Abstract Details

Affiliation: S. N. Bose National Centre for Basic Sciences
Conference ID: ASI2017_715
Title : Stellar population and the star formation histories of distant Galactic HII regions NGC 2282 and Sh 2-149 Complex
Authors and Co-Authors : Soumen Mondal, S.N. Bose National Centre for Basic Sciences, Kolkata 700106, India Jessy Jose, Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian District, Beijing 100871, China Ramkrishna Das S.N. Bose National Centre for Basic Sciences, Kolkata 700106, India
Abstract Type : Oral
Abstract Category : Stars,ISM and the Galaxy
Abstract : In spite of profound influence on their host galaxies, the formation and evolution of massive stars are not well understood. HII regions are low-density cloud of ionized gas excited by UV radiation from massive stars (e.g. O and early B-type). Galactic HII regions containing massive stars provide the best platform to understand both high- and low-mass star formations. The massive stars within HII regions furnish its neighborhood in the form of their strong stellar winds, energetic radiation and eventually supernova explosion. Understanding the interaction between the massive stars and surrounding dense molecular gas is important for characterizing triggered star formation. We studied the stellar contents and star formation activities of a few distant Galactic HII regions (e.g. NGC 2282, Sh2-149) using deep optical, near-infrared, mid-infrared data sets and 12CO(2-1) molecular line observations. From optical spectroscopic analysis of 8 bright sources in NGC 2282, we have classified three early B-type members including a new Herbig Ae/Be star. Using IR color-color (CC) criteria and H⍺-emission properties, we have identified more than 150 candidate young stellar objects (YSOs), of which, 50% are classified as Class II, 6% are Class I YSOs. From time series CCD photometry at I-band (~ 20.5 mag) on NGC 2282, a total of 65 stars were found as photometric variable, and majority of them are PMS. The morphology of the region has been studied from spatial distribution of YSOs, stellar density distribution, signature of dust in various optical-infrared images along with the K-band extinction map. From our studies on Sh2-149 complex, we have identified few optically bright ionizing sources, and their spectral types are estimated to be massive O7-B0 V using the optical spectra. We detected several infrared excess stars from NIR and IRAC CC diagrams. These YSOs are spatially distributed along the dust ridge, which indicates that the region is an active star formation site. The morphology from 12CO(1-0) map identifies various clumps including a stream line flow towards South-West. Mid-IR dust structure suggests that millimeter contours encompass two filamentary structures, one towards West and another towards East, which is an ionized boundary layer associated with Sh2-152. The core region of Sh2-149 is extended towards South-East, which is associated to 2MASX J22555978+5814424 via an ionized layer. The morphology and spatial agreement among millimeter-IR observations, distribution of YSOs and ionizing stars indicate that the star-formation activity observed at filaments is probably a tentative example of triggered star formation. Our overall analysis suggests that the star formation occurs at the locations of the denser gas, and associate massive members particularly in Sh2-149, might be possible causes of the triggered star formation on its surrounding molecular medium.