Magnetospheric accretion in the intermediate-mass T Tauri star HQ Tauri^⋆

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: kim.pouilly@univ-grenoble-alpes.fr
² Departamento de Fisica – ICEx – UFMG, Av. Antônio Carlos 6627, 30270-901 Belo Horizonte, MG, Brazil
³ Bay Area Environmental Research Institute, 625 2nd St Ste. 209, Petaluma, CA 94952, USA
⁴ Univ. de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France
⁵ Crimean Astrophysical Observatory, Nauchny, Crimea 298409, Ukraine
⁶ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁷ Infrared Science Archive (IRSA), IPAC, California Institute of Technology, 1200 E. California Blvd, MS 100-22, Pasadena, CA 91125, USA

Received: 3 April 2020
Accepted: 3 August 2020

Abstract

Context. Classical T Tauri stars are pre-main sequence stars surrounded by an accretion disk. They host a strong magnetic field, and both magnetospheric accretion and ejection processes develop as the young magnetic star interacts with its disk. Studying this interaction is a major goal toward understanding the properties of young stars and their evolution.

Aims. The goal of this study is to investigate the accretion process in the young stellar system HQ Tau, an intermediate-mass T Tauri star (1.9 M_⊙).

Methods. The time variability of the system is investigated both photometrically, using Kepler-K2 and complementary light curves, and from a high-resolution spectropolarimetric time series obtained with ESPaDOnS at CFHT.

Results. The quasi-sinusoidal Kepler-K2 light curve exhibits a period of 2.424 d, which we ascribe to the rotational period of the star. The radial velocity of the system shows the same periodicity, as expected from the modulation of the photospheric line profiles by surface spots. A similar period is found in the red wing of several emission lines (e.g., HI, CaII, NaI), due to the appearance of inverse P Cygni components, indicative of accretion funnel flows. Signatures of outflows are also seen in the line profiles, some being periodic, others transient. The polarimetric analysis indicates a complex, moderately strong magnetic field which is possibly sufficient to truncate the inner disk close to the corotation radius, r_cor ∼ 3.5 R_⋆. Additionally, we report HQ Tau to be a spectroscopic binary candidate whose orbit remains to be determined.

Conclusions. The results of this study expand upon those previously reported for low-mass T Tauri stars, as they indicate that the magnetospheric accretion process may still operate in intermediate-mass pre-main sequence stars, such as HQ Tauri.