Abstract
CONTEXT: Most current radial velocity planet search programs have concentrated on stars of one solar mass. Our knowledge on the frequency of giant planets and brown dwarf companions to more massive stars is thus rather limited. In the case of solar-like stars, the frequency of short-period brown dwarf companions and very massive planets seems to be low. AIMS: Here we present evidence for a substellar companion to 30 Ari B, an F-star of 1.16 $\pm$ 0.04 $\rm M_\odot$ that is a member of a hierarchical triple system. METHODS: The companion was detected by means of precise radial velocity measurements using the 2-m Alfred-Jensch telescope and its 'echelle spectrograph. An iodine absorption cell provided the wavelength reference for precise stellar radial velocity measurements. RESULTS: We analyzed our radial velocity measurements and derived an orbit to the companion with period, P= 335.1+/-2.5 days, eccentricity e = 0.289+/-0.092, and mass function f(m) = (6.1+/-1.7)*10E-7 Modot. CONCLUSIONS: We conclude that the radial velocity variations of 30 Ari B are due to a companion with $m$ sin $i$ of $9.88\pm0.94$ $\rm M_{Jup}$ that is either a massive planet or a brown dwarf. {The object thus belongs to the rare class of massive planets and brown dwarfs orbiting main- sequence stars.
Highlights
The Li abundance derived of Ursa Major group dwarf stars is higher than in the Hyades at effective temperatures cooler than the Sun, but lower than in the younger Pleiades, a result which is independent of the exact value of the effective temperature adopted
Stellar parameters of 11 Ursa Major (UMa) group members have been derived homogeneously from spectra of both high resolving power and high signal-to-noise ratio using the methods of Fuhrmann (2004, and preceeding work)
The consistency of the analysis was proven by reproducing data for the Sun and a possible UMa group member already analysed by Fuhrmann (2004), and by comparing the spectroscopic distance with the geometric Hipparcos distance
Summary
In the 19th century, Proctor (1869) and Huggins (1871) realized that five of the A stars in the Big Dipper constellation move to a common convergence point, and are likely to move into the same direction of space. In 1909, Hertzsprung identified stars at a very large angular distance from the Big Dipper constellation that were moving towards the same convergent point, and had to be members of the same group of stars. All of these stars form an association with a central concentration, the UMa open cluster in the Big Dipper constellation, located at a distance of about 25 pc. Since the stars belonging to the UMa group probably do not form a single open cluster (Wielen 1978), the term Sirius supercluster has instead been suggested (Eggen 1994), or UMa association (Fuhrmann 2004), or UMa group. Studies of its members allow one to analyse aspects of stellar and cluster evolution
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