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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 Luminosity and Mass Functions of Low-Mass Stars in the Galactic Disk. I. The Calibration Region
We present measurements of the luminosity and mass functions of low-massstars constructed from a catalog of matched Sloan Digital Sky Survey(SDSS) and Two Micron All Sky Survey (2MASS) detections. Thisphotometric catalog contains more than 25,000 matched SDSS and 2MASSpoint sources spanning ~30 deg2 on the sky. We have obtainedfollow-up spectroscopy, complete to J = 16, of more than 500 low-massdwarf candidates within a 1 deg2 subsample, and thousands ofadditional dwarf candidates in the remaining 29 deg2. Thisspectroscopic sample verifies that the photometric sample is complete,uncontaminated, and unbiased at the 99% level globally, and at the 95%level in each color range. We use this sample to derive the luminosityand mass functions of low-mass stars over nearly a decade in mass (0.7 Msun > M * > 0.1 M sun). Theluminosity function of the Galactic disk is statistically consistentwith that measured from volume-complete samples in the solarneighborhood. We find that the logarithmically binned mass function isbest fit with an Mc = 0.29 log-normal distribution, with a90% confidence interval of Mc = 0.20-0.50. These 90%confidence intervals correspond to linearly binned mass functionspeaking between 0.27 M sun and 0.12 M sun, wherethe best fit MF turns over at 0.17 M sun. A power-law fit tothe entire mass range sampled here, however, returns a best fit ofα = 1.1 (where the Salpeter slope is α = 2.35); a brokenpower law returns α = 2.04 at masses greater than log M =-0.5 (M = 0.32 M sun), and α = 0.2 at lowermasses. These results agree well with most previous investigations,though differences in the analytic formalisms adopted to describe thosemass functions, as well as the range over which the data are fit, cangive the false impression of disagreement. Given the richness ofmodern-day astronomical data sets, we are entering the regime wherebystronger conclusions can be drawn by comparing the actual datapointsmeasured in different mass functions, rather than the results ofanalytic analyses that impose structure on the data a priori. Havingvalidated this method to generate a low-mass luminosity function frommatched SDSS/2MASS data sets, future studies will extend this techniqueto the entirety of the SDSS footprint.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| 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.
| 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.
| Space Motions of Low-Mass Stars. III.
Radial velocity observations are presented for 149 stars taken from theMcCormick lists of dwarf K and M stars in a continuing program of radialvelocities of faint nearby stars. The data will serve to derive a totalstellar density of these kinds of stars in the solar neighborhood. Thesedata were obtained with the spectrometer of the Vilnius UniversityObservatory mounted on the 1.6 m Kuiper Telescope of the StewardObservatory.
| Photometry of dwarf K and M stars
An observational program using UBVRI photometry is presented for 688stars from among the dwarf K and M stars already found spectroscopicallyby Vyssotsky (1958). Of these, 211 have not been observedphotometrically. These observations were obtained over a period ofseveral years at the Kitt Peak National Observatory using a GaAsphotomultiplier with an 0.9 m reflector. Based on night-to-nightvariations in the measures of individual stars, the internal errors maybe estimated to be roughly 0.01 mag for the colors and 0.015 for the Vmagnitudes. The photometric parallaxes reported for each star werecomputed in the manner discussed by Weis (1986).
| Catalogue de 240 couples visuels d'étoiles naines rouges
Not Available
| The space distribution of late type stars in a North galactic pole region.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67...37U&db_key=AST
| Photovisual magnitudes of 418 dwarf M stars and 34 parallax stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..219S&db_key=AST
| Dwarf M stars found spectrophotometrically .
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..201V&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Orsa Maggiore |
| Ascensione retta: | 12h03m14.85s |
| Declinazione: | +47°50'33.4" |
| Magnitudine apparente: | 10.077 |
| Distanza: | 43.141 parsec |
| Moto proprio RA: | -160.9 |
| Moto proprio Dec: | -1.5 |
| B-T magnitude: | 11.385 |
| V-T magnitude: | 10.185 |
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