Evidence for accretion in a nearby, young brown dwarf

英文摘要：

We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353$-$562112. The object has a spectral type of M7.5, it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. The space motion vector and position on the sky indicate that the brown dwarf is probably a member of the $\sim$20 Myr old Tuc-Hor association, or that it may be an ejected member of the $\sim$12 Myr old $β$ Pic association, both would imply that 2MASS J0041353$-$562112 may in fact be older than 10 Myr. No accreting star or brown dwarf was previously known in these associations. Assuming an age of 10 Myr, the brown dwarf has a mass of about 30 M$_{\rm Jup}$ and is located at 35 pc distance. The newly discovered object is the closest accreting brown dwarf known. Its membership to an association older than 10 Myr implies that either disks in brown dwarfs can survive as long as in more massive stars, perhaps even longer, or that star formation in Tuc-Hor or $β$ Pic occured more recently than previously thought. The history and evolution of this object can provide new fundamental insight into the formation process of stars, brown dwarfs, and planets.