Pre-main-sequence stars in the young open cluster NGC 1893: II. Evidence for triggered massive star formation

Abstract

(Abridged) The open cluster NGC 1893, illuminating the HII region IC410, contains a moderately large population of O-type stars and is one of the youngest clusters observable in the optical range. We have probed the stellar population of NGC 1893 in an attempt to determine its size and extent. We classify a large sample of cluster members with new intermediate resolution spectroscopy. We use H-alpha slitless spectroscopy of the field to search for emission line objects, identifying 18 emission-line PMS stars. We then combine existing optical photometry with 2MASS JHKs photometry to detect stars with infrared excesses, finding close to 20 more PMS candidates. While almost all stars earlier than B2 indicate standard reddening, all later cluster members show strong deviations from a standard reddening law, which we interpret in terms of infrared excess emission. Emission-line stars and IR-excess objects show the same spatial distribution, concentrating around two localised areas, the immediate vicinity of the pennant nebulae Sim 129 and Sim 130 and the area close to the cluster core where the rim of the molecular cloud associated with IC 410 is illuminated by the nearby O-type stars. In and around the emission nebula Sim 130 we find three Herbig Be stars with spectral types in the B1-4 range and several other fainter emission-line stars. We obtain a complete census of B-type stars by combining Stroemgren, Johnson and 2MASS photometry and find a deficit of intermediate mass stars compared to massive stars. We observe a relatively extended halo of massive stars surrounding the cluster without an accompanying population of intermediate-mass stars. The overall picture of star formation in NGC 1893 suggests a very complex process.

Acepted for publication in Astronomy & Astrophysics, 11 figures, uses new aa macro. For a version with full resolution figures (Fig. 7 and 8 in colour) use http://www.dfists.ua.es/~ignacio/download/aa6654.pdf

References in corpus (1)

• A highly abnormal massive star mass function in the Orion Nebula cluster and the dynamical decay of trapezia systems

Cited by in corpus (19)

• New Galactic Star Clusters Discovered in the VVV Survey
• The dangers of being trigger--happy
• Massive open star clusters using the VVV survey I. Presentation of the data and description of the approach
• Chronology of star formation and disk evolution in the Eagle Nebula
• Testing the role of environmental effects on the initial mass function of low-mass stars
• Multi-wavelength polarimetric study towards the open cluster NGC 1893
• Kinematic evidence for feedback-driven star formation in NGC 1893
• Sejong Open Cluster Survey (SOS). III. The Young Open Cluster NGC 1893 in the H II Region W8
• Pre-main sequence variable stars in young open cluster NGC 1893
• Mapping the distribution of OB stars and associations in Auriga
• Candidate X-ray-Emitting OB Stars in the MYStIX Massive Star-Forming Regions
• Stellar tracers of the Cygnus Arm. II: A young open cluster in Cam OB3
• Open clusters in AurOB2
• The young open cluster Berkeley 55
• The Membership and Distance of the Open Cluster Collinder 419
• The embedded clusters DBS 77, 78, 102, and 160-161 and their link with the interstellar medium
• Kinematic study of the molecular gas associated with two cometary globules in Sh2-236
• Studies of a possible new Herbig Ae/Be star in the open cluster NGC 7380
• On the photo-evaporation, dust polarization, and kinematics of two nebulae in Sh2-236