9,391 research outputs found
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 into optical continuum around H, 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 is present around the
active nucleus, it is found that the scattered H is characterized by a
very broad width 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 introduces red asymmetric
polarized profiles around H. The effects of the blended Ly 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 , a radial expansion
velocity 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 Ly by Atomic Hydrogen
We present a low energy expansion of the Kramers-Heisenberg formula for
atomic hydrogen in terms of , where and
are the angular frequencies corresponding to the Lyman limit and the incident
radiation, respectively. The leading term is proportional to
, 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 . In the
neighboring region around Ly (), we also present
an explicit expansion of the Kramers-Heisenberg formula in terms of
. The accuracy
with errors less than 4 % can be attained for with
the expansion up to the fifth order of . 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
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