Regions of Low Mass Star Formation in the Lynds 1641 Giant Molecular Cloud

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Session 96 -- YSOs and Masers
Oral presentation, Wednesday, 11, 1995, 2:00pm - 3:30pm

[96.05D] Regions of Low Mass Star Formation in the Lynds 1641 Giant Molecular Cloud

Lori E. Allen, Karen M. Strom, and Stephen E. Strom (U. Massachusetts, Amherst)

The nearest giant molecular cloud (d$\sim$480 pc), Lynds 1641, contains several regions of low mass star formation, in addition to the rich Trapezium cluster. These young stars are grouped into loose aggregates of enhanced stellar surface density ($>3\sigma$ above the background) near regions of high molecular gas opacity, molecular outflows, embedded infrared sources, and HH objects.

We present results of a multi-wavelength study of such regions, covering approximately 0.7 deg$^2$ of the cloud, and including the aggregate located near the L1641 North molecular outflow, the Cohen-Kuhi group, and the L1641 South cluster. Classification spectra in the in the $\lambda\lambda$ 5500-9000{\AA} range were obtained for $\sim$400 stars, and are combined with photometry from infrared ($J,H,K$) and optical ($R,I$) images to place the stars in the HR diagram. Mass and age estimates follow from interpolation of theoretical pre-main sequence evolutionary tracks. We find that low and intermediate mass star formation ($3.0\,M_{\odot} \,<\,M\,<\,0.08\,M_{\odot}$) has been occurring in some parts of the cloud for several million years, and for only a few million years in other parts. Both photometric (colors) and spectroscopic (emission lines) diagnostics are used to estimate the frequency of stars with circumstellar disk/envelope signatures. A high percentage ($>$50 \%) of stars in the aggregates appear to have disks or envelopes. Finally, we investigate the spatial distributions of the young stars in relation to the morphology of the surrounding molecular gas. The local environments of young stars are found to vary, ranging from regions of high extinction (${\rm A_v} > 20$), to areas of low gas column density.

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