1,579 research outputs found
The Albedos of Kepler's Close-in super-Earths
Exoplanet research focusing on the characterization of super-Earths is
currently limited to those handful targets orbiting bright stars that are
amenable to detailed study. This Letter proposes to look at alternative avenues
to probe the surface and atmospheric properties of this category of planets,
known to be ubiquitous in our galaxy. I conduct Markov Chain Monte Carlo
lightcurve analyses for 97 Kepler close-in
super-Earth candidates with the aim to detect their occultations at visible
wavelengths. Brightness temperatures and geometric albedos in the Kepler
bandpass are constrained for 27 super-Earth candidates. A hierarchical Bayesian
modeling approach is then employed to characterize the population-level
reflective properties of these close-in super-Earths. I find median geometric
albedos in the Kepler bandpass ranging between 0.16 and 0.30, once
decontaminated from thermal emission. These super-Earths geometric albedos are
statistically larger than for hot Jupiters, which have medians ranging
between 0.06 and 0.11. A subset of objects, including Kepler-10b, exhibit
significantly larger albedos (0.4). I argue that a better
understanding of the incidence of stellar irradiation on planetary surface and
atmospheric processes is key to explain the diversity in albedos observed for
close-in super-Earths.Comment: ApJ Letters, in press. 6 pages, 3 figures and 1 tabl
Understanding Trends Associated with Clouds in Irradiated Exoplanets
Unlike previously explored relationships between the properties of hot Jovian
atmospheres, the geometric albedo and the incident stellar flux do not exhibit
a clear correlation, as revealed by our re-analysis of Q0 to Q14 Kepler data.
If the albedo is primarily associated with the presence of clouds in these
irradiated atmospheres, a holistic modeling approach needs to relate the
following properties: the strength of stellar irradiation (and hence the
strength and depth of atmospheric circulation), the geometric albedo (which
controls both the fraction of starlight absorbed and the pressure level at
which it is predominantly absorbed) and the properties of the embedded cloud
particles (which determine the albedo). The anticipated diversity in cloud
properties renders any correlation between the geometric albedo and the stellar
flux to be weak and characterized by considerable scatter. In the limit of
vertically uniform populations of scatterers and absorbers, we use an
analytical model and scaling relations to relate the temperature-pressure
profile of an irradiated atmosphere and the photon deposition layer and to
estimate if a cloud particle will be lofted by atmospheric circulation. We
derive an analytical formula for computing the albedo spectrum in terms of the
cloud properties, which we compare to the measured albedo spectrum of HD
189733b by Evans et al. (2013). Furthermore, we show that whether an optical
phase curve is flat or sinusoidal depends on whether the particles are small or
large as defined by the Knudsen number. This may be an explanation for why
Kepler-7b exhibits evidence for the longitudinal variation in abundance of
condensates, while Kepler-12b shows no evidence for the presence of
condensates, despite the incident stellar flux being similar for both
exoplanets.Comment: Accepted by ApJ (on 29th August 2013). 11 pages, 5 figures, 1 table.
Minor typo in Figure 3c correcte
Rotational Mixing and Lithium Depletion
I review basic observational features in Population I stars which strongly
implicate rotation as a mixing agent; these include dispersion at fixed
temperature in coeval populations and main sequence lithium depletion for a
range of masses at a rate which decays with time. New developments related to
the possible suppression of mixing at late ages, close binary mergers and their
lithium signature, and an alternate origin for dispersion in young cool stars
tied to radius anomalies observed in active young stars are discussed. I
highlight uncertainties in models of Population II lithium depletion and
dispersion related to the treatment of angular momentum loss. Finally, the
origins of rotation are tied to conditions in the pre-main sequence, and there
is thus some evidence that enviroment and planet formation could impact stellar
rotational properties. This may be related to recent observational evidence for
cluster to cluster variations in lithium depletion and a connection between the
presence of planets and stellar lithium depletion.Comment: 6 pages, 1 figure, to appear in proceedings of IAU Symp. 268, in
pres
Emergent Exoplanet Flux: Review of the Spitzer Results
Observations using the Spitzer Space Telescope provided the first detections
of photons from extrasolar planets. Spitzer observations are allowing us to
infer the temperature structure, composition, and dynamics of exoplanet
atmospheres. The Spitzer studies extend from many hot Jupiters, to the hot
Neptune orbiting GJ436. Here I review the current status of Spitzer secondary
eclipse observations, and summarize the results from the viewpoint of what is
robust, what needs more work, and what the observations are telling us about
the physical nature of exoplanet atmospheres.Comment: 11 pages, 8 figures, to appear in Proceedings of IAU Symposium 25
Four families of maximal real algebraic hypersurfaces in
In this paper, we present four families of maximal real algebraic
hypersurfaces of even degree in constructed using O. Viro's
combinatorial patchworking method. We compare the Euler characteristic of the
real part and the signature of the complex part of double coverings of
ramified over the complex part of the constructed real
algebraic hypersurfaces. We prove that these invariants are not necessarily
equal and can even be asymptotically different.Comment: 56 pages, 15 figure
Education and "e-Inclusion": Supranational Goals and Local Productions. From European Public Policies to Aix-Marseille's Projects
International audienc
Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b
Mapping distant worlds is the next frontier for exoplanet infrared photometry
studies. Ultimately, constraining spatial and temporal properties of an
exoplanet atmosphere will provide further insight into its physics. For
tidally-locked hot Jupiters that transit and are eclipsed by their host star,
the first steps are now possible.
Our aim is to constrain an exoplanet's shape, brightness distribution (BD)
and system parameters from its light curve. Notably, we rely on the eclipse
scanning.
We use archived Spitzer 8-{\mu}m data of HD189733 (6 transits, 8 secondary
eclipses, and a phase curve) in a global MCMC procedure for mitigating
systematics. We also include HD189733's out-of-transit radial velocity
measurements.
We find a 6-{\sigma} deviation from the expected occultation of a
uniformly-bright disk. This deviation emerges mainly from HD189733b's thermal
pattern, not from its shape. We indicate that the correlation of the orbital
eccentricity, e, and BD (uniform time offset) does also depend on the stellar
density, \rho*, and the impact parameter, b (e-b-\rho*-BD correlation). For
HD189733b, we find that relaxing the e-constraint and using more complex BDs
lead to lower stellar/planetary densities and a more localized and
latitudinally-shifted hot spot. We obtain an improved constraint on the upper
limit of HD189733b's orbital eccentricity, e<0.011 (95%), when including the RV
measurements.
Our study provides new insights into the analysis of exoplanet light curves
and a proper framework for future eclipse-scanning observations. Observations
of the same exoplanet at different wavelengths will improve the constraints on
its system parameters while ultimately yielding a large-scale time-dependent 3D
map of its atmosphere. Finally, we discuss the perspective of extending our
method to observations in the visible, in particular to better understand
exoplanet albedos.Comment: Accepted for publication in A&A. Final version will be available soon
at http://www.aanda.org by Free Open Acces
The Eccentricity Distribution of Short-Period Planet Candidates Detected by Kepler in Occultation
We characterize the eccentricity distribution of a sample of ~50 short-period
planet candidates using transit and occultation measurements from NASA's Kepler
Mission. First, we evaluate the sensitivity of our hierarchical Bayesian
modeling and test its robustness to model misspecification using simulated
data. When analyzing actual data assuming a Rayleigh distribution for
eccentricity, we find that the posterior mode for the dispersion parameter is
. We find that a two-component Gaussian
mixture model for and provides a better model
than either a Rayleigh or Beta distribution. Based on our favored model, we
find that of planet candidates in our sample come from a population
with an eccentricity distribution characterized by a small dispersion
(), and come from a population with a larger dispersion
(). Finally, we investigate how the eccentricity distribution
correlates with selected planet and host star parameters. We find evidence that
suggests systems around higher metallicity stars and planet candidates with
smaller radii come from a more complex eccentricity distribution.Comment: Accepted for publication in Ap
Refraction in exoplanet atmospheres: Photometric signatures, implications for transmission spectroscopy, and search in Kepler data
Refraction deflects photons that pass through atmospheres, which affects
transit light curves. Refraction thus provides an avenue to probe physical
properties of exoplanet atmospheres and to constrain the presence of clouds and
hazes. In addition, an effective surface can be imposed by refraction, thereby
limiting the pressure levels probed by transmission spectroscopy. The main
objective of the paper is to model the effects of refraction on photometric
light curves for realistic planets and to explore the dependencies on
atmospheric physical parameters. We also explore under which circumstances
transmission spectra are significantly affected by refraction. Finally, we
search for refraction signatures in photometric residuals in Kepler data. We
use the model of Hui & Seager (2002) to compute deflection angles and
refraction transit light curves, allowing us to explore the parameter space of
atmospheric properties. The observational search is performed by stacking large
samples of transit light curves from Kepler. We find that out-of-transit
refraction shoulders are the most easily observable features, which can reach
peak amplitudes of ~10 parts per million (ppm) for planets around Sun-like
stars. More typical amplitudes are a few ppm or less for Jovians and at the
sub-ppm level for super-Earths. Interestingly, the signal-to-noise ratio of any
refraction residuals for planets orbiting Sun-like hosts are expected to be
similar for planets orbiting red dwarfs. We also find that the maximum depth
probed by transmission spectroscopy is not limited by refraction for weakly
lensing planets, but that the incidence of refraction can vary significantly
for strongly lensing planets. We find no signs of refraction features in the
stacked Kepler light curves, which is in agreement with our model predictions.Comment: Accepted for publication in A&
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