An adaptive optics multiplicity census of young stars in Upper Scorpius.
LAFRENIERE D., JAYAWARDHANA R., VAN KERKWIJK M.H., BRANDEKER A. and JANSON M.
Abstract (from CDS):
We present the results of a multiplicity survey of 91 stars spanning masses of ∼0.2-10 M☉ in the Upper Scorpius star-forming region, based on adaptive optics imaging with the Gemini North telescope. Our observations identified 29 binaries, 5 triples, and no higher order multiples. The corresponding raw multiplicity frequency is 0.37±0.05. In the regime where our observations are complete–companion separations of 0.''1-5'' (∼15-800 AU) with magnitude limits ranging from K < 9.3 at 0.''1 to K < 15.8 at 5''–the multiplicity frequency is 0.270.04+0.05. For similar separations, the multiplicity frequency in Upper Scorpius is comparable to that in other dispersed star-forming regions, but is a factor of two to three higher than in denser star-forming regions or in the field. Our sample displays a constant multiplicity frequency as a function of stellar mass. Among our sample of binaries, we find that both wider (>100 AU) and higher-mass systems tend to have companions with lower companion-to-primary mass ratios. Three of the companions identified in our survey are unambiguously substellar and have estimated masses below 0.04 M☉(two of them are new discoveries from this survey–1RXS J160929.1-210524b and HIP 78530B–although we have reported them separately in earlier papers). These three companions have projected orbital separations of 300-900 AU. Based on a statistical analysis factoring in sensitivity limits, we calculate an occurrence rate of 5-40 MJup companions of ∼4.0% for orbital separations of 250-1000 AU, compared to <1.8% at smaller separations, suggesting that such companions are more frequent on wider orbits.
binaries: general - brown dwarfs - stars: formation - stars: low-mass
VizieR on-line data:
<Available at CDS (J/ApJ/785/47): table3.dat>