An infrared imaging search for low-mass companions to members of the young nearby beta Pic and Tucana/Horologium associations

Ralph Neuhäuser, Eike W. Guenther, J. Alves, N. Huélamo, Th. Ott, A. Eckart

We present deep high dynamic range infrared images of young nearby stars

in the Tucana/Horologium and beta Pic associations, all ~ 10 to 35 Myrs

young and at ~10 to 60 pc distance. Such young nearby stars are

well-suited for direct imaging searches for brown dwarf and even

planetary companions, because young sub-stellar objects are still

self-luminous due to contraction and accretion. We performed our

observations at the ESO 3.5m NTT with the normal infrared imaging

detector SofI and the MPE speckle camera Sharp-I. Three arc sec north of

GSC 8047-0232 in Horologium a promising brown dwarf companion candidate

is detected, which needs to be confirmed by proper motion and/or

spectroscopy. Several other faint companion candidates are already

rejected by second epoch imaging. Among 21 stars observed in

Tucana/Horologium, there are not more than one to five brown dwarf

companions outside of 75 AU (1.5" at 50 pc); most certainly only <5

% of the Tuc/HorA stars have brown dwarf companions (13 to 78 Jupiter

masses) outside of 75 AU. For the first time, we can report an upper

limit for the frequency of massive planets (~ 10 M_jup) at wide

separations (~ 100 AU) using a meaningfull and homogeneous sample: Of 11

stars observed sufficiently deep in beta Pic (12 Myrs), not more than

one has a massive planet outside of ~ 100 AU, i.e. massive planets at

large separations are rare (<9 %).

Department of Astrophysics
External organisation(s)
European Southern Observatory (Chile), Max-Planck-Institut für extraterrestrische Physik, Universität zu Köln, Friedrich-Schiller-Universität Jena, Thüringer Landessternwarte Tautenburg
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