Transiting exoplanets from the CoRoT space mission. XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet

Laboratoire d'Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388, Marseille Cedex 13, France; IAG, Universidade de São Paulo, Brazil; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany; Observatoire de Haute Provence, 04670, Saint Michel l'Observatoire, France; Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014, Paris, France; Observatoire de la Côte d' Azur, Laboratoire Cassiopée, BP 4229, 06304, Nice Cedex 4, France; Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK; Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290, Sauverny, Switzerland; LESIA, Obs de Paris, Place J. Janssen, 92195, Meudon Cedex, France; Institut d'astrophysique spatiale, Université Paris-Sud 11 & CNRS (UMR 8617; Department of Physics and Astronomy, Aarhus University, 8000, Aarhus C, Denmark; Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands; Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain; Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain; University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180, Vienna, Austria; University of Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium; Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778, Tautenburg, Germany; Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042, Graz, Austria; Wise Observatory, Tel Aviv University, Tel Aviv, 69978, Israel; School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel; LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195, Meudon, France
Astronomy and Astrophysics (Impact Factor: 5.08). 01/2012; 538:145. DOI: 10.1051/0004-6361/201117681
Source: arXiv

ABSTRACT We report the discovery by the CoRoT space mission of a new giant
planet, CoRoT-20b. The planet has a mass of 4.24 ± 0.23
MJup and a radius of 0.84 ± 0.04 RJup. With
a mean density of 8.87 ± 1.10 g cm-3, it is among the
most compact planets known so far. Evolutionary models for the planet
suggest a mass of heavy elements of the order of 800 M⊕
if embedded in a central core, requiring a revision either of the planet
formation models or both planet evolution and structure models. We note
however that smaller amounts of heavy elements are expected by more
realistic models in which they are mixed throughout the envelope. The
planet orbits a G-type star with an orbital period of 9.24 days and an
eccentricity of 0.56.The star's projected rotational velocity is vsini =
4.5 ± 1.0 km s-1, corresponding to a spin period of
11.5 ± 3.1 days if its axis of rotation is perpendicular to the
orbital plane. In the framework of Darwinian theories and neglecting
stellar magnetic breaking, we calculate the tidal evolution of the
system and show that CoRoT-20b is presently one of the very few
Darwin-stable planets that is evolving toward a triple synchronous state
with equality of the orbital, planetary and stellar spin periods.

The CoRoT space mission, launched on December 27th 2006, has been
developed and is operated by CNES, with the contribution of Austria,
Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain.

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    ABSTRACT: Context. Accurate parameters of the host stars of exoplanets are needed for interpreting the new planetary systems. The CoRoT satellite recently discovered a transiting rocky planet with a density similar to the inner planets in our solar system, a so-called super Earth. The mass was determined using ground-based follow-up spectroscopy, which also revealed a second, non-transiting super Earth. Aims: These planets are orbiting a relatively faint (mV = 11.7) G9V star called CoRoT-7. We wish to refine the determination of the physical properties of the host star, which are important for the interpretation of the properties of the planetary system. Methods: We used high-quality spectra from HARPS at the ESO 3.6 m and UVES at the VLT 8.2 m. We used various methods to analyse the spectra using 1D LTE atmospheric models. From the analysis of Fe i and Fe ii lines we determined the effective temperature, surface gravity and microturbulence. We used the Balmer lines to constrain the effective temperature and pressure-sensitive Mg 1b and Ca lines to constrain the surface gravity. We analysed both single spectra and co-add spectra to identify systematic errors. We determine the projected rotational velocity and macroturbulence by fitting the line shapes of isolated lines. We finally determined an approximate absolute magnitude from the Wilson-Bappu effect. Results: From the analysis of the three best spectra, we find Teff = 5250±60 K, log g = 4.47±0.05, [M/H] = +0.12±0.06, and v sin i = 1.1+1.0-0.5 km s-1. The chemical composition of 20 analysed elements is consistent with uniform scaling by the metallicity +0.12 dex. From the analysis of spectra of stars with well-known parameters with similar parameters to CoRoT-7 (the Sun and alpha Cen B) we demonstrate that our methods are robust within the claimed uncertainties. We compared the L/M ratio with isochrones to constrain the evolutionary status. Using the age estimate of 1.2-2.3 Gyr based on stellar activity, we determine the mass and radius 0.91±0.03 M&sun; and 0.82±0.04 R&sun;. With these updated constraints we fitted the CoRoT transit light curve for CoRoT-7b. The revised planet radius is slightly smaller, R = 1.58±0.10 R_oplus, and the density becomes slightly higher, rho = 7.2±1.8 g cm-3. The CoRoT space mission, launched on December 27, 2006, has been developed and is being operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, The Research and Scientific Support Department of ESA, Germany and Spain.
    Astronomy and Astrophysics 01/2010; 519. · 5.08 Impact Factor
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    ABSTRACT: We have investigated the formation of close-in extrasolar giant planets through a coupling effect of mutual scattering, Kozai mechanism, and tidal circularization, by orbital integrations. We have carried out orbital integrations of three planets with Jupiter-mass, directly including the effect of tidal circularization. We have found that in about 30% runs close-in planets are formed, which is much higher than suggested by previous studies. We have found that Kozai mechanism by outer planets is responsible for the formation of close-in planets. During the three-planet orbital crossing, the Kozai excitation is repeated and the eccentricity is often increased secularly to values close enough to unity for tidal circularization to transform the inner planet to a close-in planet. Since a moderate eccentricity can remain for the close-in planet, this mechanism may account for the observed close-in planets with moderate eccentricities and without nearby secondary planets. Since these planets also remain a broad range of orbital inclinations (even retrograde ones), the contribution of this process would be clarified by more observations of Rossiter-McLaughlin effects for transiting planets. Comment: 15 pages, 16 figures, Accepted for publication in ApJ
    The Astrophysical Journal 01/2008; · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063 +/- 0.001 AU. It has a radius of 0.57 +/- 0.02 RJ, a mass of 0.22 +/- 0.03 MJ, and therefore a mean density 1.6 +/- 0.1 g/cm^3. With 67 % of the size of Saturn and 72 % of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g/cm^3). We estimate its content in heavy elements to be 47-63 Earth masses, and the mass of its hydrogen-helium envelope to be 7-23 Earth masses. At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than about 0.1 % over an assumed integrated lifetime of 3~Ga. Comment: 10 pages, 12 figures, accepted for publication in A&A
    Astronomy and Astrophysics 08/2010; 520(2010):A66. · 5.08 Impact Factor

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