Author name code: pallavicini ADS astronomy entries on 2022-09-14 author:"Pallavicini, Roberto" ------------------------------------------------------------------------ Title: A new arrival at the VLT: the commissioning of the X-shooter spectrograph . Authors: Di Marcantonio, P.; Santin, P.; Zacchei, A.; De Caprio, V.; Riva, M.; Spanò, P.; Zerbi, F. M.; de Ugarte Postigo, A.; Pallavicini, R.; Vernet, J.; Dekker, H.; D'Odorico, S.; X-shooter Team Bibcode: 2010MSAIS..14..230D Altcode: Starting from October 2009 a new ESO/VLT instrument will be offered to the astronomical community worldwide: the X-shooter spectrograph. This first second-generation VLT instrument is being built as a collaborative effort of several European Institutes (with INAF playing a prominent role, co-PI R. Pallavicini) and ESO.

The main features of X-shooter are high efficiency and the unique capability to cover in one "shot" a very broad spectral range, from U to K band, making the Instrument appealing for cutting-edge science. The present paper reports on the commissioning periods just held in Paranal and on the efforts made to meet all foreseen stringent requirements. Title: TW Hya: A Simultaneous Optical and X-Ray Campaign Authors: Dupree, Andrea K.; Brickhouse, N. S.; Cranmer, S. R.; Irwin, J.; Bessell, M. S.; Crause, L. A.; Lawson, W. A.; Luna, J.; Mallik, S. V.; Pallavicini, R.; Schuler, S. C. Bibcode: 2010AAS...21542904D Altcode: 2010BAAS...42..350D A world-wide campaign of spectroscopy and photometry was carried out for 17 days in February- March 2007 (JD 2454147 - 2454164) in support of an extended CHANDRA HETG observation of the nearby accreting T Tauri star: TW Hya (CD -34 7151).This program included photometry from Super WASP-South and SAAO. Spectroscopy was obtained from TNG/SARG, Vainu Bappu Observatory, SAAO, MSSO, Magellan/MIKE, Pico do Dios, and Gemini-S. The photometric period of the star derived from the periodogram of WASP-S photometry during this time was 4.76+/-0.01 d. Hα fluxes do not appear to correlate well with the photometric period nor the total X-ray flux, perhaps influenced by flaring that occurred in both optical and X-ray sequences during this time. Hα profiles from TW Hya can change dramatically during a night, with substantial systematic changes in the wind opacity signaled both in Hα and the He I 10830 Å transition. Related posters by Schneider et al., and Wolk et al. address the optical veiling and X-ray spectrum of TW Hya from this program.

Research supported in part by NASA and the Smithsonian Astrophysical Observatory. Title: Metallicity of low-mass stars in Orion Authors: D'Orazi, V.; Randich, S.; Flaccomio, E.; Palla, F.; Sacco, G. G.; Pallavicini, R. Bibcode: 2009A&A...501..973D Altcode: 2009arXiv0905.1840D Context: Determining the metal content of low-mass members of young associations provides a tool that addresses different issues, such as triggered star formation or the link between the metal-rich nature of planet-host stars and the early phases of planet formation. The Orion complex is a well known example of possible triggered star formation and is known to host a rich variety of proto-planetary disks around its low-mass stars. Available metallicity measurements yield discrepant results.
Aims: We analyzed FLAMES/UVES and Giraffe spectra of low-mass members of three groups/clusters belonging to the Orion association. Our goal is the homogeneous determination of the metallicity of the sample stars, which allows us to look for [Fe/H] differences between the three regions and for the possible presence of metal-rich stars.
Methods: Nine members of the ONC and one star each in the λ Ori cluster and OB1b subgroup were analyzed. After the veiling determination, we retrieved the metallicity by means of equivalent widths and/or spectral synthesis using MOOG.
Results: We obtain an average metallicity for the ONC [{Fe/H}] =-0.01± 0.04. No metal-rich stars were detected and the dispersion within our sample is consistent with measurement uncertainties. The metallicity of the λ Ori member is also solar, while the OB1b star has an [Fe/H] significantly below the ONC average. If confirmed by additional [Fe/H] determinations in the OB1b subgroup, this result would support the triggered star formation and the self-enrichment scenario for the Orion complex.

Based on observations collected at Paranal Observatory, ESO (Chile). Programs 072.D-0019, 074.C-0757, 076.D-0136, 076.C-0145. Title: X-ray properties of the young open cluster around λ Orionis Authors: Franciosini, E.; Sacco, G. G.; Pallavicini, R. Bibcode: 2009AIPC.1094..592F Altcode: 2009csss...15..592F We present XMM-Newton observations of the young (~1-8 Myr) cluster around the hot (O8 III) star λ Orionis. We have obtained both EPIC imaging data of the cluster and a high-resolution RGS spectrum of the hot star. We have detected 167 X-ray sources, of which 56 are identified with cluster members, and 24 are identified with new photometric candidates. We present the results of the EPIC spatial and spectral analysis of the cluster sources, and compare them with those obtained for the ``twin'' σ Ori cluster. Title: X-Shooter: A Medium-resolution, Wide-Band Spectrograph for the VLT Authors: Kaper, L.; D'Odorico, S.; Hammer, F.; Pallavicini, R.; Kjaergaard Rasmussen, P.; Dekker, H.; Francois, P.; Goldoni, P.; Guinouard, I.; Groot, P. J.; Hjorth, J.; Horrobin, M.; Navarro, R.; Royer, F.; Santin, P.; Vernet, J.; Zerbi, F. Bibcode: 2009ASSP....9..319K Altcode: 2008arXiv0803.0609K; 2009svlt.conf..319K X-shooter is the first second-generation instrument for the ESO Very Large Telescope, and will be installed in 2008. It is intended to become the most powerful optical & near-infrared medium-resolution spectrograph in the world, with a unique spectral coverage from 300 to 2500 nm in one shot. The X-shooter consortium members are from Denmark, France, Italy, The Netherlands and ESO. Title: X-SHOOTER: a unique opportunity for the Italian community . Authors: Spanò, P.; Zerbi, F. M.; Santin, P.; Pallavicini, R.; De Caprio, V.; Riva, M.; Tintori, M.; Di Marcantonio, P.; Zacchei, A.; Molinari, E.; Riva, A.; Cosentino, R.; Bruno, P.; Dekker, H.; D'Odorico, S. Bibcode: 2009MmSAI..80...44S Altcode: X-Shooter is a high-efficiency, wide band (U to K), intermediate resolution (4,000-14,000), single-object spectrograph for the Very Large Telescope (VLT). To optimize efficiency and increase wavelength coverage, light is split by dichroics into three arms: UV-Blue, Visible, and Near Infrared. It will be the first second generation instrument of the VLT instrument suite. Currently in the last phase of integration, X-Shooter will see first light in the last quarter of 2008. This paper highlights first results obtained in our facilities. Title: FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori Authors: Sacco, G. G.; Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2008A&A...488..167S Altcode: 2008arXiv0805.2914S Aims: We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters σ Ori and λ Ori.
Methods: We observed 98 and 49 low-mass (0.2-1.0 M⊙) stars in σ Ori and λ Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R∼ 17 000) HR15N grating (6470-6790 Å). We used radial velocities, Li and Hα to establish cluster membership and Hα and other optical emission lines to analyze the accretion properties of members.
Results: We identified 65 and 45 members of the σ Ori and λ Ori clusters, respectively, and discovered 16 new candidate binary systems. We also measured rotational broadening for 20 stars and estimated the mass accretion rates in 25 stars of the σ Ori cluster, finding values between 10-11 and 10-7.7~M⊙ yr-1 and in 4 stars of the λ Ori cluster, finding values between 10-11 and 10-10.1~M⊙ yr-1. Comparing our results with the infrared photometry obtained by the Spitzer satellite, we find that the fraction of stars with disks and the fraction of active disks is larger in the σ Ori cluster (52±9% and 78±16%) than in λ Ori (28±8% and 40±20%).
Conclusions: The different disk and accretion properties of the two clusters could be due either to the effect of the high-mass stars and the supernova explosion in the λ Ori cluster or to different ages of the cluster populations. Further observations are required to draw a definitive conclusion.

Based on Data collected at the ESO Very Large Telescope, Paranal Observatory, Chile [programs 074.D-0136(A) and 076.C-0125(A)].

Tables 1, 2 and 4-7 are only available in electronic form at http://www.aanda.org Title: Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261 and Melotte 66 Authors: Sestito, P.; Bragaglia, A.; Randich, S.; Pallavicini, R.; Andrievsky, S. M.; Korotin, S. A. Bibcode: 2008A&A...488..943S Altcode: 2008arXiv0807.2313S Context: Galactic open clusters are since long recognized as one of the best tools for investigating the radial distribution of iron and other metals.
Aims: We employed FLAMES at VLT to collect UVES spectra of bright giant stars in a large sample of open clusters, spanning a wide range of Galactocentric distances, ages, and metallicities. We present here the results for four clusters: Berkeley 20 and Berkeley 29, the two most distant clusters in the sample; Collinder 261, the oldest and the one with the minimum Galactocentric distance; Melotte 66.
Methods: Equivalent width analysis was carried out using the spectral code MOOG and Kurucz model atmospheres to derive abundances of Fe, Al, Mg, Si, Ca, Ti, Cr, Ni, Ba; non-LTE Na abundances were derived by direct line-profile fitting.
Results: We obtain subsolar metallicities for the two anticenter clusters Be 20 ([Fe/H] = -0.30, rms = 0.02) and Be 29 ([Fe/H] = -0.31, rms = 0.03), and for Mel 66 ([Fe/H] = -0.33, rms = 0.03), located in the third Galactic quadrant, while Cr 261, located toward the Galactic center, has higher metallicity ([Fe/H] = +0.13, rms = 0.05 dex). The α-elements Si, Ca and Ti, and the Fe-peak elements Cr and Ni are in general close to solar; the s-process element Ba is enhanced. Non-LTE computations of Na abundances indicate solar scaled values, suggesting that the enhancement in Na previously determined in giants in open clusters could be due to neglected non-LTE effects.
Conclusions: Our results support the presence of a steep negative slope of the Fe radial gradient up to about 10-11 kpc from the Galactic center, while in the outer disk the [Fe/H] distribution seems flat. All the elemental ratios measured are in very good agreement with those found for disk stars of similar metallicity and no trend with Galactocentric distance seems to be present.

Based on observations collected at ESO telescopes under GTO programmes 71.D-0065, 072.D-0019, and GO programme 076.D-0220. Tables 4-7 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/488/943 Title: VizieR Online Data Catalog: Low-mass stars in {sigma} Ori and {lambda} Ori (Sacco+, 2008) Authors: Sacco, G. G.; Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2008yCat..34880167S Altcode: Observations were carried out using the fiber-fed multi-object spectrograph FLAMES (Fiber Large Array Multi Element Spectrograph), mounted on the UT2 telescope at the VLT and operated in the MEDUSA mode (132 fibers, each with an aperture of 1.2" on the sky).

Observations were performed in service mode and were divided into separate runs of 1h duration each, including instrument overheads. The {sigma} Ori cluster was observed in 6 runs in October and December 2004, while {lambda} Ori was observed in 8 runs in October and November 2005.

(5 data files). Title: Building up a database of spectro-photometric standard stars from the UV to the near-IR: a status report Authors: Vernet, J.; Kerber, F.; Saitta, F.; Mainieri, V.; D'Odorico, S.; Lidman, C.; Mason, E.; Bohlin, R. C.; Rauch, T.; Ivanov, V. D.; Smette, A.; Walsh, J. R.; Fosbury, R. A. E.; Goldoni, P.; Groot, P.; Hammer, F.; Horrobin, M.; Kaper, L.; Kjaergaard-Rasmussen, P.; Pallavicini, R.; Royer, F. Bibcode: 2008SPIE.7016E..1GV Altcode: 2008SPIE.7016E..46V We present a project aimed at establishing a set of 12 spectro-photometric standards over a wide wavelength range from 320 to 2500 nm. Currently no such set of standard stars covering the near-IR is available. Our strategy is to extend the useful range of existing well-established optical flux standards into the near-IR by means of integral field spectroscopy with SINFONI at the VLT combined with state-of-the-art white dwarf stellar atmospheric models. As a solid reference, we use two primary HST standard white dwarfs. This ESO "Observatory Programme" has been collecting data since February 2007. The analysis of the data obtained in the first year of the project shows that a careful selection of the atmospheric windows used to measure fluxes and the stability of SINFONI make it possible to achieve an accuracy of 3- 6% depending on the wavelength band and stellar magnitude, well within our original goal of 10% accuracy. While this project was originally tailored to the needs of the wide wavelength range (320-2500 nm) of X-shooter on the VLT, it will also benefit any other near-IR spectrographs, providing a huge improvement over existing flux calibration methods. Title: VizieR Online Data Catalog: Abundances of giants in four Galactic clusters (Sestito+, 2008) Authors: Sestito, P.; Bragaglia, A.; Randich, S.; Pallavicini, R.; Andrievsky, S. M.; Korotin, S. A. Bibcode: 2008yCat..34880943S Altcode: Spectra for 2 to 6 giant stars in Be 20, Be 29, Cr 261, and Mel 66 were obtained with FLAMES@VLT using the fiber link to UVES. Abundances of Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba were derived using equivalent widths (and synthesis for Na), model atmospheres and input atmospheric parameters based on photometry.

For each member star in the four clusters we give the measured EWs.

(2 data files). Title: Building-Up a Database of Spectro-Photometric Standard Stars from the Ultraviolet to the Near-Infrared Authors: Vernet, J.; Kerber, F.; D'Odorico, S.; Bohlin, R.; Ivanov, V.; Lidman, C.; Mason, E.; Rauch, T.; Saitta, F.; Smette, A.; Walsh, J.; Fosbury, R.; Goldoni, P.; Groot, P.; Hammer, F.; Horrobin, M.; Kaper, L.; Kjaergaard-Rasmussen, P.; Pallavicini, R.; Royer, F. Bibcode: 2008eic..work..153V Altcode: No abstract at ADS Title: Chemical abundances of T Tauri stars in star forming regions Authors: D'Orazi, V.; Randich, S.; Palla, F.; Flaccomio, E.; Pallavicini, R.; Sacco, G. G. Bibcode: 2008MmSAI..79..695D Altcode: Accretion disks of T Tauri stars are commonly assumed to be the site where planets form. At the same time, surveys of old planet-host stars -the end product of planet formation- have shown that gas giant planets preferentially form around metal-rich stars. A critical question, with important implications for our understanding of planet formation, is therefore whether metal-rich T Tauri stars exist. In this context, we have started a project aimed at the determination of the metallicity of T Tauri stars in different star forming regions (SFRs): we present the results of a pilot study focusing on a few members of the Orion Nebula Cluster (ONC) and Sigma and Lambda Orionis clusters. Title: Coming Soon on Stage: X-shooter Authors: Vernet, Joel; Dekker, Hans; D'Odorico, Sandro; Pallavicini, Roberto; Kjörgaard Rasmussen, Per; Kaper, Lex; Hammer, François; Groot, Paul; X-Shooter Team Bibcode: 2007Msngr.130....5V Altcode: X-shooter is a single-target, intermediate-resolution, wide-wavelength-range (UV- to K-band) spectrograph. It will be the first of the second-generation VLT instruments to go to the telescope. First light is planned in the second half of 2008. Here we give an update on the integration status and on the expected performance. Title: XMM-Newton observation of the classical T Tauri star SU Aurigae and the surrounding field Authors: Franciosini, E.; Scelsi, L.; Pallavicini, R.; Audard, M. Bibcode: 2007A&A...471..951F Altcode: Aims: We investigate the properties of the X-ray emitting plasma of the classical T Tauri star SU Aurigae and of other sources in the field of view.
Methods: We use XMM-Newton to obtain a high-resolution RGS spectrum of SU Aur as well as EPIC imaging data and low-resolution spectra of the star and of other X-ray sources in the surrounding field. We reconstruct the emission measure distribution of SU Aur from the RGS spectrum using a line-based method, and we perform multi-temperature fits of the MOS spectra of the strongest sources both for the full observation and for selected time intervals to study their spectral variability.
Results: The emission from SU Aur is highly variable, showing three flares during the observation. The MOS spectra indicate a very hot corona, with significant emissivity up to ~40 MK in quiescence, and temperatures up to 140 MK during flares. The emission measure distribution derived from the RGS spectrum peaks at log T = 7.0; any contribution to the X-ray luminosity from cool plasma (T∼ 2 MK) cannot exceed 5% of the total emission. Abundances are ~0.3-0.6 solar with the exception of Mg and Ne that are solar. Spatial analysis of the full EPIC field results in the detection of 104 X-ray sources, 6 of which are associated with the known Taurus-Auriga members in the field of view (including SU Aur).
Conclusions: The characteristics of the X-ray emission of SU Aur are very similar to those of young active late-type stars, with a very hot corona and flares, suggesting magnetic activity as the origin of most of the X-ray emission, rather than accretion.

Table 2 is only available in electronic form at http://www.aanda.org Title: Tracing mixing in stars: new beryllium observations of the open clusters NGC 2516, Hyades, and M 67 Authors: Randich, S.; Primas, F.; Pasquini, L.; Sestito, P.; Pallavicini, R. Bibcode: 2007A&A...469..163R Altcode: 2007arXiv0705.2330R Context: Determinations of beryllium abundance in stars, together with lithium, provide a key tool to investigate the so far poorly understood extra-mixing processes at work in stellar interiors.
Aims: We measured Be in three open clusters, complementing existing Be surveys, and aiming at gathering a more complete empirical scenario of the evolution of Be as a function of stellar age and temperature.
Methods: We analyzed VLT/UVES spectra of members of NGC 2516, the Hyades, and M 67 to determine their Be and Li abundances. In the first two clusters we focused on stars cooler than 5400 K, while the M 67 sample includes stars warmer than 6150 K, as well as two subgiants and two blue stragglers. We also computed the evolution of Be for a 0.9 M⊙ star based on standard evolutionary models.
Results: We find different behaviours for stars in different temperature bins and ages. Stars warmer than 6150 K show Be depletion and follow a Be vs. Li correlation, while Be is undepleted in stars in the 6150{-}5600 K range. NGC 2516 members cooler than 5400 K have not depleted any Be, while older Hyades of similar temperature show some depletion. Be is severely depleted in the subgiants and blue stragglers.
Conclusions: The results for warm stars are in agreement with those of previous studies, supporting the hypothesis that mixing in this temperature regime is driven by rotation. The same holds for the two subgiants that have evolved from the “Li gap”. This mechanism is instead not the dominant one for solar-type stars. We show that Be depletion of cool Hyades cannot simply be explained by the effect of increasing depth of the convective zone. Finally, the different Be content of the two blue stragglers suggests that they have formed by two different processes (i.e., collisions vs. binary merging).

Based on observations collected at ESO-VLT, Paranal Observatory, Chile, Programme numbers 65.L-0427, 68.D-0491, 69.D-0454. Title: Old Stars in Young Clusters: Lithium-depleted Low-Mass Stars of the Orion Nebula Cluster Authors: Palla, F.; Randich, S.; Pavlenko, Ya. V.; Flaccomio, E.; Pallavicini, R. Bibcode: 2007ApJ...659L..41P Altcode: We measured lithium in a sample of low-mass stars (~0.1-0.3 Msolar) of the Orion Nebula cluster. We find evidence for significant Li depletion in four high-probability members, corresponding to nuclear ages between ~15 and 30 Myr. In two cases, there is excellent agreement between the mass and age based on models of Li burning and those derived from the H-R diagram, reinforcing our early findings. For the two other stars, the nuclear age is significantly larger than the isochronal one. Several Li-depleted stars display accretion activity, veiling, and emission lines. We discuss empirical evidence in favor of the old nuclear age and the implications on the star formation history of the Orion cluster.

Based on data collected at ESO-VLT, Paranal Observatory, Chile [ID 074.C-0757(A)]. Title: Lithium-depleted stars in the young σ Orionis cluster Authors: Sacco, G. G.; Randich, S.; Franciosini, E.; Pallavicini, R.; Palla, F. Bibcode: 2007A&A...462L..23S Altcode: 2006astro.ph.11880S Context: Knowledge of the age distribution of stars in young clusters and associations is crucial to constrain models of star formation. HR diagrams of different young clusters and associations suggest the presence of age spreads, but the influence of errors on the derived ages is still largely debated. Determination of lithium abundances in low-mass stars represents an alternative and robust way to infer stellar ages.
Aims: We measured lithium in a sample of low mass members of the young (4-5 Myr) σ Ori cluster with the main goal of investigating its star formation history.
Methods: Using the FLAMES multi-object spectrograph on VLT/UT2, we obtained spectra of 98 candidate cluster members. The spectra were used to determine radial velocities, to infer the presence of Hα emission, and to measure the strength of the Li i 670.8 nm absorption line.
Results: Using radial velocities, Hα and Li, together with information on X-ray emission, we identified 59 high probability cluster members. Three of them show severe Li depletion. The nuclear ages inferred for these highly depleted stars exceed 10-15 Myr; for two of them these values are in good agreement with the isochronal age, while for the third star the nuclear age exceeds the isochronal one.

Based on data collected at the ESO Very Large Telescope, Paranal Observatory, Chile [program 074.D-0136(A)]. Title: Metallicity of low-mass members of the Orion Nebula Cluster. Authors: D'Orazi, V.; Randich, S.; Palla, F.; Flaccomio, E.; Pallavicini, R. Bibcode: 2007MmSAI..78..656D Altcode: We present the results of a pilot study aimed at measuring the metallicity of seven low mass members of the Orion Nebula Cluster (ONC). We find a very close to solar metallicity for six of the sample stars, while one star might have an over-solar metallicity, with [Fe/H] = 0.3 ±0.07. Title: The X-shooter Spectrograph: A Second Generation Instrument for the VLT Authors: Covino, Stefano; Zerbi, Filippo Maria; Pallavicini, Roberto; Conconi, Paolo; Cosentino, Rosario; DeCaprio, Vincenzo; de Ugarte Postigo, Antonio; Di Marcantonio, Paolo; Riva, Marco; Santin, Paolo; Spanó, Paolo; Zacchei, A. Bibcode: 2006ChJAS...6a.361C Altcode: 2006ChJAA...6S.361C; 2006ChJAS...6..361C X-shooter is a spectrograph designed to feed the Cassegrain focus of the VLT. It may cover in a single exposure the spectral range from the UV to the H band with possible extension to the K band. The instrument is constituted by three arms, blue, visible and near-infarred, with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolution (R = 4000-14 000), sufficient to address quantitatively a vast number of astrophysical applications. Approved as second generation instrument for the VLT, X-shooter is expected to be available to the community in the first part of the year 2008. Title: VizieR Online Data Catalog: XMM observations of sigma Ori cluster (Franciosini+, 2006) Authors: Franciosini, E.; Pallavicini, R.; Sanz-Forcada, J. Bibcode: 2006yCat..34460501F Altcode: XMM-Newton observations of the sigma Ori cluster, centered on the hot star sigma Ori AB, were carried out as part of the Guaranteed Time of one of us (R.P.) using both the EPIC MOS and PN cameras and the RGS instrument. The observation (ID 0101440301) started at 21:47 UT on March 23, 2002 and ended at 9:58 UT on March 24, 2002, for a total duration of 43ks. The EPIC cameras were operated in Full Frame mode using the thick filter.

(3 data files). Title: X-shooter UV- to K-band intermediate-resolution high-efficiency spectrograph for the VLT: status report at the final design review Authors: D'Odorico, Sandro; Dekker, Hans; Mazzoleni, Ruben; Vernet, Joel; Guinouard, Isabelle; Groot, Paul; Hammer, Francois; Rasmussen, Per Kjaergaard; Kaper, Lex; Navarro, Ramon; Pallavicini, Roberto; Peroux, Celine; Zerbi, Filippo Maria Bibcode: 2006SPIE.6269E..33D Altcode: 2006SPIE.6269E..98D X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs where it will start to operate in 2008. The instrument covers in a single exposure the spectral range from the UV to the K' band. It is designed to maximize the sensitivity in this spectral range through the splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolutions (R=4000-14000, depending on wavelength and slit width) with fixed echelle spectral format (with prism cross-dispersers) in the three arms. The project has completed the Final Design Review in June 2006. In this status report, the overall concept is summarized and new results on the dichroics, the active flexure compensation system, the operation modes and the expected performance are given. The instrument is being built by a Consortium of Institutes from Denmark, France, Italy and the Netherlands in collaboration with ESO. When in operation, its wide spectral range observing capability will be unique at very large telescopes. Title: Element abundances of unevolved stars in the open cluster M 67 Authors: Randich, S.; Sestito, P.; Primas, F.; Pallavicini, R.; Pasquini, L. Bibcode: 2006A&A...450..557R Altcode: 2006astro.ph..1239R Context: .The star-to-star scatter in lithium abundances observed among otherwise similar stars in the solar-age open cluster M 67 is one of the most puzzling results in the context of the so called "lithium problem". Among other explanations, the hypothesis has been proposed that the dispersion in Li is due to star-to-star differences in Fe or other element abundances which are predicted to affect Li depletion.
Aims: .The primary goal of this study is the determination of the metallicity ([Fe/H]), α- and Fe-peak abundances in a sample of Li-poor and Li-rich stars belonging to M 67, in order to test this hypothesis. By comparison with previous studies, the present investigation also allows us to check for intrinsic differences in the abundances of evolved and unevolved cluster stars and to draw more secure conclusions on the abundance pattern of this cluster.
Methods: .We have carried out an analysis of high resolution UVES/VLT spectra of eight unevolved and two slightly evolved cluster members using MOOG and measured equivalent widths. For all the stars we have determined [Fe/H] and element abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr and Ni.
Results: .We find an average metallicity [Fe/H] = 0.03±0.01, in very good agreement with previous determinations. All the [ X/Fe] abundance ratios are very close to solar. The star-to-star scatter in [Fe/H] and [ X/Fe] ratios for all elements, including oxygen, is lower than 0.05 dex, implying that the large dispersion in lithium among cluster stars is not due to differences in these element abundances. We also find that, when using a homogeneous scale, the abundance pattern of unevolved stars in our sample is very similar to that of evolved stars, suggesting that, at least in this cluster, RGB and clump stars have not undergone any chemical processing. Finally, our results show that M 67 has a chemical composition that is representative of the solar neighborhood.
Title: XMM-Newton observations of the σ Orionis cluster. II. Spatial and spectral analysis of the full EPIC field Authors: Franciosini, E.; Pallavicini, R.; Sanz-Forcada, J. Bibcode: 2006A&A...446..501F Altcode: 2005astro.ph.10209F We present the results of an XMM-Newton observation of the young (∼ 2{-}4 Myr) cluster around the hot star σ Orionis. In a previous paper we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected eleven new possible candidate members from the 2MASS catalogue. We find that late-type stars have a median log L_X/L_bol ∼ -3.3, i.e. very close to the saturation limit. We detected significant variability in ∼ 40% of late-type members or candidates, including 10 flaring sources; rotational modulation is detected in one K-type star and possibly in another 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1∼ 0.3{-}0.8 keV and T_2∼ 1{-}3 keV, with subsolar abundances Z∼ 0.1{-}0.3 Z_⊙, similar to what is found in other star-forming regions and associations. We find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T Tauri stars. Title: Current problems of stellar astrophysics in optical spectroscopy . Authors: Pallavicini, R.; Randich, S. Bibcode: 2006MSAIS...9..189P Altcode: We present the highlights of current programs in stellar optical spectroscopy carried out with 8-10m class telescopes as well as with smaller telescopes. Topics briefly discussed here include: 1. light element abundances and their cosmological implications; 2. search for Population III stars and spectroscopy of extremely metal deficient stars; 3. abundances of different stellar populations in the Galaxy; 4. spectroscopy of resolved stars in Local Group galaxies; 5. Li and Be abundances and internal mixing in stars; 6. spectroscopy of very-low mass stars and brown dwarfs; 7. radial velocity search of extrasolar planets; 8. stellar oscillations and asteroseismology; 9. stellar magnetic activity and Doppler imaging of stellar surface features. Title: Multi-Object Spectroscopy of Open Clusters with FLAMES: Preliminary GTO Results Authors: Pallavicini, R.; Spanò, P.; Prisinzano, L.; Randich, S.; Sestito, P. Bibcode: 2006cams.book..181P Altcode: We report on preliminary results of VLT/FLAMES observations of the old open clusters NGC 2506, Mel 66 and Cr 261, obtained as part of our Guaranteed Time on this instrument. We focus in particular on the very old cluster Cr 261, one of the oldest open clusters in the Galaxy. We compare the derived Li abundances with those of other old clusters, and we discuss briefly Li depletion on the main-sequence from the age of the Hyades to ~8 Gyr. Title: XMM-Newton spectroscopy of stars in open clusters and star forming regions Authors: Pallavicini, R.; Franciosini, E.; Maggio, A.; Scelsi, L.; Sanz-Forcada, J. Bibcode: 2006AdSpR..38.1509P Altcode: We discuss observations of open clusters and star forming regions obtained with the RGS and EPIC instruments on board XMM-Newton. These observations provide a powerful tool to investigate the temperature structure, emission measure distribution and elemental abundances of stars from the pre-main sequence phase to post-main sequence evolution. We report in particular on EPIC and RGS spectroscopy of hot and cool stars in the very young cluster around σ Orionis, of two stars in the Hyades (the main-sequence star VB 50 and the clump giant VB 71) and of two pre-main sequence stars in Taurus Auriga (the classical T Tauri star SU Aur and the weak-lined T Tauri star HD 283572). The implications of these observations for models of magnetic activity in late-type stars, of wind emission in early-type stars, and of X-ray production in the early stages of stellar evolution are briefly discussed. Title: XMM-Newton Observations of the Taurus-Auriga Star-Forming Region: the Fields around SU Aur Authors: Franciosini, E.; Pallavicini, R.; Scelsi, L. Bibcode: 2006ESASP.604...77F Altcode: 2006xru..conf...77F No abstract at ADS Title: The X-shooter Spectrograph for the VLT . Authors: Zerbi, F. M.; Pallavicini, R.; Conconi, P.; Cosentino, R.; De Caprio, V.; de Ugarte Postigo, A.; Di Marcantonio, P.; Riva, M.; Santin, P.; Spanó, P.; Zacchei, A. Bibcode: 2006MSAIS...9..419Z Altcode: X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs. It covers in a single exposure the spectral range from the UV to the H band with a possible extension into part of the K band. In order to maximize the sensitivity in this spectral range the beam is splitted in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolution (R=4000-14000) sufficient to address quantitatively a vast number of astrophysical applications. Approved as second generation instrument for the VLT, X-shooter will be available to the community in the first part of the year 2008 Title: Lithium and Metallicity in the Intermediate Age Open Cluster NGC 752 Authors: Sestito, P.; Randich, S.; Pallavicini, R. Bibcode: 2006cams.book..179S Altcode: We have determined Li abundances (log n(Li)) and metallicity ([Fe/H]) in the ~2 Gyr old open cluster NGC 752. The cluster turned out to have a nearly solar Fe content, at variance with previous reports of sub-solar metallicity. The Li distribution vs. effective temperature (T eff) of NGC 752 is very similar to those of IC 4651 and NGC 3680, which have similar age but dierent [Fe/H]. Moreover, similarly to the other two clusters, NGC 752 does not show a Li scatter as large as that observed in the solar age cluster M 67. In general, the Li vs. T eff distribution does not appear to depend significantly on metallicity, as shown by the comparison of NGC 752 with IC 4651 and NGC 3680; however, a weak dependence on metallicity might be present when comparing the three clusters in the [log n(Li), mass] plane. Title: FLAMES Observations of Old Open Clusters: Constraints on the Evolution of the Galactic Disc and Mixing Processes in Stars Authors: Randich, Sofia; Bragaglia, Angela; Pastori, Livio; Prisinzano, Loredana; Sestito, Paola; Spano, Paolo; Villanova, Sandro; Carraro, Giovanni; Carretta, Eugenio; Romano, Donatella; Zaggia, Simone; Pallavicini, Roberto; Pasquini, Luca; Primas, Francesca; Tagliaferri, Gianpiero; Tosi, Monica Bibcode: 2005Msngr.121...18R Altcode: Open clusters are populous groups of stars whose members have the same age, chemical composition, and distance from the Sun. Hence, they provide homogeneous samples to investigate several important issues related to stellar and Galactic evolution. We present here an overview and preliminary results of a VLT/FLAMES programme aimed at a detailed study of seven old clusters. Our two main goals are the determination of the radial abundance gradients in the Galactic disc and their evolution with age, and the investigation of internal mixing processes in stars similar to our Sun. Title: Age Spreads in Star-forming Regions: The Lithium Test in the Orion Nebula Cluster Authors: Palla, Francesco; Randich, Sofia; Flaccomio, Ettore; Pallavicini, Roberto Bibcode: 2005ApJ...626L..49P Altcode: 2005astro.ph..5162P We present the initial results of a study of the surface lithium abundance in a sample of low-mass members (M*~0.4-1.0 Msolar) of the Orion Nebula Cluster (ONC) that provide an independent clock to estimate stellar ages. We report the discovery of a significant depletion of lithium in four stars with estimated masses of ~0.4 Msolar and ages ~10 Myr. Comparison with the predictions of numerical and analytical models shows excellent agreement between the isochronal age and lithium depletion timescale for two objects, the first such case for lithium-poor pre-main-sequence stars. Our results bear on the issue of the real age spread in the ONC and hence on the overall duration of the star formation process, indicating that the stellar population did not come into existence in a single, rapid burst.

Based on data collected at the ESO Very Large Telescope, Paranal Observatory, Chile [program 072.D-0019(B)]. Title: The σ Orionis open cluster observed with XMM-Newton: source detection and spectral properties Authors: Franciosini, E.; Pallavicini, R.; Sanz-Forcada, J. Bibcode: 2005ESASP.560..551F Altcode: 2005csss...13..551F No abstract at ADS Title: Spot the differences: the X-ray spectrum of SU Aur compared to TW Hya Authors: Smith, K.; Audard, M.; Güdel, M.; Skinner, S.; Pallavicini, R. Bibcode: 2005ESASP.560..971S Altcode: 2005csss...13..971S; 2005astro.ph..4562S We present high-resolution Chandra HETGS X-ray spectra of the classical T Tauri star SU Aur. The quiescent X-ray emission is dominated by a 20-40 MK plasma, which contrasts strongly with the cool 3 MK plasma dominating the X-ray emission of the CTTS TW Hya. A large flare occurred during the first half of our 100 ks observation, and we have modelled the emitting plasma both during this flare and during the apparently quiescent periods. During the flare, an extremely high temperature plasma component (at least 60 MK) accounts for the bulk of the emission. There is an indication of the presence of Fe XXVI emission at 1.78 Angstrom, which is maximally formed at 130 MK. Title: Lithium abundances in intermediate age and old clusters Authors: Pallavicini, R.; Randich, S.; Sestito, P. Bibcode: 2005ESASP.560..867P Altcode: 2005csss...13..867P No abstract at ADS Title: Coronal properties of active G-type stars in different evolutionary phases Authors: Scelsi, L.; Maggio, A.; Peres, G.; Pallavicini, R. Bibcode: 2005ESASP.560..939S Altcode: 2005csss...13..939S No abstract at ADS Title: High energy processes in young stars: Chandra X-Ray spectroscopy of HDE 283572, RY Tau, and LkCa 21 Authors: Audard, M.; Skinner, S. L.; Smith, K. W.; Güdel, M.; Pallavicini, R. Bibcode: 2005ESASP.560..411A Altcode: 2005csss...13..411A; 2004astro.ph..9309A Weak-lined T Tauri stars (WTTS) represent the important stage of stellar evolution between the accretion phase and the zero-age main sequence. At this stage, the star decouples from its accretion disk, and spins up to a higher rotation rate than in the preceding classical T Tauri phase. Consequently, dynamo processes can be expected to become even stronger at this stage. High energy processes can have effects on the remaining circumstellar material, possibly including protoplanets and planetesimals, and these effects may account for certain observable properties of asteroids in the current solar system. Chandra observed for 100 ks the WTTS HDE 283572 which probes the PMS stage of massive A-type stars. We present first results of the analysis of its high-resolution X-ray spectrum obtained with the High-Energy Transmission Grating Spectrometer. A wide range of Fe lines of high ionization states are observed, indicating a continuous emission measure distribution. No significant signal is detected longward of the O \textsc{viii} Ly$\alpha$ line because of the high photoelectric absorption. We also report on the preliminary analysis of the zeroth order spectra of RY Tau and LkCa21. In particular, we show evidence of an emission line in RY Tau at 6.4 keV that we identify as fluorescent emission by neutral Fe caused by a strong X-ray flare which illuminated some structure in (or surrounding) the CTTS. A comparison of X-ray spectra of classical T Tau stars, other WTTS, and young main-sequence stars is made. Title: Coronal properties of G-type stars in different evolutionary phases Authors: Scelsi, L.; Maggio, A.; Peres, G.; Pallavicini, R. Bibcode: 2005A&A...432..671S Altcode: 2005astro.ph..1631S We report on the analysis of XMM-Newton observations of three G-type stars in very different evolutionary phases: the weak-lined T Tauri star HD 283572, the Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com. They all have high X-ray luminosity (~1031 erg s-1 for HD 283572 and 31 Com and ~1030 erg s-1 for EK Dra). We compare the Emission Measure Distributions (EMDs) of these active coronal sources, derived from high-resolution XMM-Newton grating spectra, as well as the pattern of elemental abundances vs. First Ionzation Potential (FIP). We also perform time-resolved spectroscopy of a flare detected by XMM from EK Dra. We interpret the observed EMDs as the result of the emission of ensembles of magnetically confined loop-like structures with different apex temperatures. Our analysis indicates that the coronae of HD 283572 and 31 Com are very similar in terms of dominant coronal magnetic structures, in spite of differences in the evolutionary phase, surface gravity and metallicity. In the case of EK Dra the distribution appears to be slightly flatter than in the previous two cases, although the peak temperature is similar. Title: VLT/FLAMES observations of Collinder 261 Authors: Spanò, P.; Pallavicini, R.; Randic, S. Bibcode: 2005IAUS..228..111S Altcode: We report on results of VLT/FLAMES observations of the very old cluster Cr 261. We compare the results with those of other clusters older than the Hyades. Title: Some Like It Hot: The X-Ray Emission of the Giant Star YY Mensae Authors: Audard, Marc; Telleschi, Alessandra; Güdel, Manuel; Skinner, Stephen L.; Pallavicini, Roberto; Mitra-Kraev, Urmila Bibcode: 2004ApJ...617..531A Altcode: 2004astro.ph..8345A We present an analysis of the X-ray emission of the rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton. The high-resolution spectra display numerous emission lines of highly ionized species; Fe XVII to Fe XXV lines are detected, together with H-like and He-like transitions of lower Z elements. Although no obvious flare was detected, the X-ray luminosity changed by a factor of 2 between the XMM-Newton and Chandra observations taken 4 months apart (from logLX~32.2 to 32.5 ergs s-1, respectively). The coronal abundances and the emission measure distribution have been derived from three different methods using optically thin collisional ionization equilibrium models, which is justified by the absence of opacity effects in YY Men as measured from line ratios of Fe XVII transitions. The abundances show a distinct pattern as a function of the first ionization potential (FIP), suggestive of an inverse FIP effect as seen in several active RS CVn binaries. The low-FIP elements (<10 eV) are depleted relative to the high-FIP elements; when compared to its photospheric abundance, the coronal Fe abundance also appears depleted. We find a high N abundance in YY Men's corona, which we interpret as a signature of material processed in the CNO cycle and dredged up in the giant phase. The corona is dominated by a very high temperature (20-40 MK) plasma, which places YY Men among the magnetically active stars with the hottest coronae. Lower temperature plasma also coexists, albeit with much lower emission measure. Line broadening is reported in some lines, with a particularly strong significance in Ne X Lyα. We interpret such broadening as Doppler thermal broadening, although rotational broadening due to X-ray-emitting material high above the surface could be present as well. We use two different formalisms to discuss the shape of the emission measure distribution. The first one infers the properties of coronal loops, whereas the second formalism uses flares as a statistical ensemble. We find that most of the loops in the corona of YY Men have their maximum temperature equal to or slightly larger than about 30 MK. We also find that small flares could contribute significantly to the coronal heating in YY Men. Although there is no evidence of flare variability in the X-ray light curves, we argue that YY Men's distance and X-ray brightness do not allow us to detect flares with peak luminosities LX<=1031 ergs s-1 with current detectors. Title: Lithium evolution in intermediate age and old open clusters: NGC 752 revisited Authors: Sestito, P.; Randich, S.; Pallavicini, R. Bibcode: 2004A&A...426..809S Altcode: 2004astro.ph..7305S We present new high resolution spectroscopic observations of the intermediate age (∼2 Gyr) open cluster NGC 752. We investigate the Li vs. Teff distribution and we obtain a new accurate determination of the cluster metallicity. We compare the results for NGC 752 with other intermediate age and old clusters spanning the age range from the Hyades (∼0.6 Gyr) to NGC 188 (∼6-8 Gyr). We find that NGC 752 has a solar iron content ([Fe/H]=+0.01±0.04), at variance with early reports of sub-solar metallicity. We find that NGC 752 is only slightly more Li depleted than the younger Hyades and has a Li pattern almost identical to that observed in the ∼2 Gyr old IC 4651 and NGC 3680. As for the latter clusters, we find that NGC 752 is characterized by a tight Li vs. Teff distribution for solar-type stars, with no evidence for a Li spread as large as the one observed in the solar age solar metallicity M 67. We discuss these results in the framework of mixing mechanisms and Li depletion on the main sequence (MS). We conclude that the development of a large scatter in Li abundances in old open clusters might be an exception rather than the rule (additional observations of old clusters are required), and that metallicity variations of the order of ∼±0.2 dex do not affect Li depletion after the age of the Hyades.

Based on observations collected at Telescopio Nazionale Galileo, La Palma, Canary Islands. Title: XMM-Newton Proposal 03006901 Authors: Pallavicini, Roberto Bibcode: 2004xmm..prop...25P Altcode: We propose to observe the open cluster NGC 6475 (age ~220 Myr, [Fe/H] = 0.14 +- 0.06) to investigate the activity-rotation-age relationship of low-mass stars in the crucial age interval between the Pleiades and the Hyades. We will use XMM-Newton observations of the proposed cluster to go a factor of 10 deeper than ROSAT (to detect new faint candidate members) and to obtain spectral information on the brightest cluster members (to derive coronal temperatures and metallicities). These observations will provide strong constraints on the universality (or lack of) of the activity-rotation-age relationship, and hence on dynamo models of stellar coronal activity. Title: Can we use adaptive optics for UHR spectroscopy with PEPSI at the LBT? Authors: Sacco, Germano G.; Pallavicini, Roberto; Spano, Paolo; Andersen, Michael; Woche, Manfred F.; Strassmeier, Klaus G. Bibcode: 2004SPIE.5490..398S Altcode: We investigate the potential of using adaptive optics (AO) in the V, R, and I bands to reach ultra-high resolution (UHR, R >= 200,000) in echelle spectrographs at 8-10m telescopes. In particular, we investigate the possibility of implementing an UHR mode for the fiber-fed spectrograph PEPSI (Potsdam Echelle Polarimetric and Spectrographic Instrument) being developed for the Large Binocular Telescope (LBT). By simulating the performances of the advanced AO system that will be available at first light at the LBT, and by using first-order estimates of the spectrograph performances, we calculate the total efficiency and signal to noise ratio (SNR) of PEPSI in the AO mode for stars of different magnitudes, different fiber core sizes, and different fractions of incident light diverted to the wavefront sensor. We conclude that AO can provide a significant advantage, of up to a factor ~2 in the V, R and I bands, for stars brighter than mR ~ 12 - 13. However, if these stars are observed at UHR in non-AO mode, slit losses caused by the need to use a very narrow slit can be compensated more effectively by the use of image slicers. Title: Unsolved problems in observational astronomy. I. Focus on stellar spectroscopy Authors: Pallavicini, R.; Randich, S. Bibcode: 2004AN....325..462P Altcode: We present the highlights of current observational programs in stellar optical spectroscopy carried out with 8-10 m class telescopes as well as with smaller telescopes. Topics discussed include: 1. light elements abundances and their cosmological implications; 2. search for Population III stars and spectroscopy of extremely metal deficient stars; 3. abundances of different stellar populations in the Galaxy; 4. spectroscopy of resolved stars in Local Group galaxies; 5. Li and Be abundances and internal mixing in stars; 6. spectroscopy of very-low mass stars and brown dwarfs; 7. radial velocity search of extrasolar planets; 8. stellar oscillations and asteroseismology; 9. stellar magnetic activity and Doppler imaging of stellar surface features. We also highlight the role that dedicated 1-2 m automatic telescopes with spectroscopic capabilities can play in several fields of stellar optical spectroscopy. Title: X-shooter: UV-to-IR intermediate-resolution high-efficiency spectrograph for the ESO VLT Authors: D'Odorico, Sandro; Andersen, Michael I.; Conconi, Paolo; De Caprio, Vincenzo; Delabre, Bernard; Di Marcantonio, Paolo; Dekker, Hans; Downing, Mark D.; Finger, Gert; Groot, Paul; Hanenburg, Hiddo H.; Hammer, Francois; Horville, David; Hjorth, Jens; Kaper, Lex; Klougart, Jens; Kjaergaard-Rasmussen, Per; Lizon, Jean-Louis; Marteaud, Michel; Mazzoleni, Ruben; Michaelsen, Niels; Pallavicini, Roberto; Rigal, Florence; Santin, Paolo; Norup Soerensen, Anton; Spano, Paolo; Venema, Lars; Vola, Pascal; Zerbi, Filippo M. Bibcode: 2004SPIE.5492..220D Altcode: X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs. It covers in a single exposure the spectral range from the UV to the H band with a possible extension into part of the K band. It is designed to maximize the sensitivity in this spectral range through the splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolutions (R=4000-14000, depending on wavelength and slit width) sufficient to address quantitatively a vast number of astrophysical applications while working in a background-limited S/N regime in the regions of the spectrum free from strong atmospheric emission and absorption lines. The small number of moving functions (and therefore instrument modes) and fixed spectral format make it easy to operate and permit a fast response. A mini-IFU unit (1.8" x 4") can be inserted in the telescope focal plane and is reformatted in a slit of 0.6"x 12" .The instrument includes atmospheric dispersion correctors in the UV and visual arms. The project foresees the development of a fully automatic data reduction package. The name of the instrument has been inspired by its capability to observe in a single shot a source of unknown flux distribution and redshift. The instrument is being built by a Consortium of Institutes from Denmark, France, Italy and the Netherlands in collaboration with ESO. When it operation, its observing capability will be unique at very large telescopes. Title: A Multiwavelength Perspective of Flares on HR 1099: 4 Years of Coordinated Campaigns Authors: Osten, Rachel A.; Brown, Alexander; Ayres, Thomas R.; Drake, Stephen A.; Franciosini, Elena; Pallavicini, Roberto; Tagliaferri, Gianpiero; Stewart, Ron T.; Skinner, Stephen L.; Linsky, Jeffrey L. Bibcode: 2004ApJS..153..317O Altcode: 2004astro.ph..2613O We report on four years of multiple wavelength observations of the RS CVn system V711 Tau (HR 1099) from 1993, 1994, 1996, and 1998. This combination of radio, ultraviolet, extreme ultraviolet, and X-ray observations allows us to view, in the most comprehensive manner currently possible, the coronal and upper atmospheric variability of this active binary system. We report on the changing activity state of the system as recorded in the EUV and radio across the four years of the observations, and study the high energy variability using an assemblage of X-ray telescopes. (Longer abstract in paper). Title: XMM-Newton observations of the σ Ori cluster. I. The complex RGS spectrum of the hot star σ Ori AB Authors: Sanz-Forcada, J.; Franciosini, E.; Pallavicini, R. Bibcode: 2004A&A...421..715S Altcode: 2004astro.ph..4078S We present XMM-Newton observations of the young ({∼} 2{-}5 Myr) cluster around the hot (O9.5V) star σ Orionis AB, aimed at obtaining a high resolution RGS spectrum of the hot star as well as EPIC imaging data for the whole field. We show that the RGS spectrum of σ Ori AB may be contaminated by weaker nearby sources which required the development of a suitable procedure to extract a clean RGS spectrum and to determine the thermal structure and wind properties of the hot star. We also report on the detection of a flare from the B2Vp star σ Ori E and we discuss whether the flare originated from the hot star itself or rather from an unseen late-type companion. Other results of this observation include: the detection of 174 X-ray sources in the field of σ Ori of which 76 are identified as cluster members, including very low-mass stars down to the substellar limit; the discovery of rotational modulation in a late-type star near σ Ori AB; no detectable line broadenings and shifts (⪉ 800 km s-1) in the spectrum of σ Ori AB together with a remarkable low value of the O VII forbidden to intercombination line ratio and unusually high coronal abundances of CNO elements. Title: The science case of the PEPSI high-resolution echelle spectrograph and polarimeter for the LBT Authors: Strassmeier, K. G.; Pallavicini, R.; Rice, J. B.; Andersen, M. I. Bibcode: 2004AN....325..278S Altcode: We lay out the scientific rationale for and present the instrumental requirements of a high-resolution adaptive-optics Echelle spectrograph with two full-Stokes polarimeters for the Large Binocular Telescope (LBT) in Arizona. Magnetic processes just like those seen on the Sun and in the space environment of the Earth are now well recognized in many astrophysical areas. The application to other stars opened up a new field of research that became widely known as the solar-stellar connection. Late-type stars with convective envelopes are all affected by magnetic processes which give rise to a rich variety of phenomena on their surface and are largely responsible for the heating of their outer atmospheres. Magnetic fields are likely to play a crucial role in the accretion process of T-Tauri stars as well as in the acceleration and collimation of jet-like flows in young stellar objects (YSOs). Another area is the physics of active galactic nucleii (AGNs) , where the magnetic activity of the accreting black hole is now believed to be responsible for most of the behavior of these objects, including their X-ray spectrum, their notoriously dramatic variability, and the powerful relativistic jets they produce. Another is the physics of the central engines of cosmic gamma-ray bursts, the most powerful explosions in the universe, for which the extreme apparent energy release are explained through the collimation of the released energy by magnetic fields. Virtually all the physics of magnetic fields exploited in astrophysics is somehow linked to our understanding of the Sun's and the star's magnetic fields. Title: Coronal and photospheric metal abundances in Gl 355 (LQ Hya) Authors: Covino, S.; Audard, M.; Tagliaferri, G.; Randich, S.; Gudel, M.; Pallavicini, R. Bibcode: 2004cosp...35.2997C Altcode: 2004cosp.meet.2997C One of the most interesting topics in the field of coronal emission from late--type stars concerns the discrepancy seen for some stars between the metal abundances measured in the corona with respect to the values obtained for the photosphere. However, for only few objects, the quality of available data allow us to properly address the problem. First of all, there is a lack of optical spectra with S/N adequate for abundance determination. For most of the stars in this category only global metallicity is available. Regarding the X--ray spectra, it is only with the combination of high resolution gratings and high throughput provided by the Chandra and XMM--Newton missions that single element abundances in coronal plasmas can be effectively retrieved in active stars. To this aim we performed XMM--Newton observations and high-resolution optical spectroscopy of Gl355 to derive a reliable set of abundances both in the corona and in the photosphere. The XMM--Newton observation, EPIC pn and MOS, RGS and the ESO-1.5m FEROS data allowed us to derive abundances for a set of elements (i.e. C, N, O, Fe, Si, etc.). We now discuss the results of our analyses and draw some conclusions. Title: High resolution spectroscopy of open clusters with SARG Authors: Sestito, P.; Randich, S.; Pallavicini, R. Bibcode: 2004MmSAI..75...24S Altcode: We present high resolution spectroscopic observations of open clusters of different ages and metallicities obtained with SARG at TNG. We derived lithium abundances for solar-type stars in NGC 752 (∼2 Gyr) and NGC 188 (∼6-8 Gyr) and for early-K stars in Praesepe (∼600 Myr). We found that (i) Li depletion in solar-type stars might stop at an age of ∼2 Gyr; (ii) the spread in Li abundances observed in M 67 seems to be an exception rather than the rule in old clusters; (iii) Li evolution does not seem to be affected by small variations in metallicity.

Based on observations collected at TNG Title: XMM-Newton spectroscopy of stars in open clusters and star forming regions Authors: Pallavicini, R.; Franciosini, E.; Maggio, A.; Sanz-Forcada, J.; Scelsi, L. Bibcode: 2004cosp...35..195P Altcode: 2004cosp.meet..195P We present XMM-Newton RGS and EPIC spectra of stars in open clusters and star forming regions obtained as part of the Mission Scientist Guaranteed Time. The objects discussed include the hot star sigma Ori AB in the sigma Ori cluster, the late-type stars VB 50 and VB 71 in the Hyades (respectively a main-sequence star and a giant), and the pre-main sequence stars HD 283572 (a weak-line T-Tari star) and SU Aur (a classical T Tauri star) in the star forming region Taurus-Auriga. All stars were observed with the RGS at high-resolution and with EPIC at low-resolution. We investigate the thermal structure and chemical abundances of these stars and we put constraints on wind velocities (for the hot star) and densities (from He-like triplets). We discuss the implications of these observations for the understanding of coronal emission and winds in stars of different activity levels and in different evolutionary phases. Title: XMM-Newton EPIC observations of stellar clusters and star forming regions Authors: Pallavicini, R.; Franciosini, E.; Randich, S. Bibcode: 2004MmSAI..75..434P Altcode: We report on observations of open clusters (OCs) and star forming regions (SFRs) obtained with the EPIC camera as part of the Mission Scientist Guaranteed Time on XMM-Newton. These observations provide a powerful tool to investigate the evolution of coronal activity in late-type convective stars and its dependence on magnetic field generation by dynamo processes. We discuss the motivations for this program and present some results for the SFRs sigma Orionis (∼2-5 Myr) and Taurus-Auriga (∼1-10 Myr) as well as for the OCs IC 2602 (∼30 Myr), alpha Persei (∼50 Myr), Praesepe (∼600 Myr) and the Hyades (∼600 Myr). We discuss imaging and spectral data provided by the EPIC MOS and PN detectors focussing on the determination of the cluster X-ray luminosity function and of the temperature structure, chemical abundances and time variability of cluster stars.

Based on observations collected with the ESA mission XMM-Newton as part of the Mission Scientist (R. Pallavicini) Guaranteed Time Title: Coronae of Cool Stars Authors: Audard, M.; Drake, S. A.; Güdel, M.; Mewe, R.; Pallavicini, R.; Simon, T.; Singh, K. P.; Skinner, S. L.; White, N. Bibcode: 2004IAUS..219..243A Altcode: 2003IAUS..219E.188A; 2003astro.ph.10032A We present preliminary results of grating observations of YY Mensae and V824 Arae by Chandra and XMM-Newton. Spectral features are presented in the context of the emission measure distributions, the coronal abundances, and plasma electron densities. In particular, we observe a coronal N/C enhancement in YY Men believed to reflect the photospheric composition (CN cycle). Finally, we interpret line broadening in YY Men as Doppler thermal broadening in its very hot corona. 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: XMM- Newton observations of open clusters Authors: Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2003AdSpR..32.1143F Altcode: We present observations of stellar clusters obtained with XMM- Newton as part of the Guaranteed Time program. We have obtained EPIC observations of the open clusters Praesepe, a Per, o Ori and Hyades and of the Taurus-Auriga star-forming region. The results of the analysis are presented and discussed, with emphasis on the imaging data. In all clusters a large number of new X-ray sources with no known catalogued optical counterpart has been detected. In σ Ori three X-ray sources coincide with very-low mass members of the cluster, including a brown dwarf candidate. The Praesepe observation does not show the discrepancy with the Hyades found by ROSAT, supporting the suggestion that this cluster may be formed by two merged clusters of different ages. Title: New modelling of a large long-duration X-ray flare on UX Ari Authors: Livshits, I. M.; Livshits, M. A.; Pallavicini, R. Bibcode: 2003AdSpR..32.1181L Altcode: We have carried out a new gas-dynamic simulation of the physical processes occurring in a fixed amount of plasma confined in coronal loops heated in the top. We chose the solution which explains both the time behaviour of the temperature and the energetics of the X-ray emission of a long-duration X-ray flare observed by BeppoSAX on UX Ari. This analysis makes it possible to obtain the length of the loop and the distribution of the temperature and 'density along the loop (with Tmax ≈ 100 MK and ne = (1 - 3) · 10 11 cm -3), as well as to estimate the X-ray flare area S ≈ 1022 cm 2. Franciosini et al. (2001) have developed a time-dependent model of magnetic reconnection for the decay phase of the same flare. Our gas-dynamic solution corresponds to reconnection of middle-scale magnetic fields which in the model by Franciosini et al. (2001) corresponds to a degree n of the Legendre polynomial close to 5. The magnetic field strength is estimated to be about 100 G near the loop top. We argue that the shrinkage-effect plays a more important role during large long-duration X-ray stellar flares than in solar two-ribbon flares. Title: Why solar astronomers should be interested in stars Authors: Pallavicini, R. Bibcode: 2003AdSpR..32..885P Altcode: I discuss the scientific reasons why solar astronomers should be interested in other stars and why Solar Physics should be put in the broader context of Stellar Astrophysics. Selected topics include stellar interiors and helioseismology, dynamo action and activity cycles, stellar surface activity, stellar chromospheres, coronae and winds, and the study of the Sun in time. Title: The evolution of lithium depletion in young open clusters: NGC 6475. Authors: Sestito, P.; Randich, S.; Mermilliod, J. -C.; Pallavicini, R. Bibcode: 2003A&A...407..289S Altcode: 2003astro.ph..5394S We have carried out a high resolution spectroscopic survey of the 220-250 Myr old cluster NGC 6475: our main purpose is to investigate Li evolution during the early stages of the Main Sequence. We have determined Li abundances for 33 late F to K-type X-ray selected cluster candidates, extending the samples already available in the literature; for part of the stars we obtained radial and rotational velocities, allowing us to confirm the membership and to check for binarity. We also estimated the cluster metallicity which turned out to be over-solar ([Fe/H]=+0.14 +/- 0.06). Our Li analysis evidenced that (i) late F-type stars (Teff >≈ 6000 K) undergo a very small amount of Li depletion during the early phases on the ZAMS; (ii) G-type stars (6000 >≈ Teff >≈ 5500 K) instead do deplete lithium soon after arrival on the ZAMS. Whereas this result is not new, we show that the time scale for Li depletion in these stars is almost constant between 100 and 600 Myr; (iii) we confirm that the spread observed in early K-type stars in younger clusters has converged by 220 Myr. No constraints can be put on later-type stars. (iv) Finally, we investigate the effect of metallicity on Li depletion by comparing NGC 6475 with the similar age cluster M 34, but we show that the issue remains open, given the uncertain metallicity of the latter cluster. By using the combined NGC 6475+M 34 sample together with the Hyades and the Pleiades, we compare quantitatively Li evolution from the ZAMS to 600 Myr with theoretical predictions of standard models.

Based on observations collected at the European Southern Observatory. Title: Is Praesepe really different from the coeval Hyades cluster? The XMM-Newton view Authors: Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2003A&A...405..551F Altcode: 2003astro.ph..4519F The Praesepe open cluster represents a puzzle since it has about the same age as the Hyades, and only slightly different metallicity, yet previous ROSAT observations resulted in a detection rate of cluster sources significantly lower than for the Hyades. We present a new 50 ksec observation of Praesepe performed with the EPIC instrument on board XMM-Newton, which resulted in the detection of ~ 200 sources, including 48 cluster members. We detected all solar-type (F-G) stars in the field of view, ~ 90% of the K stars and ~ 70% of the M stars. We find that the distribution of X-ray luminosities of solar-type Praesepe members is comparable to that of the Hyades, in contrast with the previous ROSAT results; however, the disagreement between the ROSAT and XMM-Newton results appears to be mostly due to X-ray faint Praesepe members falling outside the XMM-Newton field of view, while it is considerably reduced when considering only the subsample of stars in the ROSAT survey in common with the present observation. The finding supports an earlier suggestion that Praesepe may be formed by two merged clusters of different age. Title: The ICE spectrograph for PEPSI at the LBT: preliminary optical design Authors: Pallavicini, Roberto; Zerbi, Filippo M.; Spano, Paolo; Conconi, Paolo; Mazzoleni, Ruben; Molinari, Emilio; Strassmeier, Klaus G. Bibcode: 2003SPIE.4841.1345P Altcode: We present a preliminary design study for a high-resolution echelle spectrograph (ICE) to be used with the spectropolarimeter PEPSI under development at the LBT. In order to meet the scientific requirements and take full advantage of the peculiarities of the LBT (i.e. the binocular nature and the adaptive optics capabilities), we have designed a fiber-fed bench mounted instrument for both high resolution (R ≍ 100,000; non-AO polarimetric and integral light modes) and ultra-high resolution (R ≍ 300,000; AO integral light mode). In both cases, 4 spectra per order (two for each primary mirror) shall be accomodated in a 2-dimensional cross dispersed echelle format. In order to obtain a resolution-slit product of ≍ 100,000 as required by the science case, we have considered two alternative designs, one with two R4 echelles in series and the other with a sigle R4 echelle and fiber slicing. A white-pupil design, VPH cross-dispersers and two cameras of different focal length for the AO and non-AO modes are adopted in both cases. It is concluded that the single-echelle fiber-slicer solution has to be preferred in terms of performances, complexity and cost. It can be implemented at the LBT in two phases, with the long-camera AO mode added in a second phase depending on the availability of funds and the time-scale for implementation of the AO system. Title: XMM-Newton Proposal 02002101 Authors: Pallavicini, Roberto Bibcode: 2003xmm..prop...11P Altcode: We propose to observe the open cluster NGC 6475 (age ~200 Myr) to investigate the activity-rotation-age relationship of low-mass stars emerged from ROSAT observations. We will use XMM observations of the proposed cluster to go a factor of 10 deeper than ROSAT (to detect possible previously unseen low-luminosity populations) and to obtain spectral information on the brightest cluster members. We will compare the X-ray luminosity function of the cluster with the similar age cluster NGC 1039 and with younger and older clusters already observed by us with XMM. This comparison will provide strong constraints on the universality (or lack of) of the activity-rotation-age relationship in the crucial age interval between the Pleiades and the Hyades. Title: The Hot Corona of the Giant YY Mensae with Chandra and XMM-Newton Authors: Audard, M.; Güdel, M.; Skinner, S. L.; Pallavicini, R.; Drake, S. A.; Mewe, R. Bibcode: 2003HEAD....7.1202A Altcode: 2003BAAS...35..616A We present Chandra and XMM-Newton high-resolution X-ray spectra of the rapidly rotating giant YY Mensae. It belongs to the class of ``FK Com stars'', i.e. single cool giant stars with projected equatorial velocities measured up to 110 km/s. Chandra and XMM-Newton provide excellent high-resolution X-ray spectra to study the properties of this extreme coronal source. The X-ray spectrum is dominated by a strong continuum component with bright emission lines, mostly from H-like transitions and highly ionized Fe lines (up to Fe XXV), indicative of a very high coronal temperature (≈ 3 keV). The Chandra High-Energy Transmission Grating Spectrometer data are ideal to study at very high resolution this hot coronal source. The Reflection Grating Spectrometer onboard XMM-Newton however provides better information on the cool coronal plasma, and on the carbon and nitrogen abundances. Although no obvious flare was detected in the light curves, YY Men's X-ray luminosity varied by a factor of two between the Chandra and XMM-Newton observations (log LX ≈ 32.16 - 32.42). We derive the coronal emission measure distribution, elemental abundances, and density estimates.

We acknowledge support by SAO grant GO2-3016X. Title: The AVES adaptive optics spectrograph for the VLT: status report Authors: Pallavicini, Roberto; Delabre, Bernard; Pasquini, Luca; Zerbi, Filippo M.; Bonanno, Giovanni; Comari, Maurizio; Conconi, Paolo; Mazzoleni, Ruben; Santin, Paolo; Damiani, Francesco; Di Marcantonio, Paolo; Franchini, Mariagrazia; Spano, Paolo; Bonifacio, P.; Catalano, Santo; Molaro, Paolo P.; Randich, S.; Rodono, Marcello Bibcode: 2003SPIE.4841..715P Altcode: We report on the status of AVES, the Adaptive-optics Visual Echelle Spectrograph proposed for the secondary port of the Nasmyth Adaptive Optics System (NAOS) recently installed at the VLT. AVES is an intermediate resolution (R ≍ 16,000) high-efficiency fixed- format echelle spectrograph which operates in the spectral band 500 - 1,000 nm. In addition to a high intrinsic efficiency, comparable to that of ESI at Keck II, it takes advantage of the adaptive optics correction provided by NAOS to reduce the sky and detector contribution in background-limited observations of weak sources, thus allowing a further magnitude gain with respect to comparable non-adaptive optics spectrographs. Simulations show that the instrument will be capable of reaching a magnitude V = 22.5 at S/N > 10 in two hours, two magnitudes weaker than GIRAFFE at the same resolution and 3 magnitudes weaker than the higher resolution UVES spectrograph. Imaging and coronographic functions have also been implemented in the design. We present the results of the final design study and we dicuss the technical and operational issues related to its implementation at the VLT as a visitor instrument. We also discuss the possibility of using a scaled-up non-adaptive optics version of the same design as an element of a double- or triple-arm intermediate-resolution spectrograph for the VLT. Such an option looks attractive in the context of a high-efficiency large-bandwidth (320 - 1,500 nm) spectrograph ("fast-shooter") being considered by ESO as a 2nd-generation VLT instrument. Title: BeppoSAX observations of CF Tucanae and TY Pyxidis Authors: Franciosini, E.; Pallavicini, R.; Tagliaferri, G. Bibcode: 2003A&A...399..279F Altcode: We present the results of BeppoSAX observations of the RS CVn binary systems CF Tuc and TY Pyx. A long-duration flare was detected on CF Tuc just at the beginning of the observation; a second smaller flare occurred about half a period later. The light curve of TY Pyx shows a significant orbital modulation of the quiescent emission with possible evidence for eclipses, and strong flares. We find that the coronae of the two stars are very similar: both systems have quiescent temperatures of ~ 10 and 20-25 MK, with only a factor of two difference in the emission measures. During the flares, temperatures of ~ 30-40 MK are reached; these temperatures are not high enough to give detectable hard X-ray emission in the PDS. Both stars have subsolar coronal metallicities: we confirm the very low coronal abundance of CF Tuc (Z ~ 0.1-0.2 Zsun), while for TY Pyx we find Z ~ 0.5-0.6 Zsun. For both stars the coronal metallicities are in good agreement with their measured photospheric abundances. Title: PEPSI spectro-polarimeter for the LBT Authors: Strassmeier, Klaus G.; Hofmann, Axel; Woche, Manfred F.; Rice, John B.; Keller, Christoph U.; Piskunov, N. E.; Pallavicini, Roberto Bibcode: 2003SPIE.4843..180S Altcode: PEPSI (Postham Echelle Polarimetric and Spectroscopic Instrument) is to use the unique feature of the LBT and its powerful double mirror configuration to provide high and extremely high spectral resolution full-Stokes four-vector spectra in the wavelength range 450-1100nm. For the given aperture of 8.4m in single mirror mode and 11.8m in double mirror mode, and at a spectral resolution of 40,000-300,000 as designed for the fiber-fed Echelle spectrograph, a polarimetric accuracy between 10-4 and 10-2 can be reached for targets with visual magnitudes of up to 17th magnitude. A polarimetric accuracy better than 10-4 can only be reached for either targets brighter than approximately 10th magnitude together wiht a substantial trade-off wiht the spectral resolution or with spectrum deconvolution techniques. At 10-2, however, we will be able to observe the brightest AGNs down to 17th magnitude. Title: Evolution of lithium beyond the solar age: A Li survey of the old open cluster NGC 188 Authors: Randich, S.; Sestito, P.; Pallavicini, R. Bibcode: 2003A&A...399..133R Altcode: 2002astro.ph.12098R We have determined Li abundances for 11 G-type stars in the 6-8 Gyr old open cluster NGC 188. These data significantly enlarge the number of cluster stars with Li measurements, allowing us to extend the investigation of Li depletion in open clusters to ages well beyond the age of the Sun. We have also inferred the cluster metallicity which turns out to be solar. We find that solar-type stars in NGC 188 are only slightly more Li depleted than the much younger Hyades and no more Li depleted than stars of similar temperature in the 2-4 Gyr younger cluster M 67. At variance with M 67, NGC 188 members show virtually no scatter in their Li abundances. Surprisingly, no solar-type star in NGC 188 appears as Li depleted as the Sun or as the most Li depleted stars in M 67. We discuss the implications of these results for mechanisms of internal mixing and Li depletion in main sequence stars.

Based on observations collected at the Italian National Telescope Galileo. Title: Galactic open clusters: key tracers of stellar structure and evolution Authors: Pallavicini, R. Bibcode: 2003MSAIS...3...74P Altcode: Galactic open clusters are homogeneous samples of stars with approximately the same age and chemical composition but different masses, effective temperatures, rotation rates and magnetic activity. They provide a fundamental tool to test models of stellar structure and evolution and to investigate the formation and chemical evolution of the galactic disk. Recent advances in the study of open clusters are reviewed with emphasis on the determination of lithium and berillium abundances as tracers of internal mixing mechanisms and on the investigation of coronal activity and evolution from the X-ray emission of cluster stars.

Based on ground-based observations collected at ESO and TNG and on space observations collected with XMM-Newton Title: The complex XMM-RGS spectrum of the hot star sigma Orionis Authors: Pallavicini, R.; Sanz-Forcada, J.; Franciosini, E. Bibcode: 2002hrxs.confE..29P Altcode: We present a preliminary analysis of an XMM-Newton observation of the sigma Orionis cluster centered on the O9.5V star sigma Ori. In addition to the EPIC image, which shows the presence of about 240 sources, mostly low-mass PMS stars belonging to the cluster, a high statistics RGS spectrum is obtained for the central source. The EPIC image shows the presence of nearby sources, including a flaring one, which, although weaker, may contaminate the RGS spectrum of the central star. We present an analysis of the RGS and EPIC spectra of sigma Ori and of the EPIC spectra of the nearby sources and we discuss the possible contamination of the hot star RGS spectrum by the other sources. Title: XMM-Newton Observations of X-ray Luminous G-type Stellar Coronae Authors: Scelsi, L.; Maggio, A.; Peres, G.; Sanz-Forcada, J.; Gondoin, Ph.; Pallavicini, R. Bibcode: 2002hrxs.confE..22S Altcode: We present results obtained from the analysis of XMM-Newton spectra of the Hertzsprung-gap giant 31 Com and of the pre-main-sequence star HD 283572, two G-type stars in very different evolutionary phases, but having similar high X-ray luminosities. We discuss methodological issues related to the data analysis, as well as the results on the inferred properties of the stellar coronae. Title: XMM-Newton Spectroscopy of Two Hyades Stars Authors: Franciosini, E.; Sanz-Forcada, J.; Maggio, A.; Pallavicini, R. Bibcode: 2002hrxs.confE..15F Altcode: We present the results of XMM-Newton observations of two Hyades stars: the giant theta1 Tau and the solar-type star VB 50. From the analysis of RGS and EPIC spectra we derive the temperature structure and chemical abundances of the coronae of the two stars. Title: Chandra and XMM-Newton X-Ray Spectroscopy of the Hot Corona of YY Mensae Authors: Audard, M.; Güdel, M.; Skinner, S. L.; Pallavicini, R.; Drake, S. A.; Mewe, R. Bibcode: 2002AAS...201.3307A Altcode: 2002BAAS...34.1156A We present Chandra and XMM-Newton X-ray spectra of the rapidly rotating K giant YY Mensae (d = 290 pc). YY Men is a member of a loosely-defined class of rapidly rotating single cool giant stars (``FK Com stars''), whose outstanding property is a projected equatorial velocity measured up to 110 km/s, in contrast with the expected maximum of 6 km/s for giants. One of the leading theories to explain the extreme properties of FK Com stars suggests that they were formed by coalescence of a contact binary when one of the components entered into the giant stage. Previous observations have shown that its corona displays plasma with a very hot temperature of about 3 keV, with probably no or very little plasma at temperatures below 1 keV. The new X-ray observatories now provide excellent high-resolution X-ray spectra to study the coronal properties of this extreme coronal source. The X-ray spectrum is dominated by a strong continuum and by bright emission lines, mostly from H-like transitions and Fe XXIV lines. Thanks to its wavelength range and its sensitivity, the Reflection Grating Spectrometer onboard XMM-Newton provides important information on the presence of cool coronal plasma, mostly seen at wavelengths between 20 and 40 Å. Simultaneous EPIC CCD spectra also constrain the high-temperature component of the emission measure distribution. The Chandra High-Energy Transmission Grating Spectrometer data are ideal to study at very high resolution the short wavelength range of this hot coronal source. We derive the coronal emission measure distribution, elemental abundances, and density estimates. We acknowledge support by SAO grant GO2-3016X. Title: Multiwavelength analysis of Gl 355 (LQ Hya) Authors: Covino, S.; Tagliaferri, G.; Bertone, E.; Cutispoto, G.; Messina, S.; Panzera, M. R.; Pasquini, L.; Pallavicini, R.; Randich, S.; Rodonò, M.; Setiawan, J. Bibcode: 2002ASPC..277..357C Altcode: 2002sccx.conf..357C No abstract at ADS Title: BeppoSAX observations of CF Tuc and TY Pyx Authors: Franciosini, E.; Pallavicini, R.; Maggio, A.; Tagliaferri, G.; Covino, S. Bibcode: 2002ASPC..277..473F Altcode: 2002sccx.conf..473F No abstract at ADS Title: High-resolution ground-based spectroscopy: where and how ? Authors: Pallavicini, R. Bibcode: 2002AN....323..288P Altcode: An overview is presented of high-resolution optical spectrographs in operation or under development at large telescopes, with emphasis on those facilities best suited for the study of late-type stars and stellar surface inhomogeneities. Plans for the development of new high-resolution spectroscopic instruments are discussed with emphasis on the ICE spectrograph for the PEPSI spectropolarimeter at the LBT. Title: A new concept and a preliminary design for a high resolution (HR) and very-high resolution (VHR) spectrograph for the LBT Authors: Zerbi, F. M.; Spanò, P.; Conconi, P.; Molinari, E.; Mazzoleni, R.; Pallavicini, R.; Strassmeier, K. G. Bibcode: 2002AN....323..499Z Altcode: 2002astro.ph..3039Z A way to fully exploit the large collecting area of modern 8-10m class telescopes is high resolution spectroscopy. Many astrophysical problems from planetary science to cosmology benefit from spectroscopic observations at the highest resolution currently achievable and would benefit from even higher resolutions. Indeed in the era of 8-10m class telescopes no longer the telescope collecting area but the size of the beam - which is related to the maximum size in which reflection gratings are manufactured - is what mainly limits the resolution. A resolution-slit product Rvarphi =~ 40,000 is the maximum currently provided by a beam of 20 cm illuminating the largest grating mosaics. We present a conceptual design for a spectrograph with Rvarphi =~ 80,000, i.e. twice as large as that of existing instruments. Examples of the possible exploitation of such a high Rvarphi value, including spectropolarimetry and very high resolution (R ~ 300,000), are discussed in detail. The new concept is illustrated through the specific case of a high resolution spectropolarimeter for the Large Binocular Telescope. Title: UVES Be observations of early-G dwarfs in old clusters Authors: Randich, S.; Primas, F.; Pasquini, L.; Pallavicini, R. Bibcode: 2002A&A...387..222R Altcode: 2002astro.ph..3155R We have obtained the first beryllium measurements of late F/early G-type stars in the old open cluster M 67 (4.5 Gyr) and in the intermediate age cluster IC 4651 (1.7 Gyr). One member of the young cluster IC 2391 ( ~ 50 Myr) was also observed. Our sample stars have effective temperatures within a range of +30-+380 K from the solar temperature. All our sample stars, including the Sun and the young cluster star have, within the errors, the same Be abundance. This result implies that late F/early G-type stars undergo very little (if any) Be depletion during their main-sequence life-time. Since these stars have undergone some Li depletion, our finding is indicative of shallow mixing, i.e. of a mixing process that can transport surface material deep enough for Li burning to occur, but not deep enough for Be burning. As shown in previous studies, the Li vs. Be diagram is a powerful diagnostic of stellar interiors. In this context, we do not find any evidence of correlated Li and Be depletion; furthermore, a comparison with various models shows that the Be pattern of our sample stars is compatible only with models including gravity waves. This class of models, however, cannot reproduce the Li observations of M 67. Based on observations collected at European Southern Observatory, Chile (65.L-0427). Part of the data were obtained as part of an ESO Service Mode run. Title: Beryllium abundances in old open clusters Authors: Randich, S.; Primas, F.; Pasquini, L.; Pallavicini, R. Bibcode: 2002ASPC..274..240R Altcode: 2002ohds.conf..240R No abstract at ADS Title: Observations of stellar coronae with XMM-Newton Authors: Franciosini, E.; Sanz-Forcada, J.; Maggio, A.; Pallavicini, R. Bibcode: 2002cosp...34E.457F Altcode: 2002cosp.meetE.457F We present observations of stars and stellar clusters obtained with XMM-Newton as part of the Guaranteed Time program. We have performed EPIC observations of the open clusters Praesepe,Per and Hyades and of the Taurus-Aurigae star-forming region. RGS spectra have been obtained for two stars in the Hyades (1 Tau = VB 71 and VB 50) and two stars in Taurus-Aurigae (HD 283572 and SU Aur). The results of the spatial and spectral analysis will be presented and discussed. Title: High-energy radiation from outer stellar atmospheres Authors: Pallavicini, R. Bibcode: 2002css1.book..875P Altcode: No abstract at ADS Title: Scientific Objectives and Design Study of an Adaptive Optics Visual Echelle Spectrograph and Imager Coronograph (AVES-IMCO) for the NAOS Visitor Focus at the VLT Authors: Pallavicini, Roberto; Zerbi, Filippo; Beuzit, Jean-Luc; Bonanno, Giovanni; Bonifacio, Piercarlo; Comari, Maurizio; Conconi, Paolo; Delabre, Bernard; Franchini, Mariagrazia; di Marcantonio, Paolo; Lagrange, Anne-Marie; Mazzoleni, Ruben; Molaro, Paolo; Pasquini, Luca; Santin, Paolo Bibcode: 2002sdef.conf..205P Altcode: We present the scientific case for an Adaptive Optics Visual Echelle Spectrograph and Imager Coronograph (AVES-IMCO) that we propose as a visitor instrument for the secondary port of NAOS at the VLT. We show that such an instrument would be ideal for intermediate resolution (R=16,000) spectroscopy of faint sky-limited objects down to a magnitude of V=24.0 and will complement very effectively the near-IR imaging capabilities of CONICA. We present examples of science programmes that could be carried out with such an instrument and which cannot be addressed with existing VLT instruments. We also report on the result of a two-year design study of the instrument, with specific reference to its use as parallel instrument of NAOS. Title: Multiwavelenght analysis of Gl 355 (LQ Hya) Authors: Covino, S.; Tagliaferri, G.; Bertone, E.; Cutispoto, G.; Messina, S.; Panzera, M. R.; Pasquini, L.; Pallavicini, R.; Randich, S.; Rodono', M.; Setiawan, J. Bibcode: 2001astro.ph..9410C Altcode: We discuss ROSAT, ASCA, {\it Beppo}SAX and optical observations of the young active star Gl 355. During the ROSAT observation a strong flare was detected with a peak flux more than an order of magnitude larger than the quiescent level. Spectral analysis of the data allows us to study the temperature and emission measure distribution, and the coronal metal abundance, for the quiescent phase and, in the case of ROSAT, also during the evolution of the flare. We have modeled the flare and derived a loop semi--length of the order of $\sim 1.5$ stellar radii. ROSAT, ASCA and {\it Beppo}SAX data suggest that the coronal abundance of Gl 355 is subsolar, in the range $0.1 ÷0.3 Z/Z_\odot$. A preliminary analysis of optical spectra allows us to compare the photospheric and coronal metal abundances. Title: BeppoSAX observation of a large long-duration X-ray flare from UX Arietis Authors: Franciosini, E.; Pallavicini, R.; Tagliaferri, G. Bibcode: 2001A&A...375..196F Altcode: We present two X-ray observations of the RS CVn binary system UX Arietis performed with BeppoSAX in August 1997 and August 1998. A large flare lasting for about 1 day was detected during the first observation, while the star was quiescent during the second one. Hard X-ray emission up to ~ 50 keV was detected in the PDS instrument during the rise and at the peak of the flare. Time-resolved spectroscopy of the flare with the LECS and MECS detectors shows that temperatures as high as ~ 100 MK were reached at the flare peak; such high temperatures are responsible for the high-energy tail seen in the PDS. We confirm that the coronal abundance of UX Ari is strongly subsolar (Z/Zsun =~ 0.2-0.3); no significant variation of the metallicity is observed during the flare. We show that the new LECS response matrices released in January 2000 seem to solve the problem of the high hydrogen column densities systematically found in previous BeppoSAX observations of stellar coronae. We find in fact for the quiescent spectrum N_H = 2.6 x 1019 cm-2, compatible with the expected value; during the flare N_H is higher by a factor 5, probably due to the ejection of material. The flare evolution has been analysed using the two-ribbon flare model by Poletto et al. (\cite{poletto88}), finding a very good agreement between the model and the observations. Title: Lithium in the intermediate age cluster NGC 3680: Following Li evolution along the C-M diagram Authors: Pasquini, L.; Randich, S.; Pallavicini, R. Bibcode: 2001A&A...374.1017P Altcode: We present an analysis of high resolution spectroscopic observations (R ~ 30 000, S/N=60-150) of 24 members of the intermediate age ( ~ 1.5 Gyr) open cluster NGC 3680, covering all regions of the cluster colour-magnitude (C-M) diagram where cluster members are known to exist. These observations represent in many aspects challenges to our understanding of stellar interior and mixing. Four main sequence G stars have, within the errors, the same Li abundance, 0.3 dex lower than similar stars in the ~ 1 Gyr younger Hyades but comparable with those observed in the coeval cluster IC 4651. The cluster shows a clear Li-dip located around the turn-off; two stars on the upper part of the turn-off are out of the dip and reach solar system meteoritic Li abundances. Just above the turn-off, in a very small range of magnitudes ( ~ 0.2 in V), a factor of ~ 5 Li depletion occurs. This sudden decrease explains puzzling results recently obtained on field subgiants but it is not at all reproduced by standard (e.g. no rotation, no diffusion) models, whereas it is in somewhat better agreement with the predictions of recent models which include rotational mixing and atomic diffusion. Out of the six cluster giants, one is probably a binary; of the remaining five single cluster members, three have a Li abundance log n(Li) ~ 1.1 while two have Li abundances from a factor 6 to more than a factor 30 lower than the other three. The star with no detected Li is the coolest and most luminous object in the sample and is most likely an AGB star; the other has instead a similar magnitude and effective temperature as the three more Li rich giants. The reasons for this difference in Li abundance among otherwise similar stars can be ascribed either to differential depletion during main-sequence or post-main sequence evolution, possibly induced by rotation, or to differences in the evolutionary status of these evolved stars. By comparing our results with those found for clusters of similar age and for field stars, we find that none of the possible scenarios gives a fully satisfactory explanation if the present population of NGC 3680 giants reflect the expected ratio of clump vs. first-ascent RGB stars. If the more abundant Li-rich giants in NGC 3680 are indeed clump giants, their relatively high Li content requires that Li is produced, or brought to the surface, between the tip of the RGB and the clump, which is not consistent with observations of the similar age cluster NGC 752, where the more abundant, presumably clump giants have low Li abundances. Finally, we have used our spectra to determine the metallicity of the cluster giants, finding [Fe/H]=-0.17+/-0.12. This value is in very good agreement with that derived from spectral indexes analysis, but substantially lower than the value inferred from Strömgren photometry. Based on observations collected at ESO, la Silla, and at the VLT. Title: Membership, lithium, and metallicity in the young open clusters IC 2602 and IC 2391: Enlarging the sample Authors: Randich, S.; Pallavicini, R.; Meola, G.; Stauffer, J. R.; Balachandran, S. C. Bibcode: 2001A&A...372..862R Altcode: 2001astro.ph..3260R We present lithium abundances for ~ 50 X-ray selected candidate members of the 30-50 Myr old open clusters IC 2602 and IC 2391. These data enlarge and extend to cooler temperatures previous Li surveys of these clusters by Stauffer et al. (\cite{sta89}) and Randich et al. (\cite{R97}). We also give for the first time an estimate of the metallicity of the two clusters which turns out to be close to solar. Radial velocity measurements together with Hα chromospheric emission and the presence/absence of other spectroscopic features are used to ascertain the membership status for the sample stars not yet confirmed as cluster members; rotational velocities have also been determined for all sample stars. Stars more massive than ~ 1 Msun in both clusters show no sign of significant Li depletion, while lower mass stars are all lithium depleted, with the amount of Li depletion increasing to cooler temperatures. We confirm that the late-G and early-K stars in IC 2602 present a star-to-star scatter in Li abundances similar to, but not as large as the one in the Pleiades. A scatter is also seen among late-K and M dwarfs. Unlike in the Pleiades and Alpha Per clusters, the scatter among early-K stars in IC 2602 shows only marginal correlation with rotation. Our data suggest that the drop-off of lithium towards lower masses may start at an earlier color in IC 2391 than in IC 2602, but larger cluster samples are needed to confirm this result. In addition, whereas G and early K stars in the two clusters are, on average, more Li rich than their counterparts in the Pleiades, a fraction of the coolest stars, in particular in IC 2391, are as depleted as the lowest-Li Pleiades stars of the same mass. If they continue depleting Li on their way to the main sequence, they are expected to be more Li depleted than the Pleiades at the age of the latter cluster. Based on observations carried out at the European Southern Observatory, La Silla, Chile. Tables 2-5 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5}) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/372/862 Title: High Resolution Spectroscopy with the LBT Authors: Pallavicini, R. Bibcode: 2001slbt.work...95P Altcode: No abstract at ADS Title: Quiescent and flare analysis for the chromospherically active star Gl 355 (LQ Hya) Authors: Covino, S.; Panzera, M. R.; Tagliaferri, G.; Pallavicini, R. Bibcode: 2001A&A...371..973C Altcode: 2001astro.ph..3473C We discuss ROSAT and ASCA observations of the young active star Gl 355. During the ROSAT observation a strong flare was detected with a peak flux more than an order of magnitude larger than the quiescent level. Spectral analysis of the data allows us to study the temperature and emission measure distribution, and the coronal metal abundance, for the quiescent phase and, in the case of ROSAT, also during the evolution of the flare. The global coronal metallicity Z/Zsun ~ 0.1 derived from both ROSAT and ASCA data is much lower than solar and presumably also much lower than the photospheric abundance expected for this very young star. The temperature structure of the quiescent corona was about the same during the various observations, with a cooler component at T1 ~ 7 MK and a hotter component (to which only ASCA was sensitive) at T2 ~ 20 MK. During the flare, the low temperature component remained approximately constant and equal to the quiescent value, while the high-temperature component was the only one that varied. We have modeled the flare with the hydrodynamic-decay sustained-heating approach of Reale at al. (1997) and we have derived a loop semi-length of the order of ~ 1.5 stellar radii, i.e. much larger than the dimensions of flares on the Sun, but comparable with the typical dimensions inferred for other stellar flares. We have compared the derived loop size with that estimated with a simpler (but physically inconsistent) approach, finding that for this, as well for several other stellar flares, the two methods give comparable loop sizes. Possible causes and consequences of this result are discussed. Title: VizieR Online Data Catalog: Lithium abundances in IC 2602 and IC 2391 (Randich+, 2001) Authors: Randich, S.; Pallavicini, R.; Meola, G.; Stauffer, J. R.; Balachandran, S. C. Bibcode: 2001yCat..33720862R Altcode: Lithium abundances and [Fe/H] for a sample of late-type stars in the young open clusters IC 2602 and IC 2391. Abundances are based on high resolution spectra obtained at ESO (3.6m + CASPEC) and CTIO (4m + echelle spectrograph) (4 data files). Title: A Long BeppoSAX Observation of YY Gem (CD-ROM Directory: contribs/tagliaf) Authors: Tagliaferri, G.; Covino, S.; Panzera, M. R.; Pallavicini, R.; Schmitt, J. H. M. M. Bibcode: 2001ASPC..223.1177T Altcode: 2001csss...11.1177T No abstract at ADS Title: Coronal X-ray Emission of HD 9770: The ASCA Observation (CD-ROM Directory: contribs/panzera) Authors: Panzera, M. R.; Covino, S.; Pallavicini, R.; Tagliaferri, G. Bibcode: 2001ASPC..223.1108P Altcode: 2001csss...11.1108P 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: The XMM-Newton view of stellar coronae: X-ray spectroscopy of the corona of AB Doradus Authors: Güdel, M.; Audard, M.; Briggs, K.; Haberl, F.; Magee, H.; Maggio, A.; Mewe, R.; Pallavicini, R.; Pye, J. Bibcode: 2001A&A...365L.336G Altcode: We report results of deep X-ray observations of AB Doradus obtained with the XMM-Newton observatory during its Performance Verification phase. The main objective of the analysis is a study of the spectral variability of coronal plasma in a very active star, including investigations of the variable thermal structure, abundance variations, and possible density changes during flares. AB Dor revealed both quiescent and flaring emission. The RGS spectra show flux changes in lines of highly ionized Fe during the flares, and an increase of the continuum. Elemental abundances increase in the early flare phases, by a factor of three. The quiescent abundances are lower than corresponding solar photospheric values, and tend to increase with increasing first ionization potential, contrary to the behavior in the solar corona. High-resolution spectra show an average density of the cool plasma of ~3 1010 cm-3; this value does not change during the flares. We analyse and model the temporal behavior of heating and cooling, and present model results for one of the flares. We find that magnetic loops with a semilength of the order of 2.5 1010 cm ~ 0.3 R_star are involved. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: Stellar coronal activity Authors: Pallavicini, R. Bibcode: 2001AdSpR..26.1713P Altcode: I review recent results on coronal activity in late-type stars stressing the similarities and differences with respect to solar coronal activity. The emphasis is on recent stellar observations by ROSAT, ASCA and SAX and on prospects for future observations by AXAF and XMM. Reviewed topics include X-ray emission in different parts of the HR diagram, cool stars in open clusters and star forming regions, and X-ray spectroscopy of coronal sources. Title: Searching for New, Unknown, Late-Type Stars, in the Coma Berenices Open Cluster (CD-ROM Directory: contribs/garcia) Authors: García López, R. J.; Randich, S.; Zapatero Osorio, M. R.; Pallavicini, R. Bibcode: 2001ASPC..223.1414G Altcode: 2001csss...11.1414G No abstract at ADS Title: X-ray emission from the active star Gl 355 (LQ Hya) Authors: Covino, S.; Panzera, M. R.; Tagliaferri, G.; Pallavicini, R. Bibcode: 2001ASPC..234..101C Altcode: 2001xras.conf..101C No abstract at ADS Title: The XMM-Newton view of stellar coronae: Coronal structure in the Castor X-ray triplet Authors: Güdel, M.; Audard, M.; Magee, H.; Franciosini, E.; Grosso, N.; Cordova, F. A.; Pallavicini, R.; Mewe, R. Bibcode: 2001A&A...365L.344G Altcode: We present results of a comprehensive X-ray investigation of the multiple stellar system Castor AB + YY Gem. The observations were obtained with the XMM-Newton observatory. We report the first spatially separated detection and identification of both Castor A and B as frequently flaring X-ray sources. Spectral modeling of the YY Gem and Castor coronal sources indicates a broad plasma distribution between 2-15 MK. Elemental abundances are found to be below solar photospheric values, with the abundance of Ne being highest ( ~ 0.7 times solar photospheric). The abundances increase during a large flare, most notably for Fe. The O Vii He-like line triplet indicates average coronal densities of the cooler plasma of a few times 1010 cm-3 for YY Gem and Castor. The YY Gem light curve shows three deep eclipses, indicating that the coronae of both binary components are similarly active and are relatively compact. A 3-D light curve inversion shows that coronal active regions follow density scale heights compatible with spectroscopically measured temperatures. The dominant densities also agree with spectroscopic values. Most active regions are located between +/- 50 degrees latitude, in agreement with findings from previous Doppler imaging. We also report the tentative detection of line broadening due to orbital motion. Based on observations obtained with {\it XMM-Newton}, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: A ROSAT HRI study of the open cluster NGC 3532 (CD-ROM Directory: contribs/francio2) Authors: Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2001ASPC..223.1408F Altcode: 2001csss...11.1408F No abstract at ADS Title: Optical follow-up of ROSAT discovered candidate members of the open cluster Coma Berenices Authors: García López, R. J.; Randich, S.; Zapatero Osorio, M. R.; Pallavicini, R. Bibcode: 2000A&A...363..958G Altcode: We have carried out an optical follow-up of twelve ROSAT discovered candidate members of the Coma Berenices open cluster. VRI photometry and low resolution ( ~ 3 Å) spectroscopy in the range 3800-7000 Åwere performed to obtain colour-magnitude diagrams, proper motions, spectral types, chromospheric activity levels and radial velocities that allow us to establish whether or not these candidates are reliable cluster members. Only four of these objects show optical photometry marginally compatible with the main sequence delineated by known cluster stars. They also exhibit spectral types corresponding to late-K and early-M, and radial velocities which are not inconsistent with membership in Coma Berenices. The proper motions of these candidates are, however, very high and incompatible with the small value associated with the cluster. Thus, none of the ROSAT candidates can be considered members of Coma Berenices. This result tends to favour the hypothesis that the mass of the cluster and its average mass density are lower than what is required for stability, allowing the cluster dissolution by the escape of the less massive stars. We discuss the probable nature of these objects on the basis of the available information. From our radial velocity observations we infer that five of them could be formed by multiple stars. In particular, we have discovered one W-type W UMa contact binary system (K6 spectral type) which is, in addition, a visual companion to a cooler star. Based on observations made with the Isaac Newton telescope, operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos, with the IAC80 telescope and with the European Space Agency OGS telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias. Title: High-Resolution X-Ray Spectroscopy of Zeta Puppis and Eta Carinae with the RGS on XMM Authors: Leutenegger, M. A.; Audard, M.; Behar, E.; den Boggende, A. J.; Brinkman, A. C.; Branduardi-Raymont, G.; Cottam, J.; Erd, C.; Ferringo, C.; Guedel, M.; den Herder, J. W.; Kaastra, J. S.; Kahn, S. M.; McGee, J.; Mewe, R.; Paerels, F. B. S.; Pallavicini, R.; Peterson, J. R.; Rasmussen, A. P.; Raux, G.; Sako, M.; Tamura, T.; Sakelliou, I.; Thomsen, K.; de Vries, C. Bibcode: 2000HEAD....5.4201L Altcode: 2000BAAS...32.1254L We present high-resolution X-ray spectra of massive stars Zeta Puppis and Eta Carinae obtained with the Reflection Grating Spectrometer (RGS) onboard the XMM/Newton observatory. The spectrum of Zeta Puppis has many emission lines, including bright, broad hydrogenic and helium-like lines from oxygen and nitrogen. Analysis of these lines indicates a plasma density of at least 1010 {cm}-3. The spectrum of Eta Carinae is dominated by the bright hydrogenic nitrogen line. We will present the analysis of the spectra and discuss implications. Title: Design study of an adaptive optics visual echelle spectrograph and imager for the VLT Authors: Pallavicini, Roberto; Pasquini, Luca; Delabre, Bernard; Hubin, Norbert N.; Conconi, Paolo; Mantegazza, L.; Mazzoleni, R.; Molinari, Emilio; Zerbi, Filippo M.; Molaro, Paolo P.; Bonifacio, P.; Santin, Paolo; Dimarcantonio, P.; Franchini, Mariagrazia; Bonanno, Giovanni; Bruno, Pietro; Cosentino, Rosario; Scuderi, Salvatore; Catalano, Santo; Rodono, M.; Caldara, Pasquale; Damiani, F.; Comari, Maurizio; Monai, S.; Passaretta, F. Bibcode: 2000SPIE.4008..167P Altcode: We present a preliminary design study for an adaptive optics visual echelle spectrograph and imager/coronograph for use as parallel instrument of the Nasmyth Adaptive Optics System (NAOS) on unit UT3 of the VLT. The spectrograph is intended for intermediate resolution spectroscopy of faint sources. It could be used for observations of late-type dwarfs in distant Galactic clusters and in galaxies of the local group as well as for spectroscopy of extra galactic objects like quasars and Lyman break galaxies down to a limiting magnitude of V equals 22.5. The implementation of an imaging gand coronograph mode increases the versatility of the instrument and its scientific objectives. The instrument takes advantage of Adaptive Optics at visible wavelengths both for imaging and spectroscopy. With NAOS at the VLT, the light concentration in these bands will be above approximately 60 percent of the flux in a 0.3 arcsec aperture for typical Paranal conditions. Simulations show that a gain of more than one magnitude with respect to compatible non-adaptive optical spectrography will be possible for sky- and/or detector limited observations. In addition, the smaller diffraction limit in the optical than in the IR will allow a significant gain in imaging and coronography as well. Finally, the instrument will allow gathering unprecedented experience on the performances of AO at visible wavelengths, which will be fundamental for further development of AO systems, in particular for very large telescopes. Title: A ROSAT HRI study of the open cluster NGC 3532 Authors: Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2000A&A...357..139F Altcode: 2000astro.ph..3091F NGC 3532 is a very rich southern open cluster of age ~ 200-350 Myr; it is therefore a good candidate to investigate the X-ray activity-age-rotation relationship at ages intermediate between the Pleiades and the Hyades, where, to our knowledge, X-ray studies exist for only one cluster (NGC 6475). We have performed an X-ray study of NGC 3532 using HRI observations retrieved from the ROSAT archive. The observations have a limiting sensitivity Lx ~ 4 x 1028 erg sec-1 in the center of the field. We detected ~ 50 X-ray sources above a 4 sigma threshold, half of which have a known optical counterpart within 10 arcsec; 15 of the X-ray sources have at least one cluster member as optical counterpart. A comparison of NGC 3532 with the nearly coeval cluster NGC 6475 indicates that the former cluster is considerably X-ray underluminous with respect to NGC 6475. However, because of the existence of possible selection effects, additional X-ray and optical observations are needed before definitively concluding that the X-ray properties of NGC 3532 and NGC 6475 are significantly different. Title: Evolution of lithium in solar-type stars: clues from intermediate age clusters Authors: Randich, S.; Pasquini, L.; Pallavicini, R. Bibcode: 2000A&A...356L..25R Altcode: 2000astro.ph..3022R We present Li abundances for 14 solar-type stars in the intermediate age ( ~ 2 Gyr) clusters IC 4651 and NGC 3680. The log n(Li) vs. effective temperature distributions are compared with those of the similar age cluster NGC 752, of the younger Hyades (600 Myr) and of the older M 67 (4.5 Gyr) and NGC 188 (6-7 Gyr) clusters. Neither IC 4651 nor NGC 3680 show the dispersion in Li which is observed in M 67. The 2 Gyr clusters have very similar Li vs. T_eff distributions; in addition, stars in the upper envelope of the M 67 distribution have the same Li content as stars in the 2 Gyr clusters, suggesting that either they have not suffered any significant depletion between ~ 2 and 4.5 Gyr or they had a much slower Li depletion. Mechanisms that lead to Li depletion on the main sequence are discussed in the light of these observations. None of the existing models seem to reproduce well the observed features. Based on observations carried out at the European Southern Observatory, La Silla, Chile Title: Twin X-ray flares and the active corona of AB Dor observed with BeppoSAX Authors: Maggio, A.; Pallavicini, R.; Reale, F.; Tagliaferri, G. Bibcode: 2000A&A...356..627M Altcode: We present two X-ray observations of the young, active star AB Dor, performed with BeppoSAX on Nov 9 and Nov 29 1997, and lasting 50 ksec and 140 ksec, respectively. Two, quite similar, large flares occurred during these observations, characterized by a 100-fold increase of the X-ray flux, peak temperatures of about 108 K, and peak emission measures of ~ 5 x 1054 cm-3. We have performed a detailed, time-resolved analysis of the LECS and MECS X-ray spectra during the flares, and also in the subsequent quiescent phases. We have derived a metal abundance of the coronal plasma about half the photospheric one, with no significant increase during the flaring events. However, abundance variations of less than a factor ~ 3 cannot be excluded, within our statistical uncertainties. The exponential decay of the X-ray light curves, and the time evolution of plasma temperature and emission measure are similar to those observed in compact solar flares. The analysis of the flare decay, following the method of Reale et al. (1997), indicates the presence of sustained heating, and yields coronal loop maximum heights smaller than (but comparable with) the stellar radius, in both cases. The flares occurred at different rotation phases, and in one case, the decay was observed for one entire rotation period with no evidence of self-eclipse by the star. We conclude that the flaring loops may be located in the circumpolar region of AB Dor, but they do not appear to be related in any way with the large magnetic structures which sustain the well-known prominences of AB Dor, at several stellar radii above the surface. During the quiescent phase, lasting two rotation periods after the second flare, we have found evidence of significant low-level variability but no indication of rotational modulation. This variability, together with the high plasma temperature ( ~ 25 MK) and large emission measure (<~ 1053 cm-3), are interpreted in the framework of a saturated corona. Title: The active binary star II Pegasi with it BeppoSAX Authors: Covino, S.; Tagliaferri, G.; Pallavicini, R.; Mewe, R.; Poretti, E. Bibcode: 2000A&A...355..681C Altcode: 1999astro.ph.11352C II Peg is an ideal target to study stellar activity and flares, since intense and long lasting flares have been frequently detected from this system at all wavelengths. We report here about a BeppoSAX observation of II Peg. We followed the system for ~ 19 hours on December 5 and 6 1997 with BeppoSAX and the X-ray light curve resembles the typical behavior of a decay phase of a long-lasting flare. The spectral analysis shows that the II Peg X-ray spectrum is described by a two-temperature components, with the two dominant temperatures centered in the range of 9-11 and 24-26 MK. The derived coronal metal abundance is low ( Z ~ 0.2 Z_sun) compared to recent determinations of the photospheric abundance (Z ~ 0.6 Z_sun). Some possible explanations for this phenomenology are reviewed. As for most other stellar coronal sources observed with BeppoSAX, we find that in order to fit the BeppoSAX spectra an interstellar column density about a factor ten higher than previously determined is required. Title: Lithium in Young Open Clusters Authors: Pallavicini, R.; Randich, S.; Stauffer, J. R.; Balachandran, S. C. Bibcode: 2000IAUS..198..350P Altcode: No abstract at ADS Title: EVN observations of the quiescent radio emission of HR1099 Authors: Trigilio, C.; Umana, G.; Catalano, S.; Pallavicini, R.; Tagliaferri, G. Bibcode: 2000evn..conf..173T Altcode: No abstract at ADS Title: High-resolution spectroscopy of X-ray serendipitous sources Authors: Tagliaferri, G.; Cutispoto, G.; Pallavicini, R.; Pastori, L.; Pasquini, L.; Randich, M. S.; Rodonò, M. Bibcode: 2000satp.work..115T Altcode: No abstract at ADS Title: A ROSAT HRI study of the open cluster NGC 6633 Authors: Franciosini, E.; Randich, S.; Pallavicini, R. Bibcode: 2000ASPC..198..447F Altcode: 2000scac.conf..447F No abstract at ADS Title: Stellar Clusters and Associations: Convection, Rotation, and Dynamos Authors: Pallavicini, R.; Micela, G.; Sciortino, S. Bibcode: 2000ASPC..198.....P Altcode: 2000scac.conf.....P No abstract at ADS Title: Lithium abundances and metallicity in the young open clusters IC 2602 and IC 2391 Authors: Meola, G.; Randich, S.; Pallavicini, R.; Stauffer, J. R.; Balachandran, S. Bibcode: 2000ASPC..198..285M Altcode: 2000scac.conf..285M No abstract at ADS Title: Lithium in the Open Cluster NGC 6475 Authors: Randich, S.; Pallavicini, R.; Mermilliod, J. -C. Bibcode: 2000IAUS..198..287R Altcode: No abstract at ADS Title: Lithium in Cool Stars Detected in EUV Surveys Authors: Tagliaferri, G.; Pastori, L.; Cutispoto, G.; Pallavicini, R. Bibcode: 2000IAUS..198..366T Altcode: No abstract at ADS Title: X-ray Spectroscopy of Stellar Coronae with BeppoSAX Authors: Pallavicini, R.; Tagliaferri, G.; Maggio, A. Bibcode: 2000AdSpR..25..517P Altcode: We report on preliminary results of stellar coronae observations by BeppoSAX with emphasis on our own observations of the RS CVn binary UX Arietis and of the young rapidly rotating star AB Doradus. We discuss the temperature, emission measure distribution and elemental abundances derived from these observations and compare the results with those obtained previously by ASCA. We also report on the detection by BeppoSAX of hard (>20 keV) X-ray emission from large stellar flares, and discuss briefly possible interpretations of this detection Title: High resolution optical spectrographs for large telescopes Authors: Pallavicini, R. Bibcode: 2000MmSAI..71..869P Altcode: No abstract at ADS Title: Lithium in open clusters Authors: Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 2000satp.work..107P Altcode: No abstract at ADS Title: Commission 36: Theory of Stellar Atmospheres: (Theorie des Atmospheres Stellaires) Authors: Pallavicini, R.; Dravins, D.; Barbuy, B.; Cram, L.; Hubeny, I.; Owocki, S.; Saio, H.; Sasselov, D.; Spite, M.; Stepien, K.; Wehrse, R. Bibcode: 2000IAUTA..24..219P Altcode: No abstract at ADS Title: Coronal X-ray Emission of II PEG: The BeppoSAX View Authors: Tagliaferri, G.; Covino, S.; Pallavicini, R.; Poretti, E. Bibcode: 2000AdSpR..25..523T Altcode: The BeppoSAX observation of II Peg confirms that this is a very active coronal source, with a possible detection of the decay of a strong X-ray flare. The NH value as determined by BeppoSAX is a factor of ten higher than expected. This is now a common result for various coronal sources observed by BeppoSAX, that still remains to be explained. The coronal metal abundance determined for II Peg by BeppoSAX is subsolar (~ 0.3), in line with the results found for many other active stars. It is still an open question if this low metal abundance is in contradiction or not with the photospheric metallicity of II Peg Title: Division IV: Stars: (Etoiles) Authors: Cram, Lawrence; Barbuy, Beatriz; Gerbaldi, Michele; Lambert, David; Pallavicini, Roberto; Zahn, Jean-Paul; Zinnecker, Hans Bibcode: 2000IAUTA..24..173C Altcode: No abstract at ADS Title: Prospects of Future X-ray Missions for Low Mass Stars and Cluster Stars Authors: Pallavicini, R. Bibcode: 2000vlms.conf..256P Altcode: No abstract at ADS Title: Lithium in population I subgiants Authors: Randich, S.; Gratton, R.; Pallavicini, R.; Pasquini, L.; Carretta, E. Bibcode: 1999A&A...348..487R Altcode: We present a lithium survey for a sample of 91 Pop. I stars. JHKL photometry was also obtained for 61 stars in the sample. Besides Li abundances, [Fe/H] values were derived. Thanks to Hipparcos parallaxes, we could infer absolute V magnitudes for our sample stars and were able to place them on the color-magnitude diagram, which allowed us to constrain their evolutionary status. Masses and ages were derived for most of the stars by comparison with evolutionary tracks. The sample was originally selected so to include class IV stars later than spectral-type F0, but, based on the location on the color-magnitude diagram, we found a posteriori that a fraction of the stars (about 20%) are either main sequence stars or evolved giants. As it is the case for dwarfs and giants, a large spread in lithium abundance is present among the subgiants in our sample. As expected, the average lithium decreases as the stars evolve along the subgiant branch; however, there is not a one-to-one relationship between the position on the color-magnitude diagram and lithium abundance, and the observed dispersion is only partially explainable as due to a dispersion in mass, metallicity, and age. In particular, a dispersion in lithium is seen among slightly evolved subgiants with masses close to solar but in the same evolutionary stage as the G2 IV star beta Hyi. The comparison of the beta Hyi-like sample with a sample of non evolved solar-like stars indeed suggests that beta Hyi has most likely evolved from a main sequence Li-rich star, rather than from a Li-poor star (like the Sun) that has dredged-up previously stored lithium. Our sample includes several stars that have completed the first-dredge up lithium dilution, but that have not yet evolved to the evolutionary point where extra-mixing in the giant phase is thought to occur. A large number of them have Li abundances considerably below the theoretical predictions of first dredge-up dilution. We confirm that this is due to the fact that the progenitors of these stars are most likely stars that have depleted lithium while on the main sequence; the fraction of post-dredge up Li rich/poor stars, in fact, is consistent with the observed distribution of Li abundances among stars that have just left the main sequence. The signature of the second mixing (or RGB extra-mixing) episode is evident in the log n(Li) vs. B-V and log n(Li) vs. M_bol distributions of the stars in the sample; it seems however that the extra-mixing occurs at luminosities lower than predicted by the models of Charbonnel (1994). Finally, a few evolved giants are found that should have passed the second mixing episode, but that do not show signs of it. At least half of them are spectroscopic binaries. Based on observations carried out at the European Southern Observatory, La Silla, Chile Title: VizieR Online Data Catalog: UBVRI photometry of EUV stellar sources (Cutispoto+ 1999) Authors: Cutispoto, G.; Pastori, L.; Tagliaferri, G.; Messina, S.; Pallavicini, R.; Rodono, M. Bibcode: 1999yCat..41380087C Altcode: We present the results of high-precision UBV(RI)c photo observations and of spectroscopic radial velocity measurements obtained at the European Southern Observatory for a sample of 51 cool stars detected in the EUV by the ROSAT Wide Field Camera (WFC). Using also recent results from HIPPARCOS, we infer spectral types and investigate the single or binary nature of the sample stars. Optical variability, with periods in the 0.4-13 day range, has been detected for the first time in 15 of these stars. (8 data files). Title: Classification of EUV stellar sources detected by the ROSAT WFC. I. Photometric and radial velocity studies Authors: Cutispoto, G.; Pastori, L.; Tagliaferri, G.; Messina, S.; Pallavicini, R. Bibcode: 1999A&AS..138...87C Altcode: We present the results of high-precision UBV(RI)_c photometric observations and of spectroscopic radial velocity measurements obtained at the European Southern Observatory for a sample of 51 cool stars detected in the EUV by the ROSAT Wide Field Camera (WFC). Using also recent results from HIPPARCOS, we infer spectral types and investigate the single or binary nature of the sample stars. Optical variability, with periods in the 0.4-13 day range, has been detected for the first time in 15 of these stars. based on data collected at the European Southern Observatory, La Silla, Chile.

Tables 1--5, Figs. 2-27 and the complete data set are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr or via http://cdsweb.u-strasbg.fr/Abstract.html Title: A it BeppoSAX observation of HD 9770: a visual triple system containing a recently discovered short-period eclipsing binary Authors: Tagliaferri, G.; Covino, S.; Cutispoto, G.; Pallavicini, R. Bibcode: 1999A&A...345..514T Altcode: 1999astro.ph..2329T We have studied the coronal X-ray emission of the recently discovered short-period eclipsing binary HD 9770 with the BeppoSAX satellite. The data from the Low Energy and Medium Energy Concentrator Spectrometers (LECS & MECS) onboard BeppoSAX allow studying the spectrum of this star from 0.1 to 8 keV, confirming that this is a very active coronal source, with strong flaring activity. The X-ray emission most likely originates from the eclipsing binary itself, rather than from the other visual component of the system. The X-ray light curves could be modulated with the orbital period of the eclipsing binary, with a hint for a different orbital modulation of the cooler and hotter plasma. The X-ray spectrum is characterized by hot plasma, with the Fe K complex at 6.7 keV clearly detected in the MECS spectrum, and it is well fitted by a 2-temperature optically thin plasma model with low metal abundances ( ~ 0.3 Z_sun). These results are in line with those found for many other active stars. As expected, during the flare the X-ray emission is dominated by hotter plasma with a temperature > 4 keV. There is an indication that the metal abundance may be somewhat higher during the flare. Title: X-ray observations of the young open cluster Blanco 1 Authors: Micela, G.; Sciortino, S.; Favata, F.; Pallavicini, R.; Pye, J. Bibcode: 1999A&A...344...83M Altcode: We present results from two deep ROSAT HRI exposures on the Blanco 1 open cluster. Blanco 1 is one of the few open clusters at large distance from the Galactic Plane. This circumstance has suggested that it may have formed through a mechanism different from that responsible for the other nearby clusters. The age of Blanco 1 is rather uncertain since, depending on the adopted age indicator, it ranges between 30 and 90 Myr. Many cluster members show chromospheric emission typical of young stars. The X-ray observations presented here reveal a high number of X-ray sources, consistent with the young age of the cluster. The typical X-ray luminosity of the cluster members is consistent with that of the Pleiades and significantly lower than the alpha Per members. These results suggest than the age of Blanco 1 is more similar to the age of the Pleiades than to that of alpha Per. The time sampling of the X-ray observations allows us to study the variability of the sources on time scales from hours to 6 months - 1 year. Title: Status of the BeppoSAX program in the field of optically thin plasmas Authors: Pallavicini, R. Bibcode: 1999NuPhS..69...56P Altcode: I present an overview of the BeppoSAX program in the field of optically thin plasmas, which comprises stellar coronae, supernova remnants and clusters of galaxies. Albeit only ~70% of the observations approved in AO1 have been carried out, and only part of the acquired data have as yet been analysed, there are already significant, and in some case unique results coming out from the ongoing program. The analysis carried out so far, although preliminary, is very important for assessing the capabilities of the BeppoSAX mission and for optimizing future observations. Title: X-ray Coronae of Stars: Some Theoretical Questions Authors: Pallavicini, R. Bibcode: 1999ASPC..158..334P Altcode: 1999ssa..conf..334P No abstract at ADS Title: BeppoSAX detection of hard (>20keV) X-ray emission from the active star UX Arietis Authors: Pallavicini, R.; Tagliaferri, G. Bibcode: 1999NuPhS..69...29P Altcode: We present preliminary results of a BeppoSAX observation of the active binary star UX Arietis. We report the first detection in a star other the Sun of hard (>20keV) X-ray emission during a large flare. Similar results were obtained a few days later for a flare observed by BeppoSAX on Algol. We analyse time-resolved spectra of the UX Ari flare obtained with the LECS and MECS detectors over the spectral range 0.1 to 10keV and we discuss possible interpretations for the high energy tail seen with the PDS detector. Title: Stellar coronae with BeppoSAX Authors: Pallavicini, R.; Tagliaferri, G. Bibcode: 1999hxra.conf..378P Altcode: No abstract at ADS Title: The eclipsing binary HD 9770: flaring activity and rotational modulation detected by the BeppoSAX satellite Authors: Tagliaferri, G.; Covino, S.; Cutispoto, G.; Pallavicini, R. Bibcode: 1999NuPhS..69...48T Altcode: No abstract at ADS Title: Lithium in ROSAT-discovered candidate members in the Alpha Persei cluster Authors: Randich, S.; Martin, E. L.; Garcia Lopez, R. J.; Pallavicini, R. Bibcode: 1998A&A...333..591R Altcode: We present lithium observations of 23 X-ray selected candidate members of alpha Per, which are part of a larger sample of stars identified through two ROSAT surveys of the cluster. Our observations on one hand allowed us to confirm membership for 18 of the candidates, thus suggesting that a high percentage of the whole X-ray selected candidates are probably cluster members. On the other hand, we had the possibility to significantly enlarge the Li database for this cluster. The distribution of Li abundances for stars in our sample (or `new' members) is in good agreement with that for previously known (or `old') members, although `new' members in the 5000 - 4700 T_eff interval stay on the upper envelope of the Li vs. T_eff diagram. The comparison of the merged `new' + `old' sample with the younger IC 2602 and IC 4665 clusters and with the older Pleiades confirms that stars more massive than the Sun do not undergo any PMS Li destruction, whereas some depletion occurs during the early phases on the ZAMS. We re-addressed the issue of the star-to-star scatter and Li-rotation connection for both alpha Per and the Pleiades; as several previous studies have pointed out, fast rotators, as a group, show higher lithium than slow rotators. At the same time, however, fast rotators exhibit a much narrower dispersion than slow rotators. We demonstrate that this dicothomy is unlikely due to projection effects and suggest that the reason for it could reside in the PMS rotational history and, in particular, in the presence (absence) of a circumstellar disk. As to very cool stars (T_eff < 4500 K), we find that alpha Per members do not seem to have higher lithium than the Pleiades. This result, however, must be confirmed with a larger sample of alpha Per stars before any conclusion can be drawn. Based on observations made with the Isaac Newton telescope, operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof\'\i sica de Canarias. Title: X-ray Spectroscopy of Active Stars with ASCA and BeppoSAX Authors: Pallavicini, R.; Maggio, A.; Ortolani, A.; Tagliaferri, G.; Covino, S. Bibcode: 1998Ap&SS.261..101P Altcode: 1999Ap&SS.261..101P We discuss representative cases of X-ray spectra of active stars obtained with ASCA and BeppoSAX. We focus in particular on our own observations of the RS CVn binaries γ And and UX Ari, of the BY Dra eclipsing binary HD9770, and of the young stars AB Dor and HD35850. Title: Lithium Abundance in NGC 3680 Authors: Pasquini, L.; Randich, S.; Pallavicini, R. Bibcode: 1998ASPC..154..947P Altcode: 1998csss...10..947P In the framework of a long-term program aimed at studying lithium abundance in solar stars belonging to intermediate and old clusters, we present the preliminary analysis of high resolution observations of 21 stars belonging to the intermediate age cluster NGC 3680. % The targets span over the whole cluster colour-magnitude % diagram. The targets range from the main sequence turnoff through the sub-giant branch. The cluster shows a clear Li-dip, and no evidence for a spread is present among the observed main sequence stars. Particularly relevant is the finding that out of the 6 giants (which have similar magnitudes and temperatures) three show a strong lithium line, while the other three are Li depleted. Title: Spectroscopic Capabilities of XMM for Stellar Coronal Studies Authors: Pallavicini, R. Bibcode: 1998ASPC..154.1138P Altcode: 1998csss...10.1138P The turn of the millennium will be a marvelous time for X-ray astronomy with the launch of powerful missions such as AXAF, XMM, and ASTRO-E. Stellar coronae, with their spectra rich in emission lines, will be primary targets to exploit the spectroscopic capabilities of these missions. In particular, the CCD cameras and reflection gratings on XMM will allow us to address a number of key questions in stellar coronal physics. The capabilities of XMM for the study of stellar coronae are illustrated by means of simulations of EPIC and RGS spectra for a variety of typical stellar coronal sources. The mission time-line and the policy for accessing the data are also briefly illustrated. Title: Lithium in ``New'' alpha Per Candidates Discovered by ROSAT Authors: Randich, S.; Martin, E.; Garcia Lopez, R.; Pallavicini, R. Bibcode: 1998ASPC..154.2136R Altcode: 1998csss...10.2136R We present the results from a lithium survey of 23 new alpha Persei candidates discovered by ROSAT. The log N(Li) vs. T_eff distribution of these stars is compared with that of previously known members: the distributions for the two samples are in good agreement, although in the 5000-4700 K T_eff range our sample stars are located on the upper envelope of previously known members. We think that this is most likely due to the X-ray selection bias in our sample. This temperature range is indeed where the rotation-Li connection is most clear. The merged ``old'' + ``new'' sample is then compared both with the Pleiades and the IC 2602 and IC 4665 clusters. alpha Per stars shows a spread in lithium, but such a spread starts to be seen at a lower effective temperature than in the Pleiades. A speculative explanation, connecting the dispersion in lithium to a spread in the timescale for disk dissipation, is given. Title: A Beppo-SAX Observation of HD 9770: a Newly Discovered Short-Period Eclipsing Binary System Authors: Tagliaferri, G.; Covino, S.; Cutispoto, G.; Pallavicini, R. Bibcode: 1998ASPC..154.1175T Altcode: 1998csss...10.1175T We present the results of a Beppo-AX} observation of the short-period eclipsing binary star HD 9770. The Beppo-SAX data confirm that this is a very active coronal source, with strong flare activity. The 0.1-10 keV light curve is modulated by the star rotation with the eclipse detected at all energies. However, there seem to be an hint of a different behaviour with energy in the eclipse. The coronal metal abundances determined with Beppo-SAX are subsolar (~0.2), in line with the results found for many other active stars. Title: Lithium in Cool Stars Detected in EUV Surveys: ZAMS, PTTS, or PMS? Authors: Pastori, L.; Tagliaferri, G.; Cutispoto, G.; Pallavicini, R. Bibcode: 1998ASPC..154..954P Altcode: 1998csss...10..954P High-resolution spectra in the region of the Li 1 6707.8 AA doublet were obtained for more than 50 stars, of spectral type from F5 to K5, EUV-selected with the ROSAT WFC. We find that one third of these stars are as young as the Pleiades or younger. In particular there are 11 stars that are between the Pleiades and IC 2602 lithium upper envelopes, which means that they are just arrived or are arriving on the ZAMS. Four stars of our sample are in a region where only PMS stars should lie. These results, though preliminary, would imply that the PMS stars detected by Neuhauser et al. (1997) are in fact due to a high concentration of young objects in the Gould Belt. Title: The XMM GT Programme on Stellar Coronae: an Overview Authors: Pallavicini, R. Bibcode: 1998sxmm.confE..11P Altcode: No abstract at ADS Title: X-Ray Coronae from Stars Authors: Pallavicini, R. Bibcode: 1998IAUS..188...13P Altcode: Hot optically thin coronal envelopes are common to stars of virtually all spectral types and luminosity classes. The study of stellar coronae provides a powerful tool to investigate the interaction of hot plasmas with the magnetic field and the mechanisms of generation, transport and dissipation of non-radiative energy in stellar atmospheres. Recent results on X-ray emission from stellar coronae obtained with ROSAT, EUVE and ASCA will be reviewed with emphasis on observations of cool stars in clusters and associations, and on spectroscopic determinations of elemental abundances and emission measure distribution. These observations have substantially increased our knowledge of stellar coronae with respect to that obtained previously with missions like Einstein, EXOSAT and GINGA. They also provide the basis for planning future observations with the coming missions AXAF, XMM and ASTRO-E. Title: Flares on AB Doradus Observed with ASCA Authors: Ortolani, A.; Pallavicini, R.; Maggio, A.; Reale, F.; White, S. M. Bibcode: 1998ASPC..154.1532O Altcode: 1998csss...10.1532O ASCA observations of the young rapidly rotating star AB Doradus are analysed with special emphasis on its flaring behaviour. Multitemperature model fits with either fixed or variable abundances are used. The results for the quiescent emission are compared with those obtained previously by Mewe et al. (1996) confirming the very low coronal metallicity (nearly one tenth solar) of this star in spite of its measured solar photospheric metallicity. The results for the flares are compared with recent models based on full hydrodynamic calculations (Reale et al. 1997) and realistic values for the loop length and the heating duration are derived. It is shown that the flare is essentially a high temperature phenomenon with little effect on the low-temperature component of the quiescent star. Title: Chromospheric models of dwarf M stars. Authors: Mauas, P. J. D.; Falchi, A.; Pasquini, L.; Pallavicini, R. Bibcode: 1997A&A...326..249M Altcode: We present chromospheric models for two dM stars considered as ``basal'' stars due to the low level of chromospheric activity, and compare them with the model for a very active, flare star obtained in a previous paper. These models are not based on a single spectral feature, but on the continuum in a broad wavelength range (3500-9000Å), on many line profiles corresponding to three different atoms (H, Ca, Na), and on the Mg II h and k flux. We show that a marked chromosphere is present even for stars with the lowest levels of activity, and that the active stars have both a chromospheric temperature rise at larger column mass and a higher chromospheric temperature. These characteristics are responsible for the presence of the Balmer lines in emission in the dMe stars. We also show that the additional energy required to transform a dM star into an active star must be deposited in the high chromosphere, just below the transition region. Title: The X-ray coronal emission of λ Andromedae observed with ASCA and ROSAT. Authors: Ortolani, A.; Maggio, A.; Pallavicini, R.; Sciortino, S.; Drake, J. J.; Drake, S. A. Bibcode: 1997A&A...325..664O Altcode: We present an observation of the long-period RS CVn binary λ And obtained with ASCA. We also discuss a previous observation by ROSAT of the same star, that we have retrieved from the public archive. There was little variation in the quiescent X-ray flux of λ And between these two observations almost 5 years apart, but they offer different, and in part complementary, views of its corona. The ASCA spectra of λ And are well described by a 2-T model with a main component at T_1_=~0.9keV and a smaller component at T_2_=~3keV, with EM_2_/EM_1_=~0.15. The fitted coronal metallicity is Z=~0.1, much lower than solar but consistent within a factor of 2 with the reported photospheric metallicity Z_phot_=~0.2. On the contrary, a successful 2-T fit of the ROSAT spectrum yields a cool component at =~0.5keV and a hotter component at =~1.4keV, with EM_2_/EM_1_=~2 and Z=~0.25. Because of these differences, we were unable to find an acceptable fit to the joint ASCA and ROSAT data. We discuss possible causes for the discrepancy, including spectral time variability, uncertainties in the plasma emission codes and in the instrumental calibration, and limitations in the adopted fitting model. The hydrogen column density toward λ And, well constrained by ROSAT, is N_H_=~1x10^19^cm^-2^, a factor ~2 larger than estimated from UV observations from Copernicus and the Hubble Space Telescope. Albeit small, this difference may indicate the presence of substantial ionization of the interstellar medium. Title: Lithium in M 67: evidence for spread in a solar age cluster. Authors: Pasquini, L.; Randich, S.; Pallavicini, R. Bibcode: 1997A&A...325..535P Altcode: We present high resolution observations of main sequence stars in the solar age, solar metallicity open cluster M 67. For the first time we show conclusively that a spread in lithium abundances exists among solar-type stars belonging to this cluster. This implies that standard models with only convection as a mixing mechanism can hardly account for the spread at each colour, and that the Li abundance is not a good age indicator for solar-type stars. The comparison of Li abundances in M 67 (age ~4.7x10^9^ yrs) with those in the younger Hyades cluster (~7x10^8^ yrs) shows that the less depleted stars in M 67 have a Li content only ~ 0.25 dex below similar stars in the Hyades. Considering the ~ 4 Gyrs difference between the two clusters, this indicates that standard lithium destruction mechanisms are very inefficient (if present at all) in many solar-type stars during most of their main sequence lifetime. On the other hand, almost 40% of our sample stars show a significant Li depletion, with values comparable to the Sun. Our sample also includes one SB2 binary, for which a very high Li abundance was previously reported. We found an abundance significantly higher than in single stars, but our spectra are inconsistent with those previously published. Title: A SAX/LECS X-ray observation of the active binary Capella. Authors: Favata, F.; Mewe, R.; Brickhouse, N. S.; Pallavicini, R.; Micela, G.; Dupree, A. K. Bibcode: 1997A&A...324L..37F Altcode: 1997astro.ph..7061F We present a SAX/LECS X-ray observation of the active binary Capella, the first coronal source observed in the SAX Guest Investigator program. The analysis of this observation, performed using the mekal plasma emission code, shows that the LECS spectrum is well fit by a two-component optically-thin plasma model. A differential emission measure (DEM) obtained by direct inversion of the X-ray spectrum shows no additional features in addition to the double-peaked structure implied by the direct two-temperature analysis. Such a simple temperature stratification is however not compatible with the EUVE emission from the same object, which is well represented by a more complex DEM, with a power-law-like tail toward the low temperatures. At the same time, the EUVE-derived DEM predicts well the softer part of the Capella LECS spectrum, but it fails to correctly reproduce the higher energy part of the Capella LECS spectrum. Possible causes for this discrepancy are discussed. The coronal metallicity derived from the SAX observation is compatible both with the EUVE-derived metallicity as well as with the photospheric metallicity of Capella, thus showing no evidence for coronal under-abundances. Title: Lithium abundances in the young open cluster IC 2602. Authors: Randich, S.; Aharpour, N.; Pallavicini, R.; Prosser, C. F.; Stauffer, J. R. Bibcode: 1997A&A...323...86R Altcode: We have obtained high-resolution spectra for 28 candidate late-type stars in the 30 Myr old cluster IC 2602. NLTE Li abundances have been derived from measured equivalent widths. The log n(Li)-T_eff_ and log n(Li)-mass distributions for our sample stars have been compared with those of the Pleiades and α Persei. Our data show that F stars in the three clusters have the same lithium content, which corresponds to the initial content for Pop. I stars. G and early-K IC 2602 stars are, on average, somewhat more Li-rich than their counterparts in the two slightly older clusters. Finally, the latest-type IC 2602 stars are heavily Li depleted, with their Li content being as low as the lowest measured among the Pleiades. As in the Pleiades and α Per, a star-to-star scatter in lithium is observed among 30 Myr old late-K/early-K dwarfs in IC 2602, indicating that this spread develops in the pre-main sequence phases. Title: Coronal X-ray emission of HD 35850: the ASCA view. Authors: Tagliaferri, G.; Covino, S.; Fleming, T. A.; Gagne, M.; Pallavicini, R.; Haardt, F.; Uchida, Y. Bibcode: 1997A&A...321..850T Altcode: 1996astro.ph.11160T We present the analysis of the X-ray data of the young active star HD 35850 obtained with ASCA and ROSAT. Our main goal was to see if there is a difference in the elemental abundances of active stars between young and more evolved objects. A two temperature plasma with subsolar abundances, of the order of Z=0.15-0.3 , is required to fit the SIS spectra. Similar results are obtained from a ROSAT PSPC observation. Metal abundances of 0.2-0.4 the solar value are required to fit both the ASCA and ROSAT data together. From a simultaneous SIS0+SIS1 spectral fit, with 2T plasma models and abundances free to vary in non-solar proportions, we find that, besides N, O and Ne for which we find very low values, all other elements have values relative to solar abundances around 0.2-0.3. These subsolar abundances are in line with those typically observed in more evolved, active stars like RS CVn and Algol-type binaries. The two temperature values required to fit the ASCA SIS spectra are about 0.5 and 1.0 keV. These temperatures, especially the higher one, are lower with respect to the values found for the RS CVn and Algol binaries or for the young star AB Dor, but higher than other single G/K stars. All our data show that this single, late F-type star is actually a very active source, indirectly confirming that this fast rotating star is probably a young object. In the simultaneous fit of the ASCA+ROSAT data, a third temperature is required. However this is not just an addition of a softer component, but is more a redistribution of the dominant temperatures. Indeed, the range spanned by the three temperatures, from 5 to 15 million degrees, is not very large. Title: VizieR Online Data Catalog: Chromospheric models of dwarf M stars (Mauas+ 1997) Authors: Mauas, P.; Falchi, A.; Pasquini, L.; Pallavicini, R. Bibcode: 1997yCat..33260249M Altcode: Tables 4 and 5 give the atmospheric parameters for our models of dM stars Gl 588 and Gl 628. The columns give the column mass in g/cm-2, the electron temperature in K, the microturbulent velocity in km/s; the continuum optical depth at 5000Å; the hydrogen, proton, and electron density in particles per cm-3; and the height h (in km) above the level where tau5000=1. (2 data files). Title: Lithium in solar-type stars of the old open cluster M 67. Authors: Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 1997MmSAI..68..933P Altcode: No abstract at ADS Title: ASCA Observation of Coronal X-Ray Emission from the Dwarf Star HD 35850 Authors: Tagliaferri, G.; Covino, S.; Pallavicini, R.; Uchida, Y. Bibcode: 1997xisc.conf..575T Altcode: No abstract at ADS Title: Cool stars in clusters and associations: magnetic activity and age indicators. Proceedings. Workshop, Palermo (Italy), 20 - 23 May 1997. Authors: Micela, G.; Pallavicini, R.; Sciortino, S. Bibcode: 1997MmSAI..68..783M Altcode: The following topics were dealt with: evolutionary models and age determinations; membership determination; proper motion surveys and CCD photometry; rotation and angular momentum evolution; lithium abundance in clusters and associations; chromospheric activity in cluster stars; X-ray observations of open clusters; star formation and young stellar objects; X-ray surveys of star forming regions; solar-type coronal loop modelling of X-ray flares. Title: Prospects for Stellar Coronae Observations Authors: Pallavicini, Roberto Bibcode: 1997ngxo.conf...27P Altcode: A brief summary is given of the current status and future prospects for X ray observations of stellar coronae. The need for high-throughput high-resolution spectroscopy on fainter and more distant objects (e.g. late-type stars in open clusters of different ages, and in star forming regions) is emphasized. A combination of large effective area (A(eff) approximately 10,000 cm2 at 1 keV) and high spectral resolution (Delta(E) approximately 2 eV at energies > 1 keV and Delta(lambda) approximately 0.03 A at energies < 1 keV) on a telescope with HEW approximately 5 arcsec is required to advance significantly beyond the capabilities of future missions like AXAF, XMM and ASTRO-E. Title: X-ray observations of the young open cluster dzeta Sculptoris. Authors: Micela, G.; Sciortino, S.; Favata, F.; Pallavicini, R.; Pye, J. Bibcode: 1997MmSAI..68..989M Altcode: No abstract at ADS Title: Abundances and Flares in the ASCA Observation of the Young k0 Star AB Doradus Authors: White, S. M.; Pallavicini, R.; Mewe, R.; Kaastra, J. S.; Lim, J. Bibcode: 1997xisc.conf..573W Altcode: No abstract at ADS Title: The Sun as a variable star Authors: Pallavicini, R. Bibcode: 1997MmSAI..68..369P Altcode: No abstract at ADS Title: Simultaneous EUVE & ASCA observations of AB Doradus: temperature structure and abundances of the quiescent corona. Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R. Bibcode: 1996A&A...315..170M Altcode: We have analyzed EUV and X-ray spectra of the non-flaring state of AB Dor, obtained from simultaneous observations with EUVE and ASCA. The coronal temperature structure and the coronal elemental abundances have been derived by jointly fitting the spectra, including lines and continuum. We have applied a multi-temperature fitting method and we have found that an optically thin plasma model with solar abundances (relative to hydrogen) does not yield a good fit. A 4-T fit allowing the abundances of the more important elements (Fe, S, Si, Mg, Ne, and O) plus four other less important abundances (N, Ar, Ca, and Ni) to vary improves the fit markedly. This results in values of the first 6 abundances relative to solar photospheric values that are significantly (a factor 2-3) below solar except for Ne, which is solar, while most of the remaining four abundances are consistent both with solar and reduced abundances. In the course of the 4-T fitting we have determined a best-fit value for the interstellar hydrogen column density of N_H_=(2.0+/-0.5)10^18^cm^-2^. We have applied four differential emission measure (DEM) distribution analysis techniques, viz.: (i) regularization method, (ii) polynomial method, (iii) clean algorithm, and (iv) genetic algorithm. The four different methods all yield a qualitatively similar DEM, showing two maxima in the temperature intervals 5-8MK and 20-30MK. Our analysis demonstrates the great value of simultaneous ASCA and EUVE observations in determining the fundamental parameters of stellar coronae. Title: Lithium abundance in the open cluster IC 2602 Authors: Randich, S.; Aharpour, N.; Pallavicini, R.; Prosser, C. F.; Stauffer, J. R.; Schmitt, J. H. M. M. Bibcode: 1996ASPC..109..379R Altcode: 1996csss....9..379R No abstract at ADS Title: A study of a sample of cool stars X-ray selected with EXO SAT using ROSAT data Authors: Panarella, A.; Tagliaferri, G.; Pallavicini, R. Bibcode: 1996ASPC..109..623P Altcode: 1996csss....9..623P No abstract at ADS Title: Atmospheric models of dM stars Authors: Falchi, A.; Pallavicini, R.; Mauas, P. J. D.; Pasquini, L. Bibcode: 1996ASPC..109..603F Altcode: 1996csss....9..603F No abstract at ADS Title: Spectroscopic Diagnostics of Astrophysical Plasmas Authors: Pallavicini, R. Bibcode: 1996LNP...468..241P Altcode: 1996plas.conf..241P This paper summarises a series of lectures on spectroscopic diagnostics of astrophysical plasmas given to graduate students. It focusses on optically thin thermal plasmas and on X-ray spectroscopy. The basic diagnostic techniques are first discussed in a general way and then applied to specific astrophysical cases, including the solar corona, stellar coronae, supernova remnants and clusters of galaxies. The limitations of current spectroscopic data in terms of both resolution and sensitivity are emphasised, and future prospects are briefly mentioned. These lectures are intended as an introduction to the field rather than as a survey of the most recent literature. The emphasis therefore is on basic concepts and the cited bibliography is limited mainly to review papers where further details and references to the original works can easily be found. Title: The X-ray spectra of flares from AB Doradus Authors: White, S. M.; Pallavicini, R.; Lim, J. Bibcode: 1996ASPC..109..299W Altcode: 1996csss....9..299W No abstract at ADS Title: An ASCA observation of HD 35850 Authors: Tagliaferri, G.; Covino, S.; Haardt, F.; Fleming, T. A.; Pallavicini, R. Bibcode: 1996ASPC..109..295T Altcode: 1996csss....9..295T No abstract at ADS Title: Millimeter Continuum Observations of Stars Authors: Pallavicini, Roberto; White, S. M. Bibcode: 1996slma.conf..268P Altcode: We review the scientific advances to be expected from millimeter continuum observations of stars by a Large Southern Array (LSA). We discuss briefly several topics including millimeter observations of the Sun, winds of hot stars, circumstellar disks of pre-main sequence stars, circumstellar shells and mass loss in cool giants, symbiotic stars, and non-thermal emission in active binaries, flare stars and accretion powered X-ray sources. We show that even in the more limited area of continuum observations, the proposed LSA will allow major advances in virtually all fields of stellar astronomy. Title: Stellar Magnetic Activity; Activity Cycles, and Dynamos Authors: Pallavicini, R. Bibcode: 1996mpsa.conf..359P Altcode: 1996IAUCo.153..359P No abstract at ADS Title: Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. III. Photometric properties. Authors: Cutispoto, G.; Tagliaferri, G.; Pallavicini, R.; Pasquini, L.; Rodono, M. Bibcode: 1996A&AS..115...41C Altcode: We present high-precision UBV(RI)_c_ photometry for a sample of active stars detected serendipitously by the EXOSAT satellite. Fourteen objects, out of 47 likely optical counterparts, turned out to be clearly variable, with periods in the range 1-8 days, including a newly discovered eclipsing binary. For most of them the optical variability is consistent with the presence of photospheric cool spots. We have used our multicolour photometry to estimate spectral classifications and distances. The derived distances indicate that some of the observed stars are previously unidentified nearby (d<=25pc) M dwarfs. When combined with the results of high resolution spectroscopy, our photometric observations allow us to investigate the stellar content of the selected X-ray sample. Young stars and RS CVn-type binaries appear to constitute a large fraction of the selected sample. Title: The corona of AB Dor: temperatures and abundances determined with ASCA and EUVE Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R. Bibcode: 1996ASPC..109..273M Altcode: 1996csss....9..273M No abstract at ADS Title: In memoriam of C.-C. Cheng Authors: Pallavicini, R. Bibcode: 1996ASPC..109...43P Altcode: 1996csss....9...43P No abstract at ADS Title: Cool stars, stellar systems, and the sun : 9 : 1995 Authors: Pallavicini, Roberto; Dupree, Andrea K. Bibcode: 1996ASPC..109.....P Altcode: 1996csss....9.....P No abstract at ADS Title: X-ray spectroscopy of RS CVn binaries: the EXOSAT and SSS spectra revisited Authors: Ortolani, A.; Pallavicini, R.; Tagliaferri, G. Bibcode: 1996ASPC..109..279O Altcode: 1996csss....9..279O No abstract at ADS Title: VizieR Online Data Catalog: UBV(RI) photometry of cool stars (Cutispoto+, 1996) Authors: Cutispoto, G.; Tagliaferri, G.; Pallavicini, R.; Pasquini, L.; Rodono, M. Bibcode: 1995yCat..41150041C Altcode: We present high-precision UBV(RI)c photometry for a sample of stars detected serendipitously by the EXOSAT satellite. Fourteen objects, out of 47 likely optical counterparts, turned out to be clearly variable, with periods in the range 1-8 days, including a newly discovered eclipsing binary. For most of them the optical variability is consistent with the presence of photospheric cool spots. We have used our multicolour photometry to estimate spectral classifications and distances. The derived distances indicate that some of the observed stars are previously unidentified nearby (d<=25pc) M dwarfs. When combined with the results of high resolution spectroscopy, our photometric observations allow us to investigate the stellar content of the selected X-ray sample. Young stars and RS CVn-type binaries appear to constitute a large fraction of the selected sample. For a description of the UBV and (RI)c photometric systems, see e.g. http://obswww.unige.ch/gcpd/ph01.html and http://obswww.unige.ch/gcpd/ph54.html. (2 data files). Title: Photometry of cool stars detected in extreme-ultraviolet (EUV) all-sky surveys. Authors: Cutispoto, G.; Pallavicini, R.; Kuerster, M.; Rodono, M. Bibcode: 1995A&A...297..764C Altcode: We present high-precision UBV(RI)_c_ photometry for a small sample of cool stars detected at EUV wavelengths by the ROSAT WFC and/or the EUVE all-sky survey. Four out of the five stars observed are variable and one of them is an eclipsing binary. Amplitudes up to 0.38 magnitudes in the V band have been observed and clear colour variations have been found. We have computed the photometric periods and deduced approximate spectral classifications and distances. Title: Lithium in Tidally Locked Binaries Authors: Pallavicini, R.; Randich, S. Bibcode: 1995lea..conf..311P Altcode: No abstract at ADS Title: Flares in Late-type Stars: X-ray Authors: Pallavicini, Roberto Bibcode: 1995LNP...454..148P Altcode: 1995flfl.conf..148P; 1995IAUCo.151..148P No abstract at ADS Title: Lithium abundances in Pop I subgiants. Authors: Randich, S.; Pallavicini, R.; Pasquini, L.; Gratton, R. Bibcode: 1995MmSAI..66..383R Altcode: No abstract at ADS Title: Lithium in Late-Type Subgiants Authors: Randich, S.; Pallavicini, R.; Pasquini, L.; Gratton, R. Bibcode: 1995lea..conf..284R Altcode: No abstract at ADS Title: ASCA X-ray Spectra of Quiescent and Flaring Emission from AB Doradus Authors: White, S. M.; Pallavicini, R.; Lim, J. Bibcode: 1995LNP...454..168W Altcode: 1995IAUCo.151..168W; 1995flfl.conf..168W No abstract at ADS Title: Stellar and interstellar lithium and primordial nucleosynthesis. Proceedings. IAU Joint Discussion 11 of the 22. IAU General Assembly: Stellar and interstellar lithium and primordial nucleosynthesis, The Hague (Netherlands), 22 Aug 1994. Authors: Spite, F.; Pallavicini, R. Bibcode: 1995MmSAI..66..307S Altcode: A collection of papers on the latest observations and theories on lithium. A few invited talks are not published in this volume. Title: Stellar and interstellar lithium and primordial nucleosynthesis Authors: Spite, Francois; Pallavicini, Roberto Bibcode: 1995silp.conf.....S Altcode: No abstract at ADS Title: Lithium abundances of nearby solar-like stars. Authors: Pasquini, L.; Liu, Q.; Pallavicini, R. Bibcode: 1994A&A...287..191P Altcode: We discuss Li abundances in a well defined sample of nearby (G0-G5) solar-like stars. High resolution (R=100,000), high S/N (>= 150) data have been analysed using state-of-the-art techniques and up-to-date atmospheric models. We have investigated whether the abundance of Li in solar-type stars can be described in terms of stellar physical parameters like T_eff_, age and metallicity. We confirm the presence of a group of stars with high Li content, but apparently old age, finding that this group is rather conspicuous and not restricted to a few exceptional cases. The analysis of our data, together with published observations of G dwarfs in open clusters, strongly suggests that for stars older than ~1Gyr another parameter in addition to the overmentioned ones plays a relevant role in Li depletion. When this additional mechanism is effective, it depletes Li by a factor 10-100, but in some stars it may not act at all during a large part of their main sequence lifetimes. We make some suggestions as to the nature of this additional parameter but none of them can be definitely proven. When compared to the other stars in our sample, the Sun appears to be representative of the low-Li stars, which comprise about one half of the G dwarfs having stellar parameters and ages similar to the Sun. We confirm that Li is not a good tracer of age for solar-type stars, but we show that a high Li content coupled to high chromospheric activity can be used to identify stars significantly younger than the Hyades. Title: Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images II. Lithium abundances Authors: Tagliaferri, G.; Cutispoto, G.; Pallavicini, R.; Randich, S.; Pasquini, L. Bibcode: 1994A&A...285..272T Altcode: We present high-resolution spectra in the Li I 6708 A region, and multicolor photometry, for a sample of active stars detected serendipitously by the EXOSAT satellite. We analyse the spectral data with a spectral synthesis code and derive Li abundances, rotation rates and metallicities. We use our multicolor photometry to infer the spectral classification and distance of the stars in the sample. The derived Li abundances are compared with those of various samples including randomly selected field stars, RS CVn binaries, and clusters and associations of different ages. We show that Li per se is not sufficient to determine unambiguously the nature and evolutionary state of the sample stars, but can provide useful constraints if used in conjunction with other diagnostics like binarity, spectral class, rotation rate and X-ray luminosity. We show in particular that at least one third of the EXOSAT sample is constituted by young stars, with ages comparable to or younger than the Pleiades (~7x10^7^ yr). Another third consists of RS CVn binaries, while the classification of the remaining objects is uncertain. They could be either young stars or evolved active binaries. We argue that a similar composition also applies to the sample of X-ray stellar sources detected serendipitously by the Einstein Observatory. Title: Emission lines in the EUVE spectra of EQ Pegasi. Authors: Fossi, B. C. Monsignori; Landini, M.; Pallavicini, R. Bibcode: 1994AAS...184.0518F Altcode: 1994BAAS...26..866M The EUV spectra of dMe flare star EQ Pegasi were obtained during a guest observation using the Extreme Ultraviolet Explorer satellite (EUVE) on August 31, 1993. The EQ Peg was detected in all three spectrometer channels, although the LW detection, apart the He II line, was mainly the result of the second order throughput. The main features of the spectra in SW and MW channels are identified: a number of lines are due to highest ionization stages of iron. Title: Lithium in RS Canum Venaticorum binaries and related chromospherically active stars. III. Northern RS CVn systems. Authors: Randich, S.; Giampapa, M. S.; Pallavicini, R. Bibcode: 1994A&A...283..893R Altcode: High-resolution spectra of Northern RS CVn binaries obtained at the NSO-Kitt Peak are analyzed with a spectrum synthesis code to derive Li abundances, metallicities and rotation rates. The data are then combined with previous observations of Southern RS CVn binaries obtained at ESO, yielding a total sample of 67 individual components in 54 catalogued RS CVn binaries. We confirm the presence of substantial amounts of Li in many chromospherically active stars in the sample, with no significant difference between the Northern and Southern samples. We specifically address the question of whether these relatively high Li abundances are due to enhanced chromospheric activity or rather are a consequence of evolutionary history in stars of sufficiently high mass. We investigate the dependence of Li abundance on mass by using mass determinations in binary systems as well as comparison with theoretical evolutionary tracks. We show that while Li abundances in subgiants and in the warmer stars of the sample may be consistent with a dependence on mass, there is no clear indication in the data that the cooler giants with larger Li abundances are also the more massive ones. Uncertainties in the comparison with evolutionary tracks may partially be responsible for this negative result. Alternatively, Li depletion and dilution in evolved stars may be more complex than predicted by standard evolutionary models. Title: A search for cold dust around post-T Tauri candidates. Authors: Gahm, G. F.; Zinnecker, H.; Pallavicini, R.; Pasquini, L. Bibcode: 1994A&A...282..123G Altcode: We have made 1.3 mm continuum observations of 15 age-dated post-T Tauri candidates that occur as secondaries in binary systems with a primary of early spectral type (so-called Lindroos systems). Most of the objects have estimated ages of 10-100 Myr. None of the companions were detected at 3 sigma upper limits ranging from 13-134 mJy. This implies upper limits on the mass of cold circumstellar dust of approximately 8 x 10-6 - 3 x 10-4 solar mass. The absence of dust emission suggests that the dust grains may have grown into planetsimals or planets, or they may have been dispersed or accreted. Our observations put a limit on the lifetime of optically thin dusty disks of order 107 yr in these systems. Two primaries were also included in this survey, again with no detections. Title: 15-30 arcsec resolution replica x-ray optics for AXAF-S Authors: Stella, Luigi; Chincarini, G.; Citterio, Oberto; Conconi, Paolo; Maccacaro, T.; Tagliaferri, G.; Trinchieri, G.; Wolter, A.; Bignami, Giovanni F.; Bocchino, F.; Maggio, A.; Micela, G.; Sciortino, Salvatore; Serio, Salvatore; Collura, Alfonso; Giommi, P.; Maraschi, L.; Pallavicini, R.; Pellegrini, S.; Peres, G. Bibcode: 1994SPIE.2011..149S Altcode: This document describes a proposal for a replica X-ray optics to be developed in Italy for NASA's X-ray spectroscopy mission AXAF-S. The program is based on state of the art technology for the production of replica X-ray optics. On the basis of the experience with the Jet-X mirror shells (to be flown on the Spectrum X-(gamma) satellite), a spatial resolution of 15 - 30 arcsec half power diameter (HPD) can be achieved for the AXAF-S optics. The characteristics of the proposed optical system are described and its performances evaluated by using the current baseline configuration for the array of X-ray calorimeters in the focal plane. The impact of the proposed replica X-ray optics is briefly outlined and a comparison with foil optics (1 - 3 arcmin HPD resolution) is carried out. Title: Optical Studies of Cool Stars Discovered by EXOSAT: Li Abundances and H alpha Spectroscopy Authors: Tagliaferri, G.; Cutispoto, G.; Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 1994ASPC...64..303T Altcode: 1994csss....8..303T No abstract at ADS Title: The Radio Spectra of Weak-Lined T Tauri Stars Authors: White, S. M.; Pallavicini, R.; Lim, J. Bibcode: 1994ASPC...64..501W Altcode: 1994csss....8..501W No abstract at ADS Title: Photometry of Serendipitous X-Ray Sources Detected by EXOSAT. II. an Update Authors: Cutispoto, G.; Rodono, M.; Pallavicini, R.; Tagliaferri, G. Bibcode: 1994ASPC...64..687C Altcode: 1994csss....8..687C No abstract at ADS Title: Lithium Abundances in Nearby Solar-Like Stars Authors: Pasquini, L.; Edvardsson, B.; Liu, Q.; Pallavicini, R. Bibcode: 1994ASPC...64..294P Altcode: 1994csss....8..294P No abstract at ADS Title: Lithium, Activity and Post-Main-Sequence Evolution (Invited Review) Authors: Pallavicini, R. Bibcode: 1994ASPC...64..244P Altcode: 1994csss....8..244P No abstract at ADS Title: Lithium in RS CVn binaries and related chromospherically active stars . II. Spectrum synthesis analysis. Authors: Randich, S.; Gratton, R.; Pallavicini, R. Bibcode: 1993A&A...273..194R Altcode: The results of the extensive survey of the Li I 6708 Å line in RS CVn binaries and other chromospherically active stars carried out by Pallavicini et al. (1992) are reanalyzed using synthetic spectra. This allows us to obtain more accurate values of Li abundances and to separate the contributions of individual components of 5B2 binaries. As a byproduct, metallicities and rotational velocities are also obtained for all stars in the sample. An effort is made to identify physically homogeneous subgroups of stars within the original sample, including: a) pre-main sequence objects; b) young and/or warm stars on the main- sequence; c) cool evolved stars at Teff ≤ 5000 K (both members of spectroscopic binaries and single K-type giants). We confirm that the latter group (which includes many catalogued RS CVn binaries) presents an excess Li abundance with respect to what typically observed in evolved stars of the same spectral type. However, the Li abundance is moderate (log n(Li) ≤ 1.5) and with no obvious dependence on activity parameters such as rotation and chromospheric emission. A significant amount of Lithium is observed only in a fraction of these active cool stars and the presence of Li does not appear to be a characteristic property of RS CVn stars as a class. We argue, in agreement with Fekel et al. (1987), that the cool giants with excess Lithium - might have evolved from main-sequence progenitors with shallow outer convective zones (M ≥ 1.5 Msun). Other possibilities discussed by Pallavicini et al. (1992), such as enhancement of the Li line in spotted stars, production of Li by spallation reactions in flares, and reduced rotationally-induced mixing in rapidly-rotating tidally-coupled binaries, cannot be excluded, but appear less likely. We find a significant metal deficiency for many stars in the sample, with no apparent correlation with Li abundance. However, the spectral lines could be significantly affected by surface activity (spots and plages) and may not represent a true metal deficiency. Finally, we briefly comment on the possible role of active binaries in the Li enrichment of the Galaxy on the galactic evolutionary timescale. Title: The effects of stellar surface activity on the strength of the lithium 6708 A line. Authors: Pallavicini, R.; Cutispoto, G.; Randich, S.; Gratton, R. Bibcode: 1993A&A...267..145P Altcode: We have investigated the effects of stellar surface activity on the strength of the Li I 6708 A line both observationally, by searching for rotational modulation of the Li line in spotted stars, and theoretically, by means of spectrum synthesis simulations. We have monitored nearly simultaneously four spotted stars in the Li I line and in broad-band multi-color photometry, finding no significant variations of the Li equivalent width (at levels as low as a few percent) in spite of the photometric variations, indicative of spots, observed at the same time. We show by means of computer simulations that the effects of surface activity on the Li line, though present, may be less pronounced than what had previously been suggested on the basis of the solar analogy and of the strong enhancement of the Li line in sunspots. We show that the lack of significant rotational modulation of the Li line in our stars is not inconsistent with the spot coverage factors inferred from the photometric variations. We also argue that large cool spots cannot be a viable explanation for the anomalously strong Li line sometimes observed in evolved RS CVn binaries and other spotted stars. Title: X-Ray Spectroscopic Diagnostics of the Hydrodynamics of Flares on M Dwarf Stars Authors: Cheng, C.; Pallavicini, R. Bibcode: 1993uxrs.conf..525C Altcode: No abstract at ADS Title: Lithium in Stars X-ray Selected by EXOSAT Authors: Tagliaferri, G.; Randich, S.; Pallavicini, R.; Cutispoto, G. Bibcode: 1993ASSL..183..307T Altcode: 1993pssc.symp..307T No abstract at ADS Title: A high resolution spectrograph for the Galileo National Telescope Authors: Gratton, R.; Bhatia, R.; Bonanno, G.; Bruno, P.; Cali, A.; Catalano, S.; Cavazza, A.; Claudi, R.; Cosentino, R.; Douglas, N.; Merighi, R.; Molaro, P.; Pallavicini, R.; Viotti, R. Bibcode: 1993MmSAI..64..672G Altcode: No abstract at ADS Title: Time Variability of Stellar X-ray Emission Authors: Pallavicini, R. Bibcode: 1993ASSL..183..237P Altcode: 1993pssc.symp..237P No abstract at ADS Title: Optical spectroscopy of post-T Tauri star candidates. Authors: Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 1992A&A...261..245P Altcode: We report on spectroscopic observations of Post-T Tauri star candidates carried out using various instruments at ESO. The program stars were taken from the list of Lindroos (1986) and are late-type secondaries of visual binaries with early-type primaries. If the binaries are physical and not just optical pairs, their late type secondaries should still be contracting toward the ZAMS, or should have recently arrived upon it. Lindroos proposed all these stars as likely members of physical systems. We have observed spectroscopically 37 of the 41 secondaries in Lindroos' list classified of spectral type later than F2. We have also observed two additional systems that were discarded by Lindroos as likely optical pairs. For all 39 objects, we obtained moderate resolution (about 2 A) spectra in a region comprising the Li I 6708-A line and H-alpha. For 32 of these, we also obtained moderate resolution (about 1 A) spectra in the Ca II H and K lines. A few bright objects were also observed at high resolution (about 0.1 A) in the red. From our spectroscopic results we conclude that only a small fraction (less than 40 percent) of the surveyed stars show clear evidence of youth, the others being more likely optical pairs. All stars that appear to be young are located in the HR diagram very close to the ZAMS. Title: High Resolution Spectroscopy of Stellar X-Ray Sources Authors: Tagliaferri, G.; Randich, S.; Pallavicini, R.; Cutispoto, G. Bibcode: 1992ESOC...40..171T Altcode: 1992hrsw.conf..171T No abstract at ADS Title: High-Resolution Spectrum Synthesis Analysis of Late-Type Spectroscopic Binaries Authors: Randich, S.; Gratton, R.; Pallavicini, R. Bibcode: 1992ESOC...40..155R Altcode: 1992hrsw.conf..155R No abstract at ADS Title: High-Resolution Optical Spectroscopy of Cool Stars Authors: Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 1992ESOC...40..151P Altcode: 1992hrsw.conf..151P No abstract at ADS Title: Radio flares and magnetic fields on weak-line T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992A&A...259..149W Altcode: We report the first detection of circular polarization in the radio emission of two weak-line T Tauri stars. This is direct confirmation of the presence of magnetic fields in the coronae of these stars. The degree of polarization at 5 GHz is small, consistent with previous observations which did not find measurable polarization. We have also observed a radio flare on one of the two stars. The rising spectrum of the radio emission together with the low degree of polarization are strong evidence that radio outbursts on this class of stars are due to nonthermal gyrosynchrotron emission which is optically thick in the microwave range. One of the two stars shows no evidence for circumstellar material, and thus can be classified as 'naked'. However the other apparently has a dust disk, and the evidence of flaring on this star indicates that the mechanism involved does not require an empty circumstellar environment. Title: X-Ray Spectroscopic Diagnostics of the Hydrodynamics of Flares on M Dwarf Stars Authors: Cheng, C. -C.; Pallavicini, R. Bibcode: 1992AAS...180.6007C Altcode: 1992BAAS...24..826C No abstract at ADS Title: A 5GHz radio survey of selected POST T Tauri and naked T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992A&A...257..557W Altcode: Results of a radio survey of weak-lined T Tauri (variably classified as either post T Tauri or naked T Tauri) stars at 5 GHz are reported. Thirty-two targets, chosen on the basis of known high-activity levels or youth indications, were observed, and 15, including eight previously unknown radio sources, were detected. It is suggested that most weak-lined T Tauris with high activity levels, e.g., as indicated by a high X-ray flux, are likely to be detectable radio sources at some time, but the radio emission goes through high and low phases. For the subsample of 14 stars observed in Taurus-Auriga which were thoroughly studied at IR, optical, and X-ray wavelengths, a clear association is found between radio activity and youth. Title: Mg II absolute line profiles for late-type stars and for spatially-resolved solar regions. Authors: Cerruti-Sola, M.; Cheng, C. -C.; Pallavicini, R. Bibcode: 1992A&A...256..185C Altcode: The authors present the results of a comparison of Mg II h and k line profiles and fluxes for late-type stars observed with IUE and for spatially resolved solar regions observed at comparable resolution by the NRL Spectrograph on Skylab. They show that the spatially resolved solar observations are in good agreement with the disk integrated stellar observations, thus suggesting that different Mg II emission levels observed in stars of similar spectral type are due to different fractions of their surface covered by magnetic regions. The authors confirm that the Mg II stellar fluxes are well correlated with other chromospheric and transition-region fluxes, and show that the spatially resolved solar data obey the same flux-flux relationships as the stellar data with virtually the same slope. They compare some important line diagnostic parameters (k/h, Δk1, Δk2, and FWHM of the k line) in disk integrated stellar data and in spatially resolved solar regions, finding no significant discrepancies between the two cases. Finally, the authors discuss the possibility and limitations of using the comparison of solar and stellar Mg II fluxes to infer the fraction of a star's surface covered by magnetic regions. Title: A Low-Resolution Spectroscopic Survey of Post-T Tauri Candidates Authors: Pallavicini, R.; Pasquini, L.; Randich, S. Bibcode: 1992ASPC...26..337P Altcode: 1992csss....7..337P No abstract at ADS Title: Solar and stellar coronae. Proceedings. IAU Joint Commission Meeting on Solar and Stellar Coronae, Buenos Aires (Argentina), 30 Jul 1991. Authors: Pallavicini, R. Bibcode: 1992MmSAI..63..537P Altcode: Dedicated to the memory of Giuseppe Vaiana. The material presented in this volume gives an up-to-date picture of the field of solar and stellar coronae just before the launch of the satellite Yohkoh and in the early stages of analysis of stellar data from ROSAT and HST. Title: Photometry of Serendipitous X-ray Sources Detected by EXOSAT Authors: Cutispoto, G.; Pallavicini, R.; Pasquini, L.; Rodono, M.; Tagliaferri, G. Bibcode: 1992ASPC...26..119C Altcode: 1992csss....7..119C No abstract at ADS Title: A Comparison of MG II h; K Lines in the Sun; Cool Stars Authors: Cerruti-Sola, M.; Cheng, C. -C.; Pallavicini, R. Bibcode: 1992ASPC...26..268C Altcode: 1992csss....7..268C No abstract at ADS Title: A 5 GHz Survey of Weak-Lined T Tauri Stars Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992ASPC...26..334W Altcode: 1992csss....7..334W No abstract at ADS Title: Optical Spectroscopy of Cool Stars Detected by EXOSAT Authors: Tagliaferri, G.; Cutispoto, G.; Giommi, P.; Pallavicini, R.; Pasquini, L.; Rodono, M. Bibcode: 1992ASPC...26..122T Altcode: 1992csss....7..122T No abstract at ADS Title: A Search for Rotational Modulation of the Lithium Line in Spotted Stars Authors: Pallavicini, R.; Cutispoto, G.; Randich, S. Bibcode: 1992LNP...397..319P Altcode: 1992sils.conf..319P No significant rotational modulation of the equivalent width of the LiI blend was detected for any of the programme stars. The derived upper limits (ΔW/W < 5-10%) are substantially smaller than what had been suggested previously on the basis of the solar analogy. If we assume that the enhancement of the equivalent width of the LiI line in starspots is about the same as for the Sun, the above upper limits imply a spot coverage factor of only a few percent, much smaller than that derived from the photometric variations (15-25%). It is clear therefore that the enhancement of the Lithium line in the spots of these stars, if present, is certainly lower than for the Sun. Title: Phase Dependent Variations of the Hα Line in Chromospherically Active Stars Authors: Cutispoto, G.; Pallavicini, R. Bibcode: 1992LNP...397..264C Altcode: 1992sils.conf..264C No abstract at ADS Title: Lithium in RS CVn binaries and related chromospherically active stars. I.Observational results. Authors: Pallavicini, R.; Randich, S.; Giampapa, M. S. Bibcode: 1992A&A...253..185P Altcode: The present survey of the Li I 6708 A line in a sample of spectral type G and K stars with luminosity classes III, IV, and V shows that many K-type stars in the sample, including a large number of RS CVn binaries, show an anomalously high Li abundance relative to typical inactive stars of the same spectral type. Only a few stars in the sample are likely to be premain sequence objects of stars which have recently arrived on the main sequence. Mechanisms that could lead to the enhanced Li absorption in chromospherically active stars are discussed; these encompass large cool spots on the stellar surface, the production of Li in stellar flares by spallation reactions, and the evolution from main-sequence progenitors without, or with very shallow, outer convective zones. Title: Variability of solar and stellar coronae. Authors: Cheng, C. -C.; Pallavicini, Roberto Bibcode: 1992MmSAI..63..697C Altcode: The time variability of the coronal emission from the sun and other late-type stars is analyzed using solar data as a guideline to interpreting the spatially unresolved stellar observations. Results of numerical simulation of solar and stellar flares are compared with observations by Exosat. It is noted that solar observations at a variety of different wavelengths have revealed, in addition to flares, the presence of less energetic shorter-lived events, 'microflares', that occur randomly in space and time. The origin of these microflares is discussed. Title: A Comparison of Star SPOT Distributions for Various Active Stars Based on Doppler Images Authors: Kürster, M.; Hatzes, A. P.; Pallavicini, R.; Randich, S. Bibcode: 1992ASPC...26..249K Altcode: 1992csss....7..249K No abstract at ADS Title: X-ray Spectroscopic Diagnostics of the Hydrodynamics of Flares on M Dwarf Stars Authors: Cheng, C. -C.; Pallavicini, R. Bibcode: 1992AAS...179.9306C Altcode: 1992BAAS...24R.684C No abstract at ADS Title: Radio observations of weak-lined T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992MmSAI..63..751W Altcode: We report the results of a search for radio-continuum emission from weak-lined T Tauri stars selected on the basis of a range of criteria. A correlation is found with strong X-ray emission and with youth. All the stars in the survey older than about 20 million years were not detected as radio sources. A flare was seen on one of the survey targets, with a rise time of several hours. Circular polarization was also seen in two of the targets, providing the first direct confirmation of the presence of magnetic fields on these stars. Title: Stellar Flares: Observations and Modelling Authors: Pallavicini, R. Bibcode: 1992ASIC..373..509P Altcode: 1992sla..conf..509P No abstract at ADS Title: Lithium Abundances in Northern RS CVn Binaries Authors: Randich, S.; Giampapa, M. S.; Pallavicini, R. Bibcode: 1992ASPC...26..576R Altcode: 1992csss....7..576R No abstract at ADS Title: Stellar Flares - Confined or Eruptive Events Authors: Pallavicini, R. Bibcode: 1992LNP...399..289P Altcode: 1992IAUCo.133..289P; 1992esf..coll..289P No abstract at ADS Title: Lithium in RS CVn Binaries and Related Chromospherically Active Stars Authors: Pallavicini, R.; Randich, S.; Giampapa, M. S. Bibcode: 1992LNP...397..108P Altcode: 1992sils.conf..108P No abstract at ADS Title: IAU, Joint Commission Meeting on Solar and Stellar Coronae, Buenos Aires, Argentina, July 30, 1991, Proceedings Authors: Pallavicini, Roberto Bibcode: 1992MmSAI..63.....P Altcode: Papers are presented on coronal emission and stellar evolution, high-resolution observations of the solar corona, modeling solar coronal loops, heating and momentum deposition in hot stars, and heating of solar and stellar chromospheres and coronae by MHD waves, and magnetized and collimated meridional outflows. Other papers are on X-ray activity and magnetic fields of T Tauri stars, X-ray spectroscopy of solar and stellar coronae, radio observations of solar and stellar coronae, stellar coronae and their relation to convection zones and rotation rates, results from an extensive Einstein Observatory survey of B-type stars, and transient optical periodicities in coronal red dwarfs. Particular attention is given to radio observations of weak-lined T Tauri, spectra of MHD turbulence in the solar corona, the thermodynamic decay scaling laws in solar loop flares, the differential emission measure and the composition of the solar corona, the structural instability of nonlinear Alfven waves, and heating of solar coronal holes by reflected Alfven waves. (For individual items see A93-26152 to A93-26175) Title: X-rays from Both Components of the Flare Star Binary Gliese 867 Authors: Pollock, A. M. T.; Tagliaferri, G.; Pallavicini, R. Bibcode: 1992LNP...397..331P Altcode: 1992sils.conf..331P No abstract at ADS Title: Numerical Simulations of Flares on Late-type Stars: Hydrodynamics and X-ray Spectra Authors: Cheng, Chung-Chieh; Pallavicini, Roberto Bibcode: 1992LNP...397..258C Altcode: 1992sils.conf..258C No abstract at ADS Title: Optical Properties of Cool Stars Discovered by EXOSAT Authors: Tagliaferri, G.; Cutispoto, G.; Giommi, P.; Pallavicini, R.; Pasquini, L.; Rodonó, M. Bibcode: 1992LNP...397..340T Altcode: 1992sils.conf..340T No abstract at ADS Title: Stellar flares: Confined or eruptive events? Authors: Pallavicini, R. Bibcode: 1992LNP...399..287P Altcode: Observations in different spectral bands have shown the existence of many similarities between solar and stellar flares, in spite of the far larger energies that are typically involved in the latter. The analogy may go as far as to include the occurrence on stars of both confined and eruptive flares similar to those observed on the Sun. The observational evidence for the existence of stellar eruptive flares is reviewed and it is shown that the data are still inconclusive in this respect. Models of stellar flares as either confined or eruptive magnetic structures are also discussed and it is concluded that models are unable at present to discriminate between the two cases. Title: Stellar Chromospheres, Coronae, and Winds Authors: Pallavicini, R. Bibcode: 1992ASIC..373..313P Altcode: 1992sla..conf..313P No abstract at ADS Title: Numerical Simulations of Flares on M Dwarf Stars. I. Hydrodynamics and Coronal X-Ray Emission Authors: Cheng, Chung-Chieh; Pallavicini, Roberto Bibcode: 1991ApJ...381..234C Altcode: Flare-loop models are utilized to simulate the time evolution and physical characteristics of stellar X-ray flares by varying the values of flare-energy input and loop parameters. The hydrodynamic evolution is studied in terms of changes in the parameters of the mass, energy, and momentum equations within an area bounded by the chromosphere and the corona. The zone supports a magnetically confined loop for which processes are described including the expansion of heated coronal gas, chromospheric evaporation, and plasma compression at loop footpoints. The intensities, time profiles, and average coronal temperatures of X-ray flares are derived from the simulations and compared to observational evidence. Because the amount of evaporated material does not vary linearly with flare-energy input, large loops are required to produce the energy measured from stellar flares. Title: H-alpha absolute chromospheric fluxes in G and K dwarfs and subgiants. Authors: Pasquini, L.; Pallavicini, R. Bibcode: 1991A&A...251..199P Altcode: High resolution, high S/N H-alpha observations for a sample of 85 dwarfs and subgiants of spectral type F8 to K5 are presented. A calibration procedure to convert the observed equivalent widths to absolute fluxes at the stellar surface is developed and these fluxes are compared with those obtained in the Ca II K line are compared. Within the observed range of spectral types there is some evidence that the ratio of H-alpha to Ca II K line fluxes increases toward cooler stars, suggesting that this effect, which is prominent in M dwarfs, is already significant for K stars. For G and early K stars the H-alpha flux is found to increase with increasing activity more slowly than the Ca II K flux, giving flux-flux relationships that are similar to those observed for solar plages. It is also found that all subgiants in the sample have very low H-alpha fluxes, typically lower than for dwarfs of the same spectral type. The survey clearly shows that the H-alpha line, although being a useful diagnostic of stellar chromospheres, and easily accessible to modern solid-state detectors, is not particularly suitable for an accurate determination of absolute chromospheric fluxes. Title: The Role of Magnetic Loops in Solar Flares Authors: Pallavicini, R. Bibcode: 1991RSPTA.336..389P Altcode: X-ray and ultraviolet observations of flares have provided much important information on their spatial structure and magnetic topology. The early observations from Skylab emphasized the role of simple loops and loop arcades, but later observations from the Solar Maximum Mission have greatly complicated this picture. Flares appear in a multitude of loops with complex spatial and temporal interrelations. In many cases, interactions between different loops appear to play a crucial role. The inferred magnetic topology of solar flares will be reviewed with emphasis on the implications for processes of energy release and transfer. It will be shown that the spatial resolution of the observations obtained so far is still inadequate for solving many basic questions of solar flare research. Title: Book-Review - Hot Thin Plasma in Astrophysics Authors: Pallavicini, R.; Boller, T. Bibcode: 1991AN....312..277P Altcode: No abstract at ADS Title: Numerical Simulations of Flares on M Dwarf Stars Authors: Cheng, C. -C.; Pallavicini, R. Bibcode: 1991BAAS...23..902C Altcode: No abstract at ADS Title: Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. I. Time variability and spectral classification of eight southern stars. Authors: Cutispoto, G.; Tagliaferri, G.; Giommi, P.; Gouiffes, C.; Pallavicini, R.; Pasquini, L.; Rodono, M. Bibcode: 1991A&AS...87..233C Altcode: As part of a larger program to study the optical properties of serendipitous Exosat sources, optical photometry and low-resolution spectroscopy are presented for eight southern stars which have been identified as optical counterparts of Exosat sources. X-ray flux variability has been detected for three of them. In all three cases the optical counterparts show RS CVn-type variability. Of the remaining five stars, two are found to be variable in the optical. The high X-ray luminosities inferred from the derived spectroscopic parallaxes indicates that these variable sources are all very active systems, possibly RS CVn binaries. The three nonvariable sources are more likely normal main-sequences stars, two of them with a rather high level of coronal emission. Title: Quiscent and flaring X-rays from both Gliese 867A and Gliese 867B. Authors: Pollock, A. M. T.; Tagliaferri, G.; Pallavicini, R. Bibcode: 1991A&A...241..451P Altcode: X-ray observations of the flare-star binary system Gliese 867AB obtained with the Low Energy instrument on the Exosat Observatory were analyzed. By applying a likelihood method, it is shown that both components of the system were contributing to the observed X-ray emission with an intensity ratio A:B of about 3:1. It is also shown that X-ray flares with energies of the order of 10 to the 32nd erg originated from both stars. In the light of these results, previous X-ray observations, made with the IPC instrument aboard the Einstein Observatory were reanalyzed, and it was found, somewhat unexpectedly, that during those observations G867B was roughly as bright as G867A. It was also found that the variations observed in the Einstein data were due to changes in both components, much like the flares observed with Exosat, rather than to the earlier suggestion by Agrawal (1988) of rotational modulation of G867A. Title: Low-Resolution Spectra of Stellar Coronae and Flares with EXOSAT: The Iron K-line Authors: Pallavicini, R.; Tagliaferri, G. Bibcode: 1991LNP...385...26P Altcode: 1991ildx.conf...26P No abstract at ADS Title: Lithium abundance and chromospheric activity. Authors: Randich, S.; Pallavicini, R. Bibcode: 1991MmSAI..62...75R Altcode: The relationship between chromospheric activity and lithium abundance in late-type stars is not well understood. For solar-type stars, it is generally believed that chromospheric emission and Li abundance should both decrease with age. However, there are a number of stars with low Ca-II emission and high Li content. The Li line is also strong in many K-type chromospherically active stars including members of RS CVn binaries. Some of these stars may be young or even pre-main-sequence objects; many other, however, are apparently evolved post-main-sequence stars. Recent observational data are presented that show the presence of lithium in the cool components of many RS CVn binaries and in other K-type stars with active chromospheres. Several possibilities to explain the observed Li excess in these stars are discussed. Title: The role of magnetic loops in solar flares. Authors: Pallavicini, R. Bibcode: 1991psf..conf..389P Altcode: The inferred magnetic topology of solar flares is reviewed with emphasis on the implications for processes of energy release and transfer. It is shown that the spatial resolution of the observations obtained so far is still inadequate for solving many basic questions of solar flare research. Title: Lithium Abundance and Rotation in Southern Chromospherically Active Stars Authors: Randich, S.; Pallavicini, R. Bibcode: 1991ASIC..340..251R Altcode: 1991amey.conf..251R No abstract at ADS Title: Chromospheric Activity in Late-Type Giants and Supergiants: Constraints on Heating Theories (With 1 Figure) Authors: Pasquini, L.; Brocato, E.; Pallavicini, R. Bibcode: 1991mcch.conf..222P Altcode: No abstract at ADS Title: Lithium in chromospherically active stars. Authors: Pallavicini, R.; Randich, S.; Giampapa, M.; Cutispoto, G. Bibcode: 1990Msngr..62...51P Altcode: No abstract at ADS Title: Chromospheric activity of evolved late-type stars - Chromospheric activity in evolved stars Authors: Pasquini, L.; Brocato, E.; Pallavicini, R. Bibcode: 1990A&A...234..277P Altcode: Ca II K emission in a homogeneous sample of late-type giants and supergiants is analyzed. The Wilson-Bappu relationship and color-temperature scales are used to construct an H-R diagram which is compared with theoretical evolutionary tracks. It is shown that in spite of the errors involved in the determination of the fundamental stellar parameters, a clear relationship between chromospheric surface activity and stellar mass is present. 5-10 solar mass stars in He burning phase show the highest levels of activity; on the other hand, less massive stars ascending along the Red Giant Branch are extremely quiet. A correlation between surface activity and rotation is found, and it is shown that a knowledge of the stellar evolutionary history is essential for understanding chromospheric emission from evolved stars. Title: X-ray emission from solar neighbourhood flare stars : a comprehensivesurvey of EXOSAT results. Authors: Pallavicini, R.; Tagliaferri, G.; Stella, L. Bibcode: 1990A&A...228..403P Altcode: Exosat Observatory observations of flare stars pertaining to 25 separate sources are examined. The Exosat instrumentation is described, and a data sample is presented. Quiescent and flaring emissions from UV Ceti-type flare stars as observed with a low-energy experiment on Exosat are discussed, and the results of the timing analysis of the low-energy data are analyzed, along with the results of the spectral analysis of the Exosat medium-energy flare data. It is observed that while all sources are detected by the low-energy experiment, the medium-energy data is limited only to large flares. It is concluded that the quiescent X-ray luminosity of different flare stars is related to the bolometric luminosity, with the quiescent X-ray emission changing little from one observation to another, and that there is a substantial variability over a different time scales, appearing in the form of either individual flares or of more gradual variations. Title: Flaring and quiescent X-rays from Castor. Authors: Pallavicini, R.; Tagliaferri, G.; Pollock, A. M. T.; Schmitt, J. H. M. M.; Rosso, C. Bibcode: 1990A&A...227..483P Altcode: Using data obtained with the Low Energy (LE) and Medium Energy instruments aboard Exosat, the first detection of both flaring and quiescent X-ray emission from the A-type visual binary Castor (alpha Gem) is reported. In the LE, Castor was clearly resolved from the nearby star YY Gem, which was also observed to flare some hours after Castor. After verifying that the Castor flare was indeed an X-ray as opposed to a UV event, physical parameters of the flaring source are derived. The detection of the quiescent emission led to reevaluation of the previous X-ray observations by the Einstein Observatory showing that, contrary to earlier reports, Castor was strongly detected in the IPC. Possible interpretations of the results are discussed by devoting some attention to the multiplicity of the Castor system, suggesting that the X-rays originate from an unseen late-type companion rather than from the A-type primaries. Title: Spectroscopy of stellar coronal sources with the medium energy experiment on EXOSAT Authors: Pallavicini, R.; Pasquini, L.; Schmitt, J. H. M. M.; Tagliaferri, G. Bibcode: 1990hrxr.conf..122P Altcode: 1990IAUCo.115..122P Results obtained on the spectral analysis of the Exosat medium-energy observations of stellar coronal sources are summarized. Special attention is given to the time-resolved spectroscopy of stellar flares and determination of the temperature structure of quiescent RS CVn binaries. Substantial differences were found between the coronae of RS CVn stars and the coronae of the sun and other single late-type stars. The results suggest that either the coronae of most RS CVn stars involve more than one family of loops (also indicated by eclipse observations of White et al., 1988) or the coronal structures in these stars have a more complex emission measure distribution than the simple power-law assumed in this study. Title: X-Ray Emission from Solar Neighbourhood Flare Stars Authors: Pallavicini, R.; Stella, L.; Tagliaferri, G. Bibcode: 1990IAUS..137..147P Altcode: No abstract at ADS Title: High-resolution spectroscopy of cool stars at ESO. Authors: Pasquini, L.; Pallavicini, R. Bibcode: 1990MmSAI..61..737P Altcode: An overview of the instrumentation presently available at La Silla for high-resolution spectroscopy is presented, and several programs that have been carried out recently using these instruments are discussed. Discussed topics include the determination of chromospheric radiative losses in the Ca II H and K lines and in H-alpha, the search for rotational modulation in H-alpha and in the Li I 6708 A line, the measurement of stellar rotation rates, and the investigation of lithium abundance in RS CVn binaries and other chromospherically active stars. Title: Time variability of stellar coronal sources observed by EXOSAT Authors: Pallavicini, R.; Schmitt, J. H. M. M. Bibcode: 1990AdSpR..10b.125P Altcode: 1990AdSpR..10..125P We present an overview of time variability in stellar coronal sources as observed with the EXOSAT satellite. We focus on M dwarf flare stars and we discuss both quiescent and flaring emission. We also outline recent developments in the modelling of stellar flares. Title: Energy Release in Stellar Flares Authors: Pallavicini, R. Bibcode: 1990IAUS..142...77P Altcode: Flarelike events similar to those observed on the sun occur on many different types of stars, particularly on late K and M dwarfs. Although the physical mechanisms responsible for these events remain largely unknown, it is likely that the flare energy derives from dissipation of magnetic fields as is the case for solar flares. The basic observational facts that suggest an analogy between solar and stellar flares are reviewed, and the ways in which the different physical conditions occurring on stars may affect the application of current solar-type models to the stellar case are discussed. It is shown that, in spite of a qualitative agreement found between model predictions and observations, there is still no convincing evidence that stellar flares are simply scaled-up versions of solar flares. Major advances in the observations of stellar flares are required before this fundamental question can be safely addressed. Title: The differential emission measure of Lambda And Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1990hrxr.conf...36L Altcode: 1990IAUCo.115...36L Results are presented from an analysis of X-ray and UV observations of Lambda And binary, carried out simultaneously on November 11, 1985 from the Exosat and the IUE. The results were used to derive the differential emission measure (DEM) as a function of temperature up to a maximum of 35 x 10 exp 6 K. The DEM exhibited a minimum around 2 x 10 exp 5 K and increased at higher temperature. The derived DEM is compatible with a loop model having a half length of 10 exp 12 cm, a cross section of 3 x 10 exp 22 sq cm, and a pressure of 15 dyn/sq cm. Title: X-ray spectroscopy of RS CVn stars with EXOSAT. Authors: Pasquini, L.; Schmitt, J. H. M. M.; Pallavicini, R. Bibcode: 1989A&A...226..225P Altcode: Results are presented of a spectral analysis of a sample of RS CVn stars which comprises all (except two) cataloged RS CVn binaries observed by Exosat. Data from both the Medium Energy and Low Energy Exosat experiments are analyzed assuming simple spectral models and the dependence of the fitted coronal parameters on the signal-to-noise ratio. Evidence is found for multitemperature coronal structures in RS CVn stars, together with indications of intrinsic differences in the temperature stratification of different stars. Title: Erratum - Calibration Stars for Cross-Correlation Studies of Stellar Rotation and an Examination of the Archival Data Authors: Soderblom, D. R.; Pendleton, J.; Pallavicini, R. Bibcode: 1989AJ.....98..737S Altcode: No abstract at ADS Title: Rotation Rates of Giant Stars Authors: Gray, David F.; Pallavicini, R. Bibcode: 1989PASP..101..695G Altcode: The rotation rates and macroturbulence dispersion of 14 G and K giants were measured using Fourier reduction of spectral-line profiles. The high-spectral-resolution, high-signal-to-noise observations were taken with the Coude Echelle Spectrometer of the European Southern Observatory. Good agreement was found between the present results and previous investigations, showing that no large systematic differences are introduced by using different spectrographs and detectors. The results generally confirm the low rotation seen for cool giants. Title: X-ray emission from stellar coronae Authors: Pallavicini, R. Bibcode: 1989A&ARv...1..177P Altcode: Stars of nearly all spectral types and luminosity classes are surrounded by tenuous high-temperature ( T≈106-107K) coronae, which emit most of their radiation in the soft X-ray part of the spectrum. This paper reviews our present observational knowledge and theoretical understanding of stellar coronae, as has emerged from the extensive observations carried out with the Einstein and EXOSAT Observatories. We argue that different physical mechanisms are likely to be responsible for coronal emission in different parts of the HR diagram and we discuss the principal scenarios that have been proposed to account for the data. We show that in spite of the enormous progress made during the past decade, our understanding of stellar coronal emission remains incomplete and largely phenomenological. We outline major unsolved problems to be addressed by future space missions. Title: Book-Review - Hot Thin Plasmas in Astrophysics Authors: Pallavicini, R. Bibcode: 1989Sci...244..996P Altcode: No abstract at ADS Title: Absolute flux calibration of the H and K lines of CA II : chromospheric radiative losses in F and G-type stars. Authors: Pasquini, L.; Pallavicini, R.; Dravins, D. Bibcode: 1989A&A...213..261P Altcode: Ca II H and K spectra of 81 (mainly Southern) F and G stars are analyzed using two different calibration methods. It is shown that, for spectra of sufficiently high resolution, and for stars of relatively low rotation rates, the calibrations of Linsky et al. (1979) and of Pasquini et al. (1988) give essentially the same results. These calibrations are used to derive absolute surface fluxes in the H and K lines of Ca II for 64 stars. It is shown that several late-F and early-G giants and supergiants have Ca II H and K fluxes in excess of about 10 to the 6th erg/sq cm s, much larger than those typically observed for normal giants of later spectral types. Title: A comparison of solar and stellar ultraviolet spectra obtained with SKYLAB and IUE. Authors: Cappelli, A.; Cerruti-Sola, M.; Cheng, C. C.; Pallavicini, R. Bibcode: 1989A&A...213..226C Altcode: A comparison is presented of 78 Short-Wavelength Primary (SWP) low-resolution IUE spectra of 45 late-type stars and 10 high-resolution Skylab spectra of spatially-resolved solar regions of various degrees of magnetic activity, including quiet areas, plage regions, and one flare. The results show that the different levels of chromospheric and transition region emission observed in stars of similar spectral types are paralleled by a similar behavior displayed by solar regions of different magnetic activity and that the spatially-resolved solar data obey the same flux-flux relationships as the stellar data over more than three order of magnitude. It is argued that the similar behavior of the solar and stellar UV line fluxes, together with the dependence of the stellar fluxes on rotation, presents an evidence that stellar activity is of magnetic origin and likely results from a dynamo process. Title: Calibration Stars for Cross-Correlation Studies of Stellar Rotation, and an Examination of the Archival Data Authors: Soderblom, David R.; Pendleton, James; Pallavicini, Roberto Bibcode: 1989AJ.....97..539S Altcode: Precise v sin i values have been measured for more than 60 F and G dwarfs. Spanning the range of 5-80 km/s, they are primarily useful for calibrating cross correlations up to about 50 km/s. The present values are compared to older ones from photographic spectra and it is found that most of the older data are adequate but have fairly large errors. However, the rotational-velocity catalog of Uesugi and Fukuda (1982) is contaminated with erroneous data and is, therefore, suspect as a source of stellar rotational information. Title: Recent advances in stellar coronal physics. Authors: Pallavicini, R. Bibcode: 1989MmSAI..60...33P Altcode: 1989MSAIt..60...33P A brief summary is given of recent advances in our understanding of X-ray emission from stellar coronae. Results from the European satellite EXOSAT are presented and discussed in some detail. Title: X-ray emission from stellar flares: EXOSAT results. Authors: Pallavicini, R.; Tagliaferri, G. Bibcode: 1989sasf.confP..17P Altcode: 1989IAUCo.104P..17P; 1988sasf.conf...17P The authors present an overview of recent observations of stellar X-ray flares obtained with the EXOSAT Observatory. They discuss a few examples of flares from M dwarf flare stars, from RS CVn and Algol-type binaries, from single late-type stars (including a GO dwarf and an A-type visual binary), and from pre-main-sequence objects. The authors also draw some general conclusions from the preliminary analysis of the EXOSAT data samples. Title: Flare energetics. Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veck, N. J. Bibcode: 1989epos.conf..377W Altcode: The authors have sought to establish a comprehensive and self-consistent picture of the sources and transport of energy within a flare. To achieve this goal, they chose five flares in 1980 that were well observed with instruments on the Solar Maximum Mission, and with other space-borne and ground-based instruments. The events were chosen to represent various types of flares. Details of the observations available for them and the corresponding physical parameters derived from these data are presented. The flares were studied from two perspectives, the impulsive and gradual phases, and then the results were compared to obtain the overall picture of the energetics of these flares. The authors also discuss the role that modeling can play in estimating the total energy of a flare when the observationally determined parameters are used as the input to a numerical model. Finally, a critique of our current understanding of flare energetics and the methods used to determine various energetics terms is outlined, and possible future directions of research in this area are suggested. Title: A giant X-ray flare from a B9 + post-T Tauri system detected by EXOSAT. Authors: Tagliaferri, G.; Giommi, P.; Angelini, L.; Osborne, J. P.; Pallavicini, R. Bibcode: 1989sasf.confP.131T Altcode: 1989IAUCo.104P.131T; 1988sasf.conf..131T The authors report the serendipitous discovery by EXOSAT of a flaring X-ray source in the field of the Seyfert type I galaxy III ZW 2. They identify this source with the visual binary HD 560 (B9V + G5Ve) and argue that virtually all of the observed X-ray flux, including the flare, came from its late-type component (HD 560 B). Optical studies have lead to the identification of HD 560 B as a post-T Tauri star. Since these stars are difficult to detect by optical methods, X-ray observations may prove to be the best way to identify them. Title: Stellar coronal physics with the High-Throughput X-Ray Spectroscopy Mission (XMM) Authors: Pallavicini, R. Bibcode: 1989MmSAI..60..289P Altcode: The High-Throughput X-Ray Spectroscopy Mission (XMM) to be flown by the end of this century is the second 'cornerstone' project in the ESA Long-Term Program for Space Science. It will consist of a high-throughput multi-mirror grazing incidence telescope coupled to dispersive and nondispersive imaging spectrometers. With its unprecedented sensitivity over a wide band, the capability of simultaneous medium- and low-resolution spectroscopy, and the continuous-look capability, it will make possible a major advance in all fields of X-ray astronomy. This paper illustrates the capabilities of XMM for the study of stellar coronae with emphasis on the determination of the physical parameters (temperature, density, fluid motions) of coronal plasmas, the investigation of coronal heating mechanisms, the determination of the geometrical and thermal structure of coronae, and the study of variability on all time scales from seconds to days. Title: An X-Ray Flare from a B9+ Post--T Tauri Star System in the Field of the Seyfert Galaxy III ZW 2 Authors: Tagliaferri, G.; Giommi, P.; Angelini, L.; Osborne, J. P.; Pallavicini, R. Bibcode: 1988ApJ...331L.113T Altcode: We report the serendipitous discovery by EXOSAT of a flaring X-ray source in the field of the Seyfert type I galaxy III Zw 2. In contrast to an earlier report that attributed the variability observed by the medium energy experiment to III Zw 2, we show that the variability was entirely due to the serendipitous source. We identify this source with the visual binary HD 560 (B9V+G5Ve) and we argue that virtually all of the observed X-ray flux from the binary, including the flare, came from its late-type component. These X-ray observations bring support to the optical classification of HD 560 B as a post-T Tauri star. Title: Modeling of long-duration two-ribbon flares on M dwarf stars. Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A. Bibcode: 1988A&A...201...93P Altcode: A time-dependent model of magnetic reconnection for the decay phase of solar two-ribbon flares is applied to long-duration stellar flares observed by the Einstein and Exosat observatories on the stars EQ Peg and Prox Cen. It is shown that the model reproduces correctly the energy release rate and temporal evolution during the decay phase of the observed events. It is concluded that the observed behavior is consistent with the interpretation of these flares as stellar counterparts of solar two-ribbon flares. In addition, taking into account recent measurements of stellar magnetic fields by Saar and Linsky (1985), it is shown that the agreement between the data and the analytical model results in a well-defined set of physical parameters for the emitting region. Title: Ultraviolet emission from the sun and stars: A comparison of IUE and SKYLAB spectra Authors: Cappelli, A.; Cerruti-Sola, M.; Cheng, C. C.; Pallavicini, R. Bibcode: 1988ESASP.281a.287C Altcode: Low-resolution IUE SWP spectra of late-type stars and high-resolution Skylab spectra of spatially-resolved solar regions of various degrees of magnetic activity (quiet areas, plages, flares) are compared. The high-resolution solar spectra are degraded to the same resolution of IUE and the solar and stellar data are analyzed in exactly the same way. It is shown that the different levels of chromospheric and transition region emission observed in stars of similar spectral types are paralleled by a similar behavior displayed by solar regions of different magnetic activity. Spatially-resolved solar data obey the same flux-flux relationships as the stellar data over more than three orders of magnitude, with virtually the same slope and similar scatter. The similar behavior of the solar and stellar UV line fluxes, together with the dependence of the stellar fluxes on rotation, are indirect evidence that stellar activity is of magnetic origin and likely results from a dynamo process. The contribution of blends, under different activity conditions, to line fluxes derived from IUE low-reslution spectra varies depending on the activity level, and may be substantial for the lines of O I at 1304 A and He II at 1640 A. Title: VLBI observations of RS CVn and Algol-type binaries. Authors: Massi, M.; Felli, M.; Pallavicini, R.; Tofani, G.; Palagi, F.; Catarzi, M. Bibcode: 1988A&A...197..200M Altcode: The authors report on intercontinental VLBI observations of four RS CVn binaries and of Algol made on 12 June 1986 at λ = 6 cm. All sources were detected at least on the shortest baselines. For one of them (UX Ari) the larger amount of data available allows to conclude that the emission came from an extended, possibly structured region, comparable in size with the binary separation. The authors compare their observations with those obtained previously by Mutel et al. (1985) and discuss briefly the physical implications of these observations for the modelling of radio emission in active late-type binaries. Title: Co-ordinated VLA and EXOSAT observations of the flrae stars UV Ceti, EQ Pegasi, YZ Canis Minoris and AD Leonis. Authors: Kundu, M. R.; Pallavicini, R.; White, S. M.; Jackson, P. D. Bibcode: 1988A&A...195..159K Altcode: The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi and AD Leo) simultaneously with the VLA and the EXOSAT satellite over continuous periods of 7 - 10 h. This is the first time that flare stars were observed simultaneously in X-rays and at microwave frequencies with high sensitivity instrumentation. All stars were detected both at the quiescent level and during flares. Although considerable activity in both X-rays and in the radio was found, there was little correlation between the two wavelength domains. The auhors discuss the significance of these observations for coronal activity in red dwarf flare stars. Title: CA II absolute line profles of southern late-type stars. Authors: Pasquini, L.; Pallavicini, R.; Pakull, M. Bibcode: 1988A&A...191..253P Altcode: The authors have used the Coudé Echelle Spectrometer and Reticon detector at the European Southern Observatory to acquire high-resolution, high-quality spectra in the H and K lines of Ca II for 50 (mostly Southern) late-type dwarfs and giants. They have developed a calibration procedure for converting the observed line profiles into absolute flux units at the star surface and derived chromospheric radiative losses in these lines. They discuss spectral features observed in stars of different effective temperature and gravity and stress the relevance of these observations for the study of stellar chromospheres. Title: Stellar coronae with EXOSAT : broad band spectroscopy of nearby coronal sources. Authors: Pallavicini, R.; Monsignori-Fossi, B. C.; Landini, M.; Schmitt, J. H. M. M. Bibcode: 1988A&A...191..109P Altcode: Broad-band observations of stellar coronae obtained with the Low Energy experiment on board the Exosat satellite are presented, together with a technique for the analysis of Exosat low-energy data. The limitations of filter spectroscopy with Exosat are discussed. Specific relationships are provided for extracting physical quantities (temperature, emission measure, luminosities) from the observed count rates for the case of nearby coronal sources. A continuous temperature distribution exists in the coronae of late-type stars; the differential emission measure distribution extends to temperatures in excess of 10 million K for flare stars and RS CVn binaries, even during quiescent conditions. Coronal loop models, similar to those developed for magnetically confined structures on the sun, should be used for interpreting spatially integrated observations of stellar coronae. Title: Temporal and Spatial Relationships between O V and Fe XXI Emissions in Solar Flares Authors: Cheng, Chung-Chieh; Pallavicini, Roberto Bibcode: 1988ApJ...324.1138C Altcode: The temporal-spatial structure of simple solar flares observed with the Ultraviolet Spectrometer and Polarimeter of the Solar Maximum mission satellite has been studied in order to investigate the relationships between the impulsive O V and the gradual Fe XXI emissions. The point-like flares are characterized by the cotemporal evolution of the O V and Fe XXI emissions. The simple loop flares have a much larger spatial extent and show two distinctive phases: an initial impulsive phase with its emission localized in loop footpoints, and a gradual phase with its emission distributed in the loop. The temporal evolution of the Fe XXI and O V emissions in a flare is found to be closely related to its spatial structure. Title: Stellar coronae. Authors: Pallavicini, R. Bibcode: 1988sscd.conf...19P Altcode: Some of the current problems in stellar coronal physics are reviewed with emphasis on the contribution given to their solution by the EXOSAT Observatory. After a brief overview of the results obtained previously with the EINSTEIN satellite, the author focuses on the structure and variability of the coronae of late-type stars. Title: Stellar coronae - The EXOSAT picture Authors: Pallavicini, R. Bibcode: 1988MmSAI..59...71P Altcode: This paper gives a summary of Exosat results on stellar coronae focussing on the following topics: (1) the temperature stratification of coronae, as has been derived from low- and medium-resolution spectral data; (2) the coronal spatial structure, as has been inferred from observations of eclipsing binary systems; (3) the time variability of coronal emission, as has been detected with the long, uninterrupted observations made possible by the highly eccentric orbit of Exosat. Title: X-ray astronomy with EXOSAT Authors: Pallavicini, R.; White, N. E. Bibcode: 1988xraw.book.....P Altcode: No abstract at ADS Title: Stellar magnetic fields: measurements and diagnostics Authors: Pallavicini, R. Bibcode: 1988ASSL..143...25P Altcode: 1988acse.conf...25P Magnetic fields are central to our understanding of surface activity in cool stars. This paper reviews recent progresses in the measurements of photospheric magnetic fields and stresses some of the main difficulties in the analysis of magnetic field observations. It also discusses indirect diagnostics of stellar magnetic fields with emphasis on recent X-ray and microwave observations. At present, these observations provide the only means to infer the topology of magnetic fields at coronal heights. Title: Modeling of long-decay stellar flares on EQ Peg and Prox Cen Authors: Pallavicini, R.; Poletto, G.; Kopp, R. A. Bibcode: 1988ASSL..143..171P Altcode: 1988acse.conf..171P A magnetic reconnection model of solar 2-ribbon flares is applied to long-duration events observed by Einstein and Exosat on the stars EQ Peg and Prox Cen. The authors show that the model is capable of reproducing the energy release rate and temporal evolution of the decay phase of the observed events, strongly supporting their identification as stellar counterparts of solar 2-R flares. The model is also used to put constraints on the physical parameters of the emitting region. Title: Variations of VLBI Structure in UX Ari Authors: Catarsi, M.; Felli, M.; Massi, M.; Palagi, F.; Pallavicini, R.; Tofani, G. Bibcode: 1988IAUS..129..283C Altcode: No abstract at ADS Title: Stellar coronae - The EXOSAT picture Authors: Pallavicini, R. Bibcode: 1988xraw.book...71P Altcode: No abstract at ADS Title: Hot thin plasmas in astrophysics Authors: Pallavicini, R. Bibcode: 1988ASIC..249.....P Altcode: 1988htpa.conf.....P No abstract at ADS Title: EXOSAT observations of quiescent and flaring emission from M dwarf flare stars Authors: Pallavicini, R. Bibcode: 1988ASSL..143..249P Altcode: 1988acse.conf..249P The author presents preliminary results of a comprehensive survey of X-ray observations of M dwarf flare stars obtained with the EXOSAT satellite. He discusses quiescent and flaring emission, and provides evidence for the occurrence on stars of both short-lived and long-duration events, closely resembling compact and 2-ribbon flares on the Sun. He concludes that there is no observational evidence in EXOSAT data for continuous low-level microflaring activity of the type recently suggested as a mechanism of coronal heating in M dwarf flare stars. Title: Some EXOSAT Results on Stellar Coronae Authors: Pallavicini, R. Bibcode: 1988ASIC..249..121P Altcode: 1988htpa.conf..121P No abstract at ADS Title: EXOSAT observations of RSCVn stars Authors: Pasquini, L.; Schmitt, J. H. M. M.; Pallavicini, R. Bibcode: 1988ASSL..143..241P Altcode: 1988acse.conf..241P EXOSAT observations of RS CVn stars are analyzed using simple spectral models; the authors argue first, that the X-ray emission from these stars requires the presence of emitting plasma continuously distributed in temperature and second, that there are intrinsic differences in the coronal temperature stratification of these stars. Title: The Gradual and Impulsive Reconnection and the Preheating of Solar Flares Authors: Li, Hong-Wei; Pallavicini, R.; Cheng, Chung-Chieh Bibcode: 1987SoPh..107..271L Altcode: We discuss the preheating phase of solar flares triggered by emerging magnetic flux. We consider the development of microinstabilities in the diffusion region during the emergence process and we propose four different types of reconnection, by which we explain the preheating, as well as the impulsive phase of flares. We find that during the emergence of new magnetic flux the current sheet will not `jump' from the initial classical state to a fully turbulent one, but will remain in a marginally turbulent state which may develop either gradually or impulsively depending on the conditions of emergence. As a consequence of this, we find that four cases of reconnection are indeed possible: a week gradual heating, a weak impulsive process, a gradual preheating followed by an impulsive phase, and violent bursty reconnection. Title: Analysis of Ultraviolet and X-Ray Observations of Three Homologous Solar Flares from SMM Authors: Cheng, Chung-Chieh; Pallavicini, Roberto Bibcode: 1987ApJ...318..459C Altcode: Three homologous flares observed in the UV lines of Fe XXI and O V and in X-rays from the SMM were studied. It was found that: (1) the homology of the flares was most noticeable in Fe XXI and soft X-ray emissions; (2) the three flares shared many of the same loop footprints which were located in O V bright kernals associated with hard X-ray bursts; and (3) in spite of the strong spatial homology, the temporal evolution in UV and X-ray emissions varied from flare to flare. A comparison between the UV observations and photospheric magnetograms revealed that the basic flare configuration was a complex loop system consisting of many loops or bundles of loops. Title: A comparison of coronal X-ray emission observed with the Einstein andEXOSAT observatories. Authors: Schmitt, J. H. M. M.; Pallavicini, R.; Monsignori-Fossi, B. C.; Harnden, F. R., Jr. Bibcode: 1987A&A...179..193S Altcode: The present Einstein and Exosat observatories' star coronal X-ray emission data are subjected to a spectral analysis which employs the Raymond and Smith (1977) and Landini and Fossi (1984) computer codes to calculate X-ray emission from optically thin plasmas that are in collisional equilibrium. It is found that the derived coronal parameters depend only loosely on the details of the calculated theoretical X-ray spectrum, although the spectra nevertheless differ in their prediction of X-ray fluxes in various lines. It is demonstrated that the Einstein spectra and Exosat filter ratios can be naturally and simultaneously explained by assuming an underlying, continuous distribution of emission measure with temperature, as in the case of the solar corona. Title: Lithium abundances of southern F, G and K dwarfs and subgiants. Authors: Pallavicini, R.; Cerruti-Sola, M.; Duncan, D. K. Bibcode: 1987A&A...174..116P Altcode: The Li abundances of 27 southern dwarfs and subgiants of spectral types F, G, and K are derived using high-resolution spectra obtained with a coude echelle spectrometer. The derived Li abundances are compared with determinations of rotation rates and chromospheric Ca II K fluxes. The relation between the Li abundance and ages is examined. The Li-6/Li-7 isotope ratio is evaluated, and an upper limit of 0.1 is obtained. The data reveal that old slowly rotating stars with low surface activity and high Li content have maintained high Li abundances by reduced metallicity, and the strong Li line in active binaries of the RS CVn type may be related to the presence of huge starspots on their surface and to the lower ionization degree of Li in cool spots. It is noted that for F8-G5 spectral stars a high Li abundance condition is required, but this condition is not adequate for the star to be young. Title: Solar and Stellar Coronae Authors: Pallavicini, R. Bibcode: 1987LNP...292...98P Altcode: 1987ssp..conf...98P Our present understanding of coronal heating, structuring and variability that has emerged from space observations of the Sun and nearby stars are reviewed. It is shown that a basic analogy exists between solar coronal physics and the phenomena observed in the coronae of other late-type stars. Recent X-ray observations of stellar coronae from EXOSAT are used to illustrate the main points. Title: Hydrodynamic Flare Modeling: Comparison of Numerical Calculations with SMM Observations of the 1980 November 12 17:00 UT Flare Authors: Peres, G.; Reale, F.; Serio, S.; Pallavicini, R. Bibcode: 1987ApJ...312..895P Altcode: The results of calculations of the evolution of flaring plasma in a simple coronal loop are compared with SMM observations of a well-studied compact flare. Calculations assuming different models of impulsive heating are performed, all starting from the same initial static loop configuration. A mechanism of local heat deposition and a mechanism of flare heating by energetic electron beams are tested with a variety of parameters. It is found that the evolution of the soft X-ray compact flare is mainly dominated by the thermodynamic and hydrodynamic properties of the confined plasma. In order to obtain a close match between calculated and observed X-ray polychromator light curves, a sizable fraction of impulsive energy must be deposited directly in the corona. Local Fe XXV brightenings in the flaring loop do not provide a good diagnostic of the site of energy deposition in solar flares. The total amount of impulsive energy necessary to match the calculated light curves with the observations depends strongly on the effective deposition depth. Title: Characterization of the Total Flare Energy Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf.5.41W Altcode: 1986epos.confE..41W No abstract at ADS Title: Energetics of the Impulsive Phase Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf..5.5W Altcode: 1986epos.confE...5W No abstract at ADS Title: Energetics of the Gradual Phase Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf.5.20W Altcode: 1986epos.confE..20W No abstract at ADS Title: Review of Impulsive Phase Phenomena Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf.5.60W Altcode: 1986epos.confE..60W No abstract at ADS Title: Flares Chosen for Energetics Study Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf.5.47W Altcode: 1986epos.confE..47W No abstract at ADS Title: Relationships among the Phases Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veek, N. J. Bibcode: 1986epos.conf.5.39W Altcode: 1986epos.confE..39W No abstract at ADS Title: X-Ray Observations of Flare Stars with EXOSAT Authors: Pallavicini, R. Bibcode: 1986BAAS...18R.962P Altcode: 1986BAAS...18Z.962P No abstract at ADS Title: Modeling of Long Duration Stellar Flares Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A. Bibcode: 1986BAAS...18Q.962P Altcode: No abstract at ADS Title: IUE and Skylab spectra of solar-type stars and of spatially-resolved solar regions Authors: Pallavicini, R.; Cerruti-Sola, M.; Cheng, C. C. Bibcode: 1986ESASP.263...45P Altcode: 1986NIA86.......45P; 1986niia.conf...45P Short-wavelength IUE spectra of nearby solar-type stars are compared with high-resolution spatially resolved ultraviolet spectra of individual solar features (quiet region, plage, flare) obtained with the slit spectrograph on board Skylab. Comparison reveals remarkable similarity between the range of emission fluxes observed in stars of various activity levels and the range of fluxes emitted by individual solar regions. Since the solar features considered differ mainly in the level of magnetic activity, it is likely that the same occurs for stars. The strong similarities between spectra of active stars and spectra of solar plages suggest that active regions cover a much larger fraction of the stellar surface in young rapidly rotating stars. Title: EXOSAT detection of an X-ray flare from the solar type star pi 1 UMa. Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R.; Piro, L. Bibcode: 1986A&A...157..217L Altcode: An X-ray flare has been detected on the G0 dwarf star π1UMa using the European satellite EXOSAT. With the exception of the Sun, this is the first time that an X-ray flare has been observed in a normal solar-type star, which is not a member of a binary system and is not a classical flare star. As a member of the Ursa Major Cluster, π1UMa is a young, rapidly rotating star with a high level of chromospheric and coronal activity. The energy emitted in X-rays by the observed flare is at least one order of magnitude higher than the total energy released in large solar flares. The authors interpret the event as occurring in one or more magnetic loops which occupy only a small fraction of the star surface. The flare is found to cool both by radiation and conduction. The authors derive physical parameters for the emitting region and compare them with transient events occurring on the Sun, on dMe flare stars and on RS CVn and Algol-type binaries. Title: Simultaneous optical and X-ray observations of a flare on BY Draconis. Authors: de Jager, C.; Heise, J.; Avgoloupis, S.; Cutispoto, G.; Kieboom, K.; Herr, R. B.; Landini, M.; Langerwerf, A. F.; Mavridis, L. N.; Melkonian, A. S.; Molenaar, R.; Monsignori-Fossi, B. C.; Nations, H. L.; Pallavicini, R.; Piirola, V.; Rodono, M.; Seeds, M. A.; van den Oord, G. H. J.; Vilhu, O.; Waelkens, C. Bibcode: 1986A&A...156...95D Altcode: The authors present a first report on a campaign for simultaneous observations in the visual, radio and X-ray ranges of stellar flares on the binary BY Dra. During two nights of observations they observed one significant flare, simultaneously in soft X-rays and visible wavelengths, and one or two smaller bursts. The main flare impulsively heated an area of ⪉2×107km2 of the stellar photosphere to a brightness temperature ⪆25000K, during about 5 min, and generated hot plasma, emitting soft X-rays. This emission reached maximum after the impulsive burst and lasted for about an hour; it covered a much larger area on the star than the optical emission. There was no significant hard X-ray component. The authors ascribe the optical continuous emission to the flare's impulsive phase, and the soft X-ray emission to the gradual phase. Title: Preliminary Catalog of Chromospheric, Transition Region and Coronal Fluxes of Late-Type Stars Authors: Governini, G.; Pallavicini, R. Bibcode: 1986LNP...254...67G Altcode: 1986csss....4...67G No abstract at ADS Title: Coronal magnetic fields Authors: Pallavicini, R. Bibcode: 1986HiA.....7..447P Altcode: The use of coronal X-ray emission in determining the configuration of the magnetic field lines in the corona is discussed. Spatially-resolved X-ray observations provided by Skylab and subsequently by missions such as OSO-8 and SMM show the solar corona to be inhomogeneous, with open and closed structures determined by the topology of the magnetic field. The scenario provided by observations from the Einstein, Exosat, and IUE satellites includes the activity in the sun and late-type stars resulting from the emergence of magnetic fields at the star surface. Data demonstrate the dependence of chromospheric and coronal emission on rotation, while there is no evidence that convection zone depths determine the level of magnetic activity, except for early F stars and possibly very late M stars. Results suggest that most late-type dwarfs of all spectral types may have coronae similar to, although often much more active than, the solar corona, and are characterized by confined magnetic structures with typical emission heights significantly smaller than the stellar radius. Title: Southern Stars Observed at ESO: Absolute Surface Fluxes in the K Line of Ca II Authors: Pasquini, L.; Pallavicini, R.; Pakull, M. Bibcode: 1986LNP...254...74P Altcode: 1986csss....4...74P No abstract at ADS Title: EXOSAT observations of quiescent and flaring emission from active late-type stars Authors: Pallavicini, R.; Monsignori-Fossi, B. C.; Landini, M.; Kundu, M. R.; Lang, K. R. Bibcode: 1986AdSpR...6h.125P Altcode: 1986AdSpR...6Q.125P The authors present the highlights of several guest investigator programs carried out with the EXOSAT satellite. They discuss quiescent as well as flaring emission from normal F to M dwarfs, from dMe flare stars and from RS CVn binaries. Title: Programmi spaziali di fisica solare: il satellite europeo SOHO. Authors: Pallavicini, R. Bibcode: 1986GAst...12....6P Altcode: No abstract at ADS Title: Coronal X-ray temperatures from Einstein and EXOSAT observations Authors: Schmitt, J. H. M. M.; Pallavicini, R.; Monsignori-Fossi, B. C.; Harnden, F. R., Jr. Bibcode: 1986AdSpR...6h.141S Altcode: 1986AdSpR...6..141S Spectral analysis of coronal X-ray emission from stars observed with both the Einstein and EXOSAT Observatories is presented. Using computer codes developed by Raymond and Smith /1/ and Landini and Fossi /2/ to calculate the X-ray emission from optically thin plasma in collisional equilibrium we find that the derived coronal parameters depend only rather insensitively on the details of the calculated theoretical X-ray spectrum and demonstrate how both the Einstein Observatory IPC spectra and the EXOSAT LE filter ratios can be naturally and simultaneously explained by assuming an underlying continuous emission measure distribution as is the case in the solar corona. Title: UV spectra of late-type stars and of representative solar features Authors: Sola, M. Cerruti; Cheng, C. C.; Pallavicini, R. Bibcode: 1986AdSpR...6h..77S Altcode: 1986AdSpR...6...77S We compare low-resolution short-wavelength IUE spectra of solar-type stars with high-resolution spatially-resolved SKYLAB spectra of individual solar features (quiet region, plage, flare). The comparison is used to obtain insights into the magnetic activity of stars. Title: X-ray, UV, optical and radio observations of the visual binary 53 AQR Authors: Pallavicini, R.; Cerruti Sola, M.; Monsignori-Fossi, B. C.; Pasquini, L. Bibcode: 1986AdSpR...6h.121P Altcode: 1986AdSpR...6..121P The authors present optical (ESO), ultraviolet (IUE), X-ray (EXOSAT) and radio (VLA) observations of the visual binary 53 Aquarii. They show that the two components of the system can be used to infer the properties of the Sun at a much earlier epoch. Title: EXOSAT Detection of a Very Large Flare on EQ Peg Authors: Pallavicini, R.; Kundu, M. R.; Jackson, P. D. Bibcode: 1986LNP...254..225P Altcode: 1986csss....4..225P No abstract at ADS Title: Coronae of Late-Type Stars Observed with EXOSAT Authors: Pallavicini, R.; Monsignori-Fossi, B. C.; Landini, M. Bibcode: 1986LNP...254..212P Altcode: 1986csss....4..212P No abstract at ADS Title: Magnetic reconnection and energy release in a long-duration stellar flare Authors: Poletto, G.; Pallavicini, R.; Kopp, R. A. Bibcode: 1986AdSpR...6h.145P Altcode: 1986AdSpR...6..145P A dynamical model of magnetic reconnection in solar two-ribbon flares is applied to EXOSAT observations of a long-decay flare from the star EQ Peg. We show that the model is able of reproducing correctly the energy release rate and temporal evolution of the decay phase of the observed flare. We conclude that the flare was the stellar counterpart of solar two-ribbon flares and we derive the physical parameters of the emitting region. Title: Coronal models of late-type stars observed with EXOSAT Authors: Monsignori-Fossi, B. C.; Landini, M.; Pallavicini, R.; Tribioli, F. Bibcode: 1986AdSpR...6h.137M Altcode: 1986AdSpR...6..137M Differential emission measure distributions for transition region and corona able to reproduce X-ray and UV emission are investigated. The EXOSAT, EINSTEIN and IUE data for the solar type star K Cet are analyzed. A multitemperature differential emission measure distribution gives a satisfactory fit of the data. Title: Flare energetics. Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.; Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner, M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.; Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres, G.; Serio, S.; Sylwester, J.; Veck, N. J. Bibcode: 1986NASCP2439....5W Altcode: In this investigation of flare energetics, the authors establish a comprehensive and self-consistent picture of the sources and transport of energy within a flare. They chose five flares in 1980 that were well observed with instruments on the SMM, and with other space-borne and ground-based instruments. Details of the observations available for them and the corresponding physical parameters derived from these data are presented. The flares were studied from two perspectives, the impulsive and gradual phases, and then the results were compared to obtain the overall picture of the energetics of these flares. The authors also discuss the role that modeling can play in estimating the total energy of a flare when the observationally determined parameters are used as the input to a numerical model. Title: Solar-type phenomena in stars: an overview of the solar-stellar connection. Authors: Pallavicini, R. Bibcode: 1986RALR...85....1P Altcode: An overview is given of the solar-stellar connection with emphasis on the following topics: (1) the relationship between convection, rotation and magnetic fields in stars possessing subphotospheric convection zones; (2) the observational evidence for the presence of solar-type phenomena in stars at various atmospheric levels; (3) the modelling of magnetically confined coronal structures during quiescent as well as flaring conditions. Title: UV spectra of late-type stars and of representative solar features Authors: Cerruti Sola, M.; Pallavicini, R.; Cheng, C. C. Bibcode: 1986AdSpR...6h..77C Altcode: 1986AdSpR...6...77C The authors compare low-resolution short-wavelength IUE spectra of solar-type stars with high-resolution spatially-resolved Skylab spectra of individual solar features (quiet region, plage, flare). The comparison is used to obtain insights into the magnetic activity of stars. Title: Southern Stars Observed at ESO: Lithium Abundances for G and K Dwarfs and Subgiants Authors: Cerruti-Sola, M.; Pallavicini, R. Bibcode: 1986LNP...254...46C Altcode: 1986csss....4...46C No abstract at ADS Title: The preheating of solar flares and reconnection Authors: Li, H. -W.; Pallavicini, R.; Cheng, C. -C. Bibcode: 1986AdSpR...6f..69L Altcode: 1986AdSpR...6...69L We discuss the preheating phase of solar flares trigerred by emerging magnetic flux. We consider the development of microinstabilities inside the diffusion region during the emergence process and propose four different types of reconnection, by which we are able to interpret the preheating, as well as the impulsive phase of flares. Title: Detection of an X-Ray Flare from a Single G Dwarf Star Authors: Monsignori-Fossi, B. C.; Pallavicini, R.; Landini, M.; Piro, L. Bibcode: 1986LNP...254..222M Altcode: 1986csss....4..222M No abstract at ADS Title: Energy release topology in a multiple-loop solar flare Authors: Cheng, C. -C.; Pallavicini, R.; Acton, L. W.; Tandberg-Hanssen, E. Bibcode: 1985ApJ...298..887C Altcode: The temporal and spatial structures of the UV and X-ray emissions and the magnetic field configuration in the November 12, 1980 flare observed from SMM have been studied. The UV observations were done in the O V and Fe XXI lines with a spatial resolution of 10 arcsec. The observations show that the impulsive UV bursts, and also the hard X-ray bursts by their temporal correlation with the impulsive O V emission, occurred in small localized kernels. By comparing the O V, Fe XXI, and X-ray raster images of the flare with the magnetogram, these emission kernels were identified as footpoints of interacting magnetic flux loops. The temporal evolution of the O V/Fe XXI emission shows that there was considerable preheating in the flare plasma some 8-9 minutes prior to the onset of the main hard X-ray bursts. The results are interpreted as indicating that the primary flare energy release occurred in a highly sheared multiloop structure, which lies along a magnetic neutral line. By either beam particle propagation or convective motion, flare energy is transported via a common footpoint to another loop which brightened later. The preheating of the flare plasma is shown to create a more favorable environment for energetic particle acceleration which resulted in the main impulsive hard X-ray bursts. Title: Multiwavelength Analysis of a Well Observed Flare from Solar Maximum Mission Authors: MacNeice, P.; Pallavicini, R.; Mason, H. E.; Simnett, G. M.; Antonucci, E.; Shine, R. A.; Rust, D. M.; Jordan, C.; Dennis, B. R. Bibcode: 1985SoPh...99..167M Altcode: We describe and analyse observations of an M1.4 flare which began at 17: 00 UT on 12 November, 1980. Ground based Hα and magnetogram data have been combined with EUV, soft and hard X-ray observations made with instruments on-board the Solar Maximum Mission (SMM) satellite. The preflare phase was marked by a gradual brightening of the flare site in Ov and the disappearance of an Hα filament. Filament ejecta were seen in Ov moving southward at a speed of about 60 km s−1, before the impulsive phase. The flare loop footpoints brightened in Hα and the CaXIX resonance line broadened dramatically 2 min before the impulsive phase. Non-thermal hard X-ray emission was detected from the loop footpoints during the impulsive phase while during the same period blue-shifts corresponding to upflows of 200-250 km s−1 were seen in Ca XIX. Evidence was found for energy deposition in both the chromosphere and corona at a number of stages during the flare. We consider two widely studied mechanisms for the production of the high temperature soft X-ray flare plasma in the corona, i.e. chromospheric evaporation, and a model in which the heating and transfer of material occurs between flux tubes during reconnection. Title: Microwave observations of late-type stars with the Very Large Array. Authors: Pallavicini, R.; Willson, R. F.; Lang, K. R. Bibcode: 1985A&A...149...95P Altcode: The Very Large Array was used to search for microwave emission from 32 stars of late spectral type including RS CVn type stars, dwarf M stars, and stars with active chromospheres, coronae, or intense magnetic fields. The RS CVn stars were detected at 6 cm wavelength, and upper limits are established for another six. Radio emission was detected from three dwarf M flare stars, UV Cet, EQ Peg and YZ CMi. Both impulsive (no more than 20 s) and more gradual (at least ten minutes) bursts were observed from the flare star YZ CMi. Radio emission was not confirmed at 6 cm from the solar type star Chi(1) Ori, with an upper limit that is three times lower than the detections reported by other observers. Microwave emission could not be detected from any other solar type star of spectral class F to K. The quiescent radio emission from dwarf M flare stars was interpreted as nonthermal gyrosynchrotron emission by mildly relativistic electrons accelerated more or less continuously in the magnetic fields of starspots. Title: VLA Observations of Late-Type Stars Authors: Lang, K.; Willson, R.; Pallavicini, R. Bibcode: 1985ASSL..116..267L Altcode: 1985rst..conf..267L The authors report the results of a program of observations of late-type stars at λ = 6 cm using the V.L.A. The source list includes stars with active chromospheres and coronae, UV Ceti-type flare stars, and RS CVn stars. Of the 31 objects surveyed, the authors have detected 6 and they have established upper limits for the remaining 25. The detected sources are all RS CVn and UV Ceti-type flare stars. No dwarf star of spectral type G and K has been detected, including the previously reported radio source χ1Ori. Title: The Solar-Stellar Connection (Invited Paper) Authors: Pallavicini, R. Bibcode: 1985ASSL..116..197P Altcode: 1985rst..conf..197P This review summarizes the many contact points between solar and stellar physics stressing the similarities and differences between phenomena observed on the sun and on stars with outer convective mantles. Topics discussed include: (1) the relationship between convection, rotation and magnetic fields as a source of magnetic activity in late-type stars; (2) the observation of solar-type phenomena (spots, plages, activity cycles etc.) on other stars; (3) the structuring and heating of high temperature coronae; (4) the observation and interpretation of radio emission from the sun and late-type stars. Title: Observations of the Physical Conditions in Solar Flare Transition Zone Plasmas from SMM Authors: Cheng, Chung-Chieh; Pallavicini, R.; Tandberg-Hanssen, E. Bibcode: 1985BAAS...17..629C Altcode: No abstract at ADS Title: EXOSAT Observations of Late-Type Stars - the Application of Coronal Loop Models Authors: Landini, M.; Monsignori-Fossi, B. C.; Pallavicini, R. Bibcode: 1985SSRv...40...43L Altcode: We apply solar-type coronal loop models to X-ray and UV observations of late-type stars. We derive from EXOSAT and IUE observations constraints on the temperature, pressure and size of the emitting structures. Title: X-ray, ultraviolet, optical and radio observations of cool stars Authors: Pallavicini, R. Bibcode: 1985MmSAI..56..813P Altcode: An outline is presented of ongoing activity, with preliminary results, at the Arcetri Observatory, where an extensive program is under way to investigate the physical properties of late-type stars using a variety of observational techniques, from X-ray to radio wavelengths. The research is largely based on Guest Investigator programs, making use of both spaceborne and ground-based facilities. The UV and X-ray emission from stellar chromospheres, transition regions and coronae is being investigated using data from IUE, Einstein, and Exosat. The optical properties of late-type stars (rotation, lithium abundance, chromospheric emission, etc.) are being studied using instrumentation available at the European Southern Observatory (ESO) in Chile. Radio emission from stars is investigated using the VLA as well as VLBI techniques. The observational data are interpreted in the framework of dynamo-generated magnetic activity, using the solar analogy as a convenient working hypothesis and exploring the extent to which solar models can be extrapolated to other stars. Title: EXOSAT observations of late-type stars: preliminary results. Authors: Landini, M.; Monsignori-Fossi, B. C.; Pallavicini, R. Bibcode: 1985xra..conf...31L Altcode: 1984xra..conf...31L The authors present preliminary results of a program of observations of late-type stars using EXOSAT. They derive temperatures and emission measures and compare their results with previous Einstein observations of the same targets. Title: Analysis of the Magnetic Field Configuration of a Filament Associated Flare from X-Ray Ultraviolet and Optical Observations Authors: Cheng, C. -C.; Pallavicini, R. Bibcode: 1984SoPh...93..337C Altcode: X-ray and ultraviolet observations from SMM of a filament-associated event on 22 November, 1980 are examined in conjunction with ground-based optical observations, in order to determine the magnetic field configuration involved in the flaring process. We find evidence that the flare was produced by gradual energy release in a large sheared magnetic loop which interacted with another smaller loop. Non-thermal processes, as indicated by hard X-ray emission and impulsive UV kernels, were produced in the interaction of the two loops. Although this flare shared some of the characteristics of Long Duration (class II) Events, we found no indication of a helmet-type configuration, as generally envisaged for class II events. On the contrary, the magnetic configuration of the 22 November, 1980 event was more similar to that of a compact (class I) flare, although on a much larger spatial scale and longer time scale. Title: Active Chromospheres and Coronae of Late-Type Stars Authors: Pallavicini, R. Bibcode: 1984iue..prop.1928P Altcode: No abstract at ADS Title: Chromospheric emission, rotation and X-ray coronae of late-type stars Authors: Pallavicini, R. Bibcode: 1984Msngr..35....5P Altcode: X-ray observations have shown that chromospheres, transition regions and coronae are common to stars throughout the HR diagram, and that magnetic fields play a fundamental role in the heating of outer stellar atmospheres. The observed emission levels are in both qualitative and quantitative disagreement with the predictions of the standard theory of coronal formation via the generation and dissipation of acoustic waves. As a result of recent emphasis on heating mechanisms which are based on the stressing and dissipation of magnetic fields generated by dynamo action in the subphotospheric convection zones, stellar rotation has assumed a central role in the heating problem as a controlling factor in dynamo process efficiency. Title: Coronal physics with the Solar and Heliospheric Observatory Authors: Pallavicini, R. Bibcode: 1984MmSAI..55..549P Altcode: Previously acquired X-ray and UV data gathered on the solar corona are summarized to indicate the progress which could be made in solar physics with the launch of an ESA Solar and Heliospheric Observatory (SOHO). The existing data base was collected with instrumentation on, e.g., Skylab, OSO-8, SMM, HRTS spacecraft. Arch-shaped coronal loops have been discovered, as has a transition region, which is significant in coronal heating, and closed and open magnetic fields. The holes are known to be the exit points for the solar wind. The SOHO spacecraft could help identify the heating source for the corona and the acceleration mechanism for the solar wind. Furthermore, SOHO could record data on the solar wind and coronal structures simultaneously, thus allowing fluctuation in one to be related to activities in the other. Title: The Solar Maximum Mission Authors: Pallavicini, R. Bibcode: 1984MmSAI..55..633P Altcode: Contents: Introduction. The spacecraft. The experiment payload: Gamma Ray Experiment, Hard X-ray Burst Spectrometer, Hard X-ray Imaging Spectrometer, Soft X-ray Polychromator, Ultraviolet Spectrometer and Polarimeter, Coronograph/Polarimeter, Active Cavity Radiometer Irradiance Monitor. Data acquisition and analysis. Highlights of results. The Italian participation. Title: Frontiers of astronomy and astrophysics Authors: Pallavicini, Roberto Bibcode: 1984faa..conf.....P Altcode: No abstract at ADS Title: Results from the Solar Maximum Mission. Authors: Pallavicini, R. Bibcode: 1984MmSAI..55C.629P Altcode: No abstract at ADS Title: Frontiers of astronomy and astrophysics. Invited papers presented at the Seventh European Regional Astronomy Meeting, held in Florence, Italy, 12 - 16 December 1983. Authors: Pallavicini, R.; Pacini, F. Bibcode: 1984faai.book.....P Altcode: No abstract at ADS Title: High-Resolution Observations of Cool Stars with the ESO Coud&eacute Echelle Spectrometer Authors: Pallavicini, R.; Pakull, M. Bibcode: 1984LNP...193..108P Altcode: 1984csss....3..108P No abstract at ADS Title: Broad-Band Spectroscopy of Late-Type Stars with EXOSAT Authors: Landini, M.; Monsignori-Fossi, B. C.; Pallavicini, R. Bibcode: 1984uxsa.coll...68L Altcode: 1984uxsa.conf...68L; 1984IAUCo..86...68L No abstract at ADS Title: Coronal Magnetic Heating in the Sun and in Late-type Stars Authors: Pallavicini, R. Bibcode: 1984faa..conf...83P Altcode: In this paper the author reviews some of the problems related to the subject of coronal magnetic heating. He also refers to a number of review papers on the same, and related, topics, which appeared recently in the literature. Title: Thin plasmas: galactic sources. Authors: Pallavicini, R. Bibcode: 1984PhST....7..181P Altcode: 1984PhyS....7..181P Papers presented in the session "Thin plasmas" during the European workshop on "Very hot astrophysical plasmas" (Nice, November 1982) are critically reviewed. Emphasis is given to problems related to emission mechanisms, solar and stellar coronae, supernova remnants, and the hot phase of the interstellar medium. Title: Closed coronal structures. V - Gasdynamic models of flaring loops and comparison with SMM observations Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G.; Acton, L.; Leibacher, J.; Rosner, R. Bibcode: 1983ApJ...270..270P Altcode: The hydrodynamic response of confined magnetic structures to strong heating perturbations is investigated by means of a time-dependent one-dimensional colde which incorporates the energy, momentum, and mass conservation equations. The entire atmospheric structure from the chromosphere to the corona is taken into account. Models with different energy input, heating time dependence, preflare conditions and heating location have been examined in the numerical simulations.

The result of model calculations are compared with observations of flares obtained with the X-ray Polychromator experiment on the Solar Maximum Mission. These include light curves of spectral lines formed over a wide range of coronal flare temperatures, as well as determinations of Doppler shifts for the high temperature plasma. Several examples are used to illustrate the range of the observational variation.

It is shown that the predictions of the numerical simulations are in good overall agreement with the observed evolution of the flare coronal plasma. The model reproduces correctly the temporal profile of X-ray spectral lines and -- to first order at least -- their relative intensities. The upflow velocities predicted by model calculations are in agreement with the observed blueshifts, supporting the interpretation of the blueshifts as due to evaporation of chromospheric material. The possibility of using the comparison of model predictions with observations to derive information on the processes of energy release and transfer in solar flares is discussed. Title: Hydrodynamics of Flaring Loops - SMM Observations and Numerical Simulations Authors: Pallavicini, R.; Peres, G. Bibcode: 1983SoPh...86..147P Altcode: The hydrodynamic response of confined magnetic structures to strong heating perturbations is investigated by means of a timedependent one-dimensional code which incorporates the energy, momentum and mass conservation equations. The entire atmospheric structure from the chromosphere to the corona is taken into account. The results of model calculations are compared with observations of flares obtained with the X-Ray Polychromator experiment on the Solar Maximum Mission. Title: Solar flares with SMM and implications for the physics of stellar flares Authors: Pallavicini, R. Bibcode: 1983ASSL..102..321P Altcode: 1983ards.proc..321P; 1983IAUCo..71..321P XUV flare observations from the Solar Maximum Mission are examined, and the results are compared with recent X-ray observations of stellar flares. Two problems of flare physics are considered in detail: (1) the role of nonthermal electrons in the overall flare energetics; and (2) the process of chromospheric evaporation during the thermal phase of a flare. Title: Meccanismi di emissione e assorbimento della radiazione in situazioniastrofisiche. Authors: Landi Degl'Innocenti, E.; Pallavicini, R. Bibcode: 1983GAst....9...25L Altcode: No abstract at ADS Title: Observations of Flares in Loops Authors: Pallavicini, R. Bibcode: 1982Obs...102..120P Altcode: No abstract at ADS Title: Temporal evolution of soft X-ray emitting plasma in solar flares. Authors: Pallavicini, R.; Peres, G. Bibcode: 1982BAAS...14..776P Altcode: No abstract at ADS Title: Chromospheric emission, stellar rotation and X-ray coronae. Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. Bibcode: 1982SAOSR.392B..77P Altcode: 1982csss....2...77P No abstract at ADS Title: Einstein detection of X-rays from the alf CEN system. Authors: Golub, L.; Harnden, F. R., Jr.; Pallavicini, R.; Rosner, R.; Vaiana, G. S. Bibcode: 1982ApJ...253..242G Altcode: Detection of quiescent X-ray emission from the stellar components of the Alpha Cen system: Alpha Cen A (G2 V) and Alpha Cen B (K1 V) is reported. Contrary to previous theoretical expectations, both stars are found to be X-ray emitters and at about the same level: Lx = 1.2 x 10 to the 27th and 2.8 x 10 to the 27th ergs/s for A and B, respectively; the sum of these values is in agreement with the emission level previously reported for Alpha Cen by Nugent and Garmire (1978). Comparison with previous chromospheric and transition region measurements suggests that Alpha Cen A and B may have changed in relative strength in recent years. The coronal temperature of the combined Cen AB source, which is dominated (approximately 2/3 of the total) by the K star is (2.1 + or - 0.4) x 10 to the 6th K, similar to that of the average solar corona; it is noted that this value is not consistent with the estimate of 5 x 10 to the 5th K quoted by Nugent and Garmire. Title: Solar flares from space - Implications of spatially resolved XUV observations Authors: Pallavicini, R. Bibcode: 1982MmSAI..53..461P Altcode: Recent X-ray and EUV observations of solar flares obtained with the Apollo Telescope Mount/Skylab and the Solar Maximum Mission are reviewed. Flares are subdivided into the physically distinct classes: compact flares and large-scale, long-decay events. The physical processes pertaining to these two classes are discussed with special attention to the space and time dependence of the energy release process as well as to the source of mass filling the flaring structure. It is suggested that flares of class II may comprise events of two different types: energetic two-ribbon flares and more gradual filament-associated events in and outside active regions. Title: Proceedings of the workshop on "Cosmic magnetic fields", in honour ofGiorgio Abetti, held in Florence, Italy, 21 - 23 October 1982, on theoccasion of the 26th annual meeting of the Italian Astronomical Society. Authors: Pallavicini, R.; Tagliaferri, G.; Paternò, L.; Fulchignoni, M.; Perinotto, M.; Salvati, M. Bibcode: 1982MmSAI..53C.789P Altcode: No abstract at ADS Title: Cosmic magnetic fields Authors: Pallavicini, R. Bibcode: 1982MmSAI..53.....P Altcode: The magnetic fields treated are those in the sun, in planets and the interplanetary medium, in stars and the interstellar medium, and in high-energy sources. Papers are presented on the solar dynamo, on the equilibrium and stability of magnetized plasmas, on spectral analysis at maximum resolution, and on radio pulse behavior above 50 MeV. Attention is also given to the central powerhouse of active galactic nuclei, to magnetic fields in galactic jets, to the theory of the magnetic activity of late-type stars, and to recent developments in flare dynamics. For individual items see A83-39227 to A83-39251 Title: Magnetic heating of solar and stellar coronae Authors: Pallavicini, R. Bibcode: 1982MmSAI..53..849P Altcode: The current status of the question is summarized, stressing the fundamental similarities between the solar and stellar cases. The treatment concentrates on late-type stars since only these stars possess, like the sun, an outer convection zone and are likely to also have differential rotation and dynamo-generated magnetic fields. It is pointed out that the heating of the coronas of early-type stars may be fundamentally different from the heating of the solar corona. For this reason it is not considered. It is shown that whereas there is ample evidence at present that the coronas of late-type stars are heated magnetically, there is still considerable uncertainty regarding the detailed way (Alfvenic surface waves or anomalous current dissipation) in which the heating may actually occur. Title: X-Ray Flare Spectroscopy: SMM Observations and Loop Modeling. Authors: Acton, L.; Pallavicini, R.; Peres, G.; Vaiana, G. Bibcode: 1982uxsa.coll....1A Altcode: 1982IAUCo..73....1A No abstract at ADS Title: Relations among stellar X-ray emission observed from Einstein, stellar rotation and bolometric luminosity. Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres, T.; Linsky, J. L. Bibcode: 1981ApJ...248..279P Altcode: The correlation between observed stellar X-ray luminosities, bolometric luminosities, and projected rotational velocities for stars of various spectral types and luminosity classes are determined. Early type stars (O3 to A5) have X-ray luminosities independent of rotational velocities, and correlating with bolometric luminosities. Late type stars of spectral type G to M have luminosities well correlated to equatorial rotational velocities, and are independent of luminosity class. The dependence of late type stars is found to be equivalent to a relation between the X-ray surface flux and the stellar angular velocity. F stars are intermediate with X-ray luminosities higher than would be predicted on the basis of the early type star relation, although lower than expected from the late type velocity dependence. The location of RS CVn stars as a class is also discussed, and it is found that the heating of late type stellar coronas does not result from direct conversion of ratational energy. Title: Closed coronal structures. III - Comparison of static models with X-ray, EUV, and radio observations Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G. S.; Golub, L.; Rosner, R. Bibcode: 1981ApJ...247..692P Altcode: Numerical models of static coronal loops in energy balance are compared with high spatial resolution observations of extreme ultraviolet lines, broad-band X-ray emission, and interferometric observations at 2.8 cm of a solar active region. Difficulties of using scaling laws to test static models of coronal loops are reviewed. The theoretical model used for the comparison is summarized; the detailed X-ray, EUV, and microwave observations of the selected active region are presented; and the comparison of the model with the observations is performed. It is shown that simple static models with conductive flux vanishing at the loop base reproduce satisfactorily the observed properties in the upper portion of loop structures from compact, high-pressure loops in the core of the region to more extended, fainter loops and to large-scale loops interconnecting different active regions. Effects of changing loop parameters are investigated, and it is argued, that in contrast to the present approach, scaling laws cannot be used to discriminate between different static energy balance models. Some discrepancy is found between model predictions and observations for the lower sections of loop structures. Possible causes of the discrepancy are discussed. Title: X-ray, EUV, and centimetric observations of solar active regions - an empirical model for bright radio sources Authors: Pallavicini, R.; Sakurai, T.; Vaiana, G. S. Bibcode: 1981A&A....98..316P Altcode: Coordinated observations of solar active regions in X-rays, EUV, and 2.8 cm radio waves, and current-free extrapolations of the photospheric magnetic field to coronal levels are used to determine the emission mechanism of bright radio sources. High spatial resolution X-ray and EUV observations of the active regions show that the temperature and density structure of the atmosphere above the sunspots differs greatly from that above the plages. Extended low brightness temperature radio sources, associated with plage areas, are consistent with thermal free-free emission from the transition region and the corona above the active centers. High brightness temperature radio sources, associated with sunspots, cannot be explained by thermal free-free emissions either in hot, dense loops or in the cooler, lower pressure loops, observed emanating from sunspot umbrae. There is evidence that thermal gyroresonance absorption at the second and third harmonics of the gyrofrequency can produce sunspots associated with bright radio sources. The empirical models of the coronal loops, based on energy balance, and the effects of electric currents flowing in the corona above the sunspots are discussed. Title: Magnetic Field Extrapolations, XUV Observations and the Nature of Microwave Emission from Sunspots Authors: Pallavicini, R.; Sakurai, T.; Vaiana, G. S. Bibcode: 1980BAAS...12..896P Altcode: No abstract at ADS Title: Transition Region and Corona in Solar Active Regions: Observations and Numerical Modeling Authors: Golub, L.; Pallavicini, R.; Peres, G.; Rosner, R.; Serio, S.; Vaiana, G. S. Bibcode: 1980BAAS...12..908G Altcode: No abstract at ADS Title: The flare of September 7, 1973: A typical example of a newly recognized class of solar transients Authors: Pallavicini, R.; Vaiana, G. S. Bibcode: 1980SoPh...67..127P Altcode: X-ray, extreme-ultraviolet and optical observations of a solar flare are discussed. It is shown that the flare exemplifies a class of transient events characterized by long duration and long decay time and by the development of high systems of loops, generally brighter at the top. Title: On the origin of microwave emission from sunspots Authors: Pallavicini, R. Bibcode: 1980IAUS...86..119P Altcode: Coordinated high-resolution XUV and centimetric observations of active regions obtained from Skylab and Stanford are compared with the aim of determining the nature of the centimetric radiation. It is concluded that the thermal gyroresonance process is the most likely emission mechanism for the bright compact radio sources associated with sunspots. Title: The coronal atmosphere above solar active regions: comparison of high spatial resolution soft X-ray and centimetric observations. Authors: Pallavicini, R.; Vaiana, G. S.; Tofani, G.; Felli, M. Bibcode: 1979ApJ...229..375P Altcode: High spatial resolution observations of solar active regions in soft X-rays and centimetric wavelengths are compared using X-ray and radio data obtained during the 1973 Skylab mission. An overall correspondence in position and size between regions of enhanced X-ray emission and regions of enhanced microwave emission was noticed. However, a closer analysis of the findings suggested that substantial differences exist between the emission properties of the atmosphere over sunspots and that over plages, with the difference probably related to the average intensity of the magnetic field, which was found to be higher over sunspot umbrae than over plage areas. Title: Ricerche su fenomeni transitori della corona solare mediante osservazioni ottiche, ultraviolette ed X. Authors: Pallavicini, R.; Serio, S.; Vaiana, G. S. Bibcode: 1979RSAI...22..163P Altcode: No abstract at ADS Title: Risultati recenti e problemi aperti in fisica solare. Authors: Pallavicini, R.; Poletto, G. Bibcode: 1979GAst....5...19P Altcode: No abstract at ADS Title: Is there anything new on the sun? Authors: Pallavicini, R.; Poletto, G. Bibcode: 1978Mercu...7...23P Altcode: The current state of knowledge regarding the sun and the processes taking place in it is examined. It is found that in addition to the neutrino problem there are many other intriguing problems. Recent observations represent a challenge with respect to basic theoretical interpretations of solar phenomena. Elementary facts about the sun are considered, taking into account the significance of the presence of sunspots with their very strong magnetic fields, flares, auroras, faculae, and the differential rotation of the sun. A description is presented of a theory which explains the high temperatures of the chromosphere and the corona. Investigations based on observations of radio waves, infrared and ultraviolet radiation, and X-rays are considered. Attention is also given to holes in the solar corona, quiescent periods in solar activity, and problems related to an occurrence of 'Maunder minima'. Title: L'evoluzione stellare. Authors: Pallavicini, R. Bibcode: 1978GAst....4..251P Altcode: No abstract at ADS Title: Study of solar active regions by means of coordinated soft X-ray and 2.8-cm observations Authors: Pallavicini, R.; Tofani, G. Bibcode: 1977MmSAI..48..829P Altcode: No abstract at ADS Title: Identificazione di due classi di brillamenti X mediante osservazioni di eventi al bordo con l'esperimento Skylab S-054. Authors: Pallavicini, R.; Serio, S.; Vaiana, G. Bibcode: 1977MmSAI..48..760P Altcode: No abstract at ADS Title: A survey of soft X-ray limb flare images: the relation between their structure in the corona and other physical parameters. Authors: Pallavicini, R.; Serio, S.; Vaiana, G. S. Bibcode: 1977ApJ...216..108P Altcode: The data used in the investigation were obtained by the American Science and Engineering S-054 experiment on board Skylab. The instrument employed was a grazing incidence X-ray telescope which records images of the sun on film. The morphology of limb flares is investigated and the observed spatial structure is related with the other physical parameters of the region (temperature, density, characteristic times, and energy density). It is concluded that two physically distinct classes of flares exist that differ both in their morphology and in the physical properties which characterize the emitting regions. Title: Aspects of the observation of solar-flare phenomena Authors: Pallavicini, R. Bibcode: 1977MmSAI..48..161P Altcode: A review is presented of electromagnetic and particle emission from solar flares, with particular emphasis on relationships between characteristic features of flares in different spectral bands. Three main phases in the development of a typical event are identified: precursor, pulsed, and gradual. The association of hard X-ray bursts with pulsed EUV and microwave bursts as well as with pulsed optical phenomena and type III bursts is discussed. Considerable attention is given to magnetic fields associated with flares and to the location of sources of different types of emission with respect to the magnetic field structure. Title: Spatially-Resolved Observations of Solar Active Regions in Soft X-Ray and Centimetric WAVELENGTHS." Authors: Pallavicini, R.; Tofani, G.; Vaiana, G. S. Bibcode: 1977uxsa.coll...44P Altcode: 1977IAUCo..43...44P No abstract at ADS Title: Non-stationary heating of solar flare plasma by non-thermal electrons. Authors: Giachetti, R.; Pallavicini, R. Bibcode: 1976A&A....53..347G Altcode: A general solution of the energy-transfer equation for nonthermal particles in an absorbing medium at constant density is obtained by the Green's function method. The derived particle distributions are used to compute the collisional heating of the high-temperature region of solar flares. The space and time dependence of the energy deposition is determined for a variety of nonthermal-particle sources. The results are discussed on the basis of presently available flare observations, and suggestions are given for the use of the computed energy-deposition functions in the investigation of flare models. Title: The spatial structure of a solar flare in soft X-rays and centimetric wavelengths. Authors: Pallavicini, R.; Vaiana, G. S. Bibcode: 1976SoPh...49..297P Altcode: High-resolution images of the decay phase of a soft X-ray flare observed by the S-054 experiment on Skylab are compared with interferometric scans of the radio burst obtained simultaneously at 2.8 cm (Felli et al., 1975). The spatial resulution of the radio instrument in one direction, although lower than the X-ray telescope resolution, is high enough for a detailed comparison. The comparison clarifies the relationship between the sources of soft X-ray and thermal radio emission in solar flares. The X-ray emission is localized in a loop-like structure which appears spatially coincident with the rapidly varying component of the radio burst. The more stable components of the radio source, which do not appear to contribute substantially to X-ray emission, are found to be spatially associated with the extremes of the X-ray loop. A model of plasma-filled loops is suggested which accounts for the emissions in both spectral ranges and for their spatial location and temporal development. Title: Spatial Structure and Temporal Development of a Solar X-Ray Flare Observed from Skylab on June 15, 1973 Authors: Pallavicini, R.; Vaiana, G. S.; Kahler, S. W.; Krieger, A. S. Bibcode: 1975SoPh...45..411P Altcode: A solar flare on June 15, 1973 has been observed with high spatial and temporal resolution by the S-054 grazing-incidence X-ray telescope on Skylab. Both morphological and quantitative analyses are presented. Some of the main results are: (a) the overall configuration of the flare is that of a compact region with a characteristic size of the order of 30″ at the intensity peak, (b) this region appears highly structured inside with complex systems of loops which change during the event, (c) a brightening over an extended portion of the active region precedes the flare onset, (d) the impulsive phase indicated by the non-thermal radio emission is a period during which a rapid brightening occurs in loop structures, (e) the X-ray emission is centered over the neutral line of longitudinal magnetic field, and the brightest structures at the flare onset bridge the neutral line, (f) loop systems at successively increasing heights form during the decay phase, finally leading to the large loops observed in the postflare phase, (g) different parts of the flare show distinctly different light curves, and the temporal development given by full disk detectors is the result of integrating the different intensity vs time profiles. Title: Thermal Models of Flaring Region Based on Observations by the SOLRAD 10 Satellite Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1975SoPh...44..101L Altcode: A number of solar X-ray bursts, observed with the SOLRAD 10 satellite on 1971 September 14, 17, November 28 and 1972 August 1, have been analysed. From the differential emission measure distribution deduced from the observations the temporal and spatial distribution in a flaring region has been evaluated and compared with models of instantaneous or continuous energy injection and conductive redistribution. Assuming a power law for the differential emission measure in dependence of electron temperature the ratios of the counting rates observed in different spectral bands have been compared with theoretical predictions so as to test the validity of this particular class of models. Title: The Structure and Intensity Evolution of a Solar Burst at 2.8 cm and the Relation with the Soft X-Ray Emitting Region Authors: Felli, M.; Pallavicini, R.; Tofani, G. Bibcode: 1975SoPh...44..135F Altcode: The decay phase of a microwave burst was observed with a one-dimensional angular resolution of 16″ at 2.8 cm. The structure was found to be composed of several bursting regions with different evolution. The event was also observed in soft X-rays by full-disk detectors. The joint analysis of these data suggests that the complete event has thermal origin and that the soft X-ray emission is associated with the rapidly varying component of the radio structure. From these results the average values of the electron temperatures and densities were computed for each component. Title: X-ray and radio emission for the June 15, 1973 solar flare. Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.; Vaiana, G. S. Bibcode: 1975MmArc.104..157P Altcode: No abstract at ADS Title: X-ray and radio emission for the June 15, 1973 solar flare Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.; Vaiana, G. S. Bibcode: 1975xtcg.work..157P Altcode: Results are summarized for observations of a solar flare by the grazing-incidence X-ray telescope on the Apollo Telescope Mount which were made with high spatial and temporal resolution. The X-ray observations are compared with ground-based radio, optical, and magnetogram observations as well as with X-ray data from other satellite instruments. The temporal development of the flare as shown by X-ray pictures is outlined, and an X-ray picture taken at the flare peak is compared with a magnetogram obtained at the end of the flare and an H-alpha picture taken during its decay. Other data used in the analysis include satellite measurements of hard and soft X-ray fluxes, and radio fluxes measured at several frequencies between 245 and 15,400 MHz. The volume, temperature, density, and emission measure of the flare region are determined along with the temporal evolution of these parameters. It is shown that the soft X-ray and microwave emissions originated from a thermal plasma whose temperature and density increased during the rising part of the event and decreased during the decay phase. It is suggested that plasma heating was due to collisional losses of nonthermal electrons accelerated during the rising phase and that conductive and radiative cooling contributed equally to the flare's decay. Title: An X-ray flare from Skylab: results and interpretations. Authors: Vaiana, G. S.; Kahler, S.; Krieger, A.; Pallavicini, R.; Silk, J. K. Bibcode: 1974BAAS....6..265V Altcode: No abstract at ADS Title: An Experimental Model of Solar Flares in the Corona Authors: Silk, J. K.; Kahler, S.; Krieger, A.; Timothy, A.; Vaiana, G.; Pallavicini, R. Bibcode: 1974BAAS....6T.294S Altcode: No abstract at ADS Title: X-ray and Radio Emission for the June 1. 1973 Solar Flare Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.; Vaiana, G. S. Bibcode: 1974OMOAA.104..157P Altcode: No abstract at ADS Title: Non-Thermal Ionization and Recombination Processes during Solar Flares Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1973SoPh...29...93L Altcode: Ionization and recombination processes are studied for a plasma of which the electrons follow a power-law energy distribution. Title: Radio flux measurement simultaneous with a flare observed from Skylab Authors: Pallavicini, R.; Patriarchi, P. Bibcode: 1973MmSAI..44..431P Altcode: No abstract at ADS Title: Ionization and Recombination Processes for Non-Thermal Plasmas Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1973sari.conf..120L Altcode: No abstract at ADS Title: Thermal and Non-Thermal Soft X-Ray Bursts Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1972SoPh...27..164L Altcode: X-ray bursts observed for energies lower than 25 keV are usually interpreted as being produced by a thermal plasma with several million degrees of temperature. Title: Thermal and Non-Thermal Soft X-Ray Bursts Authors: Landini, M.; Monsignori Fossi, B. C.; Pallavicini, R. Bibcode: 1972SSRv...13..825L Altcode: 1972IAUCo..14..825L No abstract at ADS Title: Il problema dei bursts X non termici (Rassegna) Authors: Pallavicini, R. Bibcode: 1972MmSAI..43..195P Altcode: No abstract at ADS Title: La scuola estiva "Physics and chemistry of upper atmospheres" (Congressi e Simposi) Authors: Pallavicini, R. Bibcode: 1972MmSAI..43..567P Altcode: No abstract at ADS