Circumstellar Disks in the Outer Galaxy: the Star-Forming Region NGC 1893

TL;DR

This study investigates star formation in the outer Galaxy's NGC1893 cluster, finding a high disk fraction and rich population despite less favorable environmental conditions, suggesting star formation processes are robust across different galactic environments.

Contribution

It provides the first detailed infrared and X-ray analysis of NGC1893, demonstrating successful star formation in the outer Galaxy with a rich cluster and high disk fraction.

Findings

NGC1893 hosts 242 PMS Classical T-Tauri stars and 7 Class 0/I stars.

The disk fraction in NGC1893 is approximately 67%.

Star formation in the outer Galaxy can produce rich clusters despite environmental challenges.

Abstract

It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. We investigate the population of NGC1893, a young cluster ~3-4 Myr in the outer part of the Galaxy (galactic radius >11 Kpc), to explore the effects of environmental conditions on star forming regions. We present infrared observations acquired using the IRAC camera onboard the Spitzer Space Telescope and analyze the color-color diagrams to establish the membership of stars with excesses. We also merge this information with that obtained from Chandra ACIS-I observations, to identify the Class III population. We find that the cluster is very rich, with 242 PMS Classical T-Tauri stars and 7 Class 0/I stars. We identify 110 Class III candidate cluster members in the ACIS-I field of view. We estimate a disk fraction for NGC1893 of about 67%, similar to fractions calculated for nearby star forming regions of the same age. Although environmental conditions are unfavorable, star formation can clearly be very successful in the outer Galaxy, allowing creation of a very rich cluster like NGC1893.