[X] My Assistant

[Mongo]

A method for the direct determination of the surface gravities of transiting extrasolar planets

John Southworth, Peter J. Wheatley, Giles Sams

Abstract: We show that the surface gravity of a transiting extrasolar planet can be calculated from only the spectroscopic orbit of its parent star and the analysis of its transit light curve. This does not require additional constraints, such as are often inferred from theoretical stellar models or model atmospheres. The planet's surface gravity can therefore be measured precisely and from only directly observable quantities. We outline the method and apply it to the case of the first known transiting extrasolar planet, HD 209458b. We find a surface gravity of g_p = 9.28 +/- 0.15 m/s, which is an order of magnitude more precise than the best available measurements of its mass, radius and density. This confirms that the planet has a much lower surface gravity that that predicted by published theoretical models of gas giant planets. We apply our method to all fourteen known transiting extrasolar planets and find a significant correlation between surface gravity and orbital period, which is related to the known correlation between mass and period. This correlation may be the underlying effect as surface gravity is a fundamental parameter in the evaporation of planetary atmospheres.

Summary Results (metres per second squared), from highest to lowest:

28.3 +- 4.4 -- OGLE-TR-113
21.5 +- 3.5 -- HD189733b
20.7 +- 2.6 -- TrES-2
20.1 +- 2.7 -- WASP-2
18.0 +- 6.0 -- OGLE-TR-132
17.9 +- 1.9 -- OGLE-TR-56
16.4 +- 2.5 -- HD149026b
16.1 +- 1.0 -- TrES-1
13.3 +- 4.2 -- OGLE-TR-111
13.3 +- 2.5 -- XO-1
10.6 +- 1.7 -- WASP-1
9.5 +- 2.1 -- OGLE-TR-10 (edited from 4.5 +- 2.1, an apparent typo)
9.28 +- 0.15 -- HD209458b
7.1 +- 1.1 -- HAT-P-1

By comparison, here are the surface gravities of the Solar gas giants:

23.12 -- Jupiter
11.15 -- Neptune
8.96 -- Saturn
8.69 -- Uranus

Bill

[Greg Hullender]

John: Very pleased to hear from you! So is the error in the "Summary Table of parameters for transiting planets" then?

http://obswww.unige.ch/~pont/TRANSITS.htm

I used their mass and radius values, and got excellent correlation with your paper except for OGLE-10. Agree that it's strangely bloated, but is it THAT strangely bloated?

I thought I cross-referenced it against the original paper to verify the numbers, but I don't have any of that info handy at the moment. Wouldn't be the first time a web page was wrong, after all.

Anyway, when I saw what an outlier it was in your graphs, I figured it'd be worth your while to give it another look; like I said, you get a much better correlation if the other number is correct after all.

--Greg