Strong H-alpha emission and signs of accretion in a circumbinary planetary mass companion from MUSE.

Context: Using intrinsic H-alpha emission to detect substellar companions can be advantageous for improving contrasts in direct imaging, and probing planetary formation theories through the characterisation of accreting exoplanets. Aims: In this work we aim to characterise the young circumbinary planetary mass companion 2MASS J01033563-5515561 (AB)b (Delorme 1 (AB)b) through medium resolution spectroscopy. Methods: We have used the new Narrow-Field Mode (NFM) for the MUSE integral-field spectrograph, located on the ESO Very Large Telescope, during SV time to obtain optical spectra of Delorme 1 (AB)b. Results: We report the discovery of very strong H-alpha and H-beta emission, accompanied by He I emission, consistent with an active accretion scenario. We provide accretion rate estimates obtained from several independent methods and find a likely mass of 12-15 M_Jup for Delorme 1 (AB)b, also consistent with previous estimates. Conclusions: Signs of active accretion in the Delorme 1 system could indicate a younger age than the ~30-40 Myr expected from a likely Tucana-Horologium (THA) membership. Previous works have also shown the central binary to be overluminous, which gives further indication of a younger age. However, recent discoveries of active disks in relatively old (~40 Myr), very low-mass systems suggests that ongoing accretion in Delorme 1 (AB)b might not require in and of itself that the system is younger than the age implied by its THA membership.