The accretion process in the DQ Tau binary system

Abstract

Mass accretion from the circumstellar disk onto the protostar is a fundamental process during star formation. Measuring the mass accretion rate is particularly challenging for stars belonging to binary systems, because it is often difficult to discriminate which component is accreting. DQ~Tau is an almost equal-mass spectroscopic binary system where the components orbit each other every 15.8~days. The system is known to display pulsed accretion, i.e., the periodic modulation of the accretion by the components on eccentric orbit. We present multiepoch ESO/VLT X-Shooter observations of DQ~Tau, with the aim to determine which component of this system is the main accreting source. We use the absorption lines in the spectra to determine the radial velocity of the two components, and measure the continuum veiling as a function of wavelength and time. We fit the observed spectra with non-accreting templates to correct for the photospheric and chromospheric contribution. In the corrected spectra we study in details the profiles of the emission lines and calculate mass accretion rates for the system as a function of orbital phase. In accordance with previous findings, we detect elevated accretion close to periastron. We measure that the accretion rate varies between $10^{-8.5}$ and $10^{-7.3}$ Msun/yr. The emission line profiles suggest that both stars are actively accreting and the dominant accretor is not always the same component, varying in few orbits.