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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.
| 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.
| 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.
| Lowell proper motions III : proper motion survey of the Northern Hemisphere with the 13-inch photographic telescope of the Lowell Observatory
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