Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
CCD Photometry of M92
We present Johnson B and V photometry for the galactic globular clusterM92 (NGC 6341). Photometric results for a total of 30,000 starsare obtained and are plotted on a V versus (B-V) diagram. We fittheoretical isochrones to this diagram in order to get an estimate forthe age of M92. The age which we find is 16×109years with the following values for the metallicity and He-abundance:[Fe/H] = -2.03, Y = 0.235. The distance modulus to this cluster turnsout to be m - M = 14.6 in accordance with that obtained by Stetson &Harris (1988). We also perform stellar counts in order to produce aluminosity function which is successfully fitted by the same theoreticalmodels fitted to the colour-magnitude diagram.
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| Finding Cool Subdwarfs Using a V-J Reduced Proper-Motion Diagram: Stellar Parameters for 91 Candidates
We present the results of a search for cool subdwarfs for which ourcandidates were drawn from a V-J reduced proper-motion diagramconstructed by Salim & Gould. Kinematic (U, V, and W) andself-consistent stellar parameters (Teff, logg, [Fe/H], andξt) are derived for 91 candidate subdwarfs based onhigh-resolution spectra. The observed stars span 3900K
| Wide binaries among high-velocity and metal-poor stars
A catalogue of 122 wide binaries is presented. The list was compiled bysearching for common proper-motion companions to the more than 1200high-velocity and metal-poor stars of Schuster and collaborators. Westudy the separations for the wide binaries (< a> > 25 AU), andfind that they follow Oepik's distribution all the way up to 10 000 AU.A subgroup of them, the ones with the most halo-like orbits, followOepik's distribution up to 20 000 AU. The galactic orbits of all systemsare calculated, and galactic orbital parameters are used, along with themetallicites, to assign each one to the old thin disk, the thick disk,or the halo population. Table~2 is 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/Abstract.html
| 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.
| Ages of Globular Clusters from HIPPARCOS Parallaxes of Local Subdwarfs
We report here initial but strongly conclusive results for absolute agesof Galactic globular clusters (GGCs). This study is based onhigh-precision trigonometric parallaxes from the HIPPARCOS satellitecoupled with accurate metal abundances ([Fe/H], [O/Fe], and [ alpha/Fe]) from high-resolution spectroscopy for a sample of about thirtysubdwarfs. Systematic effects due to star selection (Lutz-Kelkercorrections to parallaxes) and the possible presence of undetectedbinaries in the sample of bona fide single stars are examined, andappropriate corrections are estimated. They are found to be small forour sample. The new data allow us to reliably define the absolutelocation of the main sequence (MS) as a function of metallicity. Theseresults are then used to derive distances and ages for a carefullyselected sample of nine globular clusters having metallicitiesdetermined from high-dispersion spectra of individual giants accordingto a procedure totally consistent with that used for the fieldsubdwarfs. Very precise and homogeneous reddening values have also beenindependently determined for these clusters. Random errors for ourdistance moduli are +/-0.08 mag, and systematic errors are likely of thesame order of magnitude. These very accurate distances allow us toderive ages with internal errors of ~12% (+/-1.5 Gyr). The main resultsare: 1. HIPPARCOS parallaxes are smaller than corresponding ground-basedmeasurements, leading, in turn, to longer distance moduli (~0.2 mag) andyounger ages (~2.8 Gyr). 2. The distance to NGC 6752 derived from our MSfitting is consistent with that determined using the white dwarf coolingsequence. 3. The relation between the zero-age HB (ZAHB) absolutemagnitude and metallicity for the nine program clusters isMV({ZAHB})=(0.22+/-0.09)([{Fe}/{H}]+1.5)+(0.49+/-0.04) . Thisrelation is fairly consistent with some of the most recent theoreticalmodels. Within quoted errors, the slope is in agreement with that givenby the Baade-Wesselink (BW) analysis of RR Lyrae stars by Fernley andClementini et al., while it is somewhat shallower than the relationgiven by Sandage. The zero-point is 0.2 to 0.3 mag brighter than thatobtained with BW, while it agrees fairly well with that given bySandage. A comparison with alternative relationships is brieflydiscussed. 4. The corresponding LMC distance modulus is (m - M)0 = 18.60+/- 0.07, in good agreement with the recent values of 18.70 +/- 0.10 and18.54 +/- 0.2 derived by Feast & Catchpole and van Leeuwen et al.,respectively, from HIPPARCOS parallaxes of Galactic Cepheid and Miravariables. 5. The age of the bona fide old globular clusters (OosterhoffII and BHB), based on the absolute magnitude of the turnoff (atheoretically robust indicator) is {Age}=11.8^{+2.1}_{-2.5} {Gyr} ,wherethe error bar is the 95% confidence range. The rms scatter of individualages around the mean value is ~10%, in agreement with expectations fromobservational errors alone (that is, we do not find it necessary tointroduce a real age scatter among these clusters). A reliable study ofthe relative ages requires the use of age indicators better suited tothis purpose and data for a larger sample of GGCs. 6. Allowing for aminimum delay of 0.5 Gyr from the birth of the universe until theformation of globular clusters, our age estimate is compatible with anEinstein-de Sitter model if H0 <= 64 km s-1 Mpc-1, or H0 <= 83 kms-1 Mpc-1 in a flat universe with Omega m = 0.2. Since these upperlimits are well within the confidence range of most determinations ofH0, we conclude that the present age of globular clusters does notconflict with standard inflationary models of the universe.
| The Universe and Globular Clusters: an Age Conflict?
Chaboyer (1995) has recently shown that the range of possible ages ofglobular clusters, tau ~ 14--18 Gyr, corresponding to different choicesof distance scales, is further enlarged mainly by uncertainties inmodeling convection. Within the mixing-length theory (MLT) the result istau = 11--21 Gyr. Bolte & Hogan (1995) adopted the field subdwarfsas indicators of the distance scale and, assuming that tau isinsensitive to the treatment of convection, found that tau = (15.8 +/-2.1) Gyr. Within Chaboyer's findings, it is marginally possible to avoidan "age conflict" with the expansion age of the universe, even if thislatter is t0 = 8--11 Gyr, while this is not the case with the Bolte& Hogan (1995) conclusion. Mazzitelli, D'Antona, & Caloi (1995)have implemented updated macro- and microphysics inputs and determinedthe distance scale by fitting the horizontal-branch models to thehorizontal branch of metal-poor globular clusters. Within the MLT, theyfind tau ~= 14 Gyr. Switching from MLT to a full spectrum of turbulence(FST) model of convection (Canuto & Mazzitelli 1991) lowers thevalue of tau by 1--2 Gyr. Since the Mazzitelli et al. (1995) resultswould alleviate the age conflict to the point of making it disappear, itis important to assess their validity by answering the followingquestions. Independently of the assumptions on the distance scale: 1.What is the role of convection near turnoff on both its shape andluminosity? Chaboyer (1995) and Mazzitelli et al. (1995) find anappreciable effect, while Bolte & Hogan (1995) a priori assume nosuch effect. 2. How meaningful is the fit of the red giant branch in thedetermination of tau ? In this paper, we answer question (1) carryingout extensive new stellar model calculations. When we assume the longdistance scale, the FST results differ from the MLT values both in theshape and in the luminosity of the turnoff, while there is noappreciable difference if one employs the short distance scale. Heliumsedimentation also affects the shape of isochrones and agedetermination. The long distance scale is also shown to be consistentwith the subdwarf location. As for (2), we find that, depending on thecorrelations between Teff and colors, both FST and MLT results can bemade compatible with both distance scales. Models includingsedimentation of helium improve the agreement with the red giant--branchlocation for low ages. At present, red giant branches can even bemisleading as age indicators. In conclusion, we choose the long distancescale on the basis of both horizontal-branch luminosities and thepresent data on subdwarf location, with resulting ages of about 12 Gyrfor the most metal-poor globular clusters.
| The Age of the Galactic Globular Cluster System
A careful assessment of current uncertainties in stellar physics(opacities, nuclear reaction rates, equation of state effects,diffusion, rotation, and mass loss), in the chemistry of globularcluster (GC) stars, and in the cluster distance scale, suggests that themost metal-poor (presumably the oldest) of the Galaxy's GCs have agesnear 15 Gyr. Ages below 12 Gyr or above 20 Gyr appear to be highlyunlikely. If these {approximately equal to} 2σ limits areincreased by {approximately} 1 Gyr to account for the formation time ofthe globulars, and if standard Friedmann cosmologies with thecosmological constant set to zero are assumed, then the GC constraint onthe present age of the Universe (to > 13 Gyr) implies that the Hubbleconstant Ho <51 km s-1 Mpc-1 if the density parameter Omega = 1 or< than} 62 km s-1 Mpc-1 if Omega = 0.3.
| 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.
| UVBY - beta photometry of high-velocity and metal-poor stars. VI - A second catalogue, and stellar populations of the Galaxy
A second catalog of uvby-beta photometry for 553 high-velocity stars ispresented. Combining the catalogs, reliable (Fe/H) values are obtainedfor 1214 stars and reliable kinematic parameters for 1149. The totalsample contains at least three significant, distinct stellar populationswith properties very similar to those given in the literature of the oldthin disk, thick disk, and halo. The thick-disk component has mean(Fe/H) about -0.50 +/- 0.10 dex and sigma(Fe/H) about 0.25 +/- 0.03 dex,but there is evidence for a significant thick-disk contribution down to(Fe/H) about -1.4. A diagonal cut in the V(rot), (Fe/H) diagramindicates that there is not a chemical gradient in the Galactic halo.The mean V(rot), mean (Fe/H) curve for the whole sample indicates thatthe halo evolved mostly independently of the disk.
| An astrometric catalogue of stars in the region of M15
We present positions and proper motions with respect to the PPMcatalogue of 863 stars in a field of 8 deg x 6 deg centered on theglobular cluster M15. The catalogue is based on measurements of 136plates from the Carte du Ciel telescope of Bordeaux, the CERGA Schmidttelescope, and the double refractor of Bonn. The modal accuracy of theproper motions is +/- 0 arcsec 15/100 a.
| Halo common proper motion stars - Subdwarf distance scale, halo binary fraction, and UBVRI colors
Common proper motion stars identified by Luyten (1979, 1980) wereselected according to reduced proper motion and photometric criteria toproduce a list of candidate halo objects. UBVRI photometry was obtainedto identify genuine halo parts. About 20 percent of the stars with(Fe/H) less than -1.0 were found to have random errors not less thanseveral x 0.1 mag in distance modulus, in addition to the photometricerrors, thought to be due to the existence of close binary companions tosome of the common proper motion stars. The implications of these errorsfor kinematic studies of field Population II stars are considered.Systematic errors of order 16 percent were also detected in distancesderived from the U-B,B-V deblanketing technique. It is suggested thatPopulation II field stars did not originate in globular clusters whichsubsequently disintegrated but formed in less dense environments.Several K subdwarfs were found with very high UV excesses, comparablewith those predicted by some synthetic colors.
| 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.
| 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.
| Micrometer observations of double stars and new pairs. XIII
From a program of double star observations which emphasizes orbital,neglected, and newly discovered pairs, results obtained from October1984 to January 1987 are presented. A total of 3030 visual and 550photographic measures are listed. The positions in WDS format andDurchmusterung numbers are shown for 117 pairs for which firstobservations appear in this paper. Magnitudes are estimated for some ofthe objects.
| New subdwarfs. VI - Kinematics of 1125 high-proper-motion stars and the collapse of the Galaxy
The UVW velocity components, planar eccentricities, and angular momentaof 878 high-proper-motion stars are determined using the radial-velocitydata of Fouts and Sandage (1986) and compared with chemical abundancesand photometric parallaxes from the UBV photometry of Sandage and Kowal(1986). The results are presented, along with published data on 247additional stars, in extensive tables and graphs and characterized indetail. Two approximately equal components are differentiated: alow-velocity component identified as part of the thick disk described byGilmore and Reid (1983) and a high-velocity halo component. The data arefound to support a model of Galactic collapse (with concomitant spinupand progressive chemical enrichment) which includes a rotating bulge(the thick disk) with kinematic and metallicity properties between thoseof the old thin disk and the halo.
| New subdwarfs. V - Radial velocities for 889 high-proper-motion stars measured with the Mount Wilson 100 inch reflector
New radial velocities have been obtained from 2265 measurements of 889high-proper-motion stars taken from the subdwarf candidate list of aprevious paper. The observations were made with the Mount Wilson 100 inHooker reflector coude spectrograph with a Reticon detector, giving aninternal error of a single measurement of 4.7 km/s. From 88 stars incommon with previously known subdwarfs; the external error of the datais 6.9 km/s per measurement, and the velocity system is shown to be onthe system of the Wilson General Catalog to better than 1 km/s. Of the878 stars with nonvariable velocities in the sample, 38 have radialvelocities larger than 200 km/s, of which 22 are new. There is acorrelation between radial velocity and reduced ultraviolet excess asexpected from the previously known relations between space motion andchemical composition. The Stroemberg asymmetric drift is directlyvisible in the radial velocity and the proper-motion data separately aseach is displayed as a function of galactic longitude.
| New subdwarfs. IV - UBV photometry of 1690 high-proper-motion stars
A photometric list of 1690 stars of known high proper motion is used tosearch for potential high-velocity stars of various metallicity valuesin order to find candidates for trigonometric programs on subdwarfs andto enlarge the sample with which to study the relation between stellarkinematics and metal abundance. A list of 113 stars with tangentialspace velocities of 300 km/s or greater is obtained, the highesttangential velocity relative to the sun being 630 km/s. By using thevariation of the tangential velocity with longitude and adopting thegalactic rotation at the solar circle to be 220 km/s, the rotation ofthe subdwarf system is estimated at 0 + or - 50 km/s from the transversevelocity alone, in agreement with determinations based on other methods.
| 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.
| Not Available
Not Available
| Luminosity and motion of large proper-motion stars. I - Stars with annual proper motion larger than 1 arcsec
The luminosities and motions of stars brighter than visual magnitude 15and annual proper motion greater than one arcsec given in a catalogpublished by the author (1979) are discussed on the basis of the (RI)photometry available for these objects. Pending subsequent discussionsof data contained in two additional catalogs, it is concluded that thefirst catalog contains 100 subdwarfs extending to an infrared magnitudeof +11.5 mag. If these are halo objects, the number density-luminosityfunction has a steeper slope than the general luminosity function,indicating that the mass density may be greater than normallyrecognized. The luminosity law for the old disk stars in this catalogclosely conforms to the slope of the general luminosity function fromvisual magnitude +4.5 to +13; however, there is an excess of stars oflower luminosity.
| 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
| The often-discovered subdwarf binary +11 4571
Not Available
| Spectral types for proper motion stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..239B&db_key=AST
| Spectral Types of M Dwarf Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJS...28....1J&db_key=AST
| Stars with Incomplete Observational Data and with Possible Hyperbolic Velocities
Not Available
| The Color-Magnitude Array for Stars in the Globular Cluster M 15.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...113..344B&db_key=AST
| A list of 31 faint stars with large proper motions.
Not Available
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Пегас |
| Прямое восхождение: | 21h29m07.05s |
| Склонение: | +12°10'59.0" |
| Видимая звёздная величина: | 11.428 |
| Собственное движение RA: | 156.9 |
| Собственное движение Dec: | -457.2 |
| B-T magnitude: | 12.765 |
| V-T magnitude: | 11.539 |
Каталоги и обозначения:
|
