Discovery of a brown dwarf companion to the star HIP 64892

Abstract

We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion ($1.2705\pm 0.0023$") corresponds to a projected distance of $159\pm 12$ AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its SED and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9${}_{\hat{I}}^3\pm 1$. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of $T_{\text{eff}}=2600\pm 100$ K, and comparison of the companion photometry to the COND evolutionary models yields a mass of $\sim 29-37$ M${}_{\text{J}}$ at the estimated age of $16_{-7}^{+15}$ Myr for the system. HIP 64892 is a rare example of an extreme-mass ratio system ($q\sim 0.01$) and will be useful for testing models relating to the formation and evolution of such low-mass objects.

12 pages, 11 figures, accepted for publication in A&A