Stellar physics and evolution galex and star formation




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Дата канвертавання24.04.2016
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Red color – 30 min talks

Blue color – 15 minute talks

Green color - posters

STELLAR PHYSICS AND EVOLUTION

GALEX AND STAR FORMATION

Bianchi Luciana

Johns Hopkins University,USA
The Galaxy Evoution Explorer (GALEX) has provided far-UV and near-UV imaging over a wide sky coverage. Catalogs of >100 million UV sources enable advances in a variety of fields, from hot stellar objects in the Milky Way to QSOs and star-forming galaxies out to redshift ~2, and provide a roadmap for future UV missions. A deep, comprehensive view of the young stellar populations in hundreds of nearby galaxies, afforded by GALEX's wide-field UV imaging, allows us to characterize their spatially-resolved and time-resolved recent star formation. In addition, star formation was revealed in extreme low-density environments, where it is elusive at other wavelengths. The results shed new light on the process of star formation in different conditions, and its interplay with interstellar dust. UV measurements of more distant galaxies probe their evolution and the Universe's star-formation history since redshift ~2.
THE CRITICAL ROLE OF UV AND EUV SPECTROSCOPY IN THE STUDY OF WHITE DWARF EVOLUTION

Barstow Martin

University of Leicester, UK
This talk will review the important contributions that UV/EUV spectroscopic studies of white dwarfs have made to the study of their composition and evolution. The results from past missions such as IUE, ROSAT and EUVE will be discussed together with the more recent contributions from HST and rocket-borne spectrographs. Finally, the capabilities of the refurbished HST will be outlined before a discussion of the future needs for the study of white dwarf spectra.
YOUNG STARS

Gomez de Castro Ana Ines1 and Lamzin Sergey2

1 - UCM, Spain



2 - SAI MSU, Russia
We consider problems of young stars physics that could be solved with WSO-UV. At first we discuss in which way the character and parameters of accretion process can be found from the analysis of C IV 1550, Si IV 1400 and N V 1240 line profiles in the case of classical T Tauri stars. We also discuss where CIII 1908, Si III 1892 and molecular hydrogen lines are originated in these objects. Then we consider in which way one can extract information about the structure of inner regions of FUORs accretion disks from UV observation. A number of observational tests are proposed to investigate the nature of activity of Ae/Be Herbig stars. Finally we discuss the problem of interstellar extinction in star formation regions.


GASEOUS FLOW STRUCTURE IN CLOSE BINARY STARS

Bisikalo Dmitry

Institute of Astronomy RAS, Russia)
We discuss main features of the flow structure in close binaries (CBs). Three-dimensional HD and MHD numerical simulations are used to study the flow pattern in a close binary system after it has reached the steady-state accretion regime. It is shown that the main flow features in non-magnetic CBs are the stationary accretion disk, circum-disk halo and a number of shock waves: bow shock caused by the motion of the accretor and the disk in the gas of the circum-binary envelope; "hot line" formed due to the interaction between the circum-disk halo and stream from the inner Lagrange point L1, and two arms of the tidal shock. When the magnetic field of the accretor is taken into account, new structural elements appear: the magnetosphere region becomes distinguishable, and the matter is accreted via funnel flows. Using HD and MHD simulation results along with the Doppler tomography technique allowed us to identify the main flow features in CBs and to confirm the validity of the flow structure model.

Special attention is paid to the observational manifestations of flow structure features in the UV band.



NASA SWIFT UVOT OBSERVATIONS OF SUPERNOVAE: IDEAS FOR WSO

Peter Milne

University of Arizona, USA
We report on NUV observations of supernovae of all types as obtained by the UVOT instrument on the NASA Swift mission. Over 80 SNe have been observed since March 2005, with many campaigns being initiated very soon after the SN explosion. In particular, we find relatively modest variations within the near-peak emission from normal SNe Ia. This finding is important for large optical/NIR high-z SN surveys, as adding rest-frame NUV emission permits either more color information or larger redshift coverage. Throughout the talk, we will emphasize ideas as to how WSO might take this aspect of NUV astronomy to the next step.

UV SPECTROSCOPY OF THE EXCITING STAR OF THE PLANETARY NEBULA NGC 246

Rauch T.,1 Werner K.,1 Kruk J. W.2

1 - University of Tuebingen, Germany

2 - Johns Hopkins University, U.S.A.
The central star of the planetary nebula NGC 246 is the brightest (V = 11.78 mag) and one of the heavy-weights (about 0.9 solar masses) of the PG 1159 spectral class. These stars (about 40 known) are strongly hydrogen-deficient, with a typical abundance pattern He:C:O = 33:50:17 by mass. About every other has a surrounding planetary nebula.

We present a spectral analysis of the central star of NGC 246 by means of state-of-the-art NLTE model atmospheres based on UV spectra obtained with FUSE, HST/STIS, and IUE.

We summarize our present evolutionary picture of PG 1159 stars.

HST COS OBSERVATIONS OF THE HOT BARE STELLAR CORE H1504+65

Werner K., Rauch, T.

University of Tuebingen, Germany
We present UV spectroscopy of the unique white dwarf H1504+65 obtained with the HST Cosmic Origins Spectrograph. The stellar atmosphere has a unique composition. Being H- and He-deficient it is composed of C, O, Ne, and Mg. The evolutionary history is unclear. H1504+65 could be a naked O/Ne/Mg white dwarf, i.e. the descendant of a super-AGB star. If true, then this would be the first proof of the existence of such (single) white dwarfs.


PERIODIC VARIABILITY IN THE EMISSION SPECTRUM OF YOUNG STARS

N.Z.Ismailov1,2, F.N.Alimardanova1, O.V.Khalilov1, G.R.Baheddinova1

1 - Shamakha Astrophysical Observatory, Azerbaijan

2 - Baku State University, Azerbaijan
Results of long time spectral observations of classic T Tauri and Ae/Be Herbig type stars were presented. For investigations we have used spectral material in the visual range which was obtained in the 2 m telescope of ShAO NAS of Azerbaijan and in the ultraviolet range from archive IUE spectrums. For the star T Tau we have discovered 33 day periodic variability in both visual and UV range emission lines, which simultaneously shows synchronal periodicity in the light polarization in the visual range.

For BP Tau we have obtained a periodicity 8.275±0.005 day for intensity of the UV emission lines. But this period is unstable for different seasons of observations.

During some years on the CCD spectrograms we have studying of the Hα and Hβ emission line profiles for AB Aur. It was showed that the absorption component in the short wing of emissions Hα and Hβ are varied with characteristic time ~20 days for AB Aur. It was showed that the UV spectrum of AB Aur have some short-time variability with characteristic time a few hours. Moreover a variability of the structure of line profiles also we have derived. The basic variability in the atmosphere of АВ Aur occurs in the bottom layers of an environment, in nearby areas to the surface of the star where matter accretion velocity reaches up to 300 km/s.

For the star HD 216629 we have obtained variations in intensities, line structures of Hα and Hβ line emissions from night to night for characteristic time a few hours.



We concluded that the activity of the emission spectrum in young stars possible was occurred active dynamical processes in the circumstellar discs, which may be promote for planet formation processes.

ATMOSPHERIC PARAMETERS OF THE B-SUPERGIANT HD 198478 FROM THE UV SPECTRA

Jurkic, Tomislav; Sarta Dekovic, Mariza; Dominis Prester, Dijana; Kotnik-Karuza, Dubravka

Department of Physics, University of Rijeka, Croatia
We determined atmospheric parameters of the Galactic early B-supergiant HD198478 (55 Cyg) from the UV silicon lines taken from the high-resolution 1150-1980 Å IUE spectra. TLUSTY numerical code was used to model the stellar atmosphere and to determine the temperature and surface gravity assuming a non-LTE plane parallel hydrostatic stellar atmosphere with microturbulence. The synthesized spectra were broadened by the IUE instrumental profile, rotational and macroturbulent velocity with ROTIN numerical code. The silicon 1265 Å, 1309 Å, 1313 Å, 1417 Å, 1526 Å, 1782 Å and 1294-1303 Å multiplet lines of different ionization levels (Si II and Si III) were modeled, leading to the temperature, surface gravity, rotational and macroturbulent velocity values. Our results have shown that the line broadening cannot be explained by rotational velocity only, but additional macroturbulent velocity component should be taken into account. HD 198478 shows a significant degeneracy in velocity, which means that the individual contributions of the macroturbulence and rotation in the total velocity broadening cannot be distinguished. Adequate fit of TLUSTY models to the observed non-resonant silicon lines suggests that the non-LTE plane-parallel hydrostatic stellar model without wind contribution can be used to explain such lines. We have obtained similar results using the HST STIS spectra in the same procedure, thus showing that the IUE spectra, despite their lacking quality compared to the STIS spectra, are reliable enough in determination of the B supergiants' photospheric parameters.
SINGLE-BINARY STAR SEPARATION BY ULTRAVIOLET COLOR-INDICES DIAGRAMS

O.Yu.Malkov1, A.V.Mironov2, S.G.Sichevskij1

1 - Institute of Astronomy RAS, Russia

2 - SAI MSU, Russia
Color-indices diagrams are powerful tools for parameterization of stars. Also, detection of a composite flux in photometry can serve as an indication of a photometrically unresolved binarity and can contribute to the parameterization of the components of binary systems. A main goal of the present study is to develop a method of automatic photometric detection of binaries, based on multi-color photometry, theoretical stellar spectral energy distributions and general understanding of binary evolution. In particular, we consider an ultraviolet photometry where, in combination with optical and infrared photometry, interstellar reddening can be easier distinguished from temperature reddening.

The following procedure is applied to achieve the declared goal. One can compose possible pairs of components, based on evolution concept. This can be done for various stages of binary evolution. Theoretical spectrophotometric spectral energy distributions and response functions of ultraviolet photometric bands in appropriate sky surveys allows us to compute color-indices of such pairs, when they are unresolved, as well as of single stars. Usage of an interstellar extinction law gives us theoretical color-indices of reddened objects, both single stars and unresolved binaries. When plotted on a multidimensional color space, they allow us to indicate areas, where unresolved binaries can be easily separated from single stars, and identify binaries among objects, cross-matched in photometric surveys.



MINING THE GALEX SPECTROSCOPIC DATABASE

Emanuele Bertone

INAOE, Mexico
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations. We report the preliminary results of our analysis of the ultraviolet spectral morphology of point-like GALEX sources, focusing our attention on the thousands of stellar objects present in the data base. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution, and employed it to determine the atmospheric parameters of the stars.

ULTRAVIOLET OBSERVATIONS OF SUPERNOVAE

Filomena Bufano

INAF-OAPd, Italy
The emission in the ultraviolet (UV) domain contains valuable information about supernova (SN) explosions: it is highly sensitive to the metallicity of the SN ejecta; it gives indications on the SN progenitors structure and on how they exploded; it reveals the environment structure and thus the precursors pre-explosion activity, by mean of the ejecta-circumstellar material interaction.

Moreover, considering that the forthcoming high-redshift SN surveys will be conducted in the optical and IR ranges, which sample the UV rest-frame emission of the SN, the knowledge of the UV spectral evolution of the local SNe is essential to properly exploit the surveys outputs.Despite the wide interest, to date the sample of SN spectroscopically observed in the UV is still small.

After a general overview on our current understanding of SN UV emission, we present the entire Swift/UVOT archive of SN spectroscopic observations, obtained during its first two years of observations (2005--2006). Important steps toward the characterization of SNe in the Ultraviolet have been achieved, about both thermonuclear and core-collapse explosions.

We show also the very interesting case of SN 2005ay, the first target observed in the framework of a wide observational program for the multiwavelength study of Core Collapse SNe. We present SN 2005ay UV spectroscopy taken with GALEX, as well as the exceptional amount of spectroscopic and photometric data obtained in the Optical-NIR range (107 Optical + 19 NIR photometric epochs and 20 optical spectra) with 11 different ground-based telescopes, which makes SN 2005ay a SN with one of the best coverages ever. Finally, we show the remarkable similarity we found among the UV properties of Type IIP SNe, which, if confirmed by a future larger sample, would indicate the cosmological use of these objects as a promising prospect.



THE MOST LUMINOUS B SUPERGIANTS

Negueruela Ignacio(Universidad de Alicante, Spain), Najarro Francisco (CAB-CSIC), Clark J. Simon (Open University), Urbaneja Miguel (Institute for Astronomy, Hawaii)
We present high-quality spectra of the most luminous B-type hypergiants, Cyg OB2 and HD~80077, and derive their stellar parameters by fitting them with tailored models developed with the codes FASTWIND and CMFGEN. Both stars show little chemical evolution, in spite of huge luminosities and very high initial masses ~100Mʘfor Cyg OB2). We also present data on three very luminous ($MV~-9) B-type hypergiants in the starburst open cluster Westerlund~1, which seem to follow the redwards branch of the cluster isochrone, again suggesting that they are relatively unevolved stars. We summarise the evidence suggesting that very massive stars may appear as relatively normal, but extremely luminous B supergiants close to the end of the hydrogen core burning phase and discuss the prospects of UV spectroscopy for some of these objects.

UV LINE PROFILES AS A PROBE FOR ATOMIC DIFFUSION THEORY IN STELLAR ATMOSPHERES

Ryabchikova Tatiana1,, LeBlanc Francis2

1 - Institute of Astronomy RAS Moscow Russia

2 - Universite de Moncton, Moncton, Canada
In quiet stellar atmospheres that are stabilized, for example, by the presence of strong magnetic fields, a non-uniform distribution of chemical elements (abundance stratification) is predicted by the diffusion theory. Spectroscopic observations of magnetic Ap stars provide a strong support for the diffusion theory. Stratification predictions in the upper atmosphere, in particular, strongly depend on the magnetic field geometry. Optical lines used in stratification analysis of Ap stars do not probe the upper atmospheric layers and, hence, cannot provide reliable information on abundance gradients there. We show the expected effect of stratification on the profiles of strong lines in the UV region and how these lines may be used for constraining diffusion theory.
DETAILED CHEMICAL COMPOSITION OF STARS WITH LARGE PROPER MOTIONS ON THE SPECTRA IN GROUND-BASED UV.

V.Klochkova, T.Mishenina, V.Panchuk, S.Korotin, V.Marsakov, N.Tavolganskaya, I.Usenko.

SAO RAS, Russia
Based on spectral data (R=60000) taken with the spectrograph NES of the 6-meter telescope within the wavelength 3550-5100A, we determined parameters (effective temperature, surface gravity, microturbulent velocity metallicity, and radial velocity) of the sample of 14 metal-deficient G-K stars with large proper motions. The use of echelle spectra allowed the model atmosphere method to be applied both for the determination of abundances of 20 chemical elements including heavy metals from Sr to Dy. Abundances of Mg, Al, Sr and Ba are calculated within non-LTE approach. Taking into account chemical composition and kinematical parameters of stars studied we determined their belonging to galactic populations. Chemical composition of the star BD+80 245 distant from the galactic plane agrees with belonging to the accreting halo: besides overdeficiency of $\alpha$-process elements the star has overdeficiency of s-process element barium: [Ba/Fe]=-1.46. The ratio content of radioactive element Th to that of the r-process element Eu as well as cosmochronological age are determined for selected stars.
ORIGIN AND EVOLUTION OF THE GOULD BELT, AND A FUTURE ULTRAVIOLET VIEW

Paola Sestito, Ana Ines Gomez de Castro

UCM, Spain
The Gould Belt is a predominant feature of the local system, appearing as a partial ring of stars tilted toward the galactic plane by about 16-20 degrees. This structure contains several O- and B-type stars, and may represent the local spiral arm to which the Sun belongs.

In this review we first present a historical overview of the Gould Belt, focusing on the structural properties and origin, and revising the works carried out during the years. Then, we present an on-going investigation of the regions of major interest in the Gould Belt using data from the UV space mission GALEX: as a staring point we focus on the Taurus region, and in particular on the characterization of T Tauri stars showing variability (flares).

The statistical investigation methods adopted are discussed.

WSO AND THE WINDS OF MASSIVE STARS

Miriam Garcia Garcia



Instituto de Astrofisica de Canarias, Spain
The spectrographs at the WSO will provide again access to wavelengths shorter than 1200A. Previous observatories operating in the 1150-2000A range(such as IUE and HST-STIS) have proved extremely useful to study the outflows of OB type stars, which display wind profiles in the UV. However, the lambda<1200 range is critical as it contains important diagnostic lines for clumping and shocks in the wind, as found by FUSE-based analyses. We explore how the WSO can contribute to study the winds of massive stars.

ISSIS AND THE PURSUIT OF LOCAL GROUP BLUE MASSIVE STARS:

Miriam Garcia Garcia

Instituto de Astrofisica de Canarias, Spain
The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, the initial color-based target selection for spectroscopy, though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. 2009). The interpretation of the association's color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. 2010).

Because of its large field of view and high spatial resolution at ultraviolet (UV) wavelengths, ISSIS at the WSO is a potential discovery machine of resolved blue massive stars in nearby galaxies. Our code can be easily modified to choose candidate OB stars based on ISSIS magnitudes on the UV, where hot young massive stars are intrinsically brighter and their color degeneracy is broken. The combination of our algorithm and ISSIS's panchromatic photometry can readily produce a list of the most massive stars of the Local Group.



CRITERIA FOR THE SPECTRAL CLASSIFICATION OF NORMAL AND YOUNG B STARS IN UV

Kurchakov A.V., Knyazeva L.N., Pavlova L.A

Observatory, Fesenkov Astrophysical Institute, Almaty, Kazakhstan
We have demonstrated how high-resolution UV ( data INES) spectra can provide to estimates classification criteria normal B stars and Be Herbig stars with envelopes. Previous UV classification schemes for normal B stars have tended to rely heavily on the strongest lines in spectrum –Si IV(1400A), C IV (1550) and N V(1240) –which are known to be formed in stellar wind. The Si II lines at 1264,1310, and 1533A were assumed to be photosphere, while the lower excitation Si II lines at 1260 and 1526A were assumed to interstellar for types early than B3.

We choose for classification normal stars lines- Si IV (1393.8, 1402.8), Si III (1309A), C II (1336A), N IV (1488A) and S II (1261A), for stars with envelop in the 1200-1900 spectral region we choose - Si IV (1393.8, 1402.8), Si III(1309A), C II (1336A), N IV (1488A), C IV (1550), N IV (1720), N III (1750) and Al III (1860).



UV OBSERVATIONS OF sdB STARS

Savanov I.

Institute of Astronomy RAS, Russia

We review the basic properties of the hot subdwarf stars (which are core helium-burning stars at the blue end of the horizontal branch) with special attention to the important contributions that UV photometric and spectroscopic studies of these objects should make to the understanding of their composition and evolution. Abundance determinations, parameters of atmosphers, pulsations and the problem of the origin of the UV-upturn phenomenon should be discussed .



ENERGETIC HYDROGEN AND HYDROGEN CLOUD FORMATION AROUND HD 209458b

H. Lammer (1), M. Holmstrom (2) A. Ekenbaeck (2), P. Wurz (3), J.-M. Grießmeier (4),
F. Selsis (5, 6), M. L. Khodachenko (1)


(1) Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria

(2) Swedish Institute of Space Physics, P.O. Box 812, SE-98128 Kiruna, Sweden, (3) Physikalisches Institut, University of Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland

(4) Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo, The Netherlands

(5) Université de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l’ Observatoiré, BP 89, F-33271 Floirac Cedex, France

(6) CNRS, UMR 5804, Laboratoire d’ Astrophysique de Bordeaux, 2 rue de l`
Observatoire, BP 89, F-33271 Floirac Cedex, France

HST observations of the exoplanet HD209458b have shown a broad absorption signature about the Ly-alpha; stellar line during transit, suggesting the presence of a thick neutral hydrogen cloud around the exoplanet. We present an improved flow model of HD 209458b and use stellar wind values similar to those in our solar system. We find that the Energetic Neutral Atom (ENA) production is high enough to explain the observations, and we show that using expected values for the stellar wind and exosphere, the spatial and velocity distributions of ENAs would give absorption in good agreement with the observations. We also study how the production of ENAs depends on the exospheric parameters and establish an upper limit for the obstacle standoff distance at approximately 4 - 10 planetary radii. Finally, we compare the results obtained for the obstacle standoff distance with existing exomagnetospheric models and show how the magnetic moment of HD 209458b can be estimated from ENA observations.
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