Discovery of a ~23 Mjup Brown Dwarf Orbiting ~700 AU from the Massive Star HIP 78530 in Upper Scorpius

TL;DR

This paper reports the discovery of a young, low-mass brown dwarf companion orbiting a massive star at a wide separation of approximately 700 AU, confirmed through imaging and spectroscopy, with estimated mass around 23 Jupiter masses.

Contribution

The study presents the first direct imaging and spectroscopic confirmation of a low-mass brown dwarf companion at a wide orbit around a young, massive star in Upper Scorpius.

Findings

Companion has a mass of 19-26 Mjup based on luminosity and models.

Spectroscopy indicates an effective temperature of 2800+/-200 K and spectral type M8+/-1.

The companion has a very low mass ratio (~0.009) at a large separation (~710 AU).

Abstract

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.