EDP Sciences
Free access
Volume 488, Number 1, September II 2008
Page(s) 211 - 218
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:200810132
Published online 01 July 2008

A&A 488, 211-218 (2008)
DOI: 10.1051/0004-6361:200810132

Circumstellar disks in the outer Galaxy: the star-forming region NGC 1893

M. Caramazza1, 2, G. Micela2, L. Prisinzano2, L. Rebull3, S. Sciortino2, and J. R. Stauffer3

1  Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
    e-mail: mcarama@astropa.unipa.it
2  INAF Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3  Science Center, Caltech 314-6, Pasadena, CA 91125, USA

Received 5 May 2008 / Accepted 30 May 2008

Context. 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.
Aims. We investigate the population of NGC 1893 , a young cluster (~3-4 Myr) in the outer part of the Galaxy ( $R_{\rm G} \geq 11$  kpc), to explore the effects of environmental conditions on star forming regions.
Methods. 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.
Results. 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 NGC 1893 of about $67\%$, similar to fractions calculated for nearby star forming regions of the same age.
Conclusions. Although environmental conditions are unfavorable, star formation can clearly be very successful in the outer Galaxy, allowing creation of a very rich cluster like NGC 1893 .

Key words: stars: pre-main sequence -- stars: circumstellar matter -- Galaxy: open cluster and association: individual: NGC 1893 -- stars: formation

© ESO 2008