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

## TL;DR

This study uses ALMA and MagAO observations to analyze the GQ Lup system, revealing a compact disk around GQ Lup A, no detectable disk around the companion, and insights into the formation and orbital characteristics of the substellar companion GQ Lup B.

## Contribution

First detailed multi-wavelength observational analysis of GQ Lup B's formation environment and disk properties, suggesting in situ formation and orbital characteristics.

## Key findings

- GQ Lup A's disk is compact with a radius of ~22 AU and no gaps.
- No disk signal detected from GQ Lup B at 1.3 mm.
- GQ Lup A's disk is misaligned with its spin axis and possibly with GQ Lup B's orbit.

## Abstract

Multi-wavelength observations provide a complementary view of the formation of young directly-imaged planet-mass companions. We report the ALMA 1.3 mm and Magellan adaptive optics (MagAO) H-alpha, i', z', and Ys observations of the GQ Lup system, a classical T Tauri star with a 10-40 Mjup substellar companion at ~110 AU projected separation. We estimate the accretion rates for both components from the observed H-alpha fluxes. In our 0.05 arcsec resolution ALMA map, we resolve GQ Lup A's disk in dust continuum, but no signal is found from the companion. The disk is compact, with a radius of ~22 AU, a dust mass of ~6 Earth masses, an inclination angle of ~56 deg, 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.