Short- and long-term variations of the high mass accretion rate classical T Tauri star DR Tau

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
² CSFK, MTA Centre of Excellence, Budapest, Konkoly Thege Miklós út 15-17, 1121, Hungary
³ School of Physics and Astronomy, Sir William Henry Bragg Building, Woodhouse Ln., University of Leeds, Leeds LS2 9JT, UK
⁴ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire, AL10 9AB, UK
⁵ Institute of Physics and Astronomy, ELTE, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna, Austria
⁸ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁹ Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, 31270-901, Brazil
¹⁰ Science Division, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
¹¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹² Mt. Suhora Astronomical Observatory, University of the National Education Commission, ul. Podchorążych 2, 30-084 Kraków, Poland
¹³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany
¹⁴ Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
¹⁵ MTA-ELTE Lendület “Momentum” Milky Way Research Group, Hungary

^⋆ Corresponding author: g.zsidi@herts.ac.uk

Received: 12 February 2024
Accepted: 6 May 2025

Abstract

Context. Classical T Tauri stars are newly formed, low-mass stars, which may display both periodic and random variations in their brightness. These systems are surrounded by a circumstellar disk, from which material falls onto the stellar surface. The interaction between the star and the circumstellar disk is time dependent, leading to short- or long-term physical changes in the physical environment, and hence variability of the system.

Aims. DR Tau is a highly variable young star. By compiling a large dataset with high-cadence photometric, and high-resolution spectroscopic observations, we aim to examine the short- and long-term variability of the system, and identify the underlying physical mechanisms.

Methods. We combined multifilter ground-based optical, near-infrared, and space-based mid-infrared (Spitzer Space Telescope) monitoring observations from 2009, 2017, and 2021 with high-cadence optical Kepler K2 and TESS light curves. We complemented our photometric dataset with spectropolarimetric monitoring observations obtained with the CFHT/ESPaDOnS instrument in 2016, which provided high-resolution data at optical wavelengths.

Results. Our results reveal that DR Tau exhibits stochastic photometric variability not only on daily, but also on hourly timescales, with a peak-to-peak amplitude of 1.4 mag probably originating from accretion related variations. Our ground-based multifilter photometry shows that the shape of the light curves are similar at all wavelengths, although the amplitude of the variability decreases with increasing wavelength. This trend toward the infrared wavelengths suggests that part of the disk may be optically thick and invariable. In addition to this, the high-cadence Kepler and TESS data allowed us to carry out a detailed period analysis. The spectroscopic analysis showed that the Hα line presents the most complex line profile with several components, but the significance of the components changes over time. This suggests the presence and variation of both accretion flow and wind. Broad and narrow components can be clearly distinguished in the He I and the Ca II lines, which suggests a contribution from both the accretion flow and the post-shock region. The CFHT/ESPaDOnS data suggest that the strength of the longitudinal magnetic field varies between 400 and 1800 G.

Conclusions. DR Tau exhibits a high level of photometric and spectroscopic variability on both short and long timescales, which is caused by the combination of accretion, wind, stellar activity, and obscuration by circumstellar matter. Furthermore, the significance of the physical mechanisms that cause the observed variability changes over time.