Discovery of a Wide Substellar Companion to a Nearby Low-Mass Star

TL;DR

This paper reports the discovery of a wide, blue L5 substellar companion to a nearby M4.5 dwarf, providing insights into low-mass star formation and offering a benchmark for evolutionary models.

Contribution

The discovery of a wide, low-mass substellar companion to a nearby star, demonstrating the star formation process can produce such systems and establishing a benchmark for models.

Findings

The companion is a wide (135 AU), blue L5 object.

The system's total mass is approximately 0.21 solar masses.

Less than 2.2% of similar M dwarfs have wide substellar companions.

Abstract

We report the discovery of a wide (135+/-25 AU), unusually blue L5 companion 2MASS J17114559+4028578 to the nearby M4.5 dwarf G 203-50 as a result of a targeted search for common proper motion pairs in the Sloan Digital Sky Survey and the Two Micron All Sky Survey. Adaptive Optics imaging with Subaru indicates that neither component is a nearly equal mass binary with separation > 0.18", and places limits on the existence of additional faint companions. An examination of TiO and CaH features in the primary's spectrum is consistent with solar metallicity and provides no evidence that G 203-50 is metal poor. We estimate an age for the primary of 1-5 Gyr based on activity. Assuming coevality of the companion, its age, gravity and metallicity can be constrained from properties of the primary, making it a suitable benchmark object for the calibration of evolutionary models and for determining the atmospheric properties of peculiar blue L dwarfs. The low total mass (M_tot=0.21+/-0.03 M_sun), intermediate mass ratio (q=0.45+/-0.14), and wide separation of this system demonstrate that the star formation process is capable of forming wide, weakly bound binary systems with low mass and BD components. Based on the sensitivity of our search we find that no more than 2.2% of early-to-mid M dwarfs (9.0 < M_V < 13.0) have wide substellar companions with m > 0.06 M_sun.