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The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| The Counterarc to MS 1512-cB58 and a Companion Galaxy
We present near-infrared spectra of ``A2,'' the primary counterarc tothe gravitationally lensed galaxy MS 1512-cB58. The spectra showredshifted Hα, [N II], [O III], and Hβat z=2.729+/-0.001. We observe the same Hα/[O III]ratio as cB58, which together with the redshift confirms that A2 isindeed another image of a single background galaxy. Published lensingreconstruction reports that A2 is a magnification of the entire source,while cB58 is an image of only a part. At marginal significance, A2shows higher line-to-continuum ratios than cB58 (by a factor of ~2),suggesting a nonuniform ratio of young to old stars across the galaxy.We observe a second emission-line source in the slit. This object,``W5,'' is predicted to be a lensed image of another galaxy at aredshift similar to cB58. W5 is blueshifted from cB58 by ~400 kms-1 and has a significantly lower Hα/[O III]ratio, confirming that it is an image of a different background galaxyin a group with cB58. The Hα emission line in W5implies a star formation rate of 6 Msolar yr-1(H0=70 km s-1 Mpc-1,ΩM=0.3,ΩΛ=0.7), aftercorrecting for lensing magnification.Data presented herein were obtained at the W. M. Keck Observatory, whichis operated as a scientific partnership among the California Instituteof Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Discovery of a spectroscopic binary comprising two hot helium-rich subdwarfs
Helium-rich subdwarf B (He-sdB) stars form a very small fraction of thepopulation of hot subdwarf stars in our Galaxy. They have been foundboth in the field of our Galaxy as well as in globular clusters. Theevolution of these rare stars has recently been the subject of muchdebate involving both binary and single star evolution models. We reportour serendipitous discovery that the prototype - PG1544+488 - is a binary containing two low-mass helium-rich hotsubdwarfs. This discovery challenges existing evolutionary models forHe-sdB stars and suggests that they may be formed through close binaryevolution and following the ejection of a common envelope.Based on observations made with the William Herschel and Isaac NewtonTelescopes operated on the island of La Palma by the Isaac Newton Groupin the Spanish Observatorio del Roque de los Muchachos of the Institutode Astrofísica de Canarias and with the NASA-CNES-CSA FarUltraviolet Spectroscopic Explorer.
| WeBo 1: A Young Barium Star Surrounded by a Ringlike Planetary Nebula
WeBo 1 (PN G135.6+01.0), a previously unrecognized planetary nebula witha remarkable thin-ring morphology, was discovered serendipitously onDigitized Sky Survey images. The central star is found to be a late-typegiant with overabundances of carbon and s-process elements. The giant ischromospherically active and photometrically variable, with a probableperiod of 4.7 days; this suggests that the star is spotted, and that 4.7days is its rotation period. We propose a scenario in which onecomponent of a binary system became an asymptotic giant branch (AGB)star with a dense stellar wind enriched in C and s-process elements; aportion of the wind was accreted by the companion, contaminating itsatmosphere and spinning up its rotation. The AGB star has now become ahot subdwarf, leaving the optical companion as a freshly contaminatedbarium star inside an ionized planetary nebula.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| Search for pulsational instabililty on sdB and sdO stars.
Not Available
| Open problems in pulsating hot subdwarfs after high speed photometry in Loiano
A sample of 37 hot subdwarf stars has been observed with the two headsfast photometer at the Loiano Observatory; among them the sdO star HD128220 shows certainly pulsations, the sdB star PG 0856+121 is veryprobably pulsating, while the claim of variability of BD +37°442requires additional observations. The occurrence of pulsations in a sdOstar, far from the temperature strip corresponding to the EC 14026stars, could suggest the existence of a new class of pulsating stars.
| BI Lyncis: A hydrogen-deficient binary consisting of two low-mass giants of spectral types early-B and G
BI Lyn has previously been misclassified as anevolved binary system containing either a hot subdwarf or white dwarfand a thick accretion disk. New intermediate dispersion spectra arepresented which demonstrate clearly that the hot component is a luminouslow-mass helium star and the cool companion is a rapidly rotating G-typegiant. Techniques of spectrum synthesis have been used to establish thedimensions of both components. Although the orbital period of the systemremains unknown, other phenomena are entirely consistent with theseobserved dimensions. A ~ 0.34 d periodic photometric variation could beexplained by pulsations in the B-type primary and, by analogy with otherH-deficient binaries, it is suggested that the variable absorption inHα may be due to a gas stream flowing through the inner Lagrangianpoint. Based on observations obtained with the Isaac Newton and WilliamHerschel Telescopes, and on INES data from the IUE satellite.
| The Rest-Frame Optical Spectrum of MS 1512-CB58
Moderate-resolution, near-IR spectroscopy of MS 1512-cB58 is presented,obtained during commissioning of the near-infrared spectrometer(NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72galaxy by the foreground cluster MS 1512+36 makes it the best candidatefor detailed study of the rest-frame optical properties of Lyman-breakgalaxies. In 80 minutes of on-source integration, we have detectedHα, [N II] λλ6583, 6548, [O I] λ6300, He Iλ5876, [O III] λλ5007, 4959, Hβ, Hγ, [OII] λ3727, and a strong continuum signal in the range of1.29-2.46 μm. A redshift of z=2.7290+/-0.0007 is inferred from theemission lines, in contrast to the z=2.7233 calculated from UVobservations of interstellar absorption lines. Using the Balmer lineratios, we find an extinction of E(B-V) = 0.27. Using the linestrengths, we infer a star formation rate (SFR) of 620+/-18Msolar yr-1 (H0=75, q0=0.1,and Λ=0), which is a factor of 2 higher than that measured fromnarrowband imaging observations of the galaxy but is a factor of almost4 lower than the SFR inferred from the UV continuum luminosity. Thewidth of the Balmer lines yields a mass ofMvir=1.2x1010 Msolar. We find that theoxygen abundance is 1/3 solar, in good agreement with other estimates ofthe metallicity. However, we infer a high nitrogen abundance, which mayargue for the presence of an older stellar population. Data presentedherein were obtained at the W. M. Keck Observatory, which is operated asa scientific partnership among the California Institute of Technology,the University of California, and the National Aeronautics and SpaceAdministration. The Observatory was made possible by the generousfinancial support of the W. M. Keck Foundation.
| AGB stars in binaries and their progeny
An AGB star in a binary system is likely to pollute its companion withcarbon- and s-process-rich matter. After the AGB star has faded into anunconspicuous white dwarf, the polluted companion enters the zoo ofstars with chemical peculiarities. In this paper, the progeny of AGBstars in binary systems are identified among existing spectroscopicclasses (Abell 35-like, binary post-AGB, WIRRing, dwarf Ba and C,subgiant CH, Ba, CH, S, yellow symbiotics) and their filiation isdiscussed from the properties of their eccentricity -- period diagrams.
| ORFEUS II echelle spectra: H_2 towards the northern Galactic pole
We examine the distribution of molecular hydrogen in the localinterstellar medium towards the northern galactic pole at latitudesb>45circ. High resolution UV echelle spectra of the nearby sdOstars BD +37 1977 (l=187.1, b=+45.6) and HD 128220 (l=19.9, b=+64.9)observed during the ORFEUS II mission are analysed. Distances for thesestars are calculated to be 1030 pc and 440 pc, respectively, with anerror of about 30%. We determine column densities for H_2 rotationalexcitation states up to J=7. For BD +37 1977 we find a low total H_2column density of (2.1^{+0.4}_{-0.2})ṡ1015 cm^{-2}.Probably, the molecular gas is excited by UV pumping to an equivalentexcitation temperature of T=395+/-11 K. For HD 128220 the total H_2column density is (6.5^{+3.3}_{-4.1})ṡ1017 cm^{-2} in twounresolved absorption components. The Boltzmann excitation temperaturehas a value of T=77+/-10 K. The equivalent temperature of the stagesnormally excited by UV pumping (J=4 to 7), which are only observed inone of the components, is T<1500 K. We further obtain columndensities for H i from Lyman profile fitting and for S and Si. Only 10%or less of the H i seen in absorption is found in H i 21 cm spectra.This indicates either gas concentrated in a few (or only one) dense,possibly circumstellar clumps, or extended flocculent molecular gas inthe northern polar disk region of our Galaxy. Assuming pressureequilibrium, a layer of flocculent molecular gas at a height z = 80 pccould be possible. For that, an analysis of further lines of sight isneccessary.
| Spectroscopic investigation of old planetaries. IV. Model atmosphere analysis
The results of a NLTE model atmosphere analysis of 27 hydrogen-richcentral stars of old planetary nebulae (PN) are reported. These starswere selected from a previous paper in this series, where we gaveclassifications for a total of 38 central stars. Most of the analyzedcentral stars fill a previously reported gap in the hydrogen-richevolutionary sequence. Our observations imply the existence of twoseparated spectral evolutionary sequences for hydrogen-rich and -poorcentral stars/white dwarfs. This is in line with theoreticalevolutionary calculations, which predict that most post-AGB stars reachthe white dwarf domain with a thick hydrogen envelope of ~ 10(-4) M_sun.We determine stellar masses from the comparison with evolutionary tracksand derive a mass distribution for the hydrogen-rich central stars ofold PNe. The peak mass and the general shape of the distribution is inagreement with recent determinations of the white dwarf massdistribution. The properties of most analyzed stars are well explainedby standard post-AGB evolution. However, for eight stars of the sampleother scenarios have to be invoked. The properties of three of them areprobably best explained by born again post-AGB evolution. Two of theseare hybrid CSPN (hydrogen-rich PG 1159 stars), but surprisingly thethird star doesn't show any signs of chemical enrichment in itsatmosphere. The parameters of five stars are not in accordance withpost-AGB evolution. We discuss alternative scenarios such as thestripping of the hydrogen-rich envelope by a companion during the firstred giant phase or the formation of a common envelope with a possiblemerging of both components. Two stars (HDW 4 andHaWe 5) remain mysterious after all. They resembleordinary hot DA white dwarfs, but due to very large evolutionary agesthe presence of a PN cannot be explained. We speculate that the nebulaemay be shells produced by ancient nova outbursts. A wide spread ofhelium abundances is observed in the photospheres of central stars ofold PNe. It is shown that a good correlation between helium abundancesand luminosity is present. It is inferred that when the stars'luminosities fall below L~ 300 L_sun depletion starts and the heliumabundance steadily decreases with decreasing luminosity. The existenceof this correlation is in qualitative agreement with recent theoreticalcalculations of gravitational settling in the presence of a stellarwind.
| A search for magnetic stars in late stages of stellar evolution
No abstract submitted
| Hubble Space Telescope Goddard High Resolution Spectrograph Observations of the Be + sdO Binary phi Persei
Mass transfer during the evolution of intermediate-mass stars in a closebinary system can result in a rejuvenated and spun-up secondary star(which may appear as a rapidly rotating Be star) orbiting an unseen,stripped-down, remnant companion. One of the best candidates for such asystem is the long-period (127 days) binary phi Per. Here we present newHubble Space Telescope Goddard High Resolution Spectrograph spectra ofphi Per in several UV regions that show clearly for the first time thespectral signature of the faint remnant companion. We derive adouble-lined solution for the radial velocity curve that yields massesof 9.3 +/- 0.3 Mȯ and 1.14 +/- 0.04 Mȯ for the Be star andcompanion, respectively. A Doppler tomographic reconstruction of thesecondary spectrum shows a rich spectrum dominated by sharp Fe IV and FeV lines, similar to those observed in hot sdO stars. Non-LTE spectrumsynthesis indicates that the subdwarf has temperature Teff = 53 +/- 3 kKand gravity log g = 4.2 +/- 0.1 and that the subdwarf-to-Be star fluxratio is 0.165 +/- 0.006 and 0.154 +/- 0.009 for the 1374 and 1647Angstroms regions, respectively. The spectrum of the Be primary appearsnormal for a very rapidly rotating early B-type star, but we argue thatthe star is overluminous for its mass (perhaps owing toaccretion-induced mixing). Additional sharp lines of Fe IV appear whenthe companion is in the foreground, and we show that these form in aheated region of the Be star's disk that faces the hot subdwarf.
| Infrared flux excesses from hot subdwarfs. II. 72 more objects
In our search, started in February, 1994, for JHK excess fluxes amongthe hot subdwarf population as an indicator for the presence of binarycompanions, results for 72 more hot objects (=63 hot subdwarfs + 1Horizontal Branch B star + 7 white dwarfs + 1 non-subdwarf object)observed with the Carlos Sanchez CVF IR photometer (in June and October,1994), are presented. The exact number of binary hot subdwarfs hasgained renewed importance after the recent discovery of pulsators withG-F companions. The total number of candidates we propose may help toset some constraints; for example, out of 41 objects with excesses, 13may have G-type binary companions. From our new sample, 14 discoveriesof binary candidates have been found: BD+25 4655, Feige 108, HD 4539, HD149382, HD 216135, KPD 2109+440, LSI+63 198, LSIV+10 9, LSV+22 38, PG0011+221, PG 0116+242, PG 0314+103, PG 2151+100 and TON 139. Besides, 2more from reanalysis of February, 1994, data - BD+37 1977 and BD+481777, may now be found to be IR excess candidates. Two suspectedbinaries, PB 8555 and SB 7, are also confirmed. By fitting \cite[Kurucz(1993)]{kur93} model spectra and assuming zero-age main sequencecompanions, we find upper limits on the subdwarf gravities. Thedistributions of upper limits on log(g), mostly between about 5.25 and6.5, are nearly identical for both sdBs and sdOs. Figure~1 is onlyavailable in the electronic version of the paper(http://www.edpsciences.com)
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Hot HB stars in globular clusters: physical parameters and consequences for theory III. NGC 6752 and its long blue vertical branch.
We present spectroscopic analyses of 17 faint blue stars in the globularcluster NGC 6752, using optical and UV spectrophotometric data andintermediate resolution optical spectra. Effective temperatures, surfacegravities, and helium abundances of the stars are determined andcompared to theoretical predictions. All stars are helium deficient byfactors ranging from 3 to more than 100, indicative of gravitationalsettling of helium. Stars with effective temperatures above about 20000K(sdBs) fit well to the evolutionary tracks, whereas the cooler starsshow lower surface gravities than theoretically expected. This agreeswith earlier findings by Moehler et al. (1995A&A...294...65M) forthe faint blue stars in M 15. Deriving masses from the atmosphericparameters and the cluster distance leads to a mean mass of the sdBstars of 0.50 Msun_ and a standard deviation of about 0.043dex, which is below the value derived of the observational errors andtherefore consistent with a very narrow mass distribution. The mean massis in good agreement with the (0.49 +/- 0.02) Msun_ expectedif sdB stars are extreme horizontal branch stars with a helium core of0.48 Msun_ and an extremely thin hydrogen layer. The coolerstars however show a significantly lower mean mass of 0.30Msun_ with a standard deviation of the mean of 0.059 dex inagreement with the findings of Moehler et al. (1995A&A...294...65M)and de Boer et al. (1995A&A...303...95D) for the BHB stars in M 15and NGC 6397, respectively. The problems presented by the different massdistributions of BHB and sdB stars within one cluster are discussed.
| A search for stars with strong magnetic fields among horizontal-branch stars and hot subdwarfs
Observations obtained with the 6-m BTA telescope for a few A, Bhorizontal-branch stars and hot subdwarfs have been used to measuretheir effective magnetic fields. No magnetic fields similar to those ofAp, Bp main-sequence stars were found.
| A search for stars with strong magnetic fields among horizontal-branch stars and hot subdwarfs
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Infrared flux excesses from hot subdwarfs.
Observations of 27 hot subdwarf stars and white dwarfs have beenperformed with an IR photometer in a search for excess fluxes in the JHKbands. 22 of the objects are observed for the first time in theinfrared. In 11 of the stars a significant excess flux was found, 2 ofwhich are new discoveries: GD 274 and GD 299. We confirm the suspicionof Moehler et al. (1990) that PG0232+095 is a composite system, and wereinforce the suggestion of Thejll et al. (1991, 1994a) that Feige 34 isa composite system. The excesses are most likely due to companion stars,mainly of spectral types A - K. We estimate the subdwarf gravities,assuming zero-age main sequence companions, and thus find upper limitson log(g). For the hot sdO Feige 34 we estimate from the publishedtrigonometric parallaxes an absolute magnitude M_v_^F34^=5.6^+0.9^_-1.6_and surface gravity log(gpi_)=6.8^+0.3^_-0.7_.
| Spectroscopic binary orbits from ultraviolet radial velocities. Paper 14: HD 49798
Not Available
| HD 128220B - ein Supernova-vorlaufer ?
Not Available
| Formation and Evolution of Binary Planetary Nebula Nuclei and Related Objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..343I&db_key=AST
| NLTE Analysis of Subluminous O-Stars - the Hot Subdwarf in the Binary System HD128220
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...276..171R&db_key=AST
| Statistical Analysis of a Sample of Spectroscopic Binaries Containing Late Type Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..125B&db_key=AST
| Ultraviolet and radio observations of Milky Way halo gas
Interstellar-absorption-line and 21-cm emission-line data for sightlines to 56 stars are combined in order to study the kinematics andspatial distribution of the gas that is at great distances from theGalactic plane. Measurements of the interstellar velocities and H Icolumn densities from the 21-cm emission and Ly-alpha absorption areincluded. The problem of contamination of the interstellar Ly-alphaabsorption line by stellar Ly-alpha absorption is analyzed, and thisinformation is used to reevaluate the vertical distribution of H I. Anew method for determining lower limits on the vertical distribution ofgas by including information on the velocity structure in the gas ispresented. The data for individual sight lines are discussed.
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| קבוצת-כוכבים: | שומר הדובים |
| התרוממות ימנית: | 14h35m15.79s |
| סירוב: | +19°12'54.5" |
| גודל גלוי: | 8.509 |
| מרחק: | 4761.905 פארסק |
| תנועה נכונה: | 1.8 |
| תנועה נכונה: | -1.9 |
| B-T magnitude: | 8.775 |
| V-T magnitude: | 8.531 |
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