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 by 18 cm are presented. Polarization observations (monitoring) were performed on a large radio telescope in Nançay (France) in 2007–2024. OH maser emission is highly variable. The structure of the spectrum and the flux density of the individual features are changing. However, the radial velocities of most features changed slightly. Short-term flares of emission ion from individual features were observed. Many features have strong circular polarization, reaching 100%, but 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 km/s and –6.94L / –0.82R 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 value of the positional angle χ is calculated for linearly polarized emission of most spectral details in both main lines of 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.