Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-01-24
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
To appear in ApJ, 9 pages, 9 figures
Scientific paper
We present the discovery of a substellar companion on a wide orbit around the ~2.5 Msun star HIP 78530, which is a member of the 5 Myr-old Upper Scorpius association. We have obtained follow-up imaging over two years and show that the companion and primary share common proper motion. We have also obtained JHK spectroscopy of the companion and confirm its low surface gravity, in accordance with the young age of the system. A comparison with Drift-Phoenix synthetic spectra indicates an effective temperature of 2800+/-200 K and a comparison with template spectra of young and old dwarfs indicates a spectral type of M8+/-1. The mass of the companion is estimated to be 19-26 Mjup based on its bolometric luminosity and the predictions of evolutionary models. The angular separation of the companion is 4.5", which at the distance of the primary star, 156.7 pc, corresponds to a projected separation of ~710 AU. This companion features one of the lowest mass ratios (~0.009) of any known companion at separations greater than 100 AU.
Hauschildt Peter
Helling Christiane
Janson Markus
Jayawardhana Ray
Lafreniere David
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