Search for brown-dwarf companions of stars

By J. Sahlmann, Damien Ségransan, D. Queloz, S. Udry, Nuno C. Santos, M. Marmier, M. Mayor, D. Naef, F. Pepe, S. Zucker. 2010

147 citations recorded by the source corpus.

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 χ 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� . 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.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/cf715443cacf6172cb0c8749bd9ddc976411e988

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Citations in the corpus

Multiplicity among Solar-type Stars (2017, methodology): “A preliminary orbital solution of the HD 53680 Ca-Cb subsystem was given by Makarov et al. (2008), who found an orbital period of about 4years and a MCb;0.2Me low-mass secondary; similar values were later derived by Sahlmann et al. (2011) for a combined astrometric/ spectroscopic orbit.”
Defining and cataloging exoplanets: the exoplanet.eu database (2011, background): “A closer look reveals a flat quasi-void between ∼25–45 MJup (Sahlmann et al. 2011 – Fig.”
Stellar Multiplicity (2013, background): “…extremely low frequency of BD companions among solar-type SBs (Grether & Lineweaver 2006; Marcy, Cochran & Mayor 2000) is inconsistent with extrapolations of both the binary mass function and the planetary mass function (e.g., Howard et al. 2010, Reffert & Quirrenbach 2011, Sahlmann et al. 2011).”