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A Photometric Variability Survey of Field K and M Dwarf Stars with HATNet
Using light curves from the HATNet survey for transiting extrasolarplanets we investigate the optical broadband photometric variability ofa sample of 27, 560 field K and M dwarfs selected by color and propermotion (V - K >~ 3.0, ? > 30 mas yr-1, plusadditional cuts in J - H versus H - KS and on the reducedproper motion). We search the light curves for periodic variations andfor large-amplitude, long-duration flare events. A total of 2120 starsexhibit potential variability, including 95 stars with eclipses and 60stars with flares. Based on a visual inspection of these light curvesand an automated blending classification, we select 1568 stars,including 78 eclipsing binaries (EBs), as secure variable stardetections that are not obvious blends. We estimate that a further ~26%of these stars may be blends with fainter variables, though most ofthese blends are likely to be among the hotter stars in our sample. Wefind that only 38 of the 1568 stars, including five of the EBs, havepreviously been identified as variables or are blended with previouslyidentified variables. One of the newly identified EBs is 1RXSJ154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, forwhich we derive preliminary estimates for the component masses and radiiof M 1 = M 2 = 0.258 ± 0.008 Msun and R 1 = R 2 = 0.289 ±0.007 R sun. The radii of the component stars are larger thantheoretical expectations if the system is older than ~200 Myr. Themajority of the variables are heavily spotted BY Dra-type stars forwhich we determine rotation periods. Using this sample, we investigatethe relations between period, color, age, and activity measures,including optical flaring, for K and M dwarfs, finding that many of thewell-established relations for F, G, and K dwarfs continue into the Mdwarf regime. We find that the fraction of stars that is variable withpeak-to-peak amplitudes greater than 0.01 mag increases exponentiallywith the V - KS color such that approximately half of fielddwarfs in the solar neighborhood with M <~ 0.2 M sun arevariable at this level. Our data hint at a change in therotation-activity-age connection for stars with M <~ 0.25 Msun.
| 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.
| 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.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| 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).
| Parallaxes and proper motions from the McCormick Observatory - List 46
Trigonometric parallaxes and relative proper motions are presented for26 late-type stars observed with the Leander McCormick rafractor.Eighteen stars have no previously published parallaxes. Sixteen starsare K and M dwarfs identified by Vyssotsky and his collaborators. Thelist includes three probable Hyades cluster members, two subdwarfs, andan M dwarf at a distance of about 10 pc. New BVRI photometry has beenobtained for most stars on the list.
| A digitized version of the NLTT Catalogue of proper motions
An optically scanning data-entry machine and various manual techniquesare used to digitize the NLTT Catalogue and the first supplement to theNLTT Catalogue. Included in the catalog are stars found on over 800Palomar proper-motion survey plates to have relative annual propermotions exceeding 0.18 arcsec. The supplement contains data for 398stars having motions larger than 0.179 arcsec annually.
| Dwarf K and M stars of high proper motion found in a hemispheric survey
A recently completed visual/red spectral region objective-prism surveyof more than half the sky found some 2200 dwarf K and M stars ofnegligible proper motion (Stephenson, 1986). The present paper adds the1800-odd spectroscopically identified dwarfs that did prove to havesignificant proper motions. About half of these had previous spectralclassifications of some sort, especially by Vyssotsky (1952, 1956). Forthe great majority, the present coordinates are more accurate thanprevious data. The paper includes about 50 stars with unpublishedparallaxes, likely to have parallaxes of 0.05 arcsec or more. Combiningthe present data with the first paper suggests that the number oflow-proper-motion stars in that paper was not unreasonable.
| CX Aurigae: a K-Dwarf Variable
Not Available
| Photoelectric observations of red dwarf stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..213M&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
| Benennung von veränderlichen Sternen
Not Available
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Observation and Astrometry data
| Constellation: | Auriga |
| Right ascension: | 06h56m22.11s |
| Declination: | +46°59'26.8" |
| Apparent magnitude: | 11.018 |
| Proper motion RA: | -69.1 |
| Proper motion Dec: | -120.7 |
| B-T magnitude: | 12.723 |
| V-T magnitude: | 11.159 |
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