Search for brown-dwarf companions of stars

被引:151
作者
Sahlmann, J. [1 ,2 ]
Segransan, D. [1 ]
Queloz, D. [1 ]
Udry, S. [1 ]
Santos, N. C. [3 ,4 ]
Marmier, M. [1 ]
Mayor, M. [1 ]
Naef, D. [1 ]
Pepe, F. [1 ]
Zucker, S. [5 ]
机构
[1] Univ Geneva, Observ Geneve, CH-1290 Sauverny, Switzerland
[2] European So Observ, D-85748 Garching, Germany
[3] Univ Porto, Ctr Astrofis, P-4150762 Oporto, Portugal
[4] Univ Porto, Fac Ciencias, Dept Fis Astron, Oporto, Portugal
[5] Tel Aviv Univ, Dept Geophys & Planetary Sci, IL-69978 Tel Aviv, Israel
基金
以色列科学基金会; 欧洲研究理事会;
关键词
binaries: spectroscopic; brown dwarfs; stars: low-mass; techniques: radial velocities; astrometry; EXTRA-SOLAR PLANETS; PRECISION RADIAL-VELOCITIES; SPACE-TELESCOPE ASTROMETRY; PHASES DIFFERENTIAL ASTROMETRY; CANDIDATE EXOPLANET COMPANION; SUB-STELLAR OBJECTS; LOW-MASS COMPANIONS; CORALIE SURVEY; HARPS SEARCH; SPECTROSCOPIC BINARIES;
D O I
10.1051/0004-6361/201015427
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Context. The frequency of brown-dwarf companions in close orbit around Sun-like stars is low compared to the frequency of planetary and stellar companions. There is presently no comprehensive explanation of this lack of brown-dwarf companions. Aims. By combining the orbital solutions obtained from stellar radial-velocity curves and Hipparcos astrometric measurements, we attempt to determine the orbit inclinations and therefore the masses of the orbiting companions. By determining the masses of potential brown-dwarf companions, we improve our knowledge of the companion mass-function. Methods. The radial-velocity solutions revealing potential brown-dwarf companions are obtained for stars from the CORALIE and HARPS planet-search surveys or from the literature. The best Keplerian fit to our radial-velocity measurements is found using the Levenberg-Marquardt method. The spectroscopic elements of the radial-velocity solution constrain the fit to the intermediate astrometric data of the new Hipparcos reduction. The astrometric solution and the orbit inclination are found using non-linear chi(2)-minimisation on a two-parameter search grid. The statistical confidence of the adopted orbital solution is evaluated based on the distribution-free permutation test. Results. The discovery of nine new brown-dwarf candidates orbiting stars in the CORALIE and HARPS radial-velocity surveys is reported. New CORALIE radial velocities yielding accurate orbits of six previously-known hosts of potential brown-dwarf companions are presented. Including the literature targets, 33 hosts of potential brown-dwarf companions are examined. Employing innovative methods, we use the new reduction of the Hipparcos data to fully characterise the astrometric orbits of six objects, revealing M-dwarf companions of masses between 90 MJ and 0.52 M-circle dot. In addition, the masses of two companions can be restricted to the stellar domain. The companion to HD 137510 is found to be a brown dwarf. At 95% confidence, the companion of HD 190228 is also a brown dwarf. Twenty-three companions remain brown-dwarf candidates. On the basis of the CORALIE planet-search sample, we obtain an upper limit of 0.6% for the frequency of brown-dwarf companions around Sun-like stars. We find that the companion-mass distribution function increases toward the lower end of the brown-dwarf mass range, suggesting that we detect the high-mass tail of the planetary distribution. Conclusions. Our findings agree with the results of previous similar studies and confirm the pronounced paucity of brown-dwarf companions around Sun-like stars. They are affected by the Hipparcos astrometric precision and mission duration, which limits the minimum detectable companion mass, and some of the remaining candidates are probably brown-dwarf companions.
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页数:24
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