RESEARCH
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The HARPS search for southern extra-solar planets
XX. Planets around the active star BD-08°2823

G. Hébrard, S. Udry, G. Lo Curto, N. Robichon, D. Naef, D. Ehrenreich, W. Benz, F. Bouchy, A. Lecavelier Des Etangs, C. Lovis, M. Mayor, C. Moutou, F. Pepe, D. Queloz, N. C. Santos, D. Ségransan

Abstract
We report the detection of a planetary system around BD-08°2823, that includes at least one Uranus-mass planet and one Saturn-mass planet. This discovery serendipitously originates from a search for planetary transits in the Hipparcos photometry database. This program preferentially selected active stars and did not allow the detection of new transiting planets. It allowed however the identification of the K3V star BD-08°2823 as a target harboring a multiplanet system, that we secured and characterized thanks to an intensive monitoring with the HARPS spectrograph at the 3.6-m ESO telescope in La Silla. The stellar activity level of BD-08°2823 complicates the analysis but does not prohibit the detection of two planets around this star. BD-08°2823b has a minimum mass of 14.4 ± 2.1 M and an orbital period of 5.60 days, whereas BD-08°2823c has a minimum mass of 0.33 ± 0.03 MJup and an orbital period of 237.6 days. This new system strengthens the fact that low-mass planets are preferentially found in multiplanetary systems, but not around high-metallicity stars as this is the case for massive planets. It also supports the belief that active stars should not be neglected in exoplanet searches, even when searching for low-mass planets.

Keywords
planetary systems – techniques: radial velocities – stars: individual: BD-08°2823 - techniques: photometric

Notes
Based on observations made with HARPS spectrograph on the 3.6-m ESOtelescope at La SillaObservatory, Chile, under the programs ID 072.C-0488, 074.C-0364 and 078.C-0044.
The full version of Table 1 (HARPS measurements of BD −08°2823) is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A46

Astronomy and Astrophysics
Volume 512, Number of pages A46_1
2010 March

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Instituto de AstrofĆ­sica e CiĆŖncias do EspaƧo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
FundaĆ§Ć£o para a CiĆŖncia e a Tecnologia COMPETE 2020 PORTUGAL 2020 UniĆ£o Europeia