The Nature of Transition Circumstellar Disks I. The Ophiuchus Molecular Cloud

TL;DR

This study investigates the properties of transition circumstellar disks in the Ophiuchus cloud, revealing their heterogeneity, potential causes of inner holes, and possible planet formation signatures.

Contribution

It provides detailed observational analysis of 26 transition disks, identifying their masses, accretion rates, and potential mechanisms like photoevaporation, binarity, and planet formation.

Findings

Transition disks show a wide range of masses and accretion rates.

Some disks are likely photoevaporating or debris disks.

Evidence suggests some disks may host giant planets.

Abstract

We have obtained millimeter wavelength photometry, high-resolution optical spectroscopy and adaptive optics near-infrared imaging for a sample of 26 Spitzer-selected transition circumstellar disks. All of our targets are located in the Ophiuchus molecular cloud (d ~125 pc) and have Spectral Energy Distributions (SEDs) suggesting the presence of inner opacity holes. We use these ground-based data to estimate the disk mass, multiplicity, and accretion rate for each object in our sample in order to investigate the mechanisms potentially responsible for their inner holes. We find that transition disks are a heterogeneous group of objects, with disk masses ranging from < 0.6 to 40 M_JUP and accretion rates ranging from <1E-11 1E-7 M_solar/yr, but most tend to have much lower masses and accretion rates than "full disks" (i.e., disks without opacity holes). Eight of our targets have stellar companions: 6 of them are binaries and the other 2 are triple systems. In four cases, the stellar companions are close enough to suspect they are responsible for the inferred inner holes. We find that 9 of our 26 targets have low disk mass (< 2.5 M_JUP) and negligible accretion (< 1E-11) M_solar/yr, and are thus consistent with photoevaporating (or photoevaporated) disks. Four of these 9 non-accreting objects have fractional disk luminosities < 1E-3 and could already be in a debris disk stage. Seventeen of our transition disks are accreting. Thirteen of these accreting objects are consistent with grain growth. The remaining 4 accreting objects have SEDs suggesting the presence of sharp inner holes, and thus are excellent candidates for harboring giant planets.