Ana I. GÓMEZ DE CASTRO¹, Eva VERDUGO², and Brigitta VON REKOWSKI³

¹ Instituto de Astronomía y Geodesia (CSIC-UCM),
Universidad Complutense de Madrid, Madrid, E-28040, Spain
² ISO Data Center, ESAC-ESA, P.O.Box 50727, Madrid, E28080 Spain
³ School of Mathematics and Statistics,
University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK

ABSTRACT

Young stellar objects are an excellent laboratory to study the physics of accretion and outflow. The impact of this physics on the evolution of the constituents of pre-main sequence systems (star, disk) and the relevance of ultraviolet instrumentation to study this process are outlined. Special emphasis is made on the spectral characterization of the gravito-magnetic engine as well as on the role of the engine on the evolution of the inner disk. A recent review on the relevance of UV instrumentation to make progress in the understanding of star formation can be found in G´omez de Castro et al (2006).

Key words: UV astronomy, pre-main sequence stars, jets, winds, young planetary disks

Rosa María GONZÁLEZ DELGADO

Instituto de Astrofísica de Andalucía (CSIC),
P.O.Box 3004, 18080 Granada, Spain

ABSTRACT

Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues:
a) The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties.
b) Stellar clusters are an important mode of star formation in starbursts.
c) The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN.
d) The interaction between massive stars and the interstellar medium: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s%u22121 are ubiquitous phenomena in starbursts.
Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.
Key words: UV astronomy, massive stars, starburst galaxies, galaxy evolution

Nolan R. WALBORN¹

¹ Space Telescope Science Institute,
3700 San Martin Drive, Baltimore, Maryland 21218, USA

ABSTRACT

The systematics of OB spectra are reviewed in the optical domain, dominated by photospheric lines, and in the far ultraviolet (both IUE and FUSE ranges), in which the stellar-wind profiles dominate. First, the two-dimensional (temperature, luminosity) trends in normal spectra are surveyed. Then, the normal reference frame having been established, various categories of peculiar objects can be distinguished relative to it, which reveal several phenomena of structural and/or evolutionary significance. Included are CNO anomalies at both early and late O types, three varieties of rapid rotators, hot and cool Of/WN transition objects, and the recently discovered second known magnetic O star. The importance of both optical and UV observations to understand these phenomena is emphasized; for instance, progress in understanding the structure of the new O-type magnetic oblique rotator is hampered by the current lack of a UV spectrograph. While progress in the physical interpretation of these trends and anomalies has been and is being made, increased attention to modeling the systematics would accelerate future progress in this author´s opinion. Finally, preliminary results from a Chandra high-resolution survey of OB X-ray spectra (PI W. Waldron) are presented. They provide evidence that, just as emerged earlier in the UV, systematic morphological trends exist in the X-ray domain that are correlated with the optical spectral types, and hence the fundamental stellar parameters, contrary to prevailing opinion.

Key words: OB stars, spectroscopy, spectral classification, optical astronomy, UV astronomy, X-ray astronomy, stellar winds, standards, peculiar stars.

Luciana BIANCHI¹

¹ Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA

ABSTRACT

Massive stars dominate the chemical and dynamical evolution of the ISM, and ultimately of their parent galaxy and the universe, because of their fast evolution and intense supersonic winds. Four decades ago, the first rocket UV spectra of massive stars revealed the importance of mass loss and began to change our understanding of their evolution. Recently, advances in stellar modeling, and the observation of crucial ions in the far-UV spectral range, led to the resolution of long-standing issues in our understanding of massive star atmospheres. A revised (downwards) calibration of Teff for early spectral types is emerging as a result. Meanwhile, HST imaging, and large ground-based telescopes with multislit spectroscopic capabilities, had opened the possibility of resolved studies of stellar populations in Local Group galaxies, which sample a variety of metallicity and environment conditions. More recently, GALEX is providing a global, deep view of the young stellar populations for hundreds of nearby galaxies, revealing their recent star-formation history and modalities. The wide-field coverage and sensitivity of the GALEX UV imaging, easily detecting extremely low levels of star formation, is again changing some of our views on massive star formation in galaxies.

Key words: massive stars, stellar parameters, stellar populations, nearby galaxies

Theodore R. GULL¹, Krister E. NIELSEN^1,2, and Gladys V. KOBER^1,2

¹ NASA/ Goddard Space Flight Center, Code 667, Greenbelt, MD, USA 20771
² Catholic University of America, Washington, DC, USA

ABSTRACT

High spectral and high spatial resolutions are combined in HST/STIS
to reveal the neutral and ionic material
in the Homunculus, ejecta of Eta Carinae.

The Hubble Space Telescope`s (HST) high spatial resolution combined with the spectral resolution of Space Telescope Imaging Spectrograph (STIS) is revealing many hidden answers to questions about the character of ? Car. We are examining spatially-resolved spectra recorded from 1998.0 to 2004.3 that show major changes in the stellar and nebular spectra, tracking the 2024-day period first noted in the He I ?10830 stellar line profile.

Key words: UV astronomy, massive stars, mass loss, abundances, ejecta

Krzysztof CZART¹ and Andrzej STROBEL¹

¹ Toru´n Centre for Astronomy,
Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Torun, Poland

ABSTRACT

Distances toWolf-Rayet stars are still the subject of research. The onlyWR star with reliable Hipparcos parallax is WR 11. Other Wolf-Rayet stars have photometric distances estimations. Recently a correlation between equivalent width of interstellar Ca II H (3968 °A) and K (3933 °A) lines and Hipparcos parallaxes has been found for OB stars (Megier et al. 2005). These relations are given with formulas: p = 1/[2.78EW(K) 95] and p = 1/[4.58EW(H) 102], where p is a parallax in arcseconds and EW is equivalent width in milliangstroms. We have used these correlations to estimate distance to Wolf-Rayet star WR 134. Equivalent widths of Ca II lines have been measured in low resolution spectra with R=2000. We have got: 1.17 kpc from Ca II H and 1.18 kpc Ca II K line, while distance to this star as cited of VII Catalogue of Wolf-Rayet Stars is 1.74 kpc. WR 134 is also as a possible member of association Cyg OB3. According to new obtained distance it is more likely a member of Cyg OB1.

Key words: UV astronomy, Wolf-Rayet stars, interstellar lines, distances to stars

Luciana BIANCHI1 and James HERALD¹

1 Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA

ABSTRACT

We have identified a strong P Cygni feature (? 973) in the far-UV spectra of some very hot (Teff = 85, 000 K) central stars of planetary nebulae (CSPN) and PG 1159 stars as originating from NeVII. Using stellar atmosphere models, we reproduce this feature as it is observed in the spectra of hydrogen-deficient CSPN, as well as in PG 1159 stars. The discovery of highly ionized neon in CSPN spectra is important because an overabundance of this element is indica- tive of processed material that has been dredged up to the surface from the interior region as predicted in the `born-again` scenario, an explanation of H- deficient post-Asymptotic Giant-Branch (AGB) objects. We show the potential of this strong feature as well as weaker neon features as diagnostics in stellar atmospheres analyses for extremely hot post-AGB objects, where other diag- nostics are scarce. This diagnostic is potentially useful also in the analysis of massive stars with winds such as WO stars.

Key words: UV spectroscopy, post-ABG stars, planetary nebulae, PG1159 stars, winds, neon abundance, stellar evolution

L. BIANCHI1, B. EFREMOVA1,
J.E. HERALD1, M. LAGET2 M. VITON2 L. RODRIGUEZ,
and GALEX SCIENCE TEAM

1 Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA
2 LAM, France

ABSTRACT

We used Galaxy Evolution Explorer (GALEX) imaging survey data matched to the Sloan Digital Sky Survey (SDSS) in overlapping areas to explore the nature of the UV sources. We classify the sources by comparing their seven band photometry (GALEX far-UV, near-UV, SDSS u, g, r, i, z ) to model colors computed for different astrophysical objects, taking into account the effects of extinction. The initial sample covers mostly high galactic latitudes, and includes about 2 million sources. Based on our stellar models, we estimate that the GALEX surveys can detect hot White Dwarfs throughout the Milky Way halo (down to an estimated radius of 0.04R_o at the depth of the Medium Imaging Survey), providing an unprecedented improvement on the census of such objects in the Galaxy. Their observed surface density is consistently represented by the Milky Way models. Optical spectra available for a large subsample confirm the classification for the candidates selected from the GALEX photometry with about 97% purity for single hot stars and between 45-31% for binaries containing a hot WD and a cooler companion.

Key words: UV imaging, UV surveys, hot stars, Milky Way structure, optical surveys

D. NIKOLAIDIS ¹ E. Danezis ¹, E. Lyratzi ¹, L. %u02C7C. Popovi´c ², M. S.
Dimitrijevi´c ², A. Antoniou ¹, E. Theodossiou ^1.

¹University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics,
Panepistimioupoli, Zographou 157 84, Athens %u2013 Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

DACs and SACs phenomena in Hot Emission Stars

In this paper we present a mathematical model reproducing the complex profile of the spectral lines of Oe and Be stars that present DACs or SACs. This model presupposes that the regions, where these spectral lines are formed, are not continuous but consist of a number of independent absorbing or emitting density layers of matter and an external general absorption region. In this model we assume that the line broadening is due to the random motion of the ions and the rotation of the density regions that produce the spectral line and its satellite components. With this method we can calculate the values of the apparent rotational and radial velocities, the Gaussian standard deviation of the random motions of the ions, the random velocities of these motions, as well as the optical depth, the FullWidth at Half Maximum (FWHM), the absorbed and the emitted energy and finally the column density of the independent regions of matter which produce the main and the satellites components of the studied spectral lines.

Key words: UV astronomy, hot emission stars, DACs, SACs

Luciana BIANCHI¹, James E. HERALD1,and Miriam GARCIA²

1 Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA,
² IAC, Spain

ABSTRACT

A consistent analysis, based on non-LTE codes with sphericity and mass loss,of different ionization species in the far-UV and UV spectra of O-type starsallowed us to constrain the long-time uncertain ionization equilibrium in thestellar winds, to quantify the role of soft X-rays from shocks and to reconcileotherwise discrepant UV line diagnostics. The modeling initially performed withthe WM-basic code led to a revised (downwards) T_eff scale for Galactic O-typestars, a result with important implications for the energy-balance calculationsin HII regions and for massive star evolution. A further analysis using theCMFGEN code, including clumping effects, allowed us to resolve the remaining discrepancies in the modeling of UV lines, in particular the PV line in the far-UV, and to reconcile mass loss and photospheric parameters derived from opticaland UV lines.

Key words: UV spectroscopy, optical spectroscopy, hot massive stars, stellar parameters,mass loss

A. ANTONIOU ¹ E. Danezis ¹, E. Lyratzi ¹, D. Nikolaidis ¹, L. C. Popovi´c ²,
M. S. Dimitrijevi´c 2, E. Theodossiou ¹,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics,
Panepistimioupoli, Zographou 157 84, Athens %u2013 Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

SACs in the C IV regions of HD 93521 We examine the timescale changes of C IV spectral lines of the Oe star HD 93521, during a period of 16 years, applying the model proposed by Danezis et al. (2003, 2005a, b). We found that the spectral lines consist of one or more Satellite Absorption Components (SACs or DACs) which construct the whole spectral profile. In this paper we present the time scale variation of the rotational and random velocities.

Key words: Oe stars, HD 93521, SACs, best fit, rotational velocity, random velocity

A. LOBEL1 and R. BLOMME1

1 Royal Observatory of Belgium,
Ringlaan 3, Brussels, B-1180, Belgium

ABSTRACT

Radiative transfer calculations in three dimensions are presented to investigate dynamic structures in extended winds of massive stars .

We discuss the development of the new radiative transfer code Wind3D. It solves the non-LTE radiative transport problem in moving stellar atmosphere models in three geometric dimensions. The code accepts arbitrary 3D velocity fields in Cartesian geometry without assumptions of axial symmetry. Wind3D is currently implemented as a fully parallelized (exact) accelerated lambda iter- ation scheme with a two level atom formulation. The numerical transfer scheme is efficient and very accurate to trace small variations of local velocity gradients on line opacity in strongly scattering dominated extended stellar winds. We in- vestigate the detailed formation of P Cygni line profiles observed in ultraviolet spectra of massive stars. We compute the detailed shape of these resonance lines to model local enhancements of line opacity that can for instance be caused by clumping in supersonically expanding winds. Wind3D will be applied to hy- drodynamic models to investigate physical properties of discrete absorption line components.

Key words: UV astronomy, spectroscopy, winds, clumping, radiative transfer

Andrea F. TORRES ^1,2 and Adela E. RINGUELET ¹

¹Facultad de Ciencias Astronómicas y Geofísicas (FCAG),
Universidad Nacional de La Plata,
Paseo del Bosque S/N, B1900FWA, La Plata, Buenos Aires, Argentina
²Instituto de Astrofísica de La Plata (CONICET),
Paseo del Bosque S/N, B1900FWA, La Plata, Buenos Aires, Argentina

ABSTRACT

Analysis Of The High Temperature Region In Be Stars.

We have chosen from the INES system 50 Be stars, which are not suspected of being binaries, representative of a considerable range of temperature and whose distribution of number of stars versus V sin i reproduces the results of Huang & Struve (1960) and Yudin (2001).

We have analysed the Line Forming Regions (LFRs) of transitions that need temperatures of about or higher than 20000 K and that, consequently, constitute a separate region from the Cool Envelope (CE). We call this region the High Temperature Region (HTR) and it is there where the phenomenon of `superionization` takes place.

With the aim of providing observational results that permit us to discuss the geometry and temperature distribution of this HTR, we studied the resonance lines of Si IV, C IV and Al III and He II ? 1640. Our first conclusions are: (1) the HTR surrounds the star, (2) expansion velocities in the HTR -measured in the line cores- increase at the equator and not at the poles. We suggest that single Be stars have a Chromosphere heated up by mechanical energy and a Cool Envelope which, in turns, can be either outflowing or inflowing. Our results reinforce the hypothesis of viscous processes.

Key words: Be stars, emission line, circumstellar matter, chromospheres

E. LYRATZI ¹, E. Danezis ¹, A. Antoniou ¹, D. Nikolaidis ¹, L. C. Popovi´c 2,
M. S. Dimitrijevi´c ²,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics,
Panepistimioupoli, Zographou 157 84, Athens %u2013 Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

DACs and SACs phenomena in Ha line of 120 Be stars

In this study we apply the method proposed by Danezis et al. (2003, 2005) on the stellar spectrographs of 120 Be stars, and we examine the variations of the physical parameters, stated below, as a function of the spectral subtype and the luminosity class.

We found that in the Be-type stellar atmospheres, there are two regions that can produce the Ha Satellite Absorption Components (SACs or DACs). The first one lies in the chromosphere and the second one in the cool extended envelope. With the above method we calculate: a) For the chromospheric absorption components: the optical depth as well as the rotational and radial velocities of the independent regions of matter which produce the main and the satellites components. b) For the emission and absorption components which are created in the cool extended envelope: the FWHM, the optical depth and the radial velocities of the independent regions of matter which produce the main and the satellites components.

Key words: UV astronomy, hot emission stars, H , DACs, SACs

E. LYRATZI ¹, E. Danezis ¹, A. Antoniou ¹, D. Nikolaidis ¹, L. C. Popovi´c ²,
M. S. Dimitrijevi´c ²,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics,
Panepistimioupoli, Zographou 157 84, Athens %u2013 Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

DACs and SACs phenomena in Si IV resonance lines of 68 Be stars

In our study we apply the method proposed by Danezis et al. (2003) on the spectra of 68 Be stars, taken with I.U.E. and we examine the variations of the physical parameters, stated below, as a function of the spectral subtype.
We found that the absorption atmospherical regions where the Si IV resonance lines originated may be formed of one to five independent density layers of matter which rotate with different velocities, producing one to five Satellite Absorption Components (SACs or DACs). With the above method we calculate the values of the apparent rotational and radial velocities, as well as the optical depth of the independent regions of matter which produce the main and the satellites components of the studied spectral lines.

Key words: UV astronomy, hot emission stars, Si IV, DACs, SACs

A. ANTONIOU¹, E. Danezis ¹, E. Lyratzi ¹, D. Nikolaidis ¹, L. C. Popovi´c ²,
M. S. Dimitrijevi´c ², E. Theodossiou ¹,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics, Panepistimioupoli, Zographou 157 84, Athens %u2013 Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

Spectral lines of Oe and Be stars present DACs or SACs

In this paper we study the C IV line profiles of a sample of 20 Oe stars (from O4 to O7 spectral subtype). Using the model given by Danezis et al. (2003, 2005a,b) we found that the line shapes are very complex and that they can be fitted by a multi-component C IV region. In the sample the region may be divided into two to five subregions which show different kinematical and physical parameters. We give the kinematical parameters of subregions where the C IV resonance lines (?? 1548.155, 1550.774 °A) are formed.

Key words: Oe stars, DACs, SACs, rotational velocity, Gaussian contribution, random velocities.

A. ANTONIOU ¹, E. Danezis ¹, E. Lyratzi ¹, D. Nikolaidis ¹, L. C. Popovi´c ²,
M. S. Dimitrijevi´c ², E. Theodossiou ¹,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics, Panepistimioupoli, Zographou 157 84, Athens – Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

Spectral lines of Oe and Be stars present DACs or SACs

In this paper we study the N IV line (? 1718.8 °A) of a sample of 20 Oe stars (from O4 to O7 spectral subtype). We did a multicomponent decomposition of the N IV line and N V (1238.81 A, 1242.804 A) resonance lines using the model given by Danezis et al. (2003, 2005a,b). We give the kinematical parameters of subregions where the high-ionized N IV line is formed.

Key words: Oe stars, N IV, DACs, SACs, Gaussian contribution, random velocities, FWHM.

A. ANTONIOU ¹, E. Danezis ¹, E. Lyratzi ¹, D. Nikolaidis ¹, L. C. Popovi´c ²,
M. S. Dimitrijevi´c ², E. Theodossiou ¹,

¹ University of Athens, Faculty of Physics, Department of Astrophysics,
Astronomy and Mechanics, Panepistimioupoli, Zographou 157 84, Athens, Greece
² Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia

ABSTRACT

Spectral lines of Oe and Be stars present DACs or SACs

In this paper we study the N IV line (%u03BB 1718.8 °A) of a sample of 20 Oe stars (from O4 to O7 spectral subtype). We did a multicomponent decomposition of the N IV line and N V (1238.81 A, 1242.804 A) resonance lines using the model given by Danezis et al. (2003, 2005a,b). We give the kinematical parameters of subregions where the high-ionized N IV line is formed.

Key words: Oe stars, N IV, DACs, SACs, Gaussian contribution, random velocities, FWHM.

Valentina KLOCHKOVA¹, Sergey ERMAKOV¹,
Vladimir PANCHUK¹, and Gang ZHAO²

¹ Special Astrophysical Observatory, Nizhnij Arkhyz, Russia
² National astronomical observatories of CAS, Datun Road, Beijing, China

ABSTRACT

High resolution echelle spectroscopy in ground-based UV is a powerful facility for study of chemical evolution of early Galaxy.

An atlas of high resolution (R=60000) in the poor studied wavelength range 3550-5000°A °A for 4 metal-deficient stars in the interval of metallicity -3.0 < [Fe/H] < -0.6, effective temperature 4750 < T_eff < 5900K, surface gravity 1.6 < lg g < 5.0 is produced. Details of the method of producing a spectral atlas, line identifications, stellar atmospheric parameters determination are described. Based on these spectral data, we determined model atmosphere parameters and calculated abundances of 25 chemical elements.

Key words: Ground-based UV and blue astronomy, high resolution spectroscopy, metalpoor stars, chemical composition, spectral atlas

A. LOBEL¹

¹ Royal Observatory of Belgium,
Ringlaan 3, Brussels, B-1180, Belgium

ABSTRACT

SpectroWeb is under development as an online interactive repository for identified spectral lines in spectral standard stars.

SpectroWeb is an online maintained interactive graphical database of digital spectral atlases of spectral standard stars at http://spectra.freeshell.org . It is an efficient and user-friendly research tool for accurate analyses of stellar spec- tra observed with large spectral resolution, including the solar spectrum. The web-interface displays observed and theoretical stellar spectra, and comprehen- sively provides detailed atomic and molecular line information via user interac- tion. It fully integrates interactive spectrum visualization tools for the analysis, management, and maintenance of large volumes of spectral line-identification, -transition, and -property data. SpectroWeb 1.0 currently offers optical (3300- 6800 °A) flux normalized high-resolution spectra of Betelgeuse (M2), Arcturus (K1), The Sun (G2), Beta Aqr (G0), Procyon (F5), and Canopus (F0). The provided line identifications are based on state of the art spectrum synthesis cal- culations. The graphical database is under permanent development as an online repository of identified (absorption) lines in spectral standard reference stars, covering a broad range of stellar spectral types. Its object-oriented (Java) im- plementation offers future expansion capabilities to link and read stellar spectral atlases from various public internet sites.

Key words: spectroscopy, spectroscopic atlases, line identification, atomic data, spectral synthesis

Nicole ALLARD,^1,2 and Irakli NOSELIDZE³

¹Institut d%u2019Astrophysique de Paris, UMR 7095, CNRS,
Universit´e Pierre et Marie Curie, 98bis boulevard Arago, F-75014 Paris, France
²Observatoire de Paris-Meudon, LERMA, UMR 8112, CNRS,
F-92195, Meudon Principal Cedex, France
³ Department of Physics, Tbilisi State University,
Chavchavadze Avenue 3, 0128 Tbilisi, Georgia

ABSTRACT

Structures observed about 995 °A in the Lyman ? wing of hot white dwarfs have been demonstrated to be due to quasi-molecular absorption of H 2 molecules. We present new theoretical calculations of the line profile of Lyman that include the variation of the radiative dipole moment during the collision.

Key words: UV astronomy, Line profiles, stars: white dwarfs

Vladimir PANCHUK, Valentina KLOCHKOVA,
Ivan NAJDENOV, and Maksim YUSHKIN

Special Astrophysical Observatory, 369167 Nizhnij Arkhyz, Russia

ABSTRACT

We present high resolution echelle spectrograph NES of the 6m telescope. NES is located at the Nasmyth focus (1:30) platform. In combination with an image slicer NES posses spectral power R=75000 within the spectral region 3200-10000°A°A . Scopes of the spectrograph are illustrated by results of spectroscopy of selected stars.

Key words: Ground-based UV region, high resolution spectroscopy,

Letizia STANGHELLINI¹

¹ National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719, USA

ABSTRACT

The asymptotic giant branch (AGB) phase of stellar evolution is common to most stars of low and intermediate mass. Most of the carbon and nitrogen in the Universe is produced by AGB stars. The final fate of the AGB envelopes are represented by planetary nebulae (PN). By studying PN abundances and compare them with the yields of stellar evolution is possible to quantify carbon and nitrogen production, and to study cosmic recycling in galactic and Mag- ellanic Cloud populations. In this paper we present the latest results in PN chemical abundance analysis and their implication to the chemical evolution of the galaxy and the Magellanic Clouds, with particular attention to carbon abundance, available only thanks to ultraviolet spectroscopy.

Key words: UV astronomy, AGB and post-AGB stars, planetary nebulae, carbon abundance

Alexander KHOLTYGIN¹ and Yulia MILANOVA²

¹Astronomical Institute, Saint-Petersburg University, Russia
²Saint-Petersburg University, Russia

ABSTRACT

Method to determine the realistic abundances of carbon in planetary nebulae (PNe) based on the actual distribution functions of errors in measured line intensities was used to determine the C abundances for large sample of the galactic PNe are given. The mean temperatute and electron number thensities and the amplitudes of temperature and density fluctuations are found. The intensity of the ultraviolet lines of C ions are used to determine the more exact abundances. Basing on the newly carbon abundances the total mass losses of carbon during AGB and post-AGB stages of evolution are estimated.

Key words: AGB stars, mass loss, UV line intensities, carbon abundances, planetary nebulae

Vasilii GVARAMADZE

Sternberg Astronomical Institute, Moscow State University,
Universitetskij Pr. 13, Moscow, 119992, Russia ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it )

ABSTRACT

The proper motion of massive stars could cause them to explode far from the geometric centers of their wind-driven bubbles and thereby could affect the symmetry of the resulting diffuse supernova remnants (SNRs). We use this fact to explain the origin of SNRs consisting of two partially overlapping shells (e.g. Cygnus Loop, 3C 400.2, etc.).

Key words: ISM: bubbles, ISM: supernova remnants, ISM: individual objects: SN 1987A, RCW 86, Cygnus Loop, 3C 400.2

Knox S. LONG

Space Telescope Science Institute
3700 San Martin Drive
Baltimore, MD 21218 USA

ABSTRACT

Virtually all of the exotic objects in the Galaxy are the products of binary evo- lution, including binary pulsars, black-hole candidates, low mass X-ray binaries, cataclysmic variables and symbiotic stars. Type Ia supernovae, the standard candle of modern cosmology, are produced by them. UV spectroscopy of inter- acting binaries obtained with IUE, HST and FUSE have dramatically improved our understanding of interacting binaries and of the physical processes that characterize their emission. UV imaging has made it possible to isolate binaries and the products of binary evolution in old stellar populations and thereby test directly models of binary evolution in dense stellar systems. In this review, I will summarize some of the highlights of what we have learned about binaries and their evolution from UV observations, and suggest how further observations could resolve some of the important questions that remain

Key words: UV astronomy, binaries, winds, cataclysmic variables, symbiotic stars, globular clusters

Thomas NELSON^1,2, Marina ORIO^1,2,
Elia LEIBOWITZ³, Rosario GONZALES-RIESTRA⁴,
and Paola MUCCIARELLI⁵

¹ Department of Astronomy, University of Wisconsin-Madison,
475 N Charter St, Madison, WI, 53706, USA
² INAF Osservatorio Astronomico di Padova,
Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
³ Wise Observatory and the School of Physics and Astronomy,
Tel Aviv University, Tel Aviv 69978, Israel
⁴ XMM Science Operation Center, ESA, Villafranca Satellite Tracking Station,
PO Box 50727, 28080 Madrid, Spain
⁵ Dipartimento di Astronomia, Universita degli di Padova,
Vicolo dell’Osservatorio 3, I-35122, Padova, Italy
⁶ South African Astronomical Observatory,
PO Box 9, Observatory 7935, Cape Town, South Africa

ABSTRACT

We present X-ray observations of the recurrent nova RS Ophiuchi in outburst, obtained with the Chandra and XMM-Newton observatories on six different dates post discovery. An important goal of the observations was to study the central UEV-supersoft X-ray source. X-ray grating spectra are the best way to place constraints on the physical parameters of the white dwarfs in these systems. In the first month after the outburst, we detected emission lines of H and He -like ions of metals including Si, Mg and Ne. The presence of these lines indicates a range of plasma temperatures, and most likely we were detecting emission from red giant wind material shocked by the nova ejecta. Later spectra show a large increase in emission at longer wavelengths, peaking two months after the outburst. We attribute this to the emergence of the underlying white dwarf. We used NLTE white dwarf atmosphere models to fit the spectra, finding log g = 9, and T ~800,000K. This indicates a white dwarf mass of >1.2 M?). We also present a preliminary timing analysis of the XMM-Newton light curves. We find a period of ~ 35 s both in March and April. Although the origin of this period is still a question for debate, it may be the spin period of the white dwarf. If this is the case, the white dwarf must again be very massive, making RS Ophiuchi a likely supernova Ia progenitor.

Key words: EUV/X-ray astronomy, X-ray spectroscopy, white dwarfs, recurrent nova, RS Ophiuchi, timing analysis

Vojtech SIMON¹ and Janet A. MATTEI²

¹ Astronomical Institute, Academy of Sciences 251 65 Ondrejov, Czech Republic
² AAVSO, 25 Birch Street, Cambridge, Massachusetts 02138-1205, USA

ABSTRACT

V Sge is one of a few known super-soft X-ray sources (SSXSs) located in our Galaxy and is the representative of the V Sge class. Here we concentrate on its long-term optical activity (mostly transitions between high and low states, clustering in so-called active segments). We show that cycles are often apparent in such transitions but their length undergoes large, often gradual variations. We give the implications for the accretion wind evolution, modeled by Hachisu & Kato (2003). We also analyze the color indices and absolute magnitudes of V Sge and compare them with those of ´classical´ SSXSs with the orbital period shorter than 4 d. This approach helps compare the properties and configuration of the medium, on which soft X-rays are reprocessed in these systems. The specific properties of SSXSs, as regards their optical activity, absolute magnitudes and colors, can be the promising tools for the search for such systems in the optical and near UV passbands. SSXSs yet undetected in the X-ray passband because of absorption thus can be revealed by the photometric method.

Key words: accretion, accretion disks, radiation mechanisms: thermal, binaries: close, circumstellar matter, novae, cataclysmic variables, white dwarfs, X-rays: binaries

Steven H. SAAR¹, Vinay L. KASHYAP¹, and F. A. RINGWALD²

¹Smithsonian Astrophysical Observatory, 60 Garden Street,
Cambridge, MA 02138, USA
²Dept. of Physics, 2345 E. San Ramon Ave., California State University,
Fresno, CA 93740 USA

ABSTRACT

We report on HST observations of a mass transfer/accretion event in AM Her which appears to have been induced by a strong flare on the secondary. UV spectroscopic observations of the magnetic CV, AM Her, were made with STIS towards the end of a deep photometric minimum in late 2003. Our goal was to search for evidence of magnetic activity on the secondary (as seen in the Dopplershifted hot emission lines of C IV and Si IV), one of the fastest rotating cool stars ever studied in the UV. There was evidence for quiescent C IV emission at the velocity of the M star secondary, placing useful limits on its steady transition region emission. One strong flare was seen in C IV (and near flare peak, in Si IV and He II as well), with a velocity consistent with the M dwarf. This was accompanied by a near-simultaneous increase in continuum emission from the white dwarf; the excess had a temperature of about 100,000 K. We suggest that this strong flare may have caused an accretion event on the white dwarf, either by ejecting mass in the form of a CME, or disrupting a large prominence system.

Key words: cataclysmic variables, stellar flares, stellar activity, stellar mass loss, UV astronomy

A. LECAVELIER DES ETANGS¹

1Institut d`Astrophysique de Paris,
CNRS-UPMC, 98bis Bld Arago, F-75014 Paris, France

ABSTRACT

The present review focuses on UV observations of young planetary disks and consequently mostly on the gaseous content of those disks. Few examples are taken to illustrate the capability of the UV observatories to scrutinize in detail the gas content of low density circumstellar disks if they are seen edge-on or nearly edge-on. For instance, in the case of HD100546, FUSE observations re- vealed signatures of outflow and infall in the disk caused by interaction of the stellar magnetosphere with the circumstellar disk. Observations of numerous absorption lines from H2 around young stars give constrains on the gas temper- ature and density, and physical size of the absorbing layer. In the case of T-Tauri stars and one brown dwarf, emissions from exited H2 have been detected. In the case of Beta Pictoris, the observation of CO in the UV and search for H2 with FUSE demonstrated that the evaporation of frozen bodies like comets must produce the CO seen in the disk. Extensive observations of spectral variability of Beta Pictoris are now interpreted by extrasolar comets evaporating in the vicinity of the central star of this young planetary system.

Key words: UV astronomy, young planetary disks

Alfred VIDAL-MADJAR¹

¹ Institut d`Astrophysique de Paris,
UMR7095 CNRS, Université Pierre & Marie Curie,
98 bis boulevard Arago, F-75014 Paris, France.

ABSTRACT

More than 200 extrasolar planets have been discovered since 1995, when the first one was detected orbiting the solar type star 51 Peg. The extrasolar planets known so far show a variety of characteristics, in some cases not at all represented in our solar system. The `hot Jupiters`, in particular, were not predicted by models before being discovered: they are gas giant planets orbiting at only few stellar radii. This peculiarity gives us the unique opportunity of exploring their upper atmosphere while they transit in front of their parent star. Among the atmospheric species detected so far with this method, we can list Na_I, in the visible, and H_I, O_I and C_II in the far UV. These UV detections, in particular, unveiled a even more striking feature: the upper atmosphere of these exoplanets is evaporating at a very fast pace, almost a `blow off` process.

Key words: UV astronomy, extrasolar planets

Edward F. GUINAN1 and Scott G. ENGLE¹

¹ Department of Astronomy & Astrophysics
Villanova University, Villanova, PA 19085, USA

ABSTRACT

The evolution over time of the magnetic activity and the resulting X-ray and UV coronal and chromospheric emissions of main-sequence dG, dK, and dM stars with widely different ages are discussed. Young cool stars spin rapidly and have correspondingly very robust magnetic dynamos and strong coronal and chromospheric X-ray - UV (XUV) emissions. However, these stars spin-down with time as they lose angular momentum via magnetized winds and their magnetic generated activity and emissions significantly decrease. Studies of dK-dM stars over a wide range of ages and rotations show similar (but not identical) behavior. Particular emphasis is given to discussing the effects that XUV emissions have on the atmospheres and evolution of solar system planets as well as the increasing number of extrasolar planets found hosted by dG-dM stars. The results from modeling the early atmospheres of Venus, Earth and Mars using recently determined XUV irradiances and inferred winds of the young Sun are also briefly discussed. For example, the loss of water from juvenile Venus and Mars can be explained by action of the strong XUV emissions and robust winds of the young Sun. We also examine the effects of strong X-ray and UV coronal and chromospheric emissions (and frequent flares) that dM stars have on possible planets orbiting within their shrunken habitable zones (HZs) - located close to the low luminosity host stars (HZ = 0.4 AU). Dwarf M stars make interesting targets for further study because of their deep outer convective zones (CZs), efficient dynamos, frequent flares and strong XUV emissions. Furthermore, a large fraction of dM stars are very old (>5 Gyr), which present intriguing possibilities for the development of highly advanced modes of intelligent life on planets that may orbit them.

Key words: UV astronomy; stars: late-type, activity, evolution, rotation