8 Micrometre phase variation of HD 149026 b

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8 Micrometre phase variation of HD 149026 b

Post by Sirius_Alpha on 16th August 2009, 11:45 pm

The 8 Micron Phase Variation of the Hot Saturn HD 149026b
http://arxiv.org/abs/0908.1977

Abstract wrote:We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over slightly more than half an orbit using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma significance) in the combined planet-star flux during this interval. The minimum flux from the planet is 45% +/- 19% of the maximum planet flux, corresponding to a difference in brightness temperature of 480 +/- 140 K between the two hemispheres. We derive a new secondary eclipse depth of 0.0411% +/- 0.0076% in this band, corresponding to a dayside brightness temperature of 1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous measurement (3.0 sigma difference) in this same bandpass by Harrington et al. (2007). We re-fit the Harrington et al. (2007) data and obtain a comparably good fit with a smaller eclipse depth that is consistent with our new value. In contrast to earlier claims, our new eclipse depth suggests that this planet's dayside emission spectrum is relatively cool, with an 8 micron brightness temperature that is less than the maximum planet-wide equilibrium temperature. We measure the interval between the transit and secondary eclipse and find that that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma) than predicted for a circular orbit, a marginally significant result. This corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's orbital eccentricity and omega is the argument of pericenter.

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Re: 8 Micrometre phase variation of HD 149026 b

Post by Lazarus on 17th August 2009, 5:08 pm

It's good to see observations are getting to the point where detailed pictures of these extrasolar planets can be built up, especially since the worlds are so different from our own system.
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