* Astronomy

Title: A young stellar cluster within the RCW41 HII region: deep NIR photometry and Optical/NIR polarimetry
Authors: Fábio P. Santos, Alexandre Roman-Lopes, Gabriel A. P. Franco

The RCW41 star-forming region is embedded within the Vela Molecular Ridge, hosting a massive stellar cluster surrounded by a conspicuous HII region. Understanding the role of interstellar magnetic fields and studying the newborn stellar population is crucial to build a consistent picture of the physical processes acting on this kind of environment. We have carried out a detailed study of the interstellar polarisation toward RCW41, with data from an optical and near-infrared polarimetric survey. Additionally, deep near-infrared images from the NTT 3.5m telescope have been used to study the photometric properties of the embedded young stellar cluster, revealing several YSO's candidates. By using a set of pre-main sequence isochrones, a mean cluster age in the range 2.5 - 5.0 million years was determined, and evidence of sequential star formation were revealed. An abrupt decrease in R-band polarisation degree is noticed toward the central ionised area, probably due to low grain alignment efficiency caused by the turbulent environment and/or weak intensity of magnetic fields. The distortion of magnetic field lines exhibit a dual behaviour, with the mean orientation outside the area approximately following the borders of the star-forming region, and directed radially toward the cluster inside the ionised area, in agreement with simulations of expanding HII regions. The spectral dependence of polarisation allowed a meaningful determination of the total-to-selective extinction ratio by fittings of the Serkowski relation. Furthermore, a large rotation of polarisation angle as a function of wavelength is detected toward several embedded stars.

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