The GRAVITY young stellar object survey

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 (RBrγ = 0.011 au ∼ 1.3 R*), and it is much smaller than the K-band continuum emitting region (RK = 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.