Optical Polarimetric and Near-Infrared Photometric Study of the RCW95 Galactic HII Region

TL;DR

This study combines optical polarimetry and near-infrared photometry to analyze the magnetic field, stellar population, and ionizing sources in the RCW95 HII region, revealing aligned magnetic fields, young stellar clusters, and O4 V ionizing stars.

Contribution

It provides a comprehensive multi-wavelength analysis of RCW95, including magnetic field structure, cluster parameters, and spectral classification of ionizing stars, which is novel for this region.

Findings

Magnetic field aligned with cloud structure.

Estimated cluster ages around 3 million years.

Identified O4 V stars as main ionizing sources.

Abstract

We carried out an optical polarimetric study in the direction of the RCW95 star forming region in order to probe the sky-projected magnetic field structure by using the distribution of linear polarization segments which seem to be well aligned with the more extended cloud component. A mean polarization angle of $\theta=49.8^o\pm7.7^o$ was derived. Through the spectral dependence analysis of polarization it was possible to obtain the total-to-selective extinction ratio ($R_V$) by fitting the Serkowski function, resulting in a mean value of $R_V=2.93\pm0.47$. The foreground polarization component was estimated and is in agreement with previous studies in this direction of the Galaxy. Further, near-infrared images from Vista Variables in the Via L\'actea (VVV) survey were collected to improve the study of the stellar population associated with the HII region. The Automated Stellar Cluster Analysis (ASteCA) algorithm was employed to derive structural parameters for two clusters in the region, and a set of PAdova and TRieste Stellar Evolution Code (PARSEC) isochrones was superimposed on the decontaminated colour-magnitude diagrams (CMDs) to estimate an age of about 3 Myr for both clusters. Finally, from the near-infrared photometry study combined with spectra obtained with the Ohio State Infrared Imager and Spectrometer (OSIRIS) mounted at the Southern Astrophysics Research Telescope (SOAR) we derived the spectral classification of the main ionizing sources in the clusters associated with IRAS 15408$-$5356 and IRAS 15412$-$5359, both objects classified as O4 V stars.