TY - JOUR
T1 - The high albedo of the hot Jupiter Kepler-7b
AU - Demory, Brice Olivier
AU - Seager, Sara
AU - Madhusudhan, Nikku
AU - Kjeldsen, Hans
AU - Christensen-Dalsgaard, Jørgen
AU - Gillon, Michal
AU - Rowe, Jason F.
AU - Welsh, William F.
AU - Adams, Elisabeth R.
AU - Dupree, Andrea
AU - McCarthy, Don
AU - Kulesa, Craig
AU - Borucki, William J.
AU - Koch, David G.
PY - 2011/7/1
Y1 - 2011/7/1
N2 - Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44 ± 5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32 ± 0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase light curve with an amplitude of 42 ± 4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. First, we interpret the Kepler-7b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.
AB - Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44 ± 5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32 ± 0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase light curve with an amplitude of 42 ± 4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. First, we interpret the Kepler-7b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.
KW - planetary systems
KW - stars: individual (Kepler-7, KIC 5780885, 2MASS 19141956+4105233)
KW - techniques: photometric
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U2 - 10.1088/2041-8205/735/1/L12
DO - 10.1088/2041-8205/735/1/L12
M3 - Article
AN - SCOPUS:79960901646
SN - 2041-8205
VL - 735
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L12
ER -