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Spectroscopic observations of the rapid rotating post-AGB star IRAS 05381+1012
We report on the high-resolution stellar parameters and abundanceanalysis of the rapidly rotating post-AGB star IRAS 05381+1012. Analysisof high-resolution spectra shows that IRAS 05381+1012 has an effectivetemperature of T_eff=5200± 100 K and a surface gravity of logg=1.0± 0.5 corresponding to a spectral type G(2-3)I. Theseparameters result in an estimated luminosity of 970 Lȯand a distance of 2700 pc. We also show that IRAS 05381+1012 has aprojected rotational velocity vsin i=40± 10 km s-1.The abundance analysis based on a few available lines reveals that thisstar is an iron-deficient object with [Fe/H]=-0.8. We also analyze theabundance pattern and compare it to other classes of stars with similarstellar parameters.
| Post-AGB stars as testbeds of nucleosynthesis in AGB stars
We construct a data base of 125 post-AGB objects (including R CrB andextreme helium stars) with published photospheric parameters (effectivetemperature and gravity) and chemical composition. We estimate themasses of the post-AGB stars by comparing their position in the (logT{eff}, log g) plane with theoretical evolutionary tracks ofdifferent masses. We construct various diagrams, with the aim of findingclues to AGB nucleosynthesis. This is the first time that a large sampleof post-AGB stars has been used in a systematic way for such a purposeand we argue that, in several respects, post-AGB stars should be morepowerful than planetary nebulae to test AGB nucleosynthesis. Our mainfindings are that: the vast majority of objects which do not showevidence of N production from primary C have a low stellar mass(Mstar < 0.56 Mȯ); there is no evidencethat objects which did not experience 3rd dredge-up have a differentstellar mass distribution than objects that did; there is clear evidencethat 3rd dredge-up is more efficient at low metallicity. The sample ofknown post-AGB stars is likely to increase significantly in the nearfuture thanks to the ASTRO-F and follow-up observations, making theseobjects even more promising as testbeds for AGB nucleosynthesis.
| The evolutionary status of the bright high-latitude supergiant HD 190390
Despite its mean apparent magnitude of mV = 6.39, theevolutionary status of HD 190390 (HR7671), a luminous F-type supergiant at high galactic latitude,is still not very clear, but in most papers a post-AGB classification isassumed. New observational material has been obtained with fourdifferent instruments and is presented here. An extensive abundanceanalysis based on high resolution, high signal-to-noise NTT+EMMI spectraconfirms the metal deficiency of this object ([Fe/H] = -1.6), togetherwith a high lithium content (log ɛ(Li) = 1.9). A variabilityanalysis based on Geneva photometry over seven years reveals beatingwith a period of ~3000 days. It is, however, not clear whether thisbeating is caused by a stable triplet, or it is the consequence of smallchanges in the main frequency. More recent data obtained with theHIPPARCOS satellite and the Mercator telescope not only confirm the mainperiod, but also support the presence of a second periodicity of 11days, which was also found in the Geneva photometry. A conclusiveevolutionary status of this object is not given, but alternative to theUU Her (i.e. post-AGB) status, a W Vir classification is discussed.Based on observations collected at the European Southern Observatory, LaSilla, Chile (programme 61.E-0426), and at the Observatorio del Roque delos Muchachos, La Palma, Spain.
| A 2dF survey of the Small Magellanic Cloud
We present a catalogue of new spectral types for hot, luminous stars inthe Small Magellanic Cloud (SMC). The catalogue contains 4161 objects,giving an order-of-magnitude increase in the number of SMC stars withpublished spectroscopic classifications. The targets are primarily B-and A-type stars (2862 and 853 objects respectively), with oneWolf-Rayet, 139 O-type and 306 FG stars, sampling the main sequence to~mid-B. The selection and classification criteria are described, andobjects of particular interest are discussed, including UV-selectedtargets from the Ultraviolet Imaging Telescope (UIT) experiment, Be andB[e] stars, `anomalous A supergiants' and composite-spectrum systems. Weexamine the incidence of Balmer-line emission, and the relationshipbetween Hγ equivalent width and absolute magnitude for BA stars.
| Identification of the Mass Donor Star's Spectrum in SS 433
We present spectroscopy of the microquasar SS 433 obtained near primaryeclipse and disk precessional phase Ψ=0.0, when the accretion diskis expected to be most ``face-on.'' The likelihood of observing thespectrum of the mass donor is maximized at this combination of orbitaland precessional phases, since the donor is in the foreground and abovethe extended disk believed to be present in the system. The spectra wereobtained over four different runs centered on these special phases. Theblue spectra show clear evidence of absorption features consistent witha classification of A3-7 I. The behavior of the observed lines indicatesan origin in the mass donor. The observed radial velocity variations arein antiphase to the disk, the absorption lines strengthen at mideclipsewhen the donor star is expected to contribute its maximum percentage ofthe total flux, and the line widths are consistent with lines created inan A supergiant photosphere. We discuss and cast doubt on thepossibility that these lines represent a circumstellar shell spectrumrather than the mass donor itself. We reevaluate the mass ratio of thesystem and derive masses of 10.9+/-3.1 and 2.9+/-0.7Msolarfor the mass donor and compact object plus disk, respectively. Wesuggest that the compact object is a low-mass black hole. In addition,we review the behavior of the observed emission lines from both thedisk/wind and high-velocity jets and show that the current orbitalephemeris and disk precession/nodding model parameters are still valid.
| The nature of Hen 3-1312: A post-AGB star in a binary system
This work reports the low- and high-resolution spectroscopic diagnosticdiagrams, radial velocity, stellar parameters and abundance analysis ofthe planetary nebula Hen 3-1312. The low- and high-resolution spectrareveal that Hen 3-1312 is in fact a very-low-excitation object, in abinary system with a supergiant as a cool central star. The analysis ofthe high-resolution spectrum shows the cool stellar component to have aneffective temperature of Teff=6500±100 K and a surfacegravity of log g=0.8±0.2 corresponding to a spectral type ofF(6-7)I. These parameters result in an estimated primary luminosity of4100 Lȯ, implying a distance of 4400 pc which is inagreement with previous determinations. The abundance analysis revealsHen 3-1312 to be a metal-poor object having [Fe/H]=-1.1. The meanabundances of carbon, nitrogen and oxygen are found to be solar, howeverthe α-elements (Mg, Si and Ca) are underabundant relative to theSun. The abundance profile of Hen 3-1312 is analyzed and compared withother classes of stars with similar atmospheric parameters.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theCNPq-Observatório Nacional (Brazil).Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| Characteristics and classification of A-type supergiants in the Small Magellanic Cloud
We address the relationship between spectral type and physicalproperties for A-type supergiants in the Small Magellanic Cloud (SMC).First, we construct a self-consistent classification scheme for Asupergiants, employing the calcium K to Hɛ line ratio as atemperature-sequence discriminant. Following the precepts of the `MKprocess', the same morphological criteria are applied to Galactic andSMC spectra, with the understanding that there may not be acorrespondence in physical properties between spectral counterparts indifferent environments. Then we discuss the temperature scale,concluding that A supergiants in the SMC are systematically cooler thantheir Galactic counterparts at the same spectral type, by up to ~10 percent. Considering the relative line strengths of Hγ and the CH Gband, we extend our study to F- and early G-type supergiants, for whichsimilar effects are found. We note the implications for analyses ofluminous extragalactic supergiants, for the flux-weightedgravity-luminosity relationship and for population synthesis studies inunresolved stellar systems.
| Post-Agb Stars
In this contribution, a review is presented on the ample data obtainedon post-AGB stars, both on the central stars and their circumstellarmaterial. The fast evolutionary phase is characterized by a rapid changein the properties of the objects, but the variety is so large that thereis yet no clear consensus on how the detailed studies of individualobjects are linked together by evolutionary channels. The absence ofstrong molecular veiling in the photospheres of the central stars,together with a spread in intrinsic metallicity make post-AGB stars veryuseful in constraining AGB chemical evolutionary models. We discuss thesurprisingly wide variety of chemical signatures observed. The onset inthe creation process of the panoply of structures and shapes observed inplanetary nebulae occurs during the short post-AGB evolution, but thephysical nature of the processes involved is still badly understood. Inthe rapidly growing field of circumstellar mineralogy, post-AGB starshave their story to tell and also the molecular envelope changessignificantly due to dilution and hardening of the stellar radiation.The real-time evolution of some objects suffering a late thermal flashis reviewed and their possible link to other hydrogen-deficient objectsis discussed. Any review on stellar evolution has a section on binariesand this contribution is no exception because binaries make up asignificant fraction of the post-AGB stars known to date.
| Detection of Zinc in the Very Metal-Poor Post-AGB Star HR 4049
We report on the detection of two Zn I lines at4722.15Å and 4810.53Å in the high-quality spectrum of thevery metal-poor post-AGB star HR4049, which was obtained with the HighDispersion Spectrograph attached to the Subaru Telescope. The strengthsof these lines indicate an appreciable underabundance of Zn by ~ -1.3dex relative to the Sun. The fact that this volatile element, similarlyto others belonging to the same group (e.g., C, N, O, S), does notconform to the extreme depletion ( > 4 dex) of refractory metals(e.g., Fe), strongly suggests that grain formation has something to dowith the origin of the chemical peculiarity. This (not extremely butsignificantly) subsolar value of [Zn/H] is quantitatively discussed inconnection with those of other volatile species, especially with respectto S. We also detected a new Fe II line at5159.03Å along with the already known Fe II4923.93Å line; based on these two lines the Fe abundance of HR4049is determined to be ~ 2.8 ([Fe/H] ~ -4.7).
| The Spectrum of the Mass Donor Star in SS 433
We present results from a short series of blue, moderate-resolutionspectra of the microquasar binary SS 433. The observations were made ata time optimized to find the spectrum of the donor star, i.e., when thedonor was in the foreground and well above the plane of the obscuringdisk. In addition to the well-known stationary and jet emission lines,we find evidence of a weak absorption spectrum that resembles that of anA-type evolved star. These lines display radial velocity shifts oppositeto those associated with the disk surrounding the compact star, and theyappear strongest when the disk is maximally eclipsed. All theseproperties suggest that these absorption lines form in the atmosphere ofthe hitherto unseen mass donor star in SS 433. The radial velocityshifts observed are consistent with a mass ratioMX/MO=0.57+/-0.11 and masses ofMO=19+/-7 Msolar and MX=11+/-5Msolar. These results indicate that the system consists of anevolved, massive donor and a black hole mass gainer.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars
This is the first in a series of two papers that address the problem ofthe physical nature of luminosity classification in the late A-, F-, andearly G-type stars. In this paper, we present precise spectralclassifications of 372 stars on the MK system. For those stars in theset with Strömgren uvbyβ photometry, we derive reddenings andpresent a calibration of MK temperature types in terms of the intrinsicStrömgren (b-y)0 index. We also examine the relationshipbetween the luminosity class and the Strömgren c1 index,which measures the Balmer jump. The second paper will address thederivation of the physical parameters of these stars, and therelationships between these physical parameters and the luminosityclass. Stars classified in this paper include one new λ Bootisstar and 10 of the F- and G-type dwarfs with recently discoveredplanets.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| BVR Photometry of Northern Hemisphere Luminous Stars. IV.
CCD-based BVR photometry for 77 stars drawn from volumes II, III, and IVof the Case-Hamburg Luminous Stars in the Northern Milky Way catalog isreported. The majority of these stars lie in the first Galacticquadrant; 69 of them were previously unobserved.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Temperatures for A0-K0 Supergiants from 13-Color Photometry
Observations on the 13-color photometric system are reported for 71A0-K0 supergiant stars brighter than V=6.0. Three independent methods todetermine the effective temperatures for A0-K0 supergiants from their13C photometry are discussed: 1) Calibrations between T$eff$and reddening-free indices are developed; temperatures were collectedfrom the literature for the calibration stars, and most of them werespectroscopically determined. 2) An empirical correlation betweenintrinsic colors in the 13C system and T$eff$ has beenderived. 3) The unreddened colors are compared with synthetic colorscalculated by Kurucz (1989); this leads to simultaneous estimates forT$eff$ and log $g$. The estimated uncertainties inT$eff$ by the three methods are comparable and areapproximately plus or minus 200-300K. (SECTION: Stars)
| The Supergiant Binary BM CAS
Attracted by an earlier claim (Thiessen 1956) that BM Cas is aneclipsing binary with one component a classical Cepheid, we haveobtained new photometry and IUE ultraviolet spectra of the system. Whilewe verify that there is variability in addition to the eclipses, weconclude that there is no classical Cepheid present. The variability isirregular, and, since it is present in the uv spectra as well as in theV photometry, we believe it is associated with the hotter component. Wefind the latter to be a high-luminosity star of spectral type of A6, inclose agreement with the MK assignment of A7 Iab (Bidelman 1982), andthe secondary component most likely to be a late-K or early-M giant. Thelatter appears to fill or nearly fill it Roch lobe, while the primarystar is not far from doing so as well, implying a complex evolutionaryhistory for the syste. (SECTION: Stars)
| 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.
| Accurate Two-dimensional Classification of Stellar Spectra with Artificial Neural Networks
We present a solution to the long-standing problem of automaticallyclassifying stellar spectra of all temperature and luminosity classeswith the accuracy shown by expert human classifiers. We use the 15Angstroms resolution near-infrared spectral classification systemdescribed by Torres-Dodgen & Weaver in 1993. Using the spectrum withno manual intervention except wavelength registration, artificial neuralnetworks (ANNs) can classify these spectra with Morgan-Keenan types withan accuracy comparable to that obtained by human experts using 2Angstroms resolution blue spectra, which is about 0.5 types (subclasses)in temperature and about 0.25 classes in luminosity. Accuratetemperature classification requires a hierarchy of ANNs, whileluminosity classification is most successful with a single ANN. Wepropose an architecture for a fully automatic classification system.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Chemical composition of optically bright post-AGB stars.
We present a detailed LTE chemical analysis of 10 optically brightF-type post-AGB objects on the basis of the analysis of high-resolutionoptical spectra and compare the results with similar objects discussedin the literature. The iron content is low on average, and so confirmsthe old and hence low-mass nature of the supergiants, with a noticableexception of HD 95767. We emphasize the fact that the chemical patternsobserved are very diverse : several different classes can bedistinguished. Only a minor fraction of the objects are conform tostandard post third dredge-up theory. Only in HD 187885 (Van Winckel etal., 1996A&A...306L..37V), HD 56126 (Klochkova, 1995MNRAS.272..710K)and HD 158616 (this paper) is there conclusive chemical evidence thatthey occur in a post-AGB evolutionary phase : a high total CNOabundance, for HD 187885 a supersolar He content and-above all-a largeoverabundance of s-process elements. The other objects, together withother well studied high galactic latitude F-supergiants, display nos-process enhancement but even depletion in some cases. The high Nabondance and the mildly enhanced total CNO abundance indicate that theatmospheres of these objects contain a mixture of CNO-cycled materialand He-burning products. For some sources, however, this enhancement ofthe total CNO abundance is barely significant. HD 107369, the onlyobject in our sample with neither Hα emission nor observed IRexcess, displays also unique chemical patterns among our sample stars (aC deficiency coupled with a moderate Fe depletion of [Fe/H]=-1.1). Thisstar is the only object in our sample showing similar chemical patternsto the metal poor B stars at high galactic latitude (Conlon et al.,1993, in ASP Conf. Ser., Vol. 45, p. 146). Our chemical analysis doestherefore not point to an evolutionary connection between the dustyhigh-latitude supergiants and the metal-poor B stars, but rathersuggests that the latter evolve from stars such as HD 107369.
| Sakurai's Object---A Possible Final Helium Flash in a Planetary Nebula Nucleus
UBVRIJK photometry and optical spectroscopy of Sakurai's object anddirect imaging of the surrounding nebulosity are presented. Theprogenitor star is identified as a faint blue object of mj = 21. Thecircular planetary nebula has a diameter of 32", its distance, derivedfrom the H beta flux, is 5.5 kpc. At present, the object is a luminoussupergiant of approximate spectral type F2, having MV = -4.1, and hasclear indications of hydrogen underabundance, with carbon and oxygenoverabundance. Its photospheric radial velocity is the same as that ofthe surrounding planetary nebula, indicating that they are associated,and that there is currently no mass loss by a thick wind. A marginal IRexcess suggests the presence of some hot dust.
| Atmospheric Parameters and LTE Abundances for 22 Galactic, A-Type Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..659V&db_key=AST
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| CNO Abundances and the Evolutionary Status of Galactic, A-Type Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..839V&db_key=AST
| Neural Network Classification of the Near-Infrared Spectra of A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446..300W&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| 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.
| An atlas of the infrared spectral region. I. The early type stars (O-G0).
The Atlas illustrates the behavior of early type stars (O, B, A and Ftype) in the near infrared 8375-8770A region at a resolution of aboutone A. Intensity tracings of 76 stars are presented. Of these 51 starscover the spectral range O to G0 and luminosity classes V, III, Ib andIa. The influence of the rotational velocity is also illustrated as wellas the spectra of 19 stars with spectral peculiarities. The completeAtlas is also available under catalog number 3183 from the CDSStrasbourg and other data centers.
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| קבוצת-כוכבים: | נושא הנחש |
| התרוממות ימנית: | 16h30m29.90s |
| סירוב: | -07°30'54.0" |
| גודל גלוי: | 6.5 |
| מרחק: | 574.713 פארסק |
| תנועה נכונה: | 2.8 |
| תנועה נכונה: | 3 |
| B-T magnitude: | 6.894 |
| V-T magnitude: | 6.505 |
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