The GRAVITY Young Stellar Object survey. VII. The inner dusty disks of T Tauri stars

TL;DR

This study extends high-angular-resolution K-band interferometry to 17 T Tauri stars with GRAVITY, enabling a homogeneous look at the inner dust rims across a broader pre-main-sequence population. The data are modeled with a star-plus-ring-plus-halo geometry, revealing that inner dusty disks form wide rings with half-flux radii up to ~0.34 au (median ~0.16 au), typically larger than dust-subli mation radii and largely independent of accretion rate. Scattered light plays a significant role in the K-band, and halo components are necessary to accurately reproduce short-baseline visibilities; the N-to-K size ratio emerges as a proxy for distinguishing disk structures related to silicate features and possibly evolutionary state. A subset of sources shows misalignment between inner GRAVITY-disks and outer ALMA-disks, highlighting complex disk morphologies and the need for multi-wavelength, multi-scale modeling to understand planet-forming environments.

Abstract

These protoplanetary disks in T Tauri stars play a central role in star and planet formation. We spatially resolve at sub-au scales the innermost regions of a sample of T Tauri's disks to better understand their morphology and composition. We extended our homogeneous data set of 27 Herbig stars and collected near-IR K-band observations of 17 T Tauri stars, spanning effective temperatures and luminosities in the ranges of ~4000-6000 K and ~0.4-10 Lsun. We focus on the continuum emission and develop semi-physical geometrical models to fit the interferometric data and search for trends between the properties of the disk and the central star. The best-fit models of the disk's inner rim correspond to wide rings. We extend the Radius-luminosity relation toward the smallest luminosities (0.4-10 Lsun) and find the R~L^(1/2) trend is no longer valid, since the K-band sizes measured with GRAVITY are larger than the predicted sizes from sublimation radius computation. No clear correlation between the K-band half-flux radius and the mass accretion rate is seen. Having magnetic truncation radii in agreement with the K-band GRAVITY sizes would require magnetic fields as strong as a few kG, which should have been detected, suggesting that accretion is not the main process governing the location of the half-flux radius of the inner dusty disk. Our measurements agree with models that take into account the scattered light. The N-to-K band size ratio may be a proxy for disentangling disks with silicate features in emission from disks with weak and/or in absorption silicate features. When comparing inclinations and PA of the inner disks to those of the outer disks (ALMA) in nine objects of our sample, we detect misalignments for four objects.

Figures (15)

• Figure 1: Our T Tauri sample set in the Hertzsprung-Russell diagram. The colors of the symbols denote the star forming regions. Dashed blue lines denote the isochrones for 1, 2, 3, 5, 10, 12, and 100 Ma, and solid gray lines the iso-mass tracks from 0.6 to 3 M$_\odot$. The tracks are Pre-Main Sequence (PMS) PISA tracks PISA for solar abundances ($Z$ = 0.02 and $Y$ = 0.288), a solar-calibrated mixing length ($\alpha$ = 1.68), and an initial deuterium abundance of 2$\times$10$^{-5}$. The circles denote the fully convective stars, while the triangles denote the stars with a radiative core and a convective envelope.
• Figure 2: Histogram of the half-flux radius of the ring model in the K-band of our sample. The orange dashed line corresponds to the median value.
• Figure 3: Key size properties of our targets in the ring model approach: corotation radii $R_{\rm co}$ (black circles), magnetic truncation radii $R_{\rm mag}$ for a magnetic field of 1 kG (gray triangles), range of sublimation radii $R_{\rm sub}$ (gray lines), half-flux radii $a$ derived from the GRAVITY measurements (white squares) including 1-$\sigma$ error bars (red lines). The width-to-radius ratio $w$ is not included in this schematic view. The targets are ordered by increasing stellar luminosities, from top to bottom. For comparison, we display the achieved angular resolution (blue rectangles) defined by $\lambda_0/2B_{\rm max}$ with $\lambda_0$ = 2.15 $\mu$m the central wavelength of the K band, and $B_{\rm max}$ the maximal interferometric baseline for each dataset. All angular resolutions are converted in au by using the distances of Table 1. For DR Tau and AS 353, the blue arrows indicate the exact location of the blue mark. Two values of $R_{\rm co}$ are reported for AS205 N from the literature (see Table \ref{['tab:charac_sizes']}).
• Figure 4: Radius-Luminosity relation for our T Tauri sample (blue symbols) and for the Herbig sample (gray symbols; see Paper I). The lines correspond to different models of a passively irradiated disk with an optically thin inner cavity: dust grain temperature of 1300 K (orange) and of 1700 K (red); dust cooling efficiency of 0.1 (solid lines) and of 1 (dashed lines). The insert zooms in the T Tauri region: the numbers refer to Table 1; the circles denote the fully convective stars, while the triangles denote the stars with a radiative core and a convective envelope.
• Figure 5: Half-flux radius of the ring model in the K-band as a function of the accretion rate of our targets. The colour codes the luminosity of the central star and the numbers refer to Table \ref{['tab:param_fond']}.