465 research outputs found
Which Radial Velocity Exoplanets Have Undetected Outer Companions?
(Abridged) The observed radial velocity (RV) eccentricity distribution for
extrasolar planets in single-planet systems shows that a significant fraction
of planets are eccentric (). Here we investigate the effects on an RV
planet's eccentricity produced by undetected outer companions. We have carried
out Monte Carlo simulations of mock RV data to understand this effect and
predict its impact on the observed distribution. We first quantify the
statistical effect of undetected outer companions and show that this alone
cannot explain the observed distribution. We then modify the simulations to
consist of two populations, one of zero-eccentricity planets in double-planet
systems and the other of single planets drawn from an eccentric distribution.
Our simulations show that a good fit to the observed distribution is obtained
with 45% zero-eccentricity double-planets and 55% single eccentric planets.
Matching the observed distribution allows us to determine the probability that
a known RV planet's orbital eccentricity has been biased by an undetected
wide-separation companion. Our simulations show that moderately-eccentric
planets, with and , have a and probability, respectively, of having an undetected outer companion. We
encourage both high-contrast direct imaging and RV follow-up surveys of known
RV planets with moderate eccentricities to test our predictions and look for
previously undetected outer companions.Comment: 23 pages (12 text, 2 tables, 9 figures). Accepted to the
Astrophysical Journal 30 June 200
LSST: Comprehensive NEO Detection, Characterization, and Orbits
(Abridged) The Large Synoptic Survey Telescope (LSST) is currently by far the
most ambitious proposed ground-based optical survey. Solar System mapping is
one of the four key scientific design drivers, with emphasis on efficient
Near-Earth Object (NEO) and Potentially Hazardous Asteroid (PHA) detection,
orbit determination, and characterization. In a continuous observing campaign
of pairs of 15 second exposures of its 3,200 megapixel camera, LSST will cover
the entire available sky every three nights in two photometric bands to a depth
of V=25 per visit (two exposures), with exquisitely accurate astrometry and
photometry. Over the proposed survey lifetime of 10 years, each sky location
would be visited about 1000 times. The baseline design satisfies strong
constraints on the cadence of observations mandated by PHAs such as closely
spaced pairs of observations to link different detections and short exposures
to avoid trailing losses. Equally important, due to frequent repeat visits LSST
will effectively provide its own follow-up to derive orbits for detected moving
objects. Detailed modeling of LSST operations, incorporating real historical
weather and seeing data from LSST site at Cerro Pachon, shows that LSST using
its baseline design cadence could find 90% of the PHAs with diameters larger
than 250 m, and 75% of those greater than 140 m within ten years. However, by
optimizing sky coverage, the ongoing simulations suggest that the LSST system,
with its first light in 2013, can reach the Congressional mandate of cataloging
90% of PHAs larger than 140m by 2020.Comment: 10 pages, color figures, presented at IAU Symposium 23
The Blue Tip of the Stellar Locus: Measuring Reddening with the SDSS
We present measurements of reddening due to dust using the colors of stars in
the Sloan Digital Sky Survey (SDSS). We measure the color of main sequence
turn-off stars by finding the "blue tip" of the stellar locus: the prominent
blue edge in the distribution of stellar colors. The method is sensitive to
color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g,
g-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present
maps of the blue tip colors in each of these bands over the entire SDSS
footprint, including the new dusty southern Galactic cap data provided by the
SDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et
al. (1989) reddening laws, but are well described by a Fitzpatrick (1999)
reddening law with R_V = 3.1. The SFD dust map is found to trace the dust well,
but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r,
r-i, and i-z, largely due to the adopted reddening law. In select dusty regions
of the sky, we find evidence for problems in the SFD temperature correction. A
dust map normalization difference of 15% between the Galactic north and south
sky may be due to these dust temperature errors.Comment: 18 pages, 22 figure
Differential algebras on kappa-Minkowski space and action of the Lorentz algebra
We propose two families of differential algebras of classical dimension on
kappa-Minkowski space. The algebras are constructed using realizations of the
generators as formal power series in a Weyl super-algebra. We also propose a
novel realization of the Lorentz algebra so(1,n-1) in terms of Grassmann-type
variables. Using this realization we construct an action of so(1,n-1) on the
two families of algebras. Restriction of the action to kappa-Minkowski space is
covariant. In contrast to the standard approach the action is not Lorentz
covariant except on constant one-forms, but it does not require an extra
cotangent direction.Comment: 16 page
Differential structure on kappa-Minkowski space, and kappa-Poincare algebra
We construct realizations of the generators of the -Minkowski space
and -Poincar\'{e} algebra as formal power series in the -adic
extension of the Weyl algebra. The Hopf algebra structure of the
-Poincar\'{e} algebra related to different realizations is given. We
construct realizations of the exterior derivative and one-forms, and define a
differential calculus on -Minkowski space which is compatible with the
action of the Lorentz algebra. In contrast to the conventional bicovariant
calculus, the space of one-forms has the same dimension as the
-Minkowski space.Comment: 20 pages. Accepted for publication in International Journal of Modern
Physics
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