The onset of X-ray emission in young stellar objects: a Chandra observation of the Serpens star-forming region

TL;DR

This study uses deep Chandra X-ray observations to analyze the evolution of X-ray emissions in young stellar objects within the Serpens star-forming region, revealing the absence of X-ray emission in the youngest Class 0 protostars and characterizing properties in later stages.

Contribution

First detailed X-ray observational analysis across all evolutionary stages of YSOs in Serpens, including the non-detection of Class 0 protostars and insights into magnetic activity and disk interactions.

Findings

No X-ray detection in Class 0 protostars with luminosities > 0.4 x 10^30 erg/s.

Decreasing absorption and plasma temperature from Class I to Class III.

Detected a long-duration flare from a Class II star indicating magnetic star-disk interaction.

Abstract

AIMS: To study the properties of X-ray emissions from young stellar objects (YSOs), through their evolution from Class I to Class III and determine whether Class 0 protostars emit in X-rays. METHODS: A deep Chandra X-ray observation of the Serpens star-forming region was obtained. The Serpens Cloud Core is ideally suited for this type of investigation, being populated by a dense and extremely young cluster whose members are found in all different evolutionary stages, including six well studied Class 0 sources. RESULTS: None of the six Class 0 protostars is detected in our observations, excluding the presence of sources with X-ray luminosities > 0.4 10^30 erg/s (for column densities of the order of 4 10^{23} cm^-2, or A_V ~ 200). A total of 85 X-ray sources are detected and the light curves and spectra of 35 YSOs are derived. There is a clear trend of decreasing absorbing column densities as one moves from Class I to Class III sources, and, possibly, evidence of decreasing plasma temperatures, too. We observe a strong, long-duration, flare from a Class II low-mass star, for which we derive a flaring loop length of the order of 20 stellar radii. We interpret the flaring event as originating from a magnetic flux tube connecting the star to its circumstellar disk. The presence of such a disk is supported by the detection, in the spectrum of this star, of 6.4 keV Fe fluorescent emission.