A search for the OH 6035 MHz line in high-mass star-forming regions

TL;DR

This study conducted a comprehensive search for excited-state OH 6035 MHz maser emission in high-mass star-forming regions, discovering new sources and analyzing their variability and magnetic field properties.

Contribution

It is the first large-scale survey targeting the OH 6035 MHz line in HMYSOs, revealing new detections and variability patterns not previously documented.

Findings

37 out of 445 targets detected at 6035 MHz, including 7 new sources.

Detected sources are faint and show high variability over months.

Zeeman pairs suggest magnetic fields of 2 to 11 mG.

Abstract

The excited states of OH masers detected in the environment of high-mass young stellar objects (HMYSOs) are important for improving our understanding of the physical conditions of these objects and also provide information about their magnetic fields. We aim to search for excited-state OH 6035 MHz maser emission in HMYSOs which might have escaped detection in previous surveys or were never searched for. A sample of HMYSOs derived from untargeted surveys of the 6668 MHz methanol maser line was observed at 6035 MHz OH transition with the Torun 32 m radio telescope. The 6035 MHz detections were observed in the OH 6031 MHz line. Two-thirds of the detections were observed at least three times over a two-year period. Out of 445 targets, 37 were detected at 6035 MHz, including seven new discoveries. The 6031 MHz line was detected towards ten 6035 MHz sources, one of which was not previously reported. All the newly detected sources are faint with the peak flux density lower than 4 Jy and show significant or high variability on timescales of 4 to 20 months. Zeeman pair candidates identified in three new sources imply a magnetic field intensity of 2 to 11 mG. Comparison of our spectra with those obtained $\sim$10 yr ago indicates different degrees of variability but there is a general increase in the variability index on an $\sim$25 yr timescale, usually accompanied by significant changes in the profile shape.