The HARPS search for southern extra-solar planets

• Published in: Astronomy and astrophysics (Berlin) 2010-03, Vol.512
• Main Authors: Hébrard, G., Udry, S., Lo Curto, G., Robichon, N., Naef, D., Ehrenreich, D., Benz, W., Bouchy, F., Lecavelier des Etangs, A., Lovis, C., Mayor, M., Moutou, C., Pepe, F., Queloz, D., Santos, N. C., Ségransan, D.
• Format: Article
• Language: English
• Subjects: planetary systems; stars: individual: BD -08°2823; techniques: photometric; techniques: radial velocities
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/200913525

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, which 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 $M_{\oplus}$ 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 observation that low-mass planets are preferentially found in multiplanetary systems, but not around high-metallicity stars as 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.