Astrophys. J., 766, 67 (2013/April-1)
A hot Uranus orbiting the super metal-rich star HD 77338 and the metallicity-mass connection.
JENKINS J.S., JONES H.R.A., TUOMI M., MURGAS F., HOYER S., JONES M.I., BARNES J.R., PAVLENKO Y.V., IVANYUK O., ROJO P., JORDAN A., DAY-JONES A.C., RUIZ M.T. and PINFIELD D.J.
Abstract (from CDS):
We announce the discovery of a low-mass planet orbiting the super metal-rich K0V star HD 77338 as part of our ongoing Calan-Hertfordshire Extrasolar Planet Search. The best-fit planet solution has an orbital period of 5.7361±0.0015 days and with a radial velocity semi-amplitude of only 5.96±1.74 m/s, we find a minimum mass of 15.9+4.7–5.3 M⊕. The best-fit eccentricity from this solution is 0.09 +0.25–0.09, and we find agreement for this data set using a Bayesian analysis and a periodogram analysis. We measure a metallicity for the star of +0.35±0.06 dex, whereas another recent work finds +0.47±0.05 dex. Thus HD 77338b is one of the most metal-rich planet-host stars known and the most metal-rich star hosting a sub-Neptune-mass planet. We searched for a transit signature of HD 77338b but none was detected. We also highlight an emerging trend where metallicity and mass seem to correlate at very low masses, a discovery that would be in agreement with the core accretion model of planet formation. The trend appears to show that for Neptune-mass planets and below, higher masses are preferred when the host star is more metal-rich. Also a lower boundary is apparent in the super metal-rich regime where there are no very low mass planets yet discovered in comparison to the sub-solar metallicity regime. A Monte Carlo analysis shows that this low-mass planet desert is statistically significant with the current sample of 36 planets at the ∼4.5σ level. In addition, results from Kepler strengthen the claim for this paucity of the lowest-mass planets in super metal-rich systems. Finally, this discovery adds to the growing population of low-mass planets around low-mass and metal-rich stars and shows that very low mass planets can now be discovered with a relatively small number of data points using stable instrumentation.
planetary systems - stars: fundamental parameters - stars: individual: HD 77338 - stars: rotation
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