Evidence for an accretion bridge in the DX Cha circumbinary system from VLTI/MATISSE observations

TL;DR

This study presents interferometric observations of the DX Cha binary system, revealing a narrow, asymmetric circumbinary ring with potential accretion streamers, challenging previous models of a large inner disk cavity.

Contribution

First direct interferometric evidence of a narrow, asymmetric circumbinary ring with possible accretion streamers in DX Cha, using time-dependent modeling of VLTI/MATISSE data.

Findings

Detected a narrow circumbinary ring of 0.86 au diameter.

Observed azimuthal asymmetry and its change over time.

Suggested the presence of tidal accretion streamers rather than a stable cavity.

Abstract

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 $3.55$ micrometer interferometric observations of this source with the Multi Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) at the Very Large Telescope Interferometer (VLTI). 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 (FWHM) of $\sim$$0.13$ au ($1.23$ mas). The presence of circumstellar dust emission so close to the binary is unexpected, as previous hydrodynamic simulations predicted an inner disk cavity with a diameter of $\sim$$4$ au ($\sim$$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.