2,375 research outputs found
Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
We present a technique to extract radial velocity measurements from echelle
spectrograph observations of rapidly rotating stars ( km
s). This type of measurement is difficult because the line widths of
such stars are often comparable to the width of a single echelle order. To
compensate for the scarcity of lines and Doppler information content, we have
developed a process that forward-models the observations, fitting the radial
velocity shift of the star for all echelle orders simultaneously with the
echelle blaze function. We use our technique to extract radial velocity
measurements from a sample of rapidly rotating A- and B-type stars used as
calibrator stars observed by the California Planet Survey observations. We
measure absolute radial velocities with a precision ranging from 0.5-2.0 km
s per epoch for more than 100 A- and B-type stars. In our sample of 10
well-sampled stars with radial velocity scatter in excess of their measurement
uncertainties, three of these are single-lined binaries with long observational
baselines. From this subsample, we present detections of two previously unknown
spectroscopic binaries and one known astrometric system. Our technique will be
useful in measuring or placing upper limits on the masses of sub-stellar
companions discovered by wide-field transit surveys, and conducting future
spectroscopic binarity surveys and Galactic space-motion studies of massive
and/or young, rapidly-rotating stars.Comment: Accepted to ApJ
Exploring the Variable Sky with LINEAR. I. Photometric Recalibration with the Sloan Digital Sky Survey
We describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the overlapping ~10,000 deg^2 of sky to recalibrate LINEAR photometry and achieve errors of 0.03 mag for sources not limited by photon statistics with errors of 0.2 mag at r ~ 18. With its 200 observations per object on average, LINEAR data provide time domain information for the brightest four magnitudes of the SDSS survey. At the same time, LINEAR extends the deepest similar wide-area variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly discuss the properties of about 7000 visually confirmed periodic variables, dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary stars, and analyze their distribution in optical and infrared color-color diagrams. The LINEAR data set is publicly available from the SkyDOT Web site
SDSSJ14584479+3720215: A Benchmark JHK Blazar Light Curve from the 2MASS Calibration Scans
Active galactic nuclei (AGNs) are well-known to exhibit flux variability
across a wide range of wavelength regimes, but the precise origin of the
variability at different wavelengths remains unclear. To investigate the
relatively unexplored near-IR variability of the most luminous AGNs, we conduct
a search for variability using well sampled JHKs-band light curves from the
2MASS survey calibration fields. Our sample includes 27 known quasars with an
average of 924 epochs of observation over three years, as well as one
spectroscopically confirmed blazar (SDSSJ14584479+3720215) with 1972 epochs of
data. This is the best-sampled NIR photometric blazar light curve to date, and
it exhibits correlated, stochastic variability that we characterize with
continuous auto-regressive moving average (CARMA) models. None of the other 26
known quasars had detectable variability in the 2MASS bands above the
photometric uncertainty. A blind search of the 2MASS calibration field light
curves for AGN candidates based on fitting CARMA(1,0) models (damped-random
walk) uncovered only 7 candidates. All 7 were young stellar objects within the
{\rho} Ophiuchus star forming region, five with previous X-ray detections. A
significant {\gamma}-ray detection (5{\sigma}) for the known blazar using 4.5
years of Fermi photon data is also found. We suggest that strong NIR
variability of blazars, such as seen for SDSSJ14584479+3720215, can be used as
an efficient method of identifying previously-unidentified {\gamma}-ray
blazars, with low contamination from other AGN.Comment: 6 pages, 3 figures, ApJ Accepte
Transit Timing Observations of the Extrasolar Hot-Neptune Planet GL 436b
Gliese 436 is an M dwarf with a mass of 0.45 Msun and hosts the extrasolar
planet GL 436b [3, 6, 7, 2], which is currently the least massive transiting
planet with a mass of ~23.17 Mearth [10], and the only planet known to transit
an M dwarf. GL 436b represents the first transiting detection of the class of
extrasolar planets known as "Hot Neptunes" that have masses within a few times
that of Neptune's mass (~17 Mearth) and orbital semimajor axis <0.1 AU about
the host star. Unlike most other known transiting extrasolar planets, GL 436b
has a high eccentricity (e~0.16). This brings to light a new parameter space
for habitability zones of extrasolar planets with host star masses much smaller
than typical stars of roughly a solar mass. This unique system is an ideal
candidate for orbital perturbation and transit-time variation (TTV) studies to
detect smaller, possibly Earth-mass planets in the system. In April 2008 we
began a long-term intensive campaign to obtain complete high-precision light
curves using the Apache Point Observatory's 3.5-meter telescope, NMSU's 1-meter
telescope (located at APO), and Sommers Bausch Observatory's 24" telescope.
These light curves are being analyzed together, along with amateur and other
professional astronomer observations. Results of our analysis are discussed.
Continued measurements over the next few years are needed to determine if
additional planets reside in the system, and to study the impact of other
manifestations on the light curves, such as star spots and active regions.Comment: 4 pages, 3 figures. To appear in "Proceedings of the 15th Cambridge
Workshop on Cool Stars, Stellar Systems and the Sun", 2009, AIP Conference
Proceedings vol. 1094, ed. Eric Stempel
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