4,011 research outputs found
Choice of Observing Schedules for Astrometric Planet Searches
The Space Interferometry Mission (SIM) will make precise astrometric
measurements that can be used to detect planets around nearby stars. Since
observational time will be extremely valuable, it is important to consider how
the choice of the observing schedule influences the efficiency of SIM planet
searches. We have conducted Monte Carlo simulations of astrometric observations
to understand the effects of different scheduling algorithms. We find that the
efficiency of planet searches is relatively insensitive to the observing
schedule for most reasonable observing schedules.Comment: 29 pages, 9 figures, 2 tables, to be published in PAS
Lag of Low-Energy Photons in an X-ray Burst Oscillation: Doppler Delays
Numerous X-ray bursts show strong oscillations in their flux at several
hundred Hz as revealed by RXTE. Analyzing one such oscillation from the X-ray
binary Aql X-1, I find that low energy photons (3.5-5.7 keV) lag high energy
photons (>5.7 keV) by approximately 1 radian. The oscillations are thought to
be produced by hot spots on the spinning neutron star. The lags can then be
explained by a Doppler shifting of emission from the hot spots; higher energy
photons being emitted earlier in the spin phase as the spot approaches the
observer. A quantitative test of this simple model shows a remarkable agreement
with the data. Similar low energy lags have been measured in kilohertz
quasi-periodic oscillations and in the accreting millisecond pulsar SAX
J1808.4-3658. A Doppler delay mechanism may be at work there as well.Comment: accepted ApJ Letter
The Effects of Multiple Companions on the Efficiency of the SIM Planet Searches
The Space Interferometry Mission (SIM) is expected to make precise
astrometric measurements that can be used to detect low mass planets around
nearby stars. Since most nearby stars are members of multiple star systems,
many stars will have a measurable acceleration due to their companion, which
must be included when solving for astrometric parameters and searching for
planetary perturbations. Additionally, many of the stars with one radial
velocity planet show indications of additional planets. Therefore, astrometric
surveys like SIM must be capable of detecting planets and measuring orbital
parameters in systems with multiple stellar and/or planetary companions. We
have conducted Monte Carlo simulations to investigate how the presence of
multiple companions affects the sensitivity of an astrometric survey such as
SIM. We find that the detection efficiency for planets in wide binary systems
is relatively unaffected by the presence of a binary companion, if the
planetary orbital period is less than half the duration of the astrometric
survey. For longer orbital periods, there are significant reductions in the
sensitivity of an astrometric survey. Additionally, we find that the signal
required to detect a planet can be increased significantly due to the presence
of an additional planet orbiting the same star. Fortunately, adding a modest
number of precision radial velocity observations significantly improves the
sensitivity for many multiple planet systems. Thus, the combination of radial
velocity observations and astrometric observations by SIM will be a
particularly valuable for studying multiple planet systems.Comment: 45 pages, 16 figures, 1 table, to appear in PAS
Parallel Algorithm for Solving Kepler's Equation on Graphics Processing Units: Application to Analysis of Doppler Exoplanet Searches
[Abridged] We present the results of a highly parallel Kepler equation solver
using the Graphics Processing Unit (GPU) on a commercial nVidia GeForce 280GTX
and the "Compute Unified Device Architecture" programming environment. We apply
this to evaluate a goodness-of-fit statistic (e.g., chi^2) for Doppler
observations of stars potentially harboring multiple planetary companions
(assuming negligible planet-planet interactions). We tested multiple
implementations using single precision, double precision, pairs of single
precision, and mixed precision arithmetic. We find that the vast majority of
computations can be performed using single precision arithmetic, with selective
use of compensated summation for increased precision. However, standard single
precision is not adequate for calculating the mean anomaly from the time of
observation and orbital period when evaluating the goodness-of-fit for real
planetary systems and observational data sets. Using all double precision, our
GPU code outperforms a similar code using a modern CPU by a factor of over 60.
Using mixed-precision, our GPU code provides a speed-up factor of over 600,
when evaluating N_sys > 1024 models planetary systems each containing N_pl = 4
planets and assuming N_obs = 256 observations of each system. We conclude that
modern GPUs also offer a powerful tool for repeatedly evaluating Kepler's
equation and a goodness-of-fit statistic for orbital models when presented with
a large parameter space.Comment: 19 pages, to appear in New Astronom
Observational Constraints on Trojans of Transiting Extrasolar Planets
Theoretical studies predict that Trojans are likely a frequent byproduct of
planet formation and evolution. We present a novel method of detecting Trojan
companions to transiting extrasolar planets which involves comparing the time
of central eclipse with the time of the stellar reflex velocity null. We
demonstrate that this method offers the potential to detect terrestrial-mass
Trojans using existing ground-based observatories. This method rules out Trojan
companions to HD 209458b and HD 149026b more massive than ~13 Earth masses and
\~25 Earth masses at a 99.9% confidence level. Such a Trojan would be
dynamically stable, would not yet have been detected by photometric or
spectroscopic monitoring, and would be unrecognizable from radial velocity
observations alone. We outline the future prospects for this method, and show
that the detection of a "Hot Trojan" of any mass would place a significant
constraint on theories of orbital migration.Comment: 6 pages, 2 figures, 1 table, accepted to ApJL. Added references, new
transiting planets to table; minor correction
- …