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Characterizing the Protolunar Disk of the Accreting Companion GQ Lupi B

M. D'Onofrio, T. Stolker, S. Y. Haffert, A. Y. Kesseli, R. G. van Holstein, Y. Aoyama, J. Brinchmann, G. Cugno, J. H. Girard, G. Marleau, M. R. Meyer, J. Milli, S. P. Quanz, I. A. G. Snellen, K. O. Todorov

GQ Lup B is a young and accreting, substellar companion that appears to drive a spiral arm in the circumstellar disk of its host star. We report high-contrast imaging observations of GQ Lup B with VLT/NACO at 4–5 μm and medium-resolution integral field spectroscopy with VLT/MUSE. The optical spectrum is consistent with an M9 spectral type, shows characteristics of a low-gravity atmosphere, and exhibits strong Hα emission. The H − M' color is ≳1 mag redder than field dwarfs with similar spectral types, and a detailed analysis of the spectral energy distribution (SED) from optical to mid-infrared wavelengths reveals excess emission in the L', NB4.05, and M' bands. The excess flux is well described by a blackbody component with Tdisk ≈ 460 K and Rdisk ≈ 65 RJ and is expected to trace continuum emission from small grains in a protolunar disk. We derive an extinction of AV ≈ 2.3 mag from the broadband SED with a suspected origin in the vicinity of the companion. We also combine 15 yr of astrometric measurements and constrain the mutual inclination with the circumstellar disk to 84 ± 9 deg, indicating a tumultuous dynamical evolution or a stellar-like formation pathway. From the measured Hα flux and the estimated companion mass, Mp ≈ 30 MJ, we derive an accretion rate of M˙≈ 10−6.5 MJ yr−1 . We speculate that the disk is in a transitional stage in which the assembly of satellites from a pebble reservoir has opened a central cavity while GQ Lup B is in the final stages of its formation.

Accretion; Brown dwarfs; Direct imaging; Planet formation; Natural satellite formation; High angular resolution

Based on observations collected under ESO programmes 0101.C-0502(B), 0102.C-0649(A), and 0103.C-0524(A).

The Astronomical Journal
Volume 162, Number 6
2021 December

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia