Evidence for an Accretion Bridge in the DX Cha Circumbinary System from VLTI/MATISSE Observations

DX Cha (HD 104237) is a spectroscopic binary consisting of a Herbig A7.5Ve-A8Ve primary star and a K3-type companion. Here we report on new 3.55 μm interferometric observations of this source with the Multi Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) at the Very Large Telescope Interferometer. To model the four MATISSE observations obtained between 2020 and 2023, we constructed a time-dependent interferometric model of the system, using the oimodeler software. The model consists of an asymmetric ring and two point sources on a Keplerian orbit. Our best-fit model consists of a circumbinary ring with a diameter of 0.86 au (8.1 mas), featuring a strong azimuthal asymmetry. We found that the position angle of the asymmetry changes tens of degrees between the MATISSE epochs. The ring is relatively narrow, with a full width at half-maximum of ∼0.13 au (1.23 mas). The presence of circumstellar dust emission so close to the binary is unexpected, as previous hydrodynamic simulations predicted an inner disk cavity with a diameter of ∼4 au (∼37.5 mas). Thus, we argue that the narrow envelope of material we detected is probably not a gravitationally stable circumbinary ring but may be part of tidal accretion streamers channeling material from the inner edge of the disk toward the stars.