We present the high-resolution spectra of the D-type symbiotic stars V1016 Cygni and HM Sagittae obtained with the Bohyunsan Optical Echelle Spectrograph ( BOES) and investigate the double-peaked asymmetric profiles of the Raman scattered O vi k6825 formed through Raman scattering of O vi k1032 by atomic hydrogen. By adopting a wind accretion disk model, the O vi emission region is described by a Keplerian thin disk. The Raman scattering occurs in a neutral region near the giant, part of which is ionized by the strong UV radiation from the hot white dwarf. A Monte Carlo technique is used to compute the line profiles that are modulated by the slow spherical stellar wind from the giant component with the ionization front approximated by a hyperboloid. In order to account for the asymmetry and the central dip in the profiles, we add an O vi resonance scattering region between the hot white dwarf and the giant which hinders the incidence of slightly blue O vi photons upon the H i region. Overall good fits to the observed data are obtained from our model, which lends support to the accretion disk emission model. The best-fitting parameters for V1016 Cyg are v o ¼ 30 km s À1 , v 1 ¼ 11 km s À1 , and v c ¼ 10 km s À1 , where v o , v 1 , and v c are the velocity of the outer disk rim, the terminal velocity of the giant wind, and the velocity component of the resonance scattering O vi region along the binary axis, respectively. Similar fitting parameters v o ¼ 26 km s À1 , v 1 ¼ 10 km s À1 , and v c ¼ 7 km s À1 are obtained for HM Sge.

About 10 percent of quasars are known to exhibit deep broad absorption troughs blueward of prominent permitted emission lines, which are usually attributed to the existence of outflows slightly above the accretion disk around the supermassive black hole. Typical widths up to 0.2c of these absorption troughs indicate the velocity scales in which special relativistic effects may not be negligible. Under the assumption of the ubiquity of the broad absorption line region in quasars, the broad emission line flux will exhibit Thomson scattered components from these fast outflows. In this paper, we provide our Monte Carlo calculation of linear polarization of singly Thomson scattered line radiation with the careful considerations of special relativistic effects. The scattering region is approximated by a collection of rings that are moving outward with speeds v = cβ < 0.2c near the equatorial plane, and the scattered line photons are collected according to its direction and wavelength in the observer's rest frame. We find that the significantly extended red tail appears in the scattered radiation. We also find that the linear degree of polarization of singly Thomson scattered line radiation is wavelength-dependent and that there are significant differences in the linear degree of polarization from that computed from classical physics in the far red tail. We propose that the semi-forbidden broad emission line C III]1909 may be significantly contributed from Thomson scattering because this line has small resonance scattering optical depth in the broad absorption line region, which leads to distinct and significant polarized flux in this broad emission line.

Thomson scattering is often invoked to explain broad wing features that are seen in various objects including active galactic nuclei and symbiotic stars. Despite the wavelength‐independent scattering cross‐section of Thomson scattering, the line flux may exhibit wavelength‐dependent linear degree of polarization, because various parts of emission wings are contributed by photons with different scattering numbers. Specifically, more scattered and hence more weakly polarized photons tend to fill the farther wing parts from the line centre, while the neighbourhood of the line centre is dominated by less‐scattered photons with higher degree of polarization. Using a Monte Carlo technique, we investigate the polarization structure of Thomson‐scattered line radiation. A detailed analysis of polarization structure formation is conducted by investigating the dependence of the polarization and profile width on the scattering number for various finite electron scattering slabs. Significantly varying degree of polarization is obtained when the scattering medium has Thomson optical depth τTh≥ 1. We present our high‐resolution spectrum of the symbiotic star V1016 Cyg obtained with the Bohyunsan Optical Echelle Spectrograph (BOES) in order to fit the broad profile around Hα by electron scattering wings adopting an oblate spheroidal geometry with Thomson optical depth τTh= 0.5 and electron temperature Te= 6.2 × 104  K. Local maxima in the linear degree of polarization of Thomson‐scattered line radiation are expected to appear in the spectral regions characterized by the average scattering number ≃1.