A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with Δμ =0.1. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

Ever since the identification of 6830 and 7088 features as the Raman scattered O VI 1032, 1038 resonance doublets in symbiotic stars by Schmid (1989), Raman scattering by atomic hydrogen has been a very unique tool to investigate the mass transfer processes in symbiotic stars. Discovery of Raman scattered He II in young planetary nebulae (NGC 7027, NGC 6302, IC 5117) allow one to expect that Raman scattering can be an extremely useful tool to look into the mass loss processes in these objects. Because hydrogen is a single electron atom, their wavefunctions are known in closed form, so that exact calculations of cross sections are feasible. In this paper, I review some basic properties of Raman scattered features and present detailed and explicit matrix elements for computation of the scattering cross section of radiation with atomic hydrogen. Some astrophysical objects for which Raman scattering may be observationally pertinent are briefly mentioned.

In Lee, Kang & Byun (2001) the discovery of Raman scattered 6545 A feature was reported in symbiotic stars and the planetary nebula M2-9. The broad emission feature around 6545 A is formed as a result of Raman scattering of He II n = 6 → n = 2 photons by atomic hydrogen. In this paper, we introduce a method to compute the equivalent width of He II ⋋ 1025 line and present an optical spectrum of the symbiotic star RR Telescopii as an example for a detailed illustration. In this spectrum, we pay attention to the broad Hα wings and the Raman scattered He II 6545 feature. The broad Ha wings are also proposed to be formed through Raman scattering of continuum around Lyβ by Lee (2000), and therefore we propose that the equivalent width of the He II ⋋ 1025 emission line is obtained by a simple comparison of the strengths of the 6545 feature and the broad Hα wings. We prepare a template Hα wing profile from continuum radiation around Lyβ with the neutral scattering region that is supposed to be responsible for the formation of Raman scattered He II 6545 feature. Isolation of the 6545 feature that is blended with [N II] ⋋ 6548 is made by using the fact that [N II] ⋋ 6584 is always 3 times stronger than [N II] ⋋ 6548. We also fit the 6545 feature by a Gaussian which has a width 6.4 times that of the He II ⋋ 6527 line. A direct comparison of these two features for RR Tel yields the equivalent width EW Hel025 = 2.3 Å of He II ⋋ 1025 line. Even though this far UV emission line is not directly observable due to heavy interstellar extinction, nearby He II lines such as He II ⋋ 1085 line may be observed using far UV space instruments, which will verify this calculation and hence the origins of various features occurring in spectra around Hα.

We developed a Monte Carlo code that describes the resonant Lyα line transfer in an optically thick, dusty, and static medium. The code was tested against the analytic solution derived by Neufeld (1990). We explain the line transfer mechanism by tracing histories of photons in the medium. We find that photons experiences a series of wing scatterings at the moment of thier escape from the medium, during which polarization may develop. We examined the amount of dust extinction for a wide range of dust abundances, which are compared with the analytic solution. Brief discussions on the astrophysical application of our work are presented.