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Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2021

A faint companion around CrA-9: protoplanet or obscured binary?

V. Christiaens
  • Function : Author
M. -G. Ubeira-Gabellini
  • Function : Author
H. Cánovas
  • Function : Author
B. Pairet
  • Function : Author
O. Absil
  • Function : Author
S. Casassus
  • Function : Author
J. H. Girard
  • Function : Author
A. Zurlo
  • Function : Author
Y. Aoyama
  • Function : Author
G. -D. Marleau
  • Function : Author
L. Spina
  • Function : Author
N. van der Marel
  • Function : Author
L. Cieza
  • Function : Author
G. Lodato
  • Function : Author
S. Pérez
  • Function : Author
D. J. Price
  • Function : Author
M. Reggiani
  • Function : Author

Abstract

Understanding how giant planets form requires observational input from directly imaged protoplanets. We used VLT/NACO and VLT/SPHERE to search for companions in the transition disc of 2MASS J19005804-3645048 (hereafter CrA-9), an accreting M0.75 dwarf with an estimated age of 1-2 Myr. We found a faint point source at ∼0.7-arcsec separation from CrA-9 (∼108 au projected separation). Our 3-epoch astrometry rejects a fixed background star with a 5σ significance. The near-IR absolute magnitudes of the object point towards a planetary-mass companion. However, our analysis of the 1.0-3.8 $\,\mu$ m spectrum extracted for the companion suggests it is a young M5.5 dwarf, based on both the 1.13-μm Na index and comparison with templates of the Montreal Spectral Library. The observed spectrum is best reproduced with high effective temperature ( $3057^{+119}_{-36}$ K) BT-DUSTY and BT-SETTL models, but the corresponding photometric radius required to match the measured flux is only $0.60^{+0.01}_{-0.04}$ Jovian radius. We discuss possible explanations to reconcile our measurements, including an M-dwarf companion obscured by an edge-on circum-secondary disc or the shock-heated part of the photosphere of an accreting protoplanet. Follow-up observations covering a larger wavelength range and/or at finer spectral resolution are required to discriminate these two scenarios.
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Dates and versions

insu-03705315 , version 1 (14-04-2023)

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V. Christiaens, M. -G. Ubeira-Gabellini, H. Cánovas, P. Delorme, B. Pairet, et al.. A faint companion around CrA-9: protoplanet or obscured binary?. Monthly Notices of the Royal Astronomical Society, 2021, 502, pp.6117-6139. ⟨10.1093/mnras/stab480⟩. ⟨insu-03705315⟩
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