New ex-OH maser detections in the northern celestial hemisphere

Abstract

Aims. Molecular masers, including methanol and hydroxyl masers, and in particular the ones in excited rotational states (ex-OH masers), are one of the most informative tools for studying star-forming regions. So, the discovery, of new maser sources in these regions is of great importance. Many studies and surveys of ex-OH maser sources have been carried out in the southern celestial hemisphere, but only a few have been done in the northern hemisphere. The specific aim of this work is to close this gap. Methods. The star-forming regions in the northern hemisphere with known active methanol masers were observed to search for new ex-OH maser sources with the 32 m and 16 m radio telescopes of the Ventspils International Radio Astronomy Centre (VIRAC). Results. Three OH maser lines in the excited state at the 6035 MHz in three northern hemisphere star-forming regions are detected. The maser 189.030+0.783 was previously known, but we suggest this maser is a possible variable. We confirm recent detections of the ex-OH masers 85.41+0.00 and 90.92+1.49 by other authors. The magnetic field strength in the masering regions is estimated by using right circular polarization and left circular polarization pair splitting. The high-velocity resolution provides us with an estimation of a comparatively small magnetic field strength for the 189.030+0.783 and 90.92+1.49 star-forming regions.

An Excited-state OH Maser Survey toward WISE Point Sources

“…G85.394−0.024. The 6035 MHz maser was detected bySzymczak et al (2020) andPatoka et al (2021). A similar narrow spectrum peaked at −33.1 km s −1 was detected in these observations.…”

“…G90.921+1.487. The 6035 MHz ex-OH maser was detected bySzymczak et al (2020) andPatoka et al (2021). Compared to the observation ofSzymczak et al (2020), the spectral profile is stable, with a narrow feature peaked at −69.3 km s −1 .…”

Intensity correlation functions of microwave maser sources

“…To assess the possibility of determining g (2) 11 , let us consider the order of the quantities included in formulas ( 6)-( 10) for masers on molecules OH (λ = 18 cm) and H 2 O (λ = 1.35 cm). Assuming for estimates of θ = 2 • 10 −2 s, ν ≈ 0.7 km s -1 ≈ 4 KHz for OHmasers (Patoka et al 2021;Clegg & Cordes 1991), we obtain the following values: the coherence time is t coh ≈ 250 µs, the longitudinal coherence length is ct coh ≈ 75 km, the spatial coherence radius is ρ coh ≈ 1.8 • 10 3 km for OH maser, ρ coh ≈ 135 km for H 2 O maser.…”

Observations of Possibly New OH Excited Rotational State Masers

“…In the first phase, during the years 2018 -2020, 78 objects were studied, and excited OH masers were searched for at frequencies of 6.035 GHz and 6.031 GHz. The results of this phase, were published in Patoka et al (2021).…”

“…The system temperature was 28 -34 K and the typical observation time was about 4 hours and 3σ noise level 0.1 -0.2 Jy. For details we refer the reader to Patoka et al (2021); here we only highlight some preliminary results of our observation campaign, particularly our detections of three, to our knowledge, new excited OH maser sources.…”