The GRAVITY young stellar object survey -- XV. The star-disk interaction region of the T Tauri star DO Tau

Abstract

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. 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. 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 Br$γ$ line emitting regions. From the SPIRou spectra, we confirmed that this ~0.5 M$_\odot$ 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 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 Br$γ$ line emitting region obtained from GRAVITY is much smaller than the K-band continuum emitting region. This compact Br$γ$ emission region ($R_{Brγ} \sim$ 0.011 au) 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 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.

Figures (13)

• Figure 1: Top: Series of the near-infrared line profiles ${\rm HeI}$ 1083 nm, ${\rm Pa}\beta$, and ${\rm Br}\gamma$ plotted as a function of JD-2,460,000 (left) and rotational phase (right). The color code corresponds to successive rotational cycles. Middle: Plotted profiles superimposed in a single image to illustrate their variability. The vertical dotted line indicates the stellar rest velocity. Bottom: Two-dimensional periodograms across the line profiles. The color code reflects the periodogram power, ranging from 20 (blue) to 60% (red) of the maximum power. The FAP level of 0.1 is shown as black contours. The horizontal dotted red line drawn at a frequency of 0.195 day$^{-1}$ indicates the star's rotational period (P = 5.128 d). The white curve is the mean line profile.
• Figure 2: Near-infrared veiling in the YJHK bands ( top) and line equivalent widths for the HeI 1083 nm, ${\rm Pa}\beta$, and ${\rm Br}\gamma$ line profiles ( bottom) as a function of Julian date. The measurement error is usually smaller than the symbol size (see Table \ref{['tab:vradveiling']}).
• Figure 3: Equivalent width of the ${\rm HeI}$, ${\rm Pa}\beta$, and BrG lines as a function of veiling in the JHK bands. Each line is compared to the veiling within the same wavelength range.
• Figure 4: Veiling corrected equivalent widths, EW$\times$(1+r), of the ${\rm Pa}\beta$ and ${\rm Br}\gamma$ lines as a function of rotational phase.
• Figure 5: GRAVITY observations of DO Tau with the AT (top) and with the UT (bottom) configurations of the VLTI. The visibilities squared (left) and closure phases (middle) for the central spectral channel of binned data ($\lambda$ = 2.15 $\mu$m) are plotted as a function of the spatial frequency. The corresponding (u, v) planes over the K band are plotted in the right panels. The blue symbols at the bottom of the visibility and closure phase curves display the amplitude of the residuals of the best-fit ring models. See text for detail.