Improved Astrometry and Photometry for the Luyten Catalog. I. Bright Stars

We outline the construction of an updated version of the New Luyten Two-Tenths (NLTT) catalog of high proper motion stars, which will contain improved astrometry and photometry for the vast majority of the ~59,000 stars in NLTT. The bright end is constructed by matching NLTT stars to Hipparcos, Tycho-2, and Starnet; the faint end by matching to USNO-A and 2MASS. In this first paper, we detail the bright-end matching procedure. We show that for the majority of stars in his catalog, Luyten measured positions accurate to 1" even though he recorded his results much more coarsely. However, there is a long tail of position errors, with one error as large as 11 deg. Proper-motion errors for the stars with small position errors are 24 mas/yr (1 sigma) but deteriorate to 34 mas/yr for stars with inferior positions. NLTT is virtually 100% complete for V15 deg, but completeness in this magnitude range falls to about 75% at the Galactic plane. Incompleteness near the plane is not uniform, but is rather concentrated in the interval -80<l<20, where the Milky Way is brightest.Comment: Submitted to ApJ, 28 pages including 7 figure

Photometric Selection of QSO Candidates From GALEX Sources

We present a catalog of 36,120 QSO candidates from the Galaxy Evolution Explorer (GALEX) Release Two (GR2) UV catalog and the USNO-A2.0 optical catalog. The selection criteria are established using known quasars from the Sloan Digital Sky Survey (SDSS). The SDSS sample is then used to assign individual probabilities to our GALEX-USNO candidates. The mean probability is ~50%, and would rise to ~65% if better morphological information than that from USNO were available to eliminate galaxies. The sample is ~40% complete for i<=19.1. Candidates are cross-identified in 2MASS, FIRST, SDSS, and XMM-Newton Slewing Survey (XMMSL1), whenever such counterparts exist. The present catalog covers the 8000 square degrees of GR2 lying above 25 degrees Galactic latitude, but can be extended to all 24,000 square degress that satisfy this criterion as new GALEX data become available.Comment: AASTeX v5.2, 31 pages, 9 figures. Accepted for publication in ApJ. Extended tables available in the online edition of the journa

Completeness of USNO-B for High Proper-Motion Stars

I test the completeness of USNO-B detections of high proper-motion (mu>0.18"/yr) stars and the accuracy of its measurements by comparing them to the revised NLTT (rNLTT) catalog of Salim & Gould. For 14.5<V<18.5, only 6% of such stars are missing from USNO-B while another 4% have large errors, mostly too large to be useful. Including both classes, incompleteness is 10%. These fractions rise toward both brighter and fainter magnitudes. Incompleteness rises with proper motion to about 30% at mu=1"/yr. It also rises to about 35% at the Galactic plane, although this is only determined for relatively bright stars V<~14. For binaries, incompleteness rises from 10% at separations of 30" to 47% at 10". The proper-motion errors reported internally by USNO-B are generally correct. However, there is floor of sigma_mu~4mas/yr below which the reported errors should not be taken at face value. The small number of stars with relatively large reported errors (sigma_mu>~20mas/yr) may actually have still larger errors than tabulated.Comment: Submitted to AJ, 26 pages including 10 figure

New Hipparcos-based Parallaxes for 424 Dim Stars

We present a catalog of 424 common proper motion companions to Hipparcos stars with good (>3 sigma) parallaxes, thereby effectively providing new parallaxes for these companions. Compared to stars in the Hipparcos catalog, these stars are substantially dimmer. The catalog includes 20 WDs and an additional 29 stars with M_V>14, the great majority of the latter being M dwarfs.Comment: Submitted to ApJS, 20 page

Disk and Halo Wide Binaries from the Revised Luyten Catalog: Probes of Star Formation and MACHO Dark Matter

We present a catalog of 1147 candidate common proper motion binaries selected from the revised New Luyten Two-Tenths Catalog. Among these, we identify 999 genuine physical pairs using the measured proper-motion difference and the relative positions of each binary's components on a reduced proper-motion (RPM) diagram. The RPM positions also serve to classify them as either disk main-sequence (801), halo subdwarf (116), or pairs containing at least one white dwarf (82). The disk and halo samples are complete to separations of \theta=500" and \theta=900", which correspond to ~0.1 pc and ~1 pc, respectively. At wide separations, both distributions are well described by single power laws, dN/d\theta ~ \theta^{-\alpha}: \alpha=1.67+-0.07 for the disk and \alpha=1.55+-0.10 for the halo. The fact that these distributions have similar slopes (and similar normalizations as well) argues for similarity of the star-formation conditions of these two populations. The fact that the halo binaries obey a single power law out to ~1 pc permits strong constraints on halo dark-matter candidates. At somewhat closer separations (10"<\theta<25"), the disk distribution shows a pronounced flattening, which is detected at very high statistical significance and is not due to any obvious systematic effect. We also present a list of 11 previously unknown halo stars with parallaxes that are recognized here as companions of Hipparcos stars.Comment: 56 pages, 16 figures; replaced with version accepted for publication in Ap

Transit Target Selection Using Reduced Proper Motions

In searches for planetary transits in the field, well over half of the survey stars are typically giants or other stars that are too large to permit straightforward detection of planets. For all-sky searches of bright V<~11 stars, the fraction is ~90%. We show that the great majority of these contaminants can be removed from the sample by analyzing their reduced proper motions (RPMs): giants have much lower RPMs than dwarfs of the same color. We use Hipparcos data to design a RPM selection function that eliminates most evolved stars, while rejecting only 9% of viable transit targets. Our method can be applied using existing or soon-to-be-released all-sky data to stars V<12.5 in the northern hemisphere and V<12 in the south. The method degrades at fainter magnitudes, but does so gracefully. For example, at V=14 it can still be used to eliminate giants redward of V-I~0.95, that is, the blue edge of the red giant clump.Comment: Submitted to ApJ, 17 pages including 6 figure

The second US Naval Observatory CCD Astrograph Catalog (UCAC2)

The second USNO CCD Astrograph Catalog, UCAC2 was released in July 2003. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with 2MASS photometry for 99.5% of the sources. The catalog covers the sky area from -90 to +40 degrees declination, going up to +52 in some areas; this completely supersedes the UCAC1 released in 2001. Current epoch positions are obtained from observations with the USNO 8-inch Twin Astrograph equipped with a 4k CCD camera. The precision of the positions are 15 to 70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by utilizing over 140 ground-and space-based catalogs, including Hipparcos/Tycho, the AC2000.2, as well as yet unpublished re-measures of the AGK2 plates and scans from the NPM and SPM plates. Proper motion errors are about 1 to 3 mas/yr for stars to 12th magnitude, and about 4 to 7 mas/yr for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.Comment: accepted by AJ, AAS LaTeX, 14 figures, 10 table

Interferometric Astrometry of the Low-mass Binary Gl 791.2 (= HU Del) Using Hubble Space Telescope Fine Guidance Sensor 3: Parallax and Component Masses

With fourteen epochs of fringe tracking data spanning 1.7y from Fine Guidance Sensor 3 we have obtained a parallax (pi_abs=113.1 +- 0.3 mas) and perturbation orbit for Gl 791.2A. Contemporaneous fringe scanning observations yield only three clear detections of the secondary on both interferometer axes. They provide a mean component magnitude difference, Delta V = 3.27 +- 0.10. The period (P = 1.4731 yr) from the perturbation orbit and the semi-major axis (a = 0.963 +- 0.007 AU) from the measured component separations with our parallax provide a total system mass M_A + M_B = 0.412 +- 0.009 M_sun. Component masses are M_A=0.286 +- 0.006 M_sun and M_B = 0.126 +- 0.003 M_sun. Gl 791.2A and B are placed in a sparsely populated region of the lower main sequence mass-luminosity relation where they help define the relation because the masses have been determined to high accuracy, with errors of only 2%.Comment: 19 pages, 5 figures. The paper is to appear in August 2000 A