Merline W.J.,Southwest Research Institute |
Drummond J.D.,Air Force Research Lab |
Carry B.,French National Center for Scientific Research |
Carry B.,European Space Agency |
And 14 more authors.
With the adaptive optics (AO) system on the 10m Keck-II telescope, we acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa on 2005 January 20, when it was near opposition. The epochs covered its 5.63h rotation period and, by following its changing shape and orientation on the plane of sky, we obtained its triaxial ellipsoid dimensions and spin pole location. An independent determination from images at three epochs obtained in 2007 is in good agreement with these results. By combining these two data sets, along with a single epoch data set obtained in 2003, we have derived a global fit for (52) Europa of diameters a×b×c=(379×330×249)±(16×8×10)km, yielding a volume-equivalent spherical-diameter of abc3=315±7km, and a prograde rotational pole within 7° of [RA;Dec]=[257°;+12°] in an Equatorial J2000 reference frame (Ecliptic: 255°;+35°). Using the average of all mass determinations available for (52) Europa, we derive a density of 1.5±0.4gcm-3, typical of C-type asteroids. Comparing our images with the shape model of Michalowski et al. (2004, Astron. Astrophys. 416, 353), derived from optical lightcurves, illustrates excellent agreement, although several edge features visible in the images are not rendered by the model. We therefore derived a complete 3-D description of (52) Europa's shape using the KOALA algorithm by combining our 18 AO imaging epochs with 4 stellar occultations and 49 lightcurves. We use this 3-D shape model to assess these departures from ellipsoidal shape. Flat facets (possible giant craters) appear to be less distinct on (52) Europa than on other C-types that have been imaged in detail, (253) Mathilde and (511) Davida. We show that fewer giant craters, or smaller largest-sized craters, is consistent with its expected impact history. Overall, asteroid (52) Europa is still well modeled as a smooth triaxial ellipsoid with dimensions constrained by observations obtained over several apparitions. © 2013 Elsevier Inc. Source
Santerne A.,University of Porto |
Santerne A.,Aix - Marseille University |
Hebrard G.,University Pierre and Marie Curie |
Hebrard G.,French National Center for Scientific Research |
And 46 more authors.
Astronomy and Astrophysics
In this paper we report a new transiting warm giant planet: KOI-1257 b. It was first detected in photometry as a planet-candidate by the Kepler space telescope and then validated thanks to a radial velocity follow-up with the SOPHIE spectrograph. It orbits its host star with a period of 86.647661 d3 s and a high eccentricity of 0.7720.045. The planet transits the main star of a metal-rich, relatively old binary system with stars of mass of 0.99 0.05 M and 0.70 ± 0.07 M for the primary and secondary, respectively. This binary system is constrained thanks to a self-consistent modelling of the Kepler transit light curve, the SOPHIE radial velocities, line bisector and full-width half maximum (FWHM) variations, and the spectral energy distribution. However, future observations are needed to confirm it. The PASTIS fully-Bayesian software was used to validate the nature of the planet and to determine which star of the binary system is the transit host. By accounting for the dilution from the binary both in photometry and in radial velocity, we find that the planet has a mass of 1.45 ± 0.35 M, and a radius of 0.94 ± 0.12 R™, and thus a bulk density of 2.1 ± 1.2 g cm-3. The planet has an equilibrium temperature of 511 50 K, making it one of the few known members of the warm-Jupiter population. The HARPS-N spectrograph was also used to observe a transit of KOI-1257 b, simultaneously with a joint amateur and professional photometric follow-up, with the aim of constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin effect was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet. © 2014 ESO. Source