Abstract Details
| Name: Narendra S Affiliation: Raman Research Institute Conference ID: ASI2025_315 Title : An X‑band study of ultra‑compact HII regions using radio recombination line observations Authors and Co-Authors : S Narendra 1, Mayuri Sathyanarayana Rao 1 Abstract Type : Poster Abstract Category : Stars, Interstellar Medium, and Astrochemistry in Milky Way Abstract : Ultra-compact HII (UCHII) regions are small (< 0.1 pc) and dense (> 10^4 cm-3) regions of hot ionised gas surrounding young O-B stars embedded in dusty molecular clouds. These Galactic UCHII regions are considered one of the best tracers for studying high-mass star formation and the evolution of the interstellar medium. They are also useful secondary calibrators for submillimeter telescopes. UCHII regions are bright in radio and submillimeter frequencies, with emission dominated by free-free broad-band continuum, molecular lines and hydrogen radio recombination lines (RRLs). These RRLs can be used to determine the electron temperature and density of HII regions, providing useful information in their physical properties and in probing the environment around hot young massive stars. We present the X-band study of three UCHII regions, namely IRAS 17271-3439 (ATCA), G34.26+0.15 and W51d (VLA). We report the presence of Hα (H85α to H90α) and Hβ (H107β to H113β) RRLs in the band of 8.776 GHz to 10.824 GHz from the sources. IRAS 17271-3439 was observed with a single window of 2048 channels and a resolution of 1 MHz; G34.26+0.15 and W51d had 16 spectral windows, each of 64 channels and a resolution of 2 MHz. The data was analysed following standard reduction procedures on CASA, making continuum images and spectral cubes for each RRL. IRAS 17271-3439 and W51d were unresolved. G34.26+0.15 was resolved with two nearby hypercompact HII regions in the field, across which we observed Hα RRLs. With the observed RRLs and using the Helium-to-Hydrogen abundance ratio from the literature, we infer the electron temperature, emission measure, mean electron density, and other physical properties of these UCHII regions. |