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Author name code: pallavicini
ADS astronomy entries on 2022-09-14
author:"Pallavicini, Roberto"
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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
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. <P />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.
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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.
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. <P />Research supported in part by NASA and
the Smithsonian Astrophysical Observatory.
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Title: Metallicity of low-mass stars in Orion
Authors: D'Orazi, V.; Randich, S.; Flaccomio, E.; Palla, F.; Sacco,
G. G.; Pallavicini, R.
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. <BR />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. <BR />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. <BR />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. <P />Based on observations collected at Paranal Observatory,
ESO (Chile). Programs 072.D-0019, 074.C-0757, 076.D-0136, 076.C-0145.
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Title: X-ray properties of the young open cluster around λ Orionis
Authors: Franciosini, E.; Sacco, G. G.; Pallavicini, R.
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.
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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.
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.
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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.
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.
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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.
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 <ASTROBJ>σ Ori</ASTROBJ>
and <ASTROBJ>λ Ori</ASTROBJ>. <BR />Methods: We observed 98 and 49
low-mass (0.2-1.0 M<SUB>⊙</SUB>) stars in <ASTROBJ>σ Ori</ASTROBJ>
and <ASTROBJ>λ Ori</ASTROBJ> 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. <BR />Results:
We identified 65 and 45 members of the <ASTROBJ>σ Ori</ASTROBJ> and
<ASTROBJ>λ Ori</ASTROBJ> 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 <ASTROBJ>σ Ori</ASTROBJ> cluster, finding values between
10<SUP>-11</SUP> and 10<SUP>-7.7</SUP>~M<SUB>⊙</SUB> yr<SUP>-1</SUP>
and in 4 stars of the <ASTROBJ>λ Ori</ASTROBJ> cluster, finding
values between 10<SUP>-11</SUP> and 10<SUP>-10.1</SUP>~M<SUB>⊙</SUB>
yr<SUP>-1</SUP>. 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 <ASTROBJ>σ Ori</ASTROBJ> cluster (52±9% and 78±16%) than in
<ASTROBJ>λ Ori</ASTROBJ> (28±8% and 40±20%). <BR />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 <ASTROBJ>λ Ori</ASTROBJ> cluster or to different ages
of the cluster populations. Further observations are required to draw
a definitive conclusion. <P />Based on Data collected at the ESO Very
Large Telescope, Paranal Observatory, Chile [programs 074.D-0136(A)
and 076.C-0125(A)]. <P />Tables 1, 2 and 4-7 are only available in
electronic form at http://www.aanda.org
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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.
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. <BR />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. <BR
/>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. <BR />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. <BR />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. <P />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
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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.
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). <P
/>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. <P />(5 data files).
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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.
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.
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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.
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. <P />For each member star in the four
clusters we give the measured EWs. <P />(2 data files).
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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.
2008eic..work..153V Altcode:
No abstract at ADS
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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.
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.
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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
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.
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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.
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. <BR />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. <BR />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). <BR />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. <P />Table 2 is only available in electronic form
at http://www.aanda.org
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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.
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. <BR
/>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. <BR />Methods: We analyzed VLT/UVES spectra of members
of <ASTROBJ>NGC 2516</ASTROBJ>, the <ASTROBJ>Hyades</ASTROBJ>, and
<ASTROBJ>M 67</ASTROBJ> 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<SUB>⊙</SUB> star based on standard evolutionary
models. <BR />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. <BR />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). <P />Based on observations collected at ESO-VLT, Paranal
Observatory, Chile, Programme numbers 65.L-0427, 68.D-0491, 69.D-0454.
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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.
2007ApJ...659L..41P Altcode:
We measured lithium in a sample of low-mass stars (~0.1-0.3
M<SUB>solar</SUB>) 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. <P />Based on data collected at ESO-VLT, Paranal
Observatory, Chile [ID 074.C-0757(A)].
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Title: Lithium-depleted stars in the young σ Orionis cluster
Authors: Sacco, G. G.; Randich, S.; Franciosini, E.; Pallavicini,
R.; Palla, F.
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. <BR />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. <BR />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. <BR />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. <P />Based on data
collected at the ESO Very Large Telescope, Paranal Observatory, Chile
[program 074.D-0136(A)].
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Title: Metallicity of low-mass members of the Orion Nebula Cluster.
Authors: D'Orazi, V.; Randich, S.; Palla, F.; Flaccomio, E.;
Pallavicini, R.
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.
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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.
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.
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Title: VizieR Online Data Catalog: XMM observations of sigma Ori
cluster (Franciosini+, 2006)
Authors: Franciosini, E.; Pallavicini, R.; Sanz-Forcada, J.
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. <P />(3 data files).
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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
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.
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Title: Element abundances of unevolved stars in the open cluster M 67
Authors: Randich, S.; Sestito, P.; Primas, F.; Pallavicini, R.;
Pasquini, L.
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. <BR /> 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.<BR />
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.<BR /> 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.<BR />
---------------------------------------------------------
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.
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.
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.
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.
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.
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.
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.
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 <SUB>eff</SUB>) 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 <SUB>eff</SUB> 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
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
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<SUB>*</SUB>~0.4-1.0
M<SUB>solar</SUB>) 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 M<SUB>solar</SUB> 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. <P />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.
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.
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.
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.
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.
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.
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 <ASTROBJ>HD 283572</ASTROBJ>, the Zero Age Main Sequence star
<ASTROBJ>EK Dra</ASTROBJ> and the Hertzsprung-gap giant star <ASTROBJ>31
Com</ASTROBJ>. They all have high X-ray luminosity (~10<SUP>31</SUP>
erg s<SUP>-1</SUP> for HD 283572 and 31 Com and ~10<SUP>30</SUP>
erg s<SUP>-1</SUP> 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.
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
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 logL<SUB>X</SUB>~32.2 to 32.5 ergs s<SUP>-1</SUP>,
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 L<SUB>X</SUB><=10<SUP>31</SUP>
ergs s<SUP>-1</SUP> with current detectors.
---------------------------------------------------------
Title: Lithium evolution in intermediate age and old open clusters:
NGC 752 revisited
Authors: Sestito, P.; Randich, S.; Pallavicini, R.
2004A&A...426..809S Altcode: 2004astro.ph..7305S
We present new high resolution spectroscopic observations of the
intermediate age (∼2 Gyr) open cluster <ASTROBJ>NGC 752</ASTROBJ>. We
investigate the Li vs. T<SUB>eff</SUB> 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 <ASTROBJ>Hyades</ASTROBJ> (∼0.6
Gyr) to <ASTROBJ>NGC 188</ASTROBJ> (∼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
<ASTROBJ>IC 4651</ASTROBJ> and <ASTROBJ>NGC 3680</ASTROBJ>. As for
the latter clusters, we find that NGC 752 is characterized by a tight
Li vs. T<SUB>eff</SUB> distribution for solar-type stars, with no
evidence for a Li spread as large as the one observed in the solar age
solar metallicity <ASTROBJ>M 67</ASTROBJ>. 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. <P />Based on observations
collected at Telescopio Nazionale Galileo, La Palma, Canary Islands.
---------------------------------------------------------
Title: XMM-Newton Proposal 03006901
Authors: Pallavicini, Roberto
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.
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
m<SUB>R</SUB> ~ 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.
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.
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.
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.
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<SUP>-1</SUP>)
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.
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.
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.
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. <P />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.
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.
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. <P />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.
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.
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.
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.
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 T<SUB>max</SUB> ≈ 100 MK and n<SUB>e</SUB> = (1 -
3) · 10 <SUP>11</SUP> cm <SUP>-3</SUP>), as well as to estimate the
X-ray flare area S ≈ 1022 cm <SUP>2</SUP>. 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.
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.
2003A&A...407..289S Altcode: 2003astro.ph..5394S
We have carried out a high resolution spectroscopic survey of the
220-250 Myr old cluster <ASTROBJ>NGC 6475</ASTROBJ>: 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 (T<SUB>eff</SUB> >≈ 6000 K) undergo a very
small amount of Li depletion during the early phases on the ZAMS; (ii)
G-type stars (6000 >≈ T<SUB>eff</SUB> >≈ 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. <P />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.
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.
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
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.
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 L<SUB>X</SUB> ≈ 32.16 - 32.42). We derive the
coronal emission measure distribution, elemental abundances, and
density estimates. <P />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
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.
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 Z<SUB>sun</SUB>), while for TY Pyx we find Z ~ 0.5-0.6
Z<SUB>sun</SUB>. 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
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<SUP>-4</SUP> and 10<SUP>-2</SUP> can be reached for targets with
visual magnitudes of up to 17th magnitude. A polarimetric accuracy
better than 10<SUP>-4</SUP> 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<SUP>-2</SUP>, 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.
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 <ASTROBJ>NGC 188</ASTROBJ>. 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
<ASTROBJ>Hyades</ASTROBJ> and no more Li depleted than stars of similar
temperature in the 2-4 Gyr younger cluster <ASTROBJ>M 67</ASTROBJ>. 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. <P />Based
on observations collected at the Italian National Telescope Galileo.
---------------------------------------------------------
Title: Galactic open clusters: key tracers of stellar structure
and evolution
Authors: Pallavicini, R.
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. <P />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.
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.
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.
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.
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.
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.
2002ASPC..277..473F Altcode: 2002sccx.conf..473F
No abstract at ADS
---------------------------------------------------------
Title: High-resolution ground-based spectroscopy: where and how ?
Authors: Pallavicini, R.
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.
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.
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 <ASTROBJ>M 67</ASTROBJ> (4.5 Gyr)
and in the intermediate age cluster <ASTROBJ>IC 4651</ASTROBJ> (1.7
Gyr). One member of the young cluster <ASTROBJ>IC 2391</ASTROBJ> ( ~
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.
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.
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.
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
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.
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.
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/Z<SUB>sun</SUB>
=~ 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 10<SUP>19</SUP> cm<SUP>-2</SUP>, 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 <ASTROBJ>NGC
3680</ASTROBJ>: Following Li evolution along the C-M diagram
Authors: Pasquini, L.; Randich, S.; Pallavicini, R.
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 <ASTROBJ>IC 4651</ASTROBJ>. 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
<ASTROBJ>IC 2602</ASTROBJ> and <ASTROBJ>IC 2391</ASTROBJ>: Enlarging
the sample
Authors: Randich, S.; Pallavicini, R.; Meola, G.; Stauffer, J. R.;
Balachandran, S. C.
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 M<SUB>sun</SUB> 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 <ASTROBJ>Pleiades</ASTROBJ>. A scatter is also seen among
late-K and M dwarfs. Unlike in the Pleiades and <ASTROBJ>Alpha
Per</ASTROBJ> 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.
2001slbt.work...95P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quiescent and flare analysis for the chromospherically active
star <ASTROBJ>Gl 355</ASTROBJ> (<ASTROBJ>LQ Hya</ASTROBJ>)
Authors: Covino, S.; Panzera, M. R.; Tagliaferri, G.; Pallavicini, R.
2001A&A...371..973C Altcode: 2001astro.ph..3473C
We discuss ROSAT and ASCA observations of the young active star
<ASTROBJ>Gl 355</ASTROBJ>. 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/Z<SUB>sun</SUB> ~ 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 T<SUB>1</SUB>
~ 7 MK and a hotter component (to which only ASCA was sensitive) at
T<SUB>2</SUB> ~ 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.
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.
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.
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.
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 <ASTROBJ>AB Doradus</ASTROBJ>
Authors: Güdel, M.; Audard, M.; Briggs, K.; Haberl, F.; Magee, H.;
Maggio, A.; Mewe, R.; Pallavicini, R.; Pye, J.
2001A&A...365L.336G Altcode:
We report results of deep X-ray observations of <ASTROBJ>AB
Doradus</ASTROBJ> 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. <ASTROBJ>AB Dor</ASTROBJ> 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 10<SUP>10</SUP>
cm<SUP>-3</SUP>; 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 10<SUP>10</SUP> 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.
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.
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.
2001ASPC..234..101C Altcode: 2001xras.conf..101C
No abstract at ADS
---------------------------------------------------------
Title: The XMM-Newton view of stellar coronae: Coronal structure in
the <ASTROBJ>Castor</ASTROBJ> X-ray triplet
Authors: Güdel, M.; Audard, M.; Magee, H.; Franciosini, E.; Grosso,
N.; Cordova, F. A.; Pallavicini, R.; Mewe, R.
2001A&A...365L.344G Altcode:
We present results of a comprehensive X-ray investigation of the
multiple stellar system <ASTROBJ>Castor</ASTROBJ> AB + <ASTROBJ>YY
Gem</ASTROBJ>. The observations were obtained with the XMM-Newton
observatory. We report the first spatially separated detection
and identification of both <ASTROBJ>Castor</ASTROBJ> A and B as
frequently flaring X-ray sources. Spectral modeling of the <ASTROBJ>YY
Gem</ASTROBJ> and <ASTROBJ>Castor</ASTROBJ> 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 10<SUP>10</SUP> cm<SUP>-3</SUP> for <ASTROBJ>YY Gem</ASTROBJ>
and <ASTROBJ>Castor</ASTROBJ>. The <ASTROBJ>YY Gem</ASTROBJ> 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.
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.
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.
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 10<SUP>10</SUP> {cm}<SUP>-3</SUP>. 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.
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.
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 L<SUB>x</SUB> ~
4 x 10<SUP>28</SUP> erg sec<SUP>-1</SUP> 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.
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.
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 10<SUP>8</SUP> K, and peak
emission measures of ~ 5 x 10<SUP>54</SUP> cm<SUP>-3</SUP>. 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 (<~ 10<SUP>53</SUP> cm<SUP>-3</SUP>),
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.
2000A&A...355..681C Altcode: 1999astro.ph.11352C
<ASTROBJ>II Peg</ASTROBJ> 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 <ASTROBJ>II Peg</ASTROBJ>. 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 <ASTROBJ>II
Peg</ASTROBJ> 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.
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.
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.
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.
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.
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.
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.
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.
2000IAUS..198..366T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Spectroscopy of Stellar Coronae with BeppoSAX
Authors: Pallavicini, R.; Tagliaferri, G.; Maggio, A.
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.
2000MmSAI..71..869P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lithium in open clusters
Authors: Pallavicini, R.; Pasquini, L.; Randich, S.
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.
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.
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 N<SUB>H</SUB> 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
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.
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.
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.
1999yCat..41380087C Altcode:
We present the results of high-precision UBV(RI)<SUB>c</SUB> 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.
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. <P />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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1998sxmm.confE..11P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Coronae from Stars
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
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.
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.
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<SUP>-2</SUP>, 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<SUP>-3</SUP>; and
the height h (in km) above the level where tau<SUB>5000</SUB>=1. (2
data files).
---------------------------------------------------------
Title: Lithium in solar-type stars of the old open cluster M 67.
Authors: Pallavicini, R.; Pasquini, L.; Randich, S.
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.
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.
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
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 cm<SUP>2</SUP> 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.
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.
1997xisc.conf..573W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sun as a variable star
Authors: Pallavicini, R.
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.
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.
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.
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.
1996ASPC..109..603F Altcode: 1996csss....9..603F
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic Diagnostics of Astrophysical Plasmas
Authors: Pallavicini, R.
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.
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.
1996ASPC..109..295T Altcode: 1996csss....9..295T
No abstract at ADS
---------------------------------------------------------
Title: Millimeter Continuum Observations of Stars
Authors: Pallavicini, Roberto; White, S. M.
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.
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.
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.
1996ASPC..109..273M Altcode: 1996csss....9..273M
No abstract at ADS
---------------------------------------------------------
Title: In memoriam of C.-C. Cheng
Authors: Pallavicini, R.
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.
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.
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.
1995yCat..41150041C Altcode:
We present high-precision UBV(RI)<SUB>c</SUB> 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.
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.
1995lea..conf..311P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flares in Late-type Stars: X-ray
Authors: Pallavicini, Roberto
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.
1995MmSAI..66..383R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lithium in Late-Type Subgiants
Authors: Randich, S.; Pallavicini, R.; Pasquini, L.; Gratton, R.
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.
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.
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
1995silp.conf.....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lithium abundances of nearby solar-like stars.
Authors: Pasquini, L.; Liu, Q.; Pallavicini, R.
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.
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.
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.
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.
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<SUP>-6</SUP> - 3 x 10<SUP>-4</SUP> 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 10<SUP>7</SUP> 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.
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.
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.
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.
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.
1994ASPC...64..294P Altcode: 1994csss....8..294P
No abstract at ADS
---------------------------------------------------------
Title: Lithium, Activity and Post-Main-Sequence Evolution (Invited
Review)
Authors: Pallavicini, R.
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.
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 T<SUB>eff</SUB> ≤ 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 M<SUB>sun</SUB>). 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.
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.
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.
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.
1993MmSAI..64..672G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time Variability of Stellar X-ray Emission
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
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.
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.
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, Δk<SUB>1</SUB>, Δk<SUB>2</SUB>, 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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
1992ASPC...26..576R Altcode: 1992csss....7..576R
No abstract at ADS
---------------------------------------------------------
Title: Stellar Flares - Confined or Eruptive Events
Authors: Pallavicini, R.
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.
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
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.
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
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.
1992LNP...397..340T Altcode: 1992sils.conf..340T
No abstract at ADS
---------------------------------------------------------
Title: Stellar flares: Confined or eruptive events?
Authors: Pallavicini, R.
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.
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
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.
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.
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.
1991AN....312..277P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical Simulations of Flares on M Dwarf Stars
Authors: Cheng, C. -C.; Pallavicini, R.
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.
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.
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.
1991LNP...385...26P Altcode: 1991ildx.conf...26P
No abstract at ADS
---------------------------------------------------------
Title: Lithium abundance and chromospheric activity.
Authors: Randich, S.; Pallavicini, R.
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.
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.
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.
1991mcch.conf..222P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lithium in chromospherically active stars.
Authors: Pallavicini, R.; Randich, S.; Giampapa, M.; Cutispoto, G.
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.
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.
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.
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.
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.
1990IAUS..137..147P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-resolution spectroscopy of cool stars at ESO.
Authors: Pasquini, L.; Pallavicini, R.
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.
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.
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.
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.
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.
1989AJ.....98..737S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotation Rates of Giant Stars
Authors: Gray, David F.; Pallavicini, R.
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.
1989A&ARv...1..177P Altcode:
Stars of nearly all spectral types and luminosity classes are surrounded
by tenuous high-temperature ( T≈10<SUP>6</SUP>-10<SUP>7</SUP>K)
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
1988xraw.book.....P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar magnetic fields: measurements and diagnostics
Authors: Pallavicini, R.
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.
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.
1988IAUS..129..283C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar coronae - The EXOSAT picture
Authors: Pallavicini, R.
1988xraw.book...71P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hot thin plasmas in astrophysics
Authors: Pallavicini, R.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1986epos.conf.5.39W Altcode: 1986epos.confE..39W
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Observations of Flare Stars with EXOSAT
Authors: Pallavicini, R.
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.
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.
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.
1986A&A...157..217L Altcode:
An X-ray flare has been detected on the G0 dwarf star π<SUP>1</SUP>UMa
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,
π<SUP>1</SUP>UMa 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.
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 ⪉2×10<SUP>7</SUP>km<SUP>2</SUP> 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.
1986LNP...254...67G Altcode: 1986csss....4...67G
No abstract at ADS
---------------------------------------------------------
Title: Coronal magnetic fields
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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<SUP>−1</SUP>,
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<SUP>−1</SUP>
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.
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.
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 χ<SUP>1</SUP>Ori.
---------------------------------------------------------
Title: The Solar-Stellar Connection (Invited Paper)
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
1984iue..prop.1928P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric emission, rotation and X-ray coronae of
late-type stars
Authors: Pallavicini, R.
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.
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.
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
1984faa..conf.....P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results from the Solar Maximum Mission.
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
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. <P />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. <P
/>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.
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.
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.
1983GAst....9...25L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Flares in Loops
Authors: Pallavicini, R.
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.
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.
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.
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:
L<SUB>x</SUB> = 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.
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.
1982MmSAI..53C.789P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Cosmic magnetic fields
Authors: Pallavicini, R.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1979RSAI...22..163P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Risultati recenti e problemi aperti in fisica solare.
Authors: Pallavicini, R.; Poletto, G.
1979GAst....5...19P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Is there anything new on the sun?
Authors: Pallavicini, R.; Poletto, G.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1972SSRv...13..825L Altcode: 1972IAUCo..14..825L
No abstract at ADS
---------------------------------------------------------
Title: Il problema dei bursts X non termici (Rassegna)
Authors: Pallavicini, R.
1972MmSAI..43..195P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: La scuola estiva "Physics and chemistry of upper atmospheres"
(Congressi e Simposi)
Authors: Pallavicini, R.
1972MmSAI..43..567P Altcode:
No abstract at ADS