The Planet Formation Potential around a 45 Myr Old Accreting M Dwarf

Abstract

Debris disk detections around M dwarfs are rare, and so far no gas emission has been detected from an M dwarf debris disk. This makes the 45 Myr old M dwarf WISE J080822.18-644357.3 a bit of a curiosity; it has a strong infrared excess at an age beyond the lifetime of a typical planet-forming disk, and also exhibits broad Hα emission consistent with active accretion from a gaseous disk. To better understand the cold gas and dust properties of this system, we obtained ALMA observations of the 1.3 mm continuum and the CO/¹³CO/C¹⁸O J = 2-1 emission lines. No cold CO gas is detected from this system, ruling out a gas-rich protoplanetary disk. Unresolved dust continuum emission is detected at a flux of 198 ± 15 μJy, consistent with 0.057 ± 0.006 M _⊕ worth of optically thin dust, and consistent with being generated through a collisional cascade induced by large bodies at radii <16 au. With a sufficiently strong stellar wind, dust grains released in the outer disk can migrate inward via PR drag, potentially serving as a source of grains for the strong infrared excess.