STATISTICAL ECLIPSES OF CLOSE-INKEPLERSUB-SATURNS

Abstract

We present a method to detect small atmospheric signals in Kepler's planet candidate light curves by averaging light curves for multiple candidates with similar orbital and physical characteristics. Our statistical method allows us to measure unbiased physical properties of Kepler's planet candidates, even for candidates whose individual signal-to-noise precludes the detection of their secondary eclipse. We detect a secondary eclipse depth of 3.83 +1.10 −1.11 ppm for a group of 31 sub-Saturn (R < 6R ⊕ ) planet candidates with the greatest potential for a reflected light signature ((R p /a) 2 > 10 ppm). Including Kepler-10b in this group increases the depth to 5.08 +0.71 −0.72 ppm. For a control group with (R p /a) 2 < 1 ppm, we find a depth of 0.36 ± 0.37 ppm, consistent with no detection. We also analyze the light curve of Kepler-10b and find an eclipse depth of 7.08 ± 1.06 ppm. If the eclipses are due solely to reflected light, this corresponds to a geometric albedo of 0.22 ± 0.06 for our group of close-in sub-Saturns, 0.37 ± 0.05 if including Kepler-10b in the group, and 0.60 ± 0.09 for Kepler-10b alone. Including a thermal emission model does not change the geometric albedo appreciably, assuming A B = (2/3) * A g . Our result for Kepler-10b is consistent with previous works. Our result for close-in sub-Saturns shows that Kepler-10b is unusually reflective, but our analysis is consistent with the results of Demory (2014) for super-Earths. Our results also indicate that hot Neptunes are typically more reflective than hot Jupiters.

Discovery of the secondary eclipse of HAT-P-11 b

“…However, Kepler-10 b might also just represent a statistical outlier; after all the geometric albedos of Solar System rocky planets are small, except for Venus with its dense atmosphere. Finally, we note that in contrast to HAT-P-11 b none of the exoplanets in the samples of Sheets & Deming (2014), Esteves et al (2015), and Angerhausen et al (2015) shows a significant eccentricity. Whether this has an effect on the albedo, however, remains to be determined.…”

“…They argue that from the three cases with larger albedos probably only the result of Kepler-10 b with A g = 0.58 ± 0.25 is reliable; interestingly, Kepler-10 b (Batalha et al 2011) is a rather special planet in 4 http://nssdc.gsfc.nasa.gov/planetary/factsheet/ their sample with a very short period, small radius, and rocky composition, probably not having an atmosphere. Furthermore, Sheets & Deming (2014) published an analysis of 31 sub-Saturn Kepler candidate planets and determine the average albedo of the sample. Excluding Kepler-10 b from their sample, they find a geometric albedo of A g = 0.22 ± 0.06, whereas Kepler-10 b represents an outlier with A g = 0.60 ± 0.09.…”

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf Hip 116454

“…The model suggests that HIP 116454 b has a 1.8 R ⊕ core with virtually all of the planet's mass, surrounded by a gaseous envelope with thickness 0.35 R ⊕ , and a radiative upper atmosphere also with thickness 0.35 R ⊕ . Using different assumptions to calculate the equilibrium temperature, like imperfect heat distribution and a nonzero albedo (for instance, the value of Sheets & Deming 2014), and different assumptions about the envelope's composition and age does not change the calculated thickness and mass of the gaseous envelope by more than a factor of two. We note that this envelope fraction is consistent with the population of Kepler super-Earth and sub-Neptune-sized planets studied by Wolfgang & Lopez (2014), who found the envelope fraction of these candidates to be distributed around 1% with a scatter of 0.5 dex.…”

Refraction in exoplanet atmospheres

“…Transits with too few points are removed and the remaining stacked transits are refitted. The accuracy of the photometric baseline for each transit is checked using two tests (Sheets & Deming 2014). Firstly, a line is fitted to the first interval and projected to the other side of transit.…”

“…Light curve fits are then performed for each KOI to the stack of the transits that passed both tests. Finally, the deviations of the residuals are tested for systematics using the red-noise test presented in Sheets & Deming (2014). If the noise is solely composed of statistical fluctuations, such as for photon counting, then log(σ) ∝ −0.5 log(N), where σ is the sample standard deviation and N is the size of the bins.…”