold O.; Moon, Yong-Jae; Kim, Sung-Soo S. Bibcode: 2009JKAS...42....1B Altcode: No abstract at ADS Title: Radio Emission of the Quiet Sun Authors: Benz, Arnold O. Bibcode: 2009LanB...4B..103B Altcode: 2009LanB...4B.4116B No abstract at ADS Title: Solar Differential Rotation Determined by Tracing Low and High Brightness Temperature Regions at 8 mm Authors: Romštajn, I.; Brajša, R.; Wöhl, H.; Benz, A. O.; Temmer, M.; Roša, D.; Ruždjak, V. Bibcode: 2009CEAB...33...79R Altcode: At the wavelength of 8 mm absorption features (Low brightness Temperature Regions, LTRs) and emission features (High brightness Temperature Regions, HTRs) can be traced for determination of solar rotation. From earlier studies it is known that about two thirds of LTRs are associated with Hα filaments. The goal of the present analysis is to determine the heights of these solar structures and their rotational velocities. We used the method for the simultaneous determination of the solar synodic rotation velocity and the height of tracers. The rotation velocities were determined by the linear least-square fit of their central meridian distances as a function of time. The mean value of the low brightness temperature regions' heights is about 45 600 km. The results of solar rotation determined by tracing LTRs and HTRs are mutually compared and also compared with the results using other tracers and methods. The method for the simultaneous determination of the solar synodic rotation velocity and the height of the tracers could be applied properly only on LTRs, since a wide distribution over latitudes and central meridian distances of a large data set is necessary, which was not available for HTRs. Observational findings that HTRs rotate systematically faster than LTRs and the possibility that they can be observed at and outside the solar limb are consistent with relatively high altitudes of HTRs. It was concluded that the radiation mechanism of HTRs is thermal bremsstrahlung, probably associated with flaring active regions. Title: On the Relation Between Decimetric and Hard X-ray Emissions in the Impulsive Flare Phase Authors: Dabrowski, B. P.; Benz, A. O. Bibcode: 2009CEAB...33..221D Altcode: The emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate from accelerated, non-thermal particles. On the other hand, non-thermal hard X-rays (HXR) are well accepted results of such acceleration. Are radio emissions and HXR signatures of the same acceleration process? Good correlation of the light curves in the radio and HXR range may evidence it.

The correlation of decimetric radio emission and HXR in solar flares was analysed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer in Bleien (Switzerland). For the first time we have the possibility of a systematic search on the radio-HXR relation in the range from 100 MHz to 4 GHz.

The measured delays have a distribution with a FWHM of 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from a Gauss fitting method. The mean delay for pulsations was found to be -1.4± 0.9 seconds (minus indicates that hard X-rays emission comes first), and for narrowband spikes to -2.5±2.5 seconds. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence and position on the disc. However, we find an increase in delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux. Title: Radio Bursts of the Non-Thermal Sun Authors: Benz, Arnold O. Bibcode: 2009LanB...4B..189B Altcode: 2009LanB...4B.4128B No abstract at ADS Title: Heights of solar tracers observed at 8 mm and an interpretation of their radiation Authors: Brajša, R.; Romštajn, I.; Wöhl, H.; Benz, A. O.; Temmer, M.; Roša, D. Bibcode: 2009A&A...493..613B Altcode: Context: At the wavelength of 8 mm, emissive features (high brightness-temperatrue regions, HTRs) and absorptive features (low brightness-temperature regions, LTRs) can be traced for the determining the solar rotation. From earlier studies it is known that about two thirds of LTRs are associated with Hα filaments.
Aims: Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation mechanism can be important for explaining the observed phenomena, so we determine the heights of solar structures and interpret their radiation mechanism(s).
Methods: We use the method of simultaneous determination of the solar synodic rotation velocity and the height of tracers. The rotation velocities were determined by the linear least-square fit of their central meridian distance as a function of time. We used a procedure for calculating the brightness temperature for a given wavelength and model atmosphere, which integrates the radiative transfer equation for the thermal bremsstrahlung.
Results: The mean value of the low brightness-temperature regions' heights is about 45 600 km. This height was used as input for constructing prominence and coronal condensation models, which, when assuming thermal bremsstrahlung as the radiation mechanism, yield a decrease in the brightness temperature of 2-14%, in agreement with observations. If the same radiation mechanism is considered, the models of the solar corona above active regions give an increase in the brightness temperature of 5-19%, also in agreement with observations. In this case an indirect indication (from the rotational analysis) that the HTRs are located higher in the solar atmosphere than the LTRs was taken into account.
Conclusions: The method for simultaneously determining the solar synodic rotation velocity and the height of tracers could have only been properly applied on LTRs, since a homogeneous distribution over latitudes and central meridian distances of a large enough data set is necessary. Thermal bremsstrahlung can explain both the LTR (prominences and coronal condensations) and HTR (ordinary active regions) phenomena observed at 8 mm. At this wavelength, thermal gyromagnetic emission is almost surely excluded as a possible radiation mechanism. Title: Flare Observations Authors: Benz, Arnold O. Bibcode: 2008LRSP....5....1B Altcode: Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays at 100 MeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, and SOHO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections (CMEs), electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting reconnection of magnetic field lines as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's lower ionosphere. While flare scenarios have slowly converged over the past decades, every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Title: A Venus Flagship Mission: Exploring a World of Contrasts Authors: Senske, D.; Bullock, M.; Balint, T.; Benz, A.; Campbell, B.; Chassefiere, E.; Colaprete, A.; Cutts, J.; Glaze, L.; Gorevan, S.; Grinspoon, D.; Hall, J.; Hasimoto, G.; Head, J.; Hunter, G.; Johnson, N.; Kiefer, W.; Kolawa, E.; Kremic, T.; Kwok, J.; Limaye, S.; Mackwell, S.; Marov, M.; Peterson, C.; Schubert, G.; Spilker, T.; Stofan, E.; Svedhem, H.; Titov, D.; Treiman, A. Bibcode: 2008AGUFM.P22A..08S Altcode: Results from past missions and the current Venus Express Mission show that Venus is a world of contrasts, providing clear science drivers for renewed exploration of this planet. In early 2008, NASA's Science Mission Directorate formed a Science and Technology Definition Team (STDT) to formulate science goals and objectives, mission architecture and a technology roadmap for a flagship class mission to Venus. This 3- to 4 billon mission, to launch in the post 2020 timeframe, should revolutionize our understanding of how climate works on terrestrial planets, including the close relationship between volcanism, tectonism, the interior, and the atmosphere. It would also more clearly elucidate the geologic history of Venus, including the existence and persistence of an ancient ocean. Achieving these objectives will provide a basis to understand the habitability of extra solar terrestrial planets. To address a broad range of science questions this mission will be composed of flight elements that include an orbiter that is highlighted by an interferometric SAR to provide surface topographic and image information at scales one to two orders of magnitude greater than that achieved by any previous spacecraft to Venus. Two balloons with a projected lifetime of weeks will probe the structure and dynamics of the atmosphere at an altitude of 50 to 70-km. In addition, two descent probes will collect data synergistic to that from the balloon and analyze the geochemistry of surface rocks over a period of hours. The technology road map focuses on key areas of science instruments and enabling engineering to provide greater in situ longevity in the hostile Venus environment. Title: The Pre-flare Phase: Key to Understanding Energy and Mass Transport in Flare Loops Authors: Battaglia, M.; Fletcher, L.; Benz, A. O. Bibcode: 2008ESPM...12.2.85B Altcode: In the classical solar flare scenario, the chromosphere is heated by an incident beam of supra-thermal electrons that were accelerated in the corona, then precipitated downward along the field lines of a magnetic loop. The hot chromospheric plasma expands and fills the magnetic loops. This process has been termed chromospheric evaporation. The classical scenario causes characteristic emission in soft- and hard X-rays, both from the corona and the chromosphere. The time evolution of this emission follows a specific pattern known as the Neupert effect.

Recent observations indicate that this scenario is only applicable for about half of the observed flares (Veronig et al. 2002). The early rise phase of many events is dominated by increasing soft X-ray emission up to minutes before the onset of the hard X-ray emission. This pre-heating clearly contradicts the classical Neupert scenario and indicates that other mechanisms of energy transport such as thermal conduction have to be at work. It also implies that the pre-flare energy release is dominated by heating, not acceleration. While energy transport by thermal conduction and subsequent chromospheric evaporation has been studied in some detail for the decay phase of solar flares, we present the first comprehensive study of the early phases of 4 pre-heating events. We analyze the time evolution of those events in imaging and spectroscopy using data from the RHESSI satellite and demonstrate how this can improve our understanding of heating and evaporation processes in coronal loops and the initiation of particle acceleration. Title: Correlation of Decimetric Radio Emission and Hard X-rays in Solar Flares Authors: Dabrowski, B.; Benz, A. O. Bibcode: 2008ESPM...122.106D Altcode: The emission of decimetric radiation, in particular narrowband spikes and pulsations, is generally considered to originate from particle acceleration processes in solar flares. On the other hand, non-thermal hard X-rays are well accepted results of such acceleration. Are radio emissions and hard X-rays signatures of the same acceleration process? Good correlation of the light curves in the radio and HXR range may evidence it.

The correlation of decimetric radio emission and hard X-rays in solar flares was analyzed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer of ETH Zürich. The Phoenix-2 spectrometer in Bleien (Switzerland) records the solar radio emission from 100 MHz to 4 GHz. We found 169 well observed joint decimetric events in the complete list of observations from February 2002 (date launch of the RHESSI satellite) to December 2006. About hundred radio events were of the type of pulsations, and in around thirty events we found were spikes. For the detailed analysis, 33 groups (26 radio events) of pulsations and 12 groups (11 radio events) of spikes were chosen.

The delay between the radio and hard X-rays emission was determined by cross-correlation. The time profiles of X-ray and radio emission differ much in energy and frequency. Thus correlation is not simply a yes/no question, but must be systematically searched in various ranges. The high spectral resolution of RHESSI made it possible to carefully choose the energy range, excluding thermal emission. The broad bandwidth of Phoenix-2 allowed selecting any emission in the full decimeter range. The energy range and duration in hard X-rays, and the frequency range in radio spectrograms were chosen to optimize the correlation. The cross-correlation coefficient was then analyzed by Gauss fit in delay for each event.

The mean delay for pulsations evaluated from Gauss fitting was found to be -1.50 seconds (minus indicates that hard X-rays emission comes first). The mean delay for narrowband spikes evaluated from Gauss fitting amounts to -2.25 seconds. The delays do not depend on position on the disk, duration of the correlating sequence and maximum value of cross-correlation coefficient. However, we find an increase in delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux. This was not the case for pulsations. Title: Spectral Hardening in Large Solar Flares Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2008ApJ...683.1180G Altcode: 2007arXiv0708.2472G Observations by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are used to quantitatively study the hard X-ray evolution in five large solar flares selected for spectral hardening in the course of the event. The X-ray bremsstrahlung emission from nonthermal electrons is characterized by two spectroscopically distinct phases: impulsive and gradual. The impulsive phase usually consists of several emission spikes following a soft-hard-soft spectral pattern, whereas the gradual stage manifests itself as spectral hardening while the flux slowly decreases. Both the soft-hard-soft (impulsive) phase and the hardening (gradual) phase are well described by piecewise linear dependence of the photon spectral index on the logarithm of the hard X-ray flux. The different linear parts of this relation correspond to different rise and decay phases of emission spikes. The temporal evolution of the spectra is compared with the configuration and motion of the hard X-ray sources in RHESSI images. These observations reveal that the two stages of electron acceleration causing these two different behaviors are closely related in space and time. The transition between the impulsive and gradual phase is found to be smooth and progressive rather than abrupt. This suggests that they arise because of a slow change in a common accelerator rather than being caused by two independent and distinct acceleration processes. We propose that the hardening during the decay phase is caused by continuing particle acceleration with longer trapping in the accelerator before escape. Title: Observational evidence for return currents in solar flare loops Authors: Battaglia, M.; Benz, A. O. Bibcode: 2008A&A...487..337B Altcode: 2008arXiv0806.1701B Context: The common flare scenario comprises an acceleration site in the corona and particle transport to the chromosphere. Using satellites available to date it has become possible to distinguish between the two processes of acceleration and transport, and study the particle propagation in flare loops in detail, as well as complete comparisons with theoretical predictions.
Aims: We complete a quantitative comparison between flare hard X-ray spectra observed by RHESSI and theoretical predictions. This enables acceleration to be distinguished from transport and the nature of transport effects to be explored.
Methods: Data acquired by the RHESSI satellite were analyzed using full sun spectroscopy as well as imaging spectroscopy methods. Coronal source and footpoint spectra of well observed limb events were analyzed and quantitatively compared to theoretical predictions. New concepts are introduced to existing models to resolve discrepancies between observations and predictions.
Results: The standard thin-thick target solar flare model cannot explain the observations of all events. In the events presented here, propagation effects in the form of non-collisional energy loss are of importance to explain the observations. We demonstrate that those energy losses can be interpreted in terms of an electric field in the flare loop. One event seems consistent with particle propagation or acceleration in lower than average density in the coronal source.
Conclusions: We find observational evidence for an electric field in flare loops caused by return currents. Title: The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI): instrument and pre-launch testing Authors: de Graauw, Thijs; Whyborn, Nick; Helmich, Frank; Dieleman, Pieter; Roelfsema, Peter; Caux, Emmanuel; Phillips, Tom; Stutzki, Jürgen; Beintema, Douwe; Benz, Arnold; Biver, Nicolas; Boogert, Adwin; Boulanger, Francois; Cherednichenko, Sergey; Coeur-Joly, Odile; Comito, Claudia; Dartois, Emmanuel; de Jonge, Albrecht; de Lange, Gert; Delorme, Ian; DiGiorgio, Anna; Dubbeldam, Luc; Edwards, Kevin; Fich, Michael; Güsten, Rolf; Herpin, Fabrice; Honingh, Netty; Huisman, Robert; Jacobs, Herman; Jellema, Willem; Kawamura, Jon; Kester, Do; Klapwijk, Teun; Klein, Thomas; Kooi, Jacob; Krieg, Jean-Michel; Kramer, Carsten; Kruizenga, Bob; Laauwen, Wouter; Larsson, Bengt; Leinz, Christian; Liseau, Rene; Lord, Steve; Luinge, Willem; Marston, Anthony; Merkel, Harald; Moreno, Rafael; Morris, Patrick; Murphy, Anthony; Naber, Albert; Planesas, Pere; Martin-Pintado, Jesus; Olberg, Micheal; Orleanski, Piotr; Ossenkopf, Volker; Pearson, John; Perault, Michel; Phillip, Sabine; Rataj, Mirek; Ravera, Laurent; Saraceno, Paolo; Schieder, Rudolf; Schmuelling, Frank; Szczerba, Ryszard; Shipman, Russell; Teyssier, David; Vastel, Charlotte; Visser, Huib; Wildeman, Klaas; Wafelbakker, Kees; Ward, John; Higgins, Roonan; Aarts, Henri; Tielens, Xander; Zaal, Peer Bibcode: 2008SPIE.7010E..04D Altcode: 2008SPIE.7010E...2D This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance. Title: Concluding remarks Authors: Benz, Arnold O. Bibcode: 2008IAUS..247..366B Altcode: 2007IAUS..247..366B Waves in solar and stellar atmospheres have been proposed more than fifty years ago to heat the chromosphere and the corona. Their usefulness as a means to explain an important phenomenon gave wave science its initial impetus. However, since then, waves and oscillations have become a great astrophysical topic of their own. In an inhomogeneous medium, waves occur in immense variety. The theory of waves explores this complexity and highlights modes and properties that are important in stellar atmospheres. We have seen steady progress in this fundamental endeavour that has recently been accelerated through the use of numerical simulations. The discovery, three decades ago, of waves in the solar and stellar interiors and later in the corona, although at low energy levels, opened a new field: the diagnostic use of waves. Seismology of the interior has become a booming field of solar and stellar physics, and observed oscillations have been used to derive the magnetic field strength and to explore the corona. Title: New Evidence for Return Currents in Solar Flare Loops Authors: Battaglia, M.; Benz, A. O. Bibcode: 2008AGUSMSH51C..07B Altcode: The common flare scenario comprises particle acceleration in the corona and transport to the chromosphere along the field lines of magnetic loops. This leads to characteristic hard X-ray emission from the corona (coronal source) and the chromosphere (footpoints). Simple models presume that both emissions are caused by the same electron population. Assuming thin target bremsstrahlung emission from the coronal source and thick target bremsstrahlung from the footpoints, the shape and relations between the hard X-ray spectra of the distinct sources can be computed. With RHESSI, it has become possible to observe hard X-ray spectra both from the corona as well as from the footpoints with high spectral resolution. Therefore the so-called thin-thick target model can be tested directly. We analyzed coronal source and footpoint spectra of well observed RHESSI limb events and quantitatively compared them to theoretical predictions. In the analyzed flares, the difference in spectral hardness between the coronal and footpoint sources differs significantly from the theoretically expected value. Transport effects in the form of non-collisional energy loss were introduced to the thin-thick target model to account for the discrepancy. We show that those energy losses can be interpreted by an electric field and associated return current. This is direct evidence for return currents in solar flare loops. Title: The Results of Sub-mm Observations in the Large Magellanic Cloud with the NANTEN2 Telescope Authors: Mizuno, Yoji; Mizuno, N.; Kawamura, A.; Onishi, T.; Fukui, Y.; Ogawa, H.; Stutzki, J.; Bertoldi, F.; Koo, B. C.; Rubio, M.; Burton, M.; Benz, A. Bibcode: 2008ASSP....5..313M Altcode: 2008glv..book..313M No abstract at ADS Title: Prospectives of Herschel PDR observations Authors: Ossenkopf, V.; Gerin, M.; Güsten, R.; Benz, A.; Berne, O.; Boulanger, F.; Bruderer, S.; France, K.; Fuente, A.; Goicoechea, J.; Harris, A.; Joblin, C.; Klein, T.; Lord, S.; Kramer, C.; Martin, P.; Martin-Pintado, J.; Mookerjea, B.; Neufeld, D.; Le Petit, F.; Phillips, T.; Poelman, D.; Rizzo, R.; Röllig, M.; Simon, R.; Spaans, M.; Stutzki, J.; Teyssier, D.; Yorke, H. Bibcode: 2008EAS....31..193O Altcode: Observations using the HIFI and PACS instruments aboard the Herschel satellite provide a unique way to study the chemical inventory, the dynamics, and the energy balance in dense interstellar clouds heated by UV radiation. We propose a comprehensive observing program to reveal the details of the interaction of massive young stars with their parental molecular clouds. Title: Division II: Sun and Heliosphere Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan, Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez-Pillet, Valentin Bibcode: 2007IAUTB..26..101W Altcode: Division II provides a forum for astronomers studying a wide range of problems related to the structure, radiation and activity of the Sun, and its interaction with the Earth and the rest of the solar system. Title: Spectral Hardening of Large Solar Flares Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2007AGUFMSH53A1062G Altcode: We present quantitative studies of the hard X-ray spectral evolution of large solar flares featuring hardening trends, using RHESSI high cadence spectroscopy observations. The temporal evolution of the spectra is compared with the configuration and motion of the hard X-ray sources in RHESSI images. Both soft-hard-soft (impulsive) phases and hardening (gradual) phases are observed during the events and are well described by piecewise linear dependence of the spectral index on the logarithm of the flux. In particular, we investigate whether two different acceleration mechanisms are responsible for the impulsive and gradual phases, finding evidence that points toward a single acceleration mechanism acting in the two phases, rather than two different separated mechanisms, because the impulsive and gradual phases are closely interconnected in time and space. Title: Energetic radiation and the sulfur chemistry of protostellar envelopes: submillimeter interferometry of AFGL 2591 Authors: Benz, A. O.; Stäuber, P.; Bourke, T. L.; van der Tak, F. F. S.; van Dishoeck, E. F.; Jørgensen, J. K. Bibcode: 2007A&A...475..549B Altcode: 2007arXiv0709.0215B Context: The chemistry in the inner few thousand AU of accreting envelopes around young stellar objects is predicted to vary greatly with far-UV and X-ray irradiation by the central star.
Aims: We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope.
Methods: The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(ν2 = 1), and HC15N with 0.6'' resolution at 350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc. The SMA observations are compared with the predictions of a chemical model fitted to previous single-dish observations.
Results: The CS and SO main peaks are extended in space at the FWHM level, as predicted in the model assuming protostellar X-rays. However, the main peak sizes are found smaller than modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and HC15N, but not SO and HCN(ν2 = 1), show pedestal emissions at radii ⪉3500 AU that are not predicted. All lines except SO show a secondary peak within the approaching outflow cone. A dip or null in the visibilities caused by a sharp decrease in abundance with increasing radius is not observed in CS and only tentatively in SO.
Conclusions: The emission of protostellar X-rays is supported by the good fit of the modeled SO and CS amplitude visibilities including an extended main peak in CS. The broad pedestals can be interpreted by far-UV irradiation in a spherically non-symmetric geometry, possibly comprising outflow walls on scales of 3500-7000 AU. The extended CS and SO main peaks suggest sulfur evaporation near the 100 K temperature radius. The effects of the corresponding abundance jumps may be reduced in visibility plots by smoothing due to inhomogeneity at the evaporation radius, varying by ±10% or more in different directions.

The FITS files of SMA data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/549 Title: An Interpretation of the Coronal Holes' Visibility in the Millimeter Wavelength Range Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.; Šaina, B.; Wöhl, H. Bibcode: 2007SoPh..245..167B Altcode: Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsähovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 106 K). This can explain both the LTRs and HTRs associated with coronal holes. Title: VizieR Online Data Catalog: AFGL 2591 maps in CS, SO and HCN lines (Benz+, 2007) Authors: Benz, A. O.; Stauber, P.; Bourke, T. L.; van Det Tak, F. F. S.; van Dishoeck, E. F.; Jorgensen, J. K. Bibcode: 2007yCat..34750549B Altcode: The chemistry in the inner few thousand AU of accreting envelopes around young stellar objects is predicted to vary greatly with far-UV and X-ray irradiation by the central star.

We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope.

The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(nu2=1), and HC15N with 0.6" resolution at 350GHz probing radial scales of 600-3500AU for an assumed distance of 1kpc. The SMA observations are compared with the predictions of a chemical model fitted to previous single-dish observations.

(2 data files). Title: Electron acceleration in solar flares: observations versus numerical simulations Authors: Benz, Arnold O.; Grigis, Paolo C.; Battaglia, Marco Bibcode: 2007HiA....14...87B Altcode: We use RHESSI hard X-ray observations to constrain acceleration of solar flare electrons, generally considered to be a primary recipient of the released energy. Title: Tracing high energy radiation with molecular lines near deeply embedded protostars Authors: Stäuber, P.; Benz, A. O.; Jørgensen, J. K.; van Dishoeck, E. F.; Doty, S. D.; van der Tak, F. F. S. Bibcode: 2007A&A...466..977S Altcode: 2006astro.ph..8393S Aims:The aim is to probe high energy radiation emitted by deeply embedded protostars.
Methods: Submillimeter lines of CN, NO, CO+ and SO^+, and upper limits on SH+ and N2O are observed with the James Clerk Maxwell Telescope in two high-mass and up to nine low-mass young stellar objects and compared with chemical models.
Results: Constant fractional abundances derived from radiative transfer modeling of the line strengths are x(CN) ≈ a few ×10-11-10-8, x(NO) ≈ 10-9-10-8 and x(CO^+) ≈ 10-12-10-10. SO+ has abundances of a few × 10-11 in the high-mass objects and upper limits of ≈10-12-10-11 in the low-mass sources. All abundances are up to 1-2 orders of magnitude higher if the molecular emission is assumed to originate mainly from the inner region (≲1000 AU) of the envelope. For high-mass sources, the CN, SO+ and CO+ abundances and abundance ratios are best explained by an enhanced far-ultraviolet (FUV) field impacting gas at temperatures of a few hundred K. The observed column densities require that this region of enhanced FUV has scales comparable to the observing beam, such as in a geometry in which the enhanced FUV irradiates outflow walls. For low-mass sources, the required temperatures within the FUV models of T ≳ 300 K are much higher than found in models, so that an X-ray enhanced region close to the protostar (r ≲ 500 AU) is more plausible. Gas-phase chemical models produce more NO than observed, suggesting an additional reduction mechanism not included in current models.
Conclusions: The observed CN, CO+ and SO+ abundances can be explained with either enhanced X-rays or FUV fields from the central source. High-mass sources likely have low opacity regions that allow the FUV photons to reach large distances from the central source. X-rays are suggested to be more effective than FUV fields in the low-mass sources. The observed abundances imply X-ray fluxes for the Class 0 objects of LX ≈ 1029-1031 erg s-1, comparable to those observed from low-mass Class I protostars. Spatially resolved data are needed to clearly distinguish the effects of FUV and X-rays for individual species.

Appendices are only available in electronic form at http://www.aanda.org Title: Exploring the connection between coronal and footpoint sources in a thin-thick target solar flare model Authors: Battaglia, M.; Benz, A. O. Bibcode: 2007A&A...466..713B Altcode: 2007astro.ph..2309B Context: Hard X-ray emission of coronal sources in solar flares has been observed and studied since its discovery in Yohkoh observations. Several models have been proposed to explain the physical mechanisms causing this emission and the relations between those sources and simultaneously observed footpoint sources.
Aims: We investigate and test one of the models (intermediate thin-thick target model) developed on the basis of Yohkoh observations. The model makes precise predictions on the shape of coronal and footpoint spectra and the relations between them, that can be tested with new instruments such as RHESSI.
Methods: RHESSI observations of well observed events are studied in imaging and spectroscopy and compared to the predictions from the intermediate thin-thick target model.
Results: The results indicate that such a simple model cannot account for the observed relations between the non-thermal spectra of coronal and footpoint sources. Including non-collisional energy loss of the electrons in the flare loop due to an electric field can solve most of the inconsistencies. Title: Division II: Sun and Heliosphere Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan, Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez Pillet, Valentin Bibcode: 2007IAUTA..26...69W Altcode: Division II of the IAU provides a forum for astronomers studying a wide range of phenomena related to the structure, radiation and activity of the Sun, and its interaction with the Earth and the rest of the solar system. Division II encompasses three Commissions, 10, 12 and 49, and four working groups. During the last triennia the activities of the division involved some reorganization of the division and its working groups, developing new procedures for election of division and commission officers, promoting annual meetings from within the division and evaluating all the proposed meetings, evaluating the division's representatives for the IAU to international scientific organizations, and participating in general IAU business. Title: Commission 10: Solar Activity Authors: Melrose, Donald B.; Klimchuk, James A.; Benz, A. O.; Craig, I. J. D.; Gopalswamy, N.; Harrison, R. A.; Kozlovsky, B. Z.; Poletto, G.; Schrijver, K. J.; van Driel-Gesztelyi, L.; Wang, J. -X. Bibcode: 2007IAUTA..26...75M Altcode: Commission 10 aims at the study of various forms of solar activity, including networks, plages, pores, spots, fibrils, surges, jets, filaments/prominences, coronal loops, flares, coronal mass ejections (CMEs), solar cycle, microflares, nanoflares, coronal heating etc., which are all manifestation of the interplay of magnetic fields and solar plasma. Increasingly important is the study of solar activities as sources of various disturbances in the interplanetary space and near-Earth "space weather".Over the past three years a major component of research on the active Sun has involved data from the RHESSI spacecraft. This review starts with an update on current and planned solar observations from spacecraft. The discussion of solar flares gives emphasis to new results from RHESSI, along with updates on other aspects of flares. Recent progress on two theoretical concepts, magnetic reconnection and magnetic helicity is then summarized, followed by discussions of coronal loops and heating, the magnetic carpet and filaments. The final topic discussed is coronal mass ejections and space weather.The discussions on each topic is relatively brief, and intended as an outline to put the extensive list of references in context.The review was prepared jointly by the members of the Organizing Committee, and the names of the primary contributors to the various sections are indicated in parentheses. Title: Are There Radio-quiet Solar Flares? Authors: Benz, Arnold O.; Brajša, Roman; Magdalenić, Jasmina Bibcode: 2007SoPh..240..263B Altcode: 2007astro.ph..1570B Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 - 4000 MHz range (type I - V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source. Title: On the Visibility of Coronal Holes in Microwaves Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.; Šaina, B.; Wöhl, H.; Ruždjak, V. Bibcode: 2007CEAB...31..219B Altcode: Previous observations indicate that coronal holes generally appear as low brightness temperature regions in microwaves. However, within their borders local enhancements of radiation often occur. This is confirmed by comparing a full-disc solar image obtained at 37 GHz on 27 May 1993 with full-disc solar images obtained at various wavelengths. Microwave brightness temperatures of three coronal holes are determined and interpreted. Title: Are there Radio-quiet Solar Flares? Authors: Benz, Arnold O.; Brajsa, Roman; Magdalenic, Jasmina Bibcode: 2007astro.ph..1566B Altcode: This submission has been withdrawn by arXiv administrators because it is a duplicate of astro-ph/0701570. Title: Electron acceleration in solar flares: theory of spectral evolution Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2006A&A...458..641G Altcode: 2006astro.ph..6339G Context: .Stochastic acceleration is thought to be a key mechanism in the energization of solar flare electrons.
Aims: .We study whether stochastic acceleration can reproduce the observed soft-hard-soft evolution of the spectral features of the hard X-ray emitted by suprathermal electrons. We pay special attention to the effects of particle trapping and escape.
Methods: .The Fokker-Planck equation for the electron distribution is integrated numerically using the coefficients derived by Miller et al. for transit-time damping acceleration. The electron spectra are then converted to photon spectra for comparison with RHESSI observations of looptop sources.
Results: .The presence of particle escape softens the model spectra computed in the stochastic acceleration framework. The ratio between the efficiency of trapping and acceleration controls the spectral evolution which follows a soft-hard-soft pattern. Furthermore, a pivot point (that is, a common crossing point of the accelerated particle spectra at different times) is found at around 10 keV. It can be brought into agreement with the observed value of 20 keV by enhanced trapping through an electric potential.
Conclusions: .The model proposed here accounts for the key features observed in the spectral evolution of hard X-ray emission from looptop sources. Title: Relations between concurrent hard X-ray sources in solar flares Authors: Battaglia, M.; Benz, A. O. Bibcode: 2006A&A...456..751B Altcode: 2006astro.ph..6353B Context: .Solar flares release a large fraction of their energy into non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona and chromosphere.
Aims: .We aim to characterize the acceleration process by the coronal source and its leakage toward the footpoints in the chromosphere. The relations between the sources reflect the geometry and constrict the configuration of the flare.
Methods: .We studied solar flares of GOES class larger than M1 with three or more hard X-ray sources observed simultaneously in the course of the flare. The events were observed with the X-ray satellite RHESSI from February 2002 until July 2005. We used imaging spectroscopy methods to determine the spectral evolution of each source in each event. The images of all of the five events show two sources visible only at high energies (footpoints) and one source only visible at low energies (coronal or looptop source, in two cases situated over the limb).
Results: . We find soft-hard-soft behavior in both, coronal source and footpoints. The coronal source is nearly always softer than the footpoints. The footpoint spectra differ significantly only in one event out of five.
Conclusions: .The observations are consistent with acceleration in the coronal source and an intricate connection between the corona and chromosphere. Title: NANTEN2 Project: CO and CI Survey of the Southern Sky Authors: Fukui, Y.; Onishi, T.; Mizuno, N.; Mizuno, A.; Ogawa, H.; Yonekura, Y.; Stutzki, J.; Graf, U.; Kramer, C.; Simon, R.; Bertoldi, F.; Klein, U.; Bensch, F.; Koo, B. C.; Park, Y. S.; Bronfman, L.; May, J.; Burton, M.; Benz, A. Bibcode: 2006IAUSS...1E..21F Altcode: We present a project overview and science goals of the upcoming NANTEN2 project. This is an upgrade of the 4-m mm telescope, NANTEN, which was operated at Las Campanas Observatory, Chile. We have been carrying out extensive molecular cloud surveys in the Galaxy as well as toward the Magellanic system for seven years. The upgrade started by moving NANTEN from Las Campanas to Atacama in Northern Chile at an altitude of 4,800m in 2004 to realize a large-scale survey at sub-mm wavelengths. In this new project, we will make large-scale surveys toward the Galaxy and the nearby galaxies including the Magellanic Clouds. We will reveal the physical and chemical states of interstellar gas in various density regions with the highly excited CO (carbon-monoxide) and CI (neutral carbon) spectra in the sub-millimeter wavelength (100 - 800 GHz). With thorough extensive surveys, we will make studies of star formation process in the Local Group and investigate the dynamical effects of energetic explosive events like supernovae and supershells on the interstellar matter. The installation started at the beginning of 2004. The highest observing frequencies will be covered by KOSMA SMART (Sub-Millimeter Array Receivers for Two frequencies) receiver, a new multi-beam receiver capable of observing both 490 GHz and 800 GHz radiation simultaneously and speedily. The NANTEN2 observations provide a large database of interstellar matter in the Galaxy and the Magellanic Clouds. This database must be a useful guide for the future science with ALMA. Title: Electron Acceleration in Solar Flares: Observations versus Numerical S imulations Authors: Benz, A. O.; Grigis, P. C.; Battaglia, M. Bibcode: 2006IAUJD...1E...6B Altcode: We use RHESSI hard X-ray observations to constrict electron acceleration in solar flares, generally considered as a primary recipient of the released energy. X-ray sources in the corona have been previously discovered and tentatively associated with bremsstrahlung emission of the acceleration site. RHESSI imaging spectroscopy can temporally resolve the non-thermal spectrum of the coronal source for the first time. We compare the time behaviour with the predictions of stochastic acceleration, as described by transit-time damping of MHD turbulence excited by reconnection. The results in 5 limb events indicate soft-hard-soft (shs) behaviour of the coronal source emission in the course of an X-ray peak (the more intense, the harder the spectrum). The shs behaviour thus constitutes a conspicuous property of the acceleration process. The temporal behaviour of the spectrum can be quantitatively described a pivot point near a photon energy of 20 keV at which the spectrum remains constant in time. We solve a diffusion equation for the interaction of waves and particles including trapping, escape and particle replenishment. The solution yields a spectrum that is approximately a power-law in the observed range of energies, having a spectral index in the observed range. However, the theoretically derived pivot point is generally at energy lower than observed. For this reason we include transport effects, such as produced by an electric potential, or scattering in the coronal source (trapping) to bring the pivot energy up to the observed value. Escaping particles propagate to the base of the loop in the dense chromosphere. These precipitating particles are identified as origin of the observed hard X-ray footpoints. Observations and simulations show that solar flare electron acceleration is a process that involves interactions with the connecting loop. The observations are consistent with stochastic acceleration in a relatively dense medium (up to 10^11 cm^-3) and high wave energy densities (up to 0.001 magnetic). The comparison also constrains the global flare geo-metry, requiring coupling between the coronal source and the footpoints. Title: Water destruction by X-rays in young stellar objects Authors: Stäuber, P.; Jørgensen, J. K.; van Dishoeck, E. F.; Doty, S. D.; Benz, A. O. Bibcode: 2006A&A...453..555S Altcode: 2006astro.ph..2114S Aims.We study the H2O chemistry in star-forming environments under the influence of a central X-ray source and a central far ultraviolet (FUV) radiation field. The X-ray models are applied to envelopes around low-mass Class 0 and I young stellar objects (YSOs).
Methods.The gas-phase water chemistry is modeled as a function of time, hydrogen density and X-ray flux. To cover a wide range of physical environments, densities between nH = 10^4-109 cm-3 and temperatures between T=10-1000 K are studied.
Results.Three different regimes are found: for T<100 K, the water abundance is of order 10-7-10-6 and can be somewhat enhanced or reduced due to X-rays, depending on time and density. For 100 K ≲ T ≲ 250 K, H2O is reduced from initial x(H_2O) ≈ 10-4 following ice evaporation to x(H_2O) ≈ 10-6 for FX ≳ 10-3 erg s-1 cm-2 (t=104 yr) and for FX ≳ 10-4 erg s-1 cm-2 (t=105 yr). At higher temperatures (T ≳ 250 K) and hydrogen densities, water can persist with x({H_2O}) ≈ 10-4 even for high X-ray fluxes. Water is destroyed in both Class 0 and I envelopes on relatively short timescales (t ≈ 5000 yr) for realistic X-ray fluxes, although the effect is less prominent in Class 0 envelopes due to the higher X-ray absorbing densities there. FUV photons from the central source are not effective in destroying water.
Conclusions.X-rays reduce the water abundances especially in regions where the gas temperature is T ≲ 250-300 K for fluxes FX ≳ 10-5-10-4 erg s-1 cm-2. The affected regions can be envelopes, disks or outflow hot spots. The average water abundance in Class I sources for LX ≳ 1027 erg s-1 is predicted to be x(H_2O) ≲ 10-6. Central UV fields have a negligible influence, unless the photons can escape through cavities. Title: Comparison of Electron Stochastic Acceleration Models with RHESSI Hard X-Ray Observations of Solar Flares. Authors: Grigis, Paolo C.; Benz, A. O. Bibcode: 2006SPD....37.2802G Altcode: 2006BAAS...38..254G Acceleration of charged particles in a plasma by means of stochastic interactions with turbulent waves is very efficient and therefore is often invoked as the key mechanism acting in solar flare electron acceleration. We compare the photon spectra produced by electrons accelerated using the Transit Time Damping (TTD) mechanism with the detailed hard X-ray observations provided by RHESSI for looptop sources, showing the soft-hard-soft behavior in the spectral evolution. The TTD model with a simple leaky box escape term shows the observed correlation between the photon spectral index and flux but requires too large variations in photon flux over the range of observed spectral indices. We discuss more realistic models and further modifications needed to reproduce the RHESSI observations. Title: Relations Between Concurrent Hard X-ray Sources In Solar Flares Authors: Battaglia, Marina; Benz, A. O. Bibcode: 2006SPD....37.2801B Altcode: 2006BAAS...38..254B Solar flares release a large fraction of their energy into non-thermal electrons,but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona (coronal or looptop source) and chromosphere (footpoints).The spectral time evolution of the sources and the relations between themreflect the geometry and constrict the configuration of the flare.We studied solar flares of GOES class larger than M1 with three hard X-raysources observed simultaneously in the course of the flare. The events whereselected from observations with the X-ray satellite RHESSI from February 2002 until July 2005.We used imaging spectroscopy methods to determine the spectral time evolution ofeach source in each event. The images of all of the five events show twosources visible only at high energies (footpoints) and one source onlyvisible at low energies (coronal source).We find soft-hard-soft behavior in both, coronal source and footpoints. Thisis a strong indication that soft-hard-soft is a feature of the accelerationmechanism rather than a transport effect.The coronal source is nearly always softer than the footpoints. The footpointspectra differ significantly only in one event out of five. Title: RHESSI observation of flare elements Authors: Grigis, Paolo C.; Benz, Arnold O. Bibcode: 2006astro.ph..2302G Altcode: RHESSI observations of elementary flare bursts are presented. These solar flare elements are distinct emission peaks of a duration of some tens of seconds present in the hard X-ray light curves. They are characterized by consistent soft-hard-soft spectral behavior, which can be described in a quantitative way and compared which predictions from acceleration models. A detailed analysis of hard X-ray images for an M5 class flare shows that elementary flare bursts do not occur at distinct locations, but as twin X-ray sources move smoothly along an arcade of magnetic loops. This observation apparently contradicts the predictions of standard translation invariant 2.5-dimensional reconnection models. Title: Radio Emission of Solar Flare Particle Acceleration Authors: Benz, A. O. Bibcode: 2006pre6.conf..325B Altcode: 2006pre4.conf..325B The solar corona is a very dynamic plasma on time scales of decades to a few milliseconds. Radio missions provide diagnostic tools particularly suited for the analysis of non-thermal electron distributions, enhanced levels of various kinds of plasma waves and plasma phenomena related to electron acceleration in flares. Very intense coherent emissions are observed at frequencies below about 3 GHz, weaker ones up to 9 GHz. They are caused by plasma instabilities driving various wave modes that in turn may emit observable radio waves. The focus here is on Type III and stationary type IV bursts from about 0.2 to 4 GHz. Type III bursts can be traced back in the corona to the acceleration region of electron beams. Less known are radio emissions from magnetically trapped electrons driving loss-cone unstable waves. This is the interpretation usually given to type IV emission. It is a very powerful radiation probably also observed in stars and possibly related to acceleration after the main flare energy release phase. The comparison of the radio emissions with hard X-rays reveals surprisingly that the two emissions often do not correlate in time and thus must originate from different electron acceleration processes. In combination with other wavelengths and their recent imaging capabilities, exciting new possibilities may soon open for radio diagnostics. Title: Extended decimeter radio emission after large solar flares Authors: Benz, A. O.; Perret, H.; Saint-Hilaire, P.; Zlobec, P. Bibcode: 2006AdSpR..38..951B Altcode: The large solar flares of October and November 2003 were accompanied by extremely intense radio emissions at decimeter wavelengths. The radio emission continued long after the main phase of the flares and reached an unprecedented peak flux density at 410 MHz of 6.3(±0.7) × 105 solar flux units on 2003, October 28. The unusual number of large flares from the same active regions yields a homologous set ideal for statistical analysis. We have compared the coherent radio emissions (as observed by the Zurich and Trieste instruments) with the X-rays measured by RHESSI and GOES. As major results, we find that the total duration, the peak flux, and radiated energy of the radio emissions correlate with the flare energy released (measured in soft X-rays). Enhanced hard X-rays (>12 keV) are always observed during the time of enhanced radio emission. In 27% of the radio subpeaks covered by RHESSI, we find X-ray subpeaks. The most intense radio emissions are not due to electron beams, but are post-flare emissions apparently not directly related to the primary energy release and acceleration process. These radio emissions, generally classified as Type IV and DCIM bursts, have previously been interpreted by loss-cone emission of trapped electrons. However, radio and hard X-ray subpeaks do not show a detailed correlation or Neupert effect, and long-term trapping can be excluded. Possible acceleration mechanisms after the main flare phase are discussed and compared with the observations. Title: Rhessi Observation of Flare Elements Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2005ESASP.600E..35G Altcode: 2005ESPM...11...35G; 2005dysu.confE..35G No abstract at ADS Title: A broadband FFT spectrometer for radio and millimeter astronomy Authors: Benz, A. O.; Grigis, P. C.; Hungerbühler, V.; Meyer, H.; Monstein, C.; Stuber, B.; Zardet, D. Bibcode: 2005A&A...442..767B Altcode: 2005astro.ph..9671B The core architecture, tests in the lab and first results of a Fast Fourier Transform (FFT) spectrometer are described. It is based on a commercially available fast digital sampler (AC240) with an on-board Field Programmable Gate Array (FPGA). The spectrometer works continuously and has a remarkable total bandwidth of 1 GHz, resolved into 16,384 channels. The data is sampled with 8 bits, yielding a dynamic range of 48 dB. An Allan time of more than 2000 s and an SFDR of 37 dB were measured. First light observations with the KOSMA telescope show a perfect spectrum without internal or external spurious signals. Title: X-Ray emission from high-mass protostar AFGL 2591 Authors: Benz, Arnold Bibcode: 2005cxo..prop.1902B Altcode: 2005chan.prop.1835B; 2005cxo..prop.1835B AFGL 2591 is a prototypical, deeply embedded high-mass protostar, but is crucially and unusually for high-mass YSOs isolated from the irradiation of associated protostars. We have observed and modeled line emissions of X-ray sensitive molecules. The observed abundance of these molecules can only be interpreted by strong X-ray emission of the central object. Our models indicate that the X-ray emission must be at a level that is observable in a 30 ks observation. A non-detection would be a strong disagreement. A detection would be the first X-ray emission inferred by indirect means and a crucial test of the chemical modeling of the impact of high-energy radiation on the environment of young stars. Title: Temporal Correlation of Hard X-Rays and Meter/Decimeter Radio Structures in Solar Flares Authors: Arzner, Kaspar; Benz, Arnold O. Bibcode: 2005SoPh..231..117A Altcode: 2005astro.ph..3145A We investigate the relative timing between hard X-ray (HXR) peaks and structures in metric and decimetric radio emissions of solar flares using data from the RHESSI and Phoenix-2 instruments. The radio events under consideration are predominantly classified as type III bursts, decimetric pulsations and patches. The RHESSI data are demodulated using special techniques appropriate for a Phoenix-2 temporal resolution of 0.1 s. The absolute timing accuracy of the two instruments is found to be about 170 ms, and much better on the average. It is found that type III radio groups often coincide with enhanced HXR emission, but only a relatively small fraction (∼20%) of the groups show close correlation on time scales < 1 s. If structures correlate, the HXRs precede the type III emissions in a majority of cases, and by 0.69 ± 0.19 s on the average. Reversed drift type III bursts are also delayed, but high-frequency and harmonic emission is retarded less. The decimetric pulsations and patches (DCIM) have a larger scatter of delays, but do not have a statistically significant sign or an average different from zero. The time delay does not show a center-to-limb variation excluding simple propagation effects. The delay by scattering near the source region is suggested to be the most efficient process on the average for delaying type III radio emission. Title: X-ray chemistry in the envelopes around young stellar objects Authors: Stäuber, P.; Doty, S. D.; van Dishoeck, E. F.; Benz, A. O. Bibcode: 2005A&A...440..949S Altcode: 2005astro.ph..6306S We present chemical models of the envelope of a young stellar object (YSO) exposed to a central X-ray source. The models are applied to the massive star-forming region AFGL 2591 for different X-ray fluxes. Model results for this region show that the X-ray ionization rate with and without the effects of Compton scattering differs by only a few percent and the influence of Compton scattering on the chemistry is negligible. The total X-ray ionization rate is dominated by the “secondary” ionization rate of H2 resulting from fast electrons. The abundance profiles of several molecular and atomic species are shown to depend on the X-ray luminosity and on the distance from the source. The carbon, sulphur and nitrogen chemistries are discussed. It is found that He+ and H3+ are enhanced and trigger a peculiar chemistry. Several molecular X-ray tracers are found and compared to tracers of the far ultraviolet (FUV) field. Like ultraviolet radiation fields, X-rays enhance simple hydrides, ions and radicals. In contrast to ultraviolet photons, X-rays can penetrate deep into the envelope and affect the chemistry even at large distances from the source. Whereas the FUV enhanced species cover a region of ≈ 200{-}300 AU, the region enhanced by X-rays is ≳ 1000 AU. We find that N2O, HNO, SO, SO^+, HCO^+, CO^+, OH^+, N2H^+, SH+ and HSO+ (among others) are more enhanced by X-rays than by FUV photons even for X-ray luminosities as low as LX ≈ 1030 erg s-1. CO2 abundances are reduced in the gas-phase through X-ray induced FUV photons. For temperatures T ≲ 230 K, H2O is destroyed by X-rays with luminosities LX ≳ 1030 erg s-1. Best-fit models for AFGL 2591 predict an X-ray luminosity LX ≳ 1031 erg s-1 with a hard X-ray spectrum TX ≳ 3 × 107 K. This is the first time that the X-ray flux of a highly obscured source has been estimated by its envelope chemistry. Furthermore, we find LX/Lbol ≈ 10-6. The chemistry of the bulk of the envelope mass is dominated by cosmic-ray induced reactions rather than by X-ray induced ionization for X-ray luminosities LX ≲ 1033 erg s-1. The calculated line intensities of HCO+ and HCS+ show that high-J lines are more affected than lower J lines by the presence of X-rays due to their higher critical densities, and that such differences are detectable even with large aperture single-dish telescopes. Future instruments such as Herschel-HIFI or SOFIA will be able to observe X-ray enhanced hydrides whereas the sensitivity and spatial resolution of ALMA is well-suited to measure the size and geometry of the region affected by X-rays. Title: Size dependence of solar X-ray flare properties Authors: Battaglia, M.; Grigis, P. C.; Benz, A. O. Bibcode: 2005A&A...439..737B Altcode: 2005astro.ph..5154B Non-thermal and thermal parameters of 85 solar flares of GOES class B1 to M6 (background subtracted classes A1 to M6) have been compared to each other. The hard X-ray flux has been measured by RHESSI and a spectral fitting provided flux and spectral index of the non-thermal emission, as well as temperature and emission measure of the thermal emission. The soft X-ray flux was taken from GOES measurements. We find a linear correlation in a double logarithmic plot between the non-thermal flux and the spectral index. The higher the acceleration rate of a flare, the harder the non-thermal electron distribution. The relation is similar to the one found by a comparison of the same parameters from several sub-peaks of a single flare. Thus small flares behave like small subpeaks of large flares. Thermal flare properties such as temperature, emission measure and the soft X-ray flux also correlate with peak non-thermal flux. A large non-thermal peak flux entails an enhancement in both thermal parameters. The relation between spectral index and the non-thermal flux is an intrinsic feature of the particle acceleration process, depending on flare size. This property affects the reported frequency distribution of flare energies. Title: The Evolution of Reconnection along an Arcade of Magnetic Loops Authors: Grigis, Paolo C.; Benz, Arnold O. Bibcode: 2005ApJ...625L.143G Altcode: 2005astro.ph..4436G RHESSI observations of a solar flare showing continuous motions of double hard X-ray sources interpreted as footpoints of magnetic loops are presented. The temporal evolution shows many distinct emission peaks of duration of some tens of seconds (``elementary flare bursts''). Elementary flare bursts have been interpreted as instabilities or oscillations of the reconnection process leading to an unsteady release of magnetic energy. These interpretations based on two-dimensional concepts cannot explain these observations, showing that the flare elements are displaced in a third dimension along the arcade. Therefore, the observed flare elements are not a modulation of the reconnection process but originate as this process progresses along an arcade of magnetic loops. Contrary to previous reports, we find no correlation between footpoint motion and hard X-ray flux. This flare apparently contradicts the predictions of the standard translation invariant 2.5-dimensional reconnection models. Title: The spectral evolution of impulsive solar X-ray flares. II. Comparison of observations with models Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2005A&A...434.1173G Altcode: 2005astro.ph..1431G We study the evolution of the spectral index and the normalization (flux) of the non-thermal component of the electron spectra observed by RHESSI during 24 solar hard X-ray flares. The quantitative evolution is confronted with the predictions of simple electron acceleration models featuring the soft-hard-soft behaviour. The comparison is general in scope and can be applied to different acceleration models, provided that they make predictions for the behavior of the spectral index as a function of the normalization. A simple stochastic acceleration model yields plausible best-fit model parameters for about 77% of the 141 events consisting of rise and decay phases of individual hard X-ray peaks. However, it implies unphysically high electron acceleration rates and total energies for the others. Other simple acceleration models such as constant rate of accelerated electrons or constant input power have a similar failure rate. The peaks inconsistent with the simple acceleration models have smaller variations in the spectral index. The cases compatible with a simple stochastic model require typically a few times 1036 electrons accelerated per second beyond a threshold energy of 18 keV in the rise phases and 24 keV in the decay phases of the flare peaks. Title: Absence of linear polarization in Hα emission of solar flares Authors: Bianda, M.; Benz, A. O.; Stenflo, J. O.; Küveler, G.; Ramelli, R. Bibcode: 2005A&A...434.1183B Altcode: 2005astro.ph..2263B High sensitivity observations of Hα polarization of 30 flares of different sizes and disk positions are reported. Both filter and spectrographic techniques have been used. The ZIMPOL system eliminates spurious polarizations due to seeing and flat-field effects. We didn't find any clear linear polarization signature above our sensitivity level which was usually better than 0.1%. The observations include an X17.1 flare with gamma-ray lines reported by the RHESSI satellite. These results cast serious doubts on previous claims of linear polarization at the one percent level and more, attributed to impact polarization. The absence of linear polarization limits the anisotropy of energetic protons in the Hα emitting region. The likely causes are isotropization by collisions with neutrals in the chromosphere and defocusing by the converging magnetic field. Title: Thermal and non-thermal energies of solar flares Authors: Saint-Hilaire, P.; Benz, A. O. Bibcode: 2005A&A...435..743S Altcode: The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar flares have been determined from RHESSI observations.

The emissions have been carefully separated in the spectrum.

The turnover or cutoff in the low-energy distribution of electrons has been studied by simulation and fitting, yielding a reliable lower limit to the non-thermal energy.

It remains the largest contribution to the error budget.

Other effects, such as albedo, non-uniform target ionization, hot target, and cross-sections on the spectrum have been studied.

The errors of the thermal energy are about equally as large.

They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses.

Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction.

Our analysis suggests that the thermal and non-thermal energies are of the same magnitude.

This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma. Title: Thermal and non-thermal energies in solar flares Authors: Saint-Hilaire, Pascal; Benz, Arnold O. Bibcode: 2005astro.ph..3078S Altcode: The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar flares have been determined from RHESSI observations. The emissions have been carefully separated in the spectrum. The turnover or cutoff in the low-energy distribution of electrons has been studied by simulation and fitting, yielding a reliable lower limit to the non-thermal energy. It remains the largest contribution to the error budget. Other effects, such as albedo, non-uniform target ionization, hot target, and cross-sections on the spectrum have been studied. The errors of the thermal energy are about equally as large. They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses. Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction. Our analysis suggests that the thermal and non-thermal energies are of the same magnitude. This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma. Title: Callisto A New Concept for Solar Radio Spectrometers Authors: Benz, Arnold O.; Monstein, Christian; Meyer, Hansueli Bibcode: 2005SoPh..226..143B Altcode: 2004astro.ph.10437B A new radio spectrometer, CALLISTO, is presented. It is a dual-channel frequency-agile receiver based on commercially available consumer electronics. Its major characteristic is the low price for hardware and software, and the short assembly time, both two or more orders of magnitude below existing spectrometers. The instrument is sensitive at the physical limit and extremely stable. The total bandwidth is 825 MHz, and the width of individual channel is 300 kHz. A total of 1000 measurements can be made per second. The spectrometer is well suited for solar low-frequency radio observations pertinent to space weather research. Five instruments of the type were constructed until now and put into operation at several sites, including Bleien (Zurich) and NRAO (USA). First results in the 45-870 MHz range are presented. Some of them were recorded in a preliminary setup during the time of high solar activity in October and November 2003. Title: Survey on Solar X-ray Flares and Associated Coherent Radio Emissions Authors: Benz, Arnold O.; Grigis, Paolo C.; Csillaghy, AndrÉ; Saint-Hilaire, Pascal Bibcode: 2005SoPh..226..121B Altcode: 2004astro.ph.10436B The radio emission during 201 selected X-ray solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zürich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% are they the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines. Title: Time Evolution of the Spectral Index in Solar Flares Authors: Grigis, P. C. :; Buser, D.; Benz, A. O. Bibcode: 2005ASSL..320..199G Altcode: 2005smp..conf..199G No abstract at ADS Title: X-ray chemistry in the envelopes around young stellar objects Authors: Stäuber, Pascal; Benz, A. O.; Doty, S. D.; van Dishoeck, E. F. Bibcode: 2005ESASP.577..413S Altcode: 2004astro.ph.12281S; 2005dmu..conf..413S We have studied the influence of X-rays from a massive young stellar object (YSO) on the chemistry of its own envelope by extending the models of Doty et al. (2002) and Stäuber et al. (2004). The models are applied to the massive star-forming region AFGL 2591 for different X-ray luminosities and plasma temperatures. Enhanced column densities for several species are predicted. In addition we present first detections of CO+ and SO+ toward AFGL 2591. These molecular ions are believed to be high-energy tracers. Herschel-HIFI will be able to observe other tracers like CH and CH+ whereas ALMA is well suited to measure the size and geometry of the emitting region. Title: The spectral evolution of impulsive solar X-ray flares Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2004A&A...426.1093G Altcode: 2004astro.ph..7431G The time evolution of the spectral index and the non-thermal flux in 24 impulsive solar hard X-ray flares of GOES class M was studied in RHESSI observations. The high spectral resolution allows for a clean separation of thermal and non-thermal components in the 10-30 keV range, where most of the non-thermal photons are emitted. Spectral index and flux can thus be determined with much better accuracy than before. The spectral soft-hard-soft behavior in rise-peak-decay phases is discovered not only in the general flare development, but even more pronounced in subpeaks. An empirically found power-law dependence between the spectral index and the normalization of the non-thermal flux holds during the rise and decay phases of the emission peaks. It is still present in the combined set of all flares. We find an asymmetry in this dependence between rise and decay phases of the non-thermal emission. There is no delay between flux peak and spectral index minimum. The soft-hard-soft behavior appears to be an intrinsic signature of the elementary electron acceleration process. Title: Influence of UV radiation from a massive YSO on the chemistry of its envelope Authors: Stäuber, P.; Doty, S. D.; van Dishoeck, E. F.; Jørgensen, J. K.; Benz, A. O. Bibcode: 2004A&A...425..577S Altcode: 2004astro.ph..6540S We have studied the influence of far ultraviolet (UV) radiation (6 < hν < 13.6 eV) from a massive young stellar object (YSO) on the chemistry of its own envelope by extending the models of Doty et al. (\cite{Doty}) to include a central source of UV radiation. The models are applied to the massive star-forming region AFGL 2591 for different inner UV field strengths. Depth-dependent abundance profiles for several molecules are presented and discussed. We predict enhanced column densities for more than 30 species, especially radicals and ions. Comparison between observations and models is improved with a moderate UV field incident on the inner envelope, corresponding to an enhancement factor G0 ≈ 10-100 at 200 AU from the star with an optical depth τ ≈ 15-17. The chemical networks of various species are explored. Subtle differences are found compared with traditional models of Photon Dominated Regions (PDRs) because of the higher temperatures and higher gas-phase H2O abundance caused by evaporation of ices in the inner region. In particular, the CN/HCN ratio is not a sensitive tracer of the inner UV field, in contrast with the situation for normal PDRs: for low UV fields, the extra CN reacts with H2 in the inner dense and warm region and produces more HCN. It is found that the CH+ abundance is strongly enhanced and grows steadily with increasing UV field. In addition, the ratio CH+/CH is increased by a factor of 103-105 depending on the inner UV flux. High-J lines of molecules like CN and HCN are most sensitive to the inner dense region where UV radiation plays a role. Thus, even though the total column density affected by UV photons is small, comparison of high-J and low-J lines can selectively trace and distinguish the inner UV field from the outer one. In addition, future Herschel-HIFI observations of hydrides can sensitively probe the inner UV field. Title: Decimeter Burst Emission and Particle Acceleration Authors: Benz, Arnold O. Bibcode: 2004ASSL..314..203B Altcode: The radio emission of solar flares at decimeter wavelengths includes a variety of emission processes of a plasma thought to have a high beta. Very intense coherent emissions are observed at frequencies smaller than about 9 GHz. They are caused by plasma instabilities driving various wave modes that in turn may emit observable radio waves. Particularly important are type III bursts, caused by electron beams exciting Langmuir waves. Their sources may be used to trace the path of the electrons back in the corona to the acceleration region. Less known are radio emissions from trapped electrons driving loss-cone unstable waves, suspected for type IV bursts. These types of coherent radio emission give clues on the geometry and plasma parameters near the acceleration region. Title: Thermal and non-thermal energies of solar flares Authors: Saint-Hilaire, P.; Benz, A. O. Bibcode: 2004AAS...204.4715S Altcode: 2004BAAS...36R.740S The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 9 medium-sized and 1 X-class solar flares have been determined from RHESSI observations. The emissions in the spectrum have been carefully separated. A reliable lower limit to the non-thermal energy, and the various errors of this estimate have been studied. The effects of albedo, non-uniform target ionization, hot target, and electron cross-section on the spectrum have been estimated. The turn-over or cut-off in the low-energy distribution of electrons remains the largest contribution to the error budget. About equally large are the errors of the thermal energy. They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses. Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction. Our analysis suggests that the thermal and non-thermal energies are of the same magnitude. This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma or by additional energy input of high-energy ions, or by other flare energy input additional to the non-thermal electron channel. Title: Electron Trapping, Reconnection, or Shock Acceleration? Radio Afterglows in the 12X-Events of Oct/Nov 2003 Authors: Benz, A. O.; Perret, H.; Saint-Hilaire, P.; Zlobec, P. Bibcode: 2004cosp...35..345B Altcode: 2004cosp.meet..345B The large solar flares of October and November 2003 have been accompanied by unusually intense radio emissions at decimeter wavelengths. The emissions even had direct effects on terrestrial activities such as radar and navigation. The radio emissions continued long after the main phase of the flares. The unusual number of large flares from the same active regions allow for a detailed comparison. The radio emissions are not due to electron beams and do not seem to be related to the primary energy release and acceleration processes. We have compared the radio emissions (as observed by Phoenix-2, Callisto, Trieste, and Nançay RH) with the X-rays measured by RHESSI and GOES. The intensity and duration of the radio emission seem to be generally related to the energy released as seen in X-rays, but there are large differences between the three active regions involved. The lack of X-rays during some times of the radio emission is confirmed. It has previously been taken for evidence that the radio "afterglow" (type IV burst) is caused by trapped electrons. We present evidence that this interpretation is not likely, but that electrons are accelerated long after the impulsive phase. The possible mechanisms of acceleration and the reasons for the absence of bremsstrahlung are compared with the observations. Title: Stars as suns : activity, evolution and planets Authors: Dupree, Andrea K.; Benz, Arnold O. Bibcode: 2004IAUS..219.....D Altcode: No abstract at ADS Title: Nanoflares and the Heating of the Solar Corona Authors: Benz, A. O. Bibcode: 2004IAUS..219..461B Altcode: 2003IAUS..219E.193B There is a simmering dispute on the heating of the solar corona. Waves or flares that is the question. New observational signatures of the heating process(es) have been revealed by observations of SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet corona active region loops and the solar wind are different and must be distinguished. Prime indications come from the distribution of temperature and radiation loss in relation to height the correlation of magnetic flux and brightness nanoflares and other fluctuations line broadening and waves. The reported microevents in the quiet regions are about 3 orders of magnitude smaller than microevents reported in active regions. The effects from localized energy release regardless of the energy source must be considered. In particular the reaction of the chromosphere on energy release by evaporation has an important effect on the corona. A further requirement for the heating process is to deposit most of the heat in the low corona but heat the upper corona to even higher temperature. Finally the heating process(es) must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun Title: Time evolution of the spectral hardness in solar hard X-ray flares Authors: Grigis, P. C.; Benz, A. O. Bibcode: 2004cosp...35.1096G Altcode: 2004cosp.meet.1096G The non-thermal emission from hard X-Ray flares shows high variability in the flux and spectral hardness. It has been known for a long time that in the impulsive phase a soft-hard-soft (SHS) pattern is usually observed. The behaviour of the spectral index is of crucial importance for the estimation of the non-thermal energy content of flares and is a direct signature of the electron acceleration process. We present RHESSI observation of 20 M-class flares for which the time evolution of the photon spectral index was measured over the whole impulsive phase. The non-thermal flux and the spectral index are clearly anti-correlated in most flares. The photon spectral index vs. flux relation can be fitted by a power-law model. The observed time evolution of the spectral index can be used to put constraints on electron acceleration models, which must be able to account for the SHS behaviour. Title: Variations in Solar X-ray Flux and its Relevance to the Coronal Heating Problem Authors: Benz, A. O.; Grigis, P. C.; Krucker, S. Bibcode: 2004cosp...35..343B Altcode: 2004cosp.meet..343B The thermal X-ray and EUV emissions of the solar corona are known to fluctuate in time and space. The fluctuations seem to be of a similar nature as the flares and thus are termed microflares or nanoflares. Several forms of such small events have been observed in the solar corona by SoHO, TRACE, Yohkoh, and RHESSI. The reported nanoevents in the quiet regions are about 3 orders of magnitude smaller than microevents reported in active regions and are radio-poor. Magnetic energy dissipation by small flares is one of the scenarios for coronal heating. These micro-events obviously increase the energy in the corona and are signatures of coronal heating, the question is whether they dominate coronal heating and are the cause of the existence of the corona. The main uncertainty in determining the role of flare heating is the flare energetics, in particular the forms of energy into which the magnetic energy is dissipated. A large fraction becomes observable in electrons having energies of some tens of keV. Another less known fraction is thought to be associated with the reconnection jets and MHD waves. The heating process(es) must be able to account for the coronae of the quiet sun including coronal holes, active regions, as well as more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun. Title: Thermal vs. non-thermal energies in solar flares Authors: Saint-Hilaire, P.; Benz, A. O. Bibcode: 2004cosp...35.1576S Altcode: 2004cosp.meet.1576S The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 9 medium-sized solar flares have been determined from RHESSI observations. The emissions in the spectrum have been carefully separated. A reliable lower limit to the non-thermal energy, and the various errors of this estimate have been studied. The effects of albedo, non-uniform target ionization, hot target, and electron cross-section on the spectrum have been estimated. The turn-over or cut-off in the low-energy distribution of electrons remains the largest contribution to the error budget. About equally large are the errors of the thermal energy. They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses. Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction. Our analysis suggests that the thermal and non-thermal energies are of the same magnitude. This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma or by additional energy input of high-energy ions, or by another flare energy input, additional to the non-thermal electron channel. Title: First Detection of Hard X-ray Emission From Solar Type III Radio Bursts Authors: Christe, S.; Krucker, S.; Lin, R. P.; Arzner, K.; Benz, A. O. Bibcode: 2003AGUFMSH11D1131C Altcode: We present the first detection of non-flare related hard X-ray emission from type III radio bursts as observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). During a period of 15 minutes on 19 July 2002 14:23-14:35 UT, the WAVES instrument on the Wind spacecraft observed interplanetary type III radio bursts approximately every 2 minutes and each was accompanied by a 12-15 keV X-ray brightening observed by RHESSI. The radio and X-rays fluxes were found to be strongly correlated. No flares were reported in the SEC solar event reports during this time and only the strongest brightening is associated with a detectable enhancement in the GOES levels (A3 above a B8 background). Phoenix-2, a ground-based radio spectrometer, observed each interplanetary type III to extend down to 300 MHz (0.1 Rsun) The strongest type III was also accompagnied by a cluster of decimetric radio emission in the frequency range 1 to 2 GHz. A close correlation is found between X-ray fluxes and the decimetric fluxes. X-ray spectra show non-thermal emission (9-30 keV) with an electron spectral power-law index of ∼4, from the footpoint of a TRACE loop observed in FeXII (195 Å). Subsequently, jets are seen to originate from the RHESSI footpoint emission travelling with apparent speeds of ∼ 100 km s-1. The observed RHESSI hard X-ray fluxes require ∼1033 electrons above 10 keV. This work was supported by NASA contract NAS5-98033. Title: High-Energy Radiation Probes of Protostellar Envelopes Authors: Stäuber, P.; Benz, A. O.; Doty, S. D.; van Dishoeck, E. F.; Jørgensen, J. K. Bibcode: 2003astro.ph.11022S Altcode: We present observations of molecular high-energy radiation probes and report the first detections of CO+ toward W3 IRS5, a source containing ultracompact HII regions. UV radiation and X-rays from the central objects may enhance molecules due to photodissociation and ionization processes. To study the effects on the immediate YSO environment, we are developing time- and depth-dependant chemical models containing UV and X-ray chemistry, by extending the models of Doty et al. (2002). Molecules like CO+ or NO may be used as tracers of very early X-ray emission in regions of high extinction, from which no X-ray photons can be detected. Title: Micro-events in the active and quiet solar corona Authors: Benz, A. O.; Grigis, P. C. Bibcode: 2003AdSpR..32.1035B Altcode: 2003astro.ph..8323B The content of hot material in the corona is not constant. Soft X-ray and high-temperature EUV line observations show that new material, apparently heated and evaporated from the chromosphere, is frequently injected into the corona both in active and quiet regions. Active regions are found to exhibit transient brightenings, termed here microflares, due to such enhancements in emission measure. They appear at a rate of up to 10 per hour in RHESSI observations of 3-15 keV X-rays, occurring even during the periods of lowest solar activity so far in the mission. The RHESSI observations combined with measurements at other wavelengths yield estimates of the energy input into the corona. These observations suggest that the models for coronal heating must be complemented with respect to continuous replenishing the lower corona by chromospheric material heated to coronal temperatures. The observed micro-events are secondary phenomena, and do not represent the primary energy release, nor its total amount. Nevertheless, they are an interesting source of information on the heating process(es) of the corona. The micro-events are compared to events in quiet regions, termed here nanoflares, which seem to be a different population, well separated in temperature and emission measure from microflares. Title: Hard X-rays, ejecta, and their associated decimetric radio emission in solar flares Authors: Saint-Hilaire, Pascal; Benz, Arnold O. Bibcode: 2003SoPh..216..205S Altcode: We investigate temporal and spatial correlations in solar flares of hard X-rays (HXR) and decimetric continuum emissions, ejecta, and CMEs. The focus is on three M-class flares, supported by observations from other flares. The main conclusions of our observations are that (1) major hard X-ray flares are often associated with ejecta seen in soft X-rays or EUV. (2) Those ejecta seem to start before HXR or related decimetric radio continua (DCIM emission). (3) DCIM occurring nearly simultaneously with the first HXR peak are located very close to the HXR source. Later in the flare, DCIM generally becomes stronger, drifts to lower frequency and occurs far from the HXR source. Thus the positions at high frequency are generally closer to the HXR source. DCIM emission consists of pulses that drift in frequency. The very high and sometimes positive drift rate suggests spatially extended sources or type III like beams in an inhomogeneous source. Movies of selected flares used in this study can be found on the CD-ROM accompanying this volume. Title: VLBI observations of T Tauri South Authors: Smith, K.; Pestalozzi, M.; Güdel, M.; Conway, J.; Benz, A. O. Bibcode: 2003A&A...406..957S Altcode: 2003astro.ph..5543S We report observations of the T Tauri system at 8.4 GHz with a VLBI array comprising the VLBA, VLA and Effelsberg 100 m telescopes. We detected a compact source offset approximately 40 mas from the best infrared position of the T Tau Sb component. This source was unresolved, and constrained to be less than 0.5 mas in size, corresponding to 0.07 AU or 15 Rsun at a distance of 140 pc. The other system components (T Tau Sa, T Tau N) were not detected in the VLBI data. The separate VLA map contains extended flux not accounted for by the compact VLBI source, indicating the presence of extended emission on arcsecond scales. The compact source shows rapid variability, which together with circular polarization and its compact nature indicate that the observed flux arises from a magnetically-dominated region. Brightness temperatures in the MK range point to gyrosynchrotron as the emission mechanism for the steady component. The rapid variations are accompanied by dramatic changes in polarization, and we record an at times 100% polarized component during outbursts. This strongly suggests a coherent emission process, most probably an electron cyclotron maser. With this assumption it is possible to estimate the strength of the local magnetic field to be 1.5-3 kilogauss. Title: Resolving the Magnetosphere of T Tauri South B Authors: Smith, K. W.; Pestalozzi, M.; Conway, J.; Güdel, M.; Benz, A. O. Bibcode: 2003ANS...324R..70S Altcode: 2003ANS...324..P46S No abstract at ADS Title: Coronal Heating and Microflares in Solar Active and Quiet Regions Authors: Benz, Arnold O. Bibcode: 2003ANS...324....8B Altcode: 2003ANS...324..B02B No abstract at ADS Title: Test particle simulation of the Electron Firehose instability Authors: Paesold, G.; Benz, A. O. Bibcode: 2003A&A...401..711P Altcode: In the course of the energization of { electrons to energies of some tens of keV during the impulsive phase of a solar flare, the velocity distribution function of the electrons is predicted to become anisotropic with Teparallel >Teperpendicular to (Here, parallel and perpendicular to denote directions with respect to the background magnetic field). Such a configuration can become unstable to the so-called Electron Firehose instability (EFI). Left hand circularly polarized electromagnetic waves propagating along the magnetic field are excited via a non-resonant mechanism: electrons non-resonantly excite the waves while the protons are in resonance and carry the wave. The non-resonant nature of the instability raises the question of the response of the electron population to the growing waves. Test particle simulations are carried out to investigate the pitch-angle development of electrons injected to single waves and wave spectra. To interpret the simulation results, a drift kinetic approach is developed. The findings in the case of single wave simulations show the scattering to larger pitch-angles in excellent agreement with the theory. The situation dramatically changes when assuming a spectrum of waves. Stochasticity is detected at small initial parallel velocities resulting in significant deviations from drift kinetic theory. It enhances the scattering rate of electrons with initial parallel velocity below to the mean thermal perpendicular velocity. Increased scattering is also noticed for electrons having initial parallel velocity within an order of magnitude of the resonance velocity. The resulting pitch-angle scattering is proposed to be an important ingredient in Fermi-type electron acceleration models, particularly transit-time acceleration by compressional MHD waves. Title: The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) - Mission Description and Early Results Authors: Lin, R. P.; Dennis, B. R.; Benz, A. O. Bibcode: 2003rrhe.conf.....L Altcode: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite was launched on 5 February 2002. Its objective is to study the energy release and particle acceleration in solar flares through observations of X-rays and gamma rays. Two novel technologies are combined to obtain both spectra and images over a broad energy range. For the spectroscopy, cooled hyperpure germanium detectors are used to cover the energy range from 3 keV to 17 MeV with unprecedented keV-class resolution. Since focusing optics are not possible for making images with such high energy photons, tungsten and molybdenum absorbing grids are used to modulate the X-rays and gamma-rays coming from the Sun as the spacecraft rotates. This allows the spatial Fourier components of the source to be determined so that images can be made in spectral ranges where astronomical images have never been produced before. These new instrumental techniques require equally innovative software to reconstruct X-ray and gamma-ray spectra and images from the observations. Ample solar activity, abundant observations, and an open data policy have attracted many researchers. Astronomers face in the RHESSI mission an exciting new scientific potential. It has unusually broad possibilities for improving our understanding of the enigmatic solar flare phenomenon that is becoming increasingly important as society depends more and more on space-based technologies. In this volume, the functioning of RHESSI is explained, the data analysis techniques including spectroscopy and image reconstruction are introduced, and the experiences of the first few months of operation are summarized. First scientific results are presented that provide the essential base for more extended studies using RHESSI data and complementary observations by instruments on other spacecraft and at ground-based solar observatories. The accompanying CD-ROM contains X-ray and EUV movies showing the dynamics of several solar flares. It also contains color versions of the graphics in the printed papers and additional material. Scientists and students will find here the latest discoveries in solar flare research, as well as inspiration for future work. The papers will serve as references for the many new discoveries to come from the continuing RHESSI observations.

http://www.wkap.nl/prod/b/1-4020-1107-5 Title: The Magnetosphere of T Tauri South Authors: Smith, Kester; Pestalozzi, Michele; Guedel, Manuel; Conway, John; Benz, Arnold Bibcode: 2003IAUS..221P.166S Altcode: We report observations of the T Tauri system at 8.4 GHz with a VLBI array comprising the VLBA VLA and Effelsberg 100m telescopes. We detected a compact source offset approximately 40mas from the best optical position of the T Tau Sb component. The other system components (T Tau Sa T Tau N) were not detected in the VLBI data. The compact source is constrained to be less than 10 solar radii in size. The VLA lightcurve shows rapid variability which together with circular polarization and its compact nature indicate that the observed flux arises from a magnetically-dominated region. One flare was observed to have 100% right-hand circular polarization suggestive of a coherent emission process most probably an electron cyclotron maser. With this assumption it is possible to estimate the strength of the local magnetic field to be 1.5-3 kilogauss. Using the assumption that the steady gyrosynchrotron emission must have brightness temperature less than 10 billion Kelvin we argue that this field must be large in size compared to the star. Title: Division II: The Sun and heliosphere (Soleil et héliosphère) Authors: Benz, Arnold O. Bibcode: 2003IAUTA..25...73B Altcode: 2003IAUTr..25A..73B No abstract at ADS Title: International low-frequency very-long-baseline interferometry network project milestones Authors: Molotov, I.; Lipatov, B.; Dementiev, A.; Antipenko, A.; Snegirev, S.; Nechaeva, M.; Reznikovak, V.; Altunin, V.; Benz, A.; Mantovani, F.; Stanghellini, C.; Gridin, A.; Ananthakrishnan, S.; Balasubramanian, V.; Sankararaman, M.; Hong, X.; Huang, X.; Shiguang, L.; Dougherty, S.; Del Rizzo, D.; Fink, A.; Liu, X.; Na, W.; Zhang, J.; Kus, A.; Borkowski, K.; Quick, J.; Nicolson, G.; Shmeld, I.; Koyama, Y.; Sekido, M.; Gorshenkov, Yu.; Poperechenko, B.; Saurin, V.; Ozolins, G.; Bezrukov, D.; Zhang, X.; Kovalenko, A.; Samodurov, V.; Tuccari, G.; Konovalenko, A.; Falkovich, I. Bibcode: 2003A&AT...22..743M Altcode: No abstract at ADS Title: Solar flare electron acceleration: Comparing theories and observations Authors: Benz, A. O.; Saint-Hilaire, P. Bibcode: 2003AdSpR..32.2415B Altcode: 2003astro.ph..8321B A popular scenario for electron acceleration in solar flares is transit-time damping of low-frequency MHD waves excited by reconnection and its outflows. The scenario requires several processes in sequence to yield energetic electrons of the observed large number. Until now there was very little evidence for this scenario, as it is even not clear where the flare energy is released. RHESSI measurements of bremsstrahlung by non-thermal flare electrons yield energy estimates as well as the position where the energy is deposited. Thus quantitative measurements can be put into the frame of the global magnetic field configuration as seen in coronal EUV line observations. We present RHESSI observations combined with TRACE data that suggest primary energy inputs mostly into electron acceleration and to a minor fraction into coronal heating and primary motion. The more sensitive and lower energy X-ray observations by RHESSI have found also small events (C class) at the time of the acceleration of electron beams exciting meter wave Type III bursts. However, not all RHESSI flares involve Type III radio emissions. The association of other decimeter radio emissions, such as narrowband spikes and pulsations, with X-rays is summarized in view of electron acceleration. Title: Radio Diagnostics of Flare Energy Release Authors: Benz, A. O. Bibcode: 2003LNP...612...80B Altcode: 2003ecpa.conf...80B The radio emission of flares at wavelengths from millimeter to decameter waves includes a large variety of emission processes. They can be considered as different diagnostic tools particularly suited for the analysis of non-thermal electron distributions, enhanced levels of various kinds of plasma waves and plasma phenomena. Incoherent gyrosynchrotron emission at millimeter and centimeter waves provides higher sensitivity for observing MeV electrons than existing hard X-ray (HXR) and gamma-ray satellites. Very intense coherent emissions are observed at wavelengths longer than about 10 cm, weaker ones from about 4 cm. They are caused by plasma instabilities driving various wave modes that in turn may emit observable radio waves. Particularly important are type III bursts, caused by electron beams exciting Langmuir waves. Their trace in the corona points back to the acceleration region of the electrons. Less known are radio emissions from trapped electrons driving loss-cone unstable waves. This is the interpretation usually given to decimetric type IV emission. These types of coherent radio emission give clues on the geometry and plasma parameters near the acceleration region. More speculative are emissions that are directly produced by the acceleration process. A possible group of such phenomena are narrowband, short peaks of emission. Narrowband spikes are seen sometimes at frequencies above the start of metric type III events. There is mounting evidence for the hypothesis that these spikes coincide with the energy release region. Much less clear and highly controversial is the situation for decimetric spikes, which are associated with HXR flares. More frequently than spikes, however, there is fluctuating broadband decimetric emission during the HXR phase of flares. The use of these coherent radio emissions as a diagnostic tool for the primary energy release requires a solid understanding of the emission process. At the moment we are still far away from an accepted theory. Only careful comparisons with complementary observations of energetic electrons and the thermal coronal background in EUV lines and soft X-rays can put coherent emissions into context and test the different scenarios. The comparison with HXR, millimeter and centimeter observations will be necessary to derive quantitative results on energy release. In combination with other wavelengths and their recent imaging capabilities, exciting new possibilities are now opening for radio diagnostics. Title: Acceleration and Enrichment of 3He in Impulsive Solar Flares by Electron Firehose Waves Authors: Paesold, G.; Kallenbach, R.; Benz, A. O. Bibcode: 2003ApJ...582..495P Altcode: 2002astro.ph..9135P A new mechanism for acceleration and enrichment of 3He during impulsive solar flares is presented. Low-frequency electromagnetic plasma waves excited by the electron firehose instability (EFI) can account for the acceleration of ions up to 1 MeV amu-1 energies as a single-stage process. The EFI arises as a direct consequence of the free energy stored in a temperature anisotropy (Te∥>Te⊥) of the bulk energized electron population during the acceleration process. In contrast to other mechanisms that require special plasma properties, the EFI is an intrinsic feature of the acceleration process of the bulk electrons. Being present as a side effect in the flaring plasma, these waves can account for the acceleration of 3He and 4He while selectively enhancing 3He as a result of the spectral energy density built up from linear growth. Linearized kinetic theory, analytic models, and test particle simulations have been applied to investigate the ability of the waves to accelerate and fractionate. As waves grow in both directions parallel to the magnetic field, they can trap resonant ions and efficiently accelerate them to the highest energies. Plausible models have been found that can explain the observed energies, spectra, and abundances of 3He and 4He. Title: Preface Authors: Lin, R.; Dennis, B.; Benz, A.; Harvey, J.; Engvold, O.; švestka, Z. Bibcode: 2002SoPh..210....1L Altcode: No abstract at ADS Title: The RHESSI Experimental Data Center Authors: Saint-Hilaire, Pascal; von Praun, Christoph; Stolte, Etzard; Alonso, Gustavo; Benz, Arnold O.; Gross, Thomas Bibcode: 2002SoPh..210..143S Altcode: The RHESSI Experimental Data Center (HEDC) at ETH Zürich aims to facilitate the use of RHESSI data. It explores new ways to speed up browsing and selecting events such as solar flares. HEDC provides pre-processed data for on-line use and allows basic data processing remotely over the Internet. In this article, we describe the functionality and contents of HEDC, as well as first experiences by users. HEDC can be accessed at http://www.hedc.ethz.ch. Additional graphical material and color versions of most figures are available on the CD-ROM accompanying this volume. Title: Energy budget and imaging spectroscopy of a compact flare Authors: Saint-Hilaire, Pascal; Benz, Arnold O. Bibcode: 2002SoPh..210..287S Altcode: 2002astro.ph.10023S We present the analysis of a compact flare that occurred on 26 February 2002 at 10:26 UT, seen by both RHESSI and TRACE. The size of the nearly circular hard X-ray source is determined to be 5.6 (±0.8)'', using different methods. The power-law distribution of non-thermal photons is observed to extend down to 10 keV without flattening, and to soften with increasing distance from the flare kernel. The former indicates that the energy of the precipitating flare electron population is larger than previously estimated: it amounts to 2.6 (±0.8)×1030 erg above 10 keV, assuming thick-target emission. The thermal energy content of the soft X-ray source (isothermal temperature of 20.8 (±0.9) MK) and its radiated power were derived from the thermal emission at low energies. TRACE has observed a low-temperature ejection in the form of a constricted bubble, which is interpreted as a reconnection jet. Its initial energy of motion is estimated. Using data from both satellites, an energy budget for this flare is derived. The kinetic energy of the jet bulk motion and the thermal and radiated energies of the flare kernel were more than an order of magnitude smaller than the derived electron beam energy. A movie is available on the CD-ROM accompanying this volume. Title: Microflares and hot component in solar active regions Authors: Benz, Arnold O.; Grigis, Paolo C. Bibcode: 2002SoPh..210..431B Altcode: 2002astro.ph.10024B Open-shutter RHESSI observations of 3-15 keV X-rays are found to exhibit active-region transient brightenings and microflares at a rate of a least 10 per hour occurring even during the periods of lowest solar activity so far in the mission. A thermal component fitted by temperatures of 6-14 MK dominates from 3 keV to about 9 keV, but can be traced up to 14 keV in some cases, and has an average duration of 131(±103) s at 7-8 keV. The duration increases with decreasing photon energy. The peak count rate defined by cross-correlation is delayed at low energies. The temperature peaks early in the event and then decreases, whereas the emission measure increases throughout the event. The properties are consistent with thermal conduction dominating the evolution. In some of the bigger events, a second component was found in the 11-14 keV range extending down to 8 keV in some cases. The duration is typically 3 times shorter and ends near the peak time of the thermal component consistent with the Neupert effect of regular flares. Therefore the second component is suggested to be of non-thermal origin, presumably causing the beam-driven evaporation of the first component. The two components can be separated and analyzed in detail for the first time. Low-keV measurements allow a reliable estimate of the energy input by microflares necessary to assess their relevance for coronal heating. Title: The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) Authors: Lin, R. P.; Dennis, B. R.; Hurford, G. J.; Smith, D. M.; Zehnder, A.; Harvey, P. R.; Curtis, D. W.; Pankow, D.; Turin, P.; Bester, M.; Csillaghy, A.; Lewis, M.; Madden, N.; van Beek, H. F.; Appleby, M.; Raudorf, T.; McTiernan, J.; Ramaty, R.; Schmahl, E.; Schwartz, R.; Krucker, S.; Abiad, R.; Quinn, T.; Berg, P.; Hashii, M.; Sterling, R.; Jackson, R.; Pratt, R.; Campbell, R. D.; Malone, D.; Landis, D.; Barrington-Leigh, C. P.; Slassi-Sennou, S.; Cork, C.; Clark, D.; Amato, D.; Orwig, L.; Boyle, R.; Banks, I. S.; Shirey, K.; Tolbert, A. K.; Zarro, D.; Snow, F.; Thomsen, K.; Henneck, R.; Mchedlishvili, A.; Ming, P.; Fivian, M.; Jordan, John; Wanner, Richard; Crubb, Jerry; Preble, J.; Matranga, M.; Benz, A.; Hudson, H.; Canfield, R. C.; Holman, G. D.; Crannell, C.; Kosugi, T.; Emslie, A. G.; Vilmer, N.; Brown, J. C.; Johns-Krull, C.; Aschwanden, M.; Metcalf, T.; Conway, A. Bibcode: 2002SoPh..210....3L Altcode: RHESSI is the sixth in the NASA line of Small Explorer (SMEX) missions and the first managed in the Principal Investigator mode, where the PI is responsible for all aspects of the mission except the launch vehicle. RHESSI is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/gamma-ray continua emitted by energetic electrons, and of gamma-ray lines produced by energetic ions. The single instrument consists of an imager, made up of nine bi-grid rotating modulation collimators (RMCs), in front of a spectrometer with nine cryogenically-cooled germanium detectors (GeDs), one behind each RMC. It provides the first high-resolution hard X-ray imaging spectroscopy, the first high-resolution gamma-ray line spectroscopy, and the first imaging above 100 keV including the first imaging of gamma-ray lines. The spatial resolution is as fine as ∼ 2.3 arc sec with a full-Sun (≳ 1°) field of view, and the spectral resolution is ∼ 1-10 keV FWHM over the energy range from soft X-rays (3 keV) to gamma-rays (17 MeV). An automated shutter system allows a wide dynamic range (>107) of flare intensities to be handled without instrument saturation. Data for every photon is stored in a solid-state memory and telemetered to the ground, thus allowing for versatile data analysis keyed to specific science objectives. The spin-stabilized (∼ 15 rpm) spacecraft is Sun-pointing to within ∼ 0.2° and operates autonomously. RHESSI was launched on 5 February 2002, into a nearly circular, 38° inclination, 600-km altitude orbit and began observations a week later. The mission is operated from Berkeley using a dedicated 11-m antenna for telemetry reception and command uplinks. All data and analysis software are made freely and immediately available to the scientific community. Title: Plasma Astrophysics, second edition Authors: Benz, Arnold Bibcode: 2002ASSL..279.....B Altcode: 2002plas.book.....B This thoroughly revised textbook is a basic introduction to plasma phenomena in solar and stellar coronae emphasizing non-MHD aspects. The natural way in which the author unifies observations and theory gives a wide perspective to the subject. An important feature is the lucidly written presentation of the fundamentals of plasma physics. The basic theory thus developed is then extended to some exemplary and important observations of coronal dynamics, such as coronal currents, particle acceleration, propagation of particle beams, and shocks. The book has grown from teaching introductory courses on plasma astrophysics at the Swiss Federal Institute of Technology (ETH). It addresses advanced undergraduates and first-year graduate students without a background in plasma physics. It will also be of interest to more senior research workers involved in coronal physics of the Sun and other stars, solar/stellar winds, and various other fields of plasma astrophysics. Title: The solar coronal origin of a slowly drifting decimetric-metric pulsation structure Authors: Khan, J. I.; Vilmer, N.; Saint-Hilaire, P.; Benz, A. O. Bibcode: 2002A&A...388..363K Altcode: We report observations associated with a short duration, slowly drifting decimetric-metric pulsation structure seen by the Phoenix-2 Radio Spectrometer on 2000 August 25. The range of frequencies over which this drifting radio feature occurred included frequencies observed by the Nançay Radioheliograph enabling the spatial location and development of such a radio source to be determined for the first time. The radio feature was closely associated with a solar flare. This flare was observed by the Yohkoh Soft X-ray Telescope (SXT) allowing us to compare the radio locations with the development of coronal structures seen in soft X-rays. The Yohkoh SXT images reveal two main soft X-ray features: a small flaring kernel region consisting of one or more bright loops located low in the corona and much fainter soft X-ray ejecta observed above the flare kernel region. The radio sources of the drifting pulsation structure moved outward with the soft X-ray ejecta. Our results indicate that the drifting decimetric-metric burst for this event was closely associated with the soft X-ray ejecta. Title: Acceleration and Enrichment of 3He in Impulsive Solar Flares by Electron Firehose Waves Authors: Paesold, G.; Kallenbach, R.; Benz, A. O. Bibcode: 2002AGUSMSH32B..02P Altcode: A new mechanism for acceleration and enrichment of 3He during impulsive solar flares is presented. Low-frequency electromagnetic plasma waves excited by the Electron Firehose Instability (EFI) account for the acceleration of ions up to 1; {MeV;amu}-1 energies as a single stage process. The EFI arises as a direct consequence of the free energy stored in a temperature anisotropy (Te_∥/Te_perpendicular to >1) of the bulk energized electron population during the acceleration process. In contrast to other mechanisms which require special plasma properties, the EFI is an intrinsic feature of the acceleration process of the bulk electrons. Being present as a side effect in the flaring plasma, these waves can account for the acceleration of 3He and 4He while selectively enhancing 3He due to the spectral energy density obtained from linear growth. Linearized kinetic theory, analytic models and test-particle simulations have been applied to investigate the ability of the waves to accelerate and fractionate. Plausible models have been found that can explain the observed energies, spectra and abundances of 3He and 4He. Title: Energy Distribution of Microevents in the Quiet Solar Corona Authors: Benz, Arnold O.; Krucker, Säm Bibcode: 2002ApJ...568..413B Altcode: 2001astro.ph..9027B Recent imaging observations of EUV line emissions have shown evidence for frequent flarelike events in a majority of the pixels in quiet regions of the solar corona. The changes in coronal emission measure indicate impulsive heating of new material to coronal temperatures. These heating or evaporation events are candidate signatures of ``nanoflares'' or ``microflares'' proposed to interpret the high temperature as well as the very existence of the corona. The energy distribution of these microevents reported in the literature differ widely, and so do the estimates of their total energy input into the corona. Here we analyze the assumptions of the different methods, compare them by using the same data set, and discuss their results. We also estimate the different forms of energy input and output, keeping in mind that the observed brightenings are most likely secondary phenomena. A rough estimate of the energy input observed by EIT on the SOHO satellite is of the order of 10% of the total radiative output in the same region. It is considerably smaller for the two reported TRACE observations. The discrepancy can be explained by flare selection and different thresholds for flare detection. There is agreement on the slope and the absolute value of the distribution if the same methods are used and a numerical error is corrected. The extrapolation of the power law to unobserved energies that are many orders of magnitude smaller remains questionable. Nevertheless, these microevents and unresolved smaller events are currently the best source of information on the heating process of the corona. Title: Das Plasma-Universum Authors: Benz, Arnold Bibcode: 2002Orion..60a...4B Altcode: 2002Orion.308....4B No abstract at ADS Title: Location of narrowband spikes in solar flares Authors: Benz, A. O.; Saint-Hilaire, P.; Vilmer, N. Bibcode: 2002A&A...383..678B Altcode: 2001astro.ph.12442B Narrowband spikes of the decimeter type have been identified in dynamic spectrograms of Phoenix-2 of ETH Zurich and located in position with the Nançay Radioheliograph at the same frequency. The spike positions have been compared with the location of hard X-ray emission and the thermal flare plasma in soft X-rays and EUV lines. The decimetric spikes are found to be single sources located some 20 arcsec to 400 arcsec away from the flare site in hard or soft X-rays. In most cases there is no bright footpoint nearby. In at least two cases the spikes are near loop tops. These observations do not confirm the widely held view that the spike emission is produced by some loss-cone instability masering near the footpoints of flare loops. On the other hand, the large distance to the flare sites and the fact that these spikes are all observed in the flare decay phase make the analyzed spike sources questionable sites for the main flare electron acceleration. They possibly indicate coronal post-flare acceleration sites. Title: Low Frequency VLBI Project Authors: Molotov, I. E.; Likhachev, S. F.; Chuprikov, A. A.; Dementiev, A.; Lipatov, B.; Nechaeva, M.; Snegirev, S.; Dugin, N.; Ananthakrishnan, S.; Balasubramanian, V.; Benz, A.; Mantovani, F.; Liu, X.; Hong, X.; Kus, A.; Molotov, E. P.; Ignatov, S. P.; Poperechenko, B. A.; Gorshenkov, Y. N.; Konovalenko, A. A. Bibcode: 2002IAUS..199..492M Altcode: No abstract at ADS Title: Micro-events in the Quiet Solar Corona Authors: Benz, A.; Krucker, S. Bibcode: 2002cosp...34E1929B Altcode: 2002cosp.meetE1929B The content of coronal material in the quiet Sun is not constant as soft X-ray and high-temperature EUV line observations have shown. New material, probably heated and evaporated from the chromosphere is occasionally injected even in the faintest parts above the magnetic network cell interiors. We discuss the characteristics of the largest of these events, based on simultaneous transition region observations (in EUV and radio) and the observed analogies to flares. Assuming that the smaller events follow the same pattern, we estimate the total mass input and compare it to the requirements observed in the solar wind. A rough estimate of the energy input observed by EIT on the SoHO satellite is of the order of 10% of the total radiative output in the same region. The simulation indicates that the extrapolation to smaller events is problematic and that smaller events may play an even more decisive role than previously assumed. The hypothesis of nanoflare heating is consistent with these observations if the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. These micro-events are currently the best source of information on the heating process of the corona. Title: Resolving the magnetosphere of T Tauri south B. Authors: Smith, K. W.; Pestalozzi, M.; Conway, J.; Guedel, M.; Benz, A. O. Bibcode: 2002AGAb...19Q..94S Altcode: No abstract at ADS Title: Flare electrons: comparing theories and observations Authors: Benz, A. Bibcode: 2002cosp...34E1930B Altcode: 2002cosp.meetE1930B The prevailing scenario for electron acceleration in solar flares is transit-time damping of low-frequency waves excited by reconnection and its outflows. The scenario requires many processes following each other in order to end up with energetic electrons of the observed large number. Until now there was very little evidence for this scenario, as it was even not clear where the reconnection takes place. RHESSI measurements of bremsstrahlung of non-thermal flare electrons yield energy estimates as well as the position where the energy is deposited. Thus quantitative measurements can be put into the frame of the global magnetic field configuration as seen in Fe-line observations. I present RHESSI observations combined with TRACE data that indicate a low reconnection site and a considerable energy input into motions. Some type III emissions are clearly secondary acceleration processes. Their propagation path points to a secondary, higher acceleration site. Nevertheless, some energy X-rays have been found at the time of the acceleration of electron beams exciting type III bursts. They are generally at lower photon energies. The association of decimetric radio emissions and X-rays is summarized in view of electron acceleration. Title: The Solar Coronal Origin of a Slowly Drifting Radio Pulsation Feature Authors: Khan, J. I.; Vilmer, N.; Saint-Hilaire, P.; Benz, A. O. Bibcode: 2002mwoc.conf..285K Altcode: No abstract at ADS Title: The Source Regions of Impulsive Solar Electron Events Authors: Benz, Arnold O.; Lin, Robert P.; Sheiner, Olga A.; Krucker, Säm; Fainberg, Joe Bibcode: 2001SoPh..203..131B Altcode: Low-energy (2-19 keV) impulsive electron events observed in interplanetary space have been traced back to the Sun, using their interplanetary type III radiation and metric/decimetric radio-spectrograms. For the first time we are able to study the highest frequencies and thus the radio signatures closest to the source region. All the selected impulsive solar electron events have been found to be associated with an interplanetary type III burst. This allows to time the particle events at the 2 MHz plasma level and identify the associated coronal radio emissions. Except for 5 out of 27 cases, the electron events were found to be associated with a coronal type III burst in the metric wavelength range. The start frequency yields a lower limit to the density in the acceleration region. We also search for narrow-band spikes at the start of the type III bursts. In about half of the observed cases we find metric spikes or enhancements of type I bursts associated with the start of the electron event. If interpreted as the plasma emission of the acceleration process, the observed average frequency of spikes suggests a source density of the order of 3×108 cm−3 consistent with the energy cut-off observed. Title: On the reliability of peak-flux distributions, with an application to solar flares Authors: Isliker, H.; Benz, A. O. Bibcode: 2001A&A...375.1040I Altcode: 2001astro.ph..6158I Narrow-band radio spikes have been recorded during a solar flare with unprecedented resolution. This unique example allows us to study the effect of low resolution in previously published peak-flux distributions of radio spikes. We give a general, analytical expression for how an actual peak-flux distribution is changed in shape if the peaks are determined with low temporal and/or frequency resolution. It turns out that, generally, low resolution tends to cause an exponential behavior at large flux values if the actual distribution is of a power-law shape. The distribution may be severely altered if the burst-duration depends on the peak-flux. The derived expression is applicable also to peak-flux distributions derived at other wavelengths (e.g. soft and hard X-rays, EUV). We show that for the analyzed spike-event the resolution was sufficient for a reliable peak flux distribution. It can be fitted by generalized power-laws or by an exponential. Title: On-the-Disk Development of the Halo Coronal Mass Ejection on 1998 May 2 Authors: Pohjolainen, S.; Maia, D.; Pick, M.; Vilmer, N.; Khan, J. I.; Otruba, W.; Warmuth, A.; Benz, A.; Alissandrakis, C.; Thompson, B. J. Bibcode: 2001ApJ...556..421P Altcode: A halo coronal mass ejection (CME) was observed at 15:03 UT on 1998 May 2 by the Solar and Heliospheric Observatory Large-Angle Spectrometric Coronagraph. The observation of the CME was preceded by a major soft X-ray flare in NOAA Active Region 8210, characterized by a delta spot magnetic configuration and some activity in region 8214. A large transequatorial interconnecting loop (TIL) seen in the soft X-rays connected AR 8210 to a faint magnetic field region in the periphery of region 8214. Smaller loop systems were also connecting AR 8210 to other fainter bipolar magnetic structures, the interconnecting loop (IL) east of AR 8210 being one of the most visible. We present here a multiwavelength analysis of the large- and small-scale coronal structures associated with the development of the flare and of the CME, with emphasis placed on radio-imaging data. In the early phases of the flare, the radio emission sources traced the propagation paths of electrons along the TIL and the IL, which are accelerated in the vicinity of AR 8210. Furthermore, jetlike flows were observed in soft X-rays and in Hα in these directions. Significantly, the TIL and IL loop systems disappeared at least partially after the CME. An EUV Imaging Telescope (EIT) dimming region of similar size and shape to the soft X-ray TIL, but noticeably offset from it, was also observed. During the ``flash'' phase of the flare, new radio sources appeared, presenting signatures of destabilization and reconnection at discrete locations of the connecting loops. We interpret these as possible signatures of the CME liftoff on the disk. An Hα Moreton wave (blast wave) and an ``EIT wave'' were also observed, originating from the flaring AR 8210. The signatures in radio, after the wave propagated high into the corona, include type II-like emissions in the spectra. The radio images link these emissions to fast-moving sources, presumably formed at locations where the blast wave encounters magnetic structures. The opening of the CME magnetic field is revealed by the radio observations, which show large and expanding moving sources overlying the later-seen EIT dimming region. Title: A nanoflare heating model for the quiet solar corona Authors: Mitra-Kraev, U.; Benz, A. O. Bibcode: 2001A&A...373..318M Altcode: 2001astro.ph..4218M The energy input into the lower solar corona by flare evaporation events has been modeled according to the available observations for quiet regions. The question is addressed whether such heating events can provide the observed average level of the coronal emission measure and thus of the observed flux of extreme ultraviolet (EUV) and X-ray emission without contradicting the observed average power spectrum of the emission measure, the typical emission measure variations observed for individual pixels and the observed flare energy distribution. As the assumed flare height influences the derived flare energy, the mathematical foundations of nanoflare distributions and their conversion to different height assumptions are studied first. This also allows a comparison with various published energy distributions differing in height assumptions and to relate the observations to the input parameters of the heating model. An analytic evaluation of the power spectrum yields the relationship between the average time profile of nanoflares (or microflares), assumed to be self-similar in energy, and the power spectrum. We find that the power spectrum is very sensitive to the chosen time profile of the flares. Models are found by numerical simulation that fit all available observations. They are not unique but severely constrained. We concentrate on a model with a flare height proportional to the square root of the flare area. The existence of a fitting model demonstrates that nanoflare heating of the corona is a viable and attractive mechanism. Title: Are Heating Events in the Quiet Solar Corona Small Flares? Authors: Krucker, S.; Benz, A. O. Bibcode: 2001AGUSM..SP52B03K Altcode: Temporary enhancements of the coronal emission measure in a quiet region have been shown to constitute a significant energy input. Here some relatively large events (Yohkoh, EIT Observations) are discussed and tested for characteristics known from full-sized impulsive flares in active regions. The differences to active region flares seem to be mainly quantitative, and the analyzed heating events may in principle be considered as microflares or large nanoflares, thus small versions of regular flares. In this presentation we focus on the following questions: (1) Are there related events seen in transient region lines (CDS/SUMER observations)? (2) What are the relative contributions of the thermal, potential, and expansion energy to the total energy released in these events. (3) Are the reported flare temperatures in quiet regions of 1-2 MK possibly higher (3-5 MK)? Title: Spatial analysis of solar type III events associated with narrow band spikes at metric wavelengths Authors: Paesold, G.; Benz, A. O.; Klein, K. -L.; Vilmer, N. Bibcode: 2001A&A...371..333P Altcode: 2001astro.ph..3491P The spatial association of narrow band metric radio spikes with type III bursts is analyzed. The analysis addresses the question of a possible causal relation between the spike emission and the acceleration of the energetic electrons causing the type III burst. The spikes are identified by the Phoenix-2 spectrometer (ETH Zurich) from survey solar observations in the frequency range from 220 MHz to 530 MHz. Simultaneous spatial information was provided by the Nançay Radioheliograph (NRH) at several frequencies. Five events were selected showing spikes at one or two and type III bursts at two or more Nançay frequencies. The 3-dimensional geometry of the single events has been reconstructed by applying different coronal density models. As a working hypothesis it is assumed that emission at the plasma frequency or its harmonic is the responsible radiation process for the spikes as well as for the type III bursts. It has been found that the spike source location is consistent with the backward extrapolation of the trajectory of the type III bursts, tracing a magnetic field line. In one of the analyzed events, type III bursts with two different trajectories originating from the same spike source could be identified. These findings support the hypothesis that narrow band metric spikes are closely related to the acceleration region. Title: A Nanoflare Heating Model for the Quiet Solar Corona Authors: Mitra Kraev, U.; Benz, A. O. Bibcode: 2001AGUSM..SP41A02M Altcode: The energy input into the lower solar corona by flare evaporation events has been modeled according to the available observations for quiet regions. The question is addressed whether such heating events can provide the observed average level of the coronal emission measure and thus of the observed flux of extreme ultraviolet (EUV) and X-ray emission without contradicting the observed average power spectrum of the emission measure, the typical emission measure variations observed for individual pixels and the observed flare energy distribution. As the assumed flare height influences the derived flare energy, the mathematical foundations of nanoflare distributions and their conversion to different height assumptions are studied first. This also allows a comparison with various published energy distributions differing in height assumptions and to relate the observations to the input parameters of the heating model. An analytic evaluation of the power spectrum yields the relationship between the average time profile of nanoflares (or microflares), assumed to be self-similar in energy, and the power spectrum. We find that the power spectrum is very sensitive to the chosen time profile of the flares. Models are found by numerical simulation that fit all available observations. They are not unique but severely constrained. We concentrate on a model with a flare height proportional to the square root of the flare area. The existence of a fitting model demonstrates that nanoflare heating of the corona is a viable and attractive mechanism. Title: Heating the Quiet Corona by Nanoflares: Evidence and Problems Authors: Benz, A. O. Bibcode: 2001AGUSM..SP51C06B Altcode: Recent imaging observations of coronal EUV line emission have shown evidence for frequent flare-like events in a majority of the pixels in quiet regions. The changes in the coronal emission measure indicate the impulsive heating of new material to coronal temperatures. Estimates of the energy input into the corona by these "nanoflares" differ widely in the literature. Here we discuss the proposed methods and interpret the different results by the various recent analyses. The results using similar EUV data from EIT/SOHO and TRACE basically agree on the power-law exponent when the same method is used. The extrapolation of the power law to energies that are many orders of magnitude smaller remains doubtful, however. Nevertheless, the inferred energy input into the corona by the micro-events in the observable range has been reported to be of the order of 10 percent of the observed radiation output by EIT observations. It is considerably smaller for TRACE. The discrepancy can be explained only partially by different thresholds for flare detection. It is pointed out that the deviation between the different analyses in the number of nanoflares per energy and time unit is more serious than the widely discussed differences in the power law index. Title: Astronomy: Brown dwarf is a radio star Authors: Benz, Arnold O. Bibcode: 2001Natur.410..310B Altcode: No abstract at ADS Title: Division II: Sun and Heliosphere Authors: Benz, Arnold O.; Bogdan, T.; Foukal, P. V.; Melrose, D. B.; Solanki, S.; Vandas, M.; Webb, D. F. Bibcode: 2001IAUTB..24..110B Altcode: No abstract at ADS Title: Heating the Quiet Corona by Nanoflares: Evidence and Problems Authors: Benz, A. O.; Krucker, S. Bibcode: 2001IAUS..203..471B Altcode: 2000astro.ph.12106B The content of coronal material in the quiet Sun is not constant as soft X-ray and high-temperature EUV line observations have shown. New material, probably heated and evaporated from the chromosphere is occasionaly injected even in the faintest parts above the magnetic network cell interiors. We discuss the characteristics of the largest of these events, based on simultaneous transition region observations (in EUV and radio) and the observed analogies to flares. Assuming that the smaller events follow the same pattern, we estimate the total energy input. Various recent analyses are compared and briefly discussed. Finally we present the results of a simulation, extrapolating the observed range of microflares to smaller energies. The simultation indicates that the extrapolation to smaller events is problematic and that smaller events may play an even more decisive role than previously assumed. The hypothesis of nanoflare heating is consistent with these observations if the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. Title: High-sensitivity observations of solar flare decimeter radiation Authors: Benz, A. O.; Messmer, P.; Monstein, C. Bibcode: 2001A&A...366..326B Altcode: 2000astro.ph.12093B A new acousto-optic radio spectrometer has observed the 1-2 GHz radio emission of solar flares with unprecedented sensitivity. The number of detected decimeter type III bursts is greatly enhanced compared to observations by conventional spectrometers observing only one frequency at the time. The observations indicate a large number of electron beams propagating in dense plasmas. For the first time, we report weak, reversed drifting type III bursts at frequencies above simultaneous narrowband decimeter spikes. The type III bursts are reliable signatures of electron beams propagating downward in the corona, apparently away from the source of the spikes. The observations contradict the most popular spike model that places the spike sources at the footpoints of loops. Conspicuous also was an apparent bidirectional type U burst forming a fish-like pattern. It occurs simultaneously with an intense U-burst at 600-370 MHz observed in Tremsdorf. We suggest that it intermodulated with strong terrestrial interference(cellular phones) causing a spurious symmetric pattern in the spectrogram at 1.4 GHz. Symmetric features in the 1-2 GHz range, some already reported in the literature, therefore must be considered with utmost caution. Title: Mechanisms for Coronal Mass Supply by Evaporative Micro-Events Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O. Bibcode: 2001IAUS..203..498B Altcode: There is extensive evidence from SoHO and other data that ``micro-events'' play an important role in sustaining at least some components of the solar corona. These are often termed coronal micro-``heating events'' though a major part of their role is feeding coronal loops through chromospheric evaporation. We consider what can be learnt from these data concerning the energy release and transport mechanisms driving the evaporation, including thermal conduction and fast particles, and what model constraints are available from other data (such as hard X-rays and radio events). We conclude, from one large event and the statistics of many small ones, that conductive evaporation alone does not fit observations and that fast particles or some other nonthermal driver must be involved. As well as the problem of single loop events, we consider the global implications for supply of the corona and wind. Title: Solar Flare Observations Authors: Benz, A. Bibcode: 2000eaa..bookE2049B Altcode: Flares are caused by the release of magnetic energy up to some 1027 J in the solar atmosphere within a few minutes (figure 1). The energy input causes a myriad of phenomena including the flaring up of the region and its surroundings at all wavelengths from radio to gamma rays, the acceleration of elementary particles to relativistic energies and the launch of a shock wave. Flares may be responsib... Title: Solar flare radio pulsations as a signature of dynamic magnetic reconnection Authors: Kliem, B.; Karlický, M.; Benz, A. O. Bibcode: 2000A&A...360..715K Altcode: 2000astro.ph..6324K Decimetric radio observations of the impulsive solar flare on October 5, 1992, 09:25 UT show a long series of quasi-periodic pulsations deeply modulating a continuum in the 0.6-2 GHz range that is slowly drifting toward lower frequencies. We propose a model in which the pulsations of the radio flux are caused by quasi-periodic particle acceleration episodes that result from a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalescence of magnetic islands (known as "secondary tearing" or "impulsive bursty" regime of reconnection), while a continuously growing plasmoid is fed by newly coalescing islands. Such a model, involving a current sheet and a growing plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama & Shibata ?). We present two-dimensional MHD simulations of dynamic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasmoid formation in flares. Title: Mechanisms for dynamic coronal mass supply via evaporative solar ``micro-events'' Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O. Bibcode: 2000A&A...359.1185B Altcode: The idea that the corona is at least in part supplied by chromospheric evaporation in loop ``micro-events" is quantified in terms of the power requirements of evaporation mechanisms, using recent analyses of data on such events in high temperature EUV lines from the SoHO EIT instrument. Estimates are derived for the pre-event and event values of loop density and temperature and it is shown, using the conductive scaling law, that the event emission measure enhancements are too large to be accounted for solely by enhanced conductive flux from coronal heating. That is, observations demand that supply of coronal mass by evaporation events need a mechanism which enhances upper chromospheric heating and not just conductively driven evaporation. Thus coronal mass supply in transients is inextricably linked to direct chromospheric heating processes. Using parametric models of a chromospheric heating function and of the pre-event chromosphere, an estimate is made of the extra power required to yield the emission measure enhancement of a large event evaporatively. The dependence of the result on just how the EUV solar images are interpreted is emphasised and observational tests are discussed for the case of heating by fast particles. Implications of the results in terms of the global supply of the hot corona and wind mass loss are briefly mentioned. Title: Bidirectional Type III Solar Radio Bursts Authors: Robinson, P. A.; Benz, A. O. Bibcode: 2000SoPh..194..345R Altcode: Bidirectional coronal type III bursts are modeled by combining a model of coronal electron heating and beam generation via time-of-flight effects with semiquantitative estimates of quasilinear relaxation. Electromagnetic emissivities are estimated by extending the recently developed theory of interplanetary type III bursts to coronal emissions, including its features of stochastic Langmuir-wave growth and three-wave interactions. The results are investigated for heating on open and closed coronal field lines and are compared with observations of normal, reverse-slope, bidirectional, and inverted-J and -U coronal type III radio bursts. Harmonic emission is predicted to dominate at plasma frequencies above roughly 100 MHz where the efficiency of fundamental emission falls off steeply, while its free-free reabsorption rises. The model also explains the observed trends in the likelihood of occurrence of normal, reverse-slope, and bidirectional coronal type III bursts. Title: Coronal Replenishment and Heating Authors: Benz, A. O.; Krucker, S.; Mitra Kraev, U. Bibcode: 2000SPD....31.0217B Altcode: 2000BAAS...32..814B The content of coronal material in the quiet Sun is not constant as soft X-ray and high-temperature EUV line observations have shown. New material, probably heated and evaporated from the chromosphere is occasionaly injected even in the faintest parts above the magnetic network cell interiors. We discuss the characteristics of the largest of these events, based on simultaneous transition region observations (in EUV and radio) and the observed analogies to flares. Assuming that the smaller events follow the same pattern, we estimate the total mass input and compare it to the requirements observed in the solar wind. Various recent analyses are compared and briefly discussed. Finally we present the results of a simulation, extrapolating the observed range of microflares to smaller energies. The simultation indicates that the extrapolation to smaller events is problematic and that smaller events may play an even more decisive role than previously assumed. The hypothesis of nanoflare heating is consistent with these observations if the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. Title: Are Heating Events in the Quiet Solar Corona Small Flares? Multiwavelength Observations of Individual Events Authors: Krucker, Säm; Benz, Arnold O. Bibcode: 2000SoPh..191..341K Altcode: 1999astro.ph.12501K Temporary enhancements of the coronal emission measure in a quiet region have been shown to constitute a significant energy input. Here some relatively large events are studied for simultaneous brightenings in transition region lines and in radio emission. Associated emissions are discussed and tested for characteristics known from full-sized impulsive flares in active regions. Heating events and flares are found to have many properties in common, including (i) associated polarized radio emission, which usually precedes the emission measure peak (Neupert effect) and sometimes has a non-thermal spectrum, and (ii) associated and often preceding peaks in O v and He i emission. On the other hand, heating events also differ from impulsive flares: (i) In half of the cases, their radio emission at centimeter waves shows a spectrum consistent with thermal radiation, (ii) the ratio of the gyro-synchrotron emission to the estimated thermal soft X-ray emission is smaller than in flares, and (iii) the associated emission in the O v transition region line shows red shifts and blue shifts, indicating upflows in the rise phase and downflows in the decay phase, respectively. Nevertheless, the differences seem to be mainly quantitative, and the analyzed heating events with thermal energies around 1026 erg may in principle be considered as microflares or large nanoflares, thus small versions of regular flares. Title: The Minimum bandwidth of narrowband spikes in solar flare decimetric radio waves Authors: Messmer, Peter; Benz, Arnold O. Bibcode: 2000A&A...354..287M Altcode: 1999astro.ph.12502M The minimum and the mean bandwidth of individual narrowband spikes in two events in decimetric radio waves is determined by means of multi-resolution analysis. Spikes of a few tens of millisecond duration occur at decimetric/microwave wavelength in the particle acceleration phase of solar flares. A first method determines the dominant spike bandwidth scale based on their scalegram, the mean squared wavelet coefficient at each frequency scale. This allows to measure the scale bandwidth independently of heuristic spike selection criteria, e.g. manual selection. The major drawback is a low resolution in the bandwidth. To overcome this uncertainty, a feature detection algorithm and a criterion for spike shape in the time-frequency plane is applied to locate the spikes. In that case, the bandwidth is measured by fitting an assumed spike profile into the denoised data. The smallest FWHM bandwidth of spikes was found at 0.17% and 0.41% of the center frequency in the two events. Knowing the shortest relevant bandwidth of spikes, the slope of the Fourier power spectrum of this two events was determined and no resemblance to a Kolmogorov spectrum detected. Additionally the correlation between spike peak flux and bandwidth was examined. Title: VLBI observations of single stars, spatial resolution and astrometry Authors: Pestalozzi, M.; Benz, A. O.; Conway, J. E.; Gudel, M.; Smith, K. Bibcode: 2000evn..conf..167P Altcode: VLBI studies can both spatially resolve single dMe stars and measure their positions at submilliarcsecond accuracy. The spatial resolution gives the brightness temperature and allows us to draw co nclusions about the nature of the emitting processes. In particular it is possib le to distinguish between thermal or non-thermal emission. The position accuracy gives better knowledge about the astrometric properties (like proper motion and parallax) especially for nearby stars. In this contribution recent results of c ontinuum VLBI observations towards two dMe stars (YZ CMi and AD Leo) at 8.4 GHz are presented. For YZ CMi an estimate of the size of the coronal emission is giv en (0.98 mas in diameter or 0.7 ±0.3 Rstar above the photosphere where Rstar refers to the photospheric radius). For AD Leo an upper limit is gi ven, i.e. the emitting region is shown to be < 0.8 Rstar. The position o f YZ CMi is found to differ by 32 mas form the Hipparcos catalogue, a discrepanc y mostly due to large errors in the listed proper motion (Pestalozzi et al. 2000 ). Title: VLBI observations of two single dMe stars: spatial resolution and astrometry Authors: Pestalozzi, M. R.; Benz, A. O.; Conway, J. E.; Güdel, M. Bibcode: 2000A&A...353..569P Altcode: 1999astro.ph.12159P We report on 3.6 cm VLA and VLBA observations of YZ CMi and AD Leo, two nearby dMe stars. We resolve YZ CMi and can fit a circular symmetrical gaussian component of FWHP of 0.98 +/-0.2 mas, corresponding to an extent of the corona above the photosphere of 1.77 x 1010 +/-8.8 x 109 cm or 0.7 +/-0.3 R_star (R_star refers to the photospheric radius). We obtain an estimate of the brightness temperature of 7.3 x 107 K, which is consistent with that expected from gyrosynchrotron emission. For AD Leo the emitting region is unresolved. We therefore set a conservative upper limit to its diameter of 1.8 times the photosphere diameter, which leads to an extent of the corona above the photosphere of <2.8x 1010cm or <0.8 R_star . We compare the radio emitting dMe stars with measured sizes with the Sun and conclude that these active stars have much more extended coronal radio emission than the Sun. The VLBA position of YZ CMi has been found to differ by 32 mas from the positions calculated from the Hipparcos catalogue. The discrepancy is caused by large errors in the listed proper motion. An improved value is given. Title: Investigations of the Acceleration Region of Energetic Electrons Associated with Decimetric Type III and X-Ray Bursts Authors: Fernandes, F. C. R.; Sawants, H. S.; Meléndez, J. L.; Benz, A. O.; Kane, S. R. Bibcode: 2000AdSpR..25.1813F Altcode: Preliminary results of the association between type III decimetric bursts, mainly having center frequency above 1000 MHz and recorded by Phoenix radio spectrometer, and seven hard X-ray flares observed by the Yohkoh/HXT from September, 1992 to October, 1993 are reported here. (a) For an assumed improved density model of the solar chromosphere, an average electron beam velocity (~ 0.16 c) and hence an average electron energy (~ 7 keV) was inferred from the average frequency drift rate (~ 1350 MHz/s) of 160 isolated type III bursts. Assuming the electrons lose energy primarily by collisions, the height of injection of the energetic electrons was estimated (1.2 × 109 - 4.5 × 109 cm). (b) In two flares at the onset of the bursts, the correlation between X-rays and radio was better at lower frequencies (<= 500 MHz). However, during the time evolution of those flares, the correlation improved for higher and higher frequencies (>= 800 MHz), suggesting that the acceleration region was displaced towards the photosphere. The estimated velocity of the acceleration region is ~ 3 × 103 - 8 × 103 km/s. (c) In two flares, the enhancement of the radio decimetric emission above 500 MHz started earlier (~ 10 s) than the X-ray emissions, suggesting in case of these two flares that the acceleration region is located near to where the decimetric emission is generated Title: The first VLBI observations with the Ventspils 32m radio telescope under the LFVN project Authors: Shmeld, I.; Benz, A.; Dementjev, A.; Lipatov, B.; Molotov, I.; Ryabov, B.; Sika, Z. Bibcode: 2000evn..conf..247S Altcode: The first Low frequency VLBI test sessions with 32 m radio telescope of Ventspils International Radioastronomy center were carried out on November 10 -14, 1999 and July 15-17, 2000 at 92 cm wavelength. A total of 39 sources plus the Sun were observed. A brief description of Ventspils radio telescope and equipment, of the Low Frequency VLBI Network and obtained results are given. Title: Commission 10: Solar Activity: (Activite Solaire) Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.; Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto, G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L. Bibcode: 2000IAUTA..24...67A Altcode: No abstract at ADS Title: Division II: The Sun and Heliosphere: (Le Soleil et Heliosphere) Authors: Foukal, Peter; Ai, Guoxiang; Benz, Arnold; Engvold, Oddbjorn; Solanki, Sami; Vandas, Marek; Verheest, Frank Bibcode: 2000IAUTA..24...65F Altcode: No abstract at ADS Title: Heating Events Observed in the Quiet Corona Authors: Benz, A. O.; Krucker, S. Bibcode: 1999ESASP.448..547B Altcode: 1999ESPM....9..547B; 1999mfsp.conf..547B No abstract at ADS Title: Heating Events in the Quiet Solar Corona Authors: Krucker, S.; Benz, A. O. Bibcode: 1999spro.proc...25K Altcode: Sensitive observations of the quiet Sun provided by (1) the SXT on board the Yohkoh satellite, (2) the EIT on board the SoHO spacecraft in high-temperature iron line emission, and (3) the Very Large Array (VLA) in the centimeter radio range are investigated in view of the coronal heating problem. The observed enhancements in coronal emission measure are interpreted as heating events (microflares) bringing chromospheric material to coronal temperatures, whereas the radio observations show the existence of non-thermal emission related to some of these heating events. Assuming an effective height of 5000~km, the thermal energy inputs by such microflares have been found in the range from 8× 1024 erg to 1.6× 1026 erg, and the total energy input amounts to about 16% of the average radiated power of the coronal plasma in the quiet corona. The frequency distribution of microflares is an approximate power-law of the form f(E) = f0 E-δ with a power-law index δ between 2.3 and 2.6. As the low-energy cutoff is due to sensitivity limitations and the power-law index is steeper than 2, these observations demonstrate the possibility that microflares dominate the energy input into the quiet corona. Title: Electron Firehose instability and acceleration of electrons in solar flares Authors: Paesold, Gunnar; Benz, Arnold O. Bibcode: 1999A&A...351..741P Altcode: 2000astro.ph..1262P An electron distribution with a temperature anisotropy T_parallel /T_perpendicular to >1 can lead to the Electron Firehose instability (Here parallel and perpendicular to denote directions relative to the background magnetic field B_0). Since possible particle acceleration mechanisms in solar flares exhibit a preference of energizing particles in parallel direction, such an anisotropy is expected during the impulsive phase of a flare. The properties of the excited waves and the thresholds for instability are investigated by using linearized kinetic theory. These thresholds were connected to the pre-flare plasma parameters by assuming an acceleration model acting exclusively in parallel direction. For usually assumed pre-flare plasma conditions the electrons become unstable during the acceleration process and lefthand circularly polarized waves with frequencies of about ~ |Omega_p | are excited at parallel propagation. Indications have been found, that the largest growth rates occur at oblique propagation and the according frequencies lie well above the proton gyrofrequency. Title: Radio counterparts to extreme X-ray YSO's Authors: Smith, Kester; Güdel, Manuel; Benz, A. O. Bibcode: 1999A&A...349..475S Altcode: We search for radio counterparts to two recently-detected strong X-ray sources associated with highly embedded young stellar objects (SVS4/EC 95 and SVS16). We detect a radio source (S68-2) consistent with the position of EC95. We fail to detect a counterpart for SVS16, and place upper limits on its quiescent radio brightness. For S68-2, we show that the radio source has a falling spectrum, suggestive of a gyrosynchrotron emission mechanism, and that it is variable on a timescale of years. We search for, but do not detect, evidence for flaring activity on timescales of minutes to hours. We also search for, but do not detect, circular polarisation. We derive the radio luminosity and compare the object to an empirical X-ray - radio luminosity relationship established for dMe stars. We find that the object is consistent with the dwarfs relation, but is unusually X-ray rich compared to other high-luminosity coronal sources. By comparing the objects to a sample of active galactic nuclei in the LX-LR diagram, we rule out the possibility that either object is a background AGN. We discuss the ways in which a normal stellar coronal model might be modified to explain the strong, X-ray rich characteristics of the source, which appears to be the most extreme stellar corona yet found. Title: Interactive image retrieval in large astronomical archives: the ASPECT system Authors: Csillaghy, A.; Benz, A. O. Bibcode: 1999SoPh..188..203C Altcode: We present a method to access efficiently and effectively images in large astronomical archives. This method allows users to interactively participate in the retrieval process. They may virtually 'navigate' through the archive for choosing images that are relevant for their purposes. The navigation process is performed by switching back and forth between three retrieval-system modes: a query mode, a browse mode and an inspection mode. The method has been applied to an image retrieval system to access solar radio spectrograms archived at ETH in Zurich. The system, called ASPECT, allows access to over 50 000 data sets on-line. Title: PHOENIX-2: A New Broadband Spectrometer for Deci- metric and Microwave Radio Bursts First Results Authors: Messmer, Peter; Benz, Arnold O.; Monstein, Christian Bibcode: 1999SoPh..187..335M Altcode: A broadband radio spectrometer has been put into operation at Bleien, Switzerland, to register the flare emission of the full Sun. In the frequency range of operation, 0.1 to 4.0 GHz, both modes of circular polarization are recorded continuously. The new system, Phoenix-2, has been developed from the experience with the previous Phoenix spectrometer. Improved, computer-controlled focal hardware allows now a complete daily calibration, a more sophisticated calibration procedure, and monitoring of all essential instrumental and environmental parameters. Calibrated data are now usually available the day after observation and are accessible through the Internet. The scientific improvements include a larger frequency range of observation, a larger number of completely recorded events due to full-day registration, more accurate measurements, particularly in circular polarization, and more reliable operation. First observations are presented and quantitative results comparing the calibration with single frequency instruments are reported. Title: Statistical analysis of high-frequency decimetric type III bursts Authors: Meléndez, J. L.; Sawant, H. S.; Fernandes, F. C. R.; Benz, A. O. Bibcode: 1999SoPh..187...77M Altcode: Here we report the statistical analysis of 160 isolated decimetric type III bursts, a majority of them (74%) having central frequency above 1000 MHz, observed in 8 flares by the spectrometer Phoenix. The most important finding of the detailed analysis is: 67% of all the bursts are reverse slope, 38% normal and 5% bi-directional. Also, we obtained the following results: (a) the best fits for the average half power duration and for the average drift rate as a function of frequency are given by t1/2=1.7×104f−0.60and /df/dt|=(0.09±0.03)f(1.35 ± 0.10), respectively; (b) the frequency range of most of the type III bursts is less than 250 MHz; (c) the number of bursts decreases with increasing starting frequency and flux; (d) peak flux decreases with increasing frequency. The relations obtained fit well for higher frequency observations. Assuming an improved density model and type III emission at 2ndharmonic, the beam parameters of type III bursts are determined. Title: Large-scale structure and coronal dynamics from joint radio, SOHO/EIT and coronagraph observations Authors: Pick, M.; Maia, D.; Vourlidas, A.; Benz, A. O.; Howard, R.; Thompson, B. J. Bibcode: 1999AIPC..471..649P Altcode: 1999sowi.conf..649P This study presents joint observations of an `halo' coronal mass ejection from the EIT telescope and LASCO coronagraphs on SOHO, from the Nançay Radioheliograph (NRH) and the Zurich ETH radiospectrograph (Phoenix-2). This event includes different manifestations: a coronal wave and a dimming region detected by EIT, a CME showing bright discrete portions above east and west limbs. Radio signatures of all these manifestations are found and the interpretation is briefly discussed. Title: Quantitative results on heating events in the quiet corona Authors: Benz, Arnold O.; Krucker, Säm Bibcode: 1999AIPC..471...67B Altcode: 1999sowi.conf...67B The emission measure of the quiet corona, defined by the plasma hotter than one million degrees, is fluctuating in nearly every 1900 km×1900 km pixel observed by EIT on SoHO. In the average, the larger the emission measure in a pixel, the more it fluctuates. Increases in emission measure constitute a major energy input into the corona, suggesting that the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. Title: Phase-reference mapping of nearby stars: status report. Authors: Alef, W.; Benz, A.; Conway, J.; Beasley, T. Bibcode: 1999evga.conf..241A Altcode: The authors have observed radio emitting stars in phase-referenced mode with both the VLBA and the EVN in order to map their brightness distributions and to determine precise astrometric parameters. While the VLBA correlator uses the CALC 8 model, the older MK3 correlator model is not sufficient to make phase-referenced mapping possible using the visibility amplitude and residual phase. In the raw MK3 correlated data they have successfully replaced the correlator model with the CALC 8 model. They have shown that phase-reference mapping is possible with MK3 data for source separations of 2 to 3 degrees. At present the authors are exploring the possibility of removing ionospheric and atmospheric contributions, which are not modelled at all in CALC 8, and which decrease the SNR in phase-reference maps in general by a factor of 2 to 3. Title: Heating events in the quiet solar corona: multiwavelength correlations Authors: Benz, Arnold O.; Krucker, Säm Bibcode: 1999A&A...341..286B Altcode: Coronal, transition region and chromospheric lines and centimeter radio emission of the quiet Sun have been simultaneously observed by SoHO and the VLA. The corona above the magnetic network has a higher pressure and is more variable than above the interior of supergranular cells. The Fourier transform in time is found to have steeper spectra in the corona and upper chromosphere than in the transition region. The temporal sequence of brightenings has been determined by cross-correlations of identical picture elements in different emissions. The method allows to study statistically the faintest fluctuations in the corona and relate them to the layers below. The cross-correlations yield that (i) the first emissions to peak in time are O V and He I originating in the transition region and the upper chromosphere, respectively. (ii) The coronal line of Fe XII lags by about 5 minutes and Fe IX/X peaks a further half a minute later in the average, latest of all emissions. The interpretation of these lags follows readily from analogy with regular flares in active regions, where O V and He I correlate closely with hard X-rays emitted by beam electrons impinging on the chromosphere. The coronal iron lines are then emitted by the evaporating plasma expanding into the corona and cooling by conducting part of the energy to increase the emission in Fe IX. (iii) The radio emission peaks before the coronal emission measure, similar to the Neupert effect in flares, but shows considerable variation relative to O V. It is proposed that there are two emission processes at work radiating both thermal emission and non-thermal gyrosynchrotron emission at various fluxes. These statistical results show that the coronal heating events follow the properties of regular solar flares and thus may be interpreted as microflares or nanoflares. Title: High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission for the next (2000) solar maximum Authors: Lin, Robert P.; Hurford, Gordon J.; Madden, Norman W.; Dennis, Brian R.; Crannell, Carol J.; Holman, Gordon D.; Ramaty, Reuven; von Rosenvinge, Tycho T.; Zehnder, Alex; van Beek, H. Frank; Bornmann, Patricia L.; Canfield, Richard C.; Emslie, A. Gordon; Hudson, Hugh S.; Benz, Arnold; Brown, John C.; Enome, Shinzo; Kosugi, Takeo; Vilmer, Nicole; Smith, David M.; McTiernan, Jim; Hawkins, Isabel; Slassi-Sennou, Said; Csillaghy, Andre; Fisher, George; Johns-Krull, Chris; Schwartz, Richard; Orwig, Larry E.; Zarro, Dominic; Schmahl, Ed; Aschwanden, Markus; Harvey, Peter; Curtis, Dave; Pankow, Dave; Clark, Dave; Boyle, Robert F.; Henneck, Reinhold; Michedlishvili, Akilo; Thomsen, K.; Preble, Jeff; Snow, Frank Bibcode: 1998SPIE.3442....2L Altcode: The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum. Title: Heating Events in the Quiet Solar Corona Authors: Benz, Arnold O.; Krucker, Säm Bibcode: 1998SoPh..182..349B Altcode: Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure time variations is approximately a power law with an exponent of 1.79±0.08 for the brightest pixels and 1.69±0.08 for the average and the faintest pixels. The more prominent enhancements are identified with previously reported X-ray network flares (Krucker et al., 1997) above the magnetic network of the quiet chromosphere. In coronal EUV iron lines they are amenable to detailed analysis suggesting that the brightenings are caused by additional plasma injected from below and heated to slightly higher temperature than the preexisting corona. Statistical investigations are consistent with the hypothesis that the weaker emission measure enhancements originate from the same parent population. The power input derived from the impulsive brightenings is linearly proportional to the radiative loss in the observed part of the corona. The absolute amount of impulsive input is model-dependent. It cannot be excluded that it can satisfy the total requirement for heating. These observations give strong evidence that a significant fraction of the heating in quiet coronal regions is impulsive. Title: Kulturelle Kontakte zu Außerirdischen? Authors: Benz, A. Bibcode: 1998A&R....35...17B Altcode: No abstract at ADS Title: A stochastic model for solar type III bursts Authors: Isliker, H.; Vlahos, L.; Benz, A. O.; Raoult, A. Bibcode: 1998A&A...336..371I Altcode: A stochastic model for type III bursts is introduced, discussed, and compared to observations. The active region is assumed to be inhomogeneous, with a large number of emerging magnetic fibers. At their bases, random energy release events take place, in the course of which electrons are accelerated, travel along the fibers and eventually undergo the bump-on-tail instability. In the non-linear regime, the formed Langmuir waves induce strong turbulence in the ambient plasma, with secondary electrostatic waves appearing. Wave-wave scattering finally leads to the emission of transverse electro-magnetic waves at the fundamental and the harmonic of the local plasma-frequency. The superposition of the emissions from all the fibers yields a model spectrogram for type III bursts (flux as a function of frequency and time). Peak-flux distributions of the model are compared to the ones of five observations of type III bursts. It turns out that, in a statistical sense, the model is largely compatible with the observations: the majority of the observations can be considered generated by a process which corresponds with the presented model. The details of the different sub-processes constituting the model play no decisive role concerning the statistical properties of the generated spectrograms, to describe them approximately by randomizing the unknown elements is sufficient. Therewith, the correspondence of the model with the data is not unique. Likewise, intrinsic shortness of observed type III events does not allow a strict enough discrimination between different possible sub-processes of the model through statistical tests. With that, the conclusion is that the observations are compatible with a model which assumes (i) a randomly structured active region, (ii) a flare-particle acceleration-process which is fragmented into a large number of sub-processes, (iii) a distribution of the accelerated particles which is a random fraction of the ambient density and of power-law form with random index, and (iv) the fragmentary acceleration events to occur randomly in time, i.e. the temporal structure of type III events to be random, without any correlations between the individual bursts. Title: Energy Distribution of Heating Processes in the Quiet Solar Corona Authors: Krucker, Säm; Benz, Arnold O. Bibcode: 1998ApJ...501L.213K Altcode: We have determined the variations in the emission measure of the solar corona using EUV Imaging Telescope/Solar and Heliospheric Observatory observations of iron lines in a quiet region of the Sun. The emission measure is found to vary significantly in at least 85% of all the pixels within 42 minutes. The variations are interpreted as heating events that bring chromospheric material above the one million degree threshold of the observed lines and that cool the coronal plasma below that limit. A method to assess heating events has been developed. The thermal energy input by such microflares is calculated from the observed increases in emission measure and the derived temperature. Heating events have been found in the range from 8×1024 to 1.6×1026 ergs. The energy input by >=3 σ events of the emission measure increase the amounts to about 16% of the average radiated power of the coronal plasma in the quiet corona. The frequency distribution of microflares is an approximate power law of the form f(E)=f0E-δ, with a power-law index δ between 2.3 and 2.6. Since the low-energy cutoff is due to sensitivity limitations and the power-law index is steeper than 2, these observations demonstrate the possibility that microflares dominate the energy input into the quiet corona. The observed power law would have to continue to about 3×1023 ergs in order to match the observed minimum heating requirement. Title: A multiwavelength analysis of an electron-dominated gamma-ray event associated with a disk solar flare Authors: Trottet, Gerard; Vilmer, Nicole; Barat, Claude; Benz, Arnold; Magun, Andreas; Kuznetsov, Alexandr; Sunyaev, Rachid; Terekhov, Oleg Bibcode: 1998A&A...334.1099T Altcode: This paper reports the first comparison of hard X-ray (HXR), gamma-ray (GR), centimetric-millimetric and metric-decimetric spectral and imaging radio observations obtained during an electron-dominated gamma-ray burst. This impulsive event,which occurred on 1990 June 11 at ~ 0943 UT, was associated with a Halpha 2B flare, located close to the disk center. The time evolution of the HXR emission consists of successive peaks of ~ 10 s duration. Several of these peaks show GR emission up to a few MeV and one of them up to ~ 56 MeV. For each of these peaks, the photon spectrum significantly hardens above a break energy varying in the 0.4-0.7 MeV range. No significant GR line (GRL) emission is detected. The main results of our analysis are: (i) even if no significant GRL emission is detected, the upper limit of the energy content in > 1MeV/nucl. ions is comparable with the energy content in > 20 keV electrons ( a few 10(29) ergs), as it is found for GRL flares; (ii) during the whole event, the centimetric-millimetric emission is radiated by ga 0.4-0.7 MeV electrons which have been accelerated since the very beginning of the flare; (iii) the different HXR/GR peaks are associated with step-wise changes of the magnetic structures to which metric-decimetric radio producing electrons have access. This latter characteristic of the 1990 June 11 burst is globally similar to the behaviour reported in the literature for GRL events, but the energy in accelerated particles is about one order of magnitude lower. Finally, the electron-dominated emitting peak with emission up to ~ 56 MeV is interpreted as a signature of an upward moving population of relativistic electrons which is strongly beamed along the magnetic field and which does not contribute significantly to the centimetric-millimetric and la 0.2 MeV HXR emissions. The metric-decimetric radio observations indicate that this happens when electrons have suddenly access to large-scale magnetic structures. Title: Intermediate drift bursts and the coronal magnetic field Authors: Benz, Arnold O.; Mann, Gottfried Bibcode: 1998A&A...333.1034B Altcode: We have analyzed 12 decimetric continuum (type IV) events during solar flares showing intermediate drift (IMD) fine structures in the 1 - 3 GHz band. This is the first time IMD patterns have been reported above 1 GHz and that the full spectrum of both continuum and IMD bursts has been covered. The IMD pattern was usually shifted to higher frequency and tends to occur later than the continuum. Average drift rates of IMD bursts per event were found by cross-correlation yielding dot nu /nu = -0.167 to -0.046 s(-1) . The average second derivative of individual IMD bursts expressed as ddot nu dot nu (-2) nu is 0.42 to 4.19. Normalized by the mean frequency, these high-frequency IMD bursts are found to be identical in their characteristics with this type of bursts below 1 GHz. The derived burst parameters require an important change in one of the two existing theories. Title: Logistic Avalanche Processes, Elementary Time Structures, and Frequency Distributions in Solar Flares Authors: Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O. Bibcode: 1998ApJ...497..972A Altcode: We analyze the elementary time structures (on timescales of ~0.1-3.0 s) and their frequency distributions in solar flares using hard X-ray (HXR) data from the Compton Gamma Ray Observatory (CGRO) and radio data from the radio spectrometers of Eidgenoessische Technische Hochschule (ETH) Zurich. The four analyzed data sets are gathered from over 600 different solar flares and include about (1) 104 HXR pulses at >=25 and >=50 keV, (2) 4000 radio type III bursts, (3) 4000 pulses of decimetric quasi-periodic broadband pulsation events, and (4) 104 elements of decimetric millisecond spike events.

The time profiles of resolved elementary time structures have a near-Gaussian shape and can be modeled with the logistic equation, which provides a quantitative measurement of the exponential growth time τG and the nonlinear saturation energy level WS of the underlying instability. Assuming a random distribution (Poisson statistics) of saturation times tS (with an e-folding constant tSe), the resulting frequency distribution of saturation energies WS or peak energy dissipation rates FS = (dW/dt)t=tS has the form of a power-law function, i.e., N(FS)~F-αS, where the power-law index α is directly related to the number of e-folding amplifications by the relation α = (1 + τG/tSe). The same mathematical formalism is used to generate power-law distributions, as in Rosner & Vaiana, but the distribution of energies released in elementary flare instabilities is not related to the global energy storage process. We assume Poissonian noise for the unamplified energy levels in unstable flare cells, implying an exponential frequency distribution of avalanche energies WS or fluxes FS in the absence of coherent amplifications. Also, in the case of coherent amplification, the Poissonian noise introduces exponential rollovers of the power law at the low and high ends of the frequency distributions.

We fit both power-law and exponential functions to the observed frequency distributions of elementary pulse fluxes N(F) in each flare separately. For HXR pulses, one-half of the flares are better fitted with power-law frequency distributions, demanding coherent amplification of the underlying energy dissipation mechanism, e.g., current exponentiation occurring in the magnetic tearing instability. The majority of type III burst flares are best fitted with power-law distributions, consistent with the interpretation in terms of beam-driven coherent emission. The frequency distributions of decimetric pulsations and decimetric millisecond spikes are found to fit exponential functions, in contrast to the expected power laws for coherent emission mechanisms generally proposed for these radio burst types. A coherent emission mechanism can be reconciled with the observed exponential frequency distributions only if nonlinear saturation occurs at a fixed amplification factor for all elementary pulses or spikes, for example, if it is produced by an oscillatory compact source (in the case of decimetric pulsations) or by a fragmented source with similar spatial cell sizes (in the case of decimetric millisecond spikes). Title: First VLBI images of a main-sequence star Authors: Benz, Arnold O.; Conway, John; Gudel, Manuel Bibcode: 1998A&A...331..596B Altcode: The binary system UV Cet A and B has been observed with the VLBA/VLA at 3.6 cm wavelength. Both dMe stars have been detected. The stronger, steady radio emitter of the two, UV Cet B, is resolved into at least two spatial components. Their relative intensities change during the 6.3 hours of observing time. One of the components is more stable and resolved, the other is possibly unresolved. The resolved component has a half-power diameter of 2.4x 10(10) cm, exceeding the size of the stellar photosphere. The separation of the two components of UV Cet B is 4.4 (+/-0.4)x 10(10) cm or 4 - 5 stellar radii. The alignment of the two components is along the axis of the binary orbit and thus parallel and very likely close to the stellar rotation axis. The apparent trapping of the gyrosynchrotron emitting energetic electrons requires large coronal loops extending to several stellar radii. At the more variable source a magnetic field between 15 and 130 G is derived. Title: Remote Radio Tracking of CMEs from Wind and ULYSSES Authors: Benz, A. O.; Reiner, M. J. Bibcode: 1998cee..workE..15B Altcode: Some interplanetary shocks associated with coronal mass ejections (CMEs) generate type II radio emissions at the local plasma frequency and/or its harmonic. These type II radio emissions provide a means of remotely tracking CMEs from the solar corona out to 1 AU and beyond. We have developed new analysis techniques for tracking CME associated radio emissions that inherently reveal the dynamics of a CME as it propagates through the interplanetary medium. The analyses make use of dynamic spectral plots of the radio intensity as a function of 1/frequency versus time. Since the interplanetary density falls off as 1/R2 (R = heliocentric distance), on these plots the frequency drifting type II emissions are organized along straight lines that converge to the solar liftoff time. The slopes of the lines vary as the ratio of the shock speed to the square root of the plasma density, normalized to 1 AU. The values of the slopes corresponding to fundamental radio emissions lie between 1-2 times 10^{-7} kHz^{-1} s^{-1} for the kilometric type II radio events so far examined from Ulysses and Wind. When in-situ measurements are also made, the method of analysis determines unequivocally whether the type II emissions occurred at the fundamental or harmonic of the local plasma frequency in the upstream or downstream regions of the CME-driven shock. Additional radio tracking is provided by the direction-finding capabilities on Wind/WAVES and Ulysses/URAP. They allow identification of specific structures in the interplanetary medium where the type II emissions were generated. We will illustrate the new techniques by using examples of type II events observed by Wind and Ulysses. Some examples show very weak diffuse emission at the harmonic frequencies and more intense, sporadic emission at the fundamental frequencies. For a very unusual event that occurred on 8--11 January 1997, we have determined that some of the type II emission was generated as the CME-driven shock passed through a corotating interaction region ( Reiner et al., 1998). Other examples indicate simultaneous type II radio emissions from regions of different densities along the shock front. All cases that we have so far examined are consistent with the fundamental and/or harmonic type II radio emissions being generated in the upstream region of the CME-driven shock. Title: Radio Emission from Solar Flares Authors: Bastian, T. S.; Benz, A. O.; Gary, D. E. Bibcode: 1998ARA&A..36..131B Altcode: Radio emission from solar flares offers a number of unique diagnostic tools to address long-standing questions about energy release, plasma heating, particle acceleration, and particle transport in magnetized plasmas. At millimeter and centimeter wavelengths, incoherent gyrosynchrotron emission from electrons with energies of tens of kilo electron volts (keV) to several mega electron volts (MeV) plays a dominant role. These electrons carry a significant fraction of the energy released during the impulsive phase of flares. At decimeter and meter wavelengths, coherent plasma radiation can play a dominant role. Particularly important are type III and type III-like radio bursts, which are due to upward- and downward-directed beams of nonthermal electrons, presumed to originate in the energy release site. With the launch of Yohkoh and the Compton Gamma-Ray Observatory, the relationship between radio emission and energetic photon emissions has been clarified. In this review, recent progress on our understanding of radio emission from impulsive flares and its relation to X-ray emission is discussed, as well as energy release in flare-like phenomena (microflares, nanoflares) and their bearing on coronal heating. Title: A search for prompt radio emission of gamma-ray bursts Authors: Benz, Arnold O.; Paesold, Gunnar Bibcode: 1998A&A...329...61B Altcode: A conducting fireball expanding at relativistic speed into an ambient magnetic field generates a rapidly changing electric current which emits coherent electromagnetic radiation at radio frequencies. The critical frequency (upper limit of the emission) strongly depends on the Lorentz factor of the expansion. We have searched for simultaneous radio emission in the data of solar radio spectrographs at times when BATSE reported a non-solar gamma-ray burst (GRB) within the beams of the radio telescopes. Solar spectrographs are less sensitive than single frequency receivers, but yield a broad overview on the spectrum ideal for discriminating against atmospheric and man-made interference. In 7 well-observed cases no radio emission was found. This puts upper and lower limits on the Lorentz factor of the fireball expansion in GRBs if the source distance is less than 1 kpc, i.e. if GRBs are local. The coherent expansion radiation is not observable with current instruments if the GRB sources are at >= 1 kpc. Title: PHOENIX-2: A Broadband Spectrometer for Decimetric and Microwave Radio Bursts: First Results Authors: Messmer, P.; Benz, A. O.; Monstein, C.; Zmoos, C. Bibcode: 1998cee..workE..55M Altcode: Phoenix-2, a new spectrometer to register solar flare radio emission in the 0.1 to 4 GHz band, has become operational. It is a frequency-agile system for measuring either both senses of circular polarization or linear polarization in Dicke mode. Spectra are obtained by sweeping through a set of frequency channels. The number of channels, their frequencies and their bandwidth are user defined. The temporal resolution has to be compromised with the number of frequency channels and can be in the range of 0.5 ms to 1 s for 1 to 2000 channels. The possibility to chose channels at any frequency in the observed band allows to detect and avoid frequencies with man made interference. Recording period for the spectra is from sunrise to sunset. The observation schedule and the interruption of observations by calibration measurements are user defined. During the night, the spectral data is automatically transfered from the observatory location (Bleien, about 50 km from Zurich) through the Internet to the Institute of Astronomy in Zurich, where all the calibration, archiving and feature extraction tasks are performed. This allows to access the spectral data one day after its measurement. Phoenix-2 incorporates parts of the old Zurich Spectrometer 'Phoenix', (Benz et al, 1991) namely the antenna, the antenna control hardware and some high-frequency components. The most important new capabilities of Phoenix-2 are: 1. Observations up to 4 GHz instead of 3 GHz 2. Larger spectra with up to 2000 different frequency channels instead of 500 3. Continuous recording from sunrise to sunset, instead of 90 minutes maximum continuous recording time during bursts 4. More accurate, automatic calibration 5. Immediate evaluation of the data instead of manual tape transport 6. Online archive of all calibrated data for later processing with more advanced feature detection methods 7. Monitoring focus instrumentation (pre-amplifier, noise source) and environmental data (weather station) During normal surveillance operation, Phoenix-2 measures broadband spectra with 200 channels, 10 MHz bandwidth and 0.1 s time resolution. Bursts are detected either manually or by searching for a set of channels exceeding a threshold value. First bursts are detected and demonstrate the functionality of the system. At the time of writing this abstract, the full qualification of the instrument was subject of ongoing research. Title: High Frequency Decimetric Type III Bursts Authors: Fernandes, F. C. R.; Melendez, J. L.; Sawant, H. S.; Benz, A. O. Bibcode: 1998cee..workE..36F Altcode: To our knowledge, there is a lack of investigations of the decimetric type III bursts above 1000 MHz. In this paper, we have carried out statistical investigations of the type III decimertic bursts, a majority (74 %) of them having central frequency above 1000 MHz, observed by the radio spectrometer Phoenix of ETH, Zurich, from September 1992 to October 1993, associated with 8 hard X-ray flares observed by the Yohkoh satellite. We found 160 isolated type III bursts suitable for detailed analysis out of 416 bursts. By using digital data we have adjusted a gaussian profile for a given frequency, considering the level of 3 sigma above the noise background, and we derived peak flux and time, corresponding to a gaussian center and half power duration of gaussian (t_{1/2}). Also, we derived the starting and ending frequencies. The frequency drift rate (df/dt) was determined from a linear regression of the maxima in the frequency - time plane. The highlights of the analysis are: (i) frequency range of most of the type III bursts is less than 250 MHz; (ii) the number of bursts decreases with increasing starting frequency and flux; (iii) flux decreases with increasing frequency; (iv) in the bursts we analysed, 64 % are reverse slope, 36 % normal and 5 % bidirectional. The best fits for the average half power duration and for the average drift rate as a function of frequency are given by t_{1/2} = 1.7 times 10^4 f^{-0.60} and mid df/dt mid = 0.09 f^{1.35}, respectively. These relations fit well at high frequency. Assuming an improved density model and type III emission at 2nd harmonic, following beam parameters of type III bursts are derived: (a) average electron beam velocity, vb ~= 0.16 c(~7 keV); (b) beam electron density, N_b ~= 6 times 10^4 cm^{-3}; (c) total number of electrons per beam, {N} ~= 6 times 1031. One bidirectional drifting type III burst starting at 1700 MHz was observed, suggesting that ocassionally, acceleration region can be located where the plasma density is ~1011 cm^{-3}. Title: Radio Wave and Soft X-ray Diagnostics of Heating Events in the Quiet Solar Corona Authors: Krucker, S.; Benz, A. O. Bibcode: 1998cee..workE...7K Altcode: Sensitive observations of the quiet Sun observed by (1) SXT on the Yohkoh satellite, (2) EIT on the SoHO satellite in high-temperature iron line emission, (3) CDS on the SoHO satellite in the He I and O V line emission, and (4) the Very Large Array (VLA) in the centimeter radio range are investigate in the view of the coronal heating problem. The observed enhancements are interpreted as heating events (mircoflares) bringing chromospheric material to coronal temperatures. The thermal energy inputs by such microflares have been found in the range from 8 times 1024erg to 1.6 times 1026erg, and the total energy input amounts to about 16% of the average radiated power of the coronal plasma in the quiet corona. The frequency distribution of microflares is an approximate power-law of the form f(E) = f_0 E^{-delta} with a power-law index delta between 2.3 and 2.6. As the low-energy cutoff is due to sensitivity limitations and the power-law index is steeper than 2, these observations demonstrate the possibility that microflares dominate the energy input into the quiet corona. Title: Logistic Avalanche Processes, Elementary Time Structures, Frequency Distributions, and Wavelet Analysis of Solar Flares Authors: Aschwanden, M. J.; Dennis, B. R.; Schwartz, R. A.; Benz, A. O.; Kliem, B.; Schwarz, U.; Kurths, J. Bibcode: 1998cee..workE..10A Altcode: Do elementary time scales exist in solar flares that could provide us a clue on the spatial fragmentation of the primary energy release process? Or is there a continuous distribution, composed of a hierarchy of unresolved time structures? We present results of two recent studies on these fundamental questions. We applied a multi-resolution analysis (using triangle-shaped wavelet transforms) to 647 solar flares observed with the COMPTON Gamma Ray Observatory (CGRO) at hard X-ray energies of >= 25 keV with a time resolution of 64 ms. From the wavelet scalegrams we infer a distribution of time scales N(T) for each flare and find a cutoff for the shortest detected time scales Tmin that is independent of the Poisson noise for strong flares. These shortest time scales Tmin are found to correlate with the flare loop radius r (Fig.1), i.e. Tmin = 0.5 (r/10^9 cm)s (measured with Yohkoh) and the collisional deflection time, Tmin > ~tDefl(n_e), (determined from the electron density n_e of trapped electrons by measuring energy-dependent time delays detected with CGRO). From these observations we infer spatial sizes of racc = 75-750 km for elementary acceleration cells. In a second study we determined the frequency distributions of elementary time structures in over 600 flares, based on some 10^4 hard X-ray pulses at 25 and 50 keV, 4000 radio type III bursts, 4000 decimetric quasi-periodic broadband pulsation events, and 10^4 decimetric millisecond spike events. All elementary time structures have a quasi-Gaussian shape and can be modeled with the logistic equation, which describes the exponential growth phase and nonlinear saturation (caused by the limited amount of available free energy) of a general instability. We derive a theoretical description of frequency distributions in terms of this logistic avalanche model and find that the power-law slope of observed frequency distributions provides a powerful diagnostic on coherent versus incoherent instabilities. Title: First Image of the Corona of a Main-Sequence Star Authors: Benz, Arnold O.; Gudel, Manuel; Conway, John Bibcode: 1998ASPC..154.1942B Altcode: 1998csss...10.1942B The binary system UV Cet A and B has been observed with the VLBA/VLA at 3.6 cm wavelength. Both dMe stars have been detected. The stronger, steady radio emitter of the two, UV Cet B, is resolved into at least two spatial components. Their relative intensities change during the 6.3 hours of observing time. One of the components is relatively stable and resolved, the other is possibly unresolved. The resolved component has a half-power diameter of about the size of the stellar photosphere or 2 x 1010 cm. The separation of the two components of UV Cet B is 4.4 (+/-0.4) x 1010 cm or 4-5 stellar radii. The alignment of the two components is along the axis of the binary orbit and thus probably close to the stellar rotation axis. The apparent trapping of the gyrosynchrotron emitting energetic electrons requires large coronal loops extending to several stellar radii. At the more variable source a magnetic field between 20 and 130 G is derived. Title: What should we call a spike burst? Authors: Benz, A. O. Bibcode: 1998cee..workE..16B Altcode: Short, narrowband spikes at decimetric wavelengths have been found to correlate with hard X-rays. For this reason they have become interesting as possible diagnostics for particle acceleration in flares. There are two competing views: one puts the spike sources at the footpoints of coronal magnetic fields where they could be caused by a loss-cone instability, the other relates it more directly with the acceleration process and predicts them to be located in the acceleration region. All we need to decide is an image of spikes and a simultaneous X-ray image showing loops or their footpoints. Unfortunately a considerable confusion has developed on the definition of spikes. 'Spikes' are reported at nearly all radio frequencies now from meter waves to millimeter, even in UV and X-ray observations people talk about 'spikes'. Worst of all, however, is the use of 'spikes' for any short burst in the decimeter wavelength range, where other short burst types have been reported, including type IV finestructures, type III and pulsations. In particular the most frequent decimetric type, type III bursts, have been reported in the literature as 'spikes'. They are not always correlated with hard X-rays. Their position is also interesting but has a completely different meaning. 'Spike' has become a synonym for 'burst' in decimeter waves. I strongly suggest that we reserve the word 'spike' for the narrowband bursts which correlate well with hard X-rays. However, if the word 'decimetric spike' or 'microwave spike' cannot be reserved for this well-defined, restricted type, we better change to 'decimetric type I bursts' or similar. Of course, a reliable classification is only possible with a high time resolution spectrometer. We have long come to accept that fact for the meter wave burst classification. Since the 1950's, the type I - V bursts are interpreted by different emission processes, and the word 'burst' would not be a valid identification. This same is the case for decimetric range, where we have different types of bursts. A radio image of an unclassified burst in coherent emission at any wavelength is rather useless. Fortunately, narrowband spikes have a very short duration which decreases with wavelength. The decay time of spikes follows a well defined relation. An rough classification is therefore possible with sufficient time resolution alone. If we do not keep to some careful classification that keeps apart what seems to be physically different, there will not be progress in the field of coherent decimetric radiation. I would like to bring up the problem to the CESRA participants, discuss it in public and come to a joint conclusion. It may be necessary to have a small discussion group at the present meeting. Title: The High Energy Solar Spectroscopic Imager (HESSI): A Small Explorer for the Start of the New Millennium Authors: Holman, G. D.; Lin, R. P.; Dennis, B. R.; Crannell, C. J.; Ramaty, R. R.; Rosenvinge, T. T.; Canfield, R. C.; Emslie, A. G.; Hudson, H. S.; Hurford, G. J.; Madden, N. W.; van Beek, H. F.; Benz, A.; Bornmann, P. L.; Brown, J. C.; Enome, S.; Kosugi, T.; Vilmer, N.; Zehnder, A. Bibcode: 1997AAS...191.7416H Altcode: 1997BAAS...29R1326H The High Energy Solar Spectroscopic Imager (HESSI) has been selected for launch in mid 2000, at the peak of the solar activity cycle. The primary scientific objective of HESSI is to understand particle acceleration and explosive energy release in the magnetized plasma at the Sun. HESSI will provide the first high-spectral-resolution x-ray and gamma -ray images of the Sun. It will obtain the first imaging above 100 keV, the first imaging of solar gamma -ray lines, and the first high-resolution spectroscopy of solar gamma -ray lines, including the first determination of line shapes. In two years HESSI is expected to obtain observations of tens of thousands of microflares, thousands of hard x-ray flares, and of order a hundred gamma -ray line flares. HESSI will also monitor and provide high-spectral-resolution observations of cosmic and terrestrial hard x-ray and gamma -ray transients, as well as imaging of the Crab Nebula. HESSI's high spectral, spatial, and temporal resolution and dynamic range will allow the first detailed studies of the evolution of both accelerated particles and hot, thermal plasma in solar flares. Title: X-Ray Network Flares of the Quiet Sun Authors: Krucker, Säm; Benz, Arnold O.; Bastian, T. S.; Acton, Loren W. Bibcode: 1997ApJ...488..499K Altcode: Temporal variations in the soft X-ray (SXR) emission and the radio emission above the solar magnetic network of the quiet corona are investigated using Yohkoh SXR images with deep exposure and VLA observations in the centimeter radio range. The SXR data show several brightenings, with an extrapolated occurrence probability of one brightening per 3 seconds on the total solar surface. During the roughly 10 minutes of enhanced flux, total radiative losses of the observed plasma are around 1025 ergs per event. These events are more than an order of magnitude smaller than previously reported X-ray bright points or active region transient brightenings. For all of the four SXR events with simultaneous radio observations, a corresponding radio source correlating in space and time can be found. There are several similarities between solar flares and the SXR/radio events presented in this paper. (1) Variations in temperature and emission measure during the SXR enhancements are consistent with evaporation of cooler material from the transition region and the chromosphere. (2) The ratio of the total energies radiated in SXR and radio frequencies is similar to that observed in flares. (3) At least one radio event shows a degree of polarization as high as 35%. (4) In three out of four substructures the centimeter radio emission peaks several tens of seconds earlier than in the SXR emission. (5) The associated radio emission tends to be more structured and to have faster rise times. These events thus appear to be flare-like and are called network flares. Title: The dispersion of radio waves in the solar corona. Authors: Benz, A. O.; Pianezzi, P. Bibcode: 1997A&A...323..250B Altcode: Different arrival times of the two magnetoionic modes in solar radio bursts have been detected. The bursts are from four decimetric radio events showing narrowband millisecond spikes. They have been observed with 2ms and 0.5ms time resolution, respectively, by the Ikarus and Phoenix spectrometers of ETH Zurich. The four events have been selected because of their low polarization. The arrival times of the left and right circularly polarized modes have been compared by cross-correlation. In all cases the weaker mode is delayed by a fraction of a millisecond. Several tests have been carried out to ensure the significance of the delay. The delay is interpreted by the difference in group velocity of the two modes due to dispersion in the coronal plasma. Simple models show that the observed difference in travel time is consistent with this interpretation. It suggests that the radiation is polarized in the ordinary mode at the location where the polarization originates. If the polarization originates in the original source region, the possible emission processes are limited to the ones radiating in ordinary mode. More likely, the polarization seems to originate at higher altitude e.g. in a quasi-transverse region. In both cases the delay is proportional to the longitudinal component of the magnetic field in the medium of propagation. Title: Decimetric Type III Radio Bursts with High Starting Frequencies and the Associated Solar Flare Hard X-Ray Emission Authors: Fernandes, F. C. R.; Sawant, H. S.; Melendez-Moreno, J. L.; Benz, A. O.; Yoshimori, M.; Kane, S. R.; McTiernan, J. M. Bibcode: 1997SPD....28.0172F Altcode: 1997BAAS...29..892F We have examined the characteristics of 160 isolated type III decimetric (100-3000 MHz) radio bursts which occurred during the period September 1992 - October 1993. Bursts associated with 13 hard X-ray flares were examined in detail. The radio observations were made with the PHOENIX solar radio spectrometer in Zurich. The X-ray flares were observed by the Hard X-ray Spectrometer (HXS) on the Yohkoh satellite. Type III radio bursts with normal, reverse as well as bi-directional drifts were observed. Characteristic parameters such as starting frequency, bandwidth, total duration, and frequency drift rate were determined for the radio bursts. Similarly power law photon spectra were fitted to the hard X-ray emission. For an assumed model of ambient density vs. height above the photosphere, the electron beam velocity and hence the electron energy was inferred from the frequency drift rate of the radio burst. Assuming that the energy loss of the energetic electrons is caused primarily by collisions, the height of injection for the radio emitting electrons was deduced. For comparison, characteristics of the energetic electrons were also inferred from the thick target model for the hard X-ray source. Implications of the results with respect to the acceleration and propagation of energetic electrons in solar flares will be discussed. Title: Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites Authors: Aschwanden, Markus J.; Benz, Arnold O. Bibcode: 1997ApJ...480..825A Altcode: We compare electron densities measured at three different locations in solar flares: (1) in soft X-ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps [nSXRe=(0.2-2.5)×1011 cm-3] (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zürich [nupflowe=(0.3-11)×1010 cm-3] and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [nacce=(0.6-10)×109 cm-3].

The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range nupflowe/nSXRe=0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., nacce/nSXRe= 0.005-0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, i.e., l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models). Title: Chromospheric Events in the Quiet Network Authors: Keller, C.; Bastian, T.; Benz, A.; Krucker, S. Bibcode: 1997SPD....28.1304K Altcode: 1997BAAS...29..917K Time sequences of a quiet network region close to disk center have been simultaneously recorded with the VLA, various instruments on SOHO, and the solar telescopes on Kitt Peak. The analysis of the Hα spectra obtained at the McMath-Pierce telescope revealed down-flows with apparent velocities of more than 2.5 km/s associated with magnetic field structures in the quiet network. During such events, the Hα spectra show a pronounced asymmetry. The photospheric magnetic field was determined from rapid scans in three iron lines with the Zurich Imaging Stokes Polarimeter. Up- and down-flow velocity excursions outside of magnetic field regions are compatible with chromospheric waves. We describe the properties of these events as seen in the observations of the visible part of the spectrum and their signatures at radio and UV wavelengths. The final goal of this study is the construction of a time-dependent 3-D picture of the quiet solar atmosphere and the understanding of the dynamical coupling of photospheric magnetic fields with the chromosphere and the corona. Title: Fine structure of the X-ray and radio emissions of the quiet solar corona. Authors: Benz, A. O.; Krucker, S.; Acton, L. W.; Bastian, T. S. Bibcode: 1997A&A...320..993B Altcode: Two deep soft X-ray exposures of a quiet region on the Sun were made with the SXT telescope on board the Yohkoh satellite on 20 Feb 1995. We report on the spatial X-ray fine structure. Regions of enhanced X-ray emission, more than two orders of magnitude fainter than previously reported X-ray bright points, are loosely associated with bipolar regions in the magnetic network. The power spectrum of quiet X-ray images at small spatial scales is similar to that of active regions, but exhibits a kink at a scale of =~25,000km, possibly connected to the supergranular structure. The spatial X-ray structures in the time averaged image amount to an rms amplitude which is 6% of the mean value. The X-ray structures correlate with contemporaneous radio maps obtained by the VLA at wavelengths of 1.3, 2.0, and 3.6cm. The amplitude of the brightness variations in the images increases with radio wavelength, i.e., with increasing height. The cross-correlation coefficient with the absolute magnetic field strength, however, generally decreases with height, consistent with the idea of bipolar regions in the network and of the magnetic field deviating from vertical in the upper chromosphere. The X-ray observations require an enhanced pressure in the corona above the magnetic network, but suggest similar temperatures. Model calculations show that, under a constant temperature, an rms density increase (relative to that in the cell interior) ranging from about 20% in the chromosphere to 60% in the low corona is sufficient to explain the observed standard deviations due to the spatial structures in radio waves and soft X-rays, respectively. Title: VLBI measurement of the size of dMe stars. Authors: Alef, W.; Benz, A. O.; Guedel, M. Bibcode: 1997A&A...317..707A Altcode: The binary system YY Gem, which consists of two dM1e stars, has been observed during an eclipse using intercontinental Very Long Baseline Interferometry (VLBI) at 1.6GHz. The stellar emission was at a low, quiescent level at all observing periods. The correlated flux decreases slightly with baseline length, indicating that the source is resolved at the longest baselines. This is confirmed by model fits, which give a FWHM size of 0.94(+/-0.24)mas (2.0x10^11^cm or 2.1 photospheric diameters) for the radio emitting source. A lower limit to the size derived from the lack of observable eclipse effects is consistent with this value. The resulting brightness temperature of 1.1x10^9^K is compatible with gyrosynchrotron emission. Deviations from circular symmetry are not significant. The loops that trap the radio emitting electrons reaching an altitude of probably more than a stellar radius appear to be distributed isotropically within the limits of the resolution. Title: Energy Release Processes in Active Regions Authors: Benz, A. O. Bibcode: 1997LNP...489..201B Altcode: 1997shpp.conf..201B A standard model of impulsive energy release has emerged during the recent years: Magnetic energy is dumped into coronal electrons (and possibly ions) accelerating them to some tens of keV. These particles mostly precipitate into the chromosphere, radiate hard X-rays and heat it to millions of degrees. The hot chromospheric material is ejected into the corona and produces the soft X-ray flare. The theory behind the energy release is reconnection, proposed for various geometries. Title: Coronal EUV and Radio Variability and Heating Authors: Krucker, S.; Benz, A. O.; Delaboudinière, J. -P. Bibcode: 1997ESASP.404..465K Altcode: 1997cswn.conf..465K No abstract at ADS Title: X-Ray/Radio Network Flares of the Quiet Sun Authors: Benz, Arnold O.; Krucker, Sam; Acton, Loren W.; Bastian, T. S. Bibcode: 1997IAUJD..19E...1B Altcode: The temporal variations in the soft X-ray (SXR) emission and the radio emission above the solar magnetic network of the quiet corona have been investigated using Yohkoh SXR images with deep exposure and VLA observations in the centimetric radio range. The SXR data show several brightenings with an extrapolated occurrence probability of one brightening per 3 seconds on the total solar surface. During the roughly 10 minutes of enhanced flux, the total radiative losses of the observed plasma are betwee () n 0.6 and 2.4 cdot 1026 erg per event. These events are more than an order of magnitude smaller than previously reported X-ray bright points or active region transient brightenings. For all of the four SXR events with simultaneous radio observations, a corresponding radio source correlating in space and time can be found. There are several similarities between these SXR/radio events and regular solar flares. These events thus appear to be flare-like and are called network flares. We will report also on very recent work using SOHO's EIT and CDS experiments combined with VLA and Kitt Peak observations. Title: YOHKOH observation of the source regions of solar narrowband, millisecond spike events. Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J. Bibcode: 1997A&A...317..569K Altcode: The source regions of metric spike events are investigated on Yohkoh soft X-ray (SXR) maps. The spikes are identified by the spectrometer Phoenix between 300MHz and 360MHz and are associated with groups of type III bursts at lower frequencies reaching also the decametric range. The Very Large Array (VLA) provides simultaneously spatial information at 333MHz, 1446MHz and 4866MHz. Similar to the previous VLA observation of a metric spike event, the new data are consistent with a high altitude of the spike sources of about 5x10^10^cm above the photosphere. The additionally available SXR data for one of the presented events give the following new informations: (i) The spike sources occur near open field lines and near regions of a slightly enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR observations of type III bursts without metric spike activity, no SXR jet is observed. (iii) At low altitude, a weak SXR enhancement occurs, peaking about 60 s after the spike event. The SXR source and the spike sources can be connected by potential field lines. The observations corroborate a model in which a metric spike event is attributed to an energy release region at high altitude, while upwards propagating electrons produce type III bursts and downward moving electrons are responsible for SXR emission of heated plasma. Title: The Neupert Effect in Active Stellar Coronae: Chromospheric Evaporation and Coronal Heating in the dMe Flare Star Binary UV Ceti Authors: Guedel, Manuel; Benz, Arnold O.; Schmitt, Juergen H. M. M.; Skinner, Stephen L. Bibcode: 1996ApJ...471.1002G Altcode: Evidence for coronal heating by chromospheric evaporation in flares of active dMe stars is presented through observations of the Neupert effect in high-frequency microwaves and soft X-rays. The Neupert effect, as originally found in solar flares, manifests itself in a close similarity between the soft X-ray light curve and the time integral of the simultaneous microwave light curve. It is interpreted as the signature of the accumulation of hot plasma due to heating by accelerated electrons in the chromosphere.

We used the ROSAT and ASCA soft X-ray observatories and the Very Large Array (VLA) radio telescope (at 6 cm and 3.6 cm wavelengths) to monitor simultaneously the nearby dMe flare star binary Gliese 65 A + B = UV Ceti during 9 hours on each of two consecutive days. We find several weakly polarized radio events that start contemporaneously (within a few minutes) with X-ray flares and then peak and decay as the X-ray flares develop gradually. A striking similarity to the temporal evolution of solar gradual events is found. We argue that the Neupert effect is best observed in relatively hard bands of the soft X-ray emission, but that its presence can be inferred from the much softer bands commonly used for stellar observations by use of the solar analogy. Together with spectral hardness observations of soft X-rays, the data suggest the operation of chromospheric evaporation on UV Cet. The observations thus indicate a causal relation between the nonthermal and thermal energies of the underlying electron populations.

We find that stellar flares are, relative to solar flares, X-ray-weak. The ratio between the total energy radiated into the radio and the soft X-ray bands closely matches the corresponding ratio between the quiescent luminosities of active stars, perhaps implying similar mechanisms and similar efficiencies for the quiescent emission and for larger, single flares. Estimating the total kinetic energy in the electrons from the radio flux, we find that only a part is observed in soft X-rays, a discrepancy well known from solar flares. Title: Metric spikes and electron acceleration in the solar corona. Authors: Benz, A. O.; Csillaghy, A.; Aschwanden, M. J. Bibcode: 1996A&A...309..291B Altcode: Short and narrowband spikes near the starting frequency of metric type III bursts have been searched and analyzed in Zurich radio spectrometer data. We find that the probability for the occurrence of metric spikes is related to the starting frequency of type III bursts; the association rate increases to 34% for groups of type III bursts with starting frequencies below 500MHz. The frequency channel containing most of spikes has been cross-correlated in time with the frequency channels of type III bursts. The correlation is significant in all selected cases and is caused by the association of individual type III bursts with groups of spikes, proving beyond doubt that spikes and type III bursts are physically related. The cross-correlation also defines the average drift rate of the type III maximum and its relation to spikes. In the average, the peak time of metric spikes coincides with the correlated type III burst, extrapolated to the same frequency. This may be interpreted as the spike radiation being emitted at the same characteristic frequency as the type III emission. The generally higher polarization of spikes helps to distinguish them from type III bursts. Contrary to spikes at higher (decimetric) frequencies, 60% of metric spike events have the same sign of circular polarization as the associated type III bursts, 33% are opposite, while the polarization was not measurable for the rest of the type III bursts. Some of the metric spike events are associated with weak flare activity in Halpha_, but none has been found to be closely associated with a hard X-ray burst or a microwave event. Metric spikes are consistent with energy release at high altitudes producing low energy electron beams. If the spikes are caused by the same electron population as the type III bursts, its acceleration site must be below or in close proximity to the spike source. Title: The High Energy Solar Spectroscopic Imager - HESSI Authors: Dennis, B. R.; Crannell, C. J.; Holman, G. D.; Ramaty, R.; von Rosenvinge, T. T.; Benz, A.; Bornmann, P. L.; Brown, J. C.; Canfield, R. C.; Emslie, A. G.; Enome, S.; Kosugi, T.; Hudson, H. S.; Hurford, G. J.; Lin, R. P.; Ling, J. C.; Madden, N. W.; van Beek, H. F.; Vilmer, N. Bibcode: 1996AAS...188.7016D Altcode: 1996BAAS...28..941D HESSI will investigate the physics of particle acceleration and energy release in solar flares through an unprecedented combination of high resolution imaging and spectroscopy of X-rays and gamma rays from 2 keV to 20 MeV during the next solar maximum. It uses Fourier-transform imaging with 12 bi-grid modulation collimators and cooled germanium and silicon detectors mounted on a Sun-pointed spin-stabilized spacecraft in a low-altitude equatorial orbit. HESSI will carry out the first imaging spectroscopy in hard X-rays with 2 arcseconds angular resolution, time resolution to tens of ms, and ~ 1 keV energy resolution; the first gamma-ray line spectroscopy from a spacecraft with ~ 1 keV energy resolution; and the first gamma-ray line and continuum imaging with 20 arcseconds angular resolution. Title: Prompt Radio Emission of Supernovae: Plasma Radiation Alternative? Authors: Benz, A. O.; Hafliger, P. D. Bibcode: 1996ASPC...93..150B Altcode: 1996ress.conf..150B No abstract at ADS Title: Soft X-Ray (Yohkoh) and Radio (VLA) Observations of Solar Narrowband, Millisecond Spike Events Authors: Krucker, Sam; Benz, Arnold O.; Aschwanden, Markus J. Bibcode: 1996ASPC..111..129K Altcode: 1997ASPC..111..129K The source regions of metric spike events are investigated on Yohkoh soft X-ray (SXR) maps. The spikes are identified by the spectrometer Phoenix between 300 MHz and 360 MHz and are associated with groups of type III bursts at lower frequencies reaching also the decametric range. The Very Large Array (VLA) provides simultaneously spatial information at 333 MHz and 1445 MHz. Similar to the previous VLA observation of a metric spike event, the new data are consistent with a high altitude of the spike sources of about 5×1010cm above the photosphere. The additionally available SXR data for one of the presented events give the following new information: (i) The spike sources occur near open field lines and near regions of a slightly enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR observations of type III bursts without metric spike activity, no SXR jet is observed. (iii) At low altitude, a weak SXR enhancement occurs, peaking about 60 s after the spike event. The SXR source and the spike sources can be connected by potential field lines. The observations corroborate a model in which a metric spike event is attributed to an energy release region at high altitude, while upwards propagating electrons produce type III bursts and downward moving electrons are responsible for SXR emission of heated plasma. Title: Coherent Radio Emission of Solar Flares in the Decimeter Range (0.3-3 GHz) Authors: Benz, A. O. Bibcode: 1996ASPC...93..347B Altcode: 1996ress.conf..347B No abstract at ADS Title: Nonthermal Microwave Emission from F Dwarfs: 71 Tau; alpha For; and Open Cluster/Moving Group Membership Authors: Gudel, M.; Benz, A. O.; Guinan, E. F.; Schmitt, J. H. M. M. Bibcode: 1996ASPC...93..306G Altcode: 1996ress.conf..306G No abstract at ADS Title: Very long baseline interferometry of solar microwave radiation. Authors: Benz, A. O.; Graham, D.; Isliker, H.; Andersson, C.; Koehnlein, W.; Mantovani, F.; Umana, G. Bibcode: 1996A&A...305..970B Altcode: The solar 2.297 GHz radiation has been observed and investigated by very long baseline interferometry (VLBI). The radio observatories of Medicina, Noto, Onsala, and Weilheim were involved yielding baselines between 360km and 3800km and a nominal resolution of 0.09"to 0.008"or 70 to 6km on the Sun. This solar VLBI network operated successfully with at least one useful baseline for 167 hours during five campaigns at the maximum of the most recent activity cycle in 1989 and 1990. The Phoenix spectrometer at Zurich was used to detect and classify the radio bursts. A total of 59 solar radio bursts were observed at the VLBI frequency, of which 26 events were analyzed, including narrowband millisecond spikes, type III bursts, patches, pulsations, and diffuse broadband (gyrosynchrotron) emission. Neither during bursts nor in quiet times significant fringes were detected. All sources were well resolved including the narrowband spikes. We interpret the result in terms of relatively large radio sources and/or by scattering to apparent source sizes larger than the lowest resolution and by the lack of `speckles'. The results are consistent with scattering of the radio emission in the corona. The upper and lower limits of the source size of spikes are discussed. For the apparent source size, l_a_, we find 65km<l_a_<16000km, and for the original source size before scattering l<~200km. Title: The Enigmatic FOV Star 47 CAS Authors: Gudel, M.; Benz, A. O.; Guinan, E. F.; Schmitt, J. H. M. M. Bibcode: 1996ASPC...93..309G Altcode: 1996ress.conf..309G No abstract at ADS Title: Radio Spectra of dMe and dKe Stars Authors: Gudel, M.; Benz, A. O. Bibcode: 1996ASPC...93..303G Altcode: 1996ress.conf..303G No abstract at ADS Title: Variability of UV Ceti in Radio and Soft X-ray Emission Authors: Benz, A. O.; Gudel, M.; Schmitt, J. H. M. M. Bibcode: 1996ASPC...93..291B Altcode: 1996ress.conf..291B No abstract at ADS Title: Radio Emission of Dwarf Novae Authors: Benz, A. O.; Gudel, M.; Mattei, J. A. Bibcode: 1996ASPC...93..188B Altcode: 1996ress.conf..188B No abstract at ADS Title: Location of Type I Radio Continuum and Bursts on YOHKOH Soft X-ray Maps Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J.; Bastian, T. S. Bibcode: 1996mpsa.conf..441K Altcode: 1996IAUCo.153..441K No abstract at ADS Title: Radio Astronomical Diagnostics Authors: Benz, A. O. Bibcode: 1996LNP...468..213B Altcode: 1996plas.conf..213B A brief introduction into the diagnostic capabilities and results of radio waves from coronal plasmas of the Sun and other late-type stars is presented. These coronal emissions show that the plasma is in a dynamic state with time scale down to a few tens of microseconds. Gyrosynchrotron emission in flares reveal the presence of relativistic electrons, which, in active stars, seem to persist even during quasi-quiet (quiescent) intervals. Coherent emissions of solar electron beams by the two-stream instability has been discovered up to 8 GHz. Particularly efficient emitters are trapped electrons having a loss-cone distribution. This is probably the most frequent cause of highly polarized stellar radio flares. Of greatest interest are emissions by unstable currents and shocks, which have been identified in the solar corona. A general introduction into some basic theories, but not a review, is given, illustrated with recent observations. A more extended introduction can be found in Benz (1993). Title: Solar Electron Beams Detected in Hard X-Rays and Radio Waves Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.; Schwartz, Richard A. Bibcode: 1995ApJ...455..347A Altcode: We present a statistical survey of electron beam signatures that are detected simultaneously at hard X-ray (HXR) and radio wavelengths during solar flares. For the identification of a simultaneous event we require a type III (normal-drifting or reverse-slope-drifting) radio burst that coincides (within ± 1 s) with a significant (≥ 3 σ HXR pulse of similar duration (≥ 1 s). Our survey covers all HXRBS/SMM and BATSE/CGRO flares that were simultaneously observed with the 0.1-1 GHz spectrometer Ikarus or the 0.1-3 GHz spectrometer Phoenix of ETH Zurich during 1980-1993. The major results and conclusions are as follows:

1. We identified 233 HXR pulses (out of 882) to be correlated with type III-like radio bursts: 77% with normal-drifting type III bursts, 34% with reverse-slope (RS)-drifting bursts, and 13% with oppositely drifting (III + RS) burst pairs. The majority of these cases provide evidence for acceleration of bidirectional electron beams.

2. The detailed correlation with type III-like radio bursts suggests that most of the subsecond fluctuations detectable in ≥ 25 keV HXR emission are related to discrete electron injections. This is also supported by the proportionality of the HXR pulse duration with the radio burst duration. The distribution of HXR pulse durations WX is found to have an exponential distribution, i.e., N(WX) ∝ exp (-WX/0.25 s) in the measured range of WX ≍ 0.5-1.5 s.

3. From oppositely drifting radio burst pairs we infer electron densities of ne = 109-1010 cm-3 at the acceleration site. From the absence of a frequency gap between the simultaneous start frequencies of upward and downward drifting radio bursts, we infer an upper limit of L ≤ 2000 km for the extent of the acceleration site and an acceleration time of Δt ≤ 3 ms for the (≥ 5 keV) radio-emitting electrons (in the case of parallel electric fields).

4. The relative timing between HXR pulses and radio bursts is best at the start frequency (of earliest radio detection), with a coincidence of ≲0.1 s in the statistical average, while the radio bursts are delayed at all other frequencies (in the statistical average). The timing is consistent with the scenario of electron injection at a mean coronal height of h ≍ 104 km. The radio-emitting electrons are found to have lower energies (≳ 5 keV) than the ≥ 25 keV HXR-emitting electrons.

5. The modulated HXR flux that correlates with electron beam signatures in radio amounts to 2%-6% of the total HXR count rate (for BATSE flares). The associated kinetic energy in electrons is estimated to be E = 4 × 1022-1027 ergs per beam, or Ne = 4 × 1028-1033 electrons per beam, considering the spread from the smallest to the largest flare detected by HXRBS.

6. The average drift rate of propagating electron beams is found here to be [dv/dt] = 0.10ν1.4 MHz km s-1 in the frequency range of ν = 200-3000 MHz, which is lower than expected from the Alvarez & Haddock relation for frequencies ≤ 550 MHz.

7. The frequency distributions of HXR fluxes (Fx) and radio type III burst fluxes (FR), which both can be characterized by a power law, are found to have a significantly different slope, i.e., N(Fx) ∝ Fx-1.87 versus N(FR) ∝ FR-1.28. The difference in the slope is attributed to the fundamental difference between incoherent and coherent emission processes.

In summary, these findings suggest a flare scenario in which bidirectional streams of electrons are accelerated during solar flares at heights of 10 km above the photosphere in rather compact regions (L ≲ 2000 km). The acceleration site is likely to be located near the top of flare loops (defined by HXR double footpoints) or in the cusp above, where electrons have also access to open field lines or larger arches. The observed bidirectionality of electron beams favors acceleration mechanisms with oppositely directed electric fields or stochastic acceleration in an X-type reconnection geometry. Title: First VLA observation of a solar narrowband, millisecond spike event. Authors: Krucker, S.; Aschwanden, M. J.; Bastian, T. S.; Benz, A. O. Bibcode: 1995A&A...302..551K Altcode: The first spatially resolved observation of solar, narrowband spikes in two dimensions is presented. The 'metric' spikes around 333MHz are classified by the broadband spectrometer Phoenix (ETH Zuerich), whereas the simultaneously observing Very Large Array (VLA) provides high angular resolution images of the solar disc. At lower frequencies, a group of associated type III bursts is detected. The spikes occur at high altitude (=~4.5x10^10^cm above the photosphere), and at least 3 separated locations of emission can be identified. The different spike sources are separated by up to 130" and show different degrees of polarization. Spikes and type III bursts have the same sense of circular polarization, and according to the extrapolated potential field lines, the polarization of the different spike sources is in x-mode. With a delay of 42s, a thermal source appears on the same extrapolated potential field lines as the spikes at the second frequency of the VLA (1446MHz). The location of the energy release relative to the spikes source is discussed. A scenario is proposed where the energy is released in or near the spike source, and in which the spikes, the type III bursts and the thermal source originate from the same energy release. Hot electrons expanding along the field lines generate a type III burst (upward direction) and heat the underlying dense plasma (thermal source). Title: Microwave emission from X-ray bright solar-like stars: the F-G main sequence and beyond. Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O. Bibcode: 1995A&A...302..775G Altcode: A sample of F and G main sequence stars and slightly evolved F and G stars, selected as the apparently strongest X-ray sources in their class as detected in the ROSAT All-Sky Survey (RASS), has been observed in microwaves to search for coronae with strong heating and populations of nonthermal particles. The microwave flux densities were observed with the VLA at 8.4GHz. Radio emission has been detected from nine targets, in both luminosity classes V and IV. Since known or unknown cool companions in binary systems may cause spurious results, we have checked the available spectroscopic and astrometric data, including unpublished CORAVEL observations. There is at least one detected object in each of the four spectral and luminosity classes of stars, FIV, FV, GIV, and GV for which no known companion can be made responsible for the observed emission. A very luminous X-ray and radio source is identified with the F0 V star HD 12230, a member of the Pleiades Moving Group with an age of the order of 50-70Myr. HD 129333 (EK Dra), a G0 V target presumably of the same age, is detected also, and the X-ray and radio modulations agree with the optically measured rotation. On the other hand, three very old stars that are leaving the main sequence and are moving towards the subgiant luminosity class are found to be strong X-ray and radio emitters; in the case of HD 20010, an F8 IV star, the hypothetical existence of an unknown spectroscopic companion would contradict astrometric data. These stars appear to define a new class of radio-luminous coronal stars. The observed microwave flux densities agree with the ratio of radio to X-ray fluxes of other active coronal stars. We report sensitive upper limits for all non-detections, up to an order of magnitude lower than in previous surveys. These observations yield first systematic evidence that stars close to the solar spectral type can maintain considerable nonthermal electron populations in their coronae, possibly due to a mechanism that involves coronal heating. They provide the crucial link between the study of the solar corona and of active coronal stars (the "solar-stellar connection"), and bridge the remaining gaps on the radio main sequence between the cooler stars and chemically peculiar Ap stars. Further, they support the view that young, near-Zero-Age Main-Sequence (ZAMS) stars are able to continually produce luminous radio emission after their arrival on the ZAMS. The strong activity resurgence in the sample of old stars moving off the main sequence may be related to an increase in convective turnover time as the internal structuring of the stars changes; this is of potential interest for the study of the stellar interior of evolved stars. Title: The corona of the young solar analog EK Draconis. Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O.; Elias, N. M., II Bibcode: 1995A&A...301..201G Altcode: First coronal microwave and new soft X-ray observations of the very active, near-Zero-Age Main-Sequence (ZAMS) dG0e star EK Dra = HD 129333 show that this analog of the young Sun is more luminous in both emissions than most single M-dwarf flare stars. Variations in the 8.4GHz flux include modulation with the optically determined rotation period of 2.7 days. This result points to a non-uniform filling of the corona with energetic electrons due to an incomplete coverage of the surface with active regions and a source volume that is not concentric with the star. The radio luminosity varying between logL_R_=13.6 and 14.6 (L_R_ in erg/s/Hz) shows evidence for unpolarized gyrosynchrotron flares, while strongly polarized flares were absent during the observations. This star is the first young, truly solar-like main sequence G star discovered in microwaves. Having just arrived on the main sequence, it conclusively proves that young, solar-like G stars can maintain very high levels of radio emission after their T Tau phase. The X-ray observations were obtained from the ROSAT All-Sky Survey (RASS). The average X-ray luminosity amounts to logL_X_=29.9 (L_X_ in erg/s). A Raymond-Smith type plasma model fit yields two plasma components at temperatures of 1.9 and 10MK, with volume emission measures of 1.2 and 2.5.10^52^cm^-3^, respectively. The X-ray light curve is significantly variable, with the photon count rate from the cooler plasma being strongly modulated by the rotation period; the emission from the hotter plasma is only weakly variable. Modeling of the source distribution in the stellar corona yields electron densities of the order of 4.10^10^cm^-3^ or higher for the cool plasma component. It indicates that a considerable portion of EK Dra's high X-ray luminosity is due to high-density plasma rather than large emission volume. Parameters for an X-ray flare indicate an electron density of 1.75.10^11^cm^-3^ and a source height of (1-2).10^10^cm, compatible with a few times the scale height of the cooler plasma component. Title: Location of Type I Radio Continuum and Bursts on YOHKOH Soft X-Ray Maps Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J.; Bastian, T. S. Bibcode: 1995SoPh..160..151K Altcode: A solar type I noise storm was observed on 30 July, 1992 with the radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board theYohkoh satellite. The spectrogram was used to identify the type I noise storm. In the VLA images at 333 MHz a fully left circular polarized (100% LCP) continuum source and several highly polarized (70% to 100% LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100″ and apparently lie on different loops as outlined by the SXR. Continuum and bursts are separated in the perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of ≈ 0.2″ min−1 along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446 MHz) show no source corresponding to the type I event. The soft X-ray emission measure and temperature were calculated. The type I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of «ne» = (1.5 ± 0.4) × 109 cm−3 and a temperature ofT = (2.1 ± 0.1) × 106 K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15″-50″ and seem to be on different loops. These observations contradict the predictions of existing type I theories. Title: VLBI observations of single main-sequence M stars. Authors: Benz, A. O.; Alef, W.; Guedel, M. Bibcode: 1995A&A...298..187B Altcode: Single dMe stars have been observed at 18cm wavelength by intercontinental very long baseline interferometry (VLBI). Here we report on two stars, EQ Peg B and AD Leo, that have been detected during flares, and one of them also at a relatively low (`quiescent') state. There are no indications that any of the stars has been spatially resolved. Upper limits on the size of the radio sources are less than 1.9 stellar diameters for flares and less than 3.7 stellar diameters for quiescence. This yields directly observed brightness temperatures beyond 2x10^10^K for flares and 2x10^9^K in quiescence. The observations suggest that the size of the closed corona is less than predicted from pressure equilibrium between plasma and magnetic field. An extent of the order of one density scale height is compatible with the observations. Title: Sequences of Correlated Hard X-Ray and Type III Bursts during Solar Flares Authors: Aschwanden, Markus J.; Montello, Maria L.; Dennis, Brian R.; Benz, Arnold O. Bibcode: 1995ApJ...440..394A Altcode: Acceleration and injection of electron beams in solar flares can be traced from radio type III (or type U) bursts and correlated hard X-ray pulses with similar timescales and nonthermal spectra. We perform a systematic survey of such correlated radio and hard X-ray (HXR) pulses with timescales of less than or approximately 2 s in flares simultaneously observed with the radio spectrometer Ikarus and the Hard X-Ray Burst Spectrometer (HXRBS) on solar maximum mission (SMM). We applied an epoch-folding technique to enhance correlated time patterns in burst sequences at the two wavelengths. We present the results from the strongest (10) flares with a HXRBS count rate greater than or = 3000 counts/s, which have a satisfactory signal-to-noise ratio for subsecond pulses. The major findings of this study are presented. These observations strongly suggest that particle acceleration in solar flares occurs in a pulsed mode where electron beams are simultaneously injected in upward and downward directions. Since the sequences of correlated HXR and radio bursts show identical durations and intervals at the two wavelengths, they are believed to reflect most directly the temporal dynamics of the underlying common accelerator. As a consequence, thick-target models should be reconsidered under the aspect of electron injection with pulse durations of 0.2-2.0 s and duty cycles of approximately = 50%. Title: A bright X-ray and radio corona on the F0V star 47 Cas? Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O. Bibcode: 1995A&A...293L..49G Altcode: X-ray and microwave observations of the nearby A7-F0V star 47 Cas reveal indications for extraordinarily strong coronal activity, characterised by X-ray and radio luminosities of L_X_=2.9x10^30^erg/s and L_R_=1.1x10^15^erg/s/Hz, respectively, and the presence of very strong X-ray flares. The rapidly rotating star is not known to possess a spectroscopic companion that may be held responsible for the observed emissions. Interpreting the X-ray modulation as rotational modulation and combining the value of the rotation period with the optically determined vsini, the stellar radius is found to be consistent with the photometrically determined radius. This may be the first non-interacting, early F V star discovered as a strong, nonthermal radio source. From kinematic arguments, 47 Cas is a likely member of the Pleiades Moving Group, and may thus be very young. Title: Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares Authors: Aschwanden, Markus J.; Benz, Arnold O. Bibcode: 1995ApJ...438..997A Altcode: We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca XIX soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T-3/2 dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyze 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Pheonix, hard X-ray data from (BATSE/CGRO) and soft X-ray data from Burst and Transient Source Experiment/Compton Gamma Ray Observatory (GOES) were available. Title: Coronal Magnetic Energy Releases Authors: Benz, Arnold O.; Krüger, Albrecht Bibcode: 1995LNP...444.....B Altcode: 1995cmer.conf.....B This book brings together a variety of review articles on dynamical phenomena in the solar corona in order to work out the unifying aspects of magnetic energy releases. The experimental data from groundbased methods of radio astronomy as well as from satellites are also discussed. The book addresses researchers in astrophysics, and planetary science but should also be accessible to graduate students. Title: Radio Emission from Flares in Single Late-type Stars Authors: Benz, Arnold O. Bibcode: 1995LNP...454...23B Altcode: 1995IAUCo.151...23B; 1995LNP...454...21B; 1995flfl.conf...23B Radio observations provide the most direct information on nonthermal electrons in stellar flares and in the coronae of late-type stars. Radio emissions of single main-sequence F, G, and of many K stars have recently been discovered, in addition to the well-known dwarf M stars. Their long-duration radio flares with low circular polarization, slow variations and broad bandwidth can be attributed to gyrosynchrotron emission of mildly relativistic electrons. The same holds for the low-level (quiescent) radio emission. On the other hand, highly polarized radio flares of M stars have been interpreted by coherent emissions from loss-cone instabilities of magnetically trapped electrons. These conjectures are consistent with recent VLBI observations. The identification of the radio emission process allows to estimate the high-energy component of the flare and compare it to the total flare energy. The weakly polarized radio emission may serve as a proxy for hard X-ray signatures of relativistic electrons. The fraction of primary energy released into energetic electrons then appears to be large and similar to solar flares. Title: Flares and Coronal Heating in the Sun and Stars Authors: Benz, A. O. Bibcode: 1995LNP...444....1B Altcode: 1995cmer.conf....1B Many forms of energy input into coronae have been proposed as the dominant heating mechanism. Here I review topical aspects of impulsive releases of magnetic energy. Several solar phenomena from bright points to coronal mass ejections are attributed to free magnetic energy apparently available in the corona. The possibility that magnetic energy release is the dominant energy input into the corona is discussed for the Sun with special emphasis on small radio events, with negative results. The evidence is better, however, for active stars where a correlation between thermal radiation and gyrosynchrotron emission by energetic electrons has been found recently. It suggests that a flare-like release of magnetic energy is the dominant coronal heating process of active, rapidly rotating stars. However, the required cadence of flares has not (yet) been found. The link between stellar coronal heating and magnetic energy release is not clear as long as the various flare-like phenomena in the solar corona are not better understood. Title: Stellar Remnants Authors: Benz, A. O.; Courvoisier, T. J. -L. Bibcode: 1995stre.conf.....B Altcode: No abstract at ADS Title: Book-Review - Plasma Astrophysics Authors: Benz, A. O.; van Oss, R. F. Bibcode: 1994SoPh..154..203B Altcode: No abstract at ADS Title: Electron beams in solar flares Authors: Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O. Bibcode: 1994umd..reptR....A Altcode: A list of publications resulting from this program includes 'The Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX'; 'Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar Flares'; 'Particle Acceleration in Flares'; 'Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares'; 'Sequences of Correlated Hard X-Ray and Type 3 Bursts During Solar Flares'; and 'Solar Electron Beams Detected in Hard X-Rays and Radiowaves.' Abstracts and reprints of each are attached to this report. Title: Discovery of Microwave Emission from Four Nearby Solar-Type G Stars Authors: Gudel, Manuel; Schmitt, Jurgen H. M. M.; Benz, Arnold O. Bibcode: 1994Sci...265..933G Altcode: Radio waves from the sun were detected 50 years ago, but the microwave detection of other single solar-type stars has remained a challenge. Here, the discovery of four solar-type radio stars is reported. These "solar twin" G stars are radio sources up to 3000 times stronger than the quiet sun. The microwaves most likely originate from a large number of relativistic electrons, possibly produced along with coronal heating, a process that is not understood. Two of the stars are younger than the sun and rotate more rapidly; the dynamo process in the stellar interior is therefore presumably more vigorous, resulting in enhanced coronal activity. One of the detections, however, is an old, metal-deficient G dwarf. Title: Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar Flares Authors: Aschwanden, Markus J.; Benz, Arnold O.; Montello, Maria L. Bibcode: 1994ApJ...431..432A Altcode: Time structures of electron beam signatures at radio wavelengths are investigated to probe correlated versus random behavior in solar flares. In particular we address the issue whether acceleration and injection of electron beams is coherently modulated by a single source, or whether the injection is driven by a stochastic (possibly spatially fragmented) process. We analyze a total of approximately = 6000 type III bursts observed by Ikarus (Zurich) in the frequency range of 100-500 MHz, during 359 solar flares with simultaneous greater than or = 25 keV hard X-ray emission, in the years 1890-1983. In 155 flares we find a total of 260 continuous type III groups, with an average number of 13 +/- 9 bursts per group, a mean duration of D = 12 +/- 14 s, a mean period of P = 2.0 +/- 1.2 s, with the highest burst rate at a frequency of nu = 310 +/- 120 MHz. Pulse periods have been measured between 0.5 and 10 s, and can be described by an exponential distribution, i.e., N(P) varies as e -P/1.0s. The period shows a frequency dependence of P(nu)=46(exp-0.6)MHzs for different flares, but is invariant during a particular flare. We measure the mean period P and its standard deviation sigma p in each type III group, and quantify the degree of periodicity (or phase-coherence) by the dimensionless parameter sigma pP. The representative sample of 260 type III burst groups shows a mean periodicity of sigma p/P = 0.37 +/- 0.12, while Monte Carlo simulations of an equivalent set of truly random time series show a distinctly different value of sigma pP = 0.93 +/- 0.26. This result indicates that the injection of electron beams is coherently modulated by a particle acceleration source which is either compact or has a global organization on a timescale of seconds, in contrast to an incoherent acceleration source, which is stochastic either in time or space. We discuss the constraints on the size of the acceleration region resulting from electron beam propagation delays and from Alfvenic synchronization during a pulse period. We discuss two periodic processes in flares, which potentially control quasi-periodic particle acceleration: (1) MHD oscillations, and (2) current sheets with oscillatory dynamics. Title: Particle Acceleration in Flares Authors: Benz, A. O.; Kosugi, T.; Aschwanden, M. J.; Benka, S. G.; Chupp, E. L.; Enome, S.; Garcia, H.; Holman, G. D.; Kurt, V. G.; Sakao, T.; Stepanov, A. V.; Volwerk, M. Bibcode: 1994SoPh..153...33B Altcode: Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, γ-rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated. Title: Directivity of the Radio Emission from the K1 Dwarf Star AB Doradus Authors: Lim, Jeremy; White, Stephen M.; Nelson, Graam J.; Benz, Arnold O. Bibcode: 1994ApJ...430..332L Altcode: We present measurements of the spectrum and polarization of the flaring radio emission from the K1 dwarf star AB Doradus, together with previously reported single frequency measurements (with no polarization information) on 3 other days. On all 4 days spanning a 6 month period, the emission was strong and, when folded with the stellar rotation period, showed similar time variations with two prominant peaks at phase 0.35 and 0.75. These peaks coincide in longitude with two large starspots identified from the stellar optical light curve and have half-powe widths as small as 0.1 rotations and no larger than 0.2 rotations. The modulated emission shows no measurable circular polarization, and its two peaks have different turnover frequencies. Title: Plasma diagnostics of the solar corona using decimetric radio waves (review) Authors: Benz, A. O. Bibcode: 1994R&QE...37..525B Altcode: The solar corona is a very dynamic plasma on time scales down to a few tens of microseconds. The various emissions at decimetric wavelength are briefly reviewed. Several of them seem to be caused by energetic (non-thermal) electrons accelerated in flares or flare-like processes releasing free magnetic energy. The use of decimetric radiation as diagnostics of the acceleration process, the ambient plasma, and the non-thermal particles requires a solid understanding of the emission process. Although we are still far from this in most cases, some information can already be derived from the observations. Title: X-ray/microwave ratio of flares and coronae Authors: Benz, A. O.; Guedel, M. Bibcode: 1994A&A...285..621B Altcode: We have carried out plasma diagnostics of solar flares using soft X-ray (SXR) and simultaneous microwave observations and have compared the ratio of X-ray to microwave luminosities of solar flares with various active late-type stars available in the published literature. Both the SXR low-level (`quiescent') emission from stellar coronae and the flaring emission from the Sun and stars are generally interpreted as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares is generally attributed to an extremely hot or nonthermal population of electrons. Solar flare SXR are conventionally measured in a narrower and harder passband than the stellar sources. Observations of the GOES-2 satellite in two energy channels have been used to estimate the luminosity of solar flares as it would appear in the ROSAT satellite passband. The solar and stellar flare luminosities fit well at the lower end of the active stellar coronae. The flare SXR/microwave ratio is similar to the ratio for stellar coronae. The average ratio follows a power-law relation L_X_{prop.to}L_R_^0.73+/-0.03^ over 10 orders of magnitude from solar microflares to RS CVn and FK Com-type coronae. Dwarf Me and Ke stars, and RS CVn stars are also compatible with a linear SXR/microwave relation, but the ratio is slightly different for each type of star. Considering the differences between solar flares, stellar flares and the various active stellar coronae, the similarity of the SXR/microwave ratios is surprising. It suggests that the energetic electrons in low-level stellar coronae observed in microwaves are related in a similar way to the coronal thermal plasma as flare electrons to the flare thermal plasma, and, consequently, that the heating mechanism of active stellar coronae is a flare-like process. Title: Multiple frequency spike emission during solar flares Authors: Krucker, S.; Benz, A. O. Bibcode: 1994SSRv...68..247K Altcode: No abstract at ADS Title: Periodic or random acceleration in solar flares? Authors: Aschwanden, Markus J.; Benz, Arnold O. Bibcode: 1994SSRv...68..193A Altcode: The issue whether acceleration and injection of electron beams is coherently modulated by a single quasi-periodic source, or whether the injection is driven by a stochastic process in time or (eventually fragmented) in space, is investigated by menas of a periodicity analysis of metric type III bursts. We analyze 260 continuous type III groups observed byIkarus (ETH Zurich) in the frequency range of 100 500 MHz during 359 solar flares with simultaneous ≥25 keV hard X-ray emission, in the years 1980 1983. Pulse periods have been measured between 0.5 and 10 s, and can be described by an exponential distribution, i.e.N(P) ∝e -P/1.0s. We measure the mean periodP and its standard deviation σp in each type III group, and quantify the degree of periodicity by the dimensionless parameter σp/P. The representative sample of 260 type III burst groups shows a mean periodicity of σp/P=0.37±0.12, while Monte-Carlo simulations of an equivalent set of truly random time series show a distinctly different value of σp/P=0.93±0.26. This result suggests that the injection of electron beams is periodically modulated by a particle acceleration source which is either compact or has a global organization on a time scale of seconds. Title: On deterministic chaos, stationarity, periodicity and intermittency in coronal bursts and flares Authors: Isliker, H.; Benz, A. O. Bibcode: 1994SSRv...68..185I Altcode: Solar and stellar flares are highly structured in space and in time, as is indicated for example by their radio signatures: the narrowband spikes, type III, type II and IV, and pulsation events. Structured in time are also the not flare related type I events (noise storms). The nature of this observationally manifest fragmentation is still not clear. Either, it can be due to stochastic boundary or initial conditions of the respective processes, such as inhomogeneities in the coronal plasma. Or else, a deterministic non-linear process is able to cause complicated patterns of these kinds. We investigate the nature of the fragmentation in time. The properties of processes we enquire are stationarity, periodicity, intermittency, and, with dimension estimating methods, we try to discriminate between stochastic and low-dimensional deterministic processes. Since the measured time series are rather short, the dimension estimate methods have to be used with care: we have developed an extended dimension estimate procedure consisting of five steps. Among others, it comprises again the questions of stationarity and intermittency, but also the more technical problems of temporal correlations, judging scaling and convergence, and limited number of data points (statistical limits). We investigate 3 events of narrowband spikes, 13 type III groups, 10 type I storms, 3 type II bursts and 1 type IV event of solar origin, and 3 pulsation-like events of stellar origin. They have in common that all of them have stationary phases, periodicities are rather seldom, and intermittency is quite abundant. However, the burst types turn out to have different characteristics. None of the investigated time series reveals a low-dimensional behaviour. This implies that they originate from complex processes having dimensions (degrees of freedom) larger than about 4 to 6, which includes infinity,i. e. stochasticity. The lower limit of the degrees of freedom is inferred from numerical experiments with known chaotic systems, using time series of similar lengths, and it depends slightly on the burst types. Title: The frequency ratio of bands of microwave spikes during solar flares Authors: Krucker, S.; Benz, A. O. Bibcode: 1994A&A...285.1038K Altcode: The frequency ratio of narrowband millisecond spikes during 17 solar flares has been measured and analyzed. The observations have been made in the frequency range 0.3-3 GHz with the ETH Zuerich spectrometers. The events have been selected from spectrograms for their harmonic structure. Auto-correlation in frequency yields the following major results: (i) The ratio of the harmonic spike groups is not integer, and therefore the term 'harmonic' is strictly speaking inappropriate. (ii) The ratios are independent of frequency. (iii) The ratios range from 1.06 to 1.54 with a prominent peak at 1.39+/-0.01. The cross-correlation of the time profile of harmonic groups peaks at zero lag, demonstrating a tight relation between individual spikes in associated groups. The results require an emission mechanism that can produce harmonic emission at a ratio 5:7 or 1:1.4 and vary significantly from this value. In several cases 3, and in one case 4 harmonic bands have been observed. Previously proposed interpretations of harmonic spike emission are discussed in view of the new observations. Title: Foreword Authors: van den Oord, Bert; Kuijpers, Jan; Kuperus, Max; Benz, A. O.; Brown, J. C.; Einaudi, G.; Kuperus, M.; Raadu, M. A.; Trottet, G.; van den Oord, G. H. J.; Vlahos, L.; Zheleznyakov, V. V.; Wijburg, Marion; Fletcher, Lyndsay; Volwerk, Martin Bibcode: 1994SSRv...68D..17V Altcode: No abstract at ADS Title: Analysis of solar spike evengs by means of symbolic dynamics methods Authors: Schwarz, U.; Kurths, J.; Witt, A.; Benz, A. O. Bibcode: 1994SSRv...68..245S Altcode: We have searched for interrelations of spikes emitted simultaneously at different frequencies during the impulsive phase of flare events (Fig.1). As the spikes are related to the flare energy release and are interpreted as emissions that originate at different sites having different magnetic field strengths, any relation in frequency is interpretated as a relation in space. Quantities of symbolic dynamics, such as mutual information, Shannon information and algorithmic complexity are appropriate to characterize such spatiotemporal patterns, whereas the popular estimate of fractal dimensions can be applied to low-dimensional systems only. The goal is to decide between two possible types of fragmentation depending on the energy release and emission processes, which we callglobal andlocal organization. In the global organization the whole region becomes supercritical, and the energy is released in independent, small regions. The alternative local scenario requires a trigger that spreads from initial localized events and ignites nearby regions. Mutual information which is a generalization of correlation indicates a relation in frequency beyond the bandwidth of individual spikes. The scans in the spectrograms with large mutual information also show a low level of Shannon information and algorithmic complexity, indicating that the simultaneous appearance of spikes at other frequencies is not a completely stochastic phenomenon (white noise). It may be caused by a nonlinear deterministic system or by a Markov process. By means of mutual information we find a memory over frequency intervals up to 60 MHz (Fig. 2). Shannon information and algorithmic complexity, however, describe spike events as a whole, i.e. a global source region. A global organization is also apparent in quasi-periodic changes of the Shannon information and algorithmic complexity in the range of 2 8 seconds (Fig. 3). This findings is compatible with a scenario of local organization in which the information of one spike event spreads spatially and hence triggers further spike events at different places. The region is not an ensemble of independently flashing sources, each representing a system that cascades in energy after an initial trigger. On the contrary, there is a causal connection between the sources at any time. The analysis of four spike events suggests that the simultaneous appearance of spikes is not stochastically independent but a process in which spikes at nearby locations are simultaneously triggered by a common exciter. We have shown in the case in the case of spikes that quantities from nonlinear dynamics used in this paper are helpful in detecting structural properties of complex spatio-temporal patterns. This approach seems to be promising also for several other astrophysical applications. Title: Non-linear properties of the dynamics of bursts and flares in the solar and stellar coronae Authors: Isliker, H.; Benz, A. O. Bibcode: 1994A&A...285..663I Altcode: Solar and stellar flares are highly structured in space and in time, as is indicated for example by their radio signatures: the narrowband spikes, type III, type II and IV, and pulsation events. Structured in time are also the not flare related type I events (noise storms). The nature of this fragmentation is still not clear. Either, it can be due to stochastic boundary or initial conditions of the respective processes, such as inhomogeneities in the coronal plasma. Or else, a deterministic non-linear process is able to cause complicated patterns of these kinds. We investigate the nature of the fragmentation in time. The properties of processes we enquire are stationarity, periodicity, intermittency, and, with dimension estimating methods, we try to discriminate between stochasticism and low-dimensional determinism. Since the measured time series are rather short, the dimension estimate methods have to be used with care: we have developed an extended dimension estimate procedure consisting of five steps. Among others, it comprises again the questions of stationarity and intermittency, but also the more technical problems of temporal correlations, judging scaling and convergence, and few data points (statistical limits). We investigate 3 events of narrowband spikes, 13 type III groups, 10 type I storms, 3 type II bursts and 1 type IV event of solar origin, and 3 pulsation-like events of stellar origin. They have in common that all of them have stationary phases, periodicities are rather seldom, and intermittency is quite abundant. However, the burst types turn out to have different characteristics. None of the investigated time series reveals a low-dimensional behaviour. This implies that they originate from complex processes having dimensions (degrees of freedom) greater than about 4 to 6, which includes infinity, i.e. stochasticity. The lower limit of the degrees of freedom is inferred from numerical experiments with known chaotic systems, using time series of similar lengths, and it depends slightly on the burst types. Title: Observations of fragmented energy release Authors: Benz, A. O. Bibcode: 1994SSRv...68..135B Altcode: Energy release into coronal plasmas is observable in the forms of heating and acceleration. In flares and active stars, heating and acceleration have been found to be related as indicated by an approximately constant ratio of microwave (synchrotron) and soft X-ray (thermal) emission. The discovery suggests a flare-like heating process for the quiescent coronae of active stars. The energy release in solar flares involves several time scales: (i) The largest is the rate of homologous flares in an active region of the order of one per five hours. (ii) Hard X-ray andH α emissions suggest a total flare duration of ten minutes, (iii) with individual episodes of contiguous acceleration of one minute. (iv) Elementary hard X-ray peaks have 5 10 s duration, corresponding to groups of beams observable as type III radio bursts. (v) The effective injection time of these beams is of the order 0.1 s. (vi) The smaller time scale is observed in narrowband radio spikes in the 0.2 8 GHz range with durations of a few times 0.01 s. Title: Catalogue of 1-3 GHz solar flare radio emission Authors: Isliker, H.; Benz, A. O. Bibcode: 1994A&AS..104..145I Altcode: Solar flares frequently radiate in the 1-3 GHz range, the lowest frequency microwaves, but not much is known about the spectral shape of these emissions. We present a catalogue of selected bursts observed with a new spectrometer at ETH Zurich in the years 1989-1993. The original data set includes 268 events of various types. Featureless broadband continua generally attributed to gyrosynchrotron emission are often observed, but they are usually much weaker than the structured emissions probably caused by coherent processes. The selection emphasizes the latter class of events. The events show a rich variety of size and structures in time and frequency. Most events can be grouped into five major classes with some overlap and transitions. The samples of this catalogue have been selected to show the breadth of each class without stressing the extremes. Title: Pulsed Acceleration in Solar Flares Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.; Kundu, Mukul R. Bibcode: 1994ApJS...90..631A Altcode: 1994IAUCo.142..631A We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which suppport the following tentative conclusions: (1) Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components ('statistical flare' produced by a fragmented primary energy release). (2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other. (3) Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar. Title: Books-Received - Plasma Astrophysics - Kinetic Processes in Solar and Stellar Coronae Authors: Benz, A. Bibcode: 1994Sci...263R.842B Altcode: No abstract at ADS Title: ROSAT Observations of Solar-Type G Stars Authors: Gudel, Manuel; Schmitt, Jurgen H. M. M.; Kurster, Martin; Benz, Arnold O. Bibcode: 1994ASPC...64...86G Altcode: 1994csss....8...86G No abstract at ADS Title: Plasma astrophysics. Lecture notes 1994. Authors: Benz, A. O.; Courvoisier, T. J. -L. Bibcode: 1994paln.book.....B Altcode: The three contributions to this book are intended as brief but thorough introductions to important aspects of plasma astrophysics for astronomers and graduate students. Title: Plasma Astrophysics Authors: Kirk, J. G.; Melrose, D. B.; Priest, E. R.; Benz, A. O.; Courvoisier, T. J. -L. Bibcode: 1994plas.conf.....K Altcode: 1994QB462.7.K57....; 1994plas.conf.....B This volume presents the lecture notes of the 24th Advanced Course of the Swiss Society for Astrophysics and Astronomy in March 1994 at Les Diablerets. In three lectures on magnetohydrodynamics, on kinetic plasma physics and on particle acceleration leading experts describe the physical basis of their subjects and extend the discussion to several applications in modern problems of astrophysics. In style and presentation the texts are well-suited for graduate work in plasma astrophysics, one of the very important tools of modern astronomy. The themes developed in this book will be helpful in understanding many processes in the universe from the solar corona to active galaxies. Title: The Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX Authors: Aschwanden, Markus J.; Benz, Arnold O.; Schwartz, Richard A. Bibcode: 1993ApJ...417..790A Altcode: We analyzed two solar flares of 1992 September 5 and 6, using the high time resolution (64 ms) hard X-ray data from BATSE/CGRO, and 100-3000 MHz radio (100 ms) dynamic spectra from PHOENIX. The broadband radio data reveal a separatrix frequency (at 620 and 750 MHz in the two flares) between normal- and reverse-drifting radio bursts, indicating a compact acceleration source where electron beams are injected in both the upward and downward direction. We find a mean injection rate of 1.2 bursts s-1 in one flare and more than 0.7 bursts s-1 in the other. From 12 broad-band, reverse-drifting radio bursts we find in five cases an unambiguous one-to-one correlation between the reverse-drifting radio bursts and hard X-ray (HXR) pulses of similar duration (400±220 ms). The high significance (15±6 σ) of the HXR pulses and the small scatter (±150 ms) in the relative timing strongly supports a close causal connection. The cross-correlation between HXR and radio pulses shows that the HXR pulses are coincident (within the instrumental time resolution) with the reverse-drifting bursts at the injection frequency (880±50 MHz), and lead the radio bursts by 270±150 ms at the highest observable frequency (1240±100 MHz). The average drift time of the downward propagating radio bursts is measured to 150 ms, corresponding to a drift rate of 2350 MHz s-1.

We examined various effects to model the observed timing of radio and HXR pulses (propagation delays, radio wave growth and damping, group velocity delays, radio wave scattering, radio wave ducting, light path differences, etc.). Assuming an exciter velocity of υR/c = 0.2±0.1 for the reverse-drifting radio bursts, we infer an altitude difference of H = 8000±3000 km between the injection site and the HXR source. The most likely explanation for the retarded radio emission seems to be a combination of the following two effects: (1) HXR-emitting (>25 keV) and radio-emitting electrons have different energies (the exciter velocity of the reverse-drifting radio bursts is associated with ≲5 keV electrons), and (2) a low (marginal) growth rate for plasma emission at the second harmonics. Delay effects caused by group velocity, collisional damping, wave scattering, and wave ducting are found to be minor (<30 ms each). Title: Quasi-periodic Particle Injection into Coronal Loops Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.; Gaizauskas, Victor Bibcode: 1993ApJ...416..857A Altcode: We present observations of the flare of 1989 June 22, 1445 UT (in active region NOAA 5555), obtained with the Hard X-Ray Burst Spectrometer (HXRBS) on SMM at energies >52 keV, and with the broad-band radio spectrometer PHOENIX at ETH/Zurich in the frequency range of 100-2800 MHz. The radio emission is dominated by a ≲100% polarized decimetric continuum at 400-1400 MHz, peaking at 750 MHz. The decimetric radio flux is highly correlated with the 50-150 keV hard X-ray flux but is delayed by 3.5-5.4 s with respect to the hard X-rays. The HXR emission shows an excess of ≳10 fast (≳100 ms) spikes (according to Poisson statistics). The radio emission exhibits weak fine structure, consisting of ≍45 quasi-periodic pulses with a mean period of 1.6 s. The frequency-time drift pattern of this fine structure is found to be consistent with segments of inverted-U type bursts, suggesting quasi-periodic injection of electron beams into a loop system. The loop system has an average height of 68,000 km and expands with a velocity of 200 km s-1 due to flare heating. Chromospheric evaporation enhances the electron density near the footpoints. The type III- exciting electrons have a mean velocity of υ/c = 0.30±0.10 (22 keV) and propagate along inverted-U burst trajectories with a mean duration of 2.5 s. For those electrons which reach the mirror point near the opposite footpoint of the loop system, we calculate (from the density and loop length) a low energy cutoff of ≥ 8 keV due to collisional deflection, yielding a propagation velocity of v/c = 0.18 and a propagation delay of 5.1±1.0 s, which agrees well with the observed delay of 5.16 s between the cross-correlated HXR and radio flux. The ≥ 8 keV electrons provide free energy for a loss cone instability near the secondary footpoint, which is observed as decimetric continuum polarized in the same sense of circular polarization as the type III bursts. The constraints from the Hα flare position and the magnetic potential field extrapolation indicate that the loss cone emission is produced in the diverging field region above the umbra of the leading sunspot, which has a photospheric field strength of -1600 G.

This flare allows us to deconvolve quasi-periodic particle injection and subsequently triggered coherent radio emission from trapped particles in flare-associated loops. It demonstrates that quasi-periodic modes of particle acceleration, particle dynamics in mirror loops, and the resulting plasma instabilities can be efficiently diagnosed from correlated hard X-ray and radio signatures. Title: Analysis of solar spike events by means of symbolic dynamics methods Authors: Schwarz, U.; Benz, A. O.; Kurths, J.; Witt, A. Bibcode: 1993A&A...277..215S Altcode: Using quantities of symbolic dynamics, such as mutual information, Shannon information and algorithmic complexity, we have searched for interrelations of spikes emitted simultaneously at different frequencies during the impulsive phase of a flare event. As the spikes are related to the flare energy release and are interpreted as emissions originating at different sites having different magnetic field strengths, any relation in frequency is interpreted as a relation in space. This approach is appropriate to characterize such spatio-temporal patterns, whereas the popular estimate of fractal dimensions can be applied to low-dimensional systems only.

Depending on the energy release and emission processes, two types of fragmentation are possible: a scenario of global organization (spikes are emitted in a succession of similar events by the same system) or a scenario of local organization (many systems triggered by an initial event).

Mutual information which is a generalization of correlation indicates a relation in frequency beyond the bandwidth of individual spikes. The scans in the spectrograms with large mutual information also show a low level of Shannon information and algorithmic complexity, indicating that the simultaneous appearance of spikes at other frequencies is not a completely stochastic phenomenon (white noise). It may be caused by a nonlinear deterministic system or by a Markov process. By means of mutual information we find a memory over frequency intervals up to 60 MHz. Shannon information and algorithmic complexity concern the whole frequency region, i.e. the global source region. A global organization is also apparent in quasi- periodic changes of the Shannon information and algorithmic complexity in the range of 2 - 8 seconds.

The finding is compatible with a scenario of local organization in which the information of one event spreads spatially and triggers further events at different places. The region is not an ensemble of independently flashing sources, each representing a system that cascades in energy after an initial trigger. On the contrary, there is a causal connection between the sources at any time. The analysis of the four spike events suggests that the structure in frequency is not stochastic but a process in which spikes at nearby locations are simultaneously triggered by a common exciter. Title: The bandwidth of millisecond radio spikes in solar flares Authors: Csillaghy, A.; Benz, A. O. Bibcode: 1993A&A...274..487C Altcode: The bandwidth of 196 individual millisecond spikes has been measured and analyzed. The spikes occurred in the impulsive phase of eight solar flares in different active regions. The measurements have been made at various frequency resolutions and spectral windows in the range from 0.1 to 8.5 GHz. The major results are (i) that the individual bandwidths show a scatter of a factor 2-3 or more within an event, (ii) that the mean bandwidth differs significantly from event to event at the same center frequency, (iii) that the mean bandwidth increases only slightly with the center frequency and (iv) that there is no qualitative difference between spikes in decimeter waves and spikes in microwaves. The results show that there is no intrinsic bandwidth of spikes, suggesting that accidental source parameters are responsible for the width of the emission. The observed decrease of the mean Δν/ν with frequency is interpreted as a decrease of the mean source diameter at lower source altitude. Title: Similar X-Ray/Microwave Ratios in Solar Flares and Coronae of Active Stars Authors: Benz, A. O.; Gudel, M. Bibcode: 1993AAS...182.4606B Altcode: 1993BAAS...25..874B We have compared the soft X-ray/microwave ratio of solar and stellar flares with the ratio of the corresponding `quiescent' emissions of active M and K stars and other active stars. Solar flare X-ray observations by the GOES satellite have been converted into total luminosities (erg/s) using the inferred temperature and emission measure, and standard X-ray model spectra. Microwave luminosities (erg/sHz) near the spectral peak of gyrosynchrotron emission (5-10 GHz) have been selected. The average ratio is 10({15.9+/-) 0.2} Hz for impulsive and gradual flares, and slightly more for microflares. Highly polarized stellar flare microwave emission is probably of different origin and cannot be compared. The only simultaneous observation of stellar flare X-rays and unpolarized microwaves in the literature has a luminosity ratio of 10(15.5) Hz. The average ratio between `quiescent' X-ray and microwave luminosities of young, rapidly rotating M and K stars has previously been reported to be 10(15.5) Hz. It is only slightly smaller for Algols, RS CVn binaries and post T Tauri stars. The observation of comparable ratios between thermal X-rays and gyrosynchrotron emission in the `quiescent' active coronae and solar/stellar flares suggests that the coronal heating mechanism and the flare energy release are similar physical processes. In particular, the heating process of active stellar coronae seems to be associated by acceleration of electrons. This research is supported by the Swiss National Science Foundation, NASA, the University of Colorado, and NIST. Title: Strong Microwave Radiation from ``Solar-Twin'' GV Stars Authors: Gudel, M.; Schmitt, J. H. M. M.; Benz, A. O. Bibcode: 1993AAS...182.4607G Altcode: 1993BAAS...25..874G We report the detection of four solar-type main-sequence G stars as strong, steady 8.5 GHz VLA microwave sources. The targets were X-ray selected based on a previously reported relation between quiescent X-ray and microwave luminosities (L_X and L_R) of active stars. L_X was obtained from the ROSAT All-Sky Survey. The fluxes of the radio detections (6<= sigma <= 13) match our predictions within ~ 0.05 -- 0.2 dex (for age estimates, see references below): \begin{tabular}{lllllll} star & spect. & d(pc) & flux (mJy) & logL_R & logL_X & age (yrs) & & & & & & Gl 97 & G1V & 13 & 0.28+/-0.035 & 13.8 & 28.9 & ~ 2* 10(9) Gl 755 & G5V & 19 & 0.19+/-0.031 & 13.9 & 29.4 & ... Gl 559.1 & dG0e & 21 & 0.34+/-0.025 & 14.3 & 29.6 & ~ 0.07* 10(9) HR 9107 & G2V & 29 & 0.19+/-0.030 & 14.3 & 29.5 & ~ 10* 10(9) Gl 97 (see, e.g., Soderblom ApJS 53,1) and Gl 755 are single MS stars. Gl 559.1 is a very rapidly rotating, chromospherically extremely active young star probably just settling on the main sequence (Soderblom & Clements AJ 93, 920; Elias & Dorren AJ 100, 818). A widely separated companion has been suspected (Duquennoy & Mayor A&A 248, 485), but we reason that the radio emission comes from the G star. The surprise detection is HR 9107, a metal-deficient, high space velocity, old-disk population star just leaving the MS (see Deliyannis et al. ApJS 73, 21). Brightness temperature estimates based on an optically thin plasma likely suggest nonthermal emission, probably gyrosynchrotron as on other active stars. These detections extend the dichotomy between active and inactive stars into the range of solar-type stars. We are currently proposing detailed investigations of these stars. This research is supported by the Swiss National Science Foundation, NASA, CU, and NIST; the NRAO VLA is supported by Associated Universities, Inc. and the US NSF. Title: X-Ray/Microwave Relation of Different Types of Active Stars Authors: Guedel, Manuel; Benz, Arnold O. Bibcode: 1993ApJ...405L..63G Altcode: Coronal active stars of seven classes between spectral types F and M, single and double, are compared in their quiescent radio and X-ray luminosities L(R) and L(X). We find, largely independent of stellar class, log L(X) is less than about log L(R) + 15.5. This general relation points to an intimate connection between the nonthermal, energetic electrons causing the radio emission and the bulk plasma of the corona responsible for thermal X-rays. The relation, observed over six orders of magnitude, suggests that the heating mechanism necessarily involves particle acceleration. We derive requirements for simple models based on optically thin gyrosynchrotron emission of mildly relativistic electrons and thermal X-rays from the bulk plasma. We discuss the possibility that a portion of the accelerated particles heats the ambient plasma by collisions. More likely, plasma heating and particle acceleration may occur in parallel and in the same process, but at a fixed ratio. Title: Plasma astrophysics: Kinetic processes in solar and stellar coronae Authors: Benz, Arnold O. Bibcode: 1993ASSL..184.....B Altcode: 1993pakp.book.....B; 1993QB529.B46...... No abstract at ADS Title: VLBI Observations of a stellar flare Authors: Alef, W.; Benz, A. O.; Güdel, M.; de Vicente, P. Bibcode: 1993sara.conf...28A Altcode: No abstract at ADS Title: A General Correlation between X-Ray and Radio Luminosities of Active Stars Authors: Gudel, M.; Benz, A. O. Bibcode: 1992AAS...181.5109G Altcode: 1992BAAS...24.1206G We have studied the relation between the quiescent radio and X-ray luminosities L_6cm and L_X of a variety of late-type active stars (M and K dwarfs, BY Dra binaries, RS CVn binaries, Algol binaries, FK Comae stars, weak-lined T Tau stars). We find a general relation logL_X <= logL_R + 15.5 that is valid over 6 orders of magnitude in luminosity. RS CVn's, Algols, FK Com stars, and WTTS tend to be ``microwave-rich''. This relation points to an intimate connection between the nonthermal, energetic electrons causing the radio emission and the coronal bulk plasma responsible for thermal X-rays. We have tested the hypothesis that particles accelerated in quasi-continuous flare-like processes emit synchrotron radiation during their lifetime and finally lose energy in collisions, thereby heating the coronal plasma. This scenario requires commonly assumed values for the magnetic field strength (100 G) and produces acceptable electron lifetimes. Title: Electron Beams in the Low Corona Authors: Benz, A. O.; Magun, A.; Stehling, W.; Su, H. Bibcode: 1992SoPh..141..335B Altcode: Selected high-resolution spectrograms of solar fast-drift bursts in the 6.2-8.4 GHz range are presented. The bursts have similar characteristics as metric and decimetric type III bursts: rise and decay in a few thermal collision times, total bandwidth ≳3% of the center frequency, low polarization, drift rate of the order of the center frequency per second, and flare association. They appear in several groups per flare, each group consisting of some tens of single bursts. Fragmentation is also apparent in frequency; there are many narrowband bursts randomly scattered in the spectrum. The maximum frequency of the bursts is highly variable. Title: Millisecond microwave spikes at 8 GHz during solar flares Authors: Benz, A. O.; Su, H.; Magun, A.; Stehling, W. Bibcode: 1992A&AS...93..539B Altcode: Highly circularly polarized spikes have been observed during solar flares up to 8 GHz. The typical half-power bandwidth was 120 MHz, and the duration was less than the time resolution of 100 ms. A group of 46 spikes in the 6.5 - 8.0 GHz range has been observed at the maximum of an H-alpha flare and within 3 s of the peak of microwave emission observed at 2.7 GHz by other observatories. The peak flux of the spikes reached 60 sfu above background. These emissions closely resemble the spikes previously reported at lower frequency. If interpreted as second harmonic of the electron gyrofrequency, a magnetic field exceeding 1400 G would be requested in the corona. Title: Decimetric Solar Type U Bursts: VLA and PHOENIX Observations Authors: Aschwanden, Markus J.; Bastian, T. S.; Benz, A. O.; Brosius, J. W. Bibcode: 1992ApJ...391..380A Altcode: Observations of type U bursts, simultaneously detected by the VLA at 1.446 GHz and by the broadband spectrometer Phoenix in the 1.1-1.7 GHz frequency band on August 13, 1989 are reported. Extrapolations of the coronal magnetic field, assuming a potential configuration, indicate that the VLA 20 cm source demarcates an isodensity level. The source covers a wide angle of diverging magnetic field lines whose footpoints originate close to a magnetic intrusion of negative polarity into the main sunspot group of the active region with dominant positive polarity. The centroid of the 20-cm U-burst emission, which corresponds to the turnover frequency of the type U bursts and remains stationary during all U bursts, coincides with the apex of extrapolated potential field lines at a height of about 130,000 km. It is demonstrated that the combination of radio imaging and broadband dynamic spectra, combined with the magnetic field reconstruction from magnetograms, can constrain all physical parameters of a magnetic loop system. Title: VLA, PHOENIX and BATSE observations of an X1 flare. Authors: Willson, Robert F.; Aschwanden, Markus J.; Benz, Arnold O. Bibcode: 1992NASCP3137..515W Altcode: 1992como.work..515W The authors present observations of an X1 flare (Jul 18, 1991) detected simultaneously with the VLA, the PHOENIX Digital Radio Spectrometer and the Burst and Transient Source Experiment (BATSE) aboard the Gamma Ray Observatory. The VLA was used to produce snapshot maps of the impulsive burst emission on timescales of 1.7 sec at both 20 and 91 cm. The results indicate electron acceleration in the higher corona several minutes before the onset of the hard X-ray burst detected by BATSE. Comparisons with high spectral and temporal observations by PHOENIX reveal a variety of radio bursts at 20 cm, such as type III bursts, intermediate drift bursts, and quasi-periodic pulsations during different stages of the X1 flare. The described X1 flare is unique in the sense that it appeared at the east limb, providing the most accurate information on the vertical structure of different flare tracers visible in radio wavelengths. Title: Characteristics of the impulsive phase of flares Authors: Benz, A. O.; Aschwanden, M. J. Bibcode: 1992LNP...399..106B Altcode: 1992esf..coll..106B; 1992LNP...399..106A; 1992IAUCo.133..106B The impulsive phase of flares is an observational concept, characterized by spiky emissions from -rays to radio waves. It is generally agreed that during this time a large fraction of the. original flare energy resides in energetic particles which are manifested in these emissions. Here we concentrate on recent decimeter and microwave observations that indicate a high level of fragmentation of this energy release when related to hard X-ray (HXR) flux. Recent attempts to characterize the flare and the distribution of the radio bursts in time and frequency by statistical methods are also reviewed. Title: VLA, PHOENIX and BATSE observations of an X1 flare Authors: Willson, Robert F.; Aschwanden, Marcus J.; Benz, Arnold O. Bibcode: 1992STIN...9227935W Altcode: We present observations of an X1 flare detected simultaneously with the Very Large Array (VLA), the PHOENIX Digital Radio Spectrometer, and the Burst and Transient Source Experiment (BATSE) aboard the Gamma Ray Observatory (GRO). The VLA was used to produce snapshot maps of the impulsive burst emission in the higher corona on timescales of 1.7 seconds at both 20 and 01 cm. Our results indicate electron acceleration several minutes before the onset of the hard X-ray burst detected by BATSE. Comparisons with high spectral and spatial observations by PHOENIX reveal a variety of radio bursts at 20 cm, such as type III bursts, intermediate drift bursts, and quasi-periodic pulsations during different stages of the X1 flare. From the drift rates of these radio bursts we derive information on local density scale heights, the speed of radio exciters, and the local magnetic field. Radio emission at 90 cm shows a type IV burst moving outward with a constant velocity of 240 km/sec. The described X1 flare is unique in the sense that it appeared at the east limb (N06/E88 providing the most accurate information on the vertical structure of different flare tracers visible in radio wavelengths. Title: VLBI observations of YZ CMi - a single dMe star. Authors: Benz, A. O.; Alef, W. Bibcode: 1991A&A...252L..19B Altcode: The quiescent (nonflaring) radio emission of the single dMe star YZ CMi was detected in an intercontinental VLBI experiment at 1.7 GHz. A radio diameter of the star of 1.0 + or - 0.5 mas was found, statistically compatible with zero. The formal value corresponds to 1.7 optical stellar diameters and yields a brightness temperature of 1.7 x 10 exp 9 K with a lower limit of 4 x 10 exp 8 K. This high brightness strongly suggests emission by nonthermal particles by the gyrosynchrotron mechanism or an incoherent process. Title: The association of solar millisecond radio spikes with hard X-ray emission Authors: Guedel, M.; Benz, A. O.; Aschwanden, M. J. Bibcode: 1991A&A...251..285G Altcode: Conventional observational data regarding solar millisecond spikes are compared with data gathered simultaneously in the hard X-ray band by means of a statistical analysis. The analysis considers the association rate, correlation degree, and relative time delays between hard X-ray emissions (in the 25-438 keV range) and radio-spike events. About 95 percent of the radio-spike bursts occur during impulsive hard X-ray bursts, and approximately 43 percent of the compared events are characterized by hard X-ray time profiles that mimic the concentration of simultaneous radio spikes. The delay of the radio emission with respect to the hard X-ray bursts puts some constraints on the acceleration and propagation of particles. The time delays and the quantization into discrete radio events are theorized to be caused by the operation of the accelerator. Title: The attractor dimension of solar decimetric radio pulsations Authors: Kurths, J.; Benz, A. O.; Aschwanden, M. J. Bibcode: 1991A&A...248..270K Altcode: The temporal characteristics of decimetric pulsations and related radio emissions during solar flares are analyzed using statistical methods recently developed for nonlinear dynamic systems. The results of the analysis is consistent with earlier reports on low-dimensional attractors of such events and yield a quantitative description of their temporal characteristics and hidden order. The estimated dimensions of typical decimetric pulsations are generally in the range of 3.0 + or - 0.5. Quasi-periodic oscillations and sudden reductions may have dimensions as low as 2. Pulsations of decimetric type IV continua have typically a dimension of about 4. Title: A broadband spectrometer for decimetric and microwave radio bursts: First results Authors: Benz, A. O.; Guedel, M.; Isliker, H.; Miszkowicz, S.; Stehling, W. Bibcode: 1991SoPh..133..385B Altcode: A new spectrometer has been put into operation that registers solar flare radio emission in the 0.1 to 3 GHz band. It is a frequency-agile system which can be fully programmed to measure both senses of circular polarization at any frequency within that range at selectable bandwidth. The time resolution has to be compromized with the number of frequency channels and can be in the range of 0.5 ms to 250 ms for 1 to 500 channels. First results mainly from the 1-3 GHz band are presented, a spectral region that has never been observed with high-resolution spectrometers. Most noteworthy are the frequent appearances of myriads of narrowband, fast-drifting bursts (microwave type III), diffuse patches of continuum emission, and broad clusters of millisecond spikes sometimes extending from 0.3 to 3 GHz. Title: Coordinated VLA-PHOENIX-SMM Observations: Microwave Type U-Bursts Authors: Aschwanden, M. J.; Bastian, T. S.; Benz, A. O.; Dennis, B. R. Bibcode: 1991BAAS...23.1065A Altcode: No abstract at ADS Title: A Mechanism for Producing Plasma Radiation in the Gigahertz Range by Precipitating High Energy Protons Authors: Smith, D. F.; Benz, A. O. Bibcode: 1991SoPh..131..351S Altcode: Gamma-ray observations are discussed to determine the density of protons of about 1 MeV precipitating to the photosphere. It is shown that Coulomb collisions will produce a positive slope in the proton distribution for energies less than 0.1 MeV for traversed column depths greater than 1018 cm −2. This could lead to plasma wave emission and radiation near the plasma frequency for densities ∼ 3.1 × 1010 cm−3 and temperatures ∼ 4.0 × 104 K where collisional and collisionless damping of the plasma waves is sufficiently weak. It is expected that these conditions will only be satisfied sporadically which leads to stationary radio emission limited in frequency and time. Recent radio observations of impulsive phase non-drifting patches in the 1-3 GHz range with duration 2-4 s are presented which could be produced by this mechanism. Title: Coronal Radio Emission (With 7 Figures) Authors: Benz, A. O. Bibcode: 1991mcch.conf..140B Altcode: No abstract at ADS Title: The dynamic sun. Authors: Benz, A. O. Bibcode: 1991EN.....22...19B Altcode: No abstract at ADS Title: Simultaneous Radio and Hard X-ray Observations by PHOENIX/Zurich and HXRBS/SMM during Max'91 (June 1989) Authors: Aschwanden, M. J.; Dennis, B. R.; Benz, A. O. Bibcode: 1991max..conf..234A Altcode: No abstract at ADS Title: Solar flare microwave observations with high spectral resolution Authors: Bruggmann, G.; Magun, A.; Benz, A. O.; Stehling, W. Bibcode: 1990A&A...240..506B Altcode: The solar flare radio emission in the 6-8 GHz range was observed with a high resolution spectrometer. The observed band corresponds to the plasma frequencies and gyrofrequencies of the transition region and the lowest part of the corona in active regions. Most of the emissions were found to be broadbanded, as expected from the gyrosynchrotron mechanism. In eight out of 46 observed events, spectral structures of three types were detected: spikes below the time resolution of 100 ms, slowly drifting broadband structures, and a narrow bandwidth patch of continuum emission. These first narrowband bursts spectrally recorded in the 6-8 GHz range are generally weak. Slowly drifting structures are the only type compatible with the gyrosynchrotron emission mechanism. A simple argument based on free-free absorption shows that plasma emission can only be propagated if the radiation originates in a dense region with a small density-scale length. The same holds for maser emission at a low harmonic of the electron gyrofrequency. Possible emission mechanisms and diagnostic capabilities are discussed. Title: Hard X-Rays and Associated Weak Decimetric Bursts Authors: Sawant, H. S.; Lattari, C. J. B.; Benz, A. O.; Dennis, B. R. Bibcode: 1990SoPh..130...57S Altcode: In previous attempts to show one-to-one correlation between type III bursts and X-ray spikes, there have been ambiguities as to which of several X-ray spikes are correlated with any given type III burst. Here, we present observations that show clear associations of X-ray bursts with RS type III bursts between 16:46 UT and 16:52 UT on July 9, 1985. The hard X-ray observations were made at energies above 25 keV with HXRBS on SMM and the radio observations were made at 1.63 GHz using the 13.7m Itapetinga antenna in R and L polarization with a time resolution of 3 ms. Title: Flare fragmentation and type III productivity in the 1980 June 27 flare Authors: Aschwanden, M. J.; Benz, A. O.; Schwartz, R. A.; Lin, R. P.; Pelling, R. M.; Stehling, W. Bibcode: 1990SoPh..130...39A Altcode: We present observations of the solar flare on 1980 June 27, 16:14-16:33 UT, which was observed by a balloon-borne 300 cm2 phoswich hard X-ray detector and by the IKARUS radio spectrometer. This flare shows intense hard X-ray (HXR) emission and an extreme productivity of (at least 754) type III bursts at 200-400 MHz. A linear correlation was found between the type III burst rate and the HXR fluence, with a coefficient of ≈ 7.6 × 1027 photons keV−1 per type III burst at 20 keV. The occurrence of ≈ 10 type III bursts per second, and also the even higher rate of millisecond spikes, suggests a high degree of fragmentation in the acceleration region. This high quantization of injected beams, assuming the thick-target model, shows up in a linear relationship between hard X-ray fluence and the type III rate, but not as fine structures in the HXR time profile. Title: Preface Authors: Benz, A. O.; Magun, A. Bibcode: 1990SoPh..130....1B Altcode: No abstract at ADS Title: Time Delays Between Decimetric Type-Iii Bursts and Associated Hard X-Rays Authors: Sawant, H. S.; Lattari, C. J. B.; Benz, A. O.; Dennis, B. R. Bibcode: 1990RMxAA..21..562S Altcode: . In July, 1985 radio observations were made at 1.6 GHz using 13.7 m Itapetinga antenna with time resolution of 3 ms. The hard X-ray observations were obtained from HXRBS on SMM. Comparison of 1.6 GHz observations with dynamic spectra in the frequency range of (1000 - 100) MHz and hard X-rays shows the following results: i) In 12 cases, we identify continuation of type Ill-RD bursts up to 1.6 GHz suggesting presence of type Ill-RD bursts at 1.6 GHz. ii) For the first time, we have idetified hard X-ray peaks delayed in comparison to decimetric type Ill-RD bursts. These dalays are longer - 1 5 - than expected ( 100 ms) and have been interpreted assuming that the decimetric emission is at 2 nd harmonic and caused by the leading edge of the exciter, whereas peaks of X-rays have been attributed to entire entry of the exciter into the X-ray producing region. Keq : SUN BURSTS - SUN- Title: Alfven wave solitons and solar intermediate drift bursts Authors: Treumann, R. A.; Guedel, M.; Benz, A. O. Bibcode: 1990A&A...236..242T Altcode: Stationary resolutions for Alfven solitons propagating obliquely in a homogeneous magnetic field are investigated. Due to their dispersive nature, kinetic Alfven waves can evolve into solitonlike structures which propagate at velocities of the order of the Alfven velocity in a direction inclined to the magnetic field. In a first model, a cold plasma with beta less than m(e)/m(i) is considered. In the second model, the plasma contains two electron components, a hot one and a cold one. Differential equations are derived for the plasma density, and examples of numerical solutions for the plasma density profiles are presented. Kinetic Alfven solitons can propagate in both cases at Mach numbers M greater than 1 or M less than 1, as rarefactions or as compressions of the plasma density. It is found that, in both models, rarefaction and compressional solitons are uniquely determined by beta and the propagation velocity vector. Interactions between the hot and cold electron components turn out to be significant for rarefactions of the cold component. Conditions are given for the existence of soliton solutions. The super-Alfven kind of solitary waves are applied to solar intermediate drift radio bursts. With a model of the emission process, they can be used to determine the magnetic field and the electron density of the source. Title: VLA-PHOENIX Observations of Coronal Activity Authors: Willson, R. F.; Lang, K. R.; Benz, A. O. Bibcode: 1990BAAS...22.1196W Altcode: No abstract at ADS Title: Statistical Study of the Correlation of Hard X-Ray and Type III Radio Bursts in Solar Flares Authors: Hamilton, Russell J.; Petrosian, Vahe; Benz, A. O. Bibcode: 1990ApJ...358..644H Altcode: A large number of hard X-ray events which occurred during the maximum of solar cycle 21 have been analyzed in order to study their correlation with type III bursts. It is found that the distribution of occurrences of hard X-ray bursts correlated with type III radio bursts is significantly different from the distribution of all hard X-ray bursts. This result is consistent with the assumption that the hard X-ray and type III intensities are somewhat correlated. A bivariate distribution function of the burst intensities is fitted to the data and is used to determine that the typical ratio of X-ray intensity to type II intensity is about 10 and that the ratio of the number of X-ray producing-electrons to type III-producing electrons is about 1000. Three models which have been proposed to explain the relation between the accelerated hard X-ray and type III-producing electrons are examined in the context of these observations. Title: Book-Review - Instabilities in Space and Laboratory Plasmas Authors: Melrose, D. B.; Benz, A. O. Bibcode: 1990SoPh..128..427M Altcode: 1990IAUCo.121P.427M No abstract at ADS Title: Book reviews Authors: Rayrole, J.; Benz, A. O. Bibcode: 1990SoPh..128..427R Altcode: No abstract at ADS Title: Time profiles of solar radio spikes Authors: Guedel, M.; Benz, A. O. Bibcode: 1990A&A...231..202G Altcode: High-resolution observations are carried out to study the time profiles of individual solar radio spikes. The time profiles show a characteristic exponential decay with frequency dependent decay rates. On the assumption of the plasma hypothesis, the following empirical relation between T and the electron density n was found the emitting region. Title: Enhanced Radiation Driven by a DC Electric Field Authors: Tajima, T.; Benz, A. O.; Thaker, M.; Leboeuf, J. N. Bibcode: 1990ApJ...353..666T Altcode: Direct radiation by runaway electrons under a constant (dc) electric field is investigated. In a one-and-two-halves-dimensional relativistic EM code, an electron beam propagates along the external magnetic field parallel to the dc field and quickly decays into a runaway tail sustained by the dc field. Electrostatic and transverse waves are observed at various (fixed for each particular run) angles of wave propagation. Both plasma waves and EM radiation are strongly enhanced by the runaway tail. In the linear and early nonlinear beam stages, the EM wave energy is slightly enhanced as the associated electrostatic component of the waves (together with the dc field) traps and detraps electrons. In the late nonlinear (runaway) stage and with sufficiently large observing angle, bursts of EM wave energy occur, accompanied by fast perpendicular spreading of the distribution function, and they coincide with clamping of runaway electron momenta. A possible application is to msec radio spikes associated with solar flares. In this situation, the possibility of the present mechanism yielding radiation temperatures in excess of 10 to the 15th K is not out of the question. Title: Correlation of solar radio pulsations with hard X-ray emission Authors: Aschwanden, M. J.; Benz, A. O.; Kane, S. R. Bibcode: 1990A&A...229..206A Altcode: A systematic study of the correlation of quasi-periodic broad-band decimetric pulsations with hard X-ray (HXR) emission is carried out. It is found that, in 11 out of 56 simultaneously observed events, the decimetric quasi-periodic pulsations in the impulsive phase of flares are correlated. If events with concurring type III bursts are included, 19 cases of radio pulsations are correlated with HXR. Title: A plasma radiation model for the prompt radio emission of supernova 1987A. Authors: Benz, A. O.; Spicer, D. S. Bibcode: 1990A&A...228L..13B Altcode: We propose that the prompt radio emission of supernova 1987A a few days after the explosion is the result of a plasma interaction between the ejecta and the presupernova circumstellar matter. The emission frequency then is determined by the electron density in the front of the ejecta and the radio flux density mainly depends on the velosity of the ejecta and the circumstellar electron density. Free-free absorptions in the interaction region and by the circumstellar medium limit the emission on the high, respectively low frequency side and inhabit observable emission in the first two days. Title: Broadband Spectral Radio Observations of Flare Stars Authors: Benz, A. O.; Guedel, M.; Bastian, T. S.; Fuerst, E.; Simnett, G. M.; Pointon, L. Bibcode: 1990IAUS..137..139B Altcode: The first broadband spectrometer observation of a stellar flare event is reanalyzed and discussed. Rough estimates of the stellar source parameters are given, including the source size, exciter drift velocity, and source magnetic field. An interpretation in terms of coherent cyclotron emission is presented. Title: The Attractor Dimension of Solar Decimetric Radio Pulsations Authors: Kurths, J.; Benz, A. O.; Aschwanden, M. J. Bibcode: 1990PDHO....7..196K Altcode: 1990dysu.conf..196K; 1990ESPM....6..196K The authors have analyzed the temporal characteristics of decimetric pulsations and related radio emissions during solar flares. Title: Alfven wave solitons and solar intermediate drift bursts Authors: Treumann, R. A.; Guedel, M.; Benz, A. O. Bibcode: 1990STIN...9029287T Altcode: Stationary solutions for the Alfven solitons propagating obliquely in a homogeneous magnetic field are investigated. Due to their dispersive nature kinetic Alfven waves can evolve into soliton like structures which propagate at velocities of the order of the Alfven velocity in a direction inclined to the magnetic field. In a first model, a cold plasma with beta less than (me/m sub i) is considered. In the second model the plasma contains two electron components, a hot one and a cold one. Differential equations for the plasma density are derived and examples of numerical solutions for the plasma density profiles are presented. Kinetic Alfven solitons can propagate in both cases at Mach numbers M greater or less than 1, as rarefactions or as compressions of the plasma density. In both models rarefaction and compressional solitons are uniquely determined by beta and the propagation velocity vector. Interaction between the hot and cold electron components turn out to be significant for rarefactions of the cold component. Conditions for the existence of soliton solutions are given. The super-Alfvenic kind of solitary waves are applied to solar intermediate drift radio bursts. With a model of the emission process they can be used to determine the magnetic field and the electron density of the source. Title: Particle beams in the solar atmosphere. Authors: Benz, A. O.; Magun, Andreas Bibcode: 1990pbsa.book.....B Altcode: No abstract at ADS Title: Vla-Phoenix Observations of a Narrow-Band Decimetric Burst Authors: Willson, Robert F.; Benz, Arnold O. Bibcode: 1990IAUS..142..525W Altcode: A discussion is conducted regarding observations of a highly-circularly polarized multiply-impulsive microwave burst detected by the Very Large Array and the Phoenix Digital Radio Spectrometer. The VLA was used to resolve the burst in two dimensions, while Phoenix provided high-time-resolution information about its spectral properties. During part of the burst, positive frequency drifts were detected, suggesting inwardly propagating beams of electrons emitting type-III-like radiation. Title: Broadband spectral observations of a dMe star radio flare. Authors: Gudel, M.; Benz, A. O.; Bastian, T. S.; Furst, E.; Simnett, G. M.; Davis, R. J. Bibcode: 1989A&A...220L...5G Altcode: A flare on the dMe star AD Leonis was simultaneously observed with the radio telescopes in Effelsberg, Jodrell Bank, and Arecibo using spectrometers at 1665, 1666, and 1415 MHz with bandwidths of 25, 100, and 40 MHz, respectively. The time coincidence confirms the stellar origin of the radiation. The flare emission was resolved into a multitude of broadband pulsations. Their e-folding rise and decay times were of the order of the time resolution of the Effelsberg data (125 ms), or less. The circular polarization was about 100 percent. Similar bursts, but 4 orders of magnitude less powerful, have been observed from the sun at lower frequencies. Title: VLA detection of radio emission from a dwarf nova. Authors: Benz, A. O.; Guedel, M. Bibcode: 1989A&A...218..137B Altcode: Radio emission was detected at 4.9 GHz from a dwarf nova for the first time with the Very Large Array. This confirms earlier reports based on single or binary dish observations. Radio emission in only one out of eight dwarf novae was detected. The radio source is EM Cyg, an eclipsing binary system. It is variable on the scale of days and is circularly polarized. EM Cyg had an optical outburst, but was not eclipsed during the observations. If interpreted by synchrotron emission the observed radiation requires a source size larger than the binary separation and relatively large magnetic fields. Maser emission of nonthermal electrons reflected in the magnetic field of the white dwarf is a possibly more attractive alternative. A source field of 800-2000 Gauss then is required depending on the most efficient maser mode. Title: Radio continuum emission from the pre-main sequence Herbig AE star ABAurigae. Authors: Guedel, M.; Benz, A. O.; Catala, C.; Praderie, F. Bibcode: 1989A&A...217L...9G Altcode: Two Herbig Ae stars have been observed in the radio range with the Very Large Array for the first time. One of these stars, HD 250550, was not detected, while the other object, AB Aur, was detected twice at 3.6 cm and once at 6 cm. A slight time variation was found at 3.6 cm, and its flux agrees with free-free emission of a thermal wind source having M-dot = 1.5 x 10 to the -8th solar mass/yr (assuming an expansion velocity of 400 km/s) compatible with quasi-simultaneous optical line observations. The radio spectrum, however, deviates from a simple nu exp 0.6-law, showing excess radiation at 6 cm. The possibility exists that it originates from nonthermal electrons emitting synchrotron radiation in a magnetic field. Title: Broad-band spectrum of dMe star radio emission. Authors: Guedel, M.; Benz, A. O. Bibcode: 1989A&A...211L...5G Altcode: The dMe star UV Ceti was observed at the VLA in all available frequency bands (90, 20, 6, 3.6, 2, and 1.3 cm) on two dates separated by about one week. Beside confirming former reports about quiescent emission at 6 and at 20 cm, nonflaring radio emission has also been discovered at all smaller wavelengths. The radio spectra show a minimum or break at the 3.6 cm band. The radio spectra show a minimum or break at the 3.6 cm band. This behavior is unexpected if the low-frequency emission is synchrotron radiation, as generally believed. It may be interpreted as a different emission increasing to millimetric waves from the well known microwave component. The high frequency component is shown to be compatible with cyclotron radiation of the X-ray emitting plasma. The new component then would require magnetic fields in the source varying from at least 600 up to 2070 Gauss. This suggests nu(B)/nu(p) = 1...10 in the corona of UV Ceti. Title: Radio Emission of Dwarf Novae Authors: Benz, A. O. Bibcode: 1989ASSL..156..113B Altcode: 1989admf.proc..113B The processes giving rise to the radio emission from dwarf novae is discussed. The radiation, which is variable within days and highly polarized, is probably caused by some gyromagnetic process. If it is synchrotron emission, the magnetic field strength in the source is of the order of 40 G. If the emission is due to a cyclotron maser process, the magnetic field is 800-1800 G depending on which harmonic of the local gyrofrequency is emitted. The radio emission appears high compared to the number of available energetic electrons. The particles thus appear to be accelerated by or near the prime source of energy, the accretion disk. Title: Alfvén wave solitons and solar intermediate drift bursts. Authors: Guedel, M.; Benz, A. O.; Treumann, R. A. Bibcode: 1989plap.work...95G Altcode: The authors investigate stationary solutions for Alfvén solitons propagating obliquely in a homogeneous magnetic field. Due to their dispersive nature kinetic Alfvén waves can evolve into soliton like structures which propagate at velocities of the order of the Alfvén velocity in a direction inclined to the magnetic field. In the first model one keeps the plasma β < me/mi. Kinetic Alfvén solitons in this case can propagate at Mach numbers M > 1 or M < 1 as dilutions or as compressions of the plasma density. In the second model the plasma contains two electron components, a hot one and a cold one. The authors derive differential equations for the plasma density and present examples of numerical solutions for the plasma density profiles. They find that both dilutive and compressional solitons are uniquely determined by β and the propagation velocity vector. Conditions are given for the existence of soliton solutions. Interactions between the hot and the cold electron component turn out to be significant for dilutions of the cold component. The authors apply this kind of solitary density waves to solar intermediate drift radio bursts. Title: Particle acceleration. Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1989epos.conf..127V Altcode: Contents: 1. Introduction. 2. Phenomena associated with mildly-relativistic electrons. 3. Phenomena associated with ions and relativistic electrons in solar flares. 4. Theoretical studies of particle acceleration. 5. Achievements - outstanding questions. Title: Solar and stellar flares Authors: Benz, A. O. Bibcode: 1989HiA.....8..539B Altcode: No abstract at ADS Title: Extended coronal shock waves and electron acceleration during solar flares. Authors: Klein, K. -L.; Trottet, G.; Benz, A. O.; Kane, S. R. Bibcode: 1989plap.work..157K Altcode: Extended shock waves in the solar corona have long been thought to be responsible for the electrons of the highest observable energies during big flares where large amounts of electromagnetic radiation from hard X-rays to decametric radio waves are observed. The authors have undertaken a detailed study of the radio signature of such shock waves and of its relation to energetic electrons in the low solar atmosphere, using hard X-ray and wide-band radio observations with high time resolution. The results suggest that the extended coronal shock wave plays a minor part in the acceleration of relativistic electrons observed in the low corona. Title: A catalogue of decimetric solar flare radio emission Authors: Guedel, M.; Benz, A. O. Bibcode: 1988A&AS...75..243G Altcode: Decimetric radio emission is frequently observed during solar flares. This catalogue exhibits a representative selection of typical bursts observed with the ETH high resolution digital spectrometer in the years 1979 - 1983. The data set is confined to the spectral range of 300 - 1000 MHz and to a type of events known to generally occur during the impulsive phase of flares (thus excluding the well-known fine structures of post-flare, decimetric type IV bursts). Most events can be grouped into four major classes, which however show considerable variety. The samples of this catalogue have been selected to display the observed range of multiformity by a commensurate number of typical events. Title: A Plasma Radiation Model for the Prompt Radio Emission of Supernova 1987A Authors: Benz, A. O.; Spicer, D. S. Bibcode: 1988BAAS...20Q.961B Altcode: 1988BAAS...20Z.961B; 1988BAAS...20..961B No abstract at ADS Title: On the Electron-Cyclotron Maser Instability. II. Pulsations in the Quasi-stationary State Authors: Aschwanden, M. J.; Benz, A. O. Bibcode: 1988ApJ...332..466A Altcode: In the previous paper we have studied the electron-cyclotron maser instability of a source in quasi-equilibrium. In a situation of weak diffusion such a state will remain for a limited time regardless of the particular loss-cone instability involved. Here our major interest is in oscillations set up by small disturbances around the steady state. Both the linear growth as well as the coupled diffusion rate are subject to a common oscillation period, since wave growth and diffusion are interlocked by a Lotka-Volterra type of coupled equations. Periods in the limit of small amplitude (limit cycle) of the self-organizing wave-particle system are investigated for the magnetoionic X- and O-mode and for harmonic numbers s = 1, 2 of the maser instability. Pulsation periods in the order of 1 s, as observed in the decimetric range of solar flare emission are found exist for (1) fundamental (s = 1) O-mode for 0.3 < ωp/Ωe ≲ 1.0, and (2) harmonic (s = 2) X-mode (for 1.0 ≲ ωp/Ωe 1.4). The period is sensitive to variations of the shape of the loss-cone and therefore not stable. The proposed model provides an interpretation of the observed quasi-periodic decimetric solar pulsations as well as some of similar stellar phenomena. Title: On the Electron-Cyclotron Maser Instability. I. Quasi-linear Diffusion in the Loss Cone Authors: Aschwanden, M. J.; Benz, A. O. Bibcode: 1988ApJ...332..447A Altcode: Emission and quasi-linear velocity diffusion by the electron-cyclotron maser instability are studied under conditions of continuous operation. For the first time, the maser-induced quasi-linear diffusion is computed with the same accuracy as the well-known linear growth rates, including integration along the actual resonance space in k-space. This permits the feedback of the emission on the particle distribution to be quantified. A novel result is the discovery of relatively long diffusion time scales for typical solar conditions. Oscillations set up by small disturbances around the steady state are considered. Periods in the limit of small amplitude of the self-organizing wave-particle system are investigated for the magnetoionic X- and O-mode and for harmonic numbers s = 1, 2 of the maser instability. Pulsation periods in the order of 1 s, as observed in the decimetric range of solar flare emission, are found to exist for fundamental O-mode and for harmonic X-mode. Title: Radio emission of coronal shock waves Authors: Benz, A. O.; Thejappa, G. Bibcode: 1988A&A...202..267B Altcode: The "backbone" emission of shock initiated coronal (metric) type II solar radio bursts is considered. The source has extremely narrow bandwidth and appears to be stationary in relation to the shock. The increasingly complete understanding of the phenomena associated with the Earth's bow shock is tapped for suggestions on the responsible particles, their energies and the emission mechanism of radio waves. The authors propose that the radiation originates from electrons and ions of a few keV energy, the dominant populations of accelerated particles upstream of the bow shock. A model is developed which can explain the major observed features by wave-wave coupling between electron plasma waves themselves and with ion waves. Observational tests at interplanetary and bow shock waves are proposed. Title: Book-Review - Radio Continua during Solar Flares Authors: Benz, A. O. Bibcode: 1988ApL&C..26..376B Altcode: 1988ApL....26..376B No abstract at ADS Title: Stochastic Acceleration of Electrons in Solar Flares Authors: Benz, A. O.; Smith, D. F. Bibcode: 1987SoPh..107..299B Altcode: The generation of lower-hybrid waves by cross-field currents is applied to reconnection processes proposed for solar flares. Recent observations on fragmentation of energy release and acceleration, and on hard X-ray (HXR) spectra are taken into account to develop a model for electron acceleration by resonant stochastic interactions with lower-hybrid turbulence. The continuity of the velocity distribution is solved including collisions and escape from the turbulence region. It describes acceleration as a diffusion process in velocity space. The result indicates two regimes that are determined by the energy of the accelerating electrons which may explain the double power-law often observed in HXR spectra. The model further predicts an anticorrelation between HXR flux and spectral index in agreement with observations. Title: Small-scale structure in solar flare radio emission. Authors: Benz, A. O. Bibcode: 1987ESASP.275..105B Altcode: 1987sspp.symp..105B High resolution radio observations of type 3 solar flares and spike bursts are presented. Considerable fragmentation appears in time and spectrum, indicating that many, small sources are involved. The structure in type 3 emission requires more than 100 distinct injections or acceleration events in a flare studied. There are suggestions of orders of magnitude higher fragmentation in the acceleration process from type 3 bursts and spikes. Small scale structures in flares may control the energy release and its time scale. Title: Book-Review - Radio Continua during Solar Flares Authors: Benz, A. O.; Brown, J. C. Bibcode: 1987Obs...107..134B Altcode: No abstract at ADS Title: Book-Review - Radio Continua during Solar Flares - Workshop - Duino, Italy - 1985MAY Authors: Benz, A. O. Bibcode: 1987S&T....73Q.395B Altcode: No abstract at ADS Title: Spectra of stellar radio flares Authors: Benz, Arnold O. Bibcode: 1987Natur.326..643B Altcode: No abstract at ADS Title: Acceleration and Energization by Currents and Electric Fields Authors: Benz, A. O. Bibcode: 1987SoPh..111....1B Altcode: The acceleration of the influential ≲ 100 keV electrons in flares observed in hard X-rays and several radio emissions is unknown. Shock-waves and MHD turbulence, successfully applied to interprete interplanetary energetic particles, have recently been called in question concerning energetic flare electrons and ions. Other possible mechanisms are considered which are closely related to the primary flare energy release. In particular, runaway acceleration by the electric field of the reconnection current sheet, bulk heating by microturbulence, and cross-field ion currents due to bulk motion as a primary result of reconnection are reviewed. All three are likely to occur in some way. Their relative importance cannot be definitively assessed due to the lack of information on non-thermal, low energy protons. Title: Harmonic Emission and Polarization of Millisecond Radio Spikes Authors: Benz, A. O.; Guedel, M. Bibcode: 1987SoPh..111..175B Altcode: The spectral distribution of millisecond radio spikes observed by the Zürich spectrometers in the 200-1100 MHz range has been studied. In one event out of a total of 36 we have found clearly developed harmonic structure. The ratio between the two bands of emission was 1:1.39 ± 0.01. We have also determined the sense of circular polarization of the spike events and compared it to the magnetic polarity of the leading spot of the flaring active region. According to the `Leading Spot Rule' the majority of the events (10 out of 13) were emitted in the ordinary mode. Title: Microwave emission of solar electron beams Authors: Staehli, M.; Benz, A. O. Bibcode: 1987A&A...175..271S Altcode: Studying the microwave and decimetric emissions of solar flares the authors have found drifting microwave fine structures in the range 3100 - 5205 MHz, clearly different from millisecond spikes. Their half power duration is between 25 and 200 ms. The bandwidth is usually greater than 150 MHz, and they are slightly circularly polarized. A comparison of these microwave structures with decimetric blips (Benz et al., 1983) and with metric type III bursts shows the similarity between these three phenomena concerning frequency drift, time scale, bandwidth and polarization. The authors therefore believe that the drifting microwave bursts are also signatures of travelling electron beams. Several emission mechanisms are possible. However, the observed similarities suggest a common process for the new microwave phenomena, decimetric blips and type III bursts. The most favourable mechanism then is harmonic plasma radiation. Title: Are solar radio fluctuations real? Authors: Benz, A. O.; Fuerst, E. Bibcode: 1987A&A...175..282B Altcode: Coordinated measurements of fluctuations of the microwave radiation of the Sun have been made using the Arecibo and Effelsberg telescopes. At 4.75 GHz they have comparable beamwidths. The two outputs of nearly identical regions on the Sun generally turned out to be different. Significant correlation was found in only one run. No discrete periodic oscillation remained after cross-correlation. The possibly common part of the continuous fluctuation spectrum was extracted by the sample cross-correlation. These fluctuations were of amplitudes up to 500 Jy. A coherence length of 90 s was found. The suggestion is made that they may originate from jets recently observed in coronal EUV and that they may be of possible relevance to coronal heating. Title: Book-Review - Radio Continua during Solar Flares Authors: Benz, A. O. Bibcode: 1987Sci...235R.494B Altcode: No abstract at ADS Title: Phenomena Associated with Ions and Relativistic Electrons Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf.2.30V Altcode: 1986epos.confB..30V No abstract at ADS Title: Mechanisms for Particle Accleration in Flares Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf.2.42V Altcode: 1986epos.confB..42V No abstract at ADS Title: Phenomena Associated with Mildly Relativistic Electrons Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf..2.2V Altcode: 1986epos.confB...2V No abstract at ADS Title: The role of metric and decimetric radio emission in the understanding of solar flares Authors: Simnett, G. M.; Benz, A. O. Bibcode: 1986A&A...165..227S Altcode: The metric and decimetric radio emission from large X-ray and gamma ray flares are examined with the aim of clarifying the role of electron beams in the primary energy transfer process during the impulsive phase of solar flares. It is found that a significant fraction, ≡15%, of the flares have no detectable radio emission at these wavelengths at current levels of instrument sensitivity. In addition, for the gamma ray flares a further 43% had the start of type III burst activity delayed by 60 s or more from the onset of the hard X-ray burst. The production and propagation of type III radiation is briefly reviewed and it is concluded that modern ground-based radio telescopes should be sensitive to a beam of electrons containing ⪆1029electrons above 20 keV. It is concluded that in the type III-quiet flares there is evidence against such beams. A consequence of this conclusion is that non-thermal electron beams cannot be the dominant energy transfer mechanism during the impulsive phase in at least some flares. Title: Solar radio signatures suggestive of proton beams Authors: Benz, A. O.; Simnett, G. M. Bibcode: 1986Natur.320..508B Altcode: Electron beams propagating in the solar corona excite the ambient plasma to emit radio waves at the local plasma frequency and/or its harmonic. This general interpretation of type III radio bursts is well confirmed by in situ measurements. The rate at which peak flux drifts in frequency and time is a measure of the velocity of the exciter. Here we report a class of radio bursts with a significantly lower drift than normal; consequently, we show that they defy the usual interpretation. Possible exciters are slowly moving beams of protons. Title: The frequency-time drift of pulsations. Authors: Aschwanden, M. J.; Benz, A. O. Bibcode: 1986A&A...158..102A Altcode: A set of 1270 digitally recorded type III bursts and pulsations in the frequency range of 100 - 1000 MHz was analyzed by a structure recognizing program. Numerical fitting methods determined the drift rate with much higher accuracy than previous analysis of analog data. The analysis of the drift of solar radio bursts in frequency vs. time provides information not only about the dynamical parameters of the source but also reveals atmospherical properties. Type III events and pulsations are clearly distinguished in their drift distribution. Pulsations statistically exhibit 3 times higher drift rates than type III events, thus requiring considerably shorter local scale heights. The source direction of the type III bursts is preferentially upwards oriented, the pulsations show a downwards oriented anisotropy. Evidence is given that the pulsations have a different origin than the common type III burst, concerning the coronal environment as well as the emission mechanism. Outlines to construct models of decimetric pulsations are discussed. Title: Preface Authors: Benz, Arnold O. Bibcode: 1986SoPh..104D...7B Altcode: No abstract at ADS Title: Electron Acceleration in Flares Inferred from Radio and Hard X-Ray Emissions Authors: Benz, A. O.; Kane, S. R. Bibcode: 1986SoPh..104..179B Altcode: Properties of electron acceleration in flares, especially the density structure in the acceleration region, are deduced from a correlation study between decimetric type III, spike, and hard X-ray (HXR) bursts. The high association rate found (71%) strongly suggests that spikes also originate from energetic electrons. Spikes and type III bursts have been found to be easily identified by their different polarizations. The two types of emission generally do not overlap in frequency. A reliable lower limit to the density is derived from the starting frequency of type III and U bursts. The spike emission very likely yields an upper limit. The density inhomogeneity in the acceleration region spans more than one order of magnitude and is more than one order of magnitude larger in the associated type U sources. A peak-to-peak correlation does not always exist between type III, spike and HXR bursts. This discrepancy can be interpreted in terms of the different source conditions and propagation properties. Whereas spikes need special conditions to become visible, type III and peaks of HXR may be the product of many elementary accelerations. Title: Millisecond Radio Spikes Authors: Benz, A. O. Bibcode: 1986SoPh..104...99B Altcode: Millisecond spikes of the solar radio emission are known for more than two decades. They have recently seen a surge in interest of theoreticians who are fascinated by their high brightness temperature of up to 1015 K, their association with hard X-ray bursts, and a possibly very intimate relation to electron acceleration. This review is intended to bridge the gap that presently seems to separate theory and observations. The wide range of spike observations is summarized and brought into the perspective of recent models. It is concluded that spikes yield a considerable potential for the diagnostics of energetic particles, their origin, and history in astrophysical plasmas. Title: Radio continua during solar flares : selected contributions to the workshop held at Duino, Italy, May, 1985 Authors: Benz, A. O. Bibcode: 1986SoPh..104.....B Altcode: The conference presents papers on radio continua during flares, the fine structure in continua, the coronal environment of radio emission, radio millisecond spikes, the timing of radio emission in relation to other flare radiation, and new technologies for the next solar cycle. Particular attention is given to the relation between flare-related metric continuum bursts and coronal mass ejections, fast pulsations in flare continua, the polarization of decimetric pulsations, interplanetary phenomena and solar radio bursts, the characteristics of type IV-associated spikes at metric wavelengths, hollow beam distribution of energetic electrons and higher harmonics of electron cyclotron maser, and a model of ultrafast fine structures of microwave bursts. Papers are also presented on type IV bursts and coronal mass ejections, electron acceleration in flares inferred from radio and hard X-ray emissions gyrosynchrotron emission of solar flares, microwave diagnostics of energetic electrons in flares and decimeter continuum radio emission from a postflare loop. Title: Extremely rapid radio spikes in flares. Authors: Benz, A. O. Bibcode: 1986NASCP2449..133B Altcode: 1986rfsf.nasa..133B Radio spikes of a few to tens of milliseconds of the solar radio emission have a high brightness temperature of up to 1015K, are associated with hard X-ray bursts, and are related to electron acceleration. Their bandwidth and global distribution in frequency have quantitatively been measured only recently. This review is intended to emphasize the considerable extend of old and new observational knowledge which is hardly touched upon by theory. The wide range of spike observations is summarized and brought into the perspective of recent models. It is concluded that spikes yield a considerable potential for the diagnostics of energetic particles, their origin, and history in astrophysical plasmas. Title: Radio emission of cataclysmic variable stars. Authors: Fuerst, E.; Benz, A.; Hirth, W.; Kiplinger, A.; Geffert, M. Bibcode: 1986A&A...154..377F Altcode: Eight cataclysmic variable stars were observed at 6 cm wavelength using the Very Large Array (VLA). The objects were: CN Ori, SS Aur, YZ Cnc, SU UMa, Z Cam, V603 Aql, EM Cyg, and RZ Sge. Most of these objects were in optical high stage, but none were detected beyond flux limits between 0.1 and 0.3 mJy. Title: Particle acceleration. Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986NASCP2439....2V Altcode: Contents: 1. Introduction. 2. Phenomena associated with mildly-relativistic electrons: soft and hard X-ray source structure, location and development, microwave source structure, location and development, time structures and time delays in radio and hard X-rays, microwave rich flares, decimetric - metric observations and comparison with X-ray observations, discussion of models for X-ray and microwave emission. 3. Phenomena associated with ions and relativistic electrons: gamma-ray observations, neutron observations, implications of gamma-ray and neutron observations, interplanetary charged-particle observations, acceleration mechanisms. 4. Mechanisms for particle acceleration in flares: particle acceleration in reconnecting magnetic fields, electron acceleration along the magnetic field with sub-Dreicer electric fields, lower hybrid waves, Fermi acceleration and MHD turbulence, shock acceleration, acceleration of electrons by intense radio waves, preferential acceleration of heavy ions. 5. Achievements - outstanding questions. Title: Correlation of Solar Decimetric Radio Bursts with X-Ray Flares Authors: Aschwanden, M. J.; Wiehl, H. J.; Benz, A. O.; Kane, S. R. Bibcode: 1985SoPh...97..159A Altcode: Several hundred radio bursts in the decimetric wavelength range (300-1000 MHz) have been compared with simultaneous soft and hard X-ray emission. Long lasting (type IV) radio events have been excluded. The association of decimetric emission with hard X-rays has been found to be surprisingly high (48%). The association rate increases with bandwidth, duration, number of structural elements, and maximum frequency. Type III-like bursts are observed up to the upper limit of the observed band. This demonstrates that the corona is transparent up to densities of about 1010 cm−3, contrary to previous assumptions. This can only be explained in an inhomogeneous corona with the radio source being located in a dense structure. The short decimetric bursts generally occur during the impulsive phase, i.e. simultaneously with hard X-rays. The times of maximum flux are well correlated (within 2 s). The HXR emission lasts 4 times longer then the radio emission in the average. This work finds a close relationship between decimetric and HXR emission with sufficient statistics offering additional information on the flare process. Title: Radio Spikes and the Fragmentation of Flare Energy Release Authors: Benz, A. O. Bibcode: 1985SoPh...96..357B Altcode: Decimetric radio events with large numbers of spikes during the impulsive phase of flares have been selected. In the observing range of 100 to 1000 MHz some flares have of the order of 10000 spikes or more. The average half-power bandwidth of spikes has been measured to be only 1.5% of the spike frequency. Since the emission frequency is determined by some source parameter (such as plasma frequency or gyrofrequency) the source dimension must be a small fraction of the scale length. From the flare configuration a typical upper limit of the dimension of 200 km is found. The observed fragmentation in the radio emission cannot be explained by a patchy emission mechanism of a single and much larger source without an additional (and unknown) assumption. It is proposed that the fragmentation already occurs in the exciter. Title: Polarization of solar noise storm continuum and plasma wave density in the corona Authors: Benz, A. O.; Zolliker, P. Bibcode: 1985A&A...144..227B Altcode: A statistical method for background subtraction of polarization observations has been developed. It separates the signal from a background with a much larger time constant. The method has been applied to the continuum component of a noise storm at various frequencies. The circular polarization was found to be constant in frequency within the statistical error. Its average value in time and frequency was 89.0±1.5%. Well accepted assumptions are used to determine the fraction of the radiation emitted at the harmonic of the plasma frequency from observations. The resulting flux of the harmonic is not significantly different from zero. The observed flux of the fundamental is used to derive the plasma wave density in the source of the noise storm and to predict the flux at the harmonic from theory. Title: Different time constants of solar decimetric bursts in the range 100 1000 MHz Authors: Wiehl, H. J.; Benz, A. O.; Aschwanden, M. J. Bibcode: 1985SoPh...95..167W Altcode: Between 1980, January 1 and 1981, December 31 a total of 664 `decimetric pulsation' events, abbreviated DCIM, were observed with the Zürich spectrometers in the frequency range 100 to 1000 MHz. All of these events were recorded on film, allowing an effective resolution in time of 0.5 s, and 5 MHz in frequency. Some of these events were also recorded digitally with higher time and frequency resolution. Title: First Detection of Radio Emission From a Dwarf Nova Authors: Benz, A. O.; Furst, E.; Kiplinger, A. L. Bibcode: 1985ASSL..113..331B Altcode: 1985cvlm.proc..331B The authors describe a search for radio emission at 4.75 GHz from dwarf novae that has been carried out with the 100-m telescope at Effelsberg, F.R. Germany. They have searched for radio emission from six dwarf novae and a source was discovered at the position of SU UMa. The source could only be detected during optical outburst and was below the threshold during quiescence. The authors suggest that the radio emission arises from a non-thermal process. Title: High Resolution in Astronomy Authors: Benz, A. O.; Huber, M.; Mayor, Michel Bibcode: 1985hra..conf.....B Altcode: 1985SAAS...15.....B No abstract at ADS Title: Decimetric Radio Emission During Solar Flares Authors: Benz, A. O.; Aschwanden, M. J.; Wiehl, H. J. Bibcode: 1985spit.conf..597B Altcode: No abstract at ADS Title: Synchrotron or plasma emission in solar microwave flares? Authors: Benz, A. O. Bibcode: 1984SoPh...94..161B Altcode: The spectral indices of microwave and hard X-ray emissions of a solar flare are found to correlate. Their observed values are in agreement with the expected relation from synchrotron and bremsstrahlung theory. These results are considered as strong evidence for the synchrotron mechanism in the microwave flare, contrary to recent alternative suggestions. Title: Decimetric gyrosynchrotron emission during a solar flare Authors: Batchelor, D. A.; Benz, A. O.; Wiehl, H. J. Bibcode: 1984ApJ...280..879B Altcode: The implications of high time-resolution observations of a decimetric, microwave, and hard X-ray burst during a solar flare in which the 900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically thick spectrum of a homogeneous, thermal gyrosynchrotron source are reported and discussed. The hard X-ray spectrum from 30 to 463 keV is well represented by a thermal bremsstrahlung function, and a temperature derived from this spectrum is used to find the source area of about 10 to the 18th sq cm. An electron density of less than about 7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are deduced from elementary plasma physics considerations and the lack of Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions place the gyrosynchrotron source at high altitude in a coronal loop, in agreement with VLA observations of other flares. Title: A Multiwavelength Study of a Double Impulsive Flare Authors: Strong, K. T.; Benz, A. O.; Dennis, B. R.; Leibacher, J. W.; Mewe, R.; Poland, A. I.; Schrijver, J.; Simnett, G.; Smith, J. B., Jr.; Sylwester, J. Bibcode: 1984SoPh...91..325S Altcode: Extensive data from the Solar Maximum Mission (SMM) and ground-based observatories are presented for two flares; the first occurred at 12:48 UT on 31 August, 1980 and the second just 3 min later. They were both compact events located in the same part of the active region. The first flare appeared as a typical X-ray flare: the CaXIX X-ray lines were broadened (≡ 190±40 km s-1) and blue shifted (≡ 60±20 km s-1) during the impulsive phase, and there was a delay of about 30 s between the hard and soft X-ray maxima. The relative brightness of the two flares was different depending on the spectral region being used to observe them, the first being the brighter at microwave and hard X-ray wavelengths but fainter in soft X-rays. The second flare showed no significant mass motions, and the impulsive and gradual phases were almost simultaneous. The physical characteristics of the two flares are derived and compared. The main difference between them was in the pre-flare state of the coronal plasma at the flare site: before the first flare it was relatively cool (3 × 106 K) and tenuous (4 × 109 cm-3), but owing to the residual effects of the first flare the coronal plasma was hotter (5 × 106 K) and more dense (3 × 1011 cm-3) at the onset of the second flare. We are led to believe from these data that the plasma filling the flaring loops absorbed most of the energy released during the impulsive phase of the second flare, so that only a fraction of the energy could reach the chromosphere to produce mass motions and turbulence. Title: On coronal oscillations Authors: Roberts, B.; Edwin, P. M.; Benz, A. O. Bibcode: 1984ApJ...279..857R Altcode: Magnetoacoustic oscillations in a solar coronal inhomogeneity (e.g., coronal loop) are shown to take place with two distinct periodicities, one on an acoustic (long) time scale and the other on an Alfvenic (short) time scale. The short period modes - fast magnetoacoustic waves - are trapped in regions of low Alfven speed: typically, this corresponds to high density loops or dense open field regions. Their periods may be on the order of seconds. The form of the fast oscillations is discussed for both standing modes in a closed loop and impulsively generated disturbances in a loop or open field structure. Impulsively generated waves in a density enhancement exhibit both periodic and quasi-periodic phases. Symmetric oscillations (sausage modes) are analogous to Pekeris waves in oceanography; asymmetrical (kink) disturbances are akin to Love waves in seismology. It is suggested that fast magnetoacoustic waves may explain the observed pulsations in Type IV radio events, the sausage waves providing the desired 1 s periodicities. Magnetoacoustic oscillations provide a potentially useful diagnostic tool for determining physical conditions in the inhomogeneous corona. Title: Decimetric Type-Iii Radio Bursts and Associated Hard X-Ray Spikes Authors: Dennis, B. R.; Benz, A. O.; Ranieri, M.; Simnett, G. M. Bibcode: 1984SoPh...90..383D Altcode: A detailed comparison is made between hard X-ray spikes and decimetric type III radio bursts for a relatively weak solar flare on 1981 August 6 at 10: 32 UT. The hard X-ray observations were made at energies above 30 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and with a balloon-born coarse-imaging spectrometer from Frascati, Italy. The radio data were obtained in the frequency range from 100 to 1000 MHz with the analog and digital instruments from Zürich, Switzerland. All the data sets have a time resolution of ∼ 0.1 s or better. The dynamic radio spectrum shows many fast drift type III radio bursts with both normal and reverse slope, while the X-ray time profile contains many well resolved short spikes with durations of ≤ 1 s. Some of the X-ray spikes appear to be associated in time with reverse-slop bursts suggesting either that the electron beams producing the radio bursts contain two or three orders of magnitude more fast electrons than has previously been assumed or that the electron beams can trigger or occur in coincidence with the acceleration of additional electrons. One case is presented in which a normal slope radio burst at ∼ 600 MHz occurs in coincidence with the peak of an X-ray spike to within 0.1 s. If the coincidence is not merely accidental and if it is meaningful to compare peak times, then the short delay would indicate that the radio signal was at the harmonic and that the electrons producing the radio burst were accelerated at an altitude of ∼4 × 109 cm. Such a short delay is inconsistent with models invoking cross-field drifts to produce the electron beams that generate type III bursts but it supports the model incorporating a MASER proposed by Sprangle and Vlahos (1983). Title: The polarization of the noise storm continuum and the upper limit on harmonic emission. Authors: Benz, A. O.; Zolliker, P. Bibcode: 1984ost1.conf..167B Altcode: No abstract at ADS Title: Orages solaires de type I: Abbaye de Senanque, Gordes, France, 17-21 March 1980 Title: Orages solaires de type I: Abbaye de Senanque, Gordes, France, 17-21 March 1980 Title: Solar storms of type I Senanque Abbey, Gordes, France. Authors: Bougeret, J. L.; Benz, A. O. Bibcode: 1984ost1.conf.....B Altcode: No abstract at ADS Title: Coronal evolution and solar type I radio bursts: an ion-acoustic wavemodel. Authors: Benz, A. O.; Wentzel, D. G. Bibcode: 1984ost1.conf..127B Altcode: No abstract at ADS Title: Zukunft der Astronomie. Authors: Benz, A. Bibcode: 1984Orion..42....6B Altcode: No abstract at ADS Title: On the spatial and temporal correlation of type I radio bursts and soft X-rays. Authors: Benz, A. O.; Jaeggi, M.; Mosher, J. M.; Nelson, G. J. Bibcode: 1984ost1.conf..145B Altcode: The authors have compared type I radio burst positions and intensities with spatially resolved soft X-ray observations. The spatial coincidence is generally good, but not exact. There seems to be a time lag of about one day between maximum X-ray brightness and maximum type I activity. Title: Noise storms and their place in the solar radio zoo. Authors: Benz, A. O. Bibcode: 1984ost1.conf...35B Altcode: No abstract at ADS Title: Decimetric gyrosynchrotron emission during a solar flare Authors: Batchelor, D. A.; Benz, A. O.; Wiehl, H. J. Bibcode: 1983STIN...8416107B Altcode: A decimetric, microwave, and hard X-ray burst was observed during a solar flare in which the radio spectrum below peak flux fits an f+2 power law over more than a decade in frequency. The spectrum is interpreted to mean that the radio emission originated in a homogeneous, thermal, gyrosynchrotron source. This is the first time that gyrosynchrotron radiation has been identified at such low decimetric frequencies (900-998) MHz). The radio emission was cotemporal with the largest single hard X-ray spike burst ever reported. The spectrum of the hard X-ray burst can be well represented by a thermal bremsstrahlung function over the energy range from 30 to 463 keV at the time of maximum flux. The temporal coincidence and thermal form of both the X-ray and radio spectra suggest a common source electron distribution. The unusual low-frequency extent of the single-temperature thermal radio spectrum and its association with the hard X-ray burst imply that the source had an area approx. 10(18) sq cm a temperature approx 5x10(8) K, an electron density approx. 7.10(9) cu cm and a magnetic field of approx. 120 G. H(alpha) and 400-800 MHz evidence suggest that a loop structure of length 10,000 km existed in the flare active region which could have been the common, thermal source of the observed impulsive emissions. Title: Fast pulsations in the solar corona Authors: Roberts, B.; Edwin, P. M.; Benz, A. O. Bibcode: 1983Natur.305..688R Altcode: Pulsations in radio emission from the solar coronal plasma have been detected for over a decade1-9. The oscillations are quasiperiodic, with periods of typically a second or so. Recently, sub-second time structures have been found in hard X rays10, and simultaneously in hard X rays and microwaves11. Here we examine whether magnetohydrodynamical oscillations in a density enhancement, treated for simplicity as a straight magnetic slab, can explain the observed short periods. A dense region in the corona (for example, a loop) can act as a wave trap, and symmetrical oscillations within that trap must be of short wavelength with correspondingly short period. An impulsive source (such as a flare) naturally gives rise to a quasiperiodic disturbance. Such oscillations are closely akin to the Pekeris modes of oceanography, the Love waves of seismology and the dielectric waves of fibre optics. Title: Radio blips and hard X-rays in solar flares Authors: Benz, A. O.; Bernold, T. E. X.; Dennis, B. R. Bibcode: 1983ApJ...271..355B Altcode: The properties of short, narrow-band spikes occurring in groups at decimetric wavelengths have been extensively analyzed. The bursts, termed blips in the literature, have been found to appear in the impulsive phase of flares. They are associated with hard X-ray emission in 40 percent of all cases with simultaneous coverage. The correspondence between blips and X-ray spikes is generally not one-to-one, blips being more numerous than X-ray spikes. In some cases, however, close correlations between single events have been found. Blips have been discovered to drift in frequency and to decay in time similarly to type III bursts at lower frequency. They also resemble type III bursts in polarization. An analysis of starting frequencies, however, clearly shows that blips and type III bursts belong to different statistical populations. The narrow bandwidth of blips, the major qualitative difference with respect to type III bursts, suggests that blips are the signature of electron beams which either decay rapidly or have a locally enhanced emission due to the presence of some low-frequency wave. Blips have been shown to be an impulsive phase phenomenon occurring at densities of one to three billion per cu cm in the low corona. Title: First detection of radio emission from a dwarf nova Authors: Benz, A. O.; Fuerst, E.; Kiplinger, A. L. Bibcode: 1983Natur.302...45B Altcode: The dwarf novae represent a class of cataclysmic variable stars that typically exhibit random optical outbursts of 2-6 mag with mean outburst periods of 10-150 days. Dwarf novae are close binary systems composed of a late-type star which fills its critical Roche lobe and a white dwarf companion. The white dwarf is surrounded by a luminous accretion disk sustained by mass transfer from the late-type star. The disk is the seat of the eruptions. Although radiation has been detected from dwarf novae from IR through X-ray energies, radio emission has never been reported from these objects. We describe here a search for radio emission at 4.75 GHz from dwarf novae that has been carried out with the 100-m telescope at Effelsberg, West Germany. We have searched for radio emission from six dwarf novae and a source was discovered at the position of SU UMa. The source could only be detected during optical outbursts and was below the threshold during quiescence. We suggest here that the radio emission arises from a non-thermal process. Title: X-Ray and Radio Emissions in the Early Stages of Solar Flares Authors: Benz, A. O.; Barrow, C. H.; Dennis, B. R.; Pick, M.; Raoult, A.; Simnett, G. Bibcode: 1983SoPh...83..267B Altcode: Radio and X-ray observations are presented for three flares which show significant activity for several minutes prior to the main impulsive increase in the hard X-ray flux. The activity in this `pre-flash' phase is investigated using 3.5 to 461 keV X-ray data from the Solar Maximum Mission, 100 to 1000 MHz radio data from Zürich, and 169 MHz radio-heliograph data from Nançay. The major results of this study are as follows: Decimetric pulsations, interpreted as plasma emission at densities of 109-1010 cm−3, and soft X-rays are observed before any Hα or hard X-ray increase. Title: Solar 'blips' and the heating of X-ray areas Authors: Hirth, W.; Fuerst, E.; Benz, A. O. Bibcode: 1983KlBer..26..189H Altcode: Radioastronomy observations of the sun provide significant information regarding the processes which occur above the photosphere. The 100-m telescope in Effelsberg, West Germany, makes it possible to observe the transition layer between chromosphere and corona. This transition layer is important in connection with energy transfer to the corona. The Zuerich spectrograph, on the other hand, with its operational range from 200 to 1000 MHz, is suited for observing processes in the corona. The present investigation is concerned with observations involving very small radiation bursts, called 'blips'. It is believed that a relation exists between these phenomena and the heating of coronal areas. These blips can now be studied on the basis of data simultaneously obtained on March 2, 1979, in three different wavelength ranges. Data in the decimetric range were obtained with the Zuerich spectrograph, while the Effelsberg telescope provided data at 2.8 cm. Observations in the X-ray range were obtained with the aid of the GOES 2 satellite. The significance of the data is evaluated. Title: Solar radio storms. Proceedings of the 4th CESRA workshop on solar noise storms, held at Trieste, Italy, August 9 - 13, 1982. Authors: Benz, A. O.; Zlobec, P.; Wentzel, D. G.; House, L. L.; Dulk, G. A.; Tlamicha, A.; Melrose, D. B. Bibcode: 1983srs..work.....B Altcode: No abstract at ADS Title: Millisecond structures in noise storms and other solar radio emission. Authors: Barrow, C. H.; Benz, A. O.; Bernold, T. E. X.; Perrenoud, M. R. Bibcode: 1983srs..work..109B Altcode: Preliminary results of a high time-resolution (≡8 msec) fine structure study are reported. Fine structures, having durations of some 10 to 40 msec, have been observed in solar noise storms and also associated with type III, type IV, and type V bursts. These very short duration bursts, referred to here as solar S-bursts, have been seen to occur individually as well as in small groups where they may display a quasi-periodicity of a few milliseconds. Generally, the S-bursts are not very intense relative to the associated background emission. Title: Langmuir wave energy density in radio storm sources. Authors: Benz, A. O. Bibcode: 1983srs..work...38B Altcode: An enhanced level of Langmuir wave energy density is postulated in all plasma wave models of radio storm emission. Three different methods are described to measure this quantity: radar, observations of harmonics, and polarization measurements. These methods have been applied to solar noise storm sources. The results are presented. The best upper limit of the ratio of wave energy density to thermal (kinetic) energy density is 5×10-6 for bursts and about an order of magnitude less for the continuum. Title: Electron acceleration in impulsive solar flares Authors: Kane, S. R.; Benz, A. O.; Treumann, R. A. Bibcode: 1982ApJ...263..423K Altcode: Physical parameters relevant to the acceleration and propagation of energetic electrons during the impulsive phase of a solar flare are studied in hard X-ray, microwave and both type III and decimetric radio bursts associated with the December 4, 1978 solar flare. A one-to-one association between single type III bursts and hard X-ray peaks is established, along with a burst delay with respect to the peaks of 0.5 sec. The observed increase of the high frequency cutoff of the metric type III bursts during the impulsive phase is examined in terms of the decreasing altitude of the electron acceleration/injection region, increasing electron spectrum hardness, and decreasing acceleration time. A pulsating decimetric continuum was found to be present during and before the impulsive phase whose high frequency cutoff also systematically increased during the rise of the impulsive phase. Title: Fine structure near the starting frequency of solar type III radio bursts Authors: Benz, A. O.; Jaeggi, M.; Zlobec, P. Bibcode: 1982A&A...109..305B Altcode: An analysis of the period in time and frequency adjacent to the beginning of type III bursts digitally recorded at Bleien, Switzerland, during the second half of 1980 is presented. It is found that a high percentage (10%, possibly more than 20%) of the type III bursts show fine structure in the form of narrow-banded spikes of 0.05 s and less duration. These spikes form 'clusters' of relatively large bandwidth. They are not totally polarized and are uniformly distributed over the disk. Individual spikes often exhibit highly variable polarization, which may even change sense. The average degree of polarization of the clouds is found to have a wider distribution than that of the associated type III bursts but to have generally the same sign. It is noted that the spikes are considerably different from type I bursts. The spikes are then classified on the basis of their occurrence in relation to the beginning of type III bursts. Title: The Relation Between the Surges and Solar Radio Emission Authors: Garczynska, I. N.; Rompolt, B.; Benz, A. O.; Slottje, C.; Tlamicha, A.; Zanelli, C. Bibcode: 1982SoPh...77..277G Altcode: The 120 limb surges which have been observed by means of Wrocław Observatory coronagraph from September 1966 to November 1977 are investigated. The evolution of surges was compared with the radio data during the surges. A correlation between radio bursts and the surges was found, particularly with chains of type I radio bursts, which is the first reliable correlation found of these bursts with non-radio events. The type I correlation only applied for surges without accompanying flare, of which 43% are correlated with this type of radio emission. In 23 of 30 associated events the start of a surge coincided within 5 minutes with the start or an enhancement of the type I storm. If flares were present, the association was not significant. Title: Evidence of primary and secondary bursts in solar type III emission Authors: Benz, A. O.; Treumann, R.; Vilmer, N.; Mangeney, A.; Pick, M.; Raoult, A. Bibcode: 1982A&A...108..161B Altcode: Simultaneous observations of groups of metric type III radio bursts at high spectral, spatial, and temporal resolution are presented. They have occurred on different days and above the photospheric limb. It is found that they tend to be clustered in pairs. The two bursts in each pair have considerably different properties. The primary bursts have generally higher frequency drifts, stronger polarization, higher starting frequency, smaller size, and sometimes larger distance from the center of the sun. The hypothesis of fundamental and harmonic emission encounters serious difficulties. The observations fit better with electron beams propagating along two different (primary and secondary) paths. This suggests a model where the secondary beam originates from electrons with a different acceleration region being triggered by the first energy release and having a smaller energy input and thus smaller beam velocity. Title: Search for harmonic emission in solar type I radio bursts Authors: Jaeggi, M.; Benz, A. O. Bibcode: 1982A&A...107...88J Altcode: A statistical analysis is made of the harmonic emission of type I bursts, which is based on the latest plasma wave theories for the emission mechanism. No systematic harmonic emission is detected, although in a few single cases emission is found at the harmonic frequency, which is attributed to chance hits of an independent activity present at that frequency. An upper limit for the Langmuir wave energy density is derived, and the consequences for plasma emission theories are discussed. Title: About the relation between radio and soft X-ray emission in case of very weak solar activity Authors: Fuerst, E.; Benz, A. O.; Hirth, W. Bibcode: 1982A&A...107..178F Altcode: Centimeter and decimeter observations of very small solar soft X-ray events detected by the GOES-2 satellite on March 2, 1979, are reported. The radio events are labeled 'blips' because of their faintness at cm-wavelengths combined with fast variation of the flux and because of unusual narrow-band emission at dm-wavelengths. The blips occur mainly in the rise phase of the X-ray emission. Analysis of the blips shows that nonthermal radiation of fast electrons is the origin of their emission. The energy of fast electrons necessary to explain the cm-blip flux is roughly equal to the heat energy of the X-ray source. This is seen as a hint that the X-ray source is heated by the excess energy of the fast electrons. The X-ray source is assumed to resemble an emerging flux region with a size typical of X-ray kernels. Title: Solar Radio Storms Authors: Benz, A. O.; Zlobec, P. Bibcode: 1982srs..work.....B Altcode: No abstract at ADS Title: Millisecond structures in noise storms and other solar radio emission Authors: Barrow, C. H.; Benz, A. O.; Bernold, T. E. X.; Perrenoud, M. R. Bibcode: 1982srs..work..109B Altcode: No abstract at ADS Title: Langmuir wave energy density in radio storm sources (review) Authors: Benz, A. O. Bibcode: 1982srs..work...38B Altcode: No abstract at ADS Title: Solar type I noise storms and newly emerging magnetic flux Authors: Spicer, D. S.; Benz, A. O.; Huba, J. D. Bibcode: 1982A&A...105..221S Altcode: A new model of solar type I radio bursts is presented based on the assumption that newly emerging magnetic flux can become, on occasion, weakly super-Alfvenic and thus capable of driving weak collisionless shocks in the front of the flux as it emerges. Using the assumption that the collisionless shock is maintained near marginal stability with respect to various collisionless flute like instabilities, we compute the microturbulence level of lower hybrid waves excited by the shock. It is then argued that these obliquely propagating lower hybrid waves are capable of accelerating electrons in the wake of the weak shock. These accelerated electrons are then utilized to excite upper hybrid waves via a loss-cone instability. The resulting mode coupling between lower hybrid and upper hybrid waves is then suggested as a radiation mechanism for the type I bursts. Title: The microwave solar radar experiment. I - Observations Authors: Fitze, H. R.; Benz, A. O. Bibcode: 1981ApJ...250..782F Altcode: The first solar radar experiment in microwaves, carried out with the 300-m dish in Arecibo using a 250 kW transmitter, is described. Receiving at a displaced frequency from the transmitted radar frequency makes it possible to probe the Langmuir (plasma) wave energy density of the corona in the 170-270 MHz range. No echo is found in various regions on the sun. It is pointed out that this contradicts some models of type I radio bursts and a proposed scattering mechanism of metric solar radar echos. Neither is any echo produced in an alternative experiment, in which reception is at the transmitted frequency. It is noted that the reflectivity of the sun in microwaves is more than four orders of magnitude below the reflectivity in meter waves. Title: Solar radio blips and X-ray kernels Authors: Benz, A. O.; Perrenoud, M. R.; Fuerst, E.; Hirth, W. Bibcode: 1981Natur.291..210B Altcode: Hudson1 proposed that the primary flare energy release goes into fast electrons. Others2,3 found the flare soft X-ray emission to consist of bright, small kernels (knots and loops) embedded in a more diffuse halo. These kernels with a typical size of 5' arc s and a temperature of 6-12 × 106K emit in radio waves at 3.7 and 11 cm (ref. 4). The discovery of a radio brightness temperature equal to the temperature derived from the X rays and the radio size larger than in X rays shows that the observed radio emission is thermal (free-free) and the source optically thick at λ > 3.7 cm. Therefore, Kundu et al.4 did not observe the fast electrons expected to heat the kernels. Here we present high time resolution measurements at 2.8 cm from the Effelsberg 100-m telescope and at decimetric and metric wavelengths with the ETH Zurich spectrometers. Both instruments have detected signatures of non-thermal particles. Title: Optical and radio observations of the 1980 March 29, April 30, and June 7 flares Authors: Rust, D. M.; Benz, A.; Hurford, G. J.; Nelson, G.; Pick, M.; Ruzdjak, V. Bibcode: 1981ApJ...244L.179R Altcode: Ground-based solar observations are analyzed for three of the flares discussed in the accompanying Solar Maximum Mission reports. The principal conclusions are that H-alpha begins to brighten several minutes before the impulsive, hard X-ray bursts, that the preflare heating and impulsive phases of the three flares occurred in loop-shaped structures of about 3500 km semidiameter, and that after the impulsive phase a much larger volume (about 200 times) of flare plasma was present for the flare main phase. Evidence is presented for the escape of 100-500 keV electrons into the larger volume and into the corona during the impulsive phase. For the April 30 flare, the inferred origin of the hard X-ray burst is near the feet of the magnetic loops. Title: Über die solaren Minibursts Authors: Fürst, E.; Hirth, W.; Benz, A. Bibcode: 1981MitAG..52...66F Altcode: No abstract at ADS Title: Quasi-periodic short-term modulations during a moving type IV burst Authors: Trottet, G.; Kerdraon, A.; Benz, A. O.; Treumann, R. Bibcode: 1981A&A....93..129T Altcode: The Nancay Radioheliograph and the E.T.H. spectrometer measurements of a pulsating emission at the start of a moving type IV continuum indicated that the modulation is not strictly periodic and that the brightness temperature of the pulsating source is greater than 10 to the 9th K. The source shows two types of motions observed by the heliograph which correspond to two negative frequency drifts visible on the spectrometer: the first is a global motion with a velocity of 350 km/s typical of moving type IV, and the second has a much higher velocity of 100,000 km/s. Analysis of modulation and emission processes involving perturbations of the loss cone distribution of trapped electrons demonstrate that they provide an alternative for the interpretation of the observed characteristics. Title: Coronal evolution and solar type I radio bursts - an ion-acoustic wave model Authors: Benz, A. O.; Wentzel, D. G. Bibcode: 1981A&A....94..100B Altcode: A model is proposed for type I burst emission that can accommodate both the main burst observations and an origin for the continuum. It is assumed that ion-acoustic waves are generated in the burst source by a current that is related to the coronal magnetic evolution, in particular to magnetic nonequilibrium caused by photospheric changes (e.g. emerging magnetic field) in active regions. Radio emission arises from coalescence of ion-acoustic and plasma waves. Contrary to other plasma wave models, emission at the harmonic of the plasma frequency is below the present detection threshold (not greater than 0.1%). The ion-acoustic wave density, having a high saturation value, determines the optical depth, which reaches unity within a few meters. The brightness temperature is thus entirely given by the level of Langmuir waves. These waves may be produced by trapped non-thermal electrons from previous burst sources. The same population also provides sufficient plasma waves for the type I continuum, which may arise from interactions with low-frequency waves present in the corona during times of type I activity. Title: Activity and outer atmospheres of the sun and stars. Eleventh Advanced Course of the Swiss Society of Astronomy and Astrophysics, held in Saas-Fee, Switzerland, March 30 - April 4, 1981. Authors: Benz, A. O.; Chmielewski, Y.; Huber, M. C. E.; Nussbaumer, H. Bibcode: 1981aoas.book.....B Altcode: No abstract at ADS Title: The Impulsive Solar Flare at 0918 UT on 1980 March 29 Authors: Crannell, C. J.; Trombka, J. I.; Benz, A.; Magun, A.; Matzler, C.; Wiehl, H.; Ryan, J. M. Bibcode: 1980BAAS...12..889C Altcode: No abstract at ADS Title: Electron trapping in the solar magnetic field and emission of decimetric continuum radio bursts. Authors: Benz, A. O. Bibcode: 1980ApJ...240..892B Altcode: The conditions for confinement of energetic electrons in the solar corona are studied with respect to the influence of electrostatic waves, which have been suggested to cause type IV(dm) decimetric continuum emission. A hydrodynamic approach is taken for simplicity. The unstable growth of these waves is found to be effectively limited by a change of the particle gyroperiod in the electric field of the wave detuning the resonance. Saturation of wave energy density occurs at a low level, which is proportional to the fraction of energetic particles. The low wave level excludes induced scattering on thermal ions for the hydrodynamic instability. A new model is proposed based on conversion by interaction with low-frequency waves, in particular, lower hybrid waves, which are known to exist in loss-cone situations of the magnetosphere. The fraction of energetic particles of the plasma necessary for the observed radio flux allows trapping times of the order of minutes. Oscillations of the saturation wave amplitude are found. Title: First solar radar observations in microwaves Authors: Benz, A. O.; Fitze, H. R. Bibcode: 1980IAUS...86..247B Altcode: The first microwave radar experiment probing solar radio emission source regions is presented. The 300-m dish telescope at Arecibo was used to scatter 2380-MHz pulsed signals on coronal Langmuir waves with frequencies from 170 to 270 MHz in source regions of type I emission, and the radio signal produced by the nonlinear interaction of the two wave modes was monitored at 2600 MHz at a bandwidth of 100 MHz. The experiment has performed as expected, with a threshold sensitivity on the order of 1 Jy, however no echo has yet been detected. An upper limit to the Langmuir wave energy density of 0.0005 nKT is thus obtained from the wave-wave interaction coefficient for a source temperature of 5,000,000 K, size of 10 to the 28th cu cm and an isotropic and flat Langmuir wave spectrum. Title: Solar Radar Observations Authors: Benz, A. O. Bibcode: 1980IAUS...91..135B Altcode: No abstract at ADS Title: Solar Type-I Radio Bursts - an Ion-Acoustic Wave Model Authors: Benz, A. O.; Wentzel, D. G. Bibcode: 1980IAUS...86..251B Altcode: No abstract at ADS Title: Sonnenforschung mit Radiowellen. Authors: Benz, A. Bibcode: 1980Orion..38....9B Altcode: No abstract at ADS Title: Sonnenforschung mit Radiowellen an der ETH. Authors: Benz, A. Bibcode: 1980Orion..38...77B Altcode: No abstract at ADS Title: The evolution of polarization in type U solar radio bursts. Authors: Benz, A. O.; Urbarz, H. W.; Zlobec, P. Bibcode: 1979A&A....79..216B Altcode: Surmary. We have analyzed the polarization of type U solar radio bursts from 16 active regions. Only two of them produced events which changed sign between ascending and descending branch. These observations lead to the suggestion of weak mode coupling in quasi-transverse regions in the low corona, in contradiction to measurements at higher altitudes. The sign of polarization corresponds to ordinary emission in the field of the leading spot, which suggests an asymmetric magnetic loop with stronger field in the ascending leg. This agrees with the observed higher polarization in the ascending branch of the U-burst. Spikes in polarization in the descending branch have been found to occur before maximum flux similar to the ascending branch in contradiction to the expectation from theory. A new interpretation of the phenomenon is given in terms of the phase velocity shift of the Langinuir waves during the passage of the beam at a given place (for fundamental emission). Key words: solar radio emission - polarization of U-bursts - mode coupling - Langmuir wave phase velocity Title: Microwave radar observations of the sun. Authors: Benz, A. O.; Fitze, H. R. Bibcode: 1979A&A....76..354B Altcode: A pilot experiment on microwave radar observations of the sun has been conducted with the Arecibo 300-m telescope. Data obtained at 2600 MHz with a bandwidth of 100 MHz are presented. This frequency is shifted from the transmitted frequency by the expected Langmuir waves in the range from 170 to 270 MHz. The results show the absence of such waves in the corona with energy densities above about 0.0006, 0.08, and 0.02 nKT for a possible type I radio source region, a prominence, and streamer, respectively. Title: Type I Solar Radio Bursts Authors: Benz, A. O.; Wentzel, D. G. Bibcode: 1979BAAS...11..441B Altcode: No abstract at ADS Title: Plasma instabilities of trapped particles in solar magnetic fields. Authors: Berney, M.; Benz, A. O. Bibcode: 1978A&A....65..369B Altcode: Electromagnetic whistler and electrostatic (hydrodynamic) instabilities in a magnetized plasma are studied with reference to the loss-cone velocity distribution function of particles. In the electrostatic case, maximum growth rate and marginal stability are considered. For whistler waves, the area of instability is spatially limited by the extent of the loss-cone distribution. Thus, while the growth rate for the whistler instability peaks at the feet of the arches, the electrostatic instability is restricted to zones near places where the upper hybrid frequency of the background particles is an integer multiple of the electron cyclotron frequency. It is noted that the electrostatic instability will become saturated, i.e., in a state of quasi-equilibrium, with the losses of untrapped particles. Whistler growth, however, is limited by field curvature in a twisted magnetic field, or by refraction. Title: An extremely narrow-band solar type IVdm burst with fine structure. Authors: Tarnstrom, G. L.; Benz, A. O. Bibcode: 1978A&A....63..147T Altcode: A decimetric type IV solar burst occurring with a halfpower bandwidth of only 40 MHz is analyzed; the concurrent fine structure of the burst is concluded to be a signature for plasma wave emission rather than synchrotron emission. With plasma wave emission assumed and the most widely spread interpretation of the fine structure adopted, coronal magnetic field strengths in the range of 5.5 + or - 1.5 gauss have been computed. The magnetic field values are about half those computed for the associated type II split-band event, suggesting that entirely different conditions in two well separated sources have been detected. Title: Correlation between drift rate and polarization in solar type III radio bursts. Authors: Benz, A. O.; Zlobec, P. Bibcode: 1978A&A....63..137B Altcode: A statistically significant correlation between polarization and frequency drift rate has been found in an analysis of 463 solar type III radio bursts. The correlation is particularly marked for high degrees of polarization, small total bandwidths, or for cases involving a polarization spike before maximum intensity. It is argued that the correlation arises naturally from fundamental emission, and is due to a direct influence of drift velocity on polarization. The lack of correlation observed at low polarization may be interpreted by reference to the predominance of second harmonic emission. Title: Observations of the type I continuum radiation on July 9-13, 1978 at Dürnten Authors: Mätzler, C.; Perrenoud, M. R.; Benz, A. O. Bibcode: 1978cesra...7...18M Altcode: No abstract at ADS Title: Transient Aspects of the Corona including Flare Related Events Authors: Benz, A. O. Bibcode: 1978pfsl.conf..267B Altcode: 1978ESPM....2..267B No abstract at ADS Title: On the scattering hypothesis for type V radio bursts. Authors: Pilipp, W. G.; Benz, A. O. Bibcode: 1977A&A....56...39P Altcode: The possibility is considered that the energetic electrons producing a type III burst may excite electromagnetic instabilities which subsequently lead to scattering of the electrons and the generation of a type V burst. The nonrelativistic dispersion relation is solved for circularly polarized electromagnetic waves propagating parallel to the magnetic field in a system consisting of a thermal plasma and a uniform electron beam. It is shown that for certain beam and plasma parameters, an instability with respect to lefthand polarized waves occurs which is driven to a large extent by a 'resonant electron' instability that could result in scattering of resonant beam electrons without the need for preexisting plasma turbulence. Observations are discussed which indicate that type V bursts are preferably produced under conditions that are in qualitative agreement with those for which the present calculations yield an instability. Title: The polarization of U-shaped solar radio bursts. Authors: Benz, A. O.; Berney, M.; Santin, P. Bibcode: 1977A&A....56..123B Altcode: Circular-polarization measurements of 11 U-shaped solar radio bursts observed at 237 MHz are reported which contradict the expectation that the received polarization should have different signs in the two branches. The mean polarization of these bursts is found to be about 7% righthanded for the ascending branch and about 6% in the same sense for the descending branch. An attempt is made to discuss the observed constancy of the sign of polarization in terms of coronal propagation properties above the source region. Title: Circular Polarization and Frequency Drift Rate Correlated in Solar Type III Radio Bursts. Authors: Benz, A. O.; Zlobec, P. Bibcode: 1977BAAS....9..369B Altcode: No abstract at ADS Title: On the kinetics of solar wind acceleration. Authors: Benz, A. O.; Gold, T. Bibcode: 1977A&A....55..229B Altcode: A two-stream model of solar-wind hydrogen-plasma expansion is outlined in which protons at any one level of flux generation are divided into those that collide rapidly relative to their expansion times and those that leave the sun without significant relaxation. Proton evaporation is explicitly taken into account along with momentum and energy gains due to friction with escaping protons. This model is investigated numerically by an iteration technique, assuming a lateral expansion of the solar wind. It is found that for very low temperatures, proton acceleration is caused mainly by a lack of fast-particle collisions and that the collisional population is more accelerated and denser at higher temperatures. The results also show that evaporation over a large extent of height reduces the solar-wind heating requirements to the region of the low corona. Examination of the physical stability of the solar-wind plasma in this model indicates that no electrostatic two-stream instability can arise, the firehose-instability condition could be satisfied only with very low temperatures near the level of full evaporation, and a point of serious instability with respect to magnetosonic whistlers occurs at a heliocentric distance of about 10 solar radii. Title: Spectral features in solar hard X-ray and radio events and particle acceleration. Authors: Benz, A. O. Bibcode: 1977ApJ...211..270B Altcode: Hard X-ray and radio intensities of two major solar outbursts are found to anticorrelate in time with their spectral indices, which, furthermore, are in satisfactory correlation with each other. The radio emission must be synchrotron radiation from the same electron population that causes the X-ray bremsstrahlung. A delay of temporal features, increasing with energy, is clearly observed in one of the X-ray events. The observations are interpreted with a simple model, which assumes ion-acoustic instability in a current sheet, transformation of turbulence energy into Langmuir waves, and their escape into the ambient plasma where they accelerate particles. A power-law index of the electron energy distribution is derived for acceleration being balanced by escape of particles. Anticorrelation of intensity and spectral index then follows naturally from variations of the spectral wave energy density or the dimension of the acceleration region. The finite collision time in the acceleration region and its increase with energy introduce a perturbation which can explain the observed drift of temporal features. Title: Short, drifting spikes in the cm-dm wavelength radiation of the active sun Authors: Benz, A. O. Bibcode: 1977KlBer..20...31B Altcode: Data of the October 25, 1972, radio outburst were analyzed in the cm and dm range. They are interpreted in terms of drifting spikes. A synchrotron model is proposed in which the source magnetic field changes either because of expansion or mirror point motion. Absorption on the low frequency side is proposed to be by gyroresonance. Title: New Features in Hard X-Ray and Radio Spectra of Solar Outbursts and Implications on Particle Acceleration Authors: Benz, A. O. Bibcode: 1976BAAS....8..374B Altcode: No abstract at ADS Title: Synchrotron or plasma process emission in narrow-band type IVdm bursts? Authors: Benz, A. O.; Tarnstrom, G. L. Bibcode: 1976ApJ...204..597B Altcode: Extremely narrow-banded type IVdrn events have been selected to test the various proposed emission mechanisms. Emphasis is put on the observed spectral shape and rapid variations in intensity, and plasma-physical stability of the source model. Synchrotron emission in quasi- vacuum is excluded by the observed steep low-frequency spectral sfope. Free-free absorption of incoherent synchrotron emission is negligible compared with the Razin effect suppression. However, Razin-suppressed synchrotron emission would lead to unstably high concentrations of energetic electrons. A low-frequency cutoff due to cyclotron-resonance absorption is unlikely. The coherent synchrotron processes are shown to require either an excessively large number of relativistic electrons or an unstable pitch angle anisotropy. Plasma processes seem to be the necessary explanation for the bursts under consideration. Subject headings: plasmas - Sun: radio radiation synchrotron radiation Title: Type IV dm bursts: onset and sudden reductions. Authors: Benz, A. O.; Kuijpers, J. Bibcode: 1976SoPh...46..275B Altcode: The effect of collisions of suprathermal electrons with a thermal background plasma is investigated and is shown to cause flattening of a monotonically descending velocity distribution of fast particles. As a result flare-produced energetic electrons that are trapped in a coronal magnetic arch and that are initially distributed in energy according to a power-law, can give rise to an instability of Langmuir waves in the background plasma and the subsequent emission of continuum radiation as observed in type IV dm bursts. Title: Simulation of analog spectrograms of solar radio bursts Authors: Benz, A. O.; Asper, H. K. Bibcode: 1976KlBer..19..383B Altcode: Analog spectrograms are simulated for a well-documented solar radio burst by numerical transformation of digital data recorded on magnetic tape by a radio spectrograph. The simulations were carried out to observe how different and sometimes erroneous classifications of radio bursts may result from instrumental characteristics, such as threshold, noise figure, gain, film blackening, and frequency response. Simulated spectrograms are presented which illustrate the effects of different logarithmic compression rates and different receiver frequency responses. It is shown that suprising effects are possible with different logarithmic compression rates, that a frequency-dependent sensitivity may considerably change the drift rate of type III bursts, and that different relations between solar flux and grey level on the film can alter the morphology of a burst to a remarkable extent and result in different classifications. It is concluded that a moderately uneven frequency response has little effect on a burst shape in the frequency-time plane if the received burst signal is not near threshold. Title: The New Digitalized Solar Radio Spectrograph in Durnten. Authors: von Arx, B.; Benz, A. O.; Tarnstrom, G. L. Bibcode: 1975BAAS....7..407V Altcode: No abstract at ADS Title: Type IVdm Bursts vs. the Razin Effect. Authors: Benz, A. O.; Tarnstrom, G. L. Bibcode: 1975BAAS....7..439B Altcode: No abstract at ADS Title: First digital observation with the Duernten radio spectrograph. Authors: Perrenoud, M. R.; Benz, A. O.; Tarnstrom, G. L. Bibcode: 1975MmArc.105..121P Altcode: No abstract at ADS Title: First digital observation with the Dürnten radio spectrograph Authors: Perrenoud, M. R.; Benz, A. O.; Tarnstrom, G. L. Bibcode: 1975cesra...5..121P Altcode: No abstract at ADS Title: A possible Mechanism for Type V Bursts Authors: Benz, A. O. Bibcode: 1974cesra...4..157B Altcode: No abstract at ADS Title: The Complex Radio Burst of May 3, 1973 Authors: Benz, A. O.; Tlamicha, A.; Urbarz, H. Bibcode: 1974cesra...4..191B Altcode: No abstract at ADS Title: Harmonic Structure in a Solar Type V Burst Authors: Benz, A. O. Bibcode: 1973NPhS..242...38B Altcode: 1973Natur.242...38B WHEN type V bursts were first identified as a distinct class in 1958, their seemingly featureless continuum radiation was interpreted as synchrotron emission1. Later it was observed2, however, that the source positions at different frequencies were not identical. It has then been suggested2,3 that type V bursts are most likely due to Čerenkov radiation from coherent plasma waves caused by fast electrons (speed ≍ 1/3 c) which are magnetically trapped in the corona4. In the plasma wave theory radiation is emitted near the local plasma frequency and/or its integer multiples. In spite of the hindering large bandwidth, one would nevertheless expect to recognize (at least sporadically) harmonic structure in the spectra of type V bursts. This is generally considered to be an observational confirmation of any plasma wave emission theory. So far it has not been observed in type V bursts, save for one inconclusive indication (on May 8, 1959)2. Title: The Acceleration of Solar Wind Protons and Heavy Ions. Authors: Benz, Arnold Otto Bibcode: 1973PhDT.........8B Altcode: No abstract at ADS Title: Magnetically Trapped Particles in the Lower Solar Atmosphere Authors: Benz, A. O.; Gold, T. Bibcode: 1971SoPh...21..157B Altcode: The trapping of energetic electrons and protons in a simple, arched magnetic field imbedded in the lower solar atmosphere was considered. The lifetime of electrons with kinetic energies up to about 1.5 MeV was found to be completely determined by the motion of the mirror points, provided the gyro-synchrotron loss can be neglected. The same motion also influences the lifetimes of more energetic electrons, up to 10 MeV. This was not found to be the case for protons in the range from 1 MeV to 100 GeV. Some fluid and streaming instabilities were also considered; they pull the particles upward, raise their mirror points, and increase their lifetime. The emission of gyro-synchrotron radiation and bremsstrahlung in this model has been related to observations. Using the duration of non-thermal X-ray peaks given by Kane (1969), the altitude of injection of energetic particles was estimated.