On the Profiles and Polarization of Raman Scattered Emission Lines in Symbiotic Stars:II. Numerical Simulations

A Monte Carlo method is used to calculate the profiles and the polarization of the Raman scattered O VI lines(lambda lambda 6827,7088) in symbiotic stars. A point-like isotropic UV radiation source is assumed and a simple spherical wind model is adopted for the kinematics of the scattering material from the cool giant. We first investigate the case where the incident line photons are described by a Gaussian profile having a width of 10^4 K. We subsequently investigate the effects of the extended ionized region and non-spherical wind models including a disk-type wind and a bipolar wind. The cases where the emissin source is described by non-Gaussian profiles are briefly studied. Finally, as an additional component for the kinematics of symbiotic stars the orbital motion of the hot component around the cool giant is included and the effect on the spectropolarimetry is investigated. In this case the polarization direction changes around the red part of the Raman-scattered emission lines, when the observer's line of sight is perpendicular to the orbital plane, and no such effect is seen when the line of sight lies in the orbital plane. Furthermore, complex peak structures are seen in the degree of polarization and polarized flux, which have often been observed in several symbiotic systems including RR Tel. Brief observational consequences and preditions are discussed in relation to the present and future spectropolarimetry for symbiotic stars. It is concluded that spectropolarimetry may provide a powerful diagnostic of the physical conditions of symbiotic stars.Comment: 22 pages, Tex, 15 postscript figuer

On the Polarization of H-alpha Lines Scattered by Neutral Hydrogen in Active Galactic Nuclei

Raman scattering by atomic hydrogen converts the UV continuum around Ly$\beta$ into optical continuum around H$\alpha$, and the basic atomic physics has been discussed in several works on symbiotic stars. We propose that the same process may operate in active galactic nuclei (AGN) and calculate the linear polarization of the broad emission lines Raman-scattered by a high column neutral hydrogen compnent. The conversion efficiency of the Raman scattering process is discussed and the expected scattered flux is computed using the spectral energy distribution of an AGN given by a typical power law. The high column H {\sc i} component in AGN is suggested by many observations encompassing radio through UV and X-ray ranges. When the neutral hydrogen component with a column density $\sim 10^{22} cm^{-2}$ is present around the active nucleus, it is found that the scattered H$\alpha$ is characterized by a very broad width $\sim 20,000 km/s$ and that the strength of the polarized flux is comparable to that of the electron-scattered flux expected from a conventional unified model of narrow line AGN. The width of the scattered flux is mainly determined by the column density of the neutral scatterers where the total scattering optical depth becomes of order unity. The asymmetry in the Raman scattering cross section around Ly$\beta$ introduces red asymmetric polarized profiles around H$\alpha$. The effects of the blended Ly$\beta$ and O {\sc vi} 1034 doublet are also investigated. We briefly discuss the spectropolarimetric observations performed on the Seyfert galaxy IRAS 110548-1131 and the narrow line radio galaxy Cyg A.Comment: 11 pages, 6 figures, accepted for publication in MNRA

P-Cygni Type Lya from Starburst Galaxies

P-Cygni type Lya profiles exhibited in nearly half of starburst galaxies, both nearby and high-z, are believed to be formed by an expanding supershell surrounding a star-forming region. We apply the Monte Carlo code which was developed previously for static and plane-parallel medium to calculate the Lya line transfer in a supershell of neutral hydrogen which are expanding radially in a spherical bulk flow. We consider typical cases that the supershell has the Lya line-centre optical depth of $\tau_0=10^5-10^7$, a radial expansion velocity of $V_exp = 300 km/s, and the turbulence of b=40 km/s. We find that there appear a few emission peaks at the frequencies corresponding to (2N-1) V_exp, where the order of back scatterings N > 1. As V_exp -> b, the emergent profiles become similar to those for the static medium and the peaks are less prominent. We also investigate the effects of column density of the supershell on the emergent Lya profiles. We find that the number and the flux ratios of emission peaks are determined by interplay of$\tau_0$ and V_exp of the supershell. We discuss the effects of dust extinction and the implication of our works in relation to recent spectroscopic observations of starburst galaxies.Comment: 15 pages, 6 figures, submitted to MNRA

Rayleigh Scattering Cross Section Redward of Lyα\alpha by Atomic Hydrogen

We present a low energy expansion of the Kramers-Heisenberg formula for atomic hydrogen in terms of $(\omega/\omega_l)$, where $\omega_l$ and $\omega$ are the angular frequencies corresponding to the Lyman limit and the incident radiation, respectively. The leading term is proportional to $(\omega/\omega_l)^4$, which admits a well-known classical interpretation. With higher order terms we achieve accuracy with errors less than 4 % of the scattering cross sections in the region $\omega/\omega_l\le 0.6$. In the neighboring region around Ly$\alpha$ ($\omega/\omega_l >0.6$), we also present an explicit expansion of the Kramers-Heisenberg formula in terms of $\Delta\omega\equiv (\omega-\omega_{Ly\alpha})/\omega_{Ly\alpha}$. The accuracy with errors less than 4 % can be attained for $\omega/\omega_l \ge 0.6$ with the expansion up to the fifth order of $\Delta\omega$. We expect that these formulae will be usefully applied to the radiative transfer in high neutral column density regions, including the Gunn-Peterson absorption troughs and Rayleigh scattering in the atmospheres of giants.Comment: 5 pages, 2 figure