Resolved spectroscopy of M dwarf/L dwarf binaries. IV. Discovery of an M9 + L6 binary separated by over 100 AU

摘要

We report the discovery of a faint L6 ± 1 companion to the previously known M9 dwarf, 2MASS J01303563-4445411, based on our near-infrared imaging and spectroscopic observations with the 3 m Infrared Telescope Facility SpeX imager/spectrometer. The visual binary is separated by 3″.28 ± 0″.05 on the sky at a spectrophotometric distance of 40 ± 14 pc. The projected physical separation is 130 ± 50 AU, making it one of the widest very low mass (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 (ΔK ≈ 2.35 mag) and redder (Δ (J -Ks) ≈ 0.81 dex), consistent with component near-infrared types of M9.0 ± 0.5 and L6 ± 1 based on our resolved spectroscopy. The component types suggest a secondary mass well below 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.