SAFARI I: A SPHERE discovery of a super metal-rich M dwarf companion to the star HD 86006

• Published in: arXiv.org 2018-06
• Main Authors: Pantoja, B M, Jenkins, J S, Girard, J H, Vigan, A, Salter, G S, Jones, M I
• Format: Article
• Language: English
• Subjects: Computer simulation; Low mass stars; Luminosity; M stars; Radial velocity; Red dwarf stars; Spectra; Star & galaxy formation; Stellar age
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1806.10067

We report the direct detection of a fully convective, early-to-mid M-dwarf companion orbiting the star HD 86006, using ESO-SPHERE during Science Verification as part of the SAFARI program. HARPS+CORALIE radial velocity measurements first indicated a possible companion. Such work highlights the synergies that are now possible between these two observing methods. We studied the companion by comparing our observed spectra with BT-Settl models and template spectra, measuring spectral indices to obtain a spectral type, and used a joint radial velocity and astrometric fit to simulate the companion's orbit. The companion was found to be 4.14 mag fainter than the primary in the H2 band, residing at a physical separation of \(\sim\) 25 AU, with a \(T_\mathrm{eff}\) and spectral type of 3321 \(\pm\) 111 K and M 4.1 \(\pm\) 1.1, respectively. We note that the age derived from BT-Settl models for such a star is too low by over two orders of magnitude, similar to other known field mid-M stars. We searched for the radial velocity companion to HD 90520 without any clear detection, however we reached a low contrast level of \(\Delta\)H2 = 10.3 mag (or \(1.3 * 10^{-4}\)) at 0.2\(''\) and 12.6 mag (or \(10^{-5}\)) at 0.5\(''\), allowing us to rule out any low-mass companions with masses of 0.07 and 0.05 M\(_{\odot}\) at these separations. This discovery provides us with the exciting opportunity to better constrain the mass-luminosity relation for low-mass stars in the super metal-rich domain, expanding our understanding of the most-common types of stars and substellar objects.