On the Size Distribution of Close-In Extrasolar Giant Planets

Astrophysics, abstract
astro-ph/0504123

From: B. Scott Gaudi [view email]

Date (v1): Tue, 5 Apr 2005 20:00:03 GMT   (24kb)

Date (revised v2): Tue, 5 Apr 2005 21:16:35 GMT   (24kb)

The precisions of extrasolar planet radius measurements are reaching the
point where meaningful and discriminatory comparisons with theoretical
predictions are possible. However, care must be taken to account for selection
effects in the transit surveys that detect the transiting planets for which
radius measurements are possible. Here I identify one such selection effect,
such that the number of planets with radius R_p detected in a signal-to-noise
limited transit survey is proportional to R_p^alpha, with alpha~4-6. In the
presence of a dispersion sigma in the intrinsic distribution of planet radii,
this selection effect translates to bias b in the radii of observed planets.
Detected planets are, on average, larger by a fractional amount b ~ alpha
(sigma/<R_p>)^2 relative to the mean radius <R_p> of the underlying
distribution. I argue that the intrinsic dispersion in planetary radii is
likely to be in the range sigma = (0.05-0.18)R_J, where the lower bound is that
expected theoretically solely from the variance in stellar insolation, and the
upper bound is the 95% c.l. upper limit from the scatter in observed radii.
Assuming an arbitrary but plausible value of sigma/<R_p>~10%, and thus b~6%, I
infer a mean intrinsic radius of close-in massive extrasolar planets of
<R_p>=(1.03+/-0.03)R_J. This value reinforces the case for HD209458b having an
anomalously large radius, and may be inconsistent with coreless models of
irradiated giant planets.

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