An ALMA Survey for Disks Orbiting Low-Mass Stars in the TW Hya Association

TL;DR

This ALMA survey of low-mass stars in the TW Hya Association detected cold dust in four systems and molecular gas in one, revealing the presence of disks around the lowest mass stars known to host such material.

Contribution

First ALMA survey targeting extremely low-mass stars in TWA, detecting cold dust and molecular gas, including the lowest mass star with a disk in this age range.

Findings

Detected continuum emission around 4 systems indicating cold dust.

Identified molecular gas with Keplerian rotation in TWA 34.

Lowest mass star with a disk in the 7-10 Myr age range.

Abstract

We have carried out an ALMA survey of 15 confirmed or candidate low-mass (<0.2M$_\odot$) members of the TW Hya Association (TWA) with the goal of detecting molecular gas in the form of CO emission, as well as providing constraints on continuum emission due to cold dust. Our targets have spectral types of M4-L0 and hence represent the extreme low end of the TWA's mass function. Our ALMA survey has yielded detections of 1.3mm continuum emission around 4 systems (TWA 30B, 32, 33, & 34), suggesting the presence of cold dust grains. All continuum sources are unresolved. TWA 34 further shows 12CO(2-1) emission whose velocity structure is indicative of Keplerian rotation. Among the sample of known ~7-10 Myr-old star/disk systems, TWA 34, which lies just ~50 pc from Earth, is the lowest mass star thus far identified as harboring cold molecular gas in an orbiting disk.