Elaine R. Winston

A Combined Spitzer and Chandra Survey of Young Stellar Objects in the Serpens Cloud Core

We present Spitzer and Chandra observations of the nearby (~260 pc) embedded stellar cluster in the Serpens cloud core. We observed, using Spitzers IRAC and MIPS instruments, in six wavelength bands from 3 to 70 ?m, to detect thermal emission from circumstellar disks and protostellar envelopes and to classify stars using color-color diagrams and SEDs. These data are combined with Chandra observations to examine the effects of circumstellar disks on stellar X-ray properties. Young diskless stars were also identified from their increased X-ray emission. We have identified 138 YSOs in Serpens: 22 Class 0/I, 16 flat-spectrum, 62 Class II, 17 transition disk, and 21 Class III stars; 60 of these exhibit X-ray emission. Our primary results are the following: (1) 10 protostars detected previously in the submillimeter are detected at ? 1. This may be the result of grain growth through coagulation and/or the accretion of volatiles in the Serpens cloud core.

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

Aims. To study the properties of X-ray emission from young stellar objects (YSOs) through their evolution from Class I to Class III and determine whether Class 0 protostars emit 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 d ense and extremely young cluster whose members are found in all 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 typical X-ray luminosities> 0.4× 10 30 erg s −1 (for column densities of the order of 4×10 23 cm −2 , or AV∼ 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 some 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 loo p length of the order of 20 stellar radii. We interpret the flar ing event as originating from a magnetic flux tube connecting the star t o 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 fluoresc ent emission.