A sub-AU outwardly truncated accretion disk around a classical T Tauri star

Abstract

We present the Spitzer Infrared Spectrograph (IRS) spectrum of SR20, a 5--10 AU binary T Tauri system in the $\rho$ Ophiuchi star forming region. The spectrum has features consistent with the presence of a disk; however, the continuum slope is steeper than the ${\lambda }^{-4/3}$ slope of an infinite geometrically thin, optically thick disk, indicating that the disk is outwardly truncated. Comparison with photometry from the literature shows a large increase in the mid-infrared flux from 1993 to 1996. We model the spectral energy distribution and IRS spectrum with a wall + optically thick irradiated disk, yielding an outer radius of 0.39${}_{+0.03}^{-0.01}$ AU, much smaller than predicted by models of binary orbits. Using a two temperature ${\chi }^2$ minimization model to fit the dust composition of the IRS spectrum, we find the disk has experienced significant grain growth: its spectrum is well-fit using opacities of grains larger than 1 $\mu$m. We conclude that the system experienced a significant gravitational perturbation in the 1990s.

4 pages, 4 figures, 1 table, accepted to ApJ Letters

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• Spitzer Infrared Spectrograph survey of young stars in the Chamaeleon I star-forming region
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• A circular polarisation survey for radio stars with the Australian SKA Pathfinder
• SPOTS: The Search for Planets Orbiting Two Stars. III. Complete Sample and Statistical Analysis
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• Spitzer Spectroscopy of the Circumprimary Disk in the Binary Brown Dwarf 2MASS J04414489+2301513