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PubMed2000

Sub-Saturn Planetary Candidates of HD 16141 and HD 46375.

Precision Doppler measurements from the Keck High-Resolution Echelle Spectrograph reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 days and a velocity amplitude of 11 m s-1, yielding a companion having Msini=0.22 M(JUP) and a semimajor axis of a=0.35 AU. HD 46375 (K1 IV-V) has a period of 3.024 days and a velocity amplitude of 35 m s-1, yielding a companion with Msini=0.25 M(JUP), a semimajor axis of a=0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.

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PubMed2000

A Transiting "51 Peg-like" Planet.

Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s-1 and a period of 3.5239 days, which is indicative of a "51 Peg-like" planet with a minimum mass (Msini) of 0.62 MJup and a semimajor axis of 0.046 AU. Follow-up photometry reveals a drop of 0.017 mag at the predicted time (within the errors) of transit by the companion based on the velocities. This is the first extrasolar planet observed to transit its star. The radius of the planet derived from the magnitude of the dimming is 1.42 RJup, which is consistent with models of irradiated Jupiter-mass planets. The transit implies that sini>0.993, leading to a true mass of 0.62 MJup for the planet. The resulting mean density of 0.27 g cm-3 implies that the companion is a gas giant.

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