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

Abstract

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 6035 MHz 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 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. Results. 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 2–11 mG. Comparison of our spectra with those obtained ~10 yr ago indicates different degrees of variability but there is a general increase in the variability index on an ~25 yr timescale, usually accompanied by significant changes in the profile shape.

New ex-OH maser detections in the northern celestial hemisphere

“…We observed the previously known ex-OH maser 189.030+0.783 with a better velocity resolution. We confirm the detections of 85.41+0.00 and 90.92+1.49 that were reported in Szymczak et al 2020 after this paper was submitted. Our observations with a high-velocity resolution allowed us to estimate the weak magnetic fields in the 189.030+0.783 and 90.92+1.49 masers that were not estimated early by other authors.…”

“…In this paper, we describe our source selection criteria, observation technique, and three detected masers (two of them were unknown to us when we first submitted this paper) at 6035 MHz. After the first submission of this paper, we also noted seven possible newly detected masers at 6035 MHz that were not observed, or observed but not detected, by Szymczak et al 2020 or other authors. However to confirm these new detections, some additional observations and literature studies for possible previous detections are necessary (see Section 4, below).…”

“…The peak line velocities in our observations were 3.413 and 3.398 km s −1 for LCP and RCP. Szymczak et al 2020 did not estimate the magnetic fields since the relative velocity difference between LCP and RCP was too small, given their coarser velocity resolution, in order to reliably determine a B-filed strength from the ∆(v) of the polarized line components. The velocity resolution of our observations allows us to determine small velocity shifts between the polarization components.…”

“…This source was also unsuccessfully searched for 6031 and 6035 ex-OH masers from 2017 March to 2017 August by the Shanghai TianMa 65 m telescope by Ouyang (2019). Szymczak et al 2020 recently detected a maser line at 6035 MHz with a velocity resolution of 0.1 km s −1 using the Torun 32 m radio telescope. For comparison, line parameters are shown in Table 2.…”

“…Line parameters. Parameters without asterisks are our data, one asterisk denotesSzymczak et al 2020, and two asterisks denoteAvison et al 2016. 1: 189.030+0.783, 2: 85.41+0.00, 3: 90.92+1.49.…”