Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. IV. Discovery of an M9 + L6 BInary Separated by Over 100 AU

TL;DR

This paper reports the discovery of a wide binary system consisting of an M9 dwarf and an L6 brown dwarf companion separated by over 100 AU, providing valuable data for understanding very low mass star and brown dwarf formation.

Contribution

The discovery of a wide M9 + L6 binary system with detailed spectroscopic analysis, expanding the sample of such systems and offering new insights into their formation and evolution.

Findings

The binary has a separation of approximately 130 AU.

The secondary is a brown dwarf near the hydrogen-burning limit.

The system's properties suggest an age of 2-4 Gyr and challenge dynamical ejection formation models.

Abstract

We report the discovery of a faint L6 \pm 1 companion to the previously known M9 dwarf, 2MASS J01303563-4445411, based on our near-infrared imaging and spectroscopic observations with the 3m Infrared Telescope Facility SpeX imager/spectrometer. The visual binary is separated by 3. 28 \pm 0. 05 on the sky at a spectrophotometric distance of 40 \pm 14 pc. The projected physical separation is 130 \pm 50 AU, making it one of the widest VLM field multiples containing a brown dwarf companion. 2MASS J0130-4445 is only one of ten wide VLM pairs and only one of six in the field. The secondary is considerably fainter ({\Delta}K ~ 2.35 mag) and redder ({\Delta} (J - Ks) ~ 0.81 dex), consistent with component near-infrared types of M9.0 \pm 0.5 and L6 \pm 1 based on our resolved spectroscopy. The component types suggest a secondary mass well within the hydrogen-burning limit and an age-dependent mass ratio of 0.6-0.9. The system's space motion and spectroscopic indicators suggest an age of 2-4 Gyr while the model-dependent masses and binding energies suggest that this system is unlikely to have formed via dynamical ejection. The age, composition, and separation of the 2MASS J01303563-4445411 system make it useful for tests of VLM formation theories and of condensate cloud formation in L dwarfs.