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An Overview of the Rotational Behavior of Metal-poor Stars
This paper describes the behavior of the rotational velocity inmetal-poor stars ([Fe/H] <= -0.5 dex) in different evolutionarystages, based on vsin i values from the literature. Our sample iscomprised of stars in the field and some Galactic globular clusters,including stars on the main sequence, the red giant branch (RGB), andthe horizontal branch (HB). The metal-poor stars are, mainly, slowrotators, and their vsin i distribution along the HR diagram is quitehomogeneous. Nevertheless, a few moderate to high values of vsin i arefound in stars located on the main sequence and the HB. We show that theoverall distribution of vsin i values is basically independent ofmetallicity for the stars in our sample. In particular, thefast-rotating main sequence stars in our sample present rotation ratessimilar to their metal-rich counterparts, suggesting that some of themmay actually be fairly young, in spite of their low metallicity, or elsethat at least some of them would be better classified as blue stragglerstars. We do not find significant evidence of evolution in vsin i valuesas a function of position on the RGB; in particular, we do not confirmprevious suggestions that stars close to the RGB tip rotate faster thantheir less-evolved counterparts. While the presence of fast rotatorsamong moderately cool blue HB stars has been suggested to be due toangular momentum transport from a stellar core that has retainedsignificant angular momentum during its prior evolution, we find thatany such transport mechanisms most likely operate very fast as the stararrives on the zero-age HB (ZAHB), since we do not find a link betweenevolution off the ZAHB and vsin i values. We present an extensivetabulation of all quantities discussed in this paper, including rotationvelocities, temperatures, gravities, and metallicities [Fe/H], as wellas broadband magnitudes and colors.
| Do the Nearby Blue Horizontal Branch Stars Belong to the Thick Disk or the Halo?
We study the Milky Way region (|Z|< 3.0 kpc) where the thickdisk and inner halo overlap by using the kinematics of local bluehorizontal branch (BHB) stars (within 1 kpc) and new samples of BHBstars and A-type stars from the Century Survey. We derive Galactic U, V,and W velocities for these BHB and A-type star samples using propermotions from the NOMAD catalog. The mean velocities and the velocitydispersions of the BHB samples (|Z| < 3 kpc) are characteristicof the halo, while those of the Century Survey A-type stars arecharacteristic of the thick disk. There is no evidence from our samplesthat the BHB stars rotate with the thick disk in the region |Z| <3 kpc. Nearly a third of the nearby local RR Lyrae stars have diskkinematics and are more metal rich than [Fe/H] ~ –1. Only a fewpercent of the Century Survey BHB (CBHB) stars have these properties.Only one nearby BHB star (HD 130201) is likely to be such a disk starbut selection based on high proper motions will have tended to excludesuch stars from the local sample. The scale height derived from a sampleof local RR Lyrae stars agrees with that of the CBHB stars. The localsamples of BHB stars and metal-weak red giants are too incomplete for asimilar comparison.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Stellar parameters for Pop II A-type stars from IUE spectra and new-ODF ATLAS9 model atmospheres
Stellar parameters for twenty-seven field horizontal branch A-typestars, a post-AGB star (BD +32 2188), and a possible cool sdB star (BD+00 0145) were obtained by fitting the whole IUE energy distributionstaken from the IUE-INES archive to the ultraviolet energy distributionspredicted by new-ODF ATLAS9 model atmospheres, which include theLyman-alpha H-H+ and H-H quasi-molecular absorptions near1400 Å and 1600 Å. The sample of stars was extensivelystudied by Kinman et al. (2000), who derived stellar parameters for themby using visual observations and also an ultraviolet color index. Theeffective temperatures obtained by fitting the IUE spectra to thenew-ODF models agree with T_eff derived by Kinman et al. (2000) for mostof the stars in the sample. The gravities from UV agree with those fromKinman et al. (2000) for stars hotter than about 8700 K, while they arelower, on average, by 0.3 dex for the cooler stars. The same discrepancyis present when log g from the ultraviolet energy distribution iscompared with log g from the visible energy distribution. The differenceis insensitive to reddening, microturbulent velocity, metallicity, ormixing-length parameter for the treatment of the convection. Figures A.1to A.15 are only available in electronic form athttp://www.edpsciences.org
| A spectroscopic study of field BHB star candidates
New spectroscopic observations are presented for a sample of thirty-oneblue horizontal branch (BHB) star candidates that are sufficientlynearby to have reliable proper motions. Comments are given on a furthertwenty-five stars that have previously been suggested as BHB starcandidates but which were not included in our sample. Moderatelyhigh-resolution spectra (lambda /Delta lambda ~ 15 000) of twenty fiveof our program stars were taken with the coudé feed spectrographat Kitt Peak. Twelve of the program stars were also observed with theCAT spectrograph at ESO. Six of these program stars were observed fromboth hemispheres. IUE low-resolution spectra are available for most ofour candidates and were used, in addition to other methods, in thedetermination of their Teff and reddening. A compilation ofthe visual photometry for these stars (including new photometry obtainedat Kitt Peak) is also given. Abundances were obtained from these spectrausing models computed by Castelli with an updated version of the ATLAS9code (Kurucz 1993a). All thirty one candidates are halo stars. Of these,twenty eight are classified as BHB stars because: [(1)]they lie close tothe ZAHB (in a similar position to the BHB stars in globular clusters)in the Teff versus log g plot. For all but one of thesestars, far-UV data were available which were consistent with other data(Strömgren photometry, energy distributions, Hγ profiles) forderiving Teff and log g. [(2)]they have a distribution of kms-1i (<=40 km s-1) that is similar to thatfound for the BHB in globular clusters. Peterson et al. (1995) and Cohen& McCarthy (1997) have shown that the BHB stars in the globularclusters M13 and M92 have a higher km s-1i (<= 40 kms-1) than those in M3 and NGC 288 (<=20 kms-1). The mean deprojected rotational velocity (/line{v}) wascalculated for both the two globular clusters and the nearby BHB starsamples. A comparison of these suggests that both globular cluster kms-1i types are present in our nearby sample. No obvious trendis seen between km s-1i and either (B-V)o or [Fe/H].[(3)]they have -0.99>=[Fe/H]>=-2.95 (mean [Fe/H] -1.67; dispersion0.42 dex), which is similar to that found for field halo RR Lyrae andred HB stars. These local halo field stars appear (on average) to bemore metal-poor than the halo globular clusters. The local sample of redgiant stars given by Chiba & Yoshii (1998) contains a greaterfraction of metal-poor stars than either our halo samples or the haloglobular clusters. The stars in our sample that have a Teffthat exceeds about 8 500 K show the He i (lambda 4471) line with astrength that corresponds to the solar helium abundance. [(4)]they showa similar enhancement of the alpha -elements (< [Mg/Fe]right > =+0.43+/-0.04 and also < [Ti/Fe]right > = +0.44+/-0.02) to thatfound for other halo field stars of similar metallicity. Based onobservations obtained at KPNO, operated by the Association ofUniversities for Research in Astronomy, Inc., under contract with theNational Science Foundation, and the European Southern Observatory,Chile. Tables 4 and 5 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr
| Kinematical trends among the field horizontal branch stars
Horizontal branch (HB) stars in the field of the Milky Way can be usedas tracers for the study of early stages of the evolution of our galaxy.Since the age of individual HB stars is not known a priori, we havestudied the kinematics of a sample of field HB stars measured withHipparcos to look for signs of age and population nature. Our samplecomprises 14 HBA, 2 HBB and 5 sdB/O stars. We found that the kinematicsof the HBA stars is very different from that of the sdB/O stars(including those from an earlier study). The HBA stars have low orbitalvelocities, some are even on retrograde orbits. Their orbits have largeeccentricities and in many cases reach large distances above thegalactic plane. In contrast, the sdB/O stars show disk-like orbitalcharacteristics. The few HBB stars (with T_eff> 10,000 K) in oursample seem to have kinematics similar to that of the sdB/O stars. Inorder to see if there is a trend among the HB stars in their kinematics,we investigated also RR Lyrae stars measured with Hipparcos. Here wefound a mixed kinematical behaviour, which was already known fromprevious studies. Some RR Lyrae stars have disk-like orbits (most ofthese being metal rich) but the majority has halo-like orbits, verysimilar to those of our HBA stars. Since the atmospheres of most typesof HB stars do not reflect original metallicities any more thekinematics is the only aspect left to study the origin and populationmembership of these stars. Thus, the clear trend found in kinematics ofstars along the HB, which is also a sequence in stellar mass, shows thatthe different kinds of field HB stars arose from stars having differentorigins in age and, e.g., metallicity or mass loss rate. Based in parton HIPPARCOS data
| Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
We discuss a spectroscopic and photometric technique that enables theidentification and classification of field horizontal-branch (FHB) andother A-type stars, even from relatively low signal-to-noise ratiomedium-resolution spectra. This technique makes use of broadband UBVcolors predicted from model atmosphere calculations and Balmer lineprofiles and Ca II K equivalent widths determined from synthetic spectrato estimate the physical parameters T_eff, log g, and [Fe/H] for starsin the effective temperature range 6000-10,000 K. A comparison of ourmethod with high signal-to-noise ratio spectra of standard starsindicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K,sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precisionallows for a separation of low surface gravity FHB and other, generallyhigher surface gravity, A-type (and somewhat later) stars. We alsodevelop a synthetic-template comparison technique, which is veryeffective in the identification of metallic-line and peculiar A-typestars. A detailed investigation of the influence of noise in the spectraon the determination of physical parameters shows that, for spectra withsignal-to-noise ratios in the range 10
| The absolute magnitude of field metal-poor horizontal branch stars
Hipparcos satellite parallaxes for 22 metal-poor field horizontal branchstars with V_0<9 are used to derive their absolute magnitude. Theweighted mean value is M_V=+0.69+/-0.10 for an average metallicity of[Fe/H]=-1.41 a somewhat brighter average magnitude of M_V=+0.60+/-0.12for an average metallicity of [Fe/H]=-1.51 is obtained by eliminating HD17072, which might be on the first ascent of the giant branch ratherthan on the horizontal branch. The present values agree with thedeterminations based on proper motions and application of theBaade-Wesselink method to field RR Lyraes; they are 0.1-0.2 mag fainterthan those based on calibration of cluster distances obtained by usinglocal subdwarfs and on alternative distance calibrators for the LargeMagellanic Cloud (LMC). The possibility that there is a real differencebetween the luminosity of the horizontal branch for clusters and thefield is briefly commented on.
| The Abundance of CN. Calcium and Heavy Elements in High Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..825E&db_key=AST
| Calibrating horizontal-branch stars with Hipparcos.
Not Available
| The Ross 451 Group of Halo Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2661E&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.
| 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
| Heisse Horizontalaststerne im Feld der Milchstrasse und in Kugelsternhaufen.
Not Available
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Starbursts, blue stragglers, and binary stars in local superclusters and groups. II - The old disk and halo populations
A study of the distribution in the HR diagram of stars in severalold-disk population aggregates and in several halo-population aggregatesindicates that the blue straggler phenomenon is ubiquitous. In all thecases considered, several stars are found to lie far from the locusdefined by a semiempirical isochrone that best fits the distribution ofthe bulk of the stars in the aggregate. The results support thestarburst interpretation of blue stragglers in young-disk aggregates.
| Radial velocities and spectral types for a sample of faint blue stars.
Not Available
| Four-color UVBY and H-beta photometry of high-velocity and metal-poor stars. I - The catalogue of observations
A catalog of four-color uvby and H-beta photometry for 711 high-velocityand metal-poor stars is given. The selection of the stars and theobserving and reduction techniques used to obtain these data arediscussed. The photometry has been transformed closely onto the standarduvby-beta system. The errors of the data have been estimated using bothinternal and external comparisons. The data are uniform over the sky;that is, there are no significant north-south differences. For the largemajority of stars the mean errors of V, m1, c1, and beta are less than +or - 0.008 mag, and the error of b-y is less than + or - 0.005 mag.Values of V, b-y and beta and rough photometric classifications aregiven for 63 red and/or evolved stars that fall outside the range of thephotometric transformations.
| Oxygen abundances in horizontal branch stars
Based on observations made between June 11 and June 14, 1985 with the3.6-m ESO telescope CASPEC spectrograph, oxygen abundances in NGC 6397and NGC 6752 HB stars were determined to check the results from theirred giants. The IR triplet at 7772-7775 A found for HD 86986 is in goodagreement with previous findings. The results show oxygen abundancesspanning a range of a factor of six in this star sample, with the mostoxygen-poor star being relatively iron rich.
| Weak-lined stars in the Michigan spectral survey. I - A-, F-, and G-type stars
Data from intermediate-band and H-beta photometric observations of 89early-type stars classified as weak-lined by Bidelman and MacConnell(1973), Houk and Cowley (1975), or Houk (1978 and 1982) are presented intables and graphs and analyzed. The group is found to comprise 55 diskstars and 34 halo stars (Fe/H less than -0.65), including 21 near themain-sequence turnoff, seven red horizontal-branch stars, one bluehorizontal-branch star, one suprahorizontal-branch object, and four bluestragglers; five of the newly identified halo stars are shown to haveradial velocities in excess of 100 km/s. Special consideration is givento the 17 early-type members of Kapetyn's star group (Eggen, 1977), andthe mean luminosity and Fe/H ratio of the four very-short-periodCepheids of this group are determined as 0.75 mag and -1.7.
| Field horizontal-branch stars at ultraviolet and visual wavelengths
The spectra of 17 field horizontal-branch (FHB) stars observed at about5-A resolution between 1150 and 3200 A with the IUE and about 8-Aresolution between 3600 and 5800 A with the Reticon of Pine BlufObservatory are compared with data of Population I stars of similartemperatures and with theoretical model atmospheres. The FHB stars haveweaker spectral lines and are brighter than Population I stars atwavelengths below 1800 A. The models are too bright below 1600 A toproperly match the Population II star energy distributions. Temperaturesfor the FHB stars which are consistent for the wavelength range observedare obtained.
| The nature of the Yale Common Proper Motion groups of stars
Attention is given to a large group of approximately 90 stars, twogroups of 20-30 stars, and 12 groups of a few stars each, taken from DDOsystem image tube spectral classification and intermediate bandphotometry for the Yale Common Proper Motion groups of 180 southernstars. Spectroscopic and photometric analyses of these groups haveindicated a very scattered Pop I main sequence in their color-magnitudediagrams. Distance moduli of 5 or less were derived from the averagespectroscopic parallaxes, in keeping with the proper motion amplitude of0.1 arcsec/year. The main sequence of each group shows scatter whenplotted in an HR diagram, indicating that they are probably nothomogeneous groups of stars sharing common physical origins.
| Early-type high-velocity stars in the solar neighborhood. III - Radial velocities, rotation indices, and line-strength indices for southern candidates
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983AJ.....88.1349S&db_key=AST
| Early-type high-velocity stars in the solar neighborhood. I - List of candidates
Suspected nearby high-velocity stars of spectral types B and A areidentified by their proper motions, which are generally too small forthe stars to have been included in previous catalogs of high-velocitystars. The same selection process is then extended to spectral type Fstars, in order to both provide a companion sample and investigatewhether the hypothetical high-velocity, metal-rich population continuesto later spectral types. Of the presented list of 371 stars withconfirmed proper motions, 168 are of A and B spectral types. Photometricand spectroscopic observations of these stars are required to eliminatethose with misclassified spectra and convert proper motions into spacevelocities. The identification of type of stars is important forunderstanding apparent exceptions to the correlation between stellarages, metal abundances, and kinematic properties.
| Photometry of faint blue stars. V - A third list of southern stars
Stromgren photometry is presented for 37 faint blue stars, six of whichhave been identified by ultraviolet observations made with the ESRO TD-1satellite. The stars are classified using their observed photometricindices.
| Intermediate-band photometry of late-type stars. VIII - Nonvariable stars in the halo population near the sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979ApJ...229..158E&db_key=AST
| Kinematical and orbital properties for selected southern high-velocity stars
Using the model of the Galaxy presented by Eggen, Lynden-Bell, andSandage (1962), plane galactic orbits have been calculated for severalsouthern high-velocity stars which possess parallax, proper motion, andradial velocity data. Extensive lists of both raw and computed data forthese stars are included. Published values of U-B and B-V for some ofthese stars were used in plots of each of the orbital parameters versusU-B, B-V, or the ultraviolet excess. Also, a comparison is made betweenthe H-R diagrams for the southern high-velocity star group and that ofM3, a globular cluster, and again for M67, an old open cluster. Thehigh-velocity star group is found to resemble an old open cluster morethan a globular cluster.
| Intermediate band photometry of late-type stars. II - Some stellar groups
Observations on the (R, I) system and a modified Stromgren system ofmembers of six stellar groups are used to demonstrate the chemicalhomogeneity of some 70% or 80% of the members assigned to the groups onthe basis of kinematics. The groups discussed are the Hyades, Wolf 630,Arcturus, Groombridge 1830, and Kapteyn's Star Groups as well as ananonymous group of a half dozen subdwarfs with (U, V) near (-150, -320)km/s. Standards for a previously described photometric system areextended, and additional F- and G-type standards for the (R, I) systemare presented. A simple relation is derived for computing the Fe/Habundance ratio for most stars in the corrected (R-I) interval from +0.2to +0.45 magnitude.
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| Csillagkép: | Farkas |
| Rektaszcenzió: | 15h42m52.82s |
| Deklináció: | -44°56'40.8" |
| Vizuális fényesség: | 8.836 |
| Távolság: | 222.222 parszek |
| RA sajátmozgás: | -189.1 |
| Dec sajátmozgás: | -90.4 |
| B-T magnitude: | 8.973 |
| V-T magnitude: | 8.848 |
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