CrA-9 protoplanet or obscured binary

Understanding how giant planets form requires observational input from directly imaged protoplanets. In this video, I present the discovery of a faint companion in the transition disc of 2MASS J19005804-3645048 (hereafter CrA-9), an accreting M0.75 dwarf with an estimated age…

CrA-9 protoplanet or obscured binary

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Understanding how giant planets form requires observational input from directly imaged protoplanets. In this video, I present the discovery of a faint companion 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 used both VLT/NACO and VLT/SPHERE and found the faint point source at ~0.7” separation from CrA-9 (~108 au projected separation). Our 3-epoch astrometry rejects a fixed background star with a 5-sigma significance. Our analysis of the 1.0–3.8µm spectrum extracted for the companion suggests a young age based on the 1.13-µm Na index, which is also confirmed by the best-fit template of the Montreal Spectral Library. The near-IR absolute magnitudes of the object point towards a planetary-mass companion, but the observed spectrum is best reproduced with high effective temperature (3000-3100K) BT-DUSTY and BT-SETTL models. The corresponding photometric radius required to match the measured flux is only 0.60+-0.02 Jovian radius.
In this video, I also briefly 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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