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The Nature of Late-Type Companions in Hot Subdwarf Composite-Spectrum Binaries
We present the results of a study of late-type companions in hotsubdwarf composite spectrum binaries. The exact nature of theselate-type companions has been disputed in the literature -- some arguethat they are main-sequence stars, and others have claimed they aresubgiants. To determine the properties of the late-type companions, wefirst conducted a survey utilizing the Two Micron All Sky Survey (2MASS)All-Sky Data Release Catalog to identify composite-colored binaries inthe Catalogue of Spectroscopically Identified Hot Subdwarfs (Kilkenny etal. 1988, 1992). We then conducted a spectroscopic study of a sub-sampleof the 2MASS composite-colored hot subdwarfs. The sample consists ofphotometrically and spectroscopically single and composite hot subdwarfs(14 single and 51 composite). We also obtained spectra of 59 singlelate-type stars with Hipparcos parallaxes for calibration. We usedmeasured equivalent width (EW) indices from the composite systems toestimate the temperature and gravity of the late-type star, taking intoaccount the dilution of its spectral features by light from the hotsubdwarf. Results from combining the spectroscopic data with modelenergy distributions indicate that the late-type companions incomposite-spectrum systems are best described by main-sequencecompanions overall.
| Studying the populations of our Galaxy using the kinematics of sdB stars
We have analysed the kinematics of a sample of 114 hot subdwarf stars.For 2/3 of the stars, new proper motions, spectroscopic and photometricdata are presented. The vast majority of the stars show a kinematicbehaviour that is similar to that of Thick Disk stars. Some stars havevelocities rather fitting to solar, i.e. Thin Disk, kinematics. About˜15 objects have orbital velocities which differ considerably fromthose of Disk stars. These are members of the Galactic Halo. Weinvestigated the velocity dispersions and calculated the orbits. Moststars feature orbits with disk character (eccentricity of less than0.5), a few reach far above the Galactic plane and have very eccentricorbits (eccentricity of more than 0.7). The intermediate eccentricityrange is poorly populated. This seems to indicate that the (Thick) Diskand the Halo are kinematically disjunct. Plotting a histogram of theorbit data points along z leads to the z-distance probabilitydistribution of the star; doing this for the whole sample leads to thez-distance probability distribution of the sample. The logarithmichistogram shows two slopes, each representing the scale height of apopulation. The disk component has a scale height of 0.9 (±0.1)kpc, which is consistent with earlier results and is similar to that ofthe Thick Disk. The other slope represents a component with a scaleheight ˜7 kpc, a much flatter gradient than for the diskcomponent. This shows that the vast majority of the sdBs are disk stars,but a Halo minority is present, too. The kinematic history andpopulation membership of the sdB stars on the whole is different fromthat of the cooler HBA stars, which are predominantly or evenexclusively Halo objects. This leads to the question, whether the HalosdB stars are of similar origin as the HBA stars, or whether theirkinematical behaviour possibly represents another origin, such asinfalling stellar aggregates or inner disk events.Based on data obtained at the 1.54 m telescope of the European SouthernObservatory, runs 58.D-0478, 60.D-0306, 62.L-0220, 64.L-0077,64.H-0023(A), 65.H-0250, 65.H-0341(A) and 68.D-0192(A).
| The Montreal-Cambridge-Tololo Survey of Southern Subluminous Blue Stars: The South Galactic Cap
Results for the south Galactic cap region of theMontréal-Cambridge-Tololo survey of blue subluminous stars arepresented. This region overlaps the 840 deg2 region studiedalmost three decades ago by Slettebak & Brundage. We present a list ofequatorial coordinates, photographic photometry, and spectroscopicidentifications, as well as finding charts, for 188 blue objects[(U-B)pg<=-0.6] brighter than Bpg=16.5 in thisarea. Completeness of the survey and comparisons with other similarefforts are discussed.
| Photometry of faint blue stars - IX
Stromgren uv by photometry is presented for 129 `faint blue' stars takenfrom various catalogues. The photometry is used to estimate photometric`classifications' for the stars, which indicate a mixture of hotsubdwarfs, horizontal-branch stars, metal-weak subdwarfs and so on.Attention is drawn to stars (from this paper and previous papers in theseries) which appear to be somewhat reddened. Some are probablybinaries, and others might be objects with peculiar colours, such ascataclysmic variables. One star, LB 9963, almost certainly falls intothe latter category. Two stars which, from their colours, are PopulationII A-F stars are variable; one of these, OM 89, is the known RR Lyraestar, VW Dor.
| The nature of the hot subdwarf SB 744
Various spectra in the visual wavelength range, one low-resolutionultraviolet spectrum, and color measurements in the red region have beentaken to clarify the nature of the hot subdwarf SB 744. The colors andweak metallic lines as well as a G-band (CH) in the visual spectraindicate the existence of a cool companion, whereas the hydrogen andhelium line spectrum is typical for a hot subdwarf. The model atmosphereanalysis of the hydrogen and helium line spectrum yields that theprimary is a typical OB-type subdwarf. There is some evidence for asimilar strange abundance pattern as in other OB-type subdwarfs. Fromthe measured colors, the strengths of the Mg I - lines, the G-band, andthe weak resonance line of Ca I at 4227 A, it becomes evident that thecompanion is a K0-star, which contributes about 20 percent to the visualmagnitude.
| Radial velocities and spectral types for a sample of faint blue stars.
Not Available
| A new analysis of the metal-rich halo-subdwarf SB 744.
Not Available
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| White Dwarfs in Wide Binaries - Part Two - Double Degenerates and Composite Spectra
Spectrophotometry of six northern visual pairs containing two degeneratestars shows that the components are quite similar in luminosity andtemperature. Presumably the two progenitors were similar and had nuclearlifetimes short compared to the subsequent cooling ages of the whitedwarfs. The white dwarfs are near twins, with dispersion in radii below14%. The mean cooling age of the pairs is 4 × l09 yr,their luminosity Mv = + 14.5 mag. One pair is relativelyyoung, with components less similar. Study of pairs containing a whitedwarf and a main-sequence star shows that a large fraction of such pairsare undiscovered. Those containing a hot white dwarf and a redmain-sequence companion, discovered from the composite spectra, arequite blue and have an infrared excess. When the fluxes in pairsobserved as resolved are added, the composite so synthesized is yellowor red, with a large violet or ultraviolet excess. Methods of discoveryof white dwarfs leave regions of the color-color diagrams untouched. Apossible technique of searching for violet excess suggested involvesmagnitudes in the infrared, visual, and blue. Analysis of old novae,spectroscopic binaries containing a white dwarf, and a dM star with afaint white dwarf companion displays composite spectra. Whether thelarge number of missing white dwarfs in noninteracting binaries exist,or whether the progenitor binaries have been dissolved, remainsundecided.
| The atmosphere of subluminous B stars. II - Analysis of 10 helium poor subdwarfs and the birthrate of sdB stars
Ultraviolet and visual spectra of 10 helium-poor hot subluminoussubdwarfs are analyzed, and the birthrate of these stars is determined.Effective temperatures range from 25,000 - 75,000 K in the group, whichincludes three binaries. sdB's occupy a narrow range in gravities andphotospheric helium content in contrast to the sdOB ranges of gravitiesbetween 5.0 and 6.3 and helium contents from 0.07 to 6 percent. Thehelium deficiency occurs by diffusion, suggesting that the sdB mass lossrate is twice as small as the sdO mass loss rate. Data suggest thatthese stars form a single evolutionary group of extended horizon branch(EHB) stars which behave like helium main sequence stars with masses ofapproximately 0.5 solar mass. The completed survey of EHB stars revealsa birthrate of 2 x 10 to the 14th stars/cu pc/yr, and that theirevolution directly into white dwarfs represents only 2 percent of thisevolutionary channel; though they contribute significantly to the lowestmass tail of the white dwarf mass distribution.
| The colors and luminosities of white dwarfs
Photoelectrically determined color indices of white dwarfs are reviewedwith particular emphasis on the possibility that a large percentage ofthese objects in the solar neighborhood are members of the Hyades andSirius superclusters. The astrometric, photometric, and spectroscopicdata now available for the best-established cases of such membership arediscussed. The color-luminosity array obtained from supercluster membersis tested against that obtained with trigonometric parallaxes determinedat the U.S. Naval Observatory.
| White dwarf candidates for trigonometrical parallax determinations.
The visual surface brightness relation is applied to the determinationof parallaxes of white dwarfs on the assumption, borne out by previousstudies of white dwarfs of known parallax, that these show only a smallrange of linear diameters.
| White Dwarf Candidates for Trigonometrical Parallax Determination
Not Available
| He-rich white dwarfs - Birth-rate and kinematics of different groups of white dwarfs
The temperatures, radii, and masses of 81 He-rich white dwarfs arecalculated from photometric data. It is shown that, on the average, theyare less massive than DA white dwarfs; 70 percent of He-rich whitedwarfs have masses of less than 0.55 solar mass. Space density andbirth-rate for different mass groups of H-rich and He-rich white dwarfsare obtained. Birth-rate is 1 x 10 to the -12th/cu pc yr and 1.5 x 10 tothe -12th/cu pc yr for He-rich and H-rich white dwarfs, respectively.The mean mass of nascent white dwarfs is about 0.55 solar mass. It isshown that VT and its dispersion sigma are correlated withthe mass of white dwarfs, and from this progenitors' masses - ofdifferent mass groups of white dwarfs are estimated.
| An infrared search for very low mass stars - JHK photometry and results for composite systems
JHK photometry for about 100 white dwarfs and 60 red dwarfs, obtainedduring a search for very low mass companions to white dwarfs, ispresented. A simple modeling technique using broad-band colors ispresented and used to deconvolve apparent composites. Individual starsdiscussed include white-red dwarf binaries, systems which may contain anaccretion disk or subdwarf primary, and stars with no excess infraredflux. Astrometric detection of some systems is considered, and newpossible proper-motion companions are listed.
| Correspondences Between Bruce Proper Motion Survey and the Bonnerdurchmusterung
Not Available
| Catalogue of white dwarfs
Not Available
| Lowell Proper Motion Survey - Summary Catalogue of GD and GR Stars
Not Available
| Applicability of the visual surface brightness relation to white dwarfs
It was previously demonstrated that a visual surface-brightnessparameter, FV, is tightly correlated with (V-R) color index.The application of this relationship to white dwarfs is investigated byanalyzing BVRI photometry of nearly all white dwarfs brighter than 13thmagnitude which have reliable parallaxes. Tests are performed toascertain the accuracy of white-dwarf angular diameters inferred fromvalues of FV. The test results show that such angulardiameters are in excellent accord with those inferred frommodel-atmosphere analyses of flux distributions. A mean radius ofapproximately 0.0132 solar radius is derived for DA white dwarfs, massesof white dwarfs with measured gravitational redshifts are estimated, andthe results are found to be unreasonable for any composition in theHamada-Salpeter (1961) theory. However, a density in excellent agreementwith the theory is computed for 40 Eri B by using parameters of thered-dwarf eclipsing binary CM Dra.
| Lowell proper motions XVIII. Proper Motion Survey in the southern hemisphere with the 13-inch photographic telescope of the Lowell Observatory.
Not Available
| Multichannel spectrophotometry and the luminosities of white dwarfs.
Abstract image available at:http://adsabs.harvard.edu/abs/1976AJ.....81..323G
| Binary Hypothesis for the Subdwarf B Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1976ApJ...204..488M
| Photometry of faint blue stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1975MNRAS.173..625K
| A New List of 52 Degenerate Stars VII
Abstract image available at:http://adsabs.harvard.edu/abs/1974ApJ...189L.131G
| A finding list of stars of spectral type A7 and earlier in regions at high galactic latitudes. VI. Near South Galactic Pole.
Not Available
| A finding list of early-type stars near the south galactic pole.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..338S&db_key=AST
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