Raman Scattering Wings of Hα in Symbiotic Stars

Nussbaumer et al. (1989) proposed that broad Hα wings can be formed through Raman scattering of Lyβ photons, and in this Letter we argue that the Hα wings prevalently seen in symbiotic stars may be indeed formed in this way. Assuming a flat incident UV radiation around Lyβ, we generate template wing profiles around Hα that are formed through Raman scattering in a plane-parallel H I region. We perform profile fitting analyses to show that the template wing profiles are in excellent agreement with the observed ones that are provided by van Winckel et al. (1993) and Ivison et al. (1994). The wing flux is determined by the scattering H I column density and the incident Lyβ flux strength and profile. From our profile analysis it is proposed that the Raman scattering component may be identified with the neutral envelope with a column density ranging 10 cm that surrounds the binary system. We briefly discuss alternative candidates for the wing formation mechanism and observational implications of Raman scattering in symbiotic stars and in other astronomical objects including planetary nebulae, post AGB stars and active galactic nuclei. Subject headings: line: formation — line: profiles — radiative transfer — scattering — (stars) binaries : symbiotic