DISCOVERY AND ROSSITER-McLAUGHLIN EFFECT OF EXOPLANET KEPLER-8b

Abstract

We report the discovery and the Rossiter-McLaughlin effect of Kepler-8b, a\ntransiting planet identified by the NASA Kepler Mission. Kepler photometry and\nKeck-HIRES radial velocities yield the radius and mass of the planet around\nthis F8IV subgiant host star. The planet has a radius RP = 1.419 RJ and a mass,\nMP = 0.60 MJ, yielding a density of 0.26 g cm^-3, among the lowest density\nplanets known. The orbital period is P = 3.523 days and orbital semima jor axis\nis 0.0483+0.0006/-0.0012 AU. The star has a large rotational v sin i of 10.5\n+/- 0.7 km s^-1 and is relatively faint (V = 13.89 mag), both properties\ndeleterious to precise Doppler measurements. The velocities are indeed noisy,\nwith scatter of 30 m s^-1, but exhibit a period and phase consistent with the\nplanet implied by the photometry. We securely detect the Rossiter-McLaughlin\neffect, confirming the planet's existence and establishing its orbit as\nprograde. We measure an inclination between the projected planetary orbital\naxis and the projected stellar rotation axis of lambda = -26.9 +/- 4.6 deg,\nindicating a moderate inclination of the planetary orbit. Rossiter-McLaughlin\nmeasurements of a large sample of transiting planets from Kepler will provide a\nstatistically robust measure of the true distribution of spin-orbit\norientations for hot jupiters in general.\n