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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.
| 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.
| Completeness of USNO-B for High Proper Motion Stars
I test the completeness of USNO-B detections of high proper motion(μ>180 mas yr-1) stars and the accuracy of itsmeasurements by comparing them to the revised New Luyten Two-Tenthscatalog of Salim & Gould. For 14.5~20 mas yr-1) may actuallyhave still larger errors than tabulated.
| 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.
| VRI photometry of late dwarf common proper motion pairs
VRI photometry and photometric distance moduli are presented for 266late dwarf common proper motion pairs. From the distance modulusdifferences between the components of each pair, it is inferred that atleast 56 percent of the pairs contain one or more additional stellarcomponents. The maximum separation of M dwarf binaries appears to be ofthe order 10,000-20,000 AU.
| Photometric parallaxes for selected stars of color class M from the NLTT Catalog. IV - The declination zone +45 to +90 deg
VRI photometry and photometric parallaxes are presented for a sample of524 stars of color class m in the NLTT Catalog Luyten (1979) for whichno trigonometric parallaxes have been measured. Additional photometry of106 stars with trigonometric parallaxes is also presented. For theprogram stars, 67 have photometric parallaxes of not less than 0.04arcsec.
| UBVRI photoelectric photometry of high proper motion stars
UBVRI photoelectric photometry is presented for 269 late spectral type,high proper motion stars belonging to the 'Lowell Proper Motion Survey'and included in the present version of the Hipparcos Input Catalogue.The observations and data reduction are described. The external errorsobtained by comparison of the results with those obtained in otherstudies are presented.
| Photometric parallaxes for selected stars of color class M from the NLTT catalog
VRI photometry is presented for a sample of 413 stars selected fromamong the stars of color class m in the NLTT catalog for which notrigonometric parallaxes have been measured and which are not known tobe on a trigonometric parallax program. Additional VRI photometry ofstars with good trigonometric parallaxes provides the basis for thecalibration of color/absolute-magnitude relations used to computephotometric parallaxes for the program stars, about 90 of which arefound to have photometric parallax greater than or equal to 0.040arscec. Attention is called to a few apparently subluminous stars ofpossible interest. On the basis of the present sample, it appears thatthe catalog color index m(pg)-m(R) will not be useful in identifyingnearby stars from among the thousands of color-class-m stars with smallproper motion in the NLTT catalog.
| Spectral classification of high-proper-motion stars
Spectral types have been found for about 900 stars of high proper motioncontained in the Lowell Observatory Northern Hemisphere proper-motionstar survey using all blue-region objective prism plates. The spectralclassification criteria are given. About eighty stars of largetangential velocity have been classified using slit spectrograms takenwith a 36-in. reflector. A new calibration of Luyten's absolutemagnitude vs reduced proper motion relation is made, and its dependenceon spectral type is investigated.
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