2,634 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
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
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
An Analysis of Jitter and Transit Timing Variations in the HAT-P-13 System
If the two planets in the HAT-P-13 system are coplanar, the orbital states
provide a probe of the internal planetary structure. Previous analyses of
radial velocity and transit timing data of the system suggested that the
observational constraints on the orbital states were rather small. We reanalyze
the available data, treating the jitter as an unknown MCMC parameter, and find
that a wide range of jitter values are plausible, hence the system parameters
are less well constrained than previously suggested. For slightly increased
levels of jitter () the eccentricity of the inner planet
can be in the range , the period and eccentricity of the
outer planet can be days and
respectively, while the relative pericenter alignment, , of the planets
can take essentially any value . It is
therefore difficult to determine whether and have evolved to
a fixed-point state or a limit cycle, or to use to probe the
internal planetary structure. We perform various transit timing variation (TTV)
analyses, demonstrating that current constraints merely restrict
, and rule out relative planetary inclinations within of , but that future observations could
significantly tighten the restriction on both these parameters. We demonstrate
that TTV profiles can readily distinguish the theoretically favored
inclinations of i_{rel}=0^{\circ}\,&\,45^{\circ}, provided that sufficiently
precise and frequent transit timing observations of HAT-P-13b can be made close
to the pericenter passage of HAT-P-13c. We note the relatively high probability
that HAT-P-13c transits and suggest observational dates and strategies.Comment: Published in Ap
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