An ALMA and MagAO Study of the Substellar Companion GQ Lup B

Abstract

Multi-wavelength observations provide a complementary view of the formation of young, directly imaged planetmass companions. We report the ALMA 1.3 mm and Magellan adaptive optics H alpha, i', z', and YS observations of the GQ Lup system, a classical T Tauri star with a 10-40 M-Jup substellar companion at similar to 110 au projected separation. We estimate the accretion rates for both components from the observed Ha fluxes. In our similar to 0.'' 05 resolution ALMA map, we resolve GQ Lup A's disk in the. dust continuum, but no signal is found from the companion. The disk is compact, with a radius of similar to 22 au, a dust mass of similar to 6M(circle plus), an inclination angle of similar to 56 degrees, and a very flat surface density profile indicative of a radial variation in dust grain sizes. No gaps or inner cavity are found in the disk, so there is unlikely a massive inner companion to scatter GQ Lup B outward. Thus, GQ Lup B might have formed in situ via disk fragmentation or prestellar core collapse. We also show that GQ Lup A's disk is misaligned with its spin axis, and possibly with GQ Lup B's orbit. Our analysis on the tidal truncation radius of GQ Lup A's disk suggests that GQ Lup B's orbit might have a low eccentricity.