2MASS J15460752-6258042: a mid-M dwarf hosting a prolonged accretion disc

Abstract

We report the discovery of the oldest (~55 Myr) mid-M type star known to host on-going accretion. 2MASS J15460752-6258042 (2M1546, spectral type M5, 59.2 pc) shows spectroscopic signs of accretion such as strong Ha, He I, and [O I] emission lines, from which we estimate an accretion rate of ~10^-10 Msun/yr. Considering the clearly detected infrared excess in all WISE bands, the shape of its spectral energy distribution and its age, we believe the star is surrounded by a transitional disc, clearly with some gas still present at inner radii. The position and kinematics of the star from Gaia DR2 and our own radial velocity measurements suggest membership in the nearby ~55 Myr-old Argus moving group. At only 59pc from Earth, 2M1546 is one of the nearest accreting mid-M dwarfs, making it an ideal target for studying the upper limit on the lifetimes of gas-rich discs around low mass stars.

arXiv comment7 pages, 6 figures, Accepted for publication in MNRAS

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