Limits on the Gas Disk Content of Two "Evolved" T Tauri Stars

TL;DR

This study places upper limits on the gas disk masses of two evolved T Tauri stars, providing constraints on planet formation theories and disk evolution during the dissipation phase.

Contribution

It presents the first upper limits on gas disk masses for these specific evolved T Tauri stars using ^{12}CO observations, informing models of disk dissipation.

Findings

Upper limits of <4.20 M⊙ on gas disk masses for both stars.

Detection of radial motion helps distinguish disk emission from ambient cloud.

Results suggest significant gas depletion in these evolved disks.

Abstract

We derived upper limits of the circumstellar gas disk masses around the T Tauri stars St 34 and RX J0432.8+1735 in order to place constraints on theories of planet formation and to explore the evolution of the gas-to-dust ratio during the epoch of disk dissipation around young sun-like stars. Since sub-millimeter lines of ^{12}CO trace of the cold, outer regions of circumstellar disks, we observed ^{12}CO J=2-1 emission with the 10 m Sub-Millimeter Telescope (SMT) for two carefully chosen targets. St 34 is a rare classical T Tauri star with an age of 8\pm3 Myr, and RX J0432.8+1735 is a rare weak-emission T Tauri star with far-infrared excess. Both exhibit radial space motion enabling us to distinguish disk emission from ambient cloud material. Assuming a ^{12}CO excitation temperature of 20 K, a ^{12}CO line-width of 5 km s^{-1}, and optically-thin emission, we derive 3{\sigma} upper limits on the H_{2} circumstellar disk mass for St 34 and RX J0432.8+1735 to be <4.20 M\odot for both disks. Placing these results in the context of other studies, we discuss their implications on planet formation models.