797 research outputs found
LUNA: An algorithm for generating dynamic planet-moon transits
It has been previously shown that moons of extrasolar planets may be
detectable with the Kepler Mission, for moon masses above ~0.2 Earth masses
Kipping et al. 2009c. Transit timing effects have been formerly identified as a
potent tool to this end, exploiting the dynamics of the system. In this work,
we explore the simulation of transit light curves of a planet plus a single
moon including not only the transit timing effects but also the light curve
signal of the moon itself. We introduce our new algorithm, LUNA, which produces
transit light curves for both bodies, analytically accounting for shadow
overlaps, stellar limb darkening and planet-moon dynamical motion. By building
the dynamics into the core of LUNA, the routine automatically accounts for
transit timing/duration variations and ingress/egress asymmetries for not only
the planet, but also the moon. We then generate some artificial data for two
feasibly detectable hypothetical systems of interest: a i) prograde and ii)
retrograde Earth-like moon around a habitable-zone Neptune for a M-dwarf
system. We fit the hypothetical systems using LUNA and demonstrate the
feasibility of detecting these cases with Kepler photometry.Comment: Accepted in MNRAS, 2011 May 16. Minor typos corrected (thanks to S.
Awiphan
Binning is sinning: morphological light-curve distortions due to finite integration time
We explore how finite integration times or equivalently temporal binning
induces morphological distortions to the transit light-curve. These
distortions, if uncorrected for, lead to the retrieval of erroneous system
parameters and may even lead to some planetary candidates being rejected as
ostensibly unphysical. We provide analytic expressions for estimating the
disturbance to the various light-curve parameters as a function of the
integration time. These effects are particularly crucial in light of the
long-cadence photometry often used for discovering new exoplanets by, for
example, Convection Rotation and Planetary Transits (COROT) and the Kepler
Mission (8.5 and 30 min). One of the dominant effects of long integration times
is a systematic underestimation of the light-curve-derived stellar density,
which has significant ramifications for transit surveys. We present a
discussion of numerical integration techniques to compensate for the effects
and produce expressions to quickly estimate the errors of such techniques, as a
function of integration time and numerical resolution. This allows for an
economic choice of resolution before attempting fits of long-cadence
light-curves. We provide a comparison of the short- and long-cadence
light-curves of TrES-2b and show that the retrieved transit parameters are
consistent using the techniques discussed here.Comment: Long delayed upload of the MNRAS accepted version, 10 pages, 3
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