Coordinated space-and ground-based monitoring of accretion bursts in a protoplanetary disc: The orbital and accretion properties of DQ Tau^★

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
² SETI Institute, Mountain View, CA 94043, USA/NASA Ames Research Center, Moffett Field, CA 94035, USA
³ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
⁴ Department of Physics, Texas State University, 749 North Comanche Street, San Marcos, TX 78666, USA
⁵ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano MI, Italy
⁶ Dipartimento di Matematica, Università degli Studi di Milano, Via Saldini 50, 20133, Milano, Italy
⁷ Department of Physics, Maynooth University, Maynooth, Co. Kildare, Ireland
⁸ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁰ Alma Mater Studiorum – Università di Bologna, Dipartimento di Fisica e Astronomia “Augusto Righi”, Via Gobetti 93/2, 40129 Bologna, Italy
¹¹ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 26 September 2025
Accepted: 8 November 2025

Abstract

Multiplicity in pre-main-sequence (PMS) systems shapes circumstellar and circumbinary discs, often resulting in morphological features such as inner cavities, spiral arms, and gas streamers that facilitate mass transfer between the disc and stars. Consequently, accretion in eccentric close binaries is highly variable and synchronized with their orbits, producing distinct bursts near periastron passages. In this study, we examine the orbital and accretion properties of the eccentric Classical T-Tauri binary star DQ Tau using medium- to high-resolution spectroscopy obtained using the Very Large Telescope (VLT) X-shooter and UVES instruments. The data have been taken at the time of a monitoring of the inner disc chemistry with JWST, and the results of our analysis are needed for a correct interpretation of the JWST data. We refine the orbital parameters of the system and report an increment in the argument of periastron of ~30º. This apsidal motion can be caused by the massive disc acting as a third body in the system. We also explore the possibility that the resulting apsidal motion is caused by a still not-detected additional (sub-)stellar companion. In this case, we estimate a lower limit of ~15 M_J for the mass of this putative companion at the cavity edge (a = 3a_bin). We investigate the accretion of the primary and secondary stars in the system using the Ca II 849.8 nm emission line. We observe the primary accretes more at the periastron compared to its previous quiescent phases. The secondary dominates the accretion at post-periastron phases. Additionally, we report an elevated L_acc at apastron, possibly due to the interaction of the stars with irregularly shaped structures near their closest approach to the circumbinary disc. Finally, we derive the accretion luminosity of each star across the disentangled epochs and compare the results to those derived by the UV excess, finding a good overall agreement. The individual L_acc values can be used as an input for the chemical models.