AN ALMA CONSTRAINT ON THE GSC 6214-210 B CIRCUM-SUBSTELLAR ACCRETION DISK MASS

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of GSC 6214-210 A and B, a solar-mass member of the 5-10 Myr Upper Scorpius association with a 15 +/- 2 M-Jup companion orbiting at approximate to 330 AU (2 ''.2). Previous photometry and spectroscopy spanning 0.3-5 mu m revealed optical and thermal excess as well as strong H alpha and Pa beta emission originating from a circum-substellar accretion disk around GSC 6214-210 B, making it the lowest-mass companion with unambiguous evidence of a subdisk. Despite ALMA's unprecedented sensitivity and angular resolution, neither component was detected in our 880 mu m (341 GHz) continuum observations down to a 3 sigma limit of 0.22 mJy/beam. The corresponding constraints on the dust mass and total mass are <0.15M(circle plus) and <0.05 M-Jup, respectively, or <0.003% and <0.3% of the mass of GSC 6214-210 B itself assuming a 100:1 gas-to-dust ratio and characteristic dust temperature of 10-20 K. If the host star possesses a putative circum-stellar disk then at most it is a meager 0.0015% of the primary mass, implying that giant planet formation has certainly ceased in this system. Considering these limits and its current accretion rate, GSC 6214210 B appears to be at the end stages of assembly and is not expected to gain any appreciable mass over the next few megayears.