Young Stars near Cometary Globule CG 30 in the Tumultuous Gum Nebula

TL;DR

This study spectroscopically characterizes 21 young stars near CG 30 in the Gum Nebula, revealing their properties, kinematics, and a shared distance of about 358 parsecs, suggesting a young, related stellar population affected by the nebula's environment.

Contribution

First detailed spectroscopic analysis of young stars around CG 30, establishing their properties, kinematics, and association distance, and assessing environmental effects on disk lifetimes.

Findings

14 stars are kinematically related to CG 30.

Distance to CG 30 complex is approximately 358 parsecs.

The association has a low accretor fraction of 29%.

Abstract

We have conducted a high-dispersion ($R \sim$ 34,000) optical spectroscopic study of 10 young stars near the cometary gloule CG 30 in the Gum Nebula, a diffuse H \textsc{ii} region home to at least 32 cometary globules. All 10 spectroscopically observed stars at the nebula's northern edge are of low mass (spectral types M4.5 - K5), have broad H$\alpha$ emission, and show spectral veiling. Eight of the 10 are classical T Tauri stars. We spectroscopically measure the photospheric properties of CG 30 IRS 4 inside CG 30. Though embedded, CG 30 IRS 4 is T Tauri-like, with relatively slow projected rotation and moderate veiling. Undepleted Li absorptions, strong H$\alpha$ emissions, and positions well above the main sequence on an HR diagram suggest the 10 stars are $\lesssim$1 Myr old. Using our measurements, previous spectroscopy, and previous photometry of 11 other young stars in the area, we determine stellar, kinematic, and accretion properties of a total of 21 young stars. Shared radial velocities, proper motions, distances, and ages suggest 14 of the young stars (including CG 30 IRS 4) are kinematically related to CG 30. From \textit{Gaia} DR2 distances to 6 of these stars, we derive a distance of $358.1\pm2.2$ pc to the cometary globule complex CG 30/31/38. The CG 30 association has an accretor fraction of $29\pm14$\%, low for quiescent clusters of similar age but consistent with other irradiated clusters. The Gum Nebula's moderate radiation environment ($G_0=6.6^{+3.2}_{-2.7}$ at CG 30) may be strong enough to shorten disk lifetimes.