The HARPS search for southern extra-solar planets: XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period - AstrophysicsReport as inadecuate




The HARPS search for southern extra-solar planets: XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period - Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: A 10.24 days Neptune-mass planet was recently announced to orbit the nearbyM2 dwarf Gl 176, based on 28 radial velocities measured with the HRSspectrograph on the Hobby-Heberly Telescope HET. We obtained 57 radialvelocities of Gl 176 with the ESO 3.6m telescope and the HARPS spectrograph,which is known for its sub-m-s stability. The median photon-noise standarderror of our measurements is 1.1 m-s, significantly lower than the 4.7 m-s ofthe HET velocities, and the 4 years period over which they were obtained hasmuch overlap with the epochs of the HET measurements. The HARPS measurementsshow no evidence for a signal at the period of the putative HET planet,suggesting that its detection was spurious. We do find, on the other hand,strong evidence for a lower mass 8.4 Mearth planet, in a quasi-circular orbitand at the different period of 8.78 days. The host star has moderate magneticactivity and rotates on a 39-days period, which we confirm through modulationof both contemporaneous photometry and chromospheric indices. We detect thatperiod as well in the radial velocities, but it is well removed from theorbital period and no cause for confusion. This new detection of a super-Earth2 Mearth < M sini < 10 Mearth around an M dwarf adds to the growingevidence that such planets are common around very low mass stars: a third ofthe 20 known planets with M sini < 0.1 Mjup and 3 of the 7 known planets withM sini < 10 Mearth orbit an M dwarf, in contrast to just 4 of the ~300 knownJupiter-mass planets.



Author: T. Forveille, X. Bonfils, X. Delfosse, M. Gillon, S. Udry, F. Bouchy, C. Lovis, M. Mayor, F. Pepe, C. Perrier, D. Queloz, N. Sant

Source: https://arxiv.org/







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