Paper: astro-ph/0508427
Date: Fri, 19 Aug 2005 15:52:28 GMT (189kb)

Title: Low-mass companions to Hyades stars

Authors: E.W. Guenther, D.B. Paulson, W.D. Cochran, J. Patience, A.P. Hatzes,
B. Macintosh

Comments: 10 pages, 10 figures
\\
It is now well established that a large fraction of the low-mass stars are
binaries or higher order multiples. Similarly a sizable fraction have giant
planets. In contrast to these, the situation for brown dwarf companions is
complicated: While close systems seem to be extremely rare, wide systems are
possibly more common. In this paper, we present new results on a survey for
low-mass companions in the Hyades. After measuring precisely the radial
velocity of 98 Hyades dwarf stars for 5 years, we have selected all stars that
show low-amplitude long-period trends. With AO-observations of these 14 stars
we found companion candidates around nine of them, where one star has two
companions. The two companions of HIP 16548 have masses between 0.07 to 0.08
Mo, and are thus either brown dwarfs or very low mass stars. In the case of HAN
172 we found a companion with a mass between 0.08 to 0.10 Mo, which is again
between a star and a brown dwarf. The other seven stars all have stellar
companions. In two additional cases, the RV-variations are presumably caused by
stellar activity, and in another case the companion could be a short-period
binary. The images of the remaining two stars are slightly elongated, which
might imply that even these are binaries. Because at least 12 of the 14 stars
showing low-amplitude RV trends turn out to have companions with a mass greater
than 70 MJupiter, or are just active, we finally estimate the number of
companions with masses between 10 MJupiter and 70 MJupiter within 8 AU of the
host stars in the Hyades as less equal 2%.

\\ ( http://arXiv.org/abs/astro-ph/0508427 , 189kb)