Author name code: bastian ADS astronomy entries on 2022-09-14 author:"Bastian, Timothy S." OR author:"Bastian, Tim" ------------------------------------------------------------------------ Title: Solar Observing with the Atacama Large Millimeter-Submillimeter Array Authors: Bastian, Timothy; Shimojo, Masumi; Barta, Miroslav; White, Stephen; Iwai, Kazumasa Bibcode: 2022arXiv220901659B Altcode: The Atacama Large Millimeter-submillimeter Array (ALMA), sited on the high desert plains of Chajnantor in Chile, has opened a new window onto solar physics in 2016 by providing continuum observations at millimeter and sub-millimeter wavelengths with an angular resolution comparable to that available at optical (O), ultraviolet (UV), extreme ultraviolet (EUV), and X-ray wavelengths, and with superior time resolution. In the intervening years, progress has been made testing and commissioning new observing modes and capabilities, in developing data calibration strategies, and in data imaging and restoration techniques. Here we review ALMA current solar observing capabilities, the process by which a user may propose to use the instrument, and summarize the observing process and work flow. We then discuss some of the challenges users may encounter in imaging and analyzing their data. We conclude with a discussion of additional solar observing capabilities and modes under consideration that are intended to further exploit the unique spectral coverage provided by ALMA. Title: The quiet Sun at mm Wavelengths as Seen by ALMA Authors: Alissandrakis, Costas; Bastian, Timothy; Brajša, Roman Bibcode: 2022arXiv220902569A Altcode: Solar observations at sub-mm, mm and cm wavelengths offer a straightforward diagnostic of physical conditions in the solar atmosphere because they yield measurement of brightness temperature which, for optically thick features, equals intrinsic temperature - much unlike solar diagnostics in other spectral ranges. The Atacama Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a new, hitherto underexplored, spectral window for studying the enigmatic solar chromosphere. In this review we discuss initial ALMA studies of the quiet chromosphere that used both single-dish and compact-array interferometric observing modes. We present results on the temperature structure of the chromosphere, comparison with classic empirical models of the chromosphere, and observations of the chromospheric network and spicules. Furthermore, we discuss what may be expected in the future, since the ALMA capabilities continuously expand and improve towards higher angular resolution, wavelength coverage, and polarization measurement for magnetometry. Title: Radio Emission from UV Cet: Auroral Emission from a Stellar Magnetosphere Authors: Bastian, T. S.; Cotton, W. D.; Hallinan, G. Bibcode: 2022ApJ...935...99B Altcode: 2022arXiv220614099B The archetypical flare star UV Cet was observed by MeerKAT on 2021 October 5-6. A large radio outburst with a duration of ~2 hr was observed between 886 and 1682 MHz, with a time resolution of 8 s and a frequency resolution of 0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is characterized by three peaks containing a multitude of broadband arcs or partial arcs in the time-frequency domain. In general, the arcs are highly right-hand circularly polarized. At the end of the third peak, brief bursts occur that are significantly elliptically polarized. We present a simple model that appears to be broadly consistent with the characteristics of the radio emission from UV Cet. Briefly, the stellar magnetic field is modeled as a dipole aligned with the rotational axis of the star. The radio emission mechanism is assumed to be due to the cyclotron maser instability, where x-mode radiation near the electron gyrofrequency is amplified. While the elliptically polarized bursts may be intrinsic to the source, rather stringent limits are imposed on the plasma density in the source and along the propagation path. We suggest that the elliptically polarized radiation may instead be the result of reflection on an overdense plasma structure at some distance from the source. The radio emission from UV Cet shares both stellar and planetary attributes. Title: Understanding the Correlation between Solar Coronal Abundances and F10.7 Radio Emission Authors: To, Andy S. H.; Baker, Deborah; Long, David; James, Alexander; Brooks, David; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Bastian, Tim; Lomuscio, Samantha; Stansby, David Bibcode: 2022cosp...44.2592T Altcode: Solar corona plasma composition, derived from full-Sun spectra, and the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r = 0.88) during the recent weak solar cycle. However, this correlation becomes nonlinear at times of increased solar magnetic activity. We used co-temporal, high spatial resolution, radio (JVLA), and EUV (Hinode/EIS) images of the Sun taken on the 3 and 7 April 2020 to understand the underlying causes of the non-linearity of the FIP bias-F10.7 solar index correlation. We then calculated differential emission measures from AIA images, and paired them with the observed FIP bias to predict the bremsstrahlung component of F10.7 radio emission. Results of this study provide constraints on the amplitude of composition variability related to solar cycle amplitude, and provide an alternative method to calculate coronal composition. Title: A first look at the submillimeter Sun with ALMA Authors: Alissandrakis, C. E.; Bastian, T. S.; Nindos, A. Bibcode: 2022A&A...661L...4A Altcode: 2022arXiv220501008A We present the first full-disk solar images obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7 (0.86 mm; 347 GHz). In spite of the low spatial resolution (21″), several interesting results were obtained. During our observation, the sun was practically devoid of active regions. Quiet Sun structures on the disk are similar to those in Atmospheric Imaging Assembly images at 1600 Å and 304 Å, after the latter are smoothed to the ALMA resolution, as noted previously for Band 6 (1.26 mm) and Band 3 (3 mm) images; they are also similar to negative Hα images of equivalent resolution. Polar coronal holes, which are clearly seen in the 304 Å band and small Hα filaments, are not detectable at 0.86 mm. We computed the center-to-limb variation of the brightness temperature, Tb, in Band 7, as well as in Bands 6 and 3, which were obtained during the same campaign, and we combined them to a unique curve of Tb(log μ100), where μ100 is the cosine of the heliocentric angle reduced to 100 GHz. Assuming that the absolute calibration of the Band 3 commissioning observations is accurate, we deduced a brightness temperature at the center of the disk of 6085 K for Band 7, instead of the value of 5500 K, extrapolated from the recommended values for Bands 3 and 6. More importantly, the Tb(log μ100) curve flattens at large values of μ100, and so does the corresponding Te(log τ100) at large τ100. This is probably an indication that we are approaching the temperature minimum. Title: Novel Magnetic Field and Electron Density Measurements of CMEs (within AU) with the Proposed Multiview Observatory for Solar Terrestrial Science (MOST) Mission Authors: Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Fung, Shing; Gopalswamy, Nat; Jian, Lan; Kenny, Megan; Kooi, Jason; Lazio, Joseph; Li, Lihua; Nieves-Chinchilla, Teresa; Pevtsov, Alexei; Wexler, David; Wilson, Lynn; Wood, Brian; Bale, Stuart; Bastian, Tim Bibcode: 2021AGUFMSH33A..08J Altcode: The Multiview Observatory for Solar Terrestrial Science (MOST) mission concept will be the most advanced solar observatory to date (Gopalswamy et al, SH0001, 2021). Comprising four spacecraft, two located in the L4 and ahead of L4 position and two located in the L5 and behind of the L5 position, the four lines-of-sight (LOSs) form the basis for the unique Faraday Effect Tracker of Coronal and Heliospheric Structures (FETCH) instrument (Wexler et al, SH0019, 2021). We report on our modeling into the expected Faraday rotation (FR) caused by an Earth-directed CME crossing the MOST/FETCH radio-sensing paths using a heliospheric 3-D MHD model to obtain the necessary LOS data on electron density and magnetic field components (see example image). Specifically, we utilized simulation data of the 2005 May 13 CME (Manchester IV et al., 2014, Plasma Phys. Control. Fusion), which erupted from the north-south polarity inversion line of AR 10759 at 16:03 UT, reaching speeds around 2000 km/s in the corona. The trajectory of the CME at an acute angle to the Earth-Sun line crosses each FETCH LOS at a different time. Two LOSs are at different viewing angles with little overlap between the CME sheath and magnetic flux rope core. A blind test fitting of the Faraday rotation functions (Figures 6 and 7 in Jensen et al., 2010, Sol. Phys.) to the simulated FETCH observations reproduced the orientation of the CME for its handedness as well as its associated complementary degenerate solution. In conclusion, one of the four LOSs will be more sensitive to observing CME flux rope structure of Earthward CMEs, depending on their trajectory. We find that two of the four LOSs enable analyzing CME evolution, whereas the other two LOSs enable analyzing the average magnetic field vector in the corresponding high density regions dominating the measurements at that time. For example, the average sheath magnetic field vector can be partially measured in the plane of the ecliptic due to the angular differences between 2 LOSs. We discuss future work as this effort develops. Title: FETCH Concept: Investigating Quiescent and Transient Magnetic Structures in the Inner Heliosphere using Faraday Rotation of Spacecraft Radio Signals Authors: Wexler, David; Jensen, Elizabeth; Gopalswamy, Nat; Wilson, Lynn; Fung, Shing; Nieves-Chinchilla, Teresa; Jian, Lan; Bastian, Tim; Pevtsov, Alexei; Manchester, Ward; Kenny, Megan; Lazio, Joseph; Wood, Brian; Kooi, Jason Bibcode: 2021AGUFMSH31A..05W Altcode: The Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH) is a new instrument concept being developed to probe coronal and interplanetary magnetic field structures in the ambient solar wind, corotating interaction regions and coronal mass ejections (CMEs) as they evolve in the inner heliosphere. FETCH is one of the instruments that constitute the Multiview Observatory for Solar Terrestrial (MOST) science mission. FETCH will measure Faraday rotation (FR) of linearly polarized spacecraft radio signals transmitted along four lines of sight provided by the four MOST spacecraft: two large spacecraft deployed at Sun-Earth Lagrange points 4 and 5 and two smaller spacecraft, one ahead of L4 and the other behind L5. FETCH will transmit and receive at selected radio frequencies in the 1-100 MHz range for lines of sight with solar impact parameters < 0.5 AU. FR yields the line-of-sight (LOS) integrated product of electron number density and LOS-projected magnetic field strengths. The FR measurements will be obtained from the Stokes polarization parameters while additional plasma parameters, such as electron column density, will be extracted from other signal diagnostics. The multifrequency FR data and four lines-of-sight will be used to constrain the magnetic field topology and dynamics of interplanetary plasma structures upstream from Earth. Unique to this FR experiment, the FETCH transmitter-receiver instrumentation is positioned such that the entire sensing path remains in interplanetary space, thus avoiding the complications of trans-ionospheric FR observations. The FETCH key science objectives include: (1) characterizing CME magnetic field structure and flux rope orientation, (2) tracking CME propagation and shock signatures, (3) understanding the magnetic field features of corotating interaction regions in the extended corona and inner heliosphere, and (4) determination of large-scale MHD wave organization in regions of developed ambient solar wind and its evolution during perturbed flows. The MOST mission will build upon the achievements of the Solar Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) missions during the last couple of decades. FETCH will help fill the long-standing measurement gap of magnetic field data in the inner heliosphere. Title: The Multiview Observatory for Solar Terrestrial Science (MOST) Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall, Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe, Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung, Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward; Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy; DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi, Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal; DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran; Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei; Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan Bibcode: 2021AGUFMSH12A..07G Altcode: The Multiview Observatory for Solar Terrestrial Science (MOST) is a comprehensive mission concept targeting the magnetic coupling between the solar interior and the heliosphere. The wide-ranging imagery and time series data from MOST will help understand the solar drivers and the heliospheric responses as a system, discerning and tracking 3D magnetic field structures, both transient and quiescent in the inner heliosphere. MOST will have seven remote-sensing and three in-situ instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate surface and subsurface magnetism by exploiting the combination of helioseismic and magnetic-field measurements in the photosphere; (2) Inner Coronal Imager in EUV (ICIE) to study large-scale structures such as active regions, coronal holes and eruptive structures by capturing the magnetic connection between the photosphere and the corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to seamlessly study transient and quiescent large-scale coronal structures extending from the ICIE field of view (FOV); (5) Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a novel radio package to determine the magnetic field structure and plasma column density, and their evolution within 0.5 au; (6) Heliospheric Imager with Polarization (HIP) to track solar features beyond the WCOR FOV, study their impact on Earth, and provide important context for FETCH; (7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams and shocks propagating into the heliosphere via passive radio emission; (8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra of electrons, and ions from H to Fe at multiple spatial locations and use energetic particles as tracers of magnetic connectivity; (9) Solar Wind Magnetometer (MAG) to characterize magnetic structures at 1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma structures at 1 au. MOST will have two large spacecraft with identical payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4 and behind L5 to carry additional FETCH elements. MOST will build upon SOHO and STEREO achievements to expand the multiview observational approach into the first half of the 21st Century. Title: ALMA observations of the variability of the quiet Sun at millimeter wavelengths Authors: Nindos, A.; Patsourakos, S.; Alissandrakis, C. E.; Bastian, T. S. Bibcode: 2021A&A...652A..92N Altcode: 2021arXiv210604220N
Aims: We address the variability of the quiet solar chromosphere at 1.26 mm and 3 mm with a focus on the study of spatially resolved oscillations and transient brightenings, which are small, weak events of energy release. Both phenomena may have a bearing on the heating of the chromosphere.
Methods: We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quiet Sun at 1.26 mm and 3 mm. The spatial and temporal resolution of the data were 1 − 2″ and 1 s, respectively. The concatenation of light curves from different scans yielded a frequency resolution in spectral power of 0.5−0.6 mHz. At 1.26 mm, in addition to power spectra of the original data, we degraded the images to the spatial resolution of the 3 mm images and used fields of view that were equal in area for both data sets. The detection of transient brightenings was made after the effect of oscillations was removed.
Results: At both frequencies, we detected p-mode oscillations in the range 3.6−4.4 mHz. The corrections for spatial resolution and field of view at 1.26 mm decreased the root mean square (rms) of the oscillations by a factor of 1.6 and 1.1, respectively. In the corrected data sets, the oscillations at 1.26 mm and 3 mm showed brightness temperature fluctuations of ∼1.7 − 1.8% with respect to the average quiet Sun, corresponding to 137 and 107 K, respectively. We detected 77 transient brightenings at 1.26 mm and 115 at 3 mm. Although their majority occurred in the cell interior, the occurrence rate per unit area of the 1.26 mm events was higher than that of the 3 mm events; this conclusion does not change if we take into account differences in spatial resolution and noise levels. The energy associated with the transient brightenings ranged from 1.8 × 1023 to 1.1 × 1026 erg and from 7.2 × 1023 to 1.7 × 1026 erg for the 1.26 mm and 3 mm events, respectively. The corresponding power-law indices of the energy distribution were 1.64 and 1.73. We also found that ALMA bright network structures corresponded to dark mottles or spicules that can be seen in broadband Hα images from the GONG network.
Conclusions: The fluctuations associated with the p-mode oscillations represent a fraction of 0.55−0.68 of the full power spectrum. Their energy density at 1.26 mm is 3 × 10−2 erg cm−3. The computed low-end energy of the 1.26 mm transient brightenings is among the smallest ever reported, irrespective of the wavelength of the observation. Although the occurrence rate per unit area of the 1.26 mm transient brightenings was higher than that of the 3 mm events, their power per unit area is smaller likely due to the detection of many weak 1.26 mm events. Title: Enhancing ALMA's Future Observing Capabilities Authors: Maud, L.; Villard, E.; Takahashi, S.; Asaki, Y.; Bastian, T.; Cortes, P.; Crew, G.; Fomalont, E.; Hales, A.; Ishii, S.; Matthews, L.; Messias, H.; Nagai, H.; Sawada, T.; Schieven, G.; Shimojo, M.; Vila-Vilaro, B.; Biggs, A.; Petry, D.; Phillips, N.; Paladino, R. Bibcode: 2021Msngr.183...13M Altcode: With each observing cycle at the Atacama Large Millimeter/submillimeter Array (ALMA) new features and observing modes are offered. Here we provide some background about how these new capabilities are tested and then made available to ALMA users. These activities help to drive the cutting-edge science conducted with ALMA and to maintain ALMA's position as the foremost interferometric array operating at millimetre and submillimetre wavelengths. We focus in particular on opening up high-frequency observing using ALMA's longest baselines, which offers the highest possible angular resolution. Title: Solar Radio Burst Effects on Radio- and Radar-Based Systems Authors: Gary, Dale E.; Bastian, Timothy S. Bibcode: 2021GMS...262..141G Altcode: Radio emission from solar flares can attain such high flux density that the Sun becomes the dominant source of broadband radio noise in the terrestrial environment. The effects of this radio noise on wireless communication and navigation systems can take many forms, depending on the design and operation of the affected system. These effects can be of special concern for regional or global systems, since the effects can occur simultaneously over the entire sunlit hemisphere of Earth. This chapter reviews the origin of solar radio bursts, the threat they pose based on statistics of the flux-density distribution of such events vs. frequency, and some of the effects that have been documented in the literature. The chapter concludes with a discussion of the potential impacts on current and future technology and how these impacts can be mitigated (1) through improved radio monitoring of the Sun in both circular polarizations to supply meaningful real-time warnings, (2) through improved scientific understanding of the solar phenomena underlying the radio bursts, and (3) through improved system design that takes account of solar radio noise. Title: The ObsMode 2020 Process Authors: Takahashi, Satoko; Fomalont, Edward B.; Asaki, Yoshiharu; Crew, Geoff; Matthews, Lynn D.; Cortes, Paulo; Vila-Vilaro, Baltasar; Bastian, Tim; Shimojo, Masumi; Biggs, Andy; Messias, Hugo; Hales, Antonio; Villard, Eric; Humphreys, Elizabeth Bibcode: 2021arXiv210412681T Altcode: ObsMode is a yearly process which aims at preparing capabilities for future ALMA Observing cycles. The process has been running for a number of years tied to each ALMA observing cycle, with various leaderships. This document specifically summarizes the ObsMode2020 process (April- October 2020) with a new scheme led by the Joint ALMA Observatory. In the ObsMode2020 process, seven capabilities are identified as high priority items, for which it was originally aimed to be ready for Cycle 9. However, because of the observatory shutdown due to the covid-19 pandemic, we were forced to delay the test plan by one year. While no new data sets were obtained during the observatory shutdown, verifications using the existing data allowed us to offer the 7m-array polarization capability (in ACA standalone mode, single field) for Cycle 8 starting from October, 2021. In addition, subsystem readiness and policy-side preparations for the phased array observing mode were improved for Cycle 8. Other high priority items were decided to be carried over to the ObsMode2021 process. Title: Radio Spectral Imaging of an M8.4 Eruptive Solar Flare: Possible Evidence of a Termination Shock Authors: Luo, Yingjie; Chen, Bin; Yu, Sijie; Bastian, T. S.; Krucker, Säm Bibcode: 2021ApJ...911....4L Altcode: 2021arXiv210206259L Solar flare termination shocks have been suggested as one of the viable mechanisms for accelerating electrons and ions to high energies. Observational evidence of such shocks, however, remains rare. Using radio dynamic spectroscopic imaging of a long-duration C1.9 flare obtained by the Karl G. Jansky Very Large Array (VLA), Chen et al. suggested that a type of coherent radio bursts, referred to as "stochastic spike bursts," were radio signatures of nonthermal electrons interacting with myriad density fluctuations at the front of a flare termination shock. Here we report another stochastic spike burst event recorded during the extended energy release phase of a long-duration M8.4-class eruptive flare on 2012 March 10. VLA radio spectroscopic imaging of the spikes in 1.0-1.6 GHz shows that, similar to the case of Chen et al., the burst centroids form an extended, ∼10″-long structure in the corona. By combining extreme-ultraviolet imaging observations of the flare from two vantage points with hard X-ray and ultraviolet observations of the flare ribbon brightenings, we reconstruct the flare arcade in three dimensions. The results show that the spike source is located at ∼60 Mm above the flare arcade, where a diffuse supra-arcade fan and multitudes of plasma downflows are present. Although the flare arcade and ribbons seen during the impulsive phase do not allow us to clearly understand how the observed spike source location is connected to the flare geometry, the cooling flare arcade observed 2 hr later suggests that the spikes are located in the above-the-loop-top region, where a termination shock presumably forms. Title: Multiwavelength Observations of the Formation and Eruption of a Complex Filament Authors: Zhang, Y.; Bastian, T. S.; Liu, J. H.; Yu, S. J.; Feng, S.; Chen, J.; Yan, Y. H. Bibcode: 2021ApJ...910...40Z Altcode: We present an analysis of the formation and eruption of a filament and fast coronal mass ejection associated with a flare that occurred in active region 11429 using observations in the ultraviolet, extreme ultraviolet, X-ray, and radio wavelength bands. Precursor activity began as an interaction between two filaments, F1 and F2, that are identified as having twisted magnetic flux ropes (MFRs). Transient brightenings in all wavelengths are observed as a result of this interaction, likely the result of magnetic reconnection between the two filaments. This interaction results in a reconfiguration of the two filaments into a long overlying filament and a shorter low-lying filament. The upper filament subsequently undergoes a partial confined eruption. Plasma flows originating near the east footpoint of F1 lead to an extension of the upper filament into the filament channel to the west, resulting in a new active region filament (ARF). This new filament begins a slow rise and expansion. During its slowly rising phase, the MFR in which the filament is embedded becomes visible, with both the filament and flux rope rising and expanding simultaneously. The twist of the magnetic rope is determined as four turns. The erupting configuration changes from a twisted arch shape to a reversed γ shape within ∼75 s at the beginning of the fast-rise phase, representing a transformation from twist to writhe. The observations provide a clear example of filament formation via the tether-cutting reconnection of two nearby filaments. A helical kink instability may be the trigger of the ARF eruption. Title: ALMA and IRIS Observations of the Solar Chromosphere. II. Structure and Dynamics of Chromospheric Plages Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora, Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.; Sainz Dalda, Alberto Bibcode: 2021ApJ...906...83C Altcode: 2020arXiv201205970C We propose and employ a novel empirical method for determining chromospheric plage regions, which seems to better isolate a plage from its surrounding regions than other methods commonly used. We caution that isolating a plage from its immediate surroundings must be done with care in order to successfully mitigate statistical biases that, for instance, can impact quantitative comparisons between different chromospheric observables. Using this methodology, our analysis suggests that λ = 1.25 mm free-free emission in plage regions observed with the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may not form in the low chromosphere as previously thought, but rather in the upper chromospheric parts of dynamic plage features (such as spicules and other bright structures), i.e., near geometric heights of transition-region temperatures. We investigate the high degree of similarity between chromospheric plage features observed in ALMA/Band6 (at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph (IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are not as well correlated with ALMA/Band6 as was previously thought, and we discuss discrepancies with previous works. Lastly, we report indications of chromospheric heating due to propagating shocks supported by the ALMA/Band6 observations. Title: ALMA and IRIS Observations of the Solar Chromosphere. I. An On-disk Type II Spicule Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora, Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.; Sainz Dalda, Alberto Bibcode: 2021ApJ...906...82C Altcode: 2020arXiv200512717C We present observations of the solar chromosphere obtained simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph. The observatories targeted a chromospheric plage region of which the spatial distribution (split between strongly and weakly magnetized regions) allowed the study of linear-like structures in isolation, free of contamination from background emission. Using these observations in conjunction with a radiative magnetohydrodynamic 2.5D model covering the upper convection zone all the way to the corona that considers nonequilibrium ionization effects, we report the detection of an on-disk chromospheric spicule with ALMA and confirm its multithermal nature. Title: Next-Generation Solar Radio Imaging Spectroscopy Authors: Gary, D. E.; Bastian, T.; Chen, B.; Saint-Hilaire, P.; White, S. M. Bibcode: 2020AGUFMSH056..07G Altcode: Recent progress using instruments such as the Expanded Owens Valley Solar Array (EOVSA) and the Jansky Very Large Array (JVLA) have amply demonstrated the power of radio imaging spectroscopy at centimeter and decimeter wavelengths for quantitative diagnostics of both flaring and non-flaring solar plasma. For example, the unique sensitivity of radio emission to the flaring coronal magnetic field has been dramatically shown in a series of recent EOVSA papers, along with accelerated electron diagnostics in the same volume. JVLA observations have been used to probe particle acceleration in a termination shock during a flare. In addition, multi-frequency full-disk imaging of the non-flaring Sun with EOVSA is showing promise for quantitative diagnostics of electron-based emission measure and active region magnetic field and temperature structure. But EOVSA and the JVLA are mere demonstrators for a far more advanced solar radio instrument, the Frequency Agile Solar Radiotelescope (FASR), that is designed to address a much more comprehensive science program with much greater precision than is possible with EOVSA or non-solar-dedicated instruments like the JVLA. This includes direct imaging of Coronal Mass Ejections (CMEs) and their associated energetic particles both on and off the solar disk, routine coronal magnetic field measurements at high cadence, and continuous sampling of the full-Sun coronal temperature and emission measure. Here we use examples from EOVSA and the JVLA to envision what FASR's advanced design will be capable of. When paired with highly complementary new X-ray-based diagnostics from space, the remote sensing of high-energy particles through radio imaging spectroscopy from the ground provides a far more complete picture of the broad range of energetic phenomena that occur on the Sun than either alone. Scientists interested in high-energy solar phenomena have ample incentive to coordinate their efforts to ensure that space- and ground-based capabilities advance together. Title: Detection of 2-4 GHz Continuum Emission from ɛ Eridani Authors: Suresh, A.; Chatterjee, S.; Cordes, J. M.; Bastian, T. S.; Hallinan, G. Bibcode: 2020ApJ...904..138S Altcode: 2020arXiv201005929S The nearby star ɛ Eridani has been a frequent target of radio surveys for stellar emission and extraterrestrial intelligence. Using deep 2-4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with ɛ Eridani to within 0"06 (≲2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of ɛ Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2-6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α ≃ 2) of the 2-6 GHz spectrum strongly disfavors its interpretation as stellar-wind-associated thermal bremsstrahlung (α ≃ 0.6). Attributing the entire observed 2-4 GHz flux density to thermal free-free wind emission, we thus derive a stringent upper limit of 3 × 10-11 M⊙ yr-1 on the mass-loss rate from ɛ Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of ɛ Eridani. Title: ALMA and IRIS Observations Highlighting the Dynamics and Structure of Chromospheric Plage Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen, V. H.; de la Cruz Rodriguez, J.; Szydlarski, M.; Jafarzadeh, S.; Wedemeyer, S.; Bastian, T.; Sainz Dalda, A. Bibcode: 2020AGUFMSH0010009C Altcode: We present observations of the solar chromosphere obtained simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). The observatories targeted a chromospheric plage region of which the spatial distribution (split between strongly and weakly magnetized regions) allowed the study of linear-like structures in isolation, free of contamination from background emission. Using these observations in conjunction with a radiative magnetohydrodynamic 2.5D model covering the upper convection zone all the way to the corona that considers non-equilibrium ionization effects, we report the detection of an on-disk chromospheric spicule with ALMA and confirm its multithermal nature. In addition, we discuss the strikingly high degree of similarity between chromospheric plage features observed in ALMA/Band6 and IRIS/\ion{Si}{4} (also reproduced in our model) suggesting that ALMA/Band6 does not observe in the low chromosphere as previously thought but rather observes the upper chromospheric parts of structures such as spicules and other bright structures above plage at geometric heights near transition region temperatures. We also show that IRIS/\ion{Mg}{2} is not as well correlated with ALMA/Band6 as was previously thought. For these comparisons, we propose and employ a novel empirical method for the determination of plage regions, which seems to better isolate plage from its surrounding regions as compared to other methods commonly used. We caution that isolating plage from its immediate surroundings must be done with care to mitigate statistical bias in quantitative comparisons between different chromospheric observables. Lastly, we report indications for chromospheric heating due to traveling shocks supported by the ALMA/Band6 observations. Title: Observations of Solar Spicules at Millimeter and Ultraviolet Wavelengths Authors: Bastian, T.; De Pontieu, B.; Shimojo, M.; Iwai, K.; Alissandrakis, C.; Nindos, A.; Vial, J. C.; White, S. M. Bibcode: 2020AGUFMSH004..08B Altcode: Solar spicules are a ubiquitous chromospheric phenomenon in which multitudes of dynamic jets with temperatures of order 104 K extend thousands of kilometers into the solar atmosphere. Recent progress has been made refining the observational characteristics of spicules using the Hinode Solar Optical Telescope (SOT) and the Interface Region Imaging Spectrograph (IRIS) observations at optical and ultraviolet wavelengths, respectively. Two types of spicule have been identified. Type I spicules, prevalent in solar active regions, have upward speeds of order 25 km/s and lifetimes of 3-7 min. They may be the limb counterpart to shock-wave-driven fibrils commonly seen against the solar disk in active regions. In contrast, type II spicules, more common in quiet regions and coronal holes, display upward speeds of 50-150 km/s, lifetimes of 30-110 s, and appear to be partially heated to temperatures of 105 K and higher. These observations have provoked intense interest in spicules and have led to proposals that type II spicules play a central role as a source of hot plasma in the corona. Nevertheless, their role in mass and energy transport between the lower and upper layers of the solar atmosphere remains an outstanding problem.

Here, we report imaging observations of solar spicules at millimeter wavelengths using the Atacama Large Millimeter-submillimeter Array (ALMA) with arcsecond angular resolution. Continuum millimeter wavelength radiation forms under conditions of local thermodynamic equilibrium, thereby providing a complementary tool to UV lines, which form under non-LTE conditions. The observations were made on 2018 December 24-25 at λ=1.25 mm and λ=3 mm. The ALMA observations pose special challenges, particularly at 1.25 mm, where the limited field of view of the instrument motivated us to use a novel mosaic imaging technique: multiple pointings were assembled to form a single map with an angular resolution of 1" x 0.7" on a cadence of roughly 2 min. In contrast, we were able to image at 3 mm continuously, with a map cadence of 2 s and an angular resolution of 2.3" x 1.3".

We compare and contrast the morphology and dynamics of mm-λ observations of spicules with those obtained by IRIS at UV wavelengths and place constraints on spicule temperatures and masses using the joint millimeter-wavelength observations. Title: Radio Spectral Imaging of Another Likely Solar Flare Termination Shock Event Authors: Luo, Y.; Chen, B.; Yu, S.; Bastian, T. Bibcode: 2020SPD....5121118L Altcode: Solar flare termination shocks are believed to be produced by super-magnetosonic reconnection outflows impinging upon dense, reconnected flare loops. They have been suggested as one of the viable mechanisms for accelerating electrons and ions to high energies. Although such shocks have been indicated to exist in numerical experiments, observational evidence remains rare. Using radio dynamic spectroscopic imaging of a long-duration C1.9 flare obtained by the Karl G. Jansky Very Large Array (VLA), Chen et al. 2015 (Science, 350, 1238) found that a type of decimetric coherent bursts, referred to as "stochastic spike bursts", were likely the radio signature of nonthermal electrons interacting with myriad density fluctuations at the front of a flare termination shock. Here we report another spike burst event recorded during the gradual phase of a long-duration M8.4-class eruptive flare on 2012 March 10 by VLA in 1—2 GHz. VLA radio spectroscopic imaging of the spikes shows that, similar to the case of Chen et al. 2015, the burst centroids form an extended structure in the corona located well above the flare arcade. We combine RHESSI X-ray imaging, extreme ultraviolet imaging observations of the flare from two vantage points, one from the Solar Dynamics Observatory (SDO) against the disk and another from the Solar Terrestrial Relations Observatory Ahead (STEREO-A) from the limb, as well as radio imaging to elucidate the location of spike bursts in 3 dimensions. The results show that this structure is located in the above-the-looptop region where a termination shock presumably forms. In the close vicinity of this structure, we also find the presence of a diffuse supra-arcade fan structure where multitudes of plasma downflows are observed from both SDO and STEREO-A. Our observations provide another piece of evidence that supports the interpretation of such stochastic spike bursts as radio emission from solar flare termination shocks. Title: Modeling the quiet Sun cell and network emission with ALMA Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T. S.; Patsourakos, S. Bibcode: 2020A&A...640A..57A Altcode: 2020arXiv200609886A Observations of the Sun at millimeter wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity to investigate the temperature structure of the solar chromosphere. In this article we expand our previous work on modeling the chromospheric temperature of the quiet Sun, by including measurements of the brightness temperature in the network and cell interiors, from high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We also examine the absolute calibration of ALMA full-disk images. We suggest that the brightness temperature at the center of the solar disk in Band 6 is ∼440 K above the value recommended by White et al. (2017, Sol. Phys., 292, 88). In addition, we give improved results for the electron temperature variation of the average quiet Sun with optical depth and the derived spectrum at the center of the disk. We found that the electron temperature in the network is considerably lower than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319) and that of the cell interior considerably higher than predicted by model A. Depending on the network/cell segregation scheme, the electron temperature difference between network and cell at τ = 1 (100 GHz) ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted by the models; similarly, the electron temperature, Te ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model prediction. We also found that the network/cell Te(τ) curves diverge as τ decreases, indicating an increase of contrast with height and possibly a steeper temperature rise in the network than in the cell interior. Title: Transient brightenings in the quiet Sun detected by ALMA at 3 mm Authors: Nindos, A.; Alissandrakis, C. E.; Patsourakos, S.; Bastian, T. S. Bibcode: 2020A&A...638A..62N Altcode: 2020arXiv200407591N
Aims: We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere.
Methods: Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly.
Results: We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 - 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones).
Conclusions: We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings. Title: Modeling of the Brightness of the Chromospheric Network Based on ALMA High Resolution Observations of the Quiet Sun Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T.; Patsourakos, S. Bibcode: 2020AAS...23610607A Altcode: ALMA observations of the Sun at mm-λ offer a unique opportunity to investigate the temperature/density structure of the solar chromosphere. In a previous work (Alissandrakis et al 2017, A&A 605, A78) we measured the center-to-limb variation of the brightness temperature, Tb, using low resolution ALMA full-disk observations in Band 3 (3mm) and Band 6 (1.26 mm), together with data at 0.85 mm from Bastian et al. 1993 (ApJ, 415, 364). Combining all data and inverting the solution of the transfer equation we found that the electron temperature, Te, in the range of 0.34 < τ100 < 12, where τ100 is the optical depth at 100 GHz, was ~5% (~300 K) below the one predicted by model C (average quiet sun) of FAL93 (Fontenla, Avrett, & Loeser, 1993, ApJ, 406, 319). Here we expand that work by including measurements of the brightness temperature in the network and cell interiors, from high resolution ALMA images in Bands 3 and 6. We found that the observed Tb in the network is considerably lower than predicted by the FAL93 model F and that of the cell interior considerably higher than predicted by the FAL93 model A. The observed network/cell difference of brightness temperature at the center of the disk, at 100 GHz is about 920 K, compared to ~3250 K predicted by the FAL93 models; similarly, the Tb, ratio is ~1.14, against ~1.51 of the model prediction. After inversion of the observed data, the electron temperature of cell interior at τ100=1 is ~390 K below the average (~600 K above model A) and of the network ~400 K above the average (~1800 K below model A). The implications of these results will be discussed. We will also discuss the question of the normalization of brightness temperature observed by ALMA. Title: Machine Learning in Heliophysics and Space Weather Forecasting: A White Paper of Findings and Recommendations Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov, Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin; Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh, Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen, Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale; Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland, Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu, Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus; McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey; Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie Bibcode: 2020arXiv200612224N Altcode: The authors of this white paper met on 16-17 January 2020 at the New Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that brought together a group of heliophysicists, data providers, expert modelers, and computer/data scientists. Their objective was to discuss critical developments and prospects of the application of machine and/or deep learning techniques for data analysis, modeling and forecasting in Heliophysics, and to shape a strategy for further developments in the field. The workshop combined a set of plenary sessions featuring invited introductory talks interleaved with a set of open discussion sessions. The outcome of the discussion is encapsulated in this white paper that also features a top-level list of recommendations agreed by participants. Title: The Sun at millimeter wavelengths. I. Introduction to ALMA Band 3 observations Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Eklund, Henrik; Guevara Gomez, Juan Camilo; Bastian, Tim; Fleck, Bernhard; de la Cruz Rodriguez, Jaime; Rodger, Andrew; Carlsson, Mats Bibcode: 2020A&A...635A..71W Altcode: 2020arXiv200102185W Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started regular observations of the Sun in 2016, first offering receiver Band 3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around 1.25 mm (239 GHz).
Aims: Here we present an initial study of one of the first ALMA Band 3 observations of the Sun. Our aim is to characterise the diagnostic potential of brightness temperatures measured with ALMA on the Sun.
Methods: The observation covers a duration of 48 min at a cadence of 2 s targeting a quiet Sun region at disc-centre. Corresponding time series of brightness temperature maps are constructed with the first version of the Solar ALMA Pipeline and compared to simultaneous observations with the Solar Dynamics Observatory (SDO).
Results: The angular resolution of the observations is set by the synthesised beam, an elliptical Gaussian that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit network patches, internetwork regions, and elongated thin features that are connected to large-scale magnetic loops, as confirmed by a comparison with SDO maps. The ALMA Band 3 maps correlate best with the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit network features and, although very weak in the ALMA maps, imprints of large-scale loops. A group of compact magnetic loops is very clearly visible in ALMA Band 3. The brightness temperatures in the loop tops reach values of about 8000-9000 K and in extreme moments up to 10 000 K.
Conclusions: ALMA Band 3 interferometric observations from early observing cycles already reveal temperature differences in the solar chromosphere. The weak imprint of magnetic loops and the correlation with the 171, 131, and 304 SDO channels suggests, however, that the radiation mapped in ALMA Band 3 might have contributions from a wider range of atmospheric heights than previously assumed, but the exact formation height of Band 3 needs to be investigated in more detail. The absolute brightness temperature scale as set by total power measurements remains less certain and must be improved in the future. Despite these complications and the limited angular resolution, ALMA Band 3 observations have a large potential for quantitative studies of the small-scale structure and dynamics of the solar chromosphere.

Movies are available at https://www.aanda.org Title: Observations of solar chromospheric oscillations at 3 mm with ALMA Authors: Patsourakos, S.; Alissandrakis, C. E.; Nindos, A.; Bastian, T. S. Bibcode: 2020A&A...634A..86P Altcode: 2019arXiv191203480P
Aims: We aim to study spatially resolved chromospheric oscillations of the quiet Sun (QS) in the mm-domain at a resolution of a few arcsec, typically 2.4″ × 4.5″.
Methods: We used Atacama Large millimeter and submillimeter Array (ALMA) time series of interferometric observations of the QS obtained at 3 mm with a 2-s cadence and a spatial resolution of a few arcsec. The observations were performed on March 16, 2017 and seven 80″ × 80″ fields of view (FoV) going from disk center to limb were covered, each one observed for 10 min, therefore limiting the frequency resolution of the power spectra to 1.7 mHz. For each FoV, masks for cell and network were derived, and the averaged power spectral densities (PSDs) for the entire FoV, cell, and network were computed. The resulting power spectra were fit with an analytical function in order to derive the frequency and the root-mean-square (rms) power associated with the peaks. The same analysis, over the same FoVs and for the same intervals, was performed for simultaneous Atmospheric Imaging Assembly (AIA) image sequences in 1600 Å.
Results: Spatially resolved chromospheric oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed in the QS, in both cell and network. The coherence length-scale of the oscillations is commensurate with the spatial resolution of our ALMA observations. Brightness-temperature fluctuations in individual pixels could reach up to a few hundred K, while the spatially averaged PSDs yield rms in the range ≈55-75 K, i.e., up to ≈1% of the averaged brightness temperatures and exhibit a moderate increase towards the limb. For AIA 1600 Å, the oscillation frequency is 3.7 ± 1.7 mHz. The relative rms is up to 6% of the background intensity, with a weak increase towards the disk center (cell, average). ALMA 3 mm time-series lag AIA 1600 Å by ≈100 s, which corresponds to a formation-height difference of ≈1200 km, representing a novel determination of this important parameter.
Conclusions: The ALMA oscillations that we detected exhibit higher amplitudes than those derived from previous lower (≈10″) resolution observations at 3.5 mm by the Berkeley-Illinois-Maryland Array. Chromospheric oscillations are, therefore, not fully resolved at the length-scale of the chromospheric network, and possibly not even at the spatial resolution of our ALMA observations. Any study of transient brightenings in the mm-domain should take into account the oscillations. Title: Implementation of the Sun Radio Interferometer Space Experiment (SunRISE) Mission Concept Authors: Lazio, J.; Kasper, J. C.; Romero-Wolf, A.; Bastian, T.; Cohen, C.; Landi, E.; Manchester, W.; Hegedus, A. M.; Schwadron, N.; Sokolov, I.; Bain, H. M.; Cecconi, B.; Hallinan, G.; Krupar, V.; Maksimovic, M.; Moschou, S. P.; Zaslavsky, A.; Lux, J. P.; Neilsen, T. L. Bibcode: 2019AGUFMSH31C3328L Altcode: The Sun Radio Interferometer Space Experiment (SunRISE) would provide an entirely new view on particle acceleration and transport in the heliosphere by obtaining spatially and temporally resolved observations of Decametric-Hectometric (DH, < 15 MHz) Type II and Type III radio bursts.

In order to obtain the required angular resolution, SunRISE would be a free-flying interferometer. Building on more than 50 years of experience from ground-based very long baseline interferometry (VLBI), SunRISE would fly six small spacecraft in a supersynchronous geosynchronous orbit (GEO) in a passive formation. Their orbits are designed to keep them within approximately 6 km of each other. A space-based interferometer is required because most of the DH band does not penetrate the Earth's ionosphere, due to ionospheric absorption.

Each 6U spacecraft would carry only a single science radio designed to operate in the DH band. The radio would form spectra on-board, with pre-selected sub-bands identified for downlink. This science payload radio would be integrated into a Global Positioning System (GPS) receiver, allowing precise time to be measured on board the spacecraft as well. The spacecraft would be independent of each other, as is the practice for ground-based VLBI arrays.

On a regular basis, both science data and GPS timing would be downlinked. NASA's Deep Space Network antennas would be used for the downlink, with an efficient multiple spacecraft per aperture (MSPA) mode enabling the data from three spacecraft to be downlinked simultaneously. After orbit determination, the interferometric data processing would form images of Type II and Type III solar radio bursts and identify the locations of radio emission relative to the structures of CMEs.

SunRISE would leverage advances in software-defined radios, GPS navigation and timing, and small spacecraft technologies that have been demonstrated over the past few years. An Extended Phase A study of the SunRISE mission concept is scheduled to be completed in 2019 September.

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Some of the information presented is pre-decisional and for planning and discussion purposes only. Title: Towards Next Generation Radio Imaging Spectroscopy: a Path Forward to FASR Authors: Bastian, T.; Chen, B.; Gary, D. E. Bibcode: 2019AGUFMSH31C3327B Altcode: A long term goal of the solar physics community, one that has been endorsed by several NRC decadal surveys, is the Frequency Agile Solar Radiotelescope (FASR). FASR is designed to address a broad program of fundamental solar physics, including coronal magnetic fields, magnetic energy release, particle acceleration and transport, coronal and chromospheric heating, and drivers of space weather such as coronal mass ejections. Fundamental to the FASR concept is observing the chromosphere and corona as a system using innovative measurements — ultra-broadband imaging spectropolarimetry — that will yield unique science data products that are complementary to those produced in, e.g., the O/IR and EUV/X-ray wavelength regimes. The potential of the instrument is already being demonstrated by pathfinder observations made by the Expanded Owens Valley Solar Array (EOVSA) and by the Jansky Very Large Array (JVLA). This talk discusses a step-by-step Implementation of FASR to spread out the cost (the full FASR concept would be in excess of $75M) and achieve some of the most compelling science in time for the upcoming solar maximum. This "stepping stone" approach would first build out the high frequency subsystem at Owens Valley (~1-20 GHz) and rely on other initiatives such as the OVRO Long Wavelength Array to cover the metric wavelength range, deferring the mid-frequency subsystem (~0.2-2 GHz) for the following decade. Such an approach allows a timely deployment of critical science infrastructure that can meet the demands of the wider community while training students and researchers to exploit this new asset. The talk will emphasize the great gain in image quality and science capability of the larger array relative to EOVSA and JVLA. Title: Measuring Coronal Magnetic Fields with the Jansky Very Large Array and RATAN Telescopes Authors: Bastian, T.; Gary, D. E.; Fleishman, G. D.; Nita, G. M.; Chen, B.; Kaltman, T.; Bogod, V. Bibcode: 2019AGUFMSH41B..05B Altcode: Quantitative knowledge of coronal magnetic fields is fundamental to understanding essentially all solar phenomena above the photosphere, including the structure and evolution of solar active regions, magnetic energy release, charged particle acceleration, flares, coronal mass ejections (CMEs), coronal heating, the solar wind and, ultimately, space weather and its impact on Earth. Characterized as the solar and space physics community's "dark energy" problem, useful quantitative measurements of the coronal magnetic field have been largely unavailable until recently. Although understood in principle for many years, suitable instrumentation at radio wavelengths - requiring the ability to perform wideband imaging spectropolarimetry - has not been available in practice for making quantitative maps of coronal magnetic fields. This has changed in recent years, with the advent of the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA) which are being exploited to demonstrate the utility of radio observations for measuring coronal magnetic fields.

We report radio observations of a large solar active region by the Jansky Very Large Array (JVLA). The active region, AR 12209, was mapped on four days: 18, 20, 22, and 24 November 2014 in 56 spectral windows spanning 1-8 GHz. At the lowest frequencies the emission is dominated by thermal free-free emission but at frequencies >1.5 GHz thermal gyroresonance (GR) emission at the second or third harmonic of the electron gyrofrequency dominates. GR emission enables nested coronal isogauss surfaces ranging from approximately 180 G to as high as 1400 G to be mapped. At the time these observations were obtained, the JVLA was not yet fully commissioned for solar observing. In particular, the switched-power flux calibration system was not yet implemented. We therefore cross-calibrated the JVLA observations against well-calibrated one-dimensional observations obtained by the RATAN 600 telescope in Zelenchukskaya, Russia. We present coronal magnetograms obtained by the JVLA and compare them to model calculations. Title: The Sun Radio Interferometer Space Experiment (SunRISE) Mission Concept Authors: Kasper, J. C.; Lazio, J.; Romero-Wolf, A.; Bain, H. M.; Bastian, T.; Cohen, C.; Landi, E.; Manchester, W.; Hegedus, A. M.; Schwadron, N.; Sokolov, I.; Cecconi, B.; Hallinan, G.; Krupar, V.; Maksimovic, M.; Moschou, S. P.; Zaslavsky, A.; Lux, J. P.; Neilsen, T. L. Bibcode: 2019AGUFMSH33A..02K Altcode: The Sun Radio Interferometer Space Experiment (SunRISE) would provide an entirely new view on particle acceleration and transport in the inner heliosphere by obtaining spatially and temporally resolved observations of solar Decametric-Hectometric (DH, < 15 MHz) radio bursts. These bursts are produced by electrons energized near expanding CMEs (Type II) and released by solar flares (Type III). SunRISE would track DH bursts from 2 RS to 20 RS in order to achieve two science objectives. The first objective is to discriminate competing hypotheses for the source mechanism of CME-associated SEPs by measuring the location of Type II bursts relative to expanding CMEs. By locating Type II emission relative to the overall structure of CMEs, SunRISE would reveal where particle acceleration occurs and determine if specific properties of CMEs lead to DH bursts. The second objective is to determine if a broad magnetic connection between active regions and interplanetary space is responsible for the wide longitudinal extent of some SEPs by imaging the field lines traced by Type III bursts from active regions through the corona. By tracing the radio emission from energetic electrons as they travel along magnetic field lines, SunRISE would reveal the field line topology, and its time variation, from active regions into interplanetary space.

SunRISE would consist of six 6U small spacecraft in a supersynchronous geosynchronous orbit (GEO) in a passive formation. Forming a synthetic aperture and observing at frequencies that cannot be observed on Earth due to ionospheric absorption, SunRISE would leverage advances in software-defined radios, GPS navigation and timing, and small spacecraft technologies. These advances have been flown over the past few years, making this concept finally affordable and low-risk.

An Extended Phase A study of the SunRISE mission concept is scheduled to be completed in 2019 September. This paper presents a summary of the concept study.

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Some of the information presented is pre-decisional and for planning and discussion purposes only. Title: Imaging Spectroscopic Observations of Type I Noise Storms with Ultrahigh Temporal and Spectral Resolution Authors: Yu, S.; Chen, B.; Bastian, T.; Gary, D. E. Bibcode: 2019AGUFMSH23C3336Y Altcode: Type I noise storms are the most common, but perhaps the least understood type of solar radio bursts in the decimeter-meter wavelength range. Noise storms are non-flare-related radio phenomena. Their existence indicates that energy release and particle energization can continue in the corona without notable solar activities such as flares or coronal mass ejections. Noise storms manifest themselves as intermittent short-lived narrow-band bursts superposed on a broad-band, long-lasting continuum (sometimes referred to as the noise storm continuum). However, previous studies were either based on total-power dynamic spectroscopy (without spatial resolution), or on imaging observations at one or few frequency channels. During the recent Karl G. Jansky Very Large Array (VLA) solar observing campaign, we performed dynamic imaging spectroscopic observations with unprecedentedly high temporal resolution,10 milliseconds, along with fine spectral resolution (250 kHz) in the 290-450 MHz P band. We recorded several noise storm events associated with quiescent, non-flaring solar active regions. For the first time, we are able to image these type I bursts and fully resolve them in the frequency-time domain, which are used to better elucidate the origin of these bursts. We discuss the implications of our results for understanding energy release and particle energization in the seemly quiescent solar corona. Title: Principles Of Heliophysics: a textbook on the universal processes behind planetary habitability Authors: Schrijver, Karel; Bagenal, Fran; Bastian, Tim; Beer, Juerg; Bisi, Mario; Bogdan, Tom; Bougher, Steve; Boteler, David; Brain, Dave; Brasseur, Guy; Brownlee, Don; Charbonneau, Paul; Cohen, Ofer; Christensen, Uli; Crowley, Tom; Fischer, Debrah; Forbes, Terry; Fuller-Rowell, Tim; Galand, Marina; Giacalone, Joe; Gloeckler, George; Gosling, Jack; Green, Janet; Guetersloh, Steve; Hansteen, Viggo; Hartmann, Lee; Horanyi, Mihaly; Hudson, Hugh; Jakowski, Norbert; Jokipii, Randy; Kivelson, Margaret; Krauss-Varban, Dietmar; Krupp, Norbert; Lean, Judith; Linsky, Jeff; Longcope, Dana; Marsh, Daniel; Miesch, Mark; Moldwin, Mark; Moore, Luke; Odenwald, Sten; Opher, Merav; Osten, Rachel; Rempel, Matthias; Schmidt, Hauke; Siscoe, George; Siskind, Dave; Smith, Chuck; Solomon, Stan; Stallard, Tom; Stanley, Sabine; Sojka, Jan; Tobiska, Kent; Toffoletto, Frank; Tribble, Alan; Vasyliunas, Vytenis; Walterscheid, Richard; Wang, Ji; Wood, Brian; Woods, Tom; Zapp, Neal Bibcode: 2019arXiv191014022S Altcode: This textbook gives a perspective of heliophysics in a way that emphasizes universal processes from a perspective that draws attention to what provides Earth (and similar (exo-)planets) with a relatively stable setting in which life as we know it can thrive. The book is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences. Title: Frequency Agile Solar Radiotelescope Authors: Bastian, Tim; Bain, H.; Bradley, R.; Chen, B.; Dahlin, J.; DeLuca, E.; Drake, J.; Fleishman, G.; Gary, D.; Glesener, L.; Guo, Fan; Hallinan, G.; Hurford, G.; Kasper, J.; Ji, Hantao; Klimchuk, J.; Kobelski, A.; Krucker, S.; Kuroda, N.; Loncope, D.; Lonsdale, C.; McTiernan, J.; Nita, G.; Qiu, J.; Reeves, K.; Saint-Hilaire, P.; Schonfeld, S.; Shen, Chengcai; Tun, S.; Wertheimer, D.; White, S. Bibcode: 2019astro2020U..56B Altcode: We describe the science objectives and technical requirements for a re-scoped Frequency Agile Solar Radiotelescope (FASR). FASR fulfills a long term community need for a ground-based, solar-dedicated, radio telescope - a next-generation radioheliograph - designed to perform ultra-broadband imaging spectropolarimetry. Title: Radio Spectroscopic Imaging of Solar Flare Termination Shocks: Split-band Feature and A Second Possible Event Authors: Chen, Bin; Luo, Yingjie; Yu, Sijie; Krucker, Sam; Reeves, Kathy; Shen, Chengcai; Bastian, Timothy S. Bibcode: 2019AAS...23421003C Altcode: Solar termination shocks (TSs) can form above the looptop when reconnection outflows that impinge upon newly reconnected flare arcades exceed the local fast-mode magnetosonic speed. TSs have been suggested as one of the promising drivers for particle acceleration in solar flares, yet observational evidence remains rare. By utilizing radio dynamic spectral imaging of decimetric stochastic spike bursts (SSBs) observed during a C1.9 eruptive flare on 2012 March 3, Chen et al. (2015) found that the bursts were associated with a dynamic TS-like feature above the looptop. They also showed evidence for the TS as an electron accelerator. One piece of observational evidence that strongly supports the TS interpretation is the split-band feature - a phenomenon well-known in type II radio bursts associated with CME-driven shocks, one interpretation for which attributes to radio emission from both the upstream and downstream side of the shock. We perform detailed spectral imaging analysis of the split-band feature in the 2012 March 3 SSB event, and find evidence that supports the shock upstream-downstream interpretation. We also report another SSB event observed during an M8.4 eruptive flare on 2012 March 10, and show that the radio centroids of the SSBs form a similar shock-surface-shaped structure to the earlier event, located above the reconnected flare arcades and below supra-arcade plasma downflows. Title: Radio Propagation Diagnostics of the Inner Heliosphere in the Era of the Parker Solar Probe Authors: Kobelski, Adam; Bastian, Timothy S.; Vourlidas, Angelos Bibcode: 2019AAS...23410706K Altcode: The solar wind offers and extraordinary laboratory for studying turbulence, turbulent dissipation, and heating. The Parker Solar Probe (PSP) was launched in August 2018 to study these and other important processes in the inner heliosphere. One type of observation that will complement those of PSP are radio propagation measurements of solar wind turbulence in the outer corona and the inner heliosphere. This type of observation can provide measurements of the angular broadening of distant spatially coherent background sources that transilluminate the foreground solar wind plasma. This well-known technique can be used to measure the spatial spectrum of electron density inhomogeneities in the solar wind on scales of 100s of meters to 10s of kilometers inside of 10-15 solar radii over a wide range of position angles.

Here we report the results of a pilot study of background sources using the Jansky Very Large Array (JVLA) in summer 2015. Unlike previous studies of this kind, the JVLA's much greater sensitivity allows fainter and more numerous sources to be used as probes of the foreground medium. We observed 11 background sources in 16 sessions at apparent radial distances of 2-7 solar radii. We confirm previous findings: that the spectrum is flatter than Kolmogorov and that is highly anisotropic. Unlike previous studies we find breaks into steeper spectra for some sources on short spatial scales, suggestive of a transition to dissipation.

Looking forward, we describe observations planned in August 2019 in support of the third PSP perihelion passage (35.7 solar radii). The VLA will be used to observe the corona and inner heliosphere along 70 pierce points <10 solar radii. These observations will not only provide global context about the state of the inner heliosphere at time of perihelion passage, they will also baseline key solar wind parameters that can be compared directly with PSP measurements. These include turbulence level, spectral index, degree of anisotropy, and the orientation of the magnetic field. The PSP measurements will, in turn, provide measurements that will validate key assumptions made in interpreting the radio data. Title: Advancing Understanding of Star-Planet Ecosystems in the Next Decade: The Radio Wavelength Perspective Authors: Osten, Rachel; Bastian, Tim; Bower, Geoff; Forbrich, Jan; Gudel, Manuel; Kao, Melodie M.; Lazio, Joseph; Linsky, Jeffrey; MacGregor, Meredith; Moschou, Sofia P.; Pineda, J. Sebastian; Rupen, Michael P.; Villadsen, Jackie; White, Stephen; Williams, Peter K. G.; Wolk, Scott J. Bibcode: 2019BAAS...51c.434O Altcode: 2019astro2020T.434O In this white paper we advocate for stellar radio observations as a way to advance understanding of stars in service of a better understanding of star- planet ecosystems. Specific key advances needed are sensitivity and access to a broader range of frequency space to make progress in understanding the space weather environments of exoplanets. Title: Particle Acceleration and Transport, New Perspectives from Radio, X-ray, and Gamma-Ray Observations Authors: Gary, Dale; Bastian, Timothy S.; Chen, Bin; Drake, James F.; Fleishman, Gregory; Glesener, Lindsay; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.371G Altcode: 2019astro2020T.371G Particle acceleration and particle transport are ubiquitous in astrophysics. The Sun offers an astrophysical laboratory to study these in minute detail, using radio dynamic imaging spectroscopy to measure coronal magnetic fields, time and space evolution of the electron distribution function. Title: Reconstructing Extreme Space Weather From Planet Hosting Stars Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander, D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz, M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.; Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage, K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy, N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen, A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.; Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.; Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.; Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian, A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.; Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville, V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.; Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.; Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.; Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova, S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T. Bibcode: 2019BAAS...51c.564A Altcode: 2019astro2020T.564A; 2019arXiv190306853A The goal of this white paper is to identify and describe promising key research goals to aid the theoretical characterization and observational detection of ionizing radiation from quiescent and flaring upper atmospheres of planet hosts as well as properties of stellar coronal mass ejections (CMEs) and stellar energetic particle (SEP) events. Title: Diagnostics of Space Weather Drivers Enabled by Radio Observations Authors: Bastian, Tim; Bain, Hazel; Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Glesener, Lindsay; Saint-Hilaire, Pascal; Lonsdale, Colin; White, Stephen M. Bibcode: 2019BAAS...51c.323B Altcode: 2019astro2020T.323B; 2019arXiv190405817B The Sun is an active star that can impact the Earth, its magnetosphere, and the technological infrastructure on which modern society depends. Radio emission from space weather drivers offers unique diagnostics that complement those available at other wavelengths. We discuss the requirements for an instrument to enable such diagnostics. Title: Radio, Millimeter, Submillimeter Observations of the Quiet Sun Authors: Bastian, Tim; Chen, Bin; Gary, Dale E.; Fleishman, Gregory D.; Glesener, Lindsay; Lonsdale, Colin; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.493B Altcode: 2019arXiv190405826B; 2019astro2020T.493B We point out the lack of suitable radio observations of the quiet Sun chromosphere and corona and outline requirements for next generation instrumentation to address the gap. Title: Probing Magnetic Reconnection in Solar Flares: New Perspectives from Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, Tim; Dahlin, Joel; Drake, James F.; Fleishman, Gregory; Gary, Dale; Glesener, Lindsay; Guo, Fan; Ji, Hantao; Saint-Hilaire, Pascal; Shen, Chengcai; White, Stephen M. Bibcode: 2019BAAS...51c.507C Altcode: 2019astro2020T.507C; 2019arXiv190311192C Magnetic reconnection is a fundamental physical process in many laboratory, space, and astrophysical plasma contexts. In this white paper we emphasize the unique power of remote-sensing observations of solar flares at radio wavelengths in probing fundamental physical processes in magnetic reconnection. Title: Community Input Solicited for Heliophysics Decadal Survey Midterm Assessment Committee Authors: Woods, Thomas; Millan, Robyn; Charo, Art; Bastian, Tim; Bobra, Monica; Coster, Anthea; DeLuca, Ed; England, Scott; Fuselier, Stephen; Lopez, Ramon; Luhmann, Janet; Nykyri, Katariina; Oberheide, Jens; Opher, Merav; Schrijver, Karel; Semeter, Josh; Thayer, Jeff; Title, Alan Bibcode: 2019shin.confE...6W Altcode: The National Academies of Sciences, Engineering, and Medicine has convened a committee to review the progress towards implementing the 2013 Heliophysics Decadal Survey, titled Solar and Space Physics: a Science for a Technological Society. This review serves as a midterm assessment before the next Heliophysics Decadal Survey committee would begin its formulation. This committee is interested to receive input from the heliophysics and space weather communities about the 2013-2018 progress realizing the 15 recommendations and applications specified in the 2013 Heliophysics Decadal Survey, about any suggested actions to optimize the science value during 2019-2023, about any suggestions to improve the process for the next Heliophysics Decadal Survey, and about any suggested actions to enhance all stages of careers for scientists and engineers in the solar and space physics community. This poster outlines the Heliophysics Decadal Survey recommendations and recent progress, and it also summarizes the tasks for this midterm assessment committee. There will be an opportunity to discuss your inputs with a couple of the Committee members during the SHINE meeting. Title: Radio Observational Constraints on Turbulent Astrophysical Plasmas Authors: Bastian, Tim; Cordes, James; Kasper, Justin; Kobelski, Adam; Korreck, Kelly; Howes, Gregory; Salem, Chadi; Spangler, Steve; Vourlidas, Angelos Bibcode: 2019astro2020T.307B Altcode: 2019arXiv190405807B Using radio observations of background sources, scattering phenomena may be used to characterize the properties of foreground turbulent plasma. We discuss the potential of such techniques to explore turbulence in the solar wind and interstellar medium. The Next Generation VLA will be an ideal instrument to exploit these techniques. Title: Solar Coronal Magnetic Fields: Quantitative Measurements at Radio Wavelengths Authors: Fleishman, Gregory; Bastian, Timothy S.; Chen, Bin; Gary, Dale E.; Glesener, Lindsay; Nita, Gelu; Saint-Hilaire, Pascal; White, Stephen M. Bibcode: 2019BAAS...51c.426F Altcode: 2019astro2020T.426F Quantitative measurements of coronal and chromospheric magnetic field is currently in its infancy. We describe a foundation of such observations, which is a key input for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. Title: Flat-spectrum Radio Continuum Emission Associated with ɛ Eridani Authors: Rodríguez, Luis F.; Lizano, Susana; Loinard, Laurent; Chávez-Dagostino, Miguel; Bastian, Timothy S.; Beasley, Anthony J. Bibcode: 2019ApJ...871..172R Altcode: We present Very Large Array observations at 33.0 GHz that detect emission coincident with ɛ Eridani to within 0.″07 (0.2 au at the distance of this star), with a positional accuracy of 0.″05. This result strongly supports the suggestion of previous authors that the quiescent centimeter emission comes from the star and not from a proposed giant exoplanet with a semimajor axis of ∼1.″0 (3.4 au). The centimeter emission is remarkably flat and is consistent with optically thin free-free emission. In particular, it can be modeled as a stellar wind with a mass-loss rate of the order of 6.6 × 10-11 {M}⊙ yr-1, which is 3300 times the solar value, exceeding other estimates of this star’s wind. However, interpretation of the emission in terms of other thermal mechanisms like coronal free-free and gyroresonance emission cannot be discarded. Title: Flat Spectrum Radio Continuum Emission Associated with $\epsilon$ Eridani Authors: Rodriguez, Luis F.; Lizano, Susana; Loinard, Laurent; Chávez-Dagostino, Miguel; Bastian, Timothy S.; Beasley, Anthony J. Bibcode: 2019arXiv190100903R Altcode: We present Very Large Array observations at 33.0 GHz that detect emission coincident with $\epsilon$ Eridani to within $0\rlap.{"}07$ (0.2 AU at the distance of this star), with a positional accuracy of $0\rlap.{"}05$. This result strongly supports the suggestion of previous authors that the quiescent centimeter emission comes from the star and not from a proposed giant exoplanet with a semi-major axis of $\sim1\rlap.{"}0$ (3.4 AU). The centimeter emission is remarkably flat and is consistent with optically thin free-free emission. In particular, it can be modeled as a stellar wind with a mass loss rate of the order of $6.6 \times 10^{-11}~ M_\odot ~yr^{-1}$, which is 3,300 times the solar value, exceeding other estimates of this star's wind. However, interpretation of the emission in terms of other thermal mechanisms like coronal free-free and gyroresonance emission cannot be discarded. Title: Resolved imaging of the quiet and flaring radio corona of active M dwarfs Authors: Villadsen, Jacqueline; Hallinan, Gregg; Mioduszewski, Amy; Bourke, Stephen; Bastian, Timothy Bibcode: 2019AAS...23320405V Altcode: Magnetically active M dwarfs produce non-thermal quiescent radio emission, along with coherent and incoherent flares. Very long baseline imaging (VLBI) has revealed that these luminous phenomena can occur on spatial scales significantly larger than the stellar photosphere, in processes which have no clear analog in the solar corona. This non-thermal radio emission originates directly from energetic electrons, making radio the only direct observational probe of accelerated particles in stellar coronae. I will present VLBI observations of the quiescent and flaring radio emission from two nearby active M dwarfs. These two stars with saturated coronal activity have distinctly different structure in their radio coronae, perhaps indicative of different underlying electron acceleration mechanisms responsible for the quiescent radio emission. Title: ngVLA Observations of Coronal Magnetic Fields Authors: Fleishman, G. D.; Nita, G. M.; White, S. M.; Gary, D. E.; Bastian, T. S. Bibcode: 2018ASPC..517..125F Altcode: Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting. Title: Radio Observations of Solar Flares Authors: Gary, D. E.; Bastian, T. S.; Chen, B.; Fleishman, G. D.; Glesener, L. Bibcode: 2018ASPC..517...99G Altcode: Solar flares are due to the catastrophic release of magnetic energy in the Sun's corona, resulting in plasma heating, mass motions, particle acceleration, and radiation emitted from radio to γ-ray wavelengths. They are associated with global coronal eruptions of plasma into the interplanetary medium—coronal mass ejections—that can result in a variety of “space weather” phenomena. Flares release energy over a vast range of energies, from ∼1023 ergs (nanoflares) to more than 1032 ergs. Solar flares are a phenomenon of general astrophysical interest, allowing detailed study of magnetic energy release, eruptive processes, shock formation and propagation, particle acceleration and transport, and radiative processes. Observations at radio wavelengths offer unique diagnostics of the physics of flares. To fully exploit these diagnostics requires the means of performing time-resolved imaging spectropolarimetry. Recent observations with the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by extensive development in forward modeling, have demonstrated the power of the approach. The ngVLA has the potential to bring our understanding of flare processes to a new level through its combination of high spatial resolution, broad frequency range, and imaging dynamic range—especially when used in concert with multi-wavelength observations and data at hard X-ray energies. Title: ngVLA Observations of the Solar Wind Authors: Bastian, T. S. Bibcode: 2018ASPC..517...87B Altcode: The ngVLA has the potential to play a significant role in characterizing properties of the outer corona and the heating and acceleration of the solar wind into the inner heliosphere. In particular, using distant background sources to transilluminate the foreground corona and solar wind, a variety of radio propagation phenomena can be used to map plasma properties as a function of solar elongation and position angle throughout the solar cycle. These include angular broadening, interplanetary scintillations, and differential Faraday rotation, which can be used to map the solar wind velocity, determine properties of solar wind turbulence, and constrain the solar wind magnetic field. These observations will provide a global characterization of the solar wind that will be highly complementary to in situ observations made by various spacecraft. In addition, such observations can be used to probe disturbances in the solar wind - coronal mass ejections, for example - that may impact the near-Earth environment. Title: First high-resolution look at the quiet Sun with ALMA at 3mm Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos, S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu, T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V. Bibcode: 2018A&A...619L...6N Altcode: 2018arXiv181005223N We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5″ by 4.5″. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15″ above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere. Title: Science with an ngVLA: Observations of the Solar Wind Authors: Bastian, T. S. Bibcode: 2018arXiv181006633B Altcode: The ngVLA has the potential to play a significant role in characterizing properties of the outer corona and the heating and acceleration of the solar wind into the inner heliosphere. In particular, using distant background sources to transilluminate the foreground corona and solar wind, a variety of radio propagation phenomena can be used to map plasma properties as a function of solar elongation and position angle throughout the solar cycle. These include angular broadening, interplanetary scintillations, and differential Faraday rotation, which can be used to map the solar wind velocity, determine properties of solar wind turbulence, and constrain the solar wind magnetic field. These observations will provide a global characterization of the solar wind that will be highly complementary to in situ observations made by various spacecraft. In addition, such observations can be used to probe disturbances in the solar wind -- coronal mass ejections, for example -- that may impact the near-Earth environment. Title: Magnetic Reconnection Null Points as the Origin of Semirelativistic Electron Beams in a Solar Jet Authors: Chen, Bin; Yu, Sijie; Battaglia, Marina; Farid, Samaiyah; Savcheva, Antonia; Reeves, Katharine K.; Krucker, Säm; Bastian, T. S.; Guo, Fan; Tassev, Svetlin Bibcode: 2018ApJ...866...62C Altcode: 2018arXiv180805951C Magnetic reconnection, the central engine that powers explosive phenomena throughout the universe, is also perceived to be one of the principal mechanisms for accelerating particles to high energies. Although various signatures of magnetic reconnection have been frequently reported, observational evidence that links particle acceleration directly to the reconnection site has been rare, especially for space plasma environments currently inaccessible to in situ measurements. Here we utilize broadband radio dynamic imaging spectroscopy available from the Karl G. Jansky Very Large Array to observe decimetric type III radio bursts in a solar jet with high angular (∼20″), spectral (∼1%), and temporal resolution (50 ms). These observations allow us to derive detailed trajectories of semirelativistic (tens of keV) electron beams in the low solar corona with unprecedentedly high angular precision (<0.″65). We found that each group of electron beams, which corresponds to a cluster of type III bursts with 1-2 s duration, diverges from an extremely compact region (∼600 km2) in the low solar corona. The beam-diverging sites are located behind the erupting jet spire and above the closed arcades, coinciding with the presumed location of magnetic reconnection in the jet eruption picture supported by extreme ultraviolet/X-ray data and magnetic modeling. We interpret each beam-diverging site as a reconnection null point where multitudes of magnetic flux tubes join and reconnect. Our data suggest that the null points likely consist of a high level of density inhomogeneities possibly down to 10 km scales. These results, at least in the present case, strongly favor a reconnection-driven electron-acceleration scenario. Title: Science with an ngVLA: Radio Observations of Solar Flares Authors: Gary, Dale E.; Bastian, Timothy S.; Chen, Bin; Fleishman, Gregory D.; Glesener, Lindsay Bibcode: 2018arXiv181006336G Altcode: Solar flares are due to the catastrophic release of magnetic energy in the Sun's corona, resulting in plasma heating, mass motions, particle acceleration, and radiation emitted from radio to $\gamma$-ray wavelengths. They are associated with global coronal eruptions of plasma into the interplanetary medium---coronal mass ejections---that can result in a variety of "space weather" phenomena. Flares release energy over a vast range of energies, from $\sim\!10^{23}$ ergs (nanoflares) to more than $10^{32}$ ergs. Solar flares are a phenomenon of general astrophysical interest, allowing detailed study of magnetic energy release, eruptive processes, shock formation and propagation, particle acceleration and transport, and radiative processes. Observations at radio wavelengths offer unique diagnostics of the physics of flares. To fully exploit these diagnostics requires the means of performing time-resolved imaging spectropolarimetry. Recent observations with the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by extensive development in forward modeling, have demonstrated the power of the approach. The ngVLA has the potential to bring our understanding of flare processes to a new level through its combination of high spatial resolution, broad frequency range, and imaging dynamic range---especially when used in concert with multi-wavelength observations and data at hard X-ray energies. Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth System Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan; Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao, Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa, Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale; Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland, Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander; Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens, Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent; Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet, Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth, Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha Bibcode: 2018arXiv181008728N Altcode: The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed. Title: Science with an ngVLA: ngVLA Observations of Coronal Magnetic Fields Authors: Fleishman, Gregory D.; Nita, Gelu M.; White, Stephen M.; Gary, Dale E.; Bastian, Tim S. Bibcode: 2018arXiv181006622F Altcode: Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting. Title: Radio Emission from the Exoplanetary System Epsilon Eridani Authors: Bastian, Tim; Villadsen, J.; Maps, A.; Hallinan, G.; Beasley, A. J. Bibcode: 2018shin.confE...3B Altcode: After many years of trying, radio emission from the nearby system Epsilon Eridani (3.2 pc) - containing a Title: Probing the Inner Heliosphere Using Radio Diagnostic Techniques Authors: Bastian, Tim; Kobelski, Adam Bibcode: 2018shin.confE..38B Altcode: A variety of radio propagation techniques - angular and spectral broadening, scintillation, and Faraday rotation - can be used to probe regions in the corona and solar wind that are otherwise inaccessible to direct observation. We present some recent pilot observations made by the Jansky Very Large Array to illustrate their potential for deducing key properties of solar wind turbulence in the inner heliosphere. We discuss prospects for exploiting these techniques in a more systematic way in the era of the Parker Solar Probe and the Solar Obiter. Title: Erratum: “A First Comparison of Millimeter Continuum and Mg II Ultraviolet Line Emission from the Solar Chromosphere” (2017, ApJL, 845, L19) Authors: Bastian, T. S.; Chintzoglou, G.; De Pontieu, B.; Shimojo, M.; Schmit, D.; Leenaarts, J.; Loukitcheva, M. Bibcode: 2018ApJ...860L..16B Altcode: No abstract at ADS Title: Radio Emission from the Exoplanetary System ɛ Eridani Authors: Bastian, T. S.; Villadsen, J.; Maps, A.; Hallinan, G.; Beasley, A. J. Bibcode: 2018ApJ...857..133B Altcode: 2017arXiv170607012B As part of a wider search for radio emission from nearby systems known or suspected to contain extrasolar planets, ɛ Eridani was observed by the Jansky Very Large Array (VLA) in the 2-4 GHz and 4-8 GHz frequency bands. In addition, as part of a separate survey of thermal emission from solar-like stars, ɛ Eri was observed in the 8-12 GHz and the 12-18 GHz bands of the VLA. Quasi-steady continuum radio emission from ɛ Eri was detected in the three high-frequency bands at levels ranging from 67 to 83 μJy. No significant variability is seen in the quasi-steady emission. The emission in the 2-4 GHz emission, however, is shown to be the result of a circularly polarized (up to 50%) radio pulse or flare of a few minutes in duration that occurred at the beginning of the observation. We consider the astrometric position of the radio source in each frequency band relative to the expected position of the K2V star and the purported planet. The quasi-steady radio emission at frequencies ≥8 GHz is consistent with a stellar origin. The quality of the 4-8 GHz astrometry provides no meaningful constraint on the origin of the emission. The location of the 2-4 GHz radio pulse is >2.5σ from the star; however, based on the ephemeris of Benedict et al., it is not consistent with the expected location of the planet either. If the radio pulse has a planetary origin, then either the planetary ephemeris is incorrect or the emission originates from another planet. Title: Exploring the Sun with ALMA Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu, B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson, H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S. M.; Yan, Y. Bibcode: 2018Msngr.171...25B Altcode: The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory opens a new window onto the Universe. The ability to perform continuum imaging and spectroscopy of astrophysical phenomena at millimetre and submillimetre wavelengths with unprecedented sensitivity opens up new avenues for the study of cosmology and the evolution of galaxies, the formation of stars and planets, and astrochemistry. ALMA also allows fundamentally new observations to be made of objects much closer to home, including the Sun. The Sun has long served as a touchstone for our understanding of astrophysical processes, from the nature of stellar interiors, to magnetic dynamos, non-radiative heating, stellar mass loss, and energetic phenomena such as solar flares. ALMA offers new insights into all of these processes. Title: Solar and Heliospheric Physics with the ngVLA Authors: Bastian, Timothy; ngVLA Solar Science Working Group Bibcode: 2018AAS...23134219B Altcode: The ngVLA offers unprecedented sensitivity, angular resolution, and frequency bandwidth for studies of astrophysical phenomena from millimeter to decimeter wavelengths, including the Sun and solar wind. This paper summarizes key solar and heliospheric science objectives that can be addressed by the ngVLA. For the Sun these include: 1) the quantitative measurement of coronal magnetic fields; 2) magnetic energy release; 3) particle acceration and transport; 4) drivers of space weather; and 5) the structure and dynamics of the solar chromosphere and corona. For the outer corona and the inner heliosphere the science objectives include 1) solar wind acceleration; 2) the development of solar wind turbulence; 3) transient disturbances (e.g., coronal mass ejections) in the solar wind. The techniques that will be exploited for these studies will be briefly reviewed and the necessary capabilities of the ngVLA in support of these techniques will be discussed. Title: The First ALMA Observation of a Solar Plasmoid Ejection from an X-Ray Bright Point Authors: Shimojo, M.; Hudson, H. S.; White, S. M.; Bastian, T.; Iwai, K. Bibcode: 2017AGUFMSH41A2754S Altcode: Eruptive phenomena are important features of energy releases events, such solar flares, and have the potential to improve our understanding of the dynamics of the solar atmosphere. The 304 A EUV line of helium, formed at around 10^5 K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously with ALMA, SDO/AIA, and Hinode/XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV, and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal ∼10^5 K plasma that is optically thin at 100 GHz, or a ∼10^4 K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes. Title: The Sun Radio Imaging Space Experiment (SunRISE) Mission Authors: Kasper, J. C.; Lazio, J.; Alibay, F.; Amiri, N.; Bastian, T.; Cohen, C.; Landi, E.; Hegedus, A. M.; Maksimovic, M.; Manchester, W.; Reinard, A.; Schwadron, N.; Cecconi, B.; Hallinan, G.; Krupar, V. Bibcode: 2017AGUFMSH41B2760K Altcode: Radio emission from coronal mass ejections (CMEs) is a direct tracer of particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. Energized electrons excite Langmuir waves, which then convert into intense radio emission at the local plasma frequency, with the most intense acceleration thought to occur within 20 R_S. The radio emission from CMEs is quite strong such that only a relatively small number of antennas is required to detect and map it, but many aspects of this particle acceleration and transport remain poorly constrained. Ground-based arrays would be quite capable of tracking the radio emission associated with CMEs, but absorption by the Earth's ionosphere limits the frequency coverage of ground-based arrays (nu > 15 MHz), which in turn limits the range of solar distances over which they can track the radio emission (< 3 R_S). The state-of-the-art for tracking such emission from space is defined by single antennas (Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by assuming a frequency-to-density mapping; there has been some success in triangulating the emission between the spacecraft, but considerable uncertainties remain. We describe the Sun Radio Imaging Space Experiment (SunRISE) mission concept: A constellation of small spacecraft in a geostationary graveyard orbit designed to localize and track radio emissions in the inner heliosphere. Each spacecraft would carry a receiving system for observations below 25 MHz, and SunRISE would produce the first images of CMEs more than a few solar radii from the Sun. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Title: Center-to-limb observations of the Sun with ALMA . Implications for solar atmospheric models Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian, T. S. Bibcode: 2017A&A...605A..78A Altcode:
Aims: We seek to derive information on the temperature structure of the solar chromosphere and compare these results with existing models.
Methods: We measured the center-to-limb variation of the brightness temperature, Tb, from ALMA full-disk images at two frequencies and inverted the solution of the transfer equation to obtain the electron temperature, Te as a function of optical depth, τ.
Results: The ALMA images are very similar to AIA images at 1600 Å. The brightness temperature at the center of the disk is 6180 and 7250 K at 239 and 100 GHz, respectively, with dispersions of 100 and 170 K. Plage regions stand out clearly in the 239/100 GHz intensity ratio, while faculae and filament lanes do not. The solar disk radius, reduced to 1 AU, is 961.1 ± 2.5'' and 964.1 ± 4.5'' at 239 and 100 GHz, respectively. A slight but statistically significant limb brightening is observed at both frequencies.
Conclusions: The inversion of the center-to-limb curves shows that Te varies linearly with the logarithm of optical depth for 0.34 <τ100 GHz< 12, with a slope dTe/ dlnτ = -608 K. Our results are 5% lower than predicted by the average quiet Sun model C of Fontenla et al. (1993, ApJ. 406, 319), but do not confirm previous reports that the mm-λ solar spectrum is better fitted with models of the cell interior. Title: A First Comparison of Millimeter Continuum and Mg II Ultraviolet Line Emission from the Solar Chromosphere Authors: Bastian, T. S.; Chintzoglou, G.; De Pontieu, B.; Shimojo, M.; Schmit, D.; Leenaarts, J.; Loukitcheva, M. Bibcode: 2017ApJ...845L..19B Altcode: 2017arXiv170604532B We present joint observations of the Sun by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). Both millimeter/submillimeter-λ continuum emission and ultraviolet (UV) line emission originate from the solar chromosphere and both have the potential to serve as powerful and complementary diagnostics of physical conditions in this enigmatic region of the solar atmosphere. The observations were made of a solar active region on 2015 December 18 as part of the ALMA science verification effort. A map of the Sun’s continuum emission was obtained by ALMA at a wavelength of 1.25 mm (239 GHz). A contemporaneous map was obtained by IRIS in the Mg II h doublet line at 2803.5 Å. While a clear correlation between the 1.25 mm brightness temperature TB and the Mg II h line radiation temperature Trad is observed, the slope is <1, perhaps as a result of the fact that these diagnostics are sensitive to different parts of the chromosphere and that the Mg II h line source function includes a scattering component. There is a significant difference (35%) between the mean TB (1.25 mm) and mean Trad (Mg II). Partitioning the maps into “sunspot,” “quiet areas,” and “plage regions” we find the relation between the IRIS Mg II h line Trad and the ALMA TB region-dependent. We suggest this may be the result of regional dependences of the formation heights of the IRIS and ALMA diagnostics and/or the increased degree of coupling between the UV source function and the local gas temperature in the hotter, denser gas in plage regions. Title: Solar Commissioning Observations of the Sun with ALMA Authors: White, Stephen M.; Shimojo, Masumi; Bastian, Timothy S.; Iwai, Kazumasa; Hales, Antonio; Brajsa, Roman; Skokic, Ivica; Kim, Sujin; Hudson, Hugh S.; Loukitcheva, Maria; Wedemeyer, Sven Bibcode: 2017SPD....4820402W Altcode: PI-led science observations have commenced with the Atacama Large Millimeter-submillimeter Array (ALMA) following an extensive commissioning effort. This talk will summarize that effort and discuss some of the scientific results derived from the commissioning data. As the solar cycle declines, ALMA observations will mainly address chromospheric science topics. Examples of data obtained during commissioning, both from the interferometer and from single-dish observations, will be presented. The temperatures of the layers that ALMA is most sensitive to have been determined for the two frequency bands currently used for solar observations. Curious behavior in a sunspot umbra and an observations of a small chromospheric ejection will be discussed. Title: Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric Imaging Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.; Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.; Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.; Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder, S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.; Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y. Bibcode: 2017SoPh..292...87S Altcode: 2017arXiv170403236S Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low-contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar-commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities. Title: Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota, A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales, A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki, W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.; Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.; Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann, G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y. Bibcode: 2017SoPh..292...88W Altcode: 2017arXiv170504766W The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at λ =1.3 mm. These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about 25″, the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images. Title: Center-to-limb observations of the Sun with ALMA Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian, T. S. Bibcode: 2017arXiv170509008A Altcode: We measured the center-to-limb variation of the brightness temperature, $T_b$, from ALMA full-disk images at two frequencies and inverted the solution of the transfer equation to obtain the electron temperature, $T_e$ as a function of optical depth, $\tau$. The ALMA images are very similar to AIA images at 1600Å. The brightness temperature at the center of the disk is 6180 and 7250 K at 239 and 100 GHz respectively, with dispersions of 100 and 170 K. Plage regions stand out clearly in the 239/100 GHz intensity ratio, while faculae and filament lanes do not. The solar disk radius, reduced to 1 AU, is $961.1\pm2.5$ arcsec and $964.1\pm4.5$ arcsec at 239 and 100 GHz respectively. A slight but statistically significant limb brightening is observed at both frequencies. The inversion of the center-to-limb curves shows that $T_e$ varies linearly with the logarithm of optical depth for $0.34<\tau_{100\,GHz}<12$, with a slope $d\ln T_e/d\tau=-608$ K. Our results are 5% lower than predicted by the average quiet sun model C of Fontenla et al. (1993), but do not confirm previous reports that the mm-$\lambda$ solar spectrum is better fitted with models of the cell interior. Title: The First ALMA Observation of a Solar Plasmoid Ejection from an X-Ray Bright Point Authors: Shimojo, Masumi; Hudson, Hugh S.; White, Stephen M.; Bastian, Timothy S.; Iwai, Kazumasa Bibcode: 2017ApJ...841L...5S Altcode: 2017arXiv170404881S Eruptive phenomena such as plasmoid ejections or jets are important features of solar activity and have the potential to improve our understanding of the dynamics of the solar atmosphere. Such ejections are often thought to be signatures of the outflows expected in regions of fast magnetic reconnection. The 304 Å EUV line of helium, formed at around 105 K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously at millimeter wavelengths with ALMA, at EUV wavelengths with SDO/AIA, and in soft X-rays with Hinode/XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV, and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal ∼105 K plasma that is optically thin at 100 GHz, or a ∼104 K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes. Title: Getting to know the nearest stars: Intermittent radio bursts from Ross 614 Authors: Winterhalter, Daniel; Knapp, Mary; Bastian, Tim Bibcode: 2017EGUGA..1918385W Altcode: Radio observations have been used as a search tool for exoplanets since before the confirmed discovery of the first extrasolar planet. To date, there have been no definitive detections of exoplanets in the radio regime. We are engaged in an ongoing blind radio survey of the nearest star systems for exoplanetary radio emission. The goal of this survey is to obtain meaningful upper limits on radio emission from (or modulated by) sub-stellar companions of the nearest stars. Nearby stars are strongly preferred because they suffer the least from the dilution of potential radio signals by distance. Targets are selected by distance and observability (both LOFAR and VLA) only. Other properties of target stars, such as stellar type, are not considered to avoid biasing the search. Five survey targets, Procyon, GJ 1111, GJ 725, Ross 614, and UGPSJ072227.51, have been observed with the VLA telescope L- and S-band receivers. P-band observations are ongoing. Of particular interest are, at this time, our observation of the Ross 614 System. Ross 614 is an M-dwarf binary system at a distance of about 13 Ly, with an orbital period of 16.6 years. The binary companions are classified as flare stars because strong radio emission has been detected from the location of the system in previous work. Analyses are in progress to determine if the intermittent burst are similar to solar-type burst, and/or if there is any evidence for emissions from sub-stellar companions. Title: The Sun Radio Imaging Space Experiment (SunRISE) Mission Authors: Lazio, Joseph; Kasper, Justin; Maksimovic, Milan; Alibay, Farah; Amiri, Nikta; Bastian, Tim; Cohen, Christina; Landi, Enrico; Manchester, Ward; Reinard, Alysha; Schwadron, Nathan; Cecconi, Baptiste; Hallinan, Gregg; Hegedus, Alex; Krupar, Vratislav; Zaslavsky, Arnaud Bibcode: 2017EGUGA..19.5580L Altcode: Radio emission from coronal mass ejections (CMEs) is a direct tracer of particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. Energized electrons excite Langmuir waves, which then convert into intense radio emission at the local plasma frequency, with the most intense acceleration thought to occur within 20 RS. The radio emission from CMEs is quite strong such that only a relatively small number of antennas is required to detect and map it, but many aspects of this particle acceleration and transport remain poorly constrained. Ground-based arrays would be quite capable of tracking the radio emission associated with CMEs, but absorption by the Earth's ionosphere limits the frequency coverage of ground-based arrays (ν ≳ 15 MHz), which in turn limits the range of solar distances over which they can track the radio emission (≲ 3RS). The state-of-the-art for tracking such emission from space is defined by single antennas (Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by assuming a frequency-to-density mapping; there has been some success in triangulating the emission between the spacecraft, but considerable uncertainties remain. We describe the Sun Radio Imaging Space Experiment (SunRISE) mission concept: A constellation of small spacecraft in a geostationary graveyard orbit designed to localize and track radio emissions in the inner heliosphere. Each spacecraft would carry a receiving system for observations below 25 MHz, and SunRISE would produce the first images of CMEs more than a few solar radii from the Sun. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Title: A Search for Radio Emission from Nearby Exoplanets Authors: Maps, Amethyst D.; Bastian, Timothy S.; Beasley, Anthony J. Bibcode: 2017AAS...22914635M Altcode: Since the discovery of the first extrasolar planet orbiting a main sequence star more than 20 years ago, the study of exoplanets has become a burgeoning field with more than 3300 confirmed extrasolar planets now known. A variety of techniques has been used to discover exoplanets orbiting main sequence stars and to deduce their properties: timing, radial velocities, direct imaging, microlensing, and transits in the optical/IR bands. Absent from this list so far is the detection of exoplanets at radio wavelengths, but not for lack of trying. Searches for radio emission from exoplanets predate their discovery (Winglee et al. 1986) and have continued sporadically to this day. The majority of searches for radio emission from exoplanets has searched for coherent radio emission. It is indeed the case that in our own solar system, all magnetized planets are powerful radio emitters, the likely emission mechanism being the cyclotron maser instability. The outstanding example is Jupiter, which emits 1010-1011 W at decameter wavelengths (frequencies <40 MHz). If there are Jupiter-like planets in other solar systems, many must surely emit CMI radiation. The emitted radiation could be orders of magnitude more intense than Jupiter’s if the interaction between the magnetized planet and the wind from the primary star is stronger than the Sun/Jupiter interaction - due, for example, to a more powerful wind and/or the planet being closer to the star.We have initiated a new search for radio emission from exoplanets, focusing on all known exoplanetary systems within 20 pc - more than 50 systems containing nearly 100 planets using the Jansky Very Large Array (JVLA) in three frequency bands: 1-2 GHz, 2-4 GHz, and 4-8 GHz with a target sensitivity of ~10 microJy. We have completed the 2-4 GHz survey and report our preliminary results, which include the detection of two systems. We discuss whether the emission is from a planet or from the star and the implications of our conclusions for habitability of exoplanets. Title: The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm Authors: Iwai, Kazumasa; Shimojo, Masumi; Asayama, Shinichiro; Minamidani, Tetsuhiro; White, Stephen; Bastian, Timothy; Saito, Masao Bibcode: 2017SoPh..292...22I Altcode: 2016arXiv161208241I The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor-insulator-superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is 7700 ±310 K at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations. Title: MWA Observations of Solar Radio Bursts and the Quiet Sun Authors: Cairns, I.; Oberoi, D.; Morgan, J.; Bastian, T.; Bhatnagar, S.; Bisi, M.; Benkevitch, L.; Bowman, J.; Donea, A.; Giersch, O.; Jackson, B.; Chat, G. L.; Golub, L.; Hariharan, K.; Herne, D.; Kasper, J.; Kennewell, J.; Lonsdale, C.; Lobzin, V.; Matthews, L.; Mohan, A.; Padmanabhan, J.; Pankratius, V.; Pick, M.; Subramanian, P.; Ramesh, R.; Raymond, J.; Reeves, K.; Rogers, A.; Sharma, R.; Tingay, S.; Tremblay, S.; Tripathi, D.; Webb, D.; White, S.; Abidin, Z. B. Z. Bibcode: 2017mwa..prop..A06C Altcode: A hundred hours of observing time for solar observations is requested during the 2017-A observing semester. These data will be used to address science objectives for solar burst science (Goal A), studies of weak non-thermal radiation (Goal B) and quiet sun science (Goal C). Goal A will focus on detailed investigations of individual events seen in the MWA data, using the unsurpassed spectroscopic imaging ability of the MWA to address some key solar physics questions. Detailed observations of type II bursts, of which MWA has observed two, will be one focus, with MWA polarimetric imaging observations of type III bursts another focus. Goal B will address studies of the numerous short lived and narrow band emission features, significantly weaker than those seen by most other instruments revealed by the MWA. These emission features do not resemble any known types of solar bursts, but are possible signatures of "nanoflares" which have long been suspected to play a role in coronal heating. A large database of these events is needed to be able to reliably estimate their contribution to coronal heating. These observations will contribute to this database. Goal C will focus on characterizing the Sun's background thermal emission, their short and long term variability and looking for evidence of a scattering disc around the Sun. Title: Systematic Search of the Nearest Stars for Exoplanetary Radio Emission: VLA observations in L and S Bands Authors: Winterhalter, D.; Knapp, M.; Bastian, T. Bibcode: 2016AGUFM.P13C..07W Altcode: Radio observations have been used as a search tool for exoplanets since before the confirmed discovery of the first extrasolar planet. To date, there have been no definitive detections of exoplanets in the radio regime. We are engaged in an ongoing blind radio survey of the nearest star systems for exoplanetary radio emission. The goal of this survey is to obtain meaningful upper limits on radio emission from (or modulated by) sub-stellar companions of the nearest stars. Nearby stars are strongly preferred because they suffer the least from the dilution of potential radio signals by distance. Targets are selected by distance and observability (both LOFAR and VLA) only. Other properties of target stars, such as stellar type, are not considered to avoid biasing the search. Five survey targets, Procyon, GJ 1111, GJ 725, Ross 614, and UGPSJ072227.51, have been observed with the VLA telescope L- and S-band receivers. P-band observations are ongoing. All targets have multiple L-band observations, while Procyon and Ross 614 also have S-band observations. GJ 725 has been observed with LOFAR at lower frequencies (30-75 MHz) as well. Upper limits on planetary radio flux (and implied magnetic field strength) derived from these VLA observations are presented. Title: The Sun Radio Interferometer Space Experiment (SunRISE) Authors: Alibay, F.; Lazio, J.; Kasper, J. C.; Amiri, N.; Bastian, T.; Cohen, C.; Landi, E.; Manchester, W.; Reinard, A.; Schwadron, N.; Hegedus, A. M.; Maksimovic, M.; Zaslavsky, A.; Cecconi, B.; Hallinan, G.; Krupar, V. Bibcode: 2016AGUFMSH41B2540A Altcode: Radio emission from coronal mass ejections (CMEs) is a direct tracer of the particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. However, many aspects of this particle acceleration remain poorly constrained. The radio emission from CMEs is quite strong such that only a relatively small number of antennas is required to map it. However, the state-of-the-art for tracking such emission is only defined by single antennas (Wind/WAVES, Stereo/SWAVES) in which the tracking is accomplished by assuming a frequency-to-density mapping. These are limited to tracking CMEs to only a few solar radii before the frequencies of radio emission drop below the Earth's ionospheric cutoff. Triangulation between the STEREO/SWAVES and Wind/WAVES instruments have provided some initial constraints on particle acceleration sites at larger distances (lower frequencies), but the uncertainties remain considerable. We present the Sun Radio Imaging Space Experiment (SunRISE) mission concept: a space-based array designed to localize such radio emissions. This low-cost constellation is composed of small spacecraft placed in a geostationary graveyard orbit, each carrying an HF radio receiver. In this concept, each spacecraft would perform concurrent observations below 25 MHz, which would then be correlated on the ground to produce the first images of CMEs more than a few solar radii from the Sun. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Title: Solar Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.; Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.; Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA Solar Development Team Bibcode: 2016ASPC..504..327K Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian project that opens the mm-sub mm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high-resolution imaging in frequency bands currently ranging from 84 GHz to 950 GHz (300 microns to 3 mm). It is located in the Atacama desert in northern Chile at an elevation of 5000 m. Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of matter and energy, and the in heating the outer layers of the solar atmosphere. Despite decades of research, the solar chromosphere remains a significant challenge: both to observe, owing to the complicated formation mechanisms of currently available diagnostics; and to understand, as a result of the complex nature of the structure and dynamics of the chromosphere. ALMA has the potential to change the scene substantially as it serves as a nearly linear thermometer at high spatial and temporal resolution, enabling us to study the complex interaction of magnetic fields and shock waves and yet-to-be-discovered dynamical processes. Moreover, ALMA will play an important role in the study of energetic emissions associated with solar flares at sub-THz frequencies. 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: Probing Solar Wind Turbulence with the Jansky Very Large Array Authors: Kobelski, A.; Bastian, T. S.; Betti, S. Bibcode: 2016ASPC..504...97K Altcode: The solar wind offers an extraordinary laboratory for studying MHD turbulence, turbulent dissipation, and heating. Radio propagation phenomena can be exploited as probes of the solar wind in regions that are generally inaccessible to in situ spacecraft measurements. Here, we have undertaken a study with the Jansky Very Large Array (VLA) to observe point-like sources drawn from the JVAS catalog, and 3 VLA calibrator sources, to trans-illuminate the outer corona/inner solar wind. In doing so, we will exploit angular broadening and refractive scintillation to deduce properties of the solar wind along ≍23 lines of sight within 7 solar radii of the Sun and a wide range of position angles. By fitting the complex visibilities using well-known techniques we can deduce or constrain a number of key parameters. In particular, we fit the visibilities to a function of the known source flux, displacement of the source due to refraction, source broadening due to an elliptical structure function, spectral slope of the turbulence, and the coherence scale. Of particular interest is α, the spectral slope of the turbulence which we probe at both small (km to 10s of km) and large (thousands of km) scales. This will help us determine the presence and evolution of an inner scale, measure the degree of anisotropy, and constrain the topology of the global coronal magnetic field. The inner scale is of particular interest for constraining current theories of turbulence dissipation and heating. Initial analysis show the visibilities vary notably on timescales of individual integrations (2 seconds) and that the source is not uniformly broadened. All sources appear to preferentially broaden perpendicular to the magnetic field, consistent with theories of kinetic Alfvén waves. This type of observation will also help to interpret data from the upcoming Solar Probe Plus and Solar Orbiter missions. A full set of results and analysis is forthcoming. More details on previous results can be found in Bastian (1999), which used the previous generation VLA. 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: Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Shimojo, M. Bibcode: 2015ASPC..499..341W Altcode: 2015arXiv150206379W The Atacama Large Millimeter/submillimeter Array (ALMA) will be a valuable tool for observing the chromosphere of our Sun at (sub-)millimeter wavelengths at high spatial, temporal and spectral resolution and as such has great potential to address long-standing scientific questions in solar physics. In order to make the best use of this scientific opportunity, the Solar Simulations for the Atacama Large Millimeter Observatory Network has been initiated. A key goal of this international collaboration is to support the preparation and interpretation of future observations of the Sun with ALMA. 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: Particle acceleration by a solar flare termination shock Authors: Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Gary, Dale E.; Krucker, Säm; Glesener, Lindsay Bibcode: 2015Sci...350.1238C Altcode: 2015arXiv151202237C Solar flares—the most powerful explosions in the solar system—are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares. Title: Observations and Simulations of a Termination Shock in an Eruptive Solar Flare as a Possible Particle Accelerator Authors: Chen, B.; Bastian, T.; Shen, C.; Gary, D. E.; Krucker, S.; Glesener, L. Bibcode: 2015AGUFMSH11F..05C Altcode: A termination shock has been often invoked in the standard model for eruptive solar flares as a possible driver for particle acceleration. It is hypothesized as a standing shock wave generated by super-magnetosonic reconnection outflows impinging upon dense, newly-reconnected magnetic loops during the flare energy release process. However, such shock wave has largely remained a theoretical concept inferred from model predictions due to the lack of observational evidence. Here we present observations of a termination shock in a solar flare and trace its morphology and dynamics using high-cadence radio imaging spectroscopy enabled by the upgraded Karl G. Jansky Very Large Array. The observed properties of the shock, including its location, morphology, and dynamics, are well-reproduced by magnetohydrodynamics simulations in a standard Kopp-Pneuman-type reconnection geometry for two-ribbon flares. We further show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares. Title: Solar ALMA Observations - A New View of Our Host Star Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Shimojo, M.; Hales, A.; Yagoubov, P.; Hudson, H. Bibcode: 2015ASPC..499..345W Altcode: 2015arXiv150206397W ALMA provides the necessary spatial, temporal and spectral resolution to explore central questions in contemporary solar physics with potentially far-reaching implications for stellar atmospheres and plasma physics. It can uniquely constraint the thermal and magnetic field structure in the solar chromosphere with measurements that are highly complementary to simultaneous observations with other ground-based and space-borne instruments. Here, we highlight selected science cases. Title: Fast Single-Dish Scans of the Sun Using ALMA Authors: Phillips, N.; Hills, R.; Bastian, T.; Hudson, H.; Marson, R.; Wedemeyer, S. Bibcode: 2015ASPC..499..347P Altcode: 2015arXiv150206122P We have implemented control and data-taking software that makes it possible to scan the beams of individual ALMA antennas to perform quite complex patterns while recording the signals at high rates. We conducted test observations of the Sun in September and December, 2014. The data returned have excellent quality; in particular they allow us to characterize the noise and signal fluctuations present in this kind of observation. The fast-scan experiments included both Lissajous patterns covering rectangular areas, and “double-circle” patterns of the whole disk of the Sun and smaller repeated maps of specific disk-shaped targets. With the latter we find that we can achieve roughly Nyquist sampling of the Band 6 (230 GHz) beam in 60 s over a region 300” in diameter. These maps show a peak-to-peak brightness-temperature range of up to 1000 K, while the time-series variability at any given point appears to be of order 0.5% RMS over times of a few minutes. We thus expect to be able to separate the noise contributions due to transparency fluctuations from variations in the Sun itself. Such timeseries have many advantages, in spite of the non-interferometric observations. In particular such data should make it possible to observe microflares in active regions and nanoflares in any part of the solar disk and low corona. Title: The Atacama Large Millimeter/Submillimeter Array: a New Asset for Solar and Heliospheric Physics Authors: Bastian, Timothy S.; Barta, Miroslav; Brajsa, Roman; Chen, Bin; De Pontieu, Bart; Fleishman, Gregory; Gary, Dale; Hales, Antonio; Hills, Richard; Hudson, Hugh; Iwai, Kazamasu; Shimojo, Masumi; White, Stephen; Wedemeyer, Sven; Yan, Yihua Bibcode: 2015IAUGA..2257295B Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian interferometric array that opens the mm-submm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high-resolution imaging in frequency bands ranging from 86 to 950 GHz. Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. In this paper we describe recent efforts to ensure that ALMA can be usefully exploited by the scientific community to address outstanding questions in solar physics. We summarize activities under North American and European ALMA development studies, including instrument testing, calibration and imaging strategies, a science simulations. With the support of solar observations, ALMA joins next-generation groundbased instruments that can be used alone or in combination with other ground-based and space-based instruments to address outstanding questions in solar and heliospheric physics. Opportunities for the wider community to contribute to these efforts will be highlighted. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, Sven; Bastian, Timothy S.; Brajsa, Roman; Barta, Miroslav Bibcode: 2015IAUGA..2257466W Altcode: The Atacama Large Millimeter/submillimeter Array (ALMA) provides a new powerful tool for observing the solar chromosphere at high spatial, temporal, and spectral resolution, which will allow for addressing fundamental scientific questions. Based on first solar test observations, observing strategies for regular solar campaigns are currently under development. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help in this respect, constraining and optimizing future observing modes for ALMA. On September 1st, 2014, the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) has been initiated with the aim to co-ordinate related activities and to promote the scientific potential of ALMA observations of the Sun. The network is connected to two currently ongoing ALMA development studies. As of March 18th, 57 scientists from 15 countries have joined the international SSALMONetwork. Among the affiliations are NRAO, ESO, NAOJ, the Czech ALMA ARC node at Ondrejov, ESA and many more. Since March 2015, we are building up expert teams, which work on specific tasks in preparation of future regular ALMA observations (expected to start in late 2016) and their interpretation. Registration and more information at http://www.ssalmon.uio.no. Title: Solar ALMA observations - A revolutionizing new view at our host star Authors: Wedemeyer, Sven; Brajsa, Roman; Bastian, Timothy S.; Barta, Miroslav; Hales, Antonio; Yagoubov, Pavel; Hudson, Hugh; Loukitcheva, Maria; Fleishman, Gregory Bibcode: 2015IAUGA..2256732W Altcode: Observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA) have a large potential for revolutionizing our understanding of our host star with far reaching implications for stars in general. The radiation emitted at ALMA wavelengths originates mostly from the chromosphere - a complex and dynamic layer between the photosphere and the corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere.Despite decades of intensive research, the chromosphere is still elusive and challenging to observe owing to the complicated formation mechanisms of currently available diagnostics. ALMA will change the scene substantially as it serves as a nearly linear thermometer at high spatial, temporal, and spectral resolution, enabling us to study the complex interaction of magnetic fields and shock waves and yet-to-be-discovered dynamical processes. Furthermore, radio recombination and molecular lines may have great diagnostic potential but need to be investigated first. These unprecedented capabilities promise important new findings for a large range of topics in solar physics including the structure, dynamics and energy balance of quiet Sun regions, active regions and sunspots, flares and prominences. As a part of ongoing development studies, an international network has been initiated, which aims at defining and preparing key solar science with ALMA through simulation studies: SSALMON -- Solar Simulations for the Atacama Large Millimeter Observatory Network (http://ssalmon.uio.no). Here, we give an overview of potential science cases. Title: Radio Coronal Magnetography of a Large Active Region Authors: Bastian, Timothy S.; Gary, Dale E.; White, Stephen; Fleishman, Gregory; Chen, Bin Bibcode: 2015TESS....111301B Altcode: Quantitative knowledge of coronal magnetic fields is fundamental to understanding energetic phenomena such as solar flares. Flares occur in solar active regions where strong, non-potential magnetic fields provide free energy. While constraints on the coronal magnetic field topology are readily available through high resolution SXR and EUV imaging of solar active regions, useful quantitative measurements of coronal magnetic fields have thus far been elusive. Recent progress has been made at infrared (IR) wavelengths in exploiting both the Zeeman and Hanle effects to infer the line-of-sight magnetic field strength or the orientation of the magnetic field vector in the plane of the sky above the solar limb. However, no measurements of coronal magnetic fields against the solar disk are possible using IR observations. Radio observations of gyroresonance emission from active regions offer the means of measuring coronal magnetic fields above the limb and on the solar disk. In particular, for plasma plasma conditions in the solar corona, active regions typically become optically thick to emission over a range of radio frequencies through gyroresonance absorption at a low harmonic of the electron gyrofrequency. The specific range of resonant frequencies depends on the range of coronal magnetic field strengths present in the active region.The Karl G. Jansky Very Large Array was used in November 2014 to image NOAA/USAF active region AR12209 over a continuous frequency range of 1-8 GHz, corresponding to a wavelength range of 3.75-30 cm. This frequency range is sensitive to coronal magnetic field strengths ranging from ~120-1400G. The active region was observed on four different dates - November 18, 20, 22, and 24 - during which the active region longitude ranged from -15 to +70 degrees, providing a wide range of aspect angles. In this paper we provide a preliminary description of the coronal magnetic field measurements derived from the radio observations. Title: Observation and Modeling of a Termination Shock in a Solar Eruption as a Possible Particle Accelerator Authors: Gary, Dale E.; Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Krucker, Sam Bibcode: 2015TESS....130402G Altcode: Solar eruptions and their associated solar flares are the most energetic particle accelerators in our solar system. Yet the acceleration mechanism remains uncertain. A possible candidate often invoked in the standard picture of solar eruptions is a termination shock, produced by fast reconnection outflows impinging upon dense, closed loops in a helmet-type geometry. However, the importance of termination shocks in solar particle acceleration remains controversial, mainly because there has been no direct detection of such shocks. Here we report direct imaging of the location and evolution of a termination shock during the rise phase of a solar eruption. The shock appears at radio wavelengths as a narrow surface sandwiched between multitudes of downward-moving plasma blobs and the underlying, newly-reconnected flaring loops, and evolves coherently with a loop-top hard X-ray source in the shock downstream region. The shock produces many short-lived, point-like radio sources, each interpreted as emission from a turbulence cell interacting with fast (nonthermal) electrons. These point-like radio sources clearly outline the termination shock front and their positions change in reaction to the arrival of the fast plasma blobs, which are well-reproduced by our numerical simulations based on a resistive magnetohydrodynamics reconnection model in a standard two-ribbon flare geometry. We further show that a temporary disruption of the shock coincides with a reduction of radio and hard X-ray emission associated with the energetic electron population. Our observations strongly favor a scenario in which the termination shock is responsible for accelerating electrons to high energies. Title: Solar Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) Authors: Bastian, Timothy S. Bibcode: 2015TESS....120323B Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian project that opens the mm-submm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high-resolution imaging in frequency bands currently ranging from 84 GHz to 950 GHz (300 microns to 3 mm). Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of matter and energy, and the in heating the outer layers of the solar atmosphere. Despite decades of research, the solar chromosphere remains a significant challenge: both to observe, owing to the complicated formation mechanisms of currently available diagnostics; and to understand, as a result of the complex nature of the structure and dynamics of the chromosphere. ALMA has the potential to change the scene substantially as it serves as a nearly linear thermometer at high spatial and temporal resolution, enabling us to study the complex interaction of magnetic fields and shock waves and yet-to-be-discovered dynamical processes. Moreover, ALMA will play an important role in the study of energetic emissions associated with solar flares at sub-THz frequencies.In this paper we describe recent efforts to ensure that ALMA can be usefully exploited by the scientific community to address outstanding questions in solar physics. We summarize activities by the ALMA solar development team comprised of scientists from the East Asia, North America, and Europe. These activities include instrument testing, development of calibration and imaging strategies, software requirements development, and science simulations. Opportunities for the wider community to contribute to these efforts will be highlighted. Title: Observing the Sun with ALMA: A New Window into Solar Physics Authors: Bastian, Timothy S.; Shimojo, Masumi; Wedemeyer-Bohm, Sven; ALMA North American Solar Development Team Bibcode: 2015AAS...22541301B Altcode: The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint North American, European, and East Asian interferometric array that opens the mm-submm wavelength part of the electromagnetic spectrum for general astrophysical exploration, providing high resolution imaging in frequency bands. Despite being a general purpose instrument, provisions have been made to enable solar observations with ALMA, thereby offering a new window into solar physics. Radiation emitted at ALMA wavelengths originates mostly from the chromosphere, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Despite decades of intensive research, an understanding of the chromosphere is still elusive, and challenging to observe owing to the complicated formation mechanisms of currently available diagnostics. ALMA will change the scene substantially as it serves as a nearly linear thermometer at high spatial, temporal, and spectral resolution, enabling us to study the complex interaction of magnetic fields and shock waves and yet-to-be-discovered dynamical processes.Moreover, ALMA will play an important role in the study of energetic emissions associated with solar flares at sub-THz frequencies.This presentations introduces ALMA to the solar physcis community and motivates the science that can be addressed by ALMA using a number of examples based on 3D MHD simulations. In addition, the means by which ALMA is used to acquire and calibrate solar observations will be discussed. Finally, we encourage potential users to join us in further defining and articulating the exciting science to be explored with this fundamentally new instrument. Title: Constraining Solar Coronal Magnetic Fields with New Radio Observing Techniques Authors: Chen, B.; Gary, D. E.; Bastian, T. Bibcode: 2014AGUFMSH23C..07C Altcode: Solar radio emission, produced by energetic electrons in the low-beta solar corona, is highly dependent on coronal magnetic field strength and direction, hence offering a rich potential for constraining coronal magnetic fields. However, the observed radio intensity is contributed by several different emission mechanisms and moreover, is known to be sensitive to parameters other than the magnetic field, such as the electron distribution function. Collectively, they introduce ambiguities that are difficult to resolve in the absence of high-quality, broadband radio dynamic imaging spectroscopic observations with sufficiently high spatial, spectral, and temporal resolution. Such observations have not been possible until very recently, thanks to the newly developed radio instruments such as the Karl G. Jansky Very Large Array (VLA) and the Expanded Owens Valley Solar Array (EOVSA). In this talk, we will present first results obtained from the Jansky VLA demonstrating their ability of constraining the coronal magnetic fields in active regions. We will also introduce a forward-modeling tool currently under development, which can be used to reconstruct the 3D coronal magnetic fields based on the newly available radio observations. Title: VLA Observations of Solar Decimetric Spike Bursts: Direct Signature of Accelerated Electrons in Reconnection Outflow Region Authors: Chen, B.; Bastian, T.; Gary, D. E. Bibcode: 2014AGUFMSH23A4149C Altcode: Solar decimetric spike bursts, which appear in a radio dynamic spectrum as a cluster of short-lived and narrowband brightenings, have been suggested as a possible signature of many, "elementary" particle accelerations at or near a magnetic reconnection site. Their dynamic spectral feature can be potentially used to diagnose important parameters of the reconnection site such as plasma density and spatial size of the fragmentation. Yet direct observational evidence supporting this scenario has been elusive mainly due to the lack of imaging observations. The upgraded Karl G. Jansky Very Large Array (VLA) provides the first opportunity of performing simultaneous radio imaging and dynamic spectroscopy, which allows radio sources to be imaged at every spatio-temporal pixel in the dynamic spectrum. Here we report Jansky VLA observations of decimetric spike bursts recorded during an eruptive solar limb flare. Combined with EUV and X-ray data from SDO and RHESSI, we show that the spike bursts coincide spatially with a loop-top hard X-ray source, which are located in a region where supra-arcade downflows meet the underlying hot, EUV/X-ray loops. We interpret the observed spike bursts as a direct signature of non-thermal electrons accelerated by turbulences and/or shocks in the reconnection outflow region. Title: Direct Evidence of an Eruptive, Filament-hosting Magnetic Flux Rope Leading to a Fast Solar Coronal Mass Ejection Authors: Chen, Bin; Bastian, T. S.; Gary, D. E. Bibcode: 2014ApJ...794..149C Altcode: 2014arXiv1408.6473C Magnetic flux ropes (MFRs) are believed to be at the heart of solar coronal mass ejections (CMEs). A well-known example is the prominence cavity in the low corona that sometimes makes up a three-part white-light (WL) CME upon its eruption. Such a system, which is usually observed in quiet-Sun regions, has long been suggested to be the manifestation of an MFR with relatively cool filament material collecting near its bottom. However, observational evidence of eruptive, filament-hosting MFR systems has been elusive for those originating in active regions. By utilizing multi-passband extreme-ultraviolet (EUV) observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly, we present direct evidence of an eruptive MFR in the low corona that exhibits a hot envelope and a cooler core; the latter is likely the upper part of a filament that undergoes a partial eruption, which is later observed in the upper corona as the coiled kernel of a fast, WL CME. This MFR-like structure exists more than 1 hr prior to its eruption, and displays successive stages of dynamical evolution, in which both ideal and non-ideal physical processes may be involved. The timing of the MFR kinematics is found to be well correlated with the energy release of the associated long-duration C1.9 flare. We suggest that the long-duration flare is the result of prolonged energy release associated with the vertical current sheet induced by the erupting MFR. Title: Probing Magnetic Energy Release in a Solar Flare with Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.; White, S. M. Bibcode: 2014AAS...22311804C Altcode: Solar flares involve sudden release of magnetic energy that is previously stored in the Sun's corona. Yet details of the flare energy release processes are still poorly understood. Solar radio bursts are intense and short-lived radio emissions that occur in solar flares. They are believed to be intimately related to flare energy release processes. However, their potential in diagnosing flare energy release has been greatly limited by the lack of simultaneous spatial information. The upgraded Karl G. Jansky Very Large Array (VLA) provides the first opportunity of radio synthesis imaging along with high spectral and temporal resolution, making the new technique of radio dynamic imaging spectroscopy possible. We report VLA observations of a solar flare event using this new technique, during which a rich variety of radio bursts are recorded. With the help of concurrent data in extreme ultra-violet and X-ray wavelengths, these observations allow us to establish the relation between the bursts and flare energy release, and use them to probe physical properties of the energy release site. Title: Preface Authors: Tomczyk, Steven; Zhang, Jie; Bastian, Timothy; Leibacher, John W. Bibcode: 2013SoPh..288..463T Altcode: No abstract at ADS Title: A view from the ground: Next generation instrumentation for solar and heliospheric physics Authors: Bastian, T. S. Bibcode: 2013AIPC.1539..442B Altcode: The solar and space physics community has recently completed its second decadal survey under the auspices of the National Research Council. An integrated strategy for ground and space based studies of the Sun and space physics has been recommended, with specific recommendations made regarding new instrumentation, programs, and facilities. The ground based component of these recommendations is briefly reviewed here: the Advanced Technology Solar Telescope (ATST), the Frequency Agile Solar Radiotelescope (FASR), and the Coronal Solar Magnetism Observatory (COSMO). Although not considered as part of the decadal portfolio, but of which the community should nevertheless be aware, are the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (VLA). Several additional instruments are briefly mentioned as pathfinders for those instruments recommended by the decadal survey, including the Coronal Multichannel Polarimeter (CoMP) and the Expanded Owens Valley Solar Array (EOVSA). The planned instruments discussed offer uniquely powerful observations of emissions that originate from the photosphere to well out into the solar wind. As such, they provide observations that are highly complementary to space based missions such as Solar Probe Plus and Solar Orbiter. The status and science goals of the recommended instruments are briefly reviewed. Title: Solar flares at submillimeter wavelengths Authors: Krucker, Säm; Giménez de Castro, C. G.; Hudson, H. S.; Trottet, G.; Bastian, T. S.; Hales, A. S.; Kašparová, J.; Klein, K. -L.; Kretzschmar, M.; Lüthi, T.; Mackinnon, A.; Pohjolainen, S.; White, S. M. Bibcode: 2013A&ARv..21...58K Altcode: We discuss the implications of the first systematic observations of solar flares at submillimeter wavelengths, defined here as observing wavelengths shorter than 3 mm (frequencies higher than 0.1 THz). The events observed thus far show that this wave band requires a new understanding of high-energy processes in solar flares. Several events, including observations from two different observatories, show during the impulsive phase of the flare a spectral component with a positive (increasing) slope at the highest observable frequencies (up to 405 GHz). To emphasize the increasing spectra and the possibility that these events could be even more prominent in the THz range, we term this spectral feature a "THz component". Here we review the data and methods, and critically assess the observational evidence for such distinct component(s). This evidence is convincing. We also review the several proposed explanations for these feature(s), which have been reported in three distinct flare phases. These data contain important clues to flare development and particle acceleration as a whole, but many of the theoretical issues remain open. We generally have lacked systematic observations in the millimeter-wave to far-infrared range that are needed to complete our picture of these events, and encourage observations with new facilities. Title: Tracing Electron Beams in the Sun's Corona with Radio Dynamic Imaging Spectroscopy Authors: Chen, Bin; Bastian, T. S.; White, S. M.; Gary, D. E.; Perley, R.; Rupen, M.; Carlson, B. Bibcode: 2013ApJ...763L..21C Altcode: 2012arXiv1211.3058C We report observations of type III radio bursts at decimeter wavelengths (type IIIdm bursts)—signatures of suprathermal electron beams propagating in the low corona—using the new technique of radio dynamic imaging spectroscopy provided by the recently upgraded Karl G. Jansky Very Large Array. For the first time, type IIIdm bursts were imaged with high time and frequency resolution over a broad frequency band, allowing electron beam trajectories in the corona to be deduced. Together with simultaneous hard X-ray and extreme ultraviolet observations, we show that these beams emanate from an energy release site located in the low corona at a height below ~15 Mm, and propagate along a bundle of discrete magnetic loops upward into the corona. Our observations enable direct measurements of the plasma density along the magnetic loops, and allow us to constrain the diameter of these loops to be less than 100 km. These overdense and ultra-thin loops reveal the fundamentally fibrous structure of the Sun's corona. The impulsive nature of the electron beams, their accessibility to different magnetic field lines, and the detailed structure of the magnetic release site revealed by the radio observations indicate that the localized energy release is highly fragmentary in time and space, supporting a bursty reconnection model that involves secondary magnetic structures for magnetic energy release and particle acceleration. Title: Observing the Sun at Radio Wavelengths: Current Status and Future Prospects Authors: Bastian, T.; Gary, D. Bibcode: 2012IAUSS...6E.215B Altcode: Radio emission from the Sun offers the means of probing thermal and non-thermal processes in the chromosphere and corona using diagnostics that are largely complementary to those available at optical wavelengths. This talk briefly reviews radio diagnostics and observing techniques and several of the science objectives motivating new and planned instrumentation, including coronal magnetography, magnetic energy release and particle acceleration, drivers of space weather, and the quiet solar atmosphere. New instrumentation includes ALMA, opening a new spectral window at millimeter and submillimeter wavelengths; and the Jansky Very Large Array (JVLA), a powerful new instrument operating at centimeter and decimeter wavelengths. A solar-dedicated instrument under construction is the Expanded Owens Valley Solar Array (EOVSA); and a planned, new, solar-dedicated facility is the Frequency Agile Solar Radiotelescope (FASR). EOVSA will soon pioneer dynamic imaging spectroscopy techniques. FASR will fully exploit these techniques as a general purpose radioheliograph designed to perform ultra-wideband dynamic imaging spectroscopy. Title: The Role of Inverse Compton Scattering in Solar Coronal Hard X-Ray and γ-Ray Sources Authors: Chen, Bin; Bastian, T. S. Bibcode: 2012ApJ...750...35C Altcode: 2011arXiv1108.0131C Coronal hard X-ray (HXR) and continuum γ-ray sources associated with the impulsive phase of solar flares have been the subject of renewed interest in recent years. They have been interpreted in terms of thin-target, non-thermal bremsstrahlung emission. This interpretation has led to rather extreme physical requirements in some cases. For example, in one case, essentially all of the electrons in the source must be accelerated to non-thermal energies to account for the coronal HXR source. In other cases, the extremely hard photon spectra of the coronal continuum γ-ray emission suggest that the low-energy cutoff of the electron energy distribution lies in the MeV energy range. Here, we consider the role of inverse Compton scattering (ICS) as an alternate emission mechanism in both the ultra- and mildly relativistic regimes. It is known that relativistic electrons are produced during powerful flares; these are capable of upscattering soft photospheric photons to HXR and γ-ray energies. Previously overlooked is the fact that mildly relativistic electrons, generally produced in much greater numbers in flares of all sizes, can upscatter extreme-ultraviolet/soft X-ray photons to HXR energies. We also explore ICS on anisotropic electron distributions and show that the resulting emission can be significantly enhanced over an isotropic electron distribution for favorable viewing geometries. We briefly review results from bremsstrahlung emission and reconsider circumstances under which non-thermal bremsstrahlung or ICS would be favored. Finally, we consider a selection of coronal HXR and γ-ray events and find that in some cases the ICS is a viable alternative emission mechanism. Title: Radio Spectroscopic Imaging of Electron Beams in the Solar Corona Authors: Bastian, Timothy S.; Chen, B. Bibcode: 2012AAS...22020443B Altcode: The recently upgraded Jansky Very Large Array was used to observe the radio emission from a C class solar flare. Observations were performed from 1-2 GHz with a spectral resolution of 1 MHz and time resolution of 100 ms. A number of fast-drift, type-III-like radio bursts was observed, the result of nonthermal electron beams propagating from the flare site, guided by the coronal magnetic field. Using these dynamic, imaging, spectroscopic observations, the electron beam trajectories are deduced.Implications are briefly discussed. Title: The Role of Inverse Compton Scattering in Solar Coronal Hard X-ray and γ-ray Sources Authors: Chen, B.; Bastian, T. S. Bibcode: 2011AGUFMSH44A..05C Altcode: We consider the role of inverse Compton scattering (ICS) as a means of producing coronal hard X-ray (HXR) and continuum γ-ray sources during solar flares. Coronal HXR and continuum γ-ray emission observed during solar flares has been interpreted in terms of thin-target bremsstrahlung emission. In one case, this interpretation leads to the conclusion that the number of energetic electrons required to account for the coronal HXR source must be large, implying that essentially all electrons in the source must be accelerated to energies ≥ 16 keV. In other cases, the spectral index of the photon spectrum of γ-ray sources approaches the theoretical limit for bremsstrahlung emission (α ~ 1.5 - 2). Here we investigate ICS in both the fully relativistic and mildly relativistic regimes as an alternative to non-thermal bremsstrahlung. It is known that relativistic electrons are produced during powerful flares; these are capable of up-scattering soft photospheric photons to HXR energies. Previously overlooked is the fact that mildly relativistic electrons, generally produced in much greater numbers in flares of all sizes, can up-scatter EUV/SXR photons to HXR energies. We also explore ICS on anisotropic electron distributions and show that the resulting emission can be significantly enhanced over the case of scattering on an isotropic electron distribution. We apply our results to a selection of coronal HXR and γ-ray events and find that in some cases the ICS mechanism is a viable alternative to non-thermal bremsstrahlung emission, particularly if the energetic population of electrons responsible for the emission is anisotropic. Title: Spatially and Spectrally Resolved Observations of a Zebra Pattern in a Solar Decimetric Radio Burst Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.; Jing, Ju Bibcode: 2011ApJ...736...64C Altcode: 2011arXiv1105.0715C We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral (≈1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 2006 December 14. By using OVSA to calibrate the FST, the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance model in which the radio emission occurs in resonance layers where the upper-hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop. Title: Uncovering Mechanisms of Coronal Magnetism via Advanced 3D Modeling of Flares and Active Regions Authors: Fleishman, Gregory; Gary, Dale; Nita, Gelu; Alexander, David; Aschwanden, Markus; Bastian, Tim; Hudson, Hugh; Hurford, Gordon; Kontar, Eduard; Longcope, Dana; Mikic, Zoran; DeRosa, Marc; Ryan, James; White, Stephen Bibcode: 2010arXiv1011.2800F Altcode: The coming decade will see the routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness. To capitalize on the new (or soon to be available) facilities such as SDO, ATST and FASR, and the challenges they present in the visualization and synthesis of multi-wavelength datasets, we propose that realistic, sophisticated, 3D active region and flare modeling is timely and critical, and will be a forefront of coronal studies over the coming decade. To make such modeling a reality, a broad, concerted effort is needed to capture the wealth of information resulting from the data, develop a synergistic modeling effort, and generate the necessary visualization, interpretation and model-data comparison tools to accurately extract the key physics. Title: Radiative signatures of energetic particles Authors: Bastian, Tim Bibcode: 2010hssr.book...79B Altcode: No abstract at ADS Title: Spatially and Spectrally Resolved Observations of a "Zebra” Solar Radio Burst Authors: Bastian, Timothy S.; Chen, B.; Gary, D. E. Bibcode: 2010AAS...21542201B Altcode: 2010BAAS...42..291B The FASR Subsystems Testbed (FST) is a frequency-agile three-element interferometer located at the Owens Valley Radio Observatory in California. A frequency band of 500 MHz can be dynamically selected within the 1-9 GHz frequency FST operating range. The signal from each antenna is sampled at 1 Gsps and written to disk. The full-resolution time-domain data are then correlated offline to produce amplitude and phase spectra on three interferometric baselines. The FST was used on 14 December 2006 to observe the GOES X1.5 soft X-ray flare in NOAA/USAF active region 10930 at S06W46. The FST observed the event between 1.0-1.5 GHz with a time resolution of 20 ms and a frequency resolution of approximately 1 MHz, time sharing between observations sensitive to right- and left-circularly polarized radiation. A variety of coherent radio bursts was observed, including a highly circularly polarized "Zebra” burst characterized by 7-10 regularly spaced bands of emission in the dynamic spectrum. With new constraints available on the source size and the relative source position as a function of frequency, the double-plasma resonance model is explored, wherein emission in a given band occurs at the upper hybrid frequency that is, in turn, harmonically related to the local electron cyclotron frequency. Title: Interplanetary Type II Radio Bursts and the Role of Synchrotron Radiation Authors: Chen, Bin; Bastian, T. S. Bibcode: 2009SPD....41.3709C Altcode: Type II radio bursts are a type of slow drift radio emission associated with shocks in the solar corona and in the interplanetary medium. It is widely assumed that interplanetary (IP) type II radio bursts are the result of plasma radiation from Langmuir waves excited by suprathermal electrons in the upstream region of a shock driven by a fast coronal mass ejection (CME). Alternatively, some IP type II events may instead be the result of synchrotron radiation from 1 MeV electrons. We present a sample of fast-CME/IP-type-II events characterized by smoothly varying emission and large frequency bandwidths and consider the implications of both the plasma radiation hypothesis and the synchrotron emission hypothesis. Title: Digital Instrumentation for the Radio Astronomy Community Authors: Parsons, Aaron; Werthimer, Dan; Backer, Donald; Bastian, Tim; Bower, Geoffrey; Brisken, Walter; Chen, Henry; Deller, Adam; Filiba, Terry; Gary, Dale; Greenhill, Lincoln; Hawkins, David; Jones, Glenn; Langston, Glen; Lasio, Joseph; Van Leeuwen, Joeri; Mitchell, Daniel; Manley, Jason; Siemion, Andrew; So, Hayden Kwok-Hay; Whitney, Alan; Woody, Dave; Wright, Melvyn; Zarb-Adami, Kristian Bibcode: 2009astro2010T..21P Altcode: 2009arXiv0904.1181P Time-to-science is an important figure of merit for digital instrumentation serving the astronomical community. A digital signal processing (DSP) community is forming that uses shared hardware development, signal processing libraries, and instrument architectures to reduce development time of digital instrumentation and to improve time-to-science for a wide variety of projects. We suggest prioritizing technological development supporting the needs of this nascent DSP community. After outlining several instrument classes that are relying on digital instrumentation development to achieve new science objectives, we identify key areas where technologies pertaining to interoperability and processing flexibility will reduce the time, risk, and cost of developing the digital instrumentation for radio astronomy. These areas represent focus points where support of general-purpose, open-source development for a DSP community should be prioritized in the next decade. Contributors to such technological development may be centers of support for this DSP community, science groups that contribute general-purpose DSP solutions as part of their own instrumentation needs, or engineering groups engaging in research that may be applied to next-generation DSP instrumentation. Title: Magnetospheric Emissions from Extrasolar Planets Authors: Lazio, J.; Bastian, T.; Bryden, G.; Farrell, W. M.; Griessmeier, J. -M.; Hallinan, G.; Kasper, J.; Kuiper, T.; Lecacheux, A.; Majid, W.; Osten, R.; Shklonik, E.; Stevens, I.; Winterhalter, D.; Zarka, P. Bibcode: 2009astro2010S.177L Altcode: 2009arXiv0903.0873L The magnetospheric emissions from extrasolar planets represent a science frontier for the next decade. All of the solar system giant planets and the Earth produce radio emissions as a result of interactions between their magnetic fields and the solar wind. In the case of the Earth, its magnetic field may contribute to its habitability by protecting its atmosphere from solar wind erosion and by preventing energetic particles from reaching its surface. Indirect evidence for at least some extrasolar giant planets also having magnetic fields includes the modulation of emission lines of their host stars phased with the planetary orbits, likely due to interactions between the stellar and planetary magnetic fields. If magnetic fields are a generic property of giant planets, then extrasolar giant planets should emit at radio wavelengths allowing for their direct detection. Existing observations place limits comparable to the flux densities expected from the strongest emissions. Additional sensitivity at low radio frequencies coupled with algorithmic improvements likely will enable a new means of detection and characterization of extrasolar planets within the next decade. Title: Particle Acceleration and Transport on the Sun Authors: Bastian, T. S.; Emslie, G.; Fleishman, G.; Gary, D. E.; Holman, G.; Hudson, H.; Hurford, G.; Krucker, S.; Lee, J.; Miller, J.; White, S. Bibcode: 2009astro2010S..13B Altcode: No abstract at ADS Title: Magnetically driven activity in the solar corona: a path to understanding the energetics of astrophysical plasmas Authors: Gibson, Sarah; Bastian, Tim; Lin, Haoscheng; Low, B. C.; Tomczyk Bibcode: 2009astro2010S..94G Altcode: No abstract at ADS Title: Coronal "Dark Energy" and Solar/Stellar Activity Authors: White, Stephen; Bastian, Tim; Judge, Phil; Lin, Haosheng Bibcode: 2009astro2010S.315W Altcode: No abstract at ADS Title: Broadband Quasi-periodic Radio and X-Ray Pulsations in a Solar Flare Authors: Fleishman, Gregory D.; Bastian, T. S.; Gary, Dale E. Bibcode: 2008ApJ...684.1433F Altcode: 2008arXiv0804.4037F We describe microwave and hard X-ray observations of strong quasi-periodic pulsations from the GOES X1.3 solar flare on 2003 June 15. The radio observations were made jointly by the Owens Valley Solar Array (OVSA), the Nobeyama Polarimeter (NoRP), and the Nobeyama Radioheliograph (NoRH). Hard X-ray observations were made by RHESSI. Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, differential phase, and modulation amplitudes of the radio and X-ray pulsations. Focusing on the more complete radio observations, we also examine the modulation of the degree of circular polarization and of the radio spectral index. The observed properties of the oscillations are compared with those derived from two simple models for the radio emission. In particular, we explicitly fit the observed modulation amplitude data to the two competing models. The first model considers the effects of MHD oscillations on the radio emission. The second model considers the quasi-periodic injection of fast electrons. We demonstrate that quasi-periodic acceleration and injection of fast electrons is the more likely cause of the quasi-periodic oscillations observed in the radio and hard X-ray emission, which has important implications for particle acceleration and transport in the flaring sources. Title: Ultrahigh Time Resolution Observations of Radio Bursts on AD Leonis Authors: Osten, Rachel A.; Bastian, T. S. Bibcode: 2008ApJ...674.1078O Altcode: 2007arXiv0710.5881O We report observations of a radio burst that occurred on the flare star AD Leonis over a frequency range of 1120-1620 MHz (λ ≈ 18-27 cm). These observations, made by the 305 m telescope of the Arecibo Observatory, are unique in providing the highest time resolution (1 ms) and broadest spectral coverage (Δ ν/ν = 0.36) of a stellar radio burst yet obtained. The burst was observed on 2005 April 9. It produced a peak flux density of ~500 mJy, and it was essentially 100% right-circularly polarized. The dynamic spectrum shows a rich variety of structure: patchy emission, diffuse bands, and narrowband, fast-drift striae. Focusing our attention on the fast-drift striae, we consider the possible role of dispersion, and find that it requires rather special conditions in the source to be a significant factor. We suggest that the emission may be due to the cyclotron maser instability, a mechanism known to occur in planetary magnetospheres. We briefly explore possible implications of this possibility. Title: Radio Spectral Evolution of an X-Ray-poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration Authors: Bastian, T. S.; Fleishman, G. D.; Gary, D. E. Bibcode: 2007ApJ...666.1256B Altcode: 2007arXiv0704.2413B We present radio and X-ray observations of an impulsive solar flare that was moderately intense in microwaves, yet showed very meager EUV and X-ray emission. The flare occurred on 2001 October 24 and was well observed at radio wavelengths by the Nobeyama Radioheliograph (NoRH), the Nobeyama Radio Polarimeters (NoRP), and the Owens Valley Solar Array (OVSA). It was also observed in EUV and X-ray wavelength bands by the TRACE, GOES, and Yohkoh satellites. We find that the impulsive onset of the radio emission is progressively delayed with increasing frequency relative to the onset of hard X-ray emission. In contrast, the time of flux density maximum is progressively delayed with decreasing frequency. The decay phase is independent of radio frequency. The simple source morphology and the excellent spectral coverage at radio wavelengths allowed us to employ a nonlinear χ2-minimization scheme to fit the time series of radio spectra to a source model that accounts for the observed radio emission in terms of gyrosynchrotron radiation from MeV-energy electrons in a relatively dense thermal plasma. We discuss plasma heating and electron acceleration in view of the parametric trends implied by the model fitting. We suggest that stochastic acceleration likely plays a role in accelerating the radio-emitting electrons. Title: Radio emission from the Sun, planets, and the interplanetary medium Authors: Bastian, Timothy S. Bibcode: 2007HiA....14..362B Altcode: A brief review is given of radio phenomena on the Sun, the planet Jupiter, and the interplanetary medium and its outer boundary. A brief aside is made to draw parallels between radio emission from Jupiter and extrasolar planets. Title: Synchrotron Radio Emission from a Fast Halo Coronal Mass Ejection Authors: Bastian, T. S. Bibcode: 2007ApJ...665..805B Altcode: 2007arXiv0704.3108B An interplanetary (IP) type II-like radio burst is analyzed. It occurred on 2003 June 17-18 in association with a fast halo coronal mass ejection (CME), an M6.8 soft-X-ray (SXR) flare, and it produced a solar proton event. Unlike coronal type II bursts and the majority of IP type II radio emissions, the IP type-II-like event associated with the fast halo CME on June 17-18 varies smoothly in time and frequency and has a frequency bandwidth that is several times larger than is typical for coronal and IP type II emissions. Moreover, the frequency change with time is inconsistent with that expected from plasma radiation associated with a CME-driven shock. I suggest that this IP type-II-like event, referred to here as an IP type II-S event, is not due to plasma radiation, but instead to incoherent synchrotron radiation from near-relativistic electrons entrained in the CME magnetic field or in the sheath region between the shock and the CME driver. This event may be an example of a new and distinct class of interplanetary radio phenomenon. Title: Synchrotron Radiation From A Fast Halo CME Authors: Bastian, Timothy S. Bibcode: 2007AAS...210.2922B Altcode: 2007BAAS...39..141B An interplanetary (IP) type-II-like radio burst observed by WIND/WAVES is analyzed. It occurred on 2003 June 17 in association with a fast halo coronal mass ejection (CME), an M6.8 soft-X-ray (SXR) flare, and a solar proton event. Unlike coronal type II radio bursts and majority of IP type II radio emissions, the IP type-II-like event associated with the fast halo CME varies smoothly in time and frequency and has a frequency bandwidth that is several times larger than is typical for coronal and IP type II emissions. Moreover, the frequency change with time is inconsistent with that expected from plasma radiation associated with a CME-driven shock. I suggest that this IP type-II-like event, referred to here as an IP type II-S event, is not due to plasma radiation but, rather, incoherent synchrotron radiation from relativistic electrons entrained in the CME magnetic field, or in the sheath region between the shock and the CME driver. This event may be an example of a new and distinct class of interplanetary radio phenomenon. Title: The FASR Reference Instrument Authors: Bastian, Timothy S.; FASR Design Team Bibcode: 2007AAS...210.8203B Altcode: 2007BAAS...39..191B The Frequency Agile Solar Radiotelescope (FASR) is a next-generation radioheliograph designed to perform dynamic broadband imaging spectroscopy over a frequency range of 50 MHz to 20 GHz. It will do so with high time, frequency, and angular resolution. Currently in the design stage, it will address an extremely broad science program, including coronal magnetography, energetic phenomena such as flares and coronal mass ejections, the corona and inner heliosphere, and space weather. This paper introduces the FASR reference instrument and presents the operations plan. The current project status is also discussed. Title: Progress in Understanding Radio Emission from Solar Flares: Observations with the Nobeyama Radioheliograph 1999-2004 Authors: Bastian, T. S. Bibcode: 2006spnr.conf....3B Altcode: Studies of solar flares based on observations by the Nobeyama Radioheliograph and related instruments such as the Owens Valley Solar Array, the Nançay Radioheliograph, and the Solar Submillimeter Telescope, as well as supporting instruments such as the RHESSI, TRACE, and SOHO missions, are reviewed for the period 1999-2004. Work on the classification of solar radio bursts is briefly discussed. Recent observational work on loop-top radio sources and rapidly propagating emission signatures is summarized and its interpretation in terms of electron anisotropies is described. Possible acceleration processes yielding such anisotropies are also briefly discussed. Recent work on electron acceleration and transport in a relatively dense plasma environment is summarized. Finally, recent work at millimeter and submillimeter wavelengths is described. Title: Magnetic Field Measurements in Flare Loops and CMEs Authors: Bastian, T. S. Bibcode: 2006ASPC..358..173B Altcode: Quantitative measurements of magnetic fields in flares and CMEs are critical to understanding both phenomena. In this paper we briefly explore the use of radio observations to measure coronal fields. While several radio diagnostics exist, we focus on gyrosynchrotron radiation from energetic electrons in the source. It is shown that with broadband imaging spectroscopy at decimeter and centimeter wavelengths, the magnetic field can be extracted from the data along with a number of other important physical parameters. It is expected that coronal magnetography will be a key new capability of the Frequency Agile Solar Radiotelescope (FASR), an instrument currently under development. Title: Fast-Drifting Radio Bursts Seen on the Flare Star AD Leo with the Arecibo Observatory Authors: Osten, Rachel A.; Bastian, T. Bibcode: 2006AAS...209.2914O Altcode: 2006BAAS...38..943O We report on observations of two radio bursts at wavelengths 18--27 cm seen on the flare star AD Leonis with the Arecibo Observatory in April 2005. These observations are unique in providing the highest time resolution (1 ms) and largest instantaneous contiguous frequency coverage (Δ ν 400 MHz) of stellar radio bursts. The second radio burst on April 9, 2005 near 01:14:50 UT, exhibited a combination of fast-drifting radio bursts and diffuse emission. A comparison of this data degraded to 10 ms time resolution with previous radio bursts (reported in Osten & Bastian 2006) reveals numerous similarities. However, when examined at the highest time resolution, the drifting radio bursts have predominantly negative slopes (the bursts appear at high frequency and drift to lower frequencies), with a characteristic drift rate of 3 GHz/s. We discuss this new finding in light of possible coherent emission mechanisms, and suggest that these properties are consistent with plasma radiation from beams of accelerated particles traversing AD Leo's low corona. Title: Radio Diagnostics of Magnetic Fields in the Solar Corona Authors: Bastian, T. S. Bibcode: 2006IAUJD...3E..93B Altcode: Measurement of the coronal magnetic field has been an elusive goal for many years. In recent years, however, progress has been made in developing techniques at radio and IR wavelengths to measure or constrain the magnetic field in the quiet and active corona. In this talk, radio diagnostic techniques are reviewed in a variety of contexts, including the quiet corona, active regions, flares, and coronal mass ejections. Techniques that exploit emission intrinsic to the phenomena themselves - e.g., gyrosynchrotron radiation - and those which exploit external probes such as spacecraft beacons or extragalactic background sources are both discussed. Prospects for exploiting these techniques with future generations of radio instrumentation are also considered. Title: Low Frequency Radiophysics of the Sun and Heliosphere Authors: Bastian, T. S. Bibcode: 2006IAUJD..12E...1B Altcode: The solar corona and heliosphere offer rich environments for exploration via low frequency radio techniques. Recent progress in observing and understanding both direct and indirect radio phenomena associated with flares and coronal mass ejections is discussed. In the case of flares, radio diagnostics of coronal energy release and particle acceleration are discussed. In the case of coronal mass ejections (CMEs), direct and indirect signatures of their initiation and acceleration are discussed. Magnetic field measurements of CMEs using direct measurements of their incoherent synchrotron radiation, or using observations of Faraday rotation via trans-illumination of the CME using background sidereal sources or spacecraft beacons, is also discussed. Finally, recent work on theory and observations of type II radio bursts, signatures of interplanetary shocks driven by CMEs , is briefly reviewed. Title: Quasi-periodic Radio And X-ray Pulsations In A Solar Flare Authors: Bastian, Timothy S.; Fleishman, G.; Gary, D. E. Bibcode: 2006SPD....37.1309B Altcode: 2006BAAS...38..242B We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1.3 solar flare on 15 June 2003. Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, phase differences, and modulation depths of the radio and X-ray pulsations. Focusing on the more complete radio observations, the observational properties of the oscillations are compared with those derived from models for the radio emission. Two simple models are considered: i) gyrosynchrotron emission modulated by the quasiperiodic injection of fast electrons; ii) gyrosynchrotron emission modulated by an MHD oscillation of the magnetic field. We demonstrate that quasiperiodic injection of fast electrons is the more likely cause of the observed quasiperiodic oscillations observed in the radio and hard X-ray emission. We discuss the implications of this finding for particle acceleration and transport in the flaring sources. Title: Imaging Observations of a Very High Frequency Type II Burst Authors: White, S. M.; Mercier, C.; Bradley, R.; Bastian, T.; Kerdraon, A.; Pick, M. Bibcode: 2006AGUSMSH24A..05W Altcode: A remarkable Type II burst was detected by the high-frequency system of the Green Bank Solar Radio Burst Spectrometer on 2005 November 14. The harmonic branch of the Type II extended up to 800 MHz, making it one of the highest frequency Type II bursts ever detected, but it failed to propagate to heights corresponding to frequencies below 100 MHz. At such high frequencies, it implies the formation of a shock relatively low in the corona. No coronal mass ejection was evident in the LASCO data for this east limb event. It is one of the few Type II bursts to be observable at every frequency of observation of the Nancay Radio Heliograph (164-432 MHz). Here we present analysis of images of the event, including simultaneous imaging of the fundamental and harmonic branches. Title: The FASR Reference Instrument Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kawakubo, H.; Ruf, C.; White, S. M.; Zurbuchen, T. Bibcode: 2006AGUSMSH33A..08B Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a unique, solar-dedicated radio facility slated for completion by 2012. The instrument will address an extremely broad range of solar and space weather science, including routine measurement of coronal magnetic fields, imaging coronal mass ejections near the solar surface, quantitative diagnostics of energy release and particle acceleration in flares, and the extension of the solar corona into the heliosphere. Although the precise details of the FASR design are still being developed, we present for the first time a complete high-level design referred to as the FASR Reference Instrument. The Reference Instrument meets the science requirements and will serve as the basis for cost estimates for construction and operation of the instrument. This paper gives an overview of the FASR Reference Instrument, describes the science goals and objectives, and gives the flowdown of science goals to engineering specifications. The innovative aspects of the FASR design are highlighted, and a complete, end-to-end description of the instrument is given. The instrument operations plan is also discussed. Title: Coronal Mass Ejections and their Associated Radio Emissions Authors: Bastian, T. Bibcode: 2006AGUSMSH24A..02B Altcode: Coronal mass ejections (CMEs) are important drivers of processes in the interplanetary medium and the near- Earth environment, including shocks, CMEs, and geomagnetic disturbances. Radio observations of CMEs and associated phenomena offer a number of unique diagnostics of CMEs and their environment in the nascent stages of their development. These include thermal free-free radiation, nonthermal synchrotron radiation, and plasma radiation. These emissions can be used to constrain the plasma properties of CMEs - including the plasma density and magnetic field - as they propagate outward from the Sun. Under certain conditions, they can probe the response of the corona to the CME. Some recent and suggestive observations are presented of radio emission from CMEs, as well as of associated radio bursts. Title: Wide-Band Spectroscopy of Two Radio Bursts on AD Leonis Authors: Osten, Rachel A.; Bastian, T. S. Bibcode: 2006ApJ...637.1016O Altcode: 2005astro.ph..9815O We report high time-resolution broadband spectroscopic observations of two radio bursts on the classical flare star AD Leonis. The observations were acquired by the 305 m telescope at Arecibo Observatory on 2003 June 13-14. Using the Wideband Arecibo Pulsar Processor, these observations sampled a total bandwidth of 400 MHz, distributed over a 500 MHz frequency range, 1120-1620 MHz, with a frequency resolution of 0.78 MHz and a time resolution of 10 ms. The radio burst observed on June 13 is characterized by the presence of multitudes of short-duration (Δt~30 ms), high brightness temperature (Tb>1014 K), highly circularly polarized, fast-drift radio sub-bursts, with median bandwidths Δν/ν~5%. The inverse drift rates are small and have a symmetric distribution (both positive and negative frequency drifts), with a Gaussian FWHM inverse drift rate of 4.5×10-4 s MHz-1. The fast-drift sub-bursts occur at a mean rate of 13 s-1 and show no evidence for periodic recurrence. The fast-drift radio events on AD Leo are highly reminiscent of solar decimetric spike bursts. We suggest that the emission is due to fundamental plasma radiation. A second highly circularly polarized radio burst, recorded June 14, has markedly different properties: a smoothly varying intensity profile characterized by a slow drift in frequency with time (-52 MHz s-1). Under the assumption that the source is due to a disturbance propagating through the low corona, a source size of 0.1-1 R* is inferred, implying a brightness temperature range 6×1011-6×1013 K; another example of a coherent radio burst. Title: The Radio Spectrum of TVLM 513-46546: Constraints on the Coronal Properties of a Late M Dwarf Authors: Osten, Rachel A.; Hawley, Suzanne L.; Bastian, Timothy S.; Reid, I. Neill Bibcode: 2006ApJ...637..518O Altcode: 2005astro.ph..9762O We explore the radio emission from the M9 dwarf TVLM 513-46546 at multiple radio frequencies, determining the flux spectrum of persistent radio emission, as well as constraining the levels of circular polarization. Detections at both 3.6 and 6 cm provide a spectral index measurement α (where Sν~να) of -0.4+/-0.1. A detection at 20 cm suggests that the spectral peak is between 1.4 and 5 GHz. The most stringent upper limits on circular polarization are at 3.6 and 6 cm, with V/I<15%. These characteristics agree well with those of typical parameters for early- to mid-type M dwarfs, confirming that magnetic activity is present at levels comparable with those extrapolated from earlier M dwarfs. We apply analytic models to investigate the coronal properties under simple assumptions of dipole magnetic field geometry and radially varying nonthermal electron density distributions. Requiring the spectrum to be optically thin at frequencies higher than 5 GHz and reproducing the observed 3.6 cm fluxes constrains the magnetic field at the base to be less than about 500 G. There is no statistically significant periodicity in the 3.6 cm light curve, but it is consistent with low-level variability. Title: NoRH and RHESSI Observations of Quasiperiodic Radio and X-ray Oscillations in a Solar Flare Authors: Bastian, T.; Fleishman, G.; Gary, D. Bibcode: 2006cosp...36.3251B Altcode: 2006cosp.meet.3251B We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1 3 solar flare of 15 June 2003 Using Fourier analysis we study the frequency- and energy-dependent oscillation periods phase differences and modulation depths of the radio and X-ray pulsations Focusing on the more complete radio observations the observational properties of the oscillations are compared with those derived from models for the radio emission Two simple models are considered i gyrosynchrotron emission modulated by the quasiperiodic injection of fast electrons ii gyrosynchrotron emission modulated by an MHD oscillation of the magnetic field We demonstrate that quasiperiodic injection of fast electrons is the more likely cause of the observed quasiperiodic oscillations observed in the radio and hard X-ray emission We discuss the implications of this finding for particle acceleration and transport in the flaring sources Title: Low Frequency Solar Radiophysics and Next Generation Instrumentation Authors: Bastian, T. S.; Gary, D. E. Bibcode: 2005ASPC..345..142B Altcode: Radio astronomy and solar radio astronomy developed rapidly together in the years following the Second World War. Much of this development occurred at low frequencies. In more recent decades, the emphasis has been on centimeter and millimeter wavelengths. However, motivated by both computational advances and new science drivers, there is a strong desire on the part of both the solar and astronomical communities to build modern low frequency radio telescopes. Here, some of the early work in solar radio astronomy is briefly reviewed and recent developments in solar and heliospheric physics are noted. Two next-generation radio telescopes, the Frequency Agile Solar Radiotelescope and the Long Wavelength Array, are described. Possible synergies between the two projects are discussed. Title: Low-Frequency Solar Radio Bursts from Green Bank Authors: White, S. M.; Bastian, T. S.; Bradley, R.; Parashare, C.; Wye, L. Bibcode: 2005ASPC..345..176W Altcode: A low-frequency spectrometer for the study of solar radio bursts is under development at Green Bank. Since January 2004 an 18-70 MHz system has been operating daily. The system is described and examples of data from the low-frequency system are shown.. Title: An RFI Survey at the Site of the Long Wavelength Deomonstration Array (LWDA) Authors: Stewart, K. P.; Crane, P. C.; Paravastu, N.; Hicks, B. C.; Theodorou, A.; Price, R. M.; Pihlstrom, Y. M.; Bastian, T. S.; Gary, D. E. Bibcode: 2005AAS...20713604S Altcode: 2005BAAS...37.1389S An initial survey of the radio-frequency environment at the site of the Long Wavelength Demonstration Array (LWDA) has been performed using a measurement protocol developed for both the Long Wavelength Array (LWA) and the Frequency Agile Solar Radiotelescope (FASR). The measurements cover the frequency range from 25 MHz to 18 GHz to include the LWA (23-80 MHz) and FASR (30 MHz-30 GHz). Measurements were obtained nearly continuously for a week to characterize the day/night and weekday/weekend variations expected for many sources of RFI. The equipment, antennas, and protocols are suitable for measuring strong RFI that potentially threatens the linearity of radio-astronomical receivers and may therefore rule out possible sites or influence the design of the receivers. (Weak RFI which may obscure weak signals of interest is beyond the capabilities of these measurements.) The protocol seeks only to identify RFI originating from terrestrial sources; RFI from satellites and astrophysical sources is assumed to be site independent and not a factor in site selection. Therefore, the receiving antennas provide azimuthal coverage in the direction of the horizon. This first survey, conducted prior to the start of LWDA construction, establishes a baseline for the later identification of any self-generated interference from the LWDA and its mitigation to ensure no adverse effect on the operations of the VLA. Title: Instrument Development for the Green Bank Solar Radio Burst Spectrometer (GB/SRBS) Authors: Bradley, R.; Parashare, C.; White, S. M.; Bastian, T. S. Bibcode: 2005ASPC..345..357B Altcode: Details of two on-going technical development projects for the Green Bank Solar Radio Burst Spectrometer (GB/SRBS) are presented. One is a high dynamic range active balun covering 20-350 MHz. The other is a log periodic array feed for the Green Bank 45-Foot radio telescope covering 300-3000 MHz. Basic design, fabrication, and evaluation information are included for both projects. Title: Quasiperiodic Electron Acceleration in the 15 June 2003 Solar Flare Authors: Fleishman, G. D.; Bastian, T. S.; Gary, D. E. Bibcode: 2005AGUSMSP41C..04F Altcode: We report a comprehensive analysis of strong quasiperiodic radio- and X-ray pulsations observed from the X1.3-class flare which occurred at S06E78 on 23:42-23:50 UT, 15 June 2003. Because of the favorable time of the flare, it was jointly observed by the Owens Valley Solar Array (OVSA) and the Nobeyama Solar Radio Observatory, which allowed us the advantage of combining high spectral, temporal, and spatial resolution radio observations. In addition, the part of this event displaying the strongest pulsations was also observed in hard X-rays with RHESSI. We study the frequency dependence of quantitative measures of the pulsations, including Fourier spectra, phase differences, modulation depth, as well as the degree of (radio) polarization. We compare these measures with the expectations of competing radio pulsation models, i.e., MHD loop oscillations and quasiperiodic electron injection. Although the Fourier spectra display a few significant peaks at each observing frequency, we found that none of them can be explained by the MHD-oscillations. In contrast, the model of quasiperiodic particle acceleration/injection is capable of explaining all quantitative measures observed for this event in a natural way. We discuss implications of these findings for electron acceleration and transport in solar flares. Title: The Green Bank Solar Radio Burst Spectrometer Authors: Bastian, T. S.; Bradley, R.; White, S.; Mastrantonio, E. Bibcode: 2005AGUSMSH43A..16B Altcode: The Solar Radio Burst Spectrometer (SRBS) is a project designed to 1) provide high quality radio dynamic spectra to the wider solar, heliospheric, and space weather communities; 2) serve as a development platform for ultra-wideband feeds and receivers. Dynamic spectroscopy is a powerful tool for observing radio bursts in the Sun's corona. These bursts are associated with solar flares and/or coronal mass ejections and result from coronal shocks (type II radio bursts), electron beams (type III radio bursts), and other forms of energy release in the corona. The community has been hampered by a lack of readily available dynamic spectra in the 12-24 hr UT time range, a shortcoming that has now been remedied. The instrument is located at the Green Bank Site of the National Radio Astronomy Observatory in the National Radio Quiet Zone, where the effects of radio frequency interference are much reduced compared with unprotected sites. The spectrometer is composed of two swept-frequency systems that together support observations from 18 MHz to 2 GHz with a time resolution of approximately 1 sec. The low frequency system, operating from 18-70 MHz, is a standalone dipole antenna. The high frequency system is fed by an antenna mounted at the vertex of a 13.7 m telescope and operates from 70-300 MHz; a broadband feed at the prime focus of the telescope provides frequency coverage from 300-2500 MHz. The data are available daily through a web-based interface. Both raw and background-subtracted data are available in a variety of formats. Users are encouraged to view and download selected data for research or forecasting purposes. Title: Radio observations of brown dwarfs Authors: Osten, R. A.; Hawley, S. L.; Bastian, T. S.; Reid, I. N. Bibcode: 2005ESASP.560..857O Altcode: 2005csss...13..857O No abstract at ADS Title: Radio Observations of Brown Dwarfs Authors: Quick, L. C.; Osten, R.; Bastian, T.; Hawley, S. Bibcode: 2004AAS...205.1101Q Altcode: 2004BAAS...36.1351Q Radio emission commonly signifies the presence of magnetic activity in the coronae of late-type stars, while emission from the H-alpha transition is a sign of magnetic activity in their chromospheres. Surveys of H-alpha emission from ultracool dwarfs of spectral types late M, L, and T have not shown this indicator of magnetic activity. As a result, it was believed that all magnetic activity declined in these cool bodies. Although sparse, the most recent detections of radio emission contradict this behavior. As part of a large VLA survey of nearby ultracool dwarfs out to 13pc, the aim of my research was to determine how common radio emission is in these late-type stars. Data from 9 L and T dwarfs was reduced, and evidence for emission was detected from three of these objects. This research was conducted as a part of the NRAO Summer Student program, with partial funding from the National Science Foundation. Title: Low-frequency solar radiophysics with LOFAR and FASR Authors: Bastian, T. S. Bibcode: 2004P&SS...52.1381B Altcode: Low-frequency radio observations offer unique diagnostics of the solar corona and solar wind. After a prolongued hiatus, there is renewed interest in this important frequency regime. Two new ground-based instruments will provide critical new low-frequency observations: the low-frequency array (LOFAR) and the frequency agile solar radiotelescope (FASR). This brief topical review summarizes low-frequency radio phenomena that will be accessible to detailed study by LOFAR and FASR in the coming decade. Energy release, drivers of space weather, and studies of the solar wind are emphasized. Both instruments are expected to play important roles in both basic research problems and national and international space weather capabilities. While FASR is a solar-dedicated instrument, LOFAR is not. Solar observing requirements for LOFAR are briefly discussed. Title: The radio search for extrasolar planets with LOFAR Authors: Farrell, W. M.; Lazio, T. J. W.; Zarka, P.; Bastian, T. J.; Desch, M. D.; Ryabov, B. P. Bibcode: 2004P&SS...52.1469F Altcode: The Low Frequency Array (LOFAR) will come on line with unprecedented radio sensitivity and resolution between 10 and 240 MHz. Such a system will provide a factor of 10-30 improvement in sensitivity in the pursuit of the weak radio emission from extrasolar planets. To date, previous examinations of extrasolar planetary systems with the most advanced radio telescopes have yielded a negative result. However, the improvement in sensitivity by LOFAR over current systems will increase the likelihood of extrasolar planet detection in the radio. We apply radiometric models derived previously from the study of planets in our solar system to the known extrasolar planets, and demonstrate that approximately 3-5 of them should emit in the proper frequency range and with enough power to possibly become detectable at Earth with LOFAR. Title: The Frequency Agile Solar Radiotelescope Authors: Bastian, T. S. Bibcode: 2004ASSL..314...47B Altcode: The Frequency Agile Solar Radiotelescope (FASR) will be a ground based solar-dedicated radio telescope designed and optimized to produce high resolution, high-fidelity, and high-dynamic-range images over a broad range of radio frequencies ~ 0.05-24 GHz). That is, FASR will perform broadband imaging spectroscopy, producing unique data and enabling a wide variety of radio-diagnostic tools to be exploited to study the Sun from the mid-chromosphere to coronal heights. FASR will address an extremely broad science program, including the nature and evolution of coronal magnetic fields, the physics of flares, drivers of space weather, the quiet Sun, and synoptic studies. FASR may also play an important role in forecasting solar activity and space weather. An important goal is to mainstream solar radio observations by providing a number of standard data products for use by the wider solar physics and space weather communities. Title: Radio Emission from Extrasolar Planets Authors: Farrell, W. M.; Lazio, T. Joseph W.; Desch, M. D.; Bastian, T. S.; Zarka, P. Bibcode: 2004IAUS..213...73F Altcode: By virtue of their planetary-scale magnetic fields, the Earth and all of the gas giants in our solar system possess solar-wind deformed magnetospheres. The magnetic polar regions of these ``magnetic planets'' produce intense, aurora-related radio emission from solar-wind powered electron currents. Simple scaling laws suggest that Jovian-mass planets close to their host stars should produce radio emission; detecting such emission would be the first direct detection of many of these planets. We describe searches using the Very Large Array (VLA) for radio emission from the planets orbiting HD 114762, 70 Vir, and τ Boo. Our limits are just above those predicted for the planetary emissions. We discuss the possibilities for more stringent limits and the implications that the existing observations have for the planets' radio emissions, and hence on the planetary magnetic fields and stellar wind environments. Title: Radio Emission from the Sun and Stars: New Insights into Energetic Phenomena Authors: Bastian, T. S. Bibcode: 2004IAUS..219..145B Altcode: 2003IAUS..219E..20B Energetic phenomena on the Sun pose a number of fascinating puzzles for solar physicists and more generally astrophysicists. These include solar flares involving the catastrophic release of magnetic energy in the low corona and coronal mass ejections which result from the destabilization and expulsion of a significant portion of the corona.

Radio radiation is a sensitive tracer of a variety of energetic processes on the Sun and stars. Radio observations of the Sun over the past decade have produced new insights into the physics of magnetic energy release particle acceleration and coronal and interplanetary shocks.

Energetic phenomena on stars are similar to the extent that solar flare analogs appear to be relevant in some cases. However certain phenomena are seen on stars which have no solar counterpart.

Observations from the Very Large Array the Nobeyama Radioheliograph the Nancay Radioheliograph and the space-based WIND/WAVES experiment are discussed as well as observations of stars from Arecibo and the Very Long Baseline Array. The next generation of radio telescopes that will yield new progress on these puzzles will be briefly discussed. Title: Radio Bursts on the Flare Star AD Leo from the Arecibo Observatory Authors: Osten, R. A.; Bastian, T. S. Bibcode: 2003AAS...203.4802O Altcode: 2003BAAS...35.1283O We discuss recent observations of the M dwarf flare star AD Leo taken with the Arecibo Observatory. The wide bandwidths currently available (ν eff ∼ 500 MHz) are a factor of >10 improvement over previous investigations of highly circularly polarized, high brightness temperature bursting phenomena. The large degrees of circular polarization (π c -> ±100%), coupled with large inferred brightness temperatures (Tb ≥1016K), suggest a coherent emission mechanism, but interpretation has been hindered by narrow bandwidths (Δ ν /nu ≤ few percent). We find evidence of drifting structures, whose drift rates are compatible with the range from solar type III bursts. We present a summary of the burst characteristics, and interpret the data in the framework of different coherent emission mechanisms.

RAO gratefully acknowledges support from a Jansky fellowship at NRAO. Title: Future Capabilities for Solar/Stellar Observations Authors: Carpenter, K.; Hassler, D.; Berger, T.; Bastian, T.; Pallavicini, R.; Balachandran, S. Bibcode: 2003csss...12..359C Altcode: This session outlines the potential instrumental capabilities for the observation of cool stars and the Sun. The individual contributions cover space-based solar missions (Hassler), ground-based solar optical/IR instruments (Berger), solar-stellar radio capabilities (Bastian), space-based stellar missions (Carpenter), ground-based optical (Pallavicini) and infrared facilities (Balachandran) for stellar observations. Title: Low Frequency Solar Radiophysics Authors: Bastian, T. Bibcode: 2003EAEJA.....7841B Altcode: Low frequency radio observations of the Sun - defined here to be those that comprise roughly decimeter to decameter wavelengths - offer a rich phenomenology and a number of important diagnostics of physical processes in the solar corona and the heliosphere. Of particular interest are active solar phenomena such as flares and drivers of space weather: coronal mass ejections and fast solar solar wind streams. This talk will briefly review the relevant emission mechanisms at these wavelengths and present a number of examples of recent low-frequency observations, including: 1) radio tracers of energy release in the solar corona; 2) radio precursor activity of coronal mass ejections; 3) radio signatures of coronal mass ejections; 4) radio diagnostics of the solar wind, disturbances in the solar wind, and turbulence in the solar wind. These observations motivate the need for the next generation of radio imaging instrumentation, the Low Frequency Array (LOFAR) and the Frequency Agile Solar Radiotelescope (FASR). LOFAR is a general purpose instrument designed to operate between 15-240 MHz. A key component of its science program is solar radiophysics. FASR is a solar-dedicated instrument designed to perform broadband imaging spectroscopy between ~100 MHz and 30 GHz. These two instruments are therefore complementary in their frequency coverage and will together address an outstanding science program. Title: The Frequency Agile Solar Radiotelescope (FASR) Authors: White, S. M.; Gary, D. E.; Bastian, T. S.; Hurford, G. J.; Lanzerotti, L. J. Bibcode: 2003EAEJA....11021W Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a radio interferometer designed to make high spatial resolution images of the Sun across a broad range of radio wavelengths simultaneously, allowing the technique of imaging spectroscopy to be exploited on a routine basis. The telescope will cover the frequency range 0.1-30 GHz using several sets of receiving elements that provide full-disk imaging, with of order 100 antennas at highest frequency range. FASR will be optimized for solar radio phenomena and will be the most powerful and versatile radioheliograph ever built, providing an improvement of orders of magnitude in image quality over existing instruments. FASR recently received the top ranking amongst all small projects considered by the decadal survey of the National Academy of Science Committee on Solar and Space Physics. FASR will probe all phenomena in the solar atmosphere from the mid-chromosphere outwards. In particular, FASR will provide direct measurement of coronal magnetic field strengths, will image the nonthermal solar atmosphere and show directly the locations of electrons accelerated by solar flares, will provide images of coronal mass ejections travelling outwwards through the solar corona, and supply extensive data products for forecasting and synoptic studies. A major emphasis in the project is to make FASR data as widely and easily used as possible, i.e., providing the general user with processed, fully-calibrated high-quality images that do not need particular knowledge of radio astronomy for interpretation. This paper will describe the telescope and its science goals, and summarize its current status. Title: Microwave observations of jupiter's synchrotron emission during the galileo flyby of amalthea in 2002. Authors: Klein, M. J.; Bolton, S. J.; Bastian, T. S.; Blanc, M.; Levin, S. M.; McLeod, R. J.; MacLaren, D.; Roller, J. P.; Santos-Costa, D.; Sault, R. Bibcode: 2003EAEJA....14635K Altcode: In November, 2002, the Galileo spacecraft trajectory provided a close flyby of Amalthea, one of Jupiter's inner most moons (∼2.4 RJ). During this pass, Galileo entered into a region rarely explored by spacecraft, the inner radiation belts of Jupiter. We present preliminary results from a campaign of microwave observations of Jovian synchrotron emission over a six month interval centered around the flyby. The observations were made with NASA's Deep Space Network (DSN) antennas at Goldstone, California, and the NRAO Very Large Array. We report preliminary measurements of the flux density of the synchrotron emission and the rotational beaming curves and a compare them with the long term history of Jupiter's microwave emission which varies significantly on timescales of months to years. The new data are also being examined to search for evidence of short-term variations and to compare single aperture beaming curves with the spatially resolved images obtained with the VLA. These radio astronomy data will be combined with in-situ measurements from Galileo (see companion paper by Bolton et al) to improve models of the synchrotron emission from Jupiter's radiation belts. A large percentage of the Goldstone observations were conducted by middle- and high school students from classrooms across the nation. The students and their teachers are participants in the Goldstone-Apple Valley Radio Telescope (GAVRT) science education project, which is a partnership involving NASA, the Jet Propulsion Laboratory and the Lewis Center for Educational Research (LCER) in Apple Valley, CA. Working with the Lewis Center over the Internet, GAVRT students conduct remotely controlled radio astronomy observations using 34-m antennas at Goldstone. The JPL contribution to this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration 2756 Planetary magnetospheres (5443, 5737, 6030) 6218 Jovian satellites 6220 Jupiter Planetary Sciences Title: Radio Emission from Extrasolar Planetary Systems Authors: Farrell, W. M.; Lazio, T. J.; Desch, M. D.; Zarka, P.; Bastian, T. Bibcode: 2003EAEJA.....3834F Altcode: Each of the gas giants in our solar system and the Earth possess planetary-scale magnetic fields, generated by internal dynamo currents. The magnetic polar regions of these solar system 'magnetic planets' produce intense, aurora-related radio emission, generated via coherent cyclotron radiation from solar-wind powered electron currents. Simple scaling laws suggest that Jovian-mass planets close to their host stars should produce radio emission; detecting such emission would be the first direct detection of these planetary systems. We describe a series of Very Large Array (VLA) observations of extrasolar planets, largely using its 74 MHz observing system. The predicted emission frequencies of extrasolar planet radio emission depend upon the (unknown) magnetic moments and rotation rates of the planets. Scaling from Jovian properties, it seems likely that many extrasolar planets will emit below ~100 MHz, making observations at 74 MHz a useful first effort. Our current limits are close to, but generally just above that predicted for the radiative power from planetary cyclotron emission. We discuss the implications that the existing observations have for the planet's radio emission, and hence on the planetary magnetic field and stellar wind environment, as well as the possibility for far more stringent observational limits with the Low Frequency Array (LOFAR). Title: Imaging capabilities of the Frequency Agile Solar Radiotelescope (FASR) Authors: White, Stephen; Lee, Jeongwoo; Aschwanden, Markus A.; Bastian, Tim S. Bibcode: 2003SPIE.4853..531W Altcode: The Frequency Agile Solar Radiotelescope (FASR) will observe the Sun over a wide range of radio frequencies and make high spatial resolution images at many frequencies nearly simultaneously. FASR will need to be able to observe both the very bright, usually compact emission from solar flares as well as much fainter fluctuations in the solar chromosphere across a broad range of spatial scales (from 1 arcsec to 1 degree) at high time resolution, and these constraints impose severe requirements on telescope design. We discuss the problem of imaging the Sun at radio wavelengths and present simulations of imaging the thermal free-free emission from the Sun's atmosphere using models based on EUV data. Title: Frequency agile solar radiotelescope Authors: Bastian, Tim S. Bibcode: 2003SPIE.4853...98B Altcode: The Frequency Agile Solar Radiotelescope (FASR) is a solar-dedicated, ground based, interferometric array optimized to perform broadband imaging spectroscopy from ~ 0.1-30+ GHz. It will do so with the angular, spectral, and temporal resolution required to exploit radio emission from the Sun as a diagnostic of the wide variety of astrophysical processes that occur there. FASR represents a major advance over existing radioheliographs, and is expected to remain the world's premier solar radio instrument for two decades or more after completion. FASR will be a versatile and powerful instrument, providing unique data to a broad users community. Solar, solar-terrestrial, and space physicists will exploit FASR to attack a broad science program, including problems of fundamental interest: coronal magnetography, solar flares and particle acceleration, drivers of space weather, and the thermal structure and dynamics of the solar atmosphere. A design study and implementation planning are underway. Recent progress is reviewed here. Title: The Frequency Agile Solar Radiotelescope Authors: Bastian, T. S. Bibcode: 2003AdSpR..32.2705B Altcode: The Frequency Agile Solar Radiotelescope (FASR), a telescope concept currently under study, will be a ground based solar-dedicated radio telescope designed and optimized to produce high resolution, high-fidelity, and high-dynamic-range images over a broad frequency range (∼0.1-24 GHz). As such, FASR will address an extremely broad science program, including the nature and evolution of coronal magnetic fields, the physics of flares, drivers of space weather, and the quiet Sun. An important goal is to mainstream solar radio observations by providing a number of standard data products for use by the wider solar physics community. The instrument specifications and the key science elements that FASR will address are briefly discussed, as well as several operational issues. Title: Limits on the Magnetosphere/Stellar Wind Interactions for the Extrasolar Planet about Tau Bootis Authors: Farrell, W. M.; Desch, M. D.; Lazio, T. J.; Bastian, T.; Zarka, P. Bibcode: 2003ASPC..294..151F Altcode: Among the most impressive astronomical discoveries in the past decade are the observations of Jupiter-like planets in orbit around stars similar to our sun (Mayor and Queloz 1995; Marcy 1998). These extrasolar planets are detected primarily from optical signatures of the star's orbital perturbation about the star/planet center of mass. To date, over 80 massive planets have been discovered about sun-like stars, these stars located in the near-vicinity of our own solar system (< 100 pc). By analogy with the sun's gas giant planets, it has been predicted that these extrasolar planets will have electrically-active stellar-wind driven planetary magnetospheres possibly capable of emitting long-wavelength radio emission (Burke 1992; Farrell et al. 1999; Bastian et al. 2000; Zarka et al. 2001) consistent with radiometric Bode's laws known to apply in our solar system. In 1999 and in 2002, the Very Large Array (VLA) surveyed the region near Tau Bootes for long-wavelength radio emission from its extrasolar planet. This planet had been previously predicted to be a good candidate for coherent electron cyclotron radio emission in the 10's of MHz. While no obvious signal was detected at 74 MHz to a sensitivity of <0.12 Janskys, the results can be applied to place upper limits on the stellar winds and planetary magnetic field. Title: A Search for Cyclotron Emission from known Extra-Solar Planets Authors: Langston, G. I.; Orban, C. M.; Bastian, T. S. Bibcode: 2002AAS...201.4610L Altcode: 2002BAAS...34.1176L All magnetized planets in our solar system emit intense cyclotron maser radiation. Like Jupiter, the recently discovered extra-solar planets are probably magnetized. If in addition, there is a source of energetic (keV) electrons in their magnetospheres, it is likely that extra-solar planets are also cyclotron-maser emitters. We present Green Bank 100m Radio Telescope observations at 330 MHz of 20 Extra-solar planets around nearby stars. Using the GBT spectrometer, we produced high time and frequency resolution observations, searching for flaring events. The calibration, radio interference and sensitivity limits are presented. Since cyclotron maser emission from Jupiter is episodic, long observations may be required to detect Extra-solar planets. The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Title: ALMA and the Sun Authors: Bastian, T. S. Bibcode: 2002AN....323..271B Altcode: The Atacama Large Millimeter Array (ALMA) is a large Fourier synthesis imaging telescope designed to operate at millimeter and sub-millimeter wavelengths, a wavelength regime that remains, thus far, largely unexplored. Yet this important wavelength range offers a number of unique and important diagnostics of astrophysical processes. ALMA is a general purpose instrument designed to address an extremely broad science program, including cosmology; formation of clusters, galaxies, stars, and planets; synthesis of the elements; and low temperature thermal science. ALMA is also designed to support solar observing in order to address outstanding issues in solar physics. After reviewing ALMA's instrument specifications, the problem of solar observing in the mm/submm-lambda band is discussed. The relevant emission mechanisms on the Sun are introduced and several examples of previous observations in the mm/submm-lambda range are presented. The use of ALMA for solar observing is then considered. Title: Radio Diagnostics of Magnetic Fields in CMEs Authors: Bastian, T. S. Bibcode: 2002AAS...200.6507B Altcode: 2002BAAS...34Q.752B A variety of remote sensing techniques are available at radio wavelengths for measuring or constraining the magnetic field in CMEs in the corona and inner heliosphere. Some have been exploited; for others the ``proof of concept" has been established; still others are purely speculative at this point and rely on the development of future instrumentation. They can be grouped into three distinct classes: 1) radio emission intrinsic to CMEs (synchrotron emission); 2) Faraday rotation of background radio sources viewed through CMEs; 3) studies of radio bursts associated with CMEs (type II, SA type III, and type IV). This talk will review the specific techniques available in each of these classes and describe what they can tell us about magnetic fields in CMEs. The requirements on instrumentation required to exploit these techniques will be emphasized. Title: The Frequency Agile Solar Radiotelescope Authors: Bastian, T. S. Bibcode: 2002AAS...200.4902B Altcode: 2002BAAS...34..721B The Frequency Agile Solar Radiotelescope (FASR) is a Fourier synthesis telescope designed to perform broadband imaging spectroscopy over an extremely broad frequency range ( 0.1-30 GHz). The frequency, temporal, and angular resolution of the instrument will be optimized for the many and varied radio phenomena produced by the Sun. Consequently, FASR will the most powerful and versatile radioheliograph ever built. FASR was recommended by the NAS/NRC Astronomy and Astrophysics Survey Committee for construction in the coming decade and is currently under review by the decadal survey of Solar and Space Physics. An NSF-funded study of the instrument concept is currently under way. FASR will probe all phenomena in the solar atmosphere from the mid-chromosphere to the outer corona. The range of science that FASR will address is correspondingly broad. The design and function of FASR offer several unique capabilities, to which several key science goals are well-matched: 1- The nature and evolution of coronal magnetic fields, including direct measurement of coronal magnetic fields; the temporal and spatial evolution of coronal fields; inference of coronal electric currents; the storage and release of magnetic energy. 2- Transient energetic phenomena such as energy release in flares; plasma heating; particle acceleration; electron transport; the formation and destabilization of large scale structures (filaments, coronal mass ejections). 3- Quantitative diagnostics of the three-dimensional solar atmosphere; the quiet Sun and coronal holes; origin of the solar wind; coronal heating; formation of filaments. In addition, FASR will be a powerful tool for synoptic programs and for forecasting activities. The operational model for FASR will make the data widely available for immediate use by the wider scientific community. This talk will introduce the instrument, the science drivers, and the current status and plans for the project. Title: Ultra-relativistic electrons in Jupiter's radiation belts Authors: Bolton, S. J.; Janssen, M.; Thorne, R.; Levin, S.; Klein, M.; Gulkis, S.; Bastian, T.; Sault, R.; Elachi, C.; Hofstadter, M.; Bunker, A.; Dulk, G.; Gudim, E.; Hamilton, G.; Johnson, W. T. K.; Leblanc, Y.; Liepack, O.; McLeod, R.; Roller, J.; Roth, L.; West, R. Bibcode: 2002Natur.415..987B Altcode: Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20MeV. Although most radiation belt models predict electrons at higher energies, adiabatic diffusion theory can account only for energies up to around 20MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8GHz synchrotron emission that confirm the presence of electrons with energies up to 50MeV the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20MeV are more numerous than previously believed. Title: A radio survey of fast CMEs accompanied by interplanetary type II bursts Authors: Bastian, T.; Payne, J.; Pick, M.; Kerdraon, A. Bibcode: 2002cosp...34E1872B Altcode: 2002cosp.meetE1872B Following the detection of synchrotron radiation from a fast CME at radio wavelengths by Bastian et al. (2001; ApJ 558, L65), a sample of coronal mass ejections (CMEs) was selected between 1998-2000. Using data compiled by SOHO/LASCO, the WIND/WAVES experiment, and the Nancay radioheliograph, white light CMEs were selected on the basis of three criteria: 1) that the projected speed reported by SOHO/LASCO exceeded 1200 km/s; that it was accompanied by an interplanetary type II radio burst with a start frequency >1 MHz; that it was observed by the Nancay Radioheliograph in France. The resulting sample numbers 34 events. The motivation for analyzing these events is to: 1) detect additional examples of synchrotron emission from CMEs ("radio CMEs") and determine their incidence rate; 2) constrain the conditions under which they occur.A preliminary report of our results is presented. Title: The frequency agile solar telescope (FASR) Authors: Bastian, T.; Gary, D.; White, S.; Hurford, G. Bibcode: 2002cosp...34E1870B Altcode: 2002cosp.meetE1870B The Frequency Agile Solar Radiotelescope (FASR) will be a large-N, solar- dedicated, Fourier synthesis array designed to perform broadband imaging spectroscopy across a frequency range of approximately 0.1-30 GHz with an angular resolution as high as 1" (>20 GHz). This paper reviews the FASR science drivers -- including coronal magnetic fields, energetic phenomena, and thermal physics -- and the associated instrument requirements and specifications. Applications for synoptic studies and space weather are also discussed. Ongoing activities are briefly described, including site surveys, configuration studies, science simulations, and system design. Title: Cassini, VLA and DSN Observations of Synchrotron Emission from Jupiter's Radiation Belts Authors: Bolton, S. J.; Janssen, M.; Levin, S.; Klein, M.; Gulkis, S.; Elachi, C.; Thorne, R.; Bastian, T.; Sault, R.; Dulk, G.; Leblanc, Y.; McLeod, R.; Roller, J. Bibcode: 2001DPS....33.0504B Altcode: 2001BAAS...33.1029B We report on new measurements of Jupiter's synchrotron emission from Cassini, the Very Large Array (VLA) and the NASA Deep Space Network (DSN) obtained during Cassini's flyby of Jupiter. On January 2-3, 2001, on route to Saturn, measurements of Jupiter's synchrotron emission were carried out using the radiometer subsystem of the Cassini Radar Instrument operating at 2.2 cm (13.8 GHz), the VLA operating at 20 cm (1400 MHz) and 90 cm (333 MHz) and the DSN operating at 13 cm, 3.5 cm, and 2.2 cm. The data provide new information on a wide range of energetic electrons trapped in Jupiter's magnetosphere ( ~5 to >50 MeV). At frequencies above 100 MHz, Jupiter's radio emission is comprised of both thermal emission from the atmosphere, and non-thermal synchrotron emission generated by relativistic electrons trapped in Jupiter's radiation belts. Earth-based radio telescopes cannot accurately measure and map the synchrotron radiation at wavelengths shorter than about 6 cm due to the difficulty of separating the thermal atmospheric emission from the non-thermal synchrotron emission. Because in-situ measurements of the electrons are limited, investigations are largely dependent on ground-based observations. The observations provide the first accurate measurement of Jupiter's synchrotron emission at 2.2 cm and the first high resolution maps depicting the distribution of ultra-relativistic electrons (> 50 MeV) near Jupiter. The results suggest that the relativistic electrons have a softer energy spectrum than expected, and as a result, electrons between 5-20 MeV may be more abundant than previously realized. Acknowledgements: The research reported in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Title: The Coronal Mass Ejection of 1998 April 20: Direct Imaging at Radio Wavelengths Authors: Bastian, T. S.; Pick, M.; Kerdraon, A.; Maia, D.; Vourlidas, A. Bibcode: 2001ApJ...558L..65B Altcode: We observed the fast coronal mass ejection (CME) of 1998 April 20 with the radioheliograph at Nançay, France, between 164 and 432 MHz. Spectroscopic data were obtained between 40 and 800 MHz by the spectrometer at Tremsdorf, Germany, and between 20 kHz and 14 MHz with the WAVES instrument on board the Wind spacecraft. Energetic particle data were obtained from the Wind 3D Plasma and Energetic Particle experiment. The CME was observed in white light by the Large-Angle Spectrometric COronagraph experiment on board the Solar and Heliospheric Observatory spacecraft. For the first time, the expanding CME loops are imaged directly at radio wavelengths. We show that the radio-emitting CME loops are the result of nonthermal synchrotron emission from electrons with energies of ~0.5-5 MeV interacting with magnetic fields of ~0.1 to a few gauss. They appear nearly simultaneously with the onset of an associated type II radio burst, shock-accelerated type III radio bursts, and the initiation of a solar energetic particle event. We suggest possible sources of the energetic electrons responsible for this ``radio CME'' and point out diagnostic uses for synchrotron emission from CME loops. Title: Radio Wave Propagation in the Corona and the Interplanetary Medium Authors: Bastian, T. S. Bibcode: 2001Ap&SS.277..107B Altcode: Radio wave propagation through an inhomogeneous, random plasma produces a variety of observable phenomena - group delay, Faraday rotation, refraction, angular broadening, spectral broadening, and scintillations in phase, amplitude, and frequency. These may be exploited to constrain the mean and fluctuating properties of the medium through a variety of remote sensing techniques. In the case of the solar corona and the solar wind, the mean density, magnetic field, solar wind speed, and the spatial spectrum of the density fluctuation scan all be constrained in regions that are inaccessible to in situmeasurements. Title: Observations of Jovian Synchrotron Emission Authors: Bolton, S. J.; Janssen, M.; Levin, S.; Sault, R.; Bastian, T.; Klein, M.; Gulkis, S.; Hofstadter, M.; Elachi, C.; Johnston, W.; Bunker, A.; Hamilton, G.; Liepack, O.; Roth, L.; West, R.; Dulk, G.; Leblanc, Y.; Thorne, R.; Roller, J.; McLeod, R. Bibcode: 2001AGUSM...P52A08B Altcode: On route to Saturn, the Cassini spacecraft flew past Jupiter and provided the first opportunity to observe the Jovian synchrotron radiation at a wavelength of 2.2 cm. Measurements were successfully carried out shortly after Jupiter closest approach using the radiometer subsystem of the Cassini Radar Instrument. The resulting data provide unique information on the highest energy electrons in Jupiter's magnetosphere. Earth-based radio telescopes have difficulty measuring the synchrotron radiation at wavelengths this short because of the difficulty in separating atmospheric thermal emission from the synchrotron radiation. The 2.2 cm Cassini radiometer was used to produce 20 maps covering two complete rotations of Jupiter in both horizontal and vertical linear polarization. Synchrotron emission was clearly detected distinct from the thermal emission as evidenced by its polarization and spatial distribution. A ground based campaign involving the VLA (operating at 20 and 90 cm) and the NASA Deep Space Network antennas (operating at 2.3, 8.5, 13.8 and 32 GHz) observed simultaneously with Cassini. The combined data set provides a complete picture of the electron energy spectrum and distribution in the Jovian inner radiation belts. Preliminary results from the observations and modeling efforts will be presented. The JPL contribution to this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Title: Joint EUV/Radio Observations of a Solar Filament Authors: Chiuderi Drago, F.; Alissandrakis, C. E.; Bastian, T.; Bocchialini, K.; Harrison, R. A. Bibcode: 2001SoPh..199..115C Altcode: In this paper we compare simultaneous extreme ultraviolet (EUV) line intensity and microwave observations of a filament on the disk. The EUV line intensities were observed by the CDS and SUMER instruments on board SOHO and the radio data by the Very Large Array and the Nobeyama radioheliograph. The main results of this study are the following: (1) The Lyman continuum absorption is responsible for the lower intensity observed above the filament in the EUV lines formed in the transition region (TR) at short wavelengths. In the TR lines at long wavelengths the filament is not visible. This indicates that the proper emission of the TR at the filament top is negligible. (2) The lower intensity of coronal lines and at radio wave lengths is due to the lack of coronal emission: the radio data supply the height of the prominence, while EUV coronal lines supply the missing hot matter emission measure (EM). (3) Our observations support a prominence model of cool threads embedded in the hot coronal plasma, with a sheath-like TR around them. From the missing EM we deduce the TR thickness and from the neutral hydrogen column density, derived from the Lyman continuum and He i absorption, we estimate the hydrogen density in the cool threads. Title: The Frequency-Agile Solar Radiotelescope (FASR) (invited) Authors: Gary, D. E.; Bastian, T. S.; White, S. M.; Hurford, G. J. Bibcode: 2001aprs.conf..236G Altcode: No abstract at ADS Title: Coordinated BeppoSAX and VLA observations of UX Arietis (CD-ROM Directory: contribs/francio1) Authors: Franciosini, E.; Pallavicini, R.; Bastian, T.; Chiuderi-Drago, F.; Randich, S.; Tagliaferri, G.; Massi, M.; Neidhöfer, J. Bibcode: 2001ASPC..223..930F Altcode: 2001csss...11..930F No abstract at ADS Title: Cassini RADAR/Radiometer and VLA Observations of Jupiter's Synchrotron Emission Authors: Janssen, M. A.; Bolton, S. J.; Levin, S. M.; Sault, R.; Klein, M. J.; Gulkis, S.; Hofstadter, M. D.; Elachi, C.; Johnson, W. T. K.; Bunker, A.; Gudim, E. J.; Hamilton, G. A.; Liepack, O.; Roth, L. E.; West, R. D.; Bastian, T.; Dulk, G.; Leblanc, Y.; Thorne, R.; Roller, J. P.; McLeod, R. K. Bibcode: 2001pre5.conf..229J Altcode: We present observations of Jupiter's synchrotron emission made jointly from the Earth and from the Cassini spacecraft as it recently flew past Jupiter. These include observations at the lowest and highest frequencies ever used to image this emission, which thereby provide new and unique information on the Jovian electron energy spectrum. In particular, the Cassini Radar instrument includes a passive radiometer operating at 2.2-cm wavelength that clearly detected synchrotron emission as evidenced by its polarization and spatial distribution, even though it amounted to only about 1.1 percent of the total emission from Jupiter. We conclude from this result that the population of electrons with energies in excess of about 20 MeV is several times less than expected based on the best current model. Title: Acceleration of electrons at type II shock fronts and production of shock-accelerated type III bursts Authors: Dulk, George A.; Leblanc, Yolande; Bastian, T. S.; Bougeret, Jean-Louis Bibcode: 2000JGR...10527343D Altcode: We present evidence of electron acceleration by type II-burst-emitting shocks in the corona. Some of the electrons travel outward along open magnetic field lines and produce ``shock-accelerated type III bursts'' (or SA type III bursts) along their paths. The SA type III bursts are evident in dynamic spectra that cover part or all of the range from metric to kilometric wavelengths. The unique feature of our observations is the complete or near-complete frequency coverage from about 2 GHz to <0.1 MHz, that is, <~1.01 Ro to 1 AU. A sample of eight events is presented. All would be classified as ``shock accelerated events'' at hectometric wavelengths, as first defined by Cane et al. [1981]. Our complete spectra frequently show several to many type III-like bursts emanating from near the type II burst toward low frequencies, with no trace of emission at frequencies higher than that of the type II burst. The drift rates of these SA type III bursts are similar to those of normal type III bursts, and the exciting electrons have speeds of order 0.1c to 0.2c, or energies of 3-10 keV and higher. Their intensity at hectometer wavelengths is similar to that of normal type III bursts. They often persist to the lowest frequencies observable, near the local plasma frequency at 1 AU. In most of the events examined, there were no microwave bursts from the low corona whose intensity profiles were similar to the hectometric profiles. We therefore conclude that these SA type III bursts originate in type II shocks and are caused by energetic electrons accelerated at the shocks. Of the eight events analyzed, three contain only SA type III bursts. For the remainder, normal type III bursts predominate initially, followed by SA type III bursts later in the event. We emphasize the need for spectra with near-continuous coverage, especially from decametric to kilometric wavelengths, to identify SA type III bursts unambiguously and to distinguish between the contributions of normal and SA type III bursts. Title: A Search for Radio Emission from Extrasolar Planets Authors: Bastian, T. S.; Dulk, G. A.; Leblanc, Y. Bibcode: 2000ApJ...545.1058B Altcode: All magnetized planets in the solar system emit intense cyclotron maser radiation. Like Jupiter, extrasolar giant planets are probably magnetized. If, in addition, there is a source of energetic (keV) electrons in their magnetospheres, from auroral processes or as a result of magnetic coupling between the planet and a satellite, it is likely that extrasolar planets are cyclotron-maser emitters. Detection and follow-up observations of cyclotron maser radiation from an exoplanet would reveal the presence, strength, and complexity of the planetary magnetic field, the planet's rotation rate, and possibly the presence of an Io-like moon within the planet's magnetosphere. Magnetic fields may be necessary for life to exist on the surface of planets because they provide protection from the nefarious effects of energetic particles of stellar winds, stellar flares, and cosmic rays. We have conducted a search for radio emission from extrasolar planets and brown dwarfs at decimeter and meter wavelengths using the Very Large Array (VLA). We have observed seven extrasolar planets and two brown dwarfs at 333 and 1465 MHz, and one extrasolar planet and one brown dwarf at 74 MHz. Typical (1 σ) sensitivities were 0.02-0.07 mJy at 1465 MHz, 1-10 mJy at 333 MHz, and ~50 mJy at 74 MHz. To date, no detections have been made. Title: Solar Flares: Radio Bursts Authors: Bastian, T. Bibcode: 2000eaa..bookE2293B Altcode: Energy release in solar flares heats plasma and accelerates electrons and ions to high energies. Radio bursts of various types are produced by energetic electrons interacting with the ambient plasma or with the magnetic field. They may be divided into two broad classes according to frequency range and the dominant emission mechanisms. (1) Coherent plasma radiation plays a dominant role for burst ... Title: Solar Wind: Radio Techniques for Probing Authors: Bastian, T. Bibcode: 2000eaa..bookE2599B Altcode: The solar wind is a complex magnetized plasma containing large-scale magnetohydrodynamic (MHD) structures, waves and turbulence (see SOLAR WIND PLASMA WAVES and SOLAR WIND TURBULENCE). The structure of the solar wind is modulated in both time and space by solar variability. The solar activity cycle modulates the structure of the solar wind over a time scale of years while transient energetic phen... Title: Space VLBI at Low Frequencies Authors: Jones, D. L.; Allen, R.; Basart, J.; Bastian, T.; Blume, W.; Bougeret, J. -L.; Dennison, B.; Desch, M.; Dwarakanath, K.; Erickson, W.; Farrell, W.; Finley, D.; Gopalswamy, N.; Howard, R.; Kaiser, M.; Kassim, N.; Kuiper, T.; MacDowall, R.; Mahoney, M.; Perley, R.; Preston, R.; Reiner, M.; Rodriguez, P.; Stone, R.; Unwin, S.; Weiler, K.; Woan, G.; Woo, R. Bibcode: 2000aprs.conf..265J Altcode: 2000astro.ph..3120J At sufficiently low frequencies, no ground-based radio array will be able to produce high resolution images while looking through the ionosphere. A space-based array will be needed to explore the objects and processes which dominate the sky at the lowest radio frequencies. An imaging radio interferometer based on a large number of small, inexpensive satellites would be able to track solar radio bursts associated with coronal mass ejections out to the distance of Earth, determine the frequency and duration of early epochs of nonthermal activity in galaxies, and provide unique information about the interstellar medium. This would be a ``space-space" VLBI mission, as only baselines between satellites would be used. Angular resolution would be limited only by interstellar and interplanetary scattering. Title: The ALFA Medium Explorer Mission Authors: Jones, D. L.; Allen, R. J.; Basart, J. P.; Bastian, T.; Blume, W. H.; Bougeret, J. -L.; Dennison, B. K.; Desch, M. D.; Dwarakanath, K. S.; Erickson, W. C.; Farrell, W.; Finley, D. G.; Gopalswamy, N.; Howard, R. E.; Kaiser, M. L.; Kassim, N. E.; Kuiper, T. B. H.; MacDowall, R. J.; Mahoney, M. J.; Perley, R. A.; Preston, R. A.; Reiner, M. J.; Rodriguez, P.; Stone, R. G.; Unwin, S. C.; Weiler, K. W.; Woan, G.; Woo, R. Bibcode: 2000AdSpR..26..743J Altcode: The frequency range below a few tens of MHz is unexplored with high angular resolution due to the opacity of Earth's ionosphere. An interferometer array in space providing arcminute angular resolution images at frequencies of a few MHz would allow a wide range of problems in solar, planetary, galactic, and extragalactic astronomy to be attacked. These include the evolution of solar radio emissions associated with shocks driven by coronal mass ejections and searches for coherent radio emission from supernova remnants and relativistic jets. In addition, it is likely that unexpected objects or emission processes will be discovered by such an instrument, as has always happened when high resolution astronomical observations first become possible in a new region of the electromagnetic spectrum. The Astronomical Low Frequency Array (ALFA) mission will consist of 16 identical small satellites forming an aperture synthesis array. The satellites will cover the surface of a spherical region. ~100 km in diameter, thus providing good aperture plane coverage in all directions simultaneously. The array will operate in two modes: 1) ``snapshot'' imaging of strong, rapidly changing sources such as solar radio bursts and 2) long-term aperture synthesis observations for maximum sensitivity, high dynamic range imaging. In both cases a large number of array elements is needed Title: Solar Radio Emission Authors: Bastian, T. Bibcode: 2000asqu.book..375B Altcode: No abstract at ADS Title: Propagation of Radio Waves in the Corona and Solar Wind Authors: Bastian, T. S. Bibcode: 2000GMS...119...85B Altcode: 2000ralw.conf...85B The solar corona and solar wind are plasmas characterized by large scale MHD structures, waves, and turbulence. These introduce both systematic and random variations in the refractive index which affect the propagation of radio waves. A variety of propagation phenomena occur -- regular refraction; angular, temporal, and spectral broadening; scintillations in amplitude and phase -- widely referred to as scattering phenomena. In this tutorial I review the physical basis of these phenomena and describe a variety of techniques designed to exploit observations of scattering phenomena to deduce properties of the corona and solar wind plasma. Title: The Astronomical Low Frequency Array: A Proposed Explorer Mission for Radio Astronomy Authors: Jones, D.; Allen, R.; Basart, J.; Bastian, T.; Blume, W.; Bougeret, J. -L.; Dennison, B.; Desch, M.; Dwarakanath, K.; Erickson, W.; Finley, D.; Gopalswamy, N.; Howard, R.; Kaiser, M.; Kassim, N.; Kuiper, T.; MacDowall, R.; Mahoney, M.; Perley, R.; Preston, R.; Reiner, M.; Rodriguez, P.; Stone, R.; Unwin, S.; Weiler, K.; Woan, G.; Woo, R. Bibcode: 2000GMS...119..339J Altcode: 2000ralw.conf..339J A radio interferometer array in space providing high dynamic range images with unprecedented angular resolution over the broad frequency range from 0.03 - 30 MHz will open new vistas in solar, terrestrial, galactic, and extragalactic astrophysics. The ALFA interferometer will image and track transient disturbances in the solar corona and interplanetary medium - a new capability which is crucial for understanding many aspects of solar-terrestrial interaction and space weather. ALFA will also produce the first sensitive, high-angular-resolution radio surveys of the entire sky at low frequencies. The radio sky will look entirely different below about 30 MHz. As a result, ALFA will provide a fundamentally new view of the universe and an extraordinarily large and varied science return. Title: Radio Interferometric Observations of Scattering Phenomena in the Outer Solar Corona Authors: Bastian, T. S. Bibcode: 1999ESASP.448.1131B Altcode: 1999mfsp.conf.1131B; 1999ESPM....9.1131B No abstract at ADS Title: Solar Physics with Radio Observations Authors: Bastian, T. S.; Gopalswamy, N.; Shibasaki, K. Bibcode: 1999spro.proc.....B Altcode: Radio observations contribute a unique perspective on the many physical phenomena, which occur on the Sun. From thermal bremsstrahlung emission in the quiet solar atmosphere and filaments, to thermal gyroresonance emission in strongly magnetized solar active regions, to the nonthermal emission from MeV electrons accelerated in flares, observations of radio emission provide a powerful probe of physical conditions on the Sun and provide an additional means of understanding the myriad phenomena which occur there. Moreover, radio observing techniques have led the way in developing and exploiting Fourier synthesis imaging techniques. The Nobeyama Radioheliograph, commissioned in June, 1992, soon after the launch of Yohkoh satellite in August, 1991, is the most powerful, solar-dedicated Fourier synthesis in the world, now capable of imaging the full disk of the Sun simultaneously at frequencies of 17 and 34 GHz, with an angular resolution as much as 10" and 5", respectively, and with a time resolution as fine as 100 msec. Between 27-30 October, 1998, the Nobeyama Radio Observatory and the National Astronomical Observatory of Japan hosted the Nobeyama Symposium on Solar Physics with Radio Observations, an international meeting bringing more than sixty participants together at the Seisenryo Hotel in Kiyosato, for a meeting devoted to reviewing recent progress in outstanding problems in solar physics. Emphasis was placed on radio observations and, in particular, radio observations from the very successful Nobeyama Radioheliograph. These results were compared and contrasted with those that have emerged from the Yohkoh mission. In addition, looking forward to the next solar maximum, new instruments, upgrades, and collaborative efforts were discussed. The result is the more than seventy invited and contributed papers that appear in this volume. Title: Impulsive Flares: A Microwave Perspective Authors: Bastian, T. S. Bibcode: 1999spro.proc..211B Altcode: Impulsive flares, by far the most common flares on the sun, impose strong demands on any theory of energy release and of particle acceleration. For a large flare, ~ 1037 electrons with energies >20 keV must be accelerated each second. These electrons produce hard X-rays by nonthermal bremsstrahlung emission and radio waves by plasma radiation processes and gyrosynchrotron emission. The hard X-ray emission is dominated by thick-target bremsstrahlung from fast electrons streaming directly from the acceleration site to the low corona and upper chromosphere, and by fast electrons precipitating from the magnetic trap. By contrast, microwave emission may be dominated by trapped electrons. In this paper, I briefly discuss the basic properties of microwave emission from impulsive flares: its morphology, source kinematics, and its relation to emissions at other wavelengths. I then summarize diagnostic uses of microwave emission and conclude with a description of recent work on the problem of the relative timing of HXR and microwave emission. It is shown that magnetic loops act as dispersive elements, allowing fixed-frequency observations to be used to probe electrons of differing energy. Spatially and temporally resolved observations of gyrosynchrotron emission from solar flares, such as those available from the Nobeyama Radioheliograph, enable one to constrain the evolution of the electron distribution function in time. I discuss some results of a comparative timing analysis of a sample of flares observed by the Nobeyama Radioheliograph and by the CGRO BATSE instrument. Title: Structure and Dynamics in the Transition Region Authors: Gontikakis, C. P.; Dara, H. C.; Alissandrakis, C. E.; Zachariadis, Th. G.; Vial, J. -C.; Bastian, T.; Chiuderi Drago, F. Bibcode: 1999ESASP.448..297G Altcode: 1999mfsp.conf..297G; 1999ESPM....9..297G No abstract at ADS Title: A search for radio emission from extrasolar planets. Authors: Bastian, T. S.; Dulk, G. A.; Leblanc, Y.; Sault, R. J. Bibcode: 1999BAAS...31.1086B Altcode: No abstract at ADS Title: A Search for Radio Emission from Extrasolar Planets Authors: Bastian, T. S.; Dulk, G. A.; Leblanc, Y.; Sault, R. Bibcode: 1999DPS....31.0901B Altcode: Fifteen giant planets of mass about 1--13 M_J and eleven brown dwarfs of mass 13--50 M_J have now been discovered by their gravitational effects on solar-like stars. There is reason to believe that these objects have magnetic fields and that they emit meter- or decimeter-wavelength radio radiation through the electron cyclotron maser mechanism. Although the visible and infrared radiation from exoplanets is much weaker than that of the parent stars, the radio emission need not necessarily be. Extremely intense radio emission can be generated by the electron-cyclotron maser instability. For Jupiter the cyclotron-maser radiation is 10(5-10^6) times more intense than its synchrotron emission from the radiation belts and its thermal emission from the disk. If detected from a planet, several important parameters can be deduced, e.g. its rotation period and magnetic field strength. We report the results of searchs for radio emission from a sample of confirmed extrasolar planets and brown dwarfs. The Very Large Array (VLA) was used in late 1996 to observe seven planets and two brown dwarfs at 1400 and 330 MHz. In early 1998, both 47 UMa (planet) and HD98239 (brown dwarf) were observed at 330 and the new 74 MHz system. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Title: FASR - A Frequency-Agile Solar Radiotelescope Authors: Hurford, G. J.; Gary, D. E.; Bastian, T. S.; White, S. M. Bibcode: 1999AAS...194.7603H Altcode: 1999BAAS...31..956H The Frequency-Agile Solar Radiotelescope (FASR) is a multi-frequency imaging array designed specifically for imaging spectroscopy of the Sun. Using < 100 antennas, it will combine high-quality/high spatial resolution imaging (1" resolution at 20 GHz) with spectroscopy (dnu /nu 0.01-0.03) and high time resolution (<1 s) across two decades in frequency from 0.3-30 GHz. In so doing, it will produce a continuous, dynamic, three-dimensional picture of the solar atmosphere from the chromosphere through the mid-corona. These capabilities represent a quantum leap beyond existing solar radio instruments, yet are well within reach of emerging technologies. The range of science that can be addressed by such an instrument is as broad as solar physics itself. Virtually every solar feature from within a few hundred km of the visible surface of the Sun to high in the solar corona can be studied in detail with the unique diagnostics available in the radio regime. Particular diagnostics include measuring the properties of both thermal and nonthermal electrons accelerated in solar flares from the largest events to the tiniest microflares/nanoflares, measuring coronal magnetic field strengths in active regions and elsewhere (coronal magnetography), and mapping kinetic electron temperatures throughout the chromosphere and corona. In addition, FASR's far-reaching exploration of the Sun in the radio regime gives the instrument tremendous potential for new discoveries beyond those that we can now anticipate. FASR is expected to be one of the major new ground-based solar instruments of the next decade, and can be operational by 2006, well before the decade is out. It will play a major role in supporting NASA space missions with the unique diagnostics and perspective provided by high-resolution radio imaging/spectroscopy. Title: Solar System Objects Authors: Butler, B. J.; Bastian, T. S. Bibcode: 1999ASPC..180..625B Altcode: 1999sira.conf..625B Long wavelength (λ ~> 350 microns) interferometric observations of solar system objects can yield important information on the nature of these bodies, including information on orbits, spins, surfaces, atmospheres, magnetic fields, rings, and plasma processes. This lecture will describe some of the peculiarities involved with observing of solar system bodies with synthesis arrays. These include planning, scheduling, calibration, and imaging. Title: Broadband microwave imaging spectroscopy with a solar-dedicated array Authors: Bastian, Tim S.; Gary, D. E.; White, S. M.; Hurford, Gordon J. Bibcode: 1998SPIE.3357..609B Altcode: For many years, ground-based radio observations of the Sun have proceeded into two directions: (1) high resolution imaging at a few discrete wavelengths; (2) spectroscopy with limited or no spatial resolution at centimeter, decimeter, and meter wavelengths. Full exploitation of the radio spectrum to measure coronal magnetic fields in both quiescent active regions and flares, to probe the thermal structure of the solar atmosphere, and to study energy release and particle energization in transient events, requires a solar-dedicated, frequency-agile solar radiotelescope, capable of high-time, - spatial, and -spectral resolution imaging spectroscopy. In this paper we summarize the science program and instrument requirements for such a telescope, and present a strawman interferometric array composed of many (greater than 40), small (2 m) antenna elements, each equipped with a frequency- agile receiver operating over the range 1 - 26.5 GHz. Title: Coordinated Observations with SOHO, YOHKOH and VLA Authors: Aschwanden, Markus J.; Bastian, Tim S.; Nitta, Nariaki; Newmark, Jeff; Thompson, Barbara J.; Harrison, Richard A. Bibcode: 1998ASPC..155..311A Altcode: 1998sasp.conf..311A No abstract at ADS Title: 3-Dimensional Models of Active Region Loops Authors: Aschwanden, M. J.; Neupert, W. M.; Newmark, J.; Thompson, B. J.; Brosius, J. W.; Holman, G. D.; Harrison, R. A.; Bastian, T. S.; Nitta, N.; Hudson, H. S.; Zucker, A. Bibcode: 1998ASPC..155..145A Altcode: 1998sasp.conf..145A No abstract at ADS Title: VLBA Imaging of UX Ari Authors: Beasley, A. J.; Bastian, T. S. Bibcode: 1998ASPC..144..321B Altcode: 1998rege.conf..321B; 1998IAUCo.164..321B We have used the Very Long Baseline Array (VLBA) and the Very Large Array (VLA) to perform multi-wavelength radio imaging of the RS CVn active binary UX Arietis during the period November 16-21 1995. A series of strong flaring events exhibiting optically-thick spectra peaking above 100 GHz and extended source structures consistent with inter-binary emission were detected. 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: EUV and Microwave Observations of a Filament Authors: Chiuderi-Drago, F.; Bocchialini, K.; Lamartinie, S.; Vial, J. -C.; Bastian, T.; Alissandrakis, C. E.; Harrison, R.; Delaboudiniere, J. -P.; Lemaire, P. Bibcode: 1998ASPC..150...55C Altcode: 1998IAUCo.167...55C; 1998npsp.conf...55C No abstract at ADS Title: Toward a Frequency-Agile Solar Radiotelescope Authors: Bastian, T. S.; Gary, D. E.; White, S. M.; Hurford, G. J. Bibcode: 1998ASPC..140..563B Altcode: 1998ssp..conf..563B No abstract at ADS Title: Search for radio emission of extrasolar planets Authors: Dulk, George A.; Leblanc, Yolande; Bastian, Timothy S. Bibcode: 1998pslv.conf..421D Altcode: No abstract at ADS Title: The Structure of the Solar Corona above Sunspots as Inferred from Radio, X-Ray, and Magnetic Field Observations Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J. Bibcode: 1997ApJ...489..403V Altcode: We present observations of a solar active region, NOAA/USAF no. 7123, during 1992 April 3-10. The database includes high-angular-resolution radio, soft X-ray, magnetograph, and Hα observations. The radio observations include VLA maps in the Stokes I and V parameters at 4.7 and 8.4 GHz. The soft X-ray observations were obtained by the Soft X-Ray Telescope on board the Yohkoh satellite, the magnetograms were obtained at Kitt Peak, Mt. Wilson, and Big Bear, and the Hα data were obtained at Big Bear.

The lead sunspot in the active region is studied here. In particular, the polarization properties and brightness temperature spectrum are used to constrain the thermal structure of the corona over the sunspot. It is found that the 4.7 GHz emission of the sunspot is polarized in the sense of the ordinary mode, in contradiction with simple gyroresonance models that predict that the spot should be polarized in the sense of the extraordinary mode. We model the spectral and temporal evolution of the polarization structure in two frequencies, 4.7 and 8.4 GHz, using gyroresonance models to fit one-dimensional brightness temperature profiles across the spot in each polarization and frequency. The constraints provided by the X-ray and magnetic field observations help us to derive a qualitatively self-consistent picture for the daily evolution of the spot. We attribute the excess of the o-mode emission to the magnetic field configuration and to the temperature inhomogeneities across the spot. Namely, we find that (1) the umbral and penumbral environments are distinct, with the X-rays and the o-mode radio emission coming from the hotter penumbral loops, while the observed x-mode emission originates from the cooler umbral loops; (2) there exist temperature inhomogeneities in both the radial and vertical direction over the spot; and (3) the umbral magnetic field remains more confined in the corona than that predicted by a dipole model. Instead, a field configuration based on the magnetohydrostatic equilibrium model of Low gives a better agreement with the observations. 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: On the feasibility of imaging coronal mass ejections at radio wavelengths Authors: Bastian, T. S.; Gary, D. E. Bibcode: 1997JGR...10214031B Altcode: Coronal mass ejections (CMEs) can have a profound impact on the interplanetary medium and the near-Earth environment. We discuss the feasibility of detecting coronal mass ejections at radio wavelengths with a ground-based instrument. In particular, we explore the possibility that a radio telescope employing Fourier synthesis imaging techniques can detect thermal bremsstrahlung emission from CMEs. Using a simulated database from such a telescope, we explore three detection schemes: direct detection, an approximate differential detection scheme, and an ``exact'' differential detection scheme. We conclude that thermal bremsstrahlung emission from CMEs can be detected by such a telescope provided differential techniques are employed. While the approximate differential detection scheme may be sufficient for CMEs viewed near the solar limb, detection of CMEs against the solar disk may require the more sensitive exact differential scheme. The detection and imaging of nonthermal radio emissions from CMEs is also discussed. Title: Search for Cyclotron-maser Radio Emission from Extrasolar Planets Authors: Dulk, G. A.; Leblanc, Y.; Bastian, T. S. Bibcode: 1997DPS....29.2803D Altcode: 1997BAAS...29.1025D There is reason to believe that extrasolar planets and/or brown dwarfs of mass about 1 to 50 M_J have magnetic fields, that they emit extremely intense cyclotron-maser radiation at metric wavelengths, and that this radiation may be detectable with sensitive radio telescopes like the VLA. The radiation is emitted at the electron cyclotron frequency, and has been detected from Earth, Jupiter, Saturn, Uranus and Neptune, from the Sun, from flare stars, and close binaries. The frequency range of cyclotron maser radiation is fixed by the magnetic field strength on the object. To be detected at, say 0.33 GHz, the required field strength is 118 G, which is intermediate between the 14 G field of Jupiter and the ~ 1000 G field of stellar active regions. An estimation of the flux density of the expected radiation can be made from an interpolation between Jupiter's radio emission (10(10) mJy at 5 AU) and that of nearby red dwarf stars ( ~ 100 mJy at 3 pc). Thus the flux from a planet or brown dwarf 3 to 30 times massive than Jupiter is plausibly 1 to 10 mJy, easily detectable with the VLA. If emission is detected, several important parameters about the planet can be deduced: the strength of its magnetic field, the period of its rotation, and the possible existence of a moon such as Jupiter's Io. Possible means of distinguishing stellar maser emissions from those of planets include: 1) Temporal variations and spectra differ from stars to planets. 2) The polarization is likely to be 100% circular or elliptical for planets, but not for stars. We have searched for exoplanet radio emission with 60 hours of observations with the VLA during November 1996. The observed stars with giant planets or brown dwarfs included 51 Peg, 70 Vir, 47 UMa, 55 CnC, Tau Boo, Gl 229, and HD 114762. We will present the method of observation, the limitations due to confusion and background noise, and the results. Title: Relative Timing of Microwave and HXR Bursts Authors: Bastian, T. S.; Aschwanden, M. J. Bibcode: 1997SPD....28.1803B Altcode: 1997BAAS...29..922B The close correlation between microwave and hard X-ray (HXR) emission during flares has often been cited as evidence that the same population of energetic electrons is responsible for both types of emission. The two emissions differ in detail, however. Imaging observations have demonstrated that the two are not necessarily cospatial and timing observations have demonstrated that the microwaves are often significantly delayed with respect to HXR emission, typically by several seconds, but occassionally by much longer times. Such delays are in seeming conflict with the thick target model for HXR emission in its simplest form, and with the idea that microwave and HXR emissions result from essentially the same population of electrons. One way to reconcile the delay between microwaves and HXRs in the thick target model is to suppose that that electron trapping is significant (e.g., Cornell et al., ApJ, 279, 875). For a magnetic trap containing a plasma of constant density, high energy electrons have a longer lifetime against collisions than low energy electrons (tau_ {def} ~ E(3/2) ). Hence the energetic electrons responsible for the microwaves remain in the trap longer and the microwave emission they emit peaks later than the HXR emission. Another possibility is that higher energy electrons are accelerated later than lower energy electrons (so-called ``second-step'' acceleration models; e.g., Bai and Dennis 1985, ApJ, 292, 699). To explore the question in detail we have assembled a sample of 16 flares observed simultaneously in microwaves by the Nobeyama radioheliograph and in HXRs by the BATSE instrument on board the CGRO in burst trigger mode. The former imaged the flares at 17 GHz with an angular resolution of ~ 10'' and a time resolution of either 50 msec or 1 sec. The latter obtained medium energy resolution spectra (16 channels) between 20-200 keV with a time resolution of 16 or 64 msec. We present preliminary results of our analysis. 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: High Resolution Millimeter and Submillimeter Observations of Active Stars Authors: Bastian, Tim S. Bibcode: 1997msma.conf...27B Altcode: No abstract at ADS Title: Prospects for the Solar Radio Telescope Authors: Bastian, Timothy S.; Gary, Dale E. Bibcode: 1997LNP...483..218B Altcode: 1997cprs.conf..218B The Solar Radio Telescope (SRT) is an instrument concept for a powerful solar-dedicated radio telescope. As presently conceived. it would combine a high-resolution imaging capability (2″ at 20 GHz) with a broadband spectroscopic capability (0.3-26 GHz). In other words, the SRT would perform broadband imaging spectroscopy on a wide range of quiet- and active-Sun phenomena. On 17-20 April, 1995, a workshop was held in San Juan Capistrano, California. The purpose of the workshop, which was attended by more than 40 scientists from the US and around the world, was to discuss the science that could be done with a solar-dedicated radio synthesis telescope, and to discuss the design constraints imposed by the science envisioned. Special attention was also given to nighttime uses for the instrument. We summarize the "strawman" concept for the instrument here. Title: Energy Release in the Solar Corona Authors: Bastian, Timothy S.; Vlahos, Loukas Bibcode: 1997LNP...483...68B Altcode: 1997cprs.conf...68B Energy release in the solar corona drives a wide variety of phenomena, including flares, filament/prominence eruptions, coronal mass ejections, solar particle events, as well as coronal heating and the solar wind. The basic physics of these phenomena and their relationship to each other remains a vigorous area of inquiry. The Working Group on Energy Release at Mont Evray directed its attention to recent observational and theoretical developments relevant to flares and coronal heating. Particular attention was given to the "fragmentation" of energy release in solar flares and its interpretation; to the statistics of the flare phenomenon and whether they can be understood in terms of "driven dissipative systems"; to quasisteady energy release and the problem of coronal heating; and to recent observations of flares and related phenomena. 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: Microwave and UV observations of filaments with SOHO and the VLA Authors: Alissandrakis, C. E.; Drago, F.; Bastian, T.; Bocchialini, K.; Delaboudiniere, J. -P.; Lemaire, P.; Vial, J. -C.; Harrison, R. A.; Thompson, B. Bibcode: 1997ASPC..118..289A Altcode: 1997fasp.conf..289A Observations performed in coordination between SOHO instruments and ground-based observatories offer the unique possibility to derive information simultaneously in several wavelengths formed at different altitudes and/or temperatures in the solar atmosphere. The SUMER and CDS spectrometers, the imaging telescope EIT aboard SOHO, and the VLA provide complementary information in the UV and the radio ranges. We illustrate such a coordination with observations of filaments in the transition region, performed in July 1996. The observations in the UV between 10(4) and 10(6) K provide the differential emission measure as a function of temperature; this can be used to compute the expected brightness temperature in the microwave range and check models of the filament-corona transition region. Title: High-Resolution Microwave Observations of the Quiet Solar Chromosphere Authors: Bastian, T. S.; Dulk, G. A.; Leblanc, Y. Bibcode: 1996ApJ...473..539B Altcode: The VLA was used to observe a quiet region of the Sun on 1992 September 23 at 1.3 and 2 cm. Unlike previous interferometric microwave observations of the quiet Sun, we have used the total power data to calibrate the brightness temperature distribution in an absolute sense. We find a good correlation between the time-averaged 1.3 and 2 cm brightness distributions, and, in agreement with past studies at 3.6 and 6 cm, we find that both the 1.3 and 2 cm brightness distributions are closely correlated with the network magnetic field. The mean brightness at 1.3 and 2 cm was 10,400±1230 K and 12890±1415 K, respectively. The width of the σ1.3 cm brightness distribution function is σ1.3 = 270 K, while that at 2 cm is σ2 = 460 K.

We have examined the time variability of the 1.3 and 2 cm emission on a timescale of 2 hr. The correlation between the 1.3 and 2 cm brightness distributions is maintained, as is the correlation with the underlying magnetic field. However, considerable variability in the details of the brightness distribution is evident during the course of the day.

We compare our mean brightness measurements with those of Zirin, Baumert, & Hurford and compare the ensemble of observations with semi-empirical models of the chromosphere and transition region. The MCO model proposed by Avrett, which is in agreement with carbon monoxide observations, yields a microwave brightness temperature spectrum that is in excellent agreement with the microwave observations of Zirin et al. and those reported in this paper. The need for a model that reconciles all chromospheric observations optical, UV, infrared, and radio remains however. Inhomogeneous and/or dynamic chromospheric models are likely required. Title: Multiband VLA Observations of Solar Active Regions: Implications for the Distribution of Coronal Plasma Authors: Vourlidas, A.; Bastian, T. S. Bibcode: 1996ApJ...466.1039V Altcode: We present high-quality radio observations of a solar active region (NOAA/USAF region 5131) made by the Very Large Array in the 0.33, 1.5, 4.7, and 8.4 0Hz frequency bands. The observations were made during the IAU-sanctioned International Solar Month on 1988 September 1 and 4. In addition to the radio maps, the database includes images from the Solar Maximum Mission Soft X-ray Polychromator in the Fe XVII line, photo spheric magnetograms, and Hα filtergrams. Because coverage in only a single wavelength is available, the soft X-ray data are used for qualitative comparisons.

We identify those areas of the active region from which the radio emission is predominantly due to thermal bremsstrahlung emission. To account for the observed four-point radio spectra in these areas, we examine three different models, which characterize the corona in terms of a single plasma component, two components, and multiple components. The latter differs somewhat from past models. In particular, we take explicit account of the highly inhomogeneous structure of active regions through a multilayer slab model in which the thermal distribution is constrained by the generic form of the differential emission measure. While multicomponent models provide the best agreement with the observations, we find that a complete model must include both free-free and gyroresonance opacity. We compare our radio data and model results with those resulting from previous studies. Title: On the Peculiar Radio Polarization of a Sunspot and the Distibution of the Coronal Plasma Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J. Bibcode: 1996AAS...188.3602V Altcode: 1996BAAS...28..873V A comprehensive set of microwave, soft x-ray and magnetic observations of solar active region NOAA/USAF 7123 was obtained during 4--9 April, 1992. The observations show an unusual 4.7 GHz source which is polarized in the sense of the ordinary mode over the umbra of the leading spot. A detailed analysis of the daily radio and soft X-ray maps of the spot indicates that (i) the umbral magnetic field is strongly confined, (ii) the umbral and penumbral loops have distinct atmospheres and (iii) temperature gradients may exist both radially and vertically over the spot. A possible scenario for the temporal evolution of the spot is also presented. Title: A Search for Radio Pulsations from AE Aquarii Authors: Bastian, T. S.; Beasley, A. J.; Bookbinder, J. A. Bibcode: 1996ApJ...461.1016B Altcode: AE Aquarii is classified as a DQ Herculis-type cataclysmic variable, comprising a magnetized white dwarf primary and a KS dwarf secondary. Its orbital period is 9.88 hr while the rotational period of the magnetized primary is 33.08 s. AE Aqr is characterized by coherent pulsations and quasi-periodic oscillations (QPOs) in the optical, UV, and soft X-ray wavelength bands. It also emits TeV γ-rays, which may themselves be modulated on a period near the rotation period of the primary. In addition, AE Aqr displays violent flaring activity at optical, soft X-ray, and radio wavelengths.

We have searched for coherent pulsations and QPOs in the radio emission from AE Aqr. The Very Large Array (VLA) was used on 1994 January 29 to observe AE Aqr continuously for ∼10 hr at 8.4 GHz (λ = 3.6 cm). We find no evidence for the presence of coherent pulsations or QPOs. An upper limit of 1.6% of the mean flux density is placed on the amplitude of pulsations on frequencies greater than 0.01 Hz. Over bandwidths of 1% on the known fundamental and harmonic periods, the upper limits are 0.8%. The power spectrum is characterized by red noise on frequencies less than 0.01 Hz. It is well fitted by a power law with an index of 1.8. Furthermore, comparing the present observations with data obtained at seven previous epochs, we find no evidence of a relationship between flaring activity and the orbital phase. Title: Broadband Imaging Spectroscopy with the Solar Radio Telescope Authors: Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Hudson, H. S.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1996ASPC...93..430B Altcode: 1996ress.conf..430B No abstract at ADS Title: The Time Variability of Radio Emission from AE Aquarii Authors: Bastian, T. S.; Beasley, A. J.; Bookbinder, J. A. Bibcode: 1996ASPC...93..185B Altcode: 1996ress.conf..185B No abstract at ADS Title: Radio Emission from AE Aquarii Authors: Abada-Simon, M.; Bastian, T. S.; Fletcher, L.; Horne, K.; Kuijpers, J.; Steeghs, D.; Bookbinder, J. A. Bibcode: 1996ASPC...93..182A Altcode: 1996ress.conf..182A No abstract at ADS Title: Radio Flares on Stars: Possible Solar Analogs? Authors: Bastian, T. J. Bibcode: 1996ASPC...93..447B Altcode: 1996ress.conf..447B No abstract at ADS Title: VLBA imaging of RS CVn systems: UX Ari Authors: Beasley, A. J.; Bastian, T. S. Bibcode: 1996ASPC..109..639B Altcode: 1996csss....9..639B No abstract at ADS Title: VLA Observations of Decimetric Microbuzsts in the Solar Corona Authors: Kliem, B.; Bastian, T. S. Bibcode: 1996ASPC...93..372K Altcode: 1996ress.conf..372K No abstract at ADS Title: Joint Radio and Soft X-Ray Imaging of an `Anemone' Active Region Authors: Vourlidas, A.; Bastian, T. S.; Nitta, N.; Aschwanden, M. J. Bibcode: 1996SoPh..163...99V Altcode: The Very Large Array and the Soft X-ray Telescope (SXT) aboard the Yohkoh satellite jointly observed the rapid growth and decay of a so-called `anemone' active region on 3-6 April, 1992 (AR 7124). The VLA obtained maps of the AR 7124 at 1.5, 4.7, and 8.4 GHz. In general, discrete coronal loop systems are rarely resolved at 1.5 GHz wavelengths because of limited brightness contrast due to optical depth effects and wave scattering. Due to its unusual anemone-like morphology, however, several discrete loops or loop systems are resolved by both the VLA at 1.5 GHz and the SXT in AR 7124. Title: Radio Emission from Solar and Stellar Flares Authors: Bastian, T. S. Bibcode: 1996mpsa.conf..259B Altcode: 1996IAUCo.153..259B 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: Active Region 7123: Its Peculiar Radio Polarization and the Distribution of the Umbral Coronal Plasma Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J. Bibcode: 1995AAS...18710105V Altcode: 1995BAAS...27.1426V A comprehensive set of microwave and soft x-ray observations of solar active region 7123 was obtained during 3--10 April, 1992. Here, we present a detailed analysis of the polarized radio emission from the sunspot-associated component of AR 7123. We use the VLA observations at 1.5, 4.7 and 8.4 GHz, supported by the available x-ray and magnetic data. We concentrate on understanding the 4.7 GHz o-mode polarization over the umbra of the leading spot of AR 7123 and its variation with aspect angle within the physical context provided by the x-ray observations (SXT/Yohkoh) and past work on umbral atmospheres. 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: 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: A Solar Radio Telescope for the Future: Science Summary from the SRT Workshop Authors: Gary, D. E.; Bastian, T. S.; Hudson, H. S.; Hurford, G. J.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1995SPD....26..801G Altcode: 1995BAAS...27..971G No abstract at ADS Title: Aspect Angle Dependence of the Polarized Radio Emission from AR 7123 Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M. J.; Nitta, N. Bibcode: 1995SPD....26..701V Altcode: 1995BAAS...27..965V No abstract at ADS Title: A Solar Radio Telescope for the Future: Strawman Concept from the SRT Workshop Authors: Hurford, G. J.; Bastian, T. S.; Gary, D. E.; Hudson, H. S.; Klimchuk, J. A.; Petrosian, V.; White, S. M. Bibcode: 1995SPD....26..802H Altcode: 1995BAAS...27..971H No abstract at ADS Title: Angular Scattering of Radio Waves: Implications for Mode Coupling in the Solar Corona Authors: Bastian, T. S. Bibcode: 1995ApJ...439..494B Altcode: The solar corona is highly inhomogeneous. The magnetionic modes may therefore couple under certain circumstances, and the polarization properties of solar radio sources may, as a consequence, be modified. An application of the simple theory of mode coupling to the propagation of radio waves in the solar corona leads to the expectation that mode coupling in quasi-transverse (QT) magnetic field regions should always be weak (coupling ratio Q much less than 1) at meter wavelengths. Observations to date suggest that, on the contrary, mode coupling is moderate (Q approximately 1) to strong (Q much greater than 1) in QT regions at meter wavelengths. I suggest that observations and theory can be reconciled by including the effect of turbulence on mode coupling. Specifically, angular scattering on turbulent inhomogeneities greatly reduces the spatial scale relevant to the theory at low frequencies. As a result, the coupling ratio is increased by a corresponding factor and mode coupling may be moderate to strong in QT regions at meter wavelengths. Title: Extension of the Radio Spectrum of AE Aquarii to the Sub-millimetric Range Authors: Abada-Simon, Meil; Bastian, Tim S.; Bookbinder, Jay A.; Aubier, Monique; Bromage, Gordon; Dulk, George A.; Lecacheux, Alain Bibcode: 1995LNP...454..268A Altcode: 1995IAUCo.151..268A; 1995flfl.conf..268A No abstract at ADS Title: The VLA (Very Large Array) development plan Authors: Bastian, T. S.; Bridle, Alan H. Bibcode: 1995vvla.conf.....B Altcode: No abstract at ADS Title: The Radio and Optical Flares of A.E Aquarii Authors: Abada-Simon, M.; Bastian, T. S.; Horne, K.; Robinson, E. L.; Bookbinder, J. A. Bibcode: 1995ASPC...85..355A Altcode: 1995mcv..conf..355A No abstract at ADS Title: Radio Diagnostics of Conditions in the Solar Atmosphere Authors: Bastian, T. S. Bibcode: 1995itsa.conf..115B Altcode: No abstract at ADS Title: Joint Radio and Soft X-ray Imaging of an ``Anemone'' Active Region Authors: Vourlidas, A.; Bastian, T. S.; Aschwanden, M.; Nitta, N. Bibcode: 1994AAS...185.8609V Altcode: 1994BAAS...26Q1465V The Very Large Array and the Soft X-ray Telescope aboard the Yohkoh satellite observed the rapid growth and decay of a so-called ``anemone'' active region on 3-6 April (AR 7124). In general, discrete coronal loop systems are rarely resolved at radio wavelengths due to optical depth effects and scattering. In the case of AR 7124, however, several discrete loops or loop systems are resolved by both the VLA and the SXT, probably due to its unusual ``anemone''-like morphology. Furthermore, the region exhibited a significant amount of variability, especially on April 3, marked by many subflares and intensity changes as has been reported in flare patrol observations. In the present study, physical parameters derived from multiband radio and soft x-ray techniques for discrete loops are compared. The temporal evolution of these parameters is also examined. Title: A Microwave Survey of Magnetic Cataclysmic Variables Authors: Beasley, A. J.; Bastian, T. S.; Ball, Lewis; Wu, K. Bibcode: 1994AJ....108.2207B Altcode: We present the results of a sensitive radio survey of 22 previously unobserved magnetic cataclysmic variable stars (MCVs), made by the Very Large Array (VLA) and the Australia Telescope Compact Array. In addition, we summarize the results of previous observations of 15 MCVs made with the VLA. None of the 37 MCVs were detected. Extensive observations of the star V834 Cen have failed to detect significant emission, suggesting that either the high flux densities previously reported by Wright et al. (1988) for this source are incorrect, or that it produces occasional transient emissions. Title: A Multisource Limb Flare Observed at Multiple Radio Wavelengths Authors: Kucera, T. A.; Dulk, G. A.; Gary, D. E.; Bastian, T. S. Bibcode: 1994ApJ...433..875K Altcode: A flare with several radio sources occurred on the solar limb at 2155 UT on 1989 June 20. It was observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO). The VLA data consisted of images at 1.4 GHz, while OVRO provided spectral and spatial information over the range 1-15 GHz. We develop a new gyrosynchrotron model to analyze the sources observed at flare peak. This model differs from many previous ones in that it contains spatial variations of both the magnetic field and accelerated particle density. It uses a new gyrosynchrotron approximation which is valid at very low harmonics of the gyrofrequency. For the first time we find that the cause of the change of microwave source size with frequency in the event studied was due primarily to the spatial variation of the accelerated electron density. This is contrary to the common assumption that the variation in size is due to a nonuniform magnetic field. We also investigate a polarized source which brightened later in the flare, finding that it could have been due to plasma radiation or gyrosynchrotron emission. Title: Propagation of Radio Waves in the Sun's Corona: Angular Broadening in the Limit of Small-Angle Scattering Authors: Bastian, T. S. Bibcode: 1994kofu.symp..321B Altcode: No abstract at ADS Title: VLA Stereoscopy of Solar Active Regions Authors: Aschwanden, M. J.; Bastian, T. S. Bibcode: 1994kofu.symp..357A Altcode: No abstract at ADS Title: Energy Transport During a Solar Flare: VLA Observations of the M1.9 Flare of 20 Aug 1992 Authors: Bastian, T. S.; Nitta, N.; Kiplinger, A. L.; Dulk, G. A. Bibcode: 1994kofu.symp..199B Altcode: The GOES M1.9 flare of 20 August 1992 was observed by a large complement of instruments including the VLA, Yohkoh, and a high-speed H-alpha camera. We present a brief overview of the VLA data here. The VLA acquired maps of the evolving microwave emission at 8.4 and 15 GHz with a time resolution of 0.2 s. The main observational results are as follows: i) the microwave sources consist of two, parallel, sheared loops or loop systems; these two loop systems flared sequentially; ii) the second microwave source is clearly associated with two magnetic footpoints; iii) the microwave source shows a disturbance which propagates from the initial footpoint and over the magnetic neutral line; iv) the speed of the disturbance is roughly 3000 kms^(-1). Points along the loop show a brightening that is delayed relative to that at the primary footpoint, and the two footpoints spread apart over the course of a few minutes. Title: Rotation in the Ionized Envelope of MWC 349A Authors: Rodriguez, Luis F.; Bastian, Timothy S. Bibcode: 1994ApJ...428..324R Altcode: Using the Very Large Array (VLA) in the A configuration we mapped the H92 alpha recombination line and the adjacent continuum emission at 3.6 cm from the peculiar emission-line star MWC 349A. The recombination line emission is consistent with local thermodynamic equilibrium conditions. Our data resolves spatially for the first time the kinematic structure of this envelope. The observed motions can be explained in terms of a bipolar outflow undergoing significant rotation. The inclination angle of the outflow axis with respect to the plane of the sky is estimated to be about 15 deg. Angular momentum conservation arguments indicate that this rotating gas cannot have originated from the stellar surface and most probably is photoevaporating from a disk around the star. Assuming Keplerian rotation, we estimate the mass of the star to be approximately 30 solar masses. The presence of a rotating disk in association with MWC 349A favors a pre-main-sequence nature for this object. Title: First millimetric detections of AE Aquarii Authors: Abada-Simon, M.; Lecacheux, A.; Bastian, T. S.; Bookbinder, J. A.; Dulk, G. A. Bibcode: 1994SSRv...68..291A Altcode: We report the first millimetric detections of the magnetic cataclysmic variable AE Aquarii, accompanied by contemporaneous microwave observations. These data show that the time-averaged spectrum is well fit by a power-law which extends to mm wavelengths. We suggest that the spectrum is consistent with that expected from a superposition of flare-like events. Title: Stellar flares Authors: Bastian, T. S. Bibcode: 1994SSRv...68..261B Altcode: Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are “solar-like”, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed. Title: VLA Stereoscopy of Solar Active Regions. I. Method and Tests Authors: Aschwanden, Markus J.; Bastian, T. S. Bibcode: 1994ApJ...426..425A Altcode: We develop a new technique for extracting three-dimensional information from multiday solar Very Large Array (VLA) observations. While standard stereoscopic methods provide a three-dimensional view of an object by combining simultaneous observations from two different aspect angles, we relax the condition of simultaneity and exploit solar rotation to vary the aspect angle. The solar radio images are decomposed into Gaussian source components, which are then cross-correlated in maps from preceding and following days. This provides measurements of the three-dimensional position of correlated source centroids. In this first paper, we describe the stereoscopic method and perform tests with simulated and real radio maps (from the VLA at 20 cm), in order to study the accuracy of altitude measurements, and the limitations introduced by (i) source confusion, (ii) source motion, and (iii) the assumed differential rotation rate. The tests demonstrate that (i) the information content of a VLA map relevant for stereoscopic correlation can be conveniently represented in terms of a small number of Gaussian components; (ii) the fitting of the three-dimensional source position is stable within a numerical accuracy of less than or approximately equal to 0.02 map pixels, (iii) the relative accuracy of the altitude determination is uniform over the solar disk, and (iv) source confusion does not affect the accuracy of stereoscopic position measurements for sources with a signal-to-noise ratio of greater than or approximately equal to 36. Title: VLA Stereoscopy of Solar Active Regions. II. Altitude, Relative Motion, and Center-to-Limb Darkening of 20 Centimeter Emission Authors: Aschwanden, Markus J.; Bastian, T. S. Bibcode: 1994ApJ...426..434A Altcode: A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of qA approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin2B)). 5. We find a statistical limb darkening, which can be described by the relation (TB(alpha))/TB(0)) = 0.4 + ((0.6(cos2 alpha)) for sources with TB greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance. Title: Angular Scattering of Solar Radio Emission by Coronal Turbulence Authors: Bastian, T. S. Bibcode: 1994ApJ...426..774B Altcode: With the advent of large synthesis imaging radio telescopes (e.g., the Westerbrook Synthesis Radio Telescope (WSRT) and the very large array (VLA), many solar observations have been made with a high degree of angular resolution at microwave and decimeter wavelengths. These have revealed a distinct absence of structure on small angular scales. I show that scattering on a turbulent spectrum of fluctuations in the coronal electron number density offers a plausible explanation for the absence of fine structure at radio wavelengths. I review the theory of scattering in an inhomogeneous medium as it pertains to angular broadening and describe recent work on the nature of turbulence in the Sun's outer corona and the solar wind. I then reassess the problem of scattering as it applies to the angular broadening of radio sources embedded in the solar corona in the limit of small-angle scattering. It is pointed out that angular broadening due to scattering represents a fundamental limit on the degree of angular resolution with which solar radio emission can be mapped. The techniques of speckle interferometry are of no help, with the possible exception of observations of millisecond spike bursts. Implications are briefly discussed. Title: A Multiband Study of Radio Emission from Solar Active Regions Authors: Vourlidas, Angelos; Bastian, T. S. Bibcode: 1994ASPC...68..369V Altcode: 1994sare.conf..369V No abstract at ADS Title: 850 MU M Observations of the 11 July 1991 Total Solar Eclipse Authors: Ewell, M. W., Jr.; Zirin, H.; Jensen, J. B.; Bastian, T. S. Bibcode: 1994IAUS..154..161E Altcode: No abstract at ADS Title: A Study of Solar Prominences near lambda = 1 Millimeter Authors: Bastian, T. S.; Ewell, M. W., Jr.; Zirin, H. Bibcode: 1993ApJ...418..510B Altcode: The 10.4 m Leighton telescope at the Caltech Submillimeter Observatory was used to produce full-disk and partial area raster maps of the Sun during 1991 July 9-11 in advance of the total eclipse of the Sun on July 11. Maps were made at a wavelength of 850 microns with an angular resolution of 20".6 and at 1250 microns with an angular resolution of 30".

We have analyzed the 850 microns brightness associated with Hα filaments present on the disk and find that (1) they are all associated with regions possessing a brightness comparable to or below that of the quiet Sun at the center of the disk; and (2) because of their lack of contrast with the background brightness distribution, Hα filaments are optically thin at 850 μm. We have also analyzed contemporaneous observations of a prominence above the solar limb at both 850 and 1250 mum. We show that (1) the optical depth of the prominence is τ ≍ 0.12 at 850 μm, confirming the conclusion drawn from the analysis of Hα filaments; and (2) the line-of- sight emission measure is <ne2L> = 1.3-2.0 × 1029 cm-5, and the electron number density is ne ∼ 1-3 × 1010 cm-3.

We argue that the reduced 850 microns brightness associated with Hα filaments and, more generally, magnetic neutral lines is due neither to the presence of an overlying coronal cavity nor to the presence of absorbing material, as has been suggested previously. We instead suggest that the reduced brightness is due to the structure of the underlying chromosphere where, in the case of filament channels, the predominantly horizontal magnetic field leads to a reduction of heating and/or a smaller density scale height. Title: The Center-to-Limb Brightness Variation of the Sun at lambda = 850 Microns Authors: Bastian, T. S.; Ewell, M. W., Jr.; Zirin, H. Bibcode: 1993ApJ...415..364B Altcode: The 10.4 m submillimeter telescope of the Caltech Submillimeter Observatory was used to map the full disk of the sun on July 9-10, 1991 at a wavelength 850 microns with an angular resolution of 20.6 arcsec. A maximum entropy-type deconvolution was performed to correct the map for the broad wings of the telescope beam. The brightness distribution of the resulting map shows (1) a high degree of correlation with corresponding images in H-alpha, the Ca II K line, and with the photospheric magnetogram; (2) a systematic center-to-limb brightening of the quiet sun (about 12 percent at an offset of 0.94 solar radius) with no apparent difference in the limb brightening between the EW and NS quadrants; (3) an average contrast of about 11 percent between active region plages and the quiet sun near disk center; and (4) a smaller degree of center-to-limb brightening of active region plages (about 5 percent at an offset of 0.94 solar radius), leading to a decrease in contrast between active region plages and the quiet sun from the center to limb. We compare the observed center-to-limb brightness variation of the quiet sun and plages with that expected for several chromospheric models, including those which include a 'spicular' component. We find that although the observed center-to-limb variation of the quiet sun at 850 microns is broadly consistent with the chromospheric models of Vernazza et al. (1981), it differs in detail. Title: Dynamic spectra of radio sources from 4.5 to 5.0 GHz. Authors: Lecacheux, A.; Rosolen, C.; Davis, M.; Bookbinder, J.; Bastian, T. S.; Dulk, G. A. Bibcode: 1993A&A...275..670L Altcode: We report on the first observations of astronomical sources made with the mini-Gregorian feed of the 305 m Arecibo telescope together with an acousto-optic spectrometer (AOS). Both the mini-Gregorian and the AOS have a bandwidth of 500 MHz, permitting wide bandwidth dynamic spectra of both celestial and solar sources to be obtained. In the examples reported herein, we used the 5 GHz receiver, operating between 4.5 and 5.0 GHz with a spectral resolution of 1 MHz and temporal resolution of 20 ms.

We represent observations of the flare star AD Leo, of the Sun, and of interplanetary scintillations of the quasar 0735 + 178 which, at the time it was observed, was about 8° from the Sun. Title: Multiple Wavelength Observations of an Off-Limb Eruptive Solar Flare Authors: Kucera, T. A.; Dulk, G. A.; Kiplinger, A. L.; Winglee, R. M.; Bastian, T. S.; Graeter, M. Bibcode: 1993ApJ...412..853K Altcode: The eruptive prominence and limb flare which occurred at 1454 UT on June 20, 1989 is described and analyzed. This event was observed by many different instruments providing an unusual amount and variety of data: images at 1.4 GHz, 37 GHz, and H-alpha, and spectra in hard X-ray, soft X-ray, and radio frequencies. This array of data makes it possible to explore the relationships between flare and eruptive prominence emissions at different wavelengths. VLA images at 1.4 GHz show changing sources in a set of high (about 10 exp 10 cm) coronal loops associated with the erupting prominence. We use a full gyrosynchrotron code to model a 1.4 GHz source early in the flare as a large coronal loop. The model results lead us to conclude that the initial acceleration occurs in smaller, denser loops which also produce the flare's hard X-ray emission. We also present evidence that a source at 1.4 GHz later in the event is due to second-harmonic plasma emission. This source is adjacent to a leg of the prominence and comes from a dense column of material in the magnetic structure supporting the prominence. Title: VLA Stereoscopy of Solar Active Region 7123 Authors: Aschwanden, M. J.; Bastian, T. S.; Nitta, N. Bibcode: 1993BAAS...25.1224A Altcode: No abstract at ADS Title: The M1.9 Flare of 20 August 1992: Joint Imaging with the VLA, Yohkoh, and a High Speed Hα Camera Authors: Bastian, T. S.; Nitta, N.; Kiplinger, A. Bibcode: 1993BAAS...25.1222B Altcode: No abstract at ADS Title: Multitemperature Observations of an Emerging Flux Region Authors: Bruner, M. E.; Acton, L. W.; Brown, W. A.; Lemen, J. R.; Shine, R.; Strong, K. T.; Tarbell, T.; Dulk, G.; Tsuneta, S.; Bastian, T.; Dame, L. Bibcode: 1993BAAS...25.1179B Altcode: No abstract at ADS Title: Observations of an Emerging Flux Region Authors: Brown, W. A.; Acton, L. W.; Bruner, M. E.; Lemen, J. R.; Shine, R.; Strong, K. T.; Tarbell, T.; Dulk, G.; Tsuneta, S.; Bastian, T.; Dame, L. Bibcode: 1993BAAS...25Q1214B Altcode: No abstract at ADS Title: OVRO Microwave Observations During the Max'91/CoMStOC'92 Campaign Authors: Gary, D. E.; Hurford, G. J.; Bastian, T. Bibcode: 1993BAAS...25.1224G Altcode: No abstract at ADS Title: The Spectrum and Variability of Radio Emission from AE Aquarii Authors: Abada-Simon, Meil; Lecacheux, Alain; Bastian, Tim S.; Bookbinder, Jay A.; Dulk, George A. Bibcode: 1993ApJ...406..692A Altcode: The first detections of the magnetic cataclysmic variable AE Aquarii at millimeter wavelengths are reported. AE Aqr was detected at wavelengths of 3.4 and 1.25 mm. These data are used to show that the time-averaged spectrum is generally well fitted by a power law S(nu) varies as nu exp alpha, where alpha is approximately equal to 0.35-0.60, and that the power law extends to millimeter wavelengths, i.e., the spectral turnover is at a frequency higher than 240 GHz. It is suggested that the spectrum is consistent with that expected from a superposition of flarelike events where the frequency distribution of the initial flux density is a power law f (S0) varies as S0 exp -epsilon, with index epsilon approximately equal to 1.8. Within the context of this model, the high turnover frequency of the radio spectrum implies magnetic field strengths in excess of 250 G in the source. Title: The Kinematics of the Ionized Envelope of MWC349A Authors: Rodríguez, L. F.; Bastian, T. S. Bibcode: 1993ESOC...46..468R Altcode: 1993mlab.conf..468R No abstract at ADS Title: Submillimeter Observations of the 1991 July 11 Total Solar Eclipse Authors: Ewell, M. W., Jr.; Zirin, H.; Jensen, J. B.; Bastian, T. S. Bibcode: 1993ApJ...403..426E Altcode: We present observations of the 1991 July 11 total solar eclipse at 850 microns made with the Caltech Submillimeter Observatory on Mauna Kea. We find that the 850-micron limb is 3380 +/- 140 km above the visible limb. We also find that there is a 10 percent limb brightening in the outer 7 arcsec of the solar disk, and we measure a central brightness temperature of 6400 +/- 700 K. These results require that the upper chromosphere not be in hydrostatic equilibrium, with a higher electron density than is predicted by the standard (VAL) model. We show that the dependence of limb height on wavelength is well fitted by a one-parameter model with an electron density scale height of 1200 km; there is no need to invoke complex spicule geometry to explain the observations. Title: 3D reconstruction methods of coronal structures by radio observations. Authors: Aschwanden, M. J.; White, S. M.; Bastian, T. S. Bibcode: 1992ESASP.348..217A Altcode: 1992cscl.work..217A The ability to carry out a three-dimensional reconstruction of structures in the solar corona would represent a major advance in our study of the physical properties in active regions and in flares. The authors describe several new methods which allow a geometric reconstruction of quasi-stationary coronal structures (e.g. active region loops) or dynamic structures (e.g. flaring loops): (1) steroscopy of multi-day imaging observations by the VLA. (2) Tomography of optically thin emission (in radio or soft X-rays). (3) Multi-frequency band imaging by the VLA. (4) Tracing of magnetic field lines by propagating electron beams. Title: Simultaneous Observations of Coronal Bright Points in X-Ray and Radio Wavelengths Authors: Nitta, Nariaki; Bastian, Timothy S.; Aschwanden, Markus J.; Harvey, Karen L.; Strong, Keith T. Bibcode: 1992PASJ...44L.167N Altcode: We present a first explicit comparison of coronal bright points in soft X-ray and radio wavelengths, using the Soft X-ray Telescope aboard the Yohkoh spacecraft and the Very Large Array. About half of the 33 compact sources indentified in a 20-cm full-disk map appear as X-ray bright points in the X-ray data. The other half apparently corresponds to unipolar regions with enhanced magnetic fields. Thus, the identification of radio bright points alone cannot reliably serve as a proxy for X-ray bright points. A preliminary analysis reveals that bright points commonly observed at 20 cm and in X-rays have temperatures of (1.4--2.9) times 10(6) K and emission measures of (0.4--2.5) times 10(45) cm(-3) . The observed brightness temperatures at 20 cm [(1--2.5) times 10(5) K] can be explained in terms of optically thin free-free emission from a plasma with these parameters. Title: Radio Emission from Chemically Peculiar Stars Authors: Linsky, Jeffrey L.; Drake, Stephen A.; Bastian, T. S. Bibcode: 1992ApJ...393..341L Altcode: In five VLA observing runs the initial survey of radio emission from magnetic Bp-Ap stars by Drake et al. is extended to include a total of 16 sources detected at 6 cm out of 61 observed, giving a detection rate of 26 percent. Of these stars, three are also detected at 2 cm, four at 3.6 cm, and five at 20 cm. The 11 new stars detected as radio sources have spectral types B5-A0 and are He-weak and Si-strong. No classical (SrCrEu-type) Ap stars have yet been detected. The 16 detected sources show a wide range of radio luminosities with the early-B He-S stars on average 20 times more radio luminous than the late-B He-W stars and 1000 times more luminous than Theta Aurigae. Multifrequency observations indicate flat spectra in all cases. Four stars have a detectable degree of circular polarization at one or more frequencies. It is argued that the radio-emitting CP (chemically peculiar) stars form a distinct class of radio stars that differs from both the hot star wind sources and the active late-type stars. The observed properties of radio emission from these stars may be understood in terms of optically thick gyrosynchrotron emission from a nonthermal distribution of electrons produced in a current sheet far from the star. In this model the electrons travel along magnetic fields to smaller radii and higher magnetic latitudes where they mirror and radiate microwave radiation. Title: Radio observations of the M8.1 solar flare of 23 June, 1988: Evidence for energy transport by thermal processes Authors: Bastian, T. S.; Gary, D. E. Bibcode: 1992SoPh..139..357B Altcode: The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON Hα filtergrams, and by a KPNO photospheric magnetogram. 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: Model of Gyrosynchrotron Emission from a High Coronal Loop Authors: Kucera, T. A.; Dulk, G. A.; Bastian, T. S. Bibcode: 1992AAS...180.4205K Altcode: 1992BAAS...24..796K Gyrosynchrotron emission is a main source of microwave emission from solar flares. We have developed a model of a high, face-on, coronal flare loop with a dipole magnetic field. The loop is divided into homogeneous segments to which are applied a general gyrosynchrotron code. We compare the model with observations made of an off-limb flare taken in June of 1989 during the first Max '91 campaign. These observations force a strong set of constraints upon the model. VLA imaging data at 1.4 GHz dictate the source position, shape and brightness at that frequency. Radiometer data from RSTN and Bern provide microwave spectra to compare to model-produced spectra, and there are constraints from SMM/HXRBS hard X-ray spectra and derived emission measures. The model is also compared with general results from previous measurements of source parameters at other frequencies. Title: Scattering of Radio Waves in the Solar Corona Authors: Bastian, T. S. Bibcode: 1992AAS...180.1107B Altcode: 1992BAAS...24..747B Over the past two decades, our understanding of turbulence in the solar wind and the outer corona has progressed significantly. Coupled with this have come many important developments in the theory of radiation transport in random media. While the importance of scattering of radio waves at meter wavelengths emitted by sources embedded in the solar corona has long been recognized, the formalism used to describe the scattering has not been brought up to date. In this paper I point out several developments which modify and extend our understanding of scattering of radio waves in the solar corona. Specifically, I show i) the importance of scattering of radio waves emitted by sources embedded in the solar corona extends to microwaves; ii) the potential importance of refractive scintillation at meter wavelengths. The practical consequences of these developments are briefly explored. Title: The Structure of Solar Active Regions Authors: Vourlidas, A.; Bastian, T. S. Bibcode: 1992AAS...180.4204V Altcode: 1992BAAS...24..796V In past years, x-ray observations of solar active regions have lead to the expectation of greater brightness temperatures at radio wavelengths than those typically observed. It has been suggested that cool plasma in the corona along the line of sight attenuates radio emission via free-free absorption. If such plasma is present, it has consequences for both the microwave spectrum and its polarization properties. In order to test these ideas, high quality radio and x-ray maps are required. We present a comprehensive set of observations of a large solar active region (NOAO/USAF number 5131) made during the IAU sanctioned International Solar Month in September, 1988. The VLA was used to image the Sun in the 90, 20, 6 and 3.6 cm bands between 1--4 September. To improve the image quality we used the technique of frequency synthesis at 3.6, 6 and 20 cm. The final maps are among the best in dynamic range yet obtained. In addition to the radio maps, the data base includes images from the SMM XRP in Fe XVII, magnetograms, and Hα observations. We reconcile the x-ray and radio observations with a simple model which differs somewhat from past models. Rather than relying on a screen of cool plasma between the source and the observer, we take explicit account of the highly inhomogeneous structure of solar active regions. We briefly compare and contrast the consequences of this model with existing models. Title: Solar Radio Pulsation Event Observed by the VLA and OVRO Authors: Aschwanden, M. J.; Bastian, T. S.; Gary, D. E. Bibcode: 1992AAS...180.4505A Altcode: 1992BAAS...24..802A We investigate interpretational aspects of the radio pulsation event which has been observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO) on December 21, 1990, 1930 UT, during the second MAX'91 observing campaign. The VLA was observing with a time resolution of 0.4 s at 0.33, 1.4 and 4.9 GHz, while OVRO used a time resolution of 0.2 s at 1.2, 1.4, 1.6, 1.8 and 2.0 GHz. The radio pulsation event was triggered by a C3.3 class flare in soft X-rays in active region 6412 (NOAA). The time profile of the quasi-periodic radio emission exhibits a period of 8.8 s and shows indications of secondary periodicities with faster periods. We investigate whether these periodicities can be explained in terms of (i) MHD eigen-modes in cylindrical fluxtubes (MHD surface modes and harmonic modes), or (ii) relaxational oscillations of a nonlinear dissipative system. We test these two options by means of Fourier spectra and by reconstruction of the ``strange attractor dimension'' of nonlinear systems. We attempt a three-dimensional reconstruction of the pulsating source by means of magnetic field extrapolation from the photospheric magnetogram and by using the constraints of the radio maps at multiple frequencies. Preliminary analysis indicates that plasma emission as well as gyrosynchrotron emission is coherently modulated in spatially diverging magnetic structures. We investigate whether the pulsating radio emission originates from plasma confined in a pulsating loop structure or whether the radio emission is driven by electron beams which are produced in a pulsating acceleration mechanism. The latter possibility would support a model where the primary energy release itself is governed by a nonlinear dissipative system, e.g. by oscillatory magnetic reconnection. Title: Detection of the H92 alpha Radio Recombination Line from the Symbiotic Star H1-36 Arae Authors: Bastian, T. S. Bibcode: 1992ApJ...387L..77B Altcode: The H92-alpha radio recombination line at 8309.383 MHz has been detected from the symbiotic star H1-36 Arae by the VLA. The continuum flux density is 73.5 mJy and the observed line-to-continuum ratio is Tl/Tc greater than about 1 percent. The line width is 46 km/s. Since the photoionized nebula may account for as little as one-half of the continuum radio flux, the true line-to-continuum ratio may be as high as 2 percent. If this is the case, and if pressure broadening is negligible, the electron temperature is between 10 exp 4 and 2 x 10 exp 4 K. If pressure broadening is marginally significant, the expansion velocity of the wind is consistent with vexp = 10 km/s, and the electron temperature drops to a range comparable to that found for certain planetary nebulae. Title: High Sensitivity; Dynamic Spectral Search for Flare Star Radio Bursts with the Arecibo Single Dish Authors: Lecacheux, A.; Abada-Simon, M.; Belkora, L.; Dulk, G. A.; Bookbinder, J.; Bastian, T. S.; Louarn, P. Bibcode: 1992ASPC...26..319L Altcode: 1992csss....7..319L No abstract at ADS Title: The Class of RadioEmitting Magnetic B Stars; a Wind-Fed Magnetospheric Model Authors: Linsky, J. L.; Drake, S. A.; Bastian, T. S. Bibcode: 1992ASPC...26..325L Altcode: 1992csss....7..325L No abstract at ADS Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1992ApJ...384..656W Altcode: Observations of an impulsive solar-radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (of about 5 x 10 exp 11/cu cm). Very Large Array images at 15 GHz show a single-loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. The possibility is explored that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties. Title: The Distribution of Magnetic Fields and Related Activity on A'D Leo Authors: Saar, S. H.; Bookbinder, J. A.; Neff, J.; Bromage, G.; Bastian, T. Bibcode: 1991BAAS...23.1383S Altcode: No abstract at ADS Title: Imaging the Sun and the Planets with a Radio Schmidt Telescope Authors: Dulk, G. A.; Bastian, T. S. Bibcode: 1991rst..work..123D Altcode: No abstract at ADS Title: Improved Solar Capabilities of the VLA Authors: Bastian, T. S. Bibcode: 1991BAAS...23R1072B Altcode: No abstract at ADS Title: Observations of Two Large Off Limb Solar Flares in the Radio, X-Rays, and Hα Authors: Kucera, T. A.; Dulk, G. A.; Winglee, R. M.; Kiplinger, A. L.; Bastian, T. S.; Gary, D. E. Bibcode: 1991BAAS...23R1065K Altcode: No abstract at ADS Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1991BAAS...23.1043W Altcode: No abstract at ADS 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: Temporally, Spectrally, and Spatially Resolved Observations of a Pulsating Solar Radio Burst Authors: Bastian, T. S.; Aschwanden, M. J.; Gary, D. E. Bibcode: 1991BAAS...23Q1072B Altcode: No abstract at ADS Title: Solar Radio Microbursts at 1.4 GHz Authors: Bastian, T. S. Bibcode: 1991ApJ...370L..49B Altcode: The Very Large Array was used for a period of about 80 minutes on September 11, 1989 to observe the sun at two frequencies in the 1.4 GHz band. In addition to a strong radio burst (700 sfu at maximum) of a duration of roughly 15 minutes, a multitude of small-amplitude, transient bursts occurred during the course of the observation. Specifically, some tens of microbursts occurred during a period of 65 minutes, ranging in amplitude from less than about 0.05 to 4 sfu, and ranging in duration from less than 10 to 40 s. A sample of these microbursts studied in detail shows that they occurred at five distinct locations in four different active regions. The microbursts are probably due to plasma radiation, although the microburst mechanism remains unknown. Their relation to known radio burst phenomena and hard X-ray microflares is unclear. Title: Observations of Two Large Limb Flares on 20 June 1989 Authors: Kucera, T. A.; Winglee, R. M.; Dulk, G. A.; Bastian, T. S.; Gary, D. E. Bibcode: 1991max..conf..172K Altcode: No abstract at ADS Title: VLA and Hα Observations of the M8.7 Flare of 17 June 1989: A Preliminary Report Authors: Bastian, T. S.; Kiplinger, A. L. Bibcode: 1991max..conf..153B Altcode: No abstract at ADS Title: Radio Emission from Flare Stars Authors: Bastian, T. S. Bibcode: 1990SoPh..130..265B Altcode: Observations of radio emission from flare stars are reviewed, including surveys of flare stars in the solar neighborhood and in stellar associations, studies of quiescent emission, and continuum and spectral studies of radio burst emission. The radio observations are placed in an observational context provided by soft X-ray, UV, and optical observations. It is stressed that, as is the case for the latter wavelength regimes, observations of rado bursts on flare stars are qualitatively similar to those on the Sun, albeit in a dramatically scaled-up fashion. Title: Dynamic Spectra of Radio Bursts from Flare Stars Authors: Bastian, T. S.; Bookbinder, J.; Dulk, G. A.; Davis, M. Bibcode: 1990ApJ...353..265B Altcode: The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation. Title: Direct Imaging of a Coherent Solar Radio Burst Authors: Bastian, T. S. Bibcode: 1990BAAS...22..824B Altcode: No abstract at ADS 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: Extension of the Class of Magnetic B-Star Nonthermal Radio Sources Authors: Linsky, Jeffrey L.; Drake, Stephen A.; Bastian, Timothy S. Bibcode: 1990ASPC....9..189L Altcode: 1990csss....6..189L A large VLA survey of radio emission from magnetic B stars is conducted at 2, 3.6, 6, and 20 cm to identify and classify the stars and check for the existence of classical Ap stars. Observations of 30 previously unidentified stars in the Sco-Cen association are reported, and 10 stars are found which have spectral types B5-A0, measured magnetic fields, and are He-weak and Si-strong. No radio emission is detected from stars later than spectral type A1, and the extreme magnetic field strength and large magnetosphere of GL Lac make it a good test for magnetosphere theories. 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: Extension of the Class of Magnetic B Star Nonthermal Radio Sources Authors: Linsky, J. L.; Drake, S. A.; Bastian, T. S. Bibcode: 1989BAAS...21Q.742L Altcode: 1989BAAS...21..742L No abstract at ADS Title: Solar Imaging with a Synthesis Telescope Authors: Bastian, Tim Bibcode: 1989ASPC....6..395B Altcode: 1989sira.conf..395B Solar Imaging with the VLA, Hardware modifications, Solar data calibration, Topics in Solar Synthesis Imaging (or: "Why Does My Solar Image Look So Awful?"), Sensitivity, The problem of calibration, The problem of confusion, The problem of u-v coverage, The problem of source variability, Solar Observing Strategies, Imaging the quiet Sun, Microwave bursts Title: Microwave Spectra and Polarization of Active Stars Authors: Slee, O. B.; Stewart, R. T.; Nelson, G. J.; Wright, Alan E.; Dulk, George A.; Bastian, T. S.; McKean, M. Bibcode: 1988ApL&C..27..247S Altcode: 1988ApL....27..247S Almost-simultaneous observations of 24 active-chromosphere stars with the VLA and the Parkes 64-m telescope at 4.9, 8.4 and 15 GHz over a 24-h interval on September 14, 1985 are reported. In all, 14 stars were detected. There is a striking difference in the power outputs and brightness temperatures of the higher-optical-luminosity stars (RS CVn, Algol-like and CAII emitters) and the low-luminosity dMe stars; this can be explained by differences in the surface areas and rotation velocities of the two groups of stars. Two three-point spectra show a broad peak in the region near 8.4 GHz, indicating a transition from optically thick to optically thin radio sources. For another three stars, two-point spectral indices are negative, indicating that their spectra peak probably well below 15 GHz; two stars with two-point positive spectral indices have higher-frequency turnovers, although perhaps below 15 GHz. Title: Radio Flares from AE Aquarii: A Low-Power Analog to Cygnus X-3?: Erratum Authors: Bastian, T. S.; Dulk, G. A.; Chanmugam, G. Bibcode: 1988ApJ...330..518B Altcode: No abstract at ADS Title: A Search for Radio Emission from Flare Stars in the Pleiades Authors: Bastian, T. S.; Dulk, G. A.; Slee, O. B. Bibcode: 1988AJ.....95..794B Altcode: The authors have used the VLA to search for radio emission from flare stars in the Pleiades. Two observational strategies were employed. First, about 1/2 deg2 of the cluster, containing ≈40 known flare stars, was mapped at 1.4 GHz at two epochs. More than 120 sources with flux densities >0.3 mJy exist on the maps. Detailed analysis shows that all but two of these sources are probably extragalactic. The two sources identified as stellar are probably not Pleiades members as judged by their proper motions; rather, based on their colors and magnitudes, they seem to be foreground G stars. The second observational strategy, where five rapidly rotating flare stars were observed at three frequencies, yielded no detections. The 0.3 mJy flux-density limit of this survey is such that only the most intense outbursts of flare stars in the solar neighborhood could have been detected if those stars were at the distance of the Pleiades. Hence, while the activity on flare stars in the Pleiades may be somewhat in excess of that on flare stars in the solar neighborhood, the "superflares" that have been occasionally reported in the Pleiades and in Orion must be very rare or nonexistent. Title: Imaging the Sun at 1.4 GHz. Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1988NRAOW..15..125B Altcode: 1988usoa.conf..125B The authors briefly describe the maximum entropy-like image reconstruction techniques employed in reconstructing images of the quiet Sun and present a representative example. Title: Variation of the quiet sun at 21 cm: 1981 - 1987. Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1988sscd.conf..386B Altcode: Using the Very Large Array (VLA), the Green Bank 91 m telescope, the Arecibo 305 m telescope, and powerful maximum entropy image reconstruction techniques, the authors have imaged the Sun at λ ≍ 21 cm during the years 1981 - 1987. While the 21 cm radio brightness distribution is in qualitative agreement with past mapping efforts, several new results have emerged. Among these, the authors have noted a systematic decrease in the quiet Sun's brightness temperature at 21 cm as the Sun declined from sunspot maximum to sunspot minumum accompanied by systematic decrease in the Sun's radius at 21 cm. Simple modeling has shown that the observed variation in the quiet Sun's brightness temperature and radius at 21 cm could have resulted from a factor of ≍2 decrease in the electron number density in the solar transition region and low corona. Title: Radio Flares from AE Aquarii: A Low-Power Analog to Cygnus X-3? Authors: Bastian, T. S.; Dulk, G. A.; Chanmugam, G. Bibcode: 1988ApJ...324..431B Altcode: The magnetic cataclysmic variable AE Aquarii has been observed at 1.5, 4.9, 15, and 22.5 GHz. The source shows temporal variations in the flux density, often with a flarelike morphology. The flux variations are at times extreme, with values ranging from 1-12 mJy at 15 GHz; the degree of variability increases with frequency. The spectrum shows a variety of short-term behavior, at times increasing as nu, at other times decreasing with nu, and at still others flat. The long-term average of the spectrum increases as nu exp 0.3-0.4. No significant degree of circular polarization was observed. The source properties can be explained as a superposition of flare events in which electrons are accelerated to relativistic energies which then emit synchrotron radiation in discrete, expanding sources. The origin of the flare events may be connected to the disruption of the accretion disk some ditance from the white dwarf primary. The radio emission of AE Aqr shows similarities to the low-level flares from Cygnus X-3. Title: The Discovery of Nonthermal Radio Emission from Magnetic Bp--Ap Stars Authors: Drake, Stephen A.; Abbott, David C.; Bastian, T. S.; Bieging, J. H.; Churchwell, E.; Dulk, G.; Linsky, Jeffrey L. Bibcode: 1987ApJ...322..902D Altcode: In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources. Title: Aperture Synthesis Observations of Solar and Stellar Radio Emission. Authors: Bastian, Timothy Stephen Bibcode: 1987PhDT........19B Altcode: The work presented in this thesis relied upon the radio astronomical instrument, The Very Large Array. The thesis is divided into three major sections. In the first I have applied maximum entropy-type image reconstruction techniques, using both single dish and iterferometer data, to generate full disk images of the Sun at a wavelength lambda ~ 21 cm. Using a set of six such images obtained during the Sun's decline from sunspot maximum to minimum, we have noted a number of previously unreported phenomena. Among these: (1) a systematic decrease in quiet Sun's brightness temperature as it declined to minimum; (2) a systematic decrease in the Sun's radius at 21 cm; (3) evidence for the evolution of polar coronal holes during the course of the solar cycle. The observed variation, though not noted previously at radio wavelengths, is entirely consistent with white light K coronagraph data. The results reported here explain the conflicting nature of a number of past observations. In the second section of the thesis, I present the results of a long term survey of magnetic cataclysmic variables (CVs). Cataclysmic variables are close binary systems which contain a white dwarf accreting mass from a late-type secondary, typically a dwarf of spectral type G, K, or M. Our survey resulted in the detection of two out of the eighteen systems observed. In the third section of the thesis, I present new results on flare stars in the solar neighborhood and in the Pleiades. We have successfully employed the technique of dynamic spectroscopy to constrain the mechanism(s) for radio flaring on other stars. In particular, we used the Very Large Array in spectral line mode to observe two intense flares on the nearby flare star UV Ceti. The second part of section three is devoted to a search for radio emission from flare stars in the Pleiades which was motivated by the evolutionary questions raised by flare stars and the Pleiades lower main sequence. Of the ~170 sources found in the Pleiades' fields, all but two were determined to be extragalactic. Neither of the two stellar radio sources is a known flare star or a Pleiades member. (Abstract shortened with permission of author.). Title: First dynamic spectra of stellar microwave flares Authors: Bastian, T. S.; Bookbinder, J. A. Bibcode: 1987Natur.326..678B Altcode: Records of radiation intensity as a function of time and frequency (dynamic spectra) have been profitably used as a probe of the Sun's corona for many years. Motivated by the possibility of using the frequency domain to constrain theoretical models of coherent microwave emission from red dwarf (dMe) flare stars, we have used the Very Large Array in spectral-line mode at 1.4 GHz to obtain the first dynamic spectra of stellar sources other than the Sun. Two very intense, highly circularly polarized, microwave outbursts were observed on the dMe flare star UV Get (L726-8B), in addition to a slowly varying, unpolarized component. One outburst was purely left circularly polarized and showed no variations as a function of frequency across the 41 MHz band, whereas the other was as much as 70% right-circularly polarized and showed distinct variations with frequency. Although the slowly varying emission is probably due to incoherent gyrosynchrotron emission, the two flaring events are the result of coherent mechanisms. We interpret the coherent emission in terms of plasma radiation and the cyclotron maser instability. Title: Stellar dynamic spectroscopy Authors: Bastian, T. S.; Dulk, G. A.; Bookbinder, J. A. Bibcode: 1987SoPh..113..289B Altcode: 1982SoPh..113..289B The dynamic spectrum, a three dimensional record of the radio intensity as a function both of time and frequency, has long been used as a probe of plasma processes in the solar corona. Beginning with the work of Wild and McCready (1950) dynamic spectroscopy has been used to distinguish between the multitude of radio wave emitting phenomena which occur in the solar corona and to infer the physical mechanisms responsible. Title: A Search for Cyclotron Maser Radiation from Substellar and Planet-like Companions of Nearby Stars Authors: Winglee, Robert M.; Dulk, George A.; Bastian, Timothy S. Bibcode: 1986ApJ...309L..59W Altcode: Several stars within 5 pc have variations in their rectilinear or Keplerian motion that suggest that they have substellar or planetlike companions. However, direct, unambiguous evidence of such companions is difficult to obtain. It is argued that such objects should commonly emit cyclotron maser radiation and that this radiation should be observable with modern radio telescopes. Its detection would confirm the presence of the companions and permit many of the properties of the stars and companions to be derived. A search was made for the cyclotron maser emission from six nearby stars with suspected companions using the VLA at frequencies of 0.33 and 1.4 GHz. None was detected. Typical observing times were 3.5 hr, and typical upper limits were 30 mJy at 0.33 GHz and 0.3 mJy at 1.4 GHz. Title: Dynamic Spectra of Microwave Outbursts on dMe Flare Stars Authors: Bastian, T. S.; Bookbinder, J. A. Bibcode: 1986BAAS...18..985B Altcode: No abstract at ADS Title: Two-Frequency Imaging of Microwave Impulsive Flares near the Solar Limb Authors: Dulk, G. A.; Bastian, T. S.; Kane, S. R. Bibcode: 1986ApJ...300..438D Altcode: Using the VLA, the authors observed two impulsive microwave and hard X-ray flares that occurred close to the solar limb on 1981 November 21 and 22. Images were obtained simultaneously at 4.9 and 15 GHz every 10 s during the 5 minutes durations of the flares. The apparently simple impulsive flares were unexpectedly complicated when imaged with arcsecond resolution: the 4.9 and 15 GHz radiation came from spatially separated sources in one flare, and there was no 4.9 GHz radiation at all in the other. The authors interpret the observations in terms of an inhomogeneous flare volume with the magnetic field strength and orientation varying with position, both transverse to and along the line of sight. The 4.9 GHz radiation of the November 22 flare probably arose mainly from thermal electrons with temperatures between 5 and 20×106K. The 15 GHz radiation of the flares on both days probably arose from electrons of E ≈ 300 keV in a weak, nonthermal tail. Title: Radio Observations of Flare Stars in the Pleiades Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1986LNP...254..256B Altcode: 1986csss....4..256B No abstract at ADS Title: Radio Emission from AM Herculis Authors: Bastian, T. S.; Dulk, G. A.; Chanmugam, G. Bibcode: 1985ASSL..116..225B Altcode: 1985rst..conf..225B Observations of the quiescent microwave emission of the magnetic cataclysmic variable AM Herculis are presented. The emission, which declined from a mean value of 0.58 mJy at 4.9 GHz to about 0.3 mJy, in rough coincidence with the entry of AM Herculis into an optical low state (mid-1983), is explained in terms of optically thick gyrosynchrotron emission. It is noted that the observation of a coherent outburst at 4.9 GHz, interpreted as the result of a cyclotron maser on the red dwarf secondary, indicates that the secondary is magnetized. Possible implications are briefly explored. Comparisons between this system and other stellar continuum radio sources are made. Title: Full disk maps of the sun at 1.4 GHz. Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1985BAAS...17R.632B Altcode: No abstract at ADS Title: Full Disk Maps of the Sun at 1.4 GHz Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1985BAAS...17..632B Altcode: No abstract at ADS Title: AM Herculis: An Outburst at 4.9 GHz Authors: Bastian, T. S.; Dulk, G. A.; Chanmugam, G. Bibcode: 1985ASSL..113..231B Altcode: 1985cvlm.proc..231B The authors report the results of radio observations of AM Her with the Very Large Array (VLA). The quiescent emission first discovered by Chanmugam and Dulk (1982) at 4.9 GHz is confirmed and upper limits to the flux density at 1.5 GHz and 15 GHz obtained. The authors also report the discovery of a remarkable outburst at 4.9 GHz which was essentially 100% circularly polarized. The outburst is probably due to an electron-cyclotron maser which operates near the red-dwarf companion in a region where the magnetic field is ≈1000 gauss. Title: Radio emission from AM Herculis : the quiescent component and an outburst. Authors: Dulk, G. A.; Bastian, T. S.; Chanmugam, G. Bibcode: 1983ApJ...273..249D Altcode: The VLA has been used to search for radio emission from the AM Her-type binaries VV Pup, EF Eri, PG 1550 + 191, CW 1103 + 354, and AN UMa, at 4.9 GHz. A remarkable 10-min outburst was detected from AM Her at 4.9 GHz, which was about 20 times more intense than the quiescent emission and was essentially 100 percent circularly polarized. It is suggested that the quiescent emission of AM Her can be accounted for by 500-keV electrons trapped in the magnetosphere of the white dwarf, provided that the electron energy spectrum is quite hard and that the spectral hardness or number density of energetic electrons increases with radius, while the outburst is probably due to an electron-cyclotron maser operating near the surface of the red dwarf companion. The implied existence of a 1000-gauss localized magnetic field and a corona on the red dwarf has consequences for mass transfer, field line interactions, and variable activity. Title: Dual Frequency Observations of Flares with the VLA Authors: Dulk, G. A.; Bastian, T. S.; Hurford, G. J. Bibcode: 1983SoPh...86..219D Altcode: We describe observations of three flares made at 5 and 15 GHz with the VLA, two subflares near the limb on 1981 November 21 and 22, and an M7.7 flare on 1981 May 8. Even though the time histories of the November flares indicated simple impulsive bursts, the VLA observed no 5 GHz radiation at all from one flare, and from the other, the 15 GHz radiation emanated from a source which was smaller, lower and displaced from the 5 GHz source. Without the spatial information, we would have derived incorrect results from the assumption that photons of different energy (both at X-ray and radio wavelengths) arose from one homogeneous volume. Title: Two-frequency imaging of impulsive microwave flares. Authors: Bastian, T. S.; Dulk, G. A. Bibcode: 1983BAAS...15..874B Altcode: No abstract at ADS Title: Gradients of galactic cosmic rays and anomalous helium to more than 23 A.U. during the increase of solar modulation in 1978-80 Authors: Bastian, T. S.; McKibben, R. B.; Pyle, K. R.; Simpson, J. A. Bibcode: 1981ICRC...10...88B Altcode: 1982ICRC...10...88B; 1981ICRC...17j..88B During the transition to solar maximum (1978-81) the radial gradient of high energy galactic cosmic rays increased slightly, while the gradients of lower energy cosmic rays and the anomalous helium decreased. It is concluded that (1) Pioneer-10 at about 23 AU was still deep in a modulation region extending to more than 50 AU for both the galactic cosmic rays and the anomalous helium component, and (2) the modulation is controlled by changes in the size/geometry of heliospheric magnetic fields and/or propagation parameters, changes associated with large solar-flare shocks in 1978 and later. Title: The Trapped Radiations of Saturn and Their Absorption by Satellites and Rings Authors: Simpson, J. A.; Bastian, T. S.; Chenette, D. L.; McKibben, R. B.; Pyle, K. R. Bibcode: 1980JGR....85.5731S Altcode: The Pioneer 11 spacecraft encounter with Saturn (closest approach September 1,1979) has resulted in the discovery of a fully developed magnetosphere with high-energy trapped radiation around Saturn, as reported in Science, 207, 400-453, 1980, by several investigators with charged-particle instruments on the spacecraft. The present paper contains in detail the final energetic charged-particle measurements and new observations obtained from the University of Chicago instrumentation on Pioneer 11, including the overall characteristics of the trapped electron, proton, and helium radiation, which was found to lie inside ~20 Saturn radii (Rs) from the planet, and the regions extending outward to beyond the planetary bow shocks and into the interplanetary medium. For analytical purposes we divided that magnetosphere into an inner magnetosphere (<5Rs), where the intensity profiles displayed the near-axial symmetry characteriscis of the sipole magnetic field alignment with the spin axis, and an outer magnetosphere whose characteristic on the sunward side inbound were significantly different from the dawn side out-bound, indicative of a possible magnetotial but with no dramatic evidence in the charged-particle data for an equatorial current sheet, as observed at Jupiter. The intensities and energy ranges of the protons and electrons were intermediate between the levels found previously at Jupiter by Pioneer 10 and 11 and at earth. Each spectra for protons and electrons and relative abundances of protons and helium nuclei are presented along with the average characteristics of particle anisotropies. At the time of encounter the magnetosphere was immersed in intense fluxes of electrons, protons, and helium nuclei of solar flare origin which are shown to penetrate from 1 Rs to 1 10 Rs into the magnetosphere, where they dominated the flux levels in the far outer magnetosphere. A corotation anisotropy has been measured at the proton energy ~1 MeV in the rotating magnetosphere after correcting the observed unidirectional anisotropy for the radial gradient of the proton flux. The principal focus of the paper is on the analysis of the trapped radiation in the inner magnetosphere, where the radiation reaches high intensity, and has a high degree of symmetry in the L shells around Saturn. Consequently, the absorption signatures in the radiation intensity profiles produced by rings and moons of Saturn can be analyzed quantitatively. Among other results the observation of the charged-particle absorption features have led to the discovery of satellite 1979 S2 at L=2.53, which corresponds with the optically detected 1979 S1. A concentration of matter probably located at a Lagrangian point in the orbital range of Mimas, and the identification of narrow rings of matter and one or more satellites inside the radiation range of the F ring dicovered by the optical-imaging investigators. It is pointed out that these discoveries will provide important tests for models of accretion of matter, satellite formation and the stability of narrow rings near planets. From the discrete character of the absorption symmetry it is shown that except for two extremely narrow intervals of Saturn's longitude, the equatorial offset of the dipole magnetic moment must be <~0.01 Rs. The inward diffusion coefficients for protons and electrons have been determined from the above absorption regions, especially at Mimas. Some questions are considered which may be resolved by the forthcoming Voyager encounters with Saturn. Title: Charged Particle Anisotropies in Saturn's Magnetosphere Authors: Bastian, T. S.; Chenette, D. L.; Simpson, J. A. Bibcode: 1980JGR....85.5763B Altcode: We report observations of anisotropies and pitch angle distributions for 0.5-1.8 MeV protons, 7-17 MeV electrons and >3.4 MeV electrons in Saturn's magnetosphere made with the University of Chicago experiments on Pioneer 11. In the outer magnetosphere (L>6) there is clear evidence for corotation of the proton flux, and the proton pitch angle distribution shows maximum flux perpendicular to the magnetic field ('pancake' distribution). Observed changes in the amplitude and shape of the pitch angle distributions suggest the existence of significant temporal variations in the outer magnetosphere. From L=6 to L=4, the proton intensity decreased by more than two orders of magnitude, and the pitch angle distribution shifted to a 'dumbbell' form (maximum flux parallel to magnetic field). The shift in pitch angle distribution most likely results from preferential absorption of large pitch angle particles by the tenuous E- ring found in the equatorial plane out to at least R=5 Rs. For L<4, the proton intensity increased inwards, implying an inner edge for the E ring at R?4 Rs. Except for regions where the flux was reduced by satellite absorption, the pitch angle distributions remained dumbbell. In absorption regions, pancake distributions were found. The observations are consistent with the suggestion by McKibben and Simpson (this issue) that inward diffusion and acceleration at Saturn may proceed primarily via large, infrequent disturbances. Electron anisotropies were measurable only for L<~4.5, and the pitch angle distributions were found to be pancake for the entire region L<4.5, suggesting that the absorbing particles in the E ring have radii that lie between the range of ~10 MeV proton and ~10 MeV electrons, or of the order of millimeters. Title: Saturnian Trapped Radiation and its Absorption by Satellites and Rings: The First Results from Pioneer 11 Authors: Simpson, J. A.; Bastian, T. S.; Chenette, D. L.; Lentz, G. A.; McKibben, R. B.; Pyle, K. R.; Tuzzolino, A. J. Bibcode: 1980Sci...207..411S Altcode: Electrons and protons accelerated and trapped in a Saturnian magnetic field have been found by the University of Chicago experiments on Pioneer 11 within 20 Saturn radii (RS) of the planet. In the innermost regions, strong absorption effects due to satellites and ring material were observed, and from ~ 4 RS inwards to the outer edge of the A ring at 2.30 RS (where the radiation is absorbed), the intensity distributions of protons (>= 0.5 million electron volts) and electrons (2 to 20 million electron volts) were axially symmetric, consistent with a centered dipole aligned with the planetary rotation axis. The maximum fluxes observed for protons (>35 million electron volts and for electrons >3.4 million electron volts) were 3 × 104 and 3 × 106 per square centimeter per second, respectively. Absorption of radiation by Mimas provides a means of estimating the radial diffusion coefficient for charged particle transport. However, the rapid flux increases observed between absorption features raise new questions concerning the physics of charged particle transport and acceleration. An absorption feature near 2.5 RS has led to the discovery of a previously unknown satellite with a diameter of [Note: Equation omitted. See the image of page 411 for this equation.] kilometers, semimajor axis of 2.51 RS, and eccentricity of 0.013. Radiation absorption features that suggest a nonuniform distribution of matter around Saturn have also been found from 2.34 to 2.36 RS, near the position of the F ring discovered by the Pioneer imaging experiment. Beneath the A,B, and C rings we continued to observe a low flux of high-energy electrons. We conclude that the inner Saturn magnetosphere, because of its near-axial symmetry and the many discrete radiation absorption regions, offers a unique opportunity to study the acceleration and transport of charged particles in a planetary magnetic field. Title: The Radial Intensity Gradients for Cosmic Rays and the Anomalous Helium from Pioneer 10 and 11 Authors: Bastian, T. S.; McKibben, R. B.; Pyle, K. R.; Simpson, J. A. Bibcode: 1979ICRC...13..405B Altcode: 1979ICRC...16m.405B No abstract at ADS Title: Recurrent Modulation of Galactic Cosmic Rays and the Anomalous Helium Authors: Bastian, T. S.; McKibben, R. B.; Simpson, J. A. Bibcode: 1979ICRC...12..324B Altcode: 1980ICRC...12..324B; 1979ICRC...16l.324B The observations of 27 day variations in the intensity of low energy cosmic ray protons (29-67 MeV) and anomalous helium (11-20 MeV/nucleon) are reported. These observations were made with instruments on IMP-8 in the earth orbit on Pioneer 11 at heliographic latitudes up to 16 deg and on Pioneer 10 at heliocentric distances of from 4 to 14 AU. 27 day variations are observed at all locations, most strongly in the anomalous helium, and reflect the very large scale structure of the interplanetary medium. Intensity minima are most often associated with high speed solar wind streams, but the physical mechanism producing the variations is not clear. Title: The Radial Intensity Gradients for Cosmic Rays and the Anomalous Helium from Pioneer 10 and 11 Authors: Bastian, T. S.; McKibben, R. B.; Pyle, K. R.; Simpson, J. A. Bibcode: 1979ICRC....5..338B Altcode: 1979ICRC...16e.338B; 1980ICRC....5..338B This report extends and updates previous studies of the heliocentric radial gradients of the integral flux of cosmic rays (E greater than 70 MeV) and of differential fluxes of protons and helium nuclei in the approximate energy windows 11-20 and 30-70 MeV/n to include data taken through the end of 1978 when Pioneer 10 had reached a distance of 18 AU from the sun, and Pioneer 11 was at a distance of 8.4 AU. Small positive gradients are found for all species considered, although the actual values of the gradients may vary as a function of time. The data suggest that the modulation region has a radial extent large compared to 18 AU. The anomalous helium component was observed at all radial distances, and is found to have a much higher flux in the outer solar system than near 1 AU. Title: Variations in the Intensity of Galactic Cosmic Rays and the Anomalous Helium as a Function of Solar Latitude Authors: Bastian, T. S.; McKibben, R. B.; Pyle, K. R.; Simpson, J. A. Bibcode: 1979ICRC...12..318B Altcode: 1979ICRC...16l.318B; 1980ICRC...12..318B Pioneer 11 rose to a heliographic latitude of 16 deg in the course of its trajectory from Jupiter to Saturn. From analysis of the fluxes of low energy protons and anomalous helium measured by Pioneer 11 as a function of latitude, it was found that the data are consistent with latitude gradients of 2% per degree for the anomalous helium and 1% per degree for 29-67 MeV protons.