170 research outputs found
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
Finding cool subdwarfs using a V-J reduced proper-motion diagram: Stellar parameters for 91 candidates
We present the results of a search for cool subdwarfs for which our
candidates were drawn from a V-J reduced proper-motion diagram constructed by
Salim & Gould (2002). Kinematic (U, V, and W) and self-consistent stellar
parameters (Teff, log g, [Fe/H], and V_t) are derived for 91 candidate
subdwarfs based on high resolution spectra. The observed stars span 3900K <
Teff < 6200K and -2.63 < [Fe/H] < 0.25 including only 3 giants (log g < 4.0).
Of the sample, 77 stars have MgH lines present in their spectra. With more than
56% of our candidate subdwarfs having [Fe/H] < -1.5, we show that the V-J
reduced proper-motion diagram readily identifies metal-poor stars.Comment: PASP (in press
The Southern Proper Motion Program III. A Near-Complete Catalog to V=17.5
We present the third installment of the Yale/San Juan Southern Proper Motion
Catalog, SPM3. Absolute proper motions, positions, and photographic B,V
photometry are given for roughly 10.7 million objects, primarily stars, down to
a magnitude of V=17.5. The Catalog covers an irregular area of 3700 square
degrees, between the declinations of -20 and -45 degrees, excluding the
Galactic plane. The proper-motion precision, for well-measured stars, is
estimated to be 4.0 mas/yr. Unlike previous releases of the SPM Catalog, the
proper motions are on the International Celestial Reference System by way of
Hipparcos Catalog stars, and have an estimated systematic uncertainty of 0.4
mas/yr. The SPM3 Catalog is available via electronic
transfer,(http://www.astro.yale.edu/astrom/) As an example of the potential of
the SPM3 proper motions, we examine the Galactocentric velocities of a group of
metal-poor, main-sequence A stars. The majority of these exhibit thick-disk
kinematics, lending support to their interpretation as thick-disk blue
stragglers, as opposed to being an accreted component.Comment: 23 pages, 10 figures, accepted for publication in Astronomical
Journa
Detection of radiation pressure acting on 2009 BD
We report the direct detection of radiation pressure on the asteroid 2009 BD,
one of the smallest multi-opposition near-Earth objects currently known, with H
~ 28.4. Under the purely gravitational model of NEODyS the object is currently
considered a possible future impactor, with impact solutions starting in 2071.
The detection of a radiation-related acceleration allows us to estimate an Area
to Mass Ratio (AMR) for the object, that can be converted (under some
assumptions) into a range of possible values for its average density. Our
result AMR = (2.97 \pm 0.33) x 10^(-4) m^2 kg^(-1) is compatible with the
object being of natural origin, and it is narrow enough to exclude a man-made
nature. The possible origin of this object, its future observability, and the
importance of radiation pressure in the impact monitoring process, are also
discussed.Comment: To be submitted for refereed publication. Preliminary analysis based
on the 2009-2010 data, published on arXiv because of the current
observability window of the targe
Substellar Companions to Main Sequence Stars: No Brown Dwarf Desert at Wide Separations
We use three field L and T dwarfs which were discovered to be wide companions
to known stars by the Two Micron All-Sky Survey (2MASS) to derive a preliminary
brown dwarf companion frequency. Observed L and T dwarfs indicate that brown
dwarfs are not unusually rare as wide (Delta >1000 A.U.) systems to F-M0
main-sequence stars (M>0.5M_sun, M_V<9.5), even though they are rare at close
separation (Delta <3 A.U.), the ``brown dwarf desert.'' Stellar companions in
these separation ranges are equally frequent, but brown dwarfs are >~ 10 times
as frequent for wide than close separations. A brown dwarf wide-companion
frequency as low as the 0.5% seen in the brown dwarf desert is ruled out by
currently-available observations.Comment: ApJL, in pres
Two nearby M dwarf binaries from the Two Micron All Sky Survey
We report the discovery of two binary M dwarf systems in the immediate solar neighbourhood using the Two Micron All Sky Survey (2MASS). The first is an M6.5 companion to the nearby G star HD 86728 (Gl 376). The known properties of HD 86728 indicate that the M dwarf (Gl 376B) is old, metal-rich and only 14.9 parsec away. The M dwarf is highly active, with both Hα and X-ray emission. Thus, Gl 376B offers the opportunity to study an old, bright, active M dwarf with known metallicity, age and luminosity. We show that it is probable that Gl 376B is itself an unresolved pair. The other system consists of an M6.5 and an M8 dwarf with 14.5 arcsec separation. We estimate a distance of ∼16 parsec for this very low-mass pair. Stronger activity is observed in the M6.5 dwarf, supporting evidence that chromospheric activity is weakening near the hydrogen-burning limit
The Southern Proper Motion Program IV. The SPM4 Catalog
We present the fourth installment of the Yale/San Juan Southern Proper Motion
Catalog, SPM4. The SPM4 contains absolute proper motions, celestial
coordinates, and (B,V) photometry for over 103 million stars and galaxies
between the south celestial pole and -20 deg declination. The catalog is
roughly complete to V=17.5 and is based on photographic and CCD observations
taken with the Yale Southern Observatory's double-astrograph at Cesco
Observatory in El Leoncito, Argentina. The proper-motion precision, for
well-measured stars, is estimated to be 2 to 3 mas/yr, depending on the type of
second-epoch material. At the bright end, proper motions are on the
International Celestial Reference System by way of Hipparcos Catalog stars,
while the faint end is anchored to the inertial system using external galaxies.
Systematic uncertainties in the absolute proper motions are on the order of 1
mas/yr.Comment: 34 pages, 8 figures, 3 tables; accepted for publication in AJ; note -
modified author list and acknowledgements sectio
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