2014MNRAS.438.1102G

Relatively massive directly imaged substellar companions around nearby stars form a very intriguing class of objects. Their relatively high mass at wide separations from their host stars might suggest a more star-like formation via gravitational collapse in protostellar discs. However, also formation by core accretion (either in situ or further in and then migrating outwards) or gravitational protoplanetary disc instability is another possibility. Determining the orbit parameters of such companions will be an important step to put constraints on masses and formation scenarios. In addition, the detection of curvature in the orbits would enable us to exclude the possibility of a by-chance alignment, and would thus prove that the primary and companion are orbiting each other. The brown dwarf companion to GSC 08047-00232 was discovered in parallel by Neuhäuser et al. and Chauvin et al. We present new astrometric measurements of this system taken in the course of the past 4 years. In addition, we analyse all previously available astrometric data points of this system. With a total time baseline of more than 10 years, we were able to clearly detect differential motion between the primary star and companion. Furthermore, we can now put some constraints on the possible orbits of the companion.