A study of the asymmetry in the H2O maser line at λ = 1.35 cm on the base of the hyperfine structure
Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis Enrique Erro No. 1, Apartado Postal 51 y 216, CP 72840 Tonantzintla, Puebla, México e-mail: firstname.lastname@example.org
2 Sternberg Astronomical Institute, 13 Univetsitetskij prospect, Moscow, 119992, Russia
3 Main (Pulkovo) Astronomical observatory of Russian Academy of Sciences, Pulkovskoe shosse 65, St.-Petersburg, 196140, Russia
Accepted: 30 September 2008
The results of analyzing asymmetry in the H2O maser lines at λ = 1.35 cm are presented. We investigated in detail the known mechanism of the asymmetry origin due to the hyperfine structure of the 616 523 transition and different (not equidistant) positions of the corresponding triplet components. The triplet of the lines is characterized by the sum of extinction factors that are continuously transformed into a single-peaked asymmetric extinction coefficient, with the increase in the Doppler widths (characterizing by effective Doppler velocity uD). A noticeable asymmetry corresponds to 0.5-1 km s-1. For higher values of uD the extinction factor approaches a Gaussian shape with the decreasing magnitude of the profile asymmetry. An appreciable asymmetry in unsaturated maser lines can only arise at 0.5 km s-1, if there are very narrow linewidths (≈ 0.2-0.4 km s-1). But observed saturated masers possess a fairly high degree of the line asymmetry, 10-40%. Most probably, this asymmetry is a result of rebroadening of the linewidth up to the value that is comparable to the width of the asymmetric extinction coefficient.
Key words: line: profiles / masers / radiative transfer
© ESO, 2008