The GRAVITY young stellar object survey

XV. The star-disk interaction region of the T Tauri star DO Tau^★

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
³ Univ. de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France
⁴ Departamento de Fisica - ICEx - UFMG, Av. Antônio Carlos 6627, 30270-901 Belo Horizonte, MG, Brazil
⁵ Department of Astronomy, University of Geneva, Chemin Pegasi, 51, Versoix 1290, Switzerland
⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
⁷ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85741 Garching bei München, Germany
⁸ INAF - Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ University College Dublin (UCD), Dublin, Ireland
¹¹ Crimean Astrophysical Observatory, 298409 Nauchny, Republic of Crimea
¹² Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
¹³ Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
¹⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70264, Ciudad de México 04510, Mexico
¹⁵ Institute of Astronomy and Astrophysics, Academia Sinica, Roosevelt Rd, Taipei 10617, Taiwan
¹⁶ Universidade de Lisboa—Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
¹⁷ LIP, Laboratory for Instrumentation and Experimental Particle Physics, Av. Prof. Gama Pinto 2, Lisbon 1649-003, Portugal
¹⁸ LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
¹⁹ Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
²⁰ CENTRA—Centro de Astrofísica e Gravitaçâo, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal

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

Received: 5 December 2025
Accepted: 2 March 2026

Abstract

Context. Protoplanetary disks around young Sun-like stars are the cradles of the vast majority of detected exoplanets. Probing these disks at multiple spatial scales is key to uncovering how planets form. The inner astronomical unit, the star-disk interaction region, is of utmost importance because most detected exoplanets occupy this zone.

Aims. We aim to spatially and spectrally resolve the inner disk and star-disk interaction region of the M0.3 T Tauri star DO Tau by combining two complementary techniques.

Methods. We used high-resolution near-infrared spectra from CFHT/SPIRou to constrain the magnetospheric star-disk interaction process and optical long-baseline interferometry with ESO VLTI/GRAVITY to determine the sizes of the K-band continuum and Brγ line emitting regions. From the SPIRou spectra, we measured the veiling in the YJHK bands along with the equivalent widths of the HeI λ1083, Paβ, and Brγ emission lines, from which we estimated the mass accretion rate. We were able to monitor the time variability of these quantities thanks to our long-sequence of observations over about 40 days. We fit the GRAVITY visibilities in the continuum and the differential quantities in the line with geometrical models to obtain the orientation and the size of the inner disk as well as the size and the on-sky displacement of the Brγ emitting region.

Results. We derived a mass accretion rate of ∼10⁻⁸−10⁻⁷ M_⊙ yr⁻¹, which confirms that this ∼0.5 M_⊙ star is a strong accretor. The HI and HeI lines exhibit strong variability on a daily timescale, consistent with the burster classification of DO Tau derived from its K2 light curve. We report a periodic modulation of the intensity of the redshifted high-velocity wings of the Brγ line profile. The modulation occurs at the rotational period of the star (5.128 d), which suggests the existence of corotating magnetospheric funnel flows. We derived an upper limit of 0.35 on the ratio between the magnetospheric truncation radius and the disk corotation radius, indicative of an ordered unstable accretion regime. The size of the Brγ line emitting region obtained from GRAVITY is quite small (R_Brγ = 0.011 au ∼ 1.3 R_*), and it is much smaller than the K-band continuum emitting region (R_K = 0.09 au ∼ 11 R_*). Such a compact Brγ emission region suggests that most of the line flux originates from the magnetospheric accretion region and/or from an inner wind close to the magnetosphere-disk interface. The on-sky displacements of the blue and red Brγ line velocity channels suggest a rotation pattern of the emitting gas, as they appear to be nearly aligned along the position angle of the disk. The inclination we derived for the inner disk (∼45-55°) differs from that of the outer disk inferred from the ALMA continuum (∼30°). This points toward a misalignment or warp of the outer disk that may originate from the suspected past encounter with the neighboring HV Tau system.

Conclusions. Based on combining high-resolution spectroscopy and long baseline interferometry, we find that the T Tauri star DO Tau appears to be a strong accretor undergoing magnetospheric accretion in an ordered unstable regime, with a Brγ line emitting region as compact (∼0.01 au) as the size of its magnetosphere.