2020A&A...642A.145S

Context. 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.
Aims. We aim to search for excited-state OH 6035MHz maser emission in HMYSOs which might have escaped detection in previous surveys or were never searched for.
Methods. A sample of HMYSOs derived from untargeted surveys of the 6668MHz methanol maser line was observed at 6035MHz OH transition with the Torun 32m radio telescope. The 6035MHz detections were observed in the OH 6031MHz line. Two-thirds of the detections were observed at least three times over a two-year period.
Results. Out of 445 targets, 37 were detected at 6035MHz, including seven new discoveries. The 6031MHz line was detected towards ten 6035MHz sources, one of which was not previously reported. All the newly detected sources are faint with the peak flux density lower than 4Jy 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 2-11mG. Comparison of our spectra with those obtained ∼10yr ago indicates different degrees of variability but there is a general increase in the variability index on an ∼25yr timescale, usually accompanied by significant changes in the profile shape.