2,017 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
figure
An Objective Bayesian Analysis of Life's Early Start and Our Late Arrival
Life emerged on the Earth within the first quintile of its habitable window,
but a technological civilization did not blossom until its last. Efforts to
infer the rate of abiogenesis, based on its early emergence, are frustrated by
the selection effect that if the evolution of intelligence is a slow process,
then life's early start may simply be a prerequisite to our existence, rather
than useful evidence for optimism. In this work, we interpret the chronology of
these two events in a Bayesian framework, extending upon previous work by
considering that the evolutionary timescale is itself an unknown that needs to
be jointly inferred, rather than fiducially set. We further adopt an objective
Bayesian approach, such that our results would be agreed upon even by those
using wildly different priors for the rates of abiogenesis and evolution -
common points of contention for this problem. It is then shown that the
earliest microfossil evidence for life indicates that the rate of abiogenesis
is at least 2.8 times more likely to be a typically rapid process, rather than
a slow one. This modest limiting Bayes factor rises to 8.7 if we accept the
more disputed evidence of C13 depleted zircon deposits (Bell et al. 2015). For
intelligence evolution, it is found that a rare-intelligence scenario is
slightly favored at 3:2 betting odds. Thus, if we re-ran Earth's clock, one
should statistically favor life to frequently re-emerge, but intelligence may
not be as inevitable
How to Weigh a Star Using a Moon
We show that for a transiting exoplanet accompanied by a moon which also
transits, the absolute masses and radii of the star, planet and moon are
determinable. For a planet-star system, it is well known that the density of
the star is calculable from the lightcurve by manipulation of Kepler's Third
Law. In an analogous way, the planetary density is calculable for a planet-moon
system which transits a star, and thus the ratio-of-densities is known. By
combining this ratio with the observed ratio-of-radii and the radial velocity
measurements of the system, we show that the absolute dimensions of the star
and planet are determinable. This means such systems could be used as
calibrators of stellar evolution. The detection of dynamical effects, such as
transit timing variations, allows the absolute mass of the moon to be
determined as well, which may be combined with the radius to infer the
satellite's composition.Comment: 5 pages; Accepted in MNRA
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