HAT-P-2b: A Direct Glimpse at the Stormiest Exoplanet

Details HAT-P-2b: A Direct Glimpse at the Stormiest Exoplanet HAT-P-2b: A Direct Glimpse at the Stormiest Exoplanet

Jun 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop..297b&link_type=abstract

Spitzer Proposal ID #297

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Scientific paper

The HATNet project has just discovered an unusual transiting exoplanet (TEP), called HAT-P-2b (Bakos et al. 2007). This is the longest period (Porb = 5.63 days), by far the most massive (Mp = 8MJ), most eccentric (e = 0.5) and highest surface gravity (~ 149m s-2 ) TEP so far, and it orbits a bright (K = 7.6) F8 star. The high eccentricity means that the stellar distance during the orbit varies by a factor of 3, and the stellar insolation by a factor 9. Another consequence of the strongly varying angular orbital velocity is that the planet's spin period cannot be synchronized with its orbit period. Instead, tidal evolution will have brought it into spin-pseudo-synchronization in which it maintains approximate co-rotation at periastron (with spin period Prot ~ 1.96 days). The orientation of the orbit, with its major axis in the sky plane (omega ~ 180 deg) is very fortuitous. After the primary transit, the planet reaches periastron in only 13 hours, and gets occulted by the star in another 13 hours. At transit the insolation is ~1600 Solar Constants (SC's); it more than doubles to 3600 SC's at periastron, then drops back to 1600 SC's at secondary eclipse. The unique properties of this object, along with the chance orientation of the orbit, combined with large expected fluxes, make HAT-P-2b the stormiest exoplanet, and the best of its kind for weather study by Spitzer. We propose to take advantage of the fact that in just 34 hours - a small fraction of the total orbital period - we can use the huge thermal forcing to study the radiative response of the planetary atmosphere. Side-results will be precise determinations of the orbital eccentricity, longitude of periastron, and the planetary radius.

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