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Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
Kirkpatrick, J. Davy; Burgasser, Adam J.; Gizis, John E. +15 more
Trigonometric parallax determinations are presented for 28 late-type dwarfs and brown dwarfs, including eight M dwarfs with spectral types between M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*) and/or near-IR wavelengths (JHK) is presented for these objects and fo…
Absolute Dimensions of the M-Type Eclipsing Binary YY Geminorum (Castor C): A Challenge to Evolutionary Models in the Lower Main Sequence
Torres, Guillermo; Ribas, Ignasi
We present new spectroscopic observations of the detached late-type double-lined eclipsing binary YY Geminorum (P=0.814 day), a member of the Castor sextuple system and one of the benchmarks for the comparison between observations and stellar evolution theory in the lower main sequence. In addition, we have reanalyzed existing light curves in seve…
Exploring the Full Stellar Population of the Upper Scorpius OB Association
Brown, Anthony G. A.; Zinnecker, Hans; Guenther, Eike +2 more
We investigate the stellar population and star formation history of the Upper Scorpius OB association, the most nearby region of recent massive star formation, over the full stellar mass range from 0.1 to 20 Msolar. The first part of this paper describes an extension of our large spectroscopic survey (Preibisch et al., published in 2001…
Post-T Tauri Stars in the Nearest OB Association
Meyer, Michael R.; Mamajek, Eric E.; Liebert, James
We present results of a spectroscopic survey of X-ray- and proper-motion-selected samples of late-type stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the…
The Palomar/MSU Nearby Star Spectroscopic Survey. IV. The Luminosity Function in the Solar Neighborhood and M Dwarf Kinematics
Hawley, Suzanne L.; Gizis, John E.; Reid, I. Neill
We have used new astrometric and spectroscopic observations to refine the volume-complete sample of M dwarfs defined in previous papers in this series. With the addition of Hipparcos astrometry, our revised VC2 sample includes 558 main-sequence stars in 448 systems. Analysis of that data set shows no evidence of any systematic kinematic…
New periodic variables from the Hipparcos epoch photometry
Koen, Chris; Eyer, Laurent
Two selection statistics are used to extract new candidate periodic variables from the epoch photometry of the Hipparcos catalogue. The primary selection criterion is a signal-to-noise ratio. The dependence of this statistic on the number of observations is calibrated using about 30000 randomly permuted Hipparcos data sets. A significance level of…
The Tycho double star catalogue
Makarov, V. V.; Fabricius, C.; Urban, S. E. +3 more
We report the discovery of 13 251 visual double stars, mostly with separations between 0.3 and 1 arcsec, from a dedicated re-reduction of the Tycho data from the star mapper of the ESA Hipparcos satellite. The new doubles are combined with 18 160 WDS systems identified in the Tycho-2two, and 1220 new Tycho-2 doubles, to form the Tycho Double Star …
Discovery of a Substellar Companion to the K2 III Giant ι Draconis
Butler, R. Paul; Fischer, Debra A.; Marcy, Geoffrey W. +3 more
We report precise radial velocity measurements of the K giant ι Dra (HD 137759, HR 5744, HIP 75458), carried out at Lick Observatory, which reveal the presence of a substellar companion orbiting the primary star. A Keplerian fit to the data yields an orbital period of about 536 days and an eccentricity of 0.70. Assuming a mass of 1.05 Msolar<…
The Star Formation History and Spatial Distribution of Stellar Populations in the Ursa Minor Dwarf Spheroidal Galaxy
Aparicio, Antonio; Martínez-Delgado, David; Alonso-García, Javier +1 more
As a part of a project devoted to the study of the Ursa Minor dwarf spheroidal (dSph) galaxy, the star formation history of the galaxy is presented. The analysis uses wide-field photometry, encompassing about 1°×1° (the total covered area being 0.75 deg2), which samples the galaxy out to its tidal radius. Derivation of the star formatio…
WIYN Open Cluster Study. X. The K-Band Magnitude of the Red Clump as a Distance Indicator
Sarajedini, Ata; Grocholski, Aaron J.
In an effort to improve the utility of the helium-burning red clump luminosity as a distance indicator, we explore the sensitivity of the K-band red clump absolute magnitude [MK(RC)] to metallicity and age. We rely upon JK photometry for 14 open clusters and two globular clusters from the Second Incremental Data Release of the Two Micro…