THE MASS OF CoRoT-7b

• Published in: The Astrophysical journal Vol. 743; no. 1; pp. 75 - jQuery1323901018598='48'
• Main Authors: Hatzes, Artie P., Fridlund, Malcolm, Nachmani, Gil, Mazeh, Tsevi, Valencia, Diana, Hébrard, Guillaume, Carone, Ludmila, Pätzold, Martin, Udry, Stephane, Bouchy, Francois, Deleuil, Magali, Moutou, Claire, Barge, Pierre, Bordé, Pascal, Deeg, Hans, Tingley, Brandon, Dvorak, Rudolf, Gandolfi, Davide, Ferraz-Mello, Sylvio, Wuchterl, Günther, Guenther, Eike, Guillot, Tristan, Rauer, Heike, Erikson, Anders, Cabrera, Juan, Csizmadia, Szilard, Léger, Alain, Lammer, Helmut, Weingrill, Jörg, Queloz, Didier, Alonso, Roi, Rouan, Daniel, Schneider, Jean
• Format: Journal Article
• Language: English
• Published: Bristol IOP 10.12.2011; American Astronomical Society
• Subjects: ACTIVITY LEVELS; AMPLITUDES; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BULK DENSITY; EARTH PLANET; Earth, ocean, space; Exact sciences and technology; MERCURY PLANET; RADIAL VELOCITY; STARS; Bulk density; Terrestrial planet; planetary systems; techniques: radial velocities; Extrasolar planets; Internal structure; Models; Radial velocity; Planetary system
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/743/1/75

The mass of CoRoT-7b, the first transiting super-Earth exoplanet, is still a subject of debate. A wide range of masses have been reported in the literature ranging from as high as 8 M {circled plus} to as low as 2.3 M {circled plus}. This range in mass is largely due to the activity level of the star that contributes a significant amount of radial velocity (RV) 'jitter' and how the various methods correct this jitter. Although most mass determinations give a density consistent with a rocky planet, the lower value permits a bulk composition that can be up to 50% water. We present an analysis of the CoRoT-7b RV measurements that uses very few and simple assumptions in treating the activity signal. By analyzing those RV data for which multiple measurements were made in a given night, we remove the activity related RV contribution without any a priori model. We argue that the contribution of activity to the final RV curve is negligible and that the K-amplitude due to the planet is well constrained. This yields a mass of 7.42 ? 1.21 M {circled plus} and a mean density of Delta *r = 10.4 ? 1.8 gm cm--3. CoRoT-7b is similar in mass and radius to the second rocky planet to be discovered, Kepler-10b, and within the errors they have identical bulk densities--they are virtual twins. These bulk densities lie close to the density-radius relationship for terrestrial planets similar to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal structure more like Mercury than the Earth.