A New 24 micron Phase Curve for upsilon Andromedae b

Details A New 24 micron Phase Curve for upsilon Andromedae b A New 24 micron Phase Curve for upsilon Andromedae b

2010-08-02

arxiv.org/abs/1008.0393v1

Astronomy and Astrophysics

Astrophysics

Earth and Planetary Astrophysics

Submitted to ApJ. 15 pages, 6 figures, 4 tables

Scientific paper

10.1088/0004-637X/723/2/1436

We report the detection of 24 micron variations from the planet-hosting upsilon Andromedae system consistent with the orbital periodicity of the system's innermost planet, upsilon And b. We find a peak-to-valley phase curve amplitude of 0.00130 times the mean system flux. Using a simple model with two hemispheres of constant surface brightness and assuming a planetary radius of 1.3 Jupiter radii gives a planetary temperature contrast of >900 K and an orbital inclination of >28 degrees. We further report the largest phase offset yet observed for an extrasolar planet: the flux maximum occurs ~80 degrees before phase 0.5. Such a large phase offset is difficult to reconcile with most current atmospheric circulation models. We improve on earlier observations of this system in several important ways: (1) observations of a flux calibrator star demonstrate the MIPS detector is stable to 10^-4 on long timescales, (2) we note that the background light varies systematically due to spacecraft operations, precluding use of this background as a flux calibrator (stellar flux measured above the background is not similarly affected), and (3) we calibrate for flux variability correlated with motion of the star on the MIPS detector. A reanalysis of our earlier observations of this system is consistent with our new result.

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