Time-resolved protoplanetary disk physics in DQ Tau with JWST

TL;DR

This work uses four JWST/MIRI spectra of the eccentric binary DQ Tau, complemented by optical/NIR spectroscopy and multi-band photometry, to trace how moderate accretion bursts sculpt the inner planet-forming disk. The inner rim shows rapid, phase-locked temperature and position changes that drive variable shadowing of the outer disk, modulating the 10 μm silicate feature, while gas tracers (CO, HCN, H2O, [Ne II]) respond to accretion level with distinct timescales. Dust mineralogy remains largely constant, dominated by large amorphous olivine/pyroxene and some crystalline enstatite, implying that illumination and dynamics, not composition, govern the observed variability. Collectively, the results establish a concrete link between episodic accretion and inner-disk thermodynamics in a circumbinary system, highlighting the impact of moderate accretion variability on planet-forming environments and motivating coordinated, time-domain studies with JWST and ground-based facilities.

Abstract

Accretion variability is ubiquitous in YSOs. While large outbursts may strongly affect the disk, the effects of moderate bursts are less understood. We aim to study the physical response of the disk around the eccentric binary system DQ Tau to its periodic accretion changes. We organized a multi-wavelength campaign centered on four JWST/MIRI spectra. We targeted three periastrons (high accretion state) and one apastron (quiescence). We used optical and near-infrared spectroscopy and photometry to measure how the accretion luminosity varies. We decomposed the multi-epoch SEDs into stellar, accretion, and rim components. We fitted the solid-state features using various opacity curves and the molecular features using slab models. We find the inner disk of DQ Tau to be highly dynamic. The temperature, luminosity, and location of the inner dust rim vary in response to the movement of stars and the L_acc variations. This causes variable shadowing of the outer disk, leading to an anti-correlation between the rim temperature and the strength of the silicate feature. The dust mineralogy remains constant, dominated by large amorphous olivine and pyroxene grains, with smaller fractions of crystalline forsterite. The excitation of CO (1550-2260 K), HCN (880-980 K), and hot H2O (740-860 K) molecules as well as the luminosity of the [NeII] line correlate with the accretion rate, while the warm (650 K) and cold (170-200 K) H2O components are mostly constant. CO emission, originating from a hot (>1500 K) region likely within the dust sublimation radius, is most sensitive to L_acc changes. In comparison with other T Tauri disks, DQ Tau is highly C-poor and displays moderately inefficient pebble drift. We conclude that even moderate accretion rate changes affect the thermal structure in the planet-forming disk regions on short timescales, providing a crucial benchmark for understanding disk evolution.

Figures (20)

• Figure 1: JWST MIRI MRS spectra of DQ Tau. Various colors mark the different observing epochs, whose dates and the corresponding orbital phases are indicated in the upper left corner. The bottom panel shows the continuum-subtracted spectra shifted along the y axis for clarity.
• Figure 2: Light curves (top) and accretion luminosity (bottom) of DQ Tau. Vertical dashed lines mark the epochs of periastrons. The solid vertical lines in color show the epochs of the JWST/MIRI observations.
• Figure 3: Accretion luminosity of DQ Tau as a function of time. The $g$ (cyan), $V$ (green), $r$ (orange), and $i$ (red) data points were first scaled to match the $B$ (blue) filter, then scaled again to convert the B magnitudes to $L_{\rm acc}$. Symbol types are as in Fig. \ref{['fig:light']}. For more details, see Sec. \ref{['sec:acc']}.
• Figure 4: Spectral energy distributions of DQ Tau at the four epochs of the JWST/MIRI observations. The spectra between $0.7-5.3\,\mu$m are from IRTF/SpeX, while the spectra between $4.9 - 27.5\,\mu$m are the line-free MIRI spectra. Colored dots are REM $JHK$ and SpeX $L'$ photometric points. The solid gray spectra are models constructed to account for the stellar and accretion contributions. The dashed gray curves are blackbodies with the indicated temperatures, representing emission from the inner rim of the dusty disk. Solid black curves are the sum of the stellar, accretion, and rim contributions.
• Figure 5: Variability of the strength of the 10$\,\mu$m silicate feature in DQ Tau. Linear continua were subtracted (left) or were used to normalize the spectra (right).