Trois candidats dans un amas ouvert.

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Trois candidats dans un amas ouvert.

Message par Stalker le Mar 27 Avr - 10:29

M. Montalto, S. Villanova et J. Koppenhoefer ont mesuré la vitesse
radiale de 139 étoiles de l'amas ouvert NGC 6253 et ont trouvé trois
possibles planètes en transit. De plus, l'une des étoiles étudiées
pourrait avoir un compagnon substellaire (planète ou naine brune)

VLT multi-epoch
radial velocity survey toward NGC 6253. Analysis of three transiting
planetary candidates

We measured the radial velocity of 139 stars in the region of NGC 6253, discussing cluster's membership and binarity in this sample, complementing our
analysis with photometric, proper motion, and radial velocity data available from
previous studies of this cluster, and analyzing three planetary transiting candidates we found in the field of NGC 6253. Spectra were obtained with the UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008.The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both radial velocities and proper motions we found 35 cluster's members, among which 12 are likely cluster's close binary systems. One star may have a sub-stellar companion, requiring a more intensive follow-up. Our results are in good agreement with past radial velocity and photometric measurements. Furthermore,using our photometry, astrometry and spectroscopy we identified a new sub-giantbranch eclipsing binary system, member of the cluster. The cluster's close binary frequency at 29% +/- 9% (34% +/-10% once including long period binaries), appears higher than the field binary frequency equal to (22% +/- 5%, though these estimates are still consistent within the uncertainties. Among the three transiting planetary candidates
the brightest one (V=15.26) is worth to be more intensively investigated with higher percision spectroscopy. We discussed the possibility to detect sub-stellar companions (brown dwarfs and planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS) around turn-off stars of old open clusters.
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