Herschel Observations of the T Cha Transition Disk: Constraining the Outer Disk Properties

TL;DR

This study uses Herschel photometry to analyze the outer disk of the T Cha transition disk, revealing it is either very small or very tenuous, with implications for understanding its planetary formation environment.

Contribution

The paper provides new Herschel far-IR data and models the entire SED of T Cha, constraining the outer disk properties and highlighting its unusual structure.

Findings

Outer disk likely contains little or no dust beyond 40 AU

Outer disk could be very compact or have a steep surface density profile

Results suggest an unusual outer disk structure with different formation implications

Abstract

T Cha is a nearby (d = 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. (2011) recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 micron) of T Cha from the "Dust, Ice, and Gas in Time" (DIGIT) Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 micron without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond 40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.