Abstract:
Using Hα grism spectroscopy and optical and Two-Micron All-Sky Survey photometry of
the fields containing NGC 1893 and two emission nebulae, Sim 129 and Sim 130, we show
the presence of a number of Hα and near-infrared excess sources towards the region between
HD 242935 and the two emission nebulae. Among them a large majority of these pre-main-
sequence candidate sources are concentrated towards regions closer to Sim 129 and Sim 130.
Age distribution of these sources (viz. main-sequence stars in the cluster, including HD 242935,
young sources located in the region between HD 242935 and two nebulae and those located
inside Sim 129) obtained from their positions in optical V, V − I colour–magnitude diagram
strongly suggest ‘small-scale sequential star formation’ along the axes of the clouds caused by
the outward advance of ionization/shock front from the H II region. The IRAS source, IRAS
05198+3325, identified with CPM 16 is a Herbig Be (B3) type star showing Hα and Ca II
triplet lines in emission. From the orientation of the two emission nebulae it is suggested that
HD 242935 is most likely responsible for the cometary morphology of the two nebulae and the
trigger of star formation in the region. From the global distribution of the interstellar material,
it is also suggested that the same source is responsible for the champagne flow causing the
entire molecular cloud to have a cometary appearance.
