Study of Maser Emission in 18 cm Lines in the Star Formation Region G 109.871+2.114 (Cep A)

The results of the study of the star formation region G 109.871+2.114 (Cep A) in OH lines at 18 cm are presented. Polarization observations (monitoring) were performed with a large Nançay radio telescope (France) in 2007–2024. OH maser emission is highly variable. The structure of the spectrum and the flux density of the individual spectral features are changing. However, the radial velocities of most features changed slightly. Short-term emission flares in individual features were observed. Many features have strong circular polarization, reaching 100%, but have weak linear polarization. A new features at –15.53 km/s and a short-term part at 1.58 km/s with high circular and low linear polarizations were detected in the 1667 MHz line. The spectral features of our monitoring were spatially identified with the maser spots on the Cohen, Argon, and Fish maps. The magnitude of the monotonic decrease in splitting, and, consequently, the longitudinal magnetic field of three Zeeman pairs (–16.2L/–14.25R and –6.94L/–0.82R km/s in the 1665 MHz line and –15.76L/–14.2R in the 1667 MHz line). For the –13.95L/–11.60R pair, no splitting change was detected in the 1665 MHz line. Broadband absorption and emission are observed in the satellite lines of 1612 and 1720 MHz, respectively. A Zeeman pair was also detected in the 1720 MHz line. The position angle \(\chi \) is calculated for linearly polarized emission of most spectral features in both main lines at 1665 and 1667 MHz. It is shown that the magnetic field in the H II regions is oriented either along the external magnetic field or along the radio jets.