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 Mjup companion orbiting at ≈330 AU
(2.2"). Previous photometry and spectroscopy spanning 0.3-5 μm revealed
optical and thermal excess as well as strong Hα and Pa~β 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 μm (341 GHz) continuum observations down
to a 3-σ limit of 0.22 mJy/beam. The corresponding constraints on the
dust mass and total mass are <0.15 Mearth and <0.05 Mjup, 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 6214-210 B appears to be at the end stages of assembly and is not expected
to gain any appreciable mass over the next few Myr.Comment: Accepted to ApJ