A high-frequency radio continuum study of massive young stellar objects

TL;DR

This study uses high-resolution radio observations to analyze the structure and properties of massive young stellar objects, confirming equatorial winds and revealing wind clumpiness through spectral and morphological data.

Contribution

It provides high-resolution radio imaging of multiple massive YSOs, confirming equatorial wind structures and modeling their ionized winds with insights into wind temperature and clumpiness.

Findings

Elongated structures perpendicular to outflows confirm equatorial winds.

Spectral indices indicate ionized stellar winds.

Wind temperatures are much lower than stellar effective temperatures.

Abstract

We present high-resolution observations made with the Very Large Array (VLA) in its A configuration at frequencies between 5 and 43 GHz of a sample of five massive young stellar objects (YSOs): LkHa101, NGC2024-IRS2, S106-IR, W75N and S140-IRS1. The resolution varied from 0.04 arcsec (at 43 GHz) to 0.5 arcsec (at 5 GHz), corresponding to a linear resolution as high as 17 AU for our nearest source. A MERLIN observation of S106-IR at 23 GHz with 0.03-arcsec resolution is also presented. S106-IR and S140-IRS1 are elongated at 43 GHz perpendicular to their large scale bipolar outflows. This confirms the equatorial wind picture for these sources seen previously in MERLIN 5 GHz observations. The other sources are marginally resolved at 43 GHz. The spectral indices we derive for the sources in our sample range from +0.2 to +0.8, generally consistent with ionized stellar winds. We have modelled our sources as uniform, isothermal spherical winds, with LkHa101 and NGC2024-IRS2 yielding the best fits. However, in all cases our fits give wind temperatures of only 2000 to 5000 K, much less than the effective temperatures of main-sequence stars of the same luminosity, a result which is likely due to the clumpy nature of the winds.