Chandra Detection of An Evolved Population of Young Stars in Serpens South

TL;DR

This study uses Chandra X-ray observations combined with infrared data to analyze the young star population and cluster structure in the Serpens South star-forming region, revealing details about star classes, disk properties, and spatial distribution.

Contribution

It provides the first detailed X-ray analysis of Serpens South, identifying young star classes, their spatial distribution, and disk properties, and estimates the cluster's distance and environment effects.

Findings

152 X-ray sources detected, 66 matched with IR counterparts.

Identified 21 Class I, 6 flat spectrum, 16 Class II, 18 Class III young stars.

High percentage of diskless Class III stars suggests environment influences disk evolution.

Abstract

We present a Chandra study of the deeply embedded Serpens South star-forming region, examining cluster structure and disk properties at the earliest stages. In total, 152 X-ray sources are detected. Combined with Spitzer and 2MASS photometry, 66 X-ray sources are reliably matched to an IR counterpart. We identify 21 class I, 6 flat spectrum, 16 class II, and 18 class III young stars; 5 were unclassified. Eighteen sources were variable in X-rays, 8 exhibiting flare-like emission, and one periodic source. The cluster X-ray luminosity distance was estimated, the best match was to the nearer distance of 260pc for the front of the Aquila Rift complex. The $N_{H}$ vs. $A_{K}$ ratio is found to be $\sim$0.68x10$^{22}$, similar to that measured in other young low mass regions, but lower than that measured in the ISM and high mass clusters ($\sim$1.6-2x10$^{22}$). We find the spatial distribution closely follows that of the dense filament from which the stars have formed, with the class II population still strongly associated with the filament. There are four sub-clusters in the field, with three forming knots in the filament, and a fourth to the west, which may not be associated but may be contributing to the distributed class III population. A high percentage of diskless class IIIs (upper limit 30% of classified X-ray sources) in such a young cluster could indicate that processing of disks is influenced by the cluster environment and is not solely time-scale dependent.