WARM SPITZER OBSERVATIONS OF THREE HOT EXOPLANETS: XO-4b, HAT-P-6b, AND HAT-P-8b

We analyze Warm Spitzer/Infrared Array Camera observations of the secondary eclipses of three planets, XO-4b, HAT-P-6b, and HAT-P-8b. We measure secondary eclipse amplitudes at 3.6 mu m and 4.5 mu m for each target. XO-4b exhibits a stronger eclipse depth at 4.5 mu m than at 3.6 mu m, which is consi...

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Bibliographic Details
Published in:The Astrophysical journal 2012-02, Vol.746 (1), p.1-13
Main Authors: TODOROV, Kamen O, DEMING, Drake, LAUGHLIN, Gregory, LANGTON, Jonathan, SHOWMAN, Adam P, LEWIS, Nikole K, KNUTSON, Heather A, BURROWS, Adam, SADA, Pedro V, COWAN, Nicolas B, AGOL, Eric, DESERT, Jean-Michel, FORTNEY, Jonathan J, CHARBONNEAU, David
Format: Article
Language:English
Subjects:
Amplitudes
Arrays
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Circular orbits
Earth, ocean, space
ECLIPSE
Eclipses
Ephemerides
Exact sciences and technology
Extrasolar planets
Orbitals
ORBITS
PLANETS
STELLAR ACTIVITY
TEMPERATURE INVERSIONS
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Summary:We analyze Warm Spitzer/Infrared Array Camera observations of the secondary eclipses of three planets, XO-4b, HAT-P-6b, and HAT-P-8b. We measure secondary eclipse amplitudes at 3.6 mu m and 4.5 mu m for each target. XO-4b exhibits a stronger eclipse depth at 4.5 mu m than at 3.6 mu m, which is consistent with the presence of a temperature inversion. HAT-P-8b shows a stronger eclipse amplitude at 3.6 mu m and is best described by models without a temperature inversion. The eclipse depths of HAT-P-6b can be fitted with models with a small or no temperature inversion. We consider our results in the context of a postulated relationship between stellar activity and temperature inversion and a relationship between irradiation level and planet dayside temperature, as discussed by Knutson et al. and Cowan & Agol, respectively. Our results are consistent with these hypotheses, but do not significantly strengthen them. To measure accurate secondary eclipse central phases, we require accurate ephemerides. We obtain primary transit observations and supplement them with publicly available observations to update the orbital ephemerides of the three planets. Based on the secondary eclipse timing, we set upper boundaries for e cos( omega ) for HAT-P-6b, HAT-P-8b, and XO-4b and find that the values are consistent with circular orbits.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/746/1/111