Astronomy and Astrophysics, volume 531A, 161-161 (2011/7-1)
On the mass determination of super-earths orbiting active stars: the CoRoT-7 system.
FERRAZ-MELLO S., TADEU DOS SANTOS M., BEAUGE C., MICHTCHENKO T.A. and RODRIGUEZ A.
Abstract (from CDS):
Star activity makes the mass determination of CoRoT-7b and CoRoT 7c uncertain. Investigators of the CoRoT team proposed several solutions, but all but one of them are larger than the initial determinations of 4.8±0.8MEarth
for CoRoT-7b and 8.4±0.9MEarth
for CoRoT 7c. This investigation uses the excellent HARPS radial velocity measurements of CoRoT-7 to redetermine the planet masses and to explore techniques for determining mass and orbital elements of planets discovered around active stars when the relative variation in the radial velocity due to the star activity cannot be considered as just noise and can exceed the variation due to the planets. The main technique used here is a self-consistent version of the high-pass filter used by Queloz et al. (2009A&A...506..303Q
) in the first mass determination of CoRoT-7b and CoRoT-7c. The results are compared to those given by two alternative techniques: (1) the approach proposed by Hatzes et al. (2010A&A...520A..93H
) using only those nights in which two or three observations were done; (2) a pure Fourier analysis. In all cases, the eccentricities are taken equal to zero as indicated by the study of the tidal evolution of the system. The periods are also kept fixed at the values given by Queloz et al. Only the observations done in the time interval BJD 2454847-873 are used because they include many nights with multiple observations; otherwise, it is not possible to separate the effects of the rotation fourth harmonic (5.91d=Prot
/4) from the alias of the orbital period of CoRoT-7b (0.853585d). The results of the various approaches are combined to give planet mass values 8.0±1.2MEarth
for CoRoT-7b and 13.6±1.4MEarth
for CoRoT 7c. An estimation of the variation of the radial velocity of the star due to its activity is also given. The results obtained with three different approaches agree to give higher masses than those in previous determinations. From the existing internal structure models they indicate that CoRoT-7b is a much denser super-Earth. The bulk density is 11±3.5g/cm3
, so CoRoT-7b may be rocky with a large iron core.
planets and satellites: detection - planets and satellites: fundamental parameters
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