The North American and Pelican Nebulae. I. Irac Observations

Abstract

We present a 9 deg 2 map of the North American and Pelican Nebulae regions obtained in all four Infrared Array Camera (IRAC) channels with the Spitzer Space Telescope. The resulting photometry is merged with that at JHK s from Two Micron All Sky Survey and a more spatially limited BVI survey from previous ground-based work. We use a mixture of color-color diagrams to select a minimally contaminated set of more than 1600 objects that we claim are young stellar objects (YSOs) associated with the star-forming region. Because our selection technique uses infrared excess as a requirement, our sample is strongly biased against inclusion of Class III YSOs. The distribution of IRAC spectral slopes for our YSOs indicates that most of these objects are Class II, with a peak toward steeper spectral slopes but a substantial contribution from a tail of Flat spectrum and Class I type objects. By studying the small fraction of the sample that is optically visible, we infer a typical age of a few Myr for the low-mass population. The young stars are clustered, with about a third of them located in eight clusters that are located within or near the LDN 935 dark cloud. Half of the YSOs are located in regions with surface densities higher than 1000 YSOs/deg 2. The Class I objects are more clustered than the Class II stars.

The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

“…The colour indices of 3 of them are those of reddened field late-type stars, and the colours of the other bright 9 sources imply strong infrared excesses, indicative of the presence of discs that dominate the far-IR emission, confirming the near-IR analyses. These are the most luminous objects found in the present work and, except for one, their positions on the IRAC two-colour diagrams correspond to the region populated by very young Class I sources (Allen et al 2004;Guieu et al 2009). These objects are labeled with the letters A, B, C, D, E, F, G and J in Figs.…”

“…It consists of an imaging study of more than 4 square degrees of the sky. The observations and statistical results of this large-scale study are described by Guieu et al (2009). We have analysed only a very small portion of these images centred at the position of G85.40-0.00.…”

Star formation in the “Gulf of Mexico”

“…The optical cluster of the low mass Hα emission-line stars is only a small portion of the total number of stars being formed there, and is only one of eight clusterings in the region according to the recent Spitzer study by Guieu et al (2009). The presence of numerous HH flows and many reddened sources indicates that this is a large site of widespread star formation, still partially embedded in the dark cloud.…”

“…In a recent study, Guieu et al (2009) have used the Spitzer Space Telescope with IRAC to identify more than 1600 YSO candidates in or near the extended L935 cloud. They identify clusters and suggest that the region of the Gulf of Mexico contains the youngest stars of the complex.…”

Inferring Rotation Periods of Young Stars from Synoptic Observations

“…Low-mass ( 1.2 M ) young stars are classified either as classical T Tauri stars (cTTs), or as weak-lined T Tauri stars (wTTs), according to the strength of their Hα emission lines. Although cTTs are surrounded by dense accretion disks that produce strong infrared excesses, and readily stand out in near-IR colour-colour diagrams and in Hα emission surveys (Guieu et al 2009), the wTTs, which dominate for clusters older than about 5 Myr (Fedele et al 2010), resemble field stars in those surveys. One can identify both wTTs and cTTs via their active chromospheres and large starspots, which give rise respectively to X-ray emission and a low-amplitude quasi-periodic variability in the optical.…”