2004/02/02 by Yang Chan Jung, Yang-Chan Jung, Hee-Won Lee +1 · 2 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2004.07666.x
published as Mon.Not.Roy.Astron.Soc. 350 (2004) 580 · 9 pages, 9 figures, accepted for publication in MNRAS
arxiv created 2004/02/02 · openalex publication_date 2004/04/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Using a Monte Carlo technique, we investigate the centre shifts that are expected to occur for the broad Hα wings and the He iiλ6545 feature as a function of the neutral hydrogen column density in symbiotic stars. These two features are proposed to be formed via Raman scattering of ultraviolet (UV) continuum around the Lyβ and He iiλ1025 emission line by neutral hydrogen. The strengths of these two features are determined by a combination of various physical parameters including the covering factor and the neutral hydrogen column density (NH i) of the scattering region. The branching ratio of Raman scattering to Rayleigh scattering for UV radiation around Lyβ is a non-linearly increasing function of the wavelength, which results in enhanced Raman optical fluxes redward of the Hα line centre as NH i increases. However, we find that the amount of wing centre shift is quite small about 20 km s−1 as NH i increases from 1020 to 1021 cm−2. Assuming that He iiλ1025 emission is characterized by a Gaussian profile, the Raman-scattered He ii 6545 feature exhibits near Gaussian profiles with the peak shifted redward for NH i < 1022 cm−2. The redward centre shift amounts to 1 Å for NH i∼ 1020 cm−2 and decreases as NH i increases up to NH i∼ 1022 cm−2, above which no centre shift is observed. The redward peak shift is due to the fact that the incident emission profile is symmetric with respect to the He iiλ1025 line centre whereas the Raman conversion rate is increasing towards the line centre of Lyβ. We emphasize that the determination of NH i by locating the exact peak position of the He ii 6545 feature will lift the degeneracy to allow a more accurate estimate of the covering factor of the neutral region, providing strong constraints on the mass-loss process occurring in symbiotic stars.