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Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| The initial-final mass relationship from white dwarfs in common proper motion pairs
Context: The initial-final mass relationship of white dwarfs, which ispoorly constrained, is of paramount importance for different aspects ofmodern astrophysics. From an observational perspective, most of thestudies up to now have been done using white dwarfs in open clusters. Aims: In order to improve the initial-final mass relationship, weexplore the possibility of deriving a semi-empirical relation studyingwhite dwarfs in common proper motion pairs. If these systems arecomprised of a white dwarf and a FGK star, the total age and themetallicity of the progenitor of the white dwarf can be inferred fromthe detailed analysis of the companion. Methods: We have performed anexhaustive search for common proper motion pairs containing a DA whitedwarf and a FGK star using the available literature and crossing theSIMBAD database with the Villanova White Dwarf Catalog. We have acquiredlong-slit spectra of the white dwarf members of the selected commonproper motion pairs, as well as high resolution spectra of theircompanions. From these observations, a full analysis of the two membersof each common proper motion pair leads to the initial and final massesof the white dwarfs. Results: These observations have allowed us toprovide updated information for the white dwarfs, since some of themwere misclassified. In the case of the DA white dwarfs, theiratmospheric parameters, masses, and cooling times have been derivedusing appropriate white dwarf models and cooling sequences. From adetailed analysis of the FGK star spectra we have inferred themetallicity. Then, using either isochrones or X-ray luminosities we haveobtained the main-sequence lifetime of the progenitors, and subsequentlytheir initial masses. Conclusions: This work is the first one usingcommon proper motion pairs to improve the initial-final massrelationship, and has also allowed us to cover the poorly exploredlow-mass domain. As in the case of studies based on white dwarfs in openclusters, the distribution of the semi-empirical data presents a largescatter, which is higher than the expected uncertainties in the derivedvalues. This suggests that the initial-final mass relationship may notbe a single-valued function.Based on observations obtained at: Calar Alto Observatory,Almería, Spain, el Roque de los Muchachos, Canary Islands, Spain,McDonald Observatory, Texas, USA, and Las Campanas Observatory, Chile.Tables [see full textsee full textsee full text], [see full textsee fulltextsee full text] and [see full textsee full textsee full text] areonly available in electronic form at http://www.aanda.org
| New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems
We perform a search for faint, common proper motion companions ofHipparcos stars using the recently published Lépine-Shara ProperMotion-North catalog of stars with proper motionμ>0.15'' yr-1. Our survey uncovers a totalof 521 systems with angular separations3''<Δθ<1500'', with 15 triplesand 1 quadruple. Our new list of wide systems with Hipparcos primariesincludes 130 systems identified here for the first time, including 44 inwhich the secondary star has V>15.0. Our census is statisticallycomplete for secondaries with angular separations20''<Δθ<300'' and apparentmagnitudes V<19.0. Overall, we find that at least 9.5% of nearby(d<100 pc) Hipparcos stars have distant stellar companions withprojected orbital separations s>1000 AU. We observe that thedistribution in orbital separations is consistent with Öpik's law,f(s)ds~s-1ds, only up to a separation s~4000 AU, beyond whichit follows a more steeply decreasing power law f(s)ds~s-ldswith l=1.6+/-0.1. We also find that the luminosity function of thesecondaries is significantly different from that of the single stars'field population, showing a relative deficiency in low-luminosity(8
| 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.
| White Dwarfs in Common Proper Motion Binary Systems: Mass Distribution and Kinematics
We present the mass distribution, gravitational redshifts, radialvelocities, and space motions of white dwarf stars in common propermotion binary systems. The mass distribution we derive for the 41 DAwhite dwarfs in this study has a mean of 0.68+/-0.04 Msolar.This distribution has a slightly higher mean and larger dispersion thanmost previous white dwarf studies. We hypothesize that this is due to ahigher fraction of cool (average Teff~10,000 K), hence old,white dwarfs in our sample. Our results indicate that samples made up ofpredominantly cool, old white dwarf stars tend to have a bimodaldistribution with a second mass peak at ~1.0 Msolar, whichskews the mean toward a higher mass. Both the mean and individual whitedwarf masses we report here are in better agreement with thosedetermined from model atmosphere spectroscopic fits to line profilesthan with most previous gravitational redshift studies of cool whitedwarfs. Our results indicate that measurement biases and weak geocoronalemission lines in the observed spectra may have affected previousgravitational redshift measurements. These have been minimized in ourstudy. We present measurements for some previously unobserved whitedwarfs, as well as independent new measurements for some that have beenreported in the literature. A list of complete space motions for 50 widebinary white dwarfs is presented, derived from radial velocitymeasurements of their nondegenerate companions. We find that the UVWspace motions and dispersions of the common proper motion binaries thatcontain white dwarf components are consistent with those of old,metal-poor disk stars.
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| Takýmyýldýz: | Av Kopekleri |
| Sað Açýklýk: | 13h57m05.50s |
| Yükselim: | +33°48'25.2" |
| Görünürdeki Parlaklýk: | 9.089 |
| özdevim Sað Açýklýk: | -157.3 |
| özdevim Yükselim: | 45.8 |
| B-T magnitude: | 9.754 |
| V-T magnitude: | 9.144 |
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