AN ALMA DISK MASS FOR THE CANDIDATE PROTOPLANETARY COMPANION TO FW TAU

作者:Kraus, Adam L.*; Andrews, Sean M.; Bowler, Brendan P.; Herczeg, Gregory; Ireland, Michael J.; Liu, Michael C.; Metchev, Stanimir; Cruz, Kelle L.
来源:Astrophysical Journal Letters, 2015, 798(1): L23.
DOI:10.1088/2041-8205/798/1/L23

摘要

We present ALMA observations of the FW Tau system, a close binary pair of M5 stars with a wide-orbit (300 AU projected separation) substellar companion. The companion is extremely faint and red in the optical and near-infrared, but boasts a weak far-infrared excess and optical/near-infrared emission lines indicative of a primordial accretion disk of gas and dust. The component-resolved 1.3mm continuum emission is found to be associated only with the companion, with a flux (1.78 +/- 0.03 mJy) that indicates a dust mass of 1-2M(circle plus). While this mass reservoir is insufficient to form a giant planet, it is more than sufficient to produce an analog of the Kepler-42 exoplanetary system or the Galilean satellites. The mass and geometry of the disk-bearing FW Tau companion remains unclear. Near-infrared spectroscopy shows deep water bands that indicate a spectral type later than M5, but substantial veiling prevents a more accurate determination of the effective temperature (and hence mass). Both a disk-bearing "planetary-mass" companion seen in direct light or a brown dwarf tertiary viewed in light scattered by an edge-on disk or envelope remain possibilities.