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מאמרים קשורים
Chemical Abundances of the Milky Way Thick Disk and Stellar Halo. I. Implications of [?/Fe] for Star Formation Histories in Their Progenitors
We present the abundance analysis of 97 nearby metal-poor (-3.3< [Fe/H] <-0.5) stars having kinematic characteristics ofthe Milky Way (MW) thick disk and inner and outer stellar halos. Thehigh-resolution, high-signal-to-noise optical spectra for the samplestars have been obtained with the High Dispersion Spectrograph mountedon the Subaru Telescope. Abundances of Fe, Mg, Si, Ca, and Ti have beenderived using a one-dimensional LTE abundance analysis code with KuruczNEWODF model atmospheres. By assigning membership of the sample stars tothe thick disk, inner halo, or outer halo components based on theirorbital parameters, we examine abundance ratios as a function of [Fe/H]and kinematics for the three subsamples in wide metallicity and orbitalparameter ranges. We show that, in the metallicity range of -1.5< [Fe/H] <=-0.5, the thick disk stars show constantly highmean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, theinner and the outer halo stars show lower mean values of these abundanceratios with larger scatter. The [Mg/Fe], [Si/Fe], and [Ca/Fe] for theinner and the outer halo stars also show weak decreasing trends with[Fe/H] in the range [Fe/H] >-2. These results favor thescenarios that the MW thick disk formed through rapid chemicalenrichment primarily through Type II supernovae of massive stars, whilethe stellar halo has formed at least in part via accretion of progenitorstellar systems having been chemically enriched with differenttimescales.
| Beryllium and Alpha-element Abundances in a Large Sample of Metal-poor Stars
The light elements, Li, Be, and B, provide tracers for many aspects ofastronomy including stellar structure, Galactic evolution, andcosmology. We have made observations of Be in 117 metal-poor starsranging in metallicity from [Fe/H] = -0.5 to -3.5 with KeckI/HIRES. Our spectra are high resolution (~42,000) and high signal tonoise (the median is 106 per pixel). We have determined the stellarparameters spectroscopically from lines of Fe I, Fe II, Ti I, and Ti II.The abundances of Be and O were derived by spectrum synthesistechniques, while abundances of Fe, Ti, and Mg were found from manyspectral line measurements. There is a linear relationship between[Fe/H] and A(Be) with a slope of +0.88 ± 0.03 over three ordersof magnitude in [Fe/H]. We find that Be is enhanced relative to Fe;[Be/Fe] is +0.40 near [Fe/H] ~-3.3 and drops to 0.0 near [Fe/H]~-1.7. For the relationship between A(Be) and [O/H], we find agradual change in slope from 0.69 ± 0.13 for the Be-poor/O-poorstars to 1.13 ± 0.10 for the Be-rich/O-rich stars. Inasmuch asthe relationship between [Fe/H] and [O/H] seems robustly linear (slope =+0.75 ± 0.03), we conclude that the slope change in Be versus Ois due to the Be abundance. Much of the Be would have been formed in thevicinity of Type II supernova (SN II) in the early history of the Galaxyand by Galactic cosmic-ray (GCR) spallation in the later eras. AlthoughBe is a by-product of CNO, we have used Ti and Mg abundances asalpha-element surrogates for O in part because O abundances are rathersensitive to both stellar temperature and surface gravity. We find thatA(Be) tracks [Ti/H] very well with a slope of 1.00 ± 0.04. Italso tracks [Mg/H] very well with a slope of 0.88 ± 0.03. We havekinematic information on 114 stars in our sample and they divide equallyinto dissipative and accretive stars. Almost the full range of [Fe/H]and [O/H] is covered in each group. There are distinct differences inthe relationships of A(Be) and [Fe/H] and of A(Be) and [O/H] for thedissipative and the accretive stars. It is likely that the formation ofBe in the accretive stars was primarily in the vicinity of SN II, whilethe Be in the dissipative stars was primarily formed by GCR spallation.We find that Be is not as good a cosmochronometer as Fe. We have found aspread in A(Be) that is valid at the 4? level between [O/H] =-0.5 and -1.0, which corresponds to -0.9 and-1.6 in [Fe/H].
| 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.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| 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
| Subdwarf studies. II - Abundances and kinematics from medium resolution spectra. III - The halo metallicity distribution
Stars previously identified as having UV excesses are observed at 1-Aresolution in the Ca II K-line region. Comparisons of these data withother samples and with Monte Carlo simulations involving a singlecomponent halo have yielded estimates of halo velocity dispersions androtation velocity, corrected for the kinematic biases in the sample. Itis suggested that the data are not consistent with a model in which thehalo formed from star formation in a dissipating, collapsing cloud; theyare, however, reconcilable with the formation of the halo stars bynumerous, independently evolving gas clouds. The metallicitydistribution of a sample of 372 kinematically selected halo stars isthen constructed, with a view to selection effects in the data. Goodagreement is noted between the globular cluster metallicity distributionand a stochastic model with a mean of 10 enrichments/fragment.
| Photoelectric Photometry of 241 Stars in the Vilnius System
Not Available
| Subdwarf studies. I - UBVRI photometry of NLTT stars
UBVRI photometry is presented for a sample of 1656 southern stars,including 1211 that were previously unmeasured, drown from the NLTTproper-motion catalog. The catalog is shown to be a rich source ofsubdwarfs. The normalized ultraviolet excess delta (U - B)0.6,photometric parallax, and interstellar reddening are calculated for eachstar when possible. Photometric parallaxes are compared withtrigonometric parallaxes from the literature. It is found that theformer do not have systematic errors greater than about 25 percent. Inagreement with other studies, the bluest subdwarfs are found at B - V =0.35. The selection of the program stars on the basis of large reducedproper motions restricted subgiant contamination of the sample to about5 percent and increased the discovery fraction of halo stars relative todisk stars. The claim is made here that the sample can be used toinvestigate the abundance distribution of the halo. The sample includesstars with ultraviolet excesses characteristic of disk abundances butwith velocities up to 150 km/s. These are believed to be stars that,quite expectedly, reside in the high-velocity tail of the disk velocitydistribution.
| Ubvy-beta photometry of high-velocity and metal-poor stars. III - Metallicities and ages of the halo stars
The interstellar color excesses, E(b-y) and the metallicities, Fe/Habundance ratio, are determined for the 711 high-velocity and metal-poorstars in the catalog of ubvy-beta photometry compiled by Schuster andNissen (1988). It is found that 220 of these are halo stars and that 15percent of these halo stars have colors that are significantly affectedby interstellar reddening. A minimum age of 18-20 Gyr is determined forthe halo stars. The results suggest that a pressure-supported slowuniform collapse controlled the formation and evolution of the Galaxy.
| 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.
| Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| 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
| Mitteilungen über neuentdeckte Veränderliche Sterne (S 10153- S 10375)
Not Available
| New proper-motion stars, (second list)
Not Available
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לינקים קשורים
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דלי |
| התרוממות ימנית: | 20h47m34.40s |
| סירוב: | -14°25'33.7" |
| גודל גלוי: | 11.005 |
| תנועה נכונה: | -296.8 |
| תנועה נכונה: | -281.6 |
| B-T magnitude: | 11.467 |
| V-T magnitude: | 11.044 |
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