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Author name code: peraiah
ADS astronomy entries on 2022-09-14
author:"Peraiah, Annamaneni"
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Title: Compton broadening effect on spectral line formation
Authors: Peraiah, A.; Srinivasa Rao, M.
2013Ap&SS.343..195P Altcode: 2012Ap&SS.tmp..337P
We have investigated the effects of Compton broadening due to electron
scattering in an expanding stellar atmospheres. The line transfer
equation is solved by including the second approximation of Edmonds
(Astrophys. J. 119:58, 1954) which is due to Compton broadening and
obtained the line profiles in (1) plane parallel (PP) (2) spherical
(SS) atmospheres. The effect on spectral line formation is studied
for different parameters like (a) optical depths (b) densities (c)
frequencies (d) temperatures (e) thickness of the atmosphere and (f)
expanding velocities. Various combination of the above parameters
are used in computing the line profiles observed at infinity. Line
profiles are compared for the above said parameters. It is noticed
that the expansion of the gases in the atmosphere produces P-Cygni
type profiles and at higher optical depths the line profiles change
from emission to absorption with their line centers shifting to blue
side in the expanding atmospheres.
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Title: Simultaneous solution of Kompaneets equation and radiative
transfer equation in the photon energy range 1-125 keV
Authors: Peraiah, A.; Srinivasa Rao, M.; Varghese, B. A.
2011JQSRT.112..820P Altcode: 2010arXiv1011.1984P
Radiative transfer equation in plane parallel geometry and Kompaneets
equation is solved simultaneously to obtain theoretical spectrum of
1-125 KeV photon energy range. Diffuse radiation field is calculated
using time-independent radiative transfer equation in plane parallel
geometry, which is developed using discrete space theory (DST)
of radiative transfer in a homogeneous medium for different optical
depths. We assumed free-free emission and absorption and emission due
to electron gas to be operating in the medium. The three terms $n,
n^2$ and $\displaystyle \bigg({\frac {\partial n}{\partial x_k}}\bigg)$
where $n$ is photon phase density and $\displaystyle x_k= \bigg({\frac
{h \nu} {k T_e}} \bigg) $, in Kompaneets equation and those due to
free-free emission are utilized to calculate the change in the photon
phase density in a hot electron gas. Two types of incident radiation
are considered: (1) isotropic radiation with the modified black body
radiation $I^{MB}$ [1] and (2) anisotropic radiation which is angle
dependent. The emergent radiation at $\tau=0$ and reflected radiation
$\tau=\tau_{max}$ are calculated by using the diffuse radiation
from the medium. The emergent and reflected radiation contain the
free-free emission and emission from the hot electron gas. Kompaneets
equation gives the changes in photon phase densities in different
types of media. Although the initial spectrum is angle dependent,
the Kompaneets equation gives a spectrum which is angle independent
after several Compton scattering times.
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Title: Radiative transfer on X-Y geometry
Authors: Peraiah, A.
2010BASI...38..115P Altcode:
A unique and non-negative solution of the radiative transfer equation
in two dimensional X-Y geometry in scattering and absorbing media is
presented. This solution facilitates asymmetric boundary conditions
both in geometry and direction from the two boundaries of geometrical
configurations such as stellar atmospheres and similar objects. Further,
it allows inhomogeneities in the physical properties that occur at
any point in the medium.
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Title: An Integral Operator Technique of Radiative Transfer in
Spherical Symmetry
Authors: Peraiah, A.
2009nrt..book..305P Altcode:
No abstract at ADS
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Title: Transfer of resonance line radiation in advected atmospheres
with partial frequency redistribution of photons
Authors: Peraiah, A.
2004BASI...32...33P Altcode:
We studied the influence of high veolcities of expansion on resonance
line radiation by taking into account of aberration and advection. We
used an angle averaged redistribution function R<SUB>II</SUB> in
spherically symmetric media. Three types of media are considered. These
are: (1) purely scattering medium (2) partly scattering and emission
from continuum medium and (3) partly scattering and continuum
and line emission medium. The spherical shells that are being used
have thicknesses equal to 2, 10 and 100 times the stellar radii. The
radiation field is shown in terms of teh source functions. Computations
are performed in the comoving frame of the gas and the line profiles
are calculated at the observer's point at infinity. The line profiles
computed in the first type of medium show P Cygni characteristics
and those computed in the second and third type of media show central
emission and self absorption.
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Title: Radiative transfer in the distorted and irradiated atmospheres
of close binary components
Authors: Peraiah, A.; Srinivasa Rao, M.
2002A&A...389..945P Altcode:
We studied the transfer of line radiation in the distorted and expanding
atmospheres of close binary components. We assumed that the distortion
of the atmosphere is caused by self rotation and tidal force exerted
by the presence of the secondary component. The distortion is measured
in terms of the ratio of angular velocities at the equator and pole
(X), mass ratio of the two components (m<SUB>2</SUB>)/(m<SUB>1</SUB>),
the ratio of centrifugal force to that of gravity at the equator of
the primary (f) and ratio of the equatorial radius of the primary to
the distance between the centres of gravity of the two components
displaystyle (r<SUB>e</SUB>)/(R). A seventh degree equation is
obtained to describe the distorted surface in terms of the above
mentioned parameters. We have used X=1 for uniform rotation throughout
and used values f=0.1 and 0.5, (m<SUB>2</SUB>)/(m<SUB>1</SUB>)=1,
and (r<SUB>e</SUB>)/(R)=0.1, 0.3, and 0.5. The equation of line
transfer is solved in the comoving frame of the expanding atmosphere
of the primary using complete redistribution in the line. We used
a linear law of velocity of expansion so that the density varies as
r<SUP>-3</SUP> where r is the radius of the star, satisfying the law of
conservation of mass. We set v<SUB>a</SUB>=0 and v<SUB>b</SUB>=10 mtu
(mean thermal units) where v<SUB>a</SUB> is the velocity at the surface
of the primary with radius r=a(=5*E<SUP>11</SUP>) cm and v<SUB>b</SUB>
is the velocity at the surface of the extended atmosphere with radius
r=b(=10<SUP>12</SUP>) cm. We also computed lines in a static atmosphere
with density changing as rho ~ r<SUP>-1</SUP>. We have considered a
primary with an effective temperature T<SUB>*</SUB> and a point source
of secondary with three different temperatures T<SUB>c</SUB> equal
to 2x 10<SUP>4</SUP> K, 3x 10<SUP>4</SUP> K, and 4x 10<SUP>4</SUP>
K. The maximum change in line fluxes is noticed when the parameters
(r<SUB>e</SUB>)/(R) and f are changed, while the changes due to
(m<SUB>2</SUB>)/(m<SUB>1</SUB>) are minimal. The expansion of the
atmosphere produces P Cygni type line profiles. The incident radiation
from the secondary increases the line fluxes and absorption in the
centre of the line is replaced by emission.
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Title: An Introduction to Radiative Transfer
Authors: Peraiah, Annamaneni
2001irt..book.....P Altcode:
Preface; 1. Definitions of fundamental quantities of the radiation
field; 2. The equation of radiative transfer; 3. Methods of solution
of transfer equation; 4. Two-point boundary problems; 5. Principle
of Invariance; 6. Discrete space theory; 7. Transfer equation in
moving media: the observer frame; 8. Radiative transfer equation
in the comoving frame; 9. Escape probability methods; 10. Operator
perturbation methods; 11. Polarization; 12. Polarization in magnetic
media; 13. Multi-dimensional radiative transfer.
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Title: An Introduction to Radiative Transfer: Methods and Applications
in Astrophysics
Authors: Peraiah, Annamaneni
2001irtm.book.....P Altcode:
No abstract at ADS
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Title: Radiative transfer in the dusty, irradiated expanding
atmospheres of close binary components
Authors: Srinivasa Rao, M.; Peraiah, A.
2000A&AS..145..525S Altcode:
We studied the formation of lines in the irradiated expanding dusty
atmospheres of the components of close binary systems. We considered
a two-level atom approximation in Non-LTE situation with complete
redistribution. The thickness of the atmosphere is set to be equal
to twice that of the stellar radius. Maximum expansion velocities
is set to be as large as 50 mean thermal units. The isotropically
scattering dust is distributed uniformly in the atmosphere. We have
computed the lines using a total optical depths 10<SUP>4</SUP> at the
line centre. The irradiation from the secondary is one, five and ten
times the self radiation. The line fluxes in the line of sight are
calculated by using the total source function which is the sum of the
source functions due to self radiation and that due to irradiation from
the secondary. The line profiles formed in dusty atmosphere are compared
with those formed in dust free atmosphere. The profiles are presented
for different velocities of expansion, different separations between
the components and several dust optical depths. P Cygni type profiles
are produced in the expanding atmosphere and the irradiation from the
secondary enhances the emission in the lines. The major effect of dust
on the formation of lines in the expanding atmospheres of the component
of close binary is to scatter photons into the line core, among others.
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Title: Principles of Invariance in Radiative Transfer
Authors: Peraiah, A.
1999SSRv...87..465P Altcode:
We have reviewed the principle of invariance, its applications and
its usefulness for obtaining the radiation field in semi-infinite and
finite atmospheres. Various laws of scattering in dispersive media and
the consequent radiation field are studied. The H-functions and X- and
Y-functions in semi-infinite and finite media respectively are derived
in a few cases. The Discrete Space Theory (DST) which is a general form
of the Principle of Invariance is described. The method of addition of
layers with general properties, is shown to describe all the properties
of multiple scattering. A few examples of the application of DST such
as polarization, line formation in expanding stellar atmospheres, etc.,
and a numerical analysis of DST are presented. Other developments in
the theory of radiative transfer are briefly described.
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Title: A series of theoretical line profiles formed in the irradiated
expanding atmospheres of close binary components
Authors: Peraiah, A.; Srinivasa Rao, M.
1998A&AS..132...45P Altcode:
We studied the effects of irradiation on the line formation in the
expanding atmospheres of the components of close binary systems. We
considered a two-level atom approximation in Non-LTE situation. The
thickness of the atmosphere is assumed to be twice that of the
stellar radius. Expansion velocities are assumed to be as large as 50
mean thermal units. We have computed the lines using total optical
depths 10(3) , 10(4) and 10(5) at the line centre. The irradiation
from the secondary is assumed to be one, five and ten times the
self radiation. The line fluxes in the line of sight are calculated
by using the total source function which is the sum of the source
functions due to self radiation and that due to irradiation. We notice
that the expansion of the medium produces P Cygni type profiles
and the irradiation enhances the emission in the lines although
the equivalent widths reduce considerably. Figures 1(1-6), 2(1-30),
3(1-8), 4(1-8), 5(1-6) and 6(1-8) are available in electronic form at
the http://www.edpsciences.com
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Title: Radiative transfer - Chandrasekhar - and after
Authors: Peraiah, A.
1996BASI...24..397P Altcode:
No abstract at ADS
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Title: Linear Polarization in Close Binaries
Authors: Parman, S. K.; Peraiah, A.
1993icpc.proc..171P Altcode: 1993IAUCo.132..171P
No abstract at ADS
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Title: Effects of Aberration and Advection on Line Formation
Authors: Peraiah, A.
1991ApJ...380..212P Altcode:
The effects of inclusion of the aberration and advection terms in
the equation of the line transfer are studied. Spherical shells whose
ratios of outer (B) to inner (A) radii (B/A) are 2, 5, and 10 and with
line-center optical depths 500, 1300, and 1350 are considered. The
velocities of expansion of the medium are set at 1000, 2000, 3000, 4000,
and 5000 km/s. The line source functions and the corresponding profiles
of lines are calculated. The individual and combined effects of the
transverse and radial velocity gradients, and those of aberration and
advection in plane-parallel and spherically symmetric geometries on the
line source functions and the emerging line profiles are considered. It
is found that large effects are generated in the radiation field when
these physical mechanisms are taken into account in the transfer of
the line radiation. The method for various velocity laws was tested
and found to be stable.
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Title: The effects of non-coherent electron scattering on spectral
line formation
Authors: Rangarajan, K. E.; Mohan Rao, D.; Peraiah, A.
1991MNRAS.250..633R Altcode:
Spectral line profiles from a plane-parallel homogeneous atmosphere have
been calculated for the complete and partial redistribution mechanisms
(CRD and PRD) including coherent and noncoherent electron scattering. It
is found that in all the cases where the electron scattering coefficient
is more than the continuous absorption coefficient, there are measurable
changes in the spectral line profiles. In such situations, the PRD
profiles have more emission hump compared to CRD profiles in the
intermediate frequency range. Extended wings and additional broadening
of the line profiles are obtained for the case of noncoherent electron
scattering compared to coherent electron scattering. These results have
implications in the derivation of physical properties (for example,
microturbulent velocities) of stellar atmospheres from spectral lines.
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Title: Aberration and Advection Effects in Expanding Spherically
Symmetric Shells
Authors: Peraiah, A.
1991ApJ...371..673P Altcode:
The extreme outer layers of supernovae, novae, AGN, QSOs, and many
supergiant stars are known to be in rapid expansion or contraction. In
this paper, aberration and advection effects in a spherical medium
scattering radiation isotropically and coherently are investigated. The
shells are assumed to be moving radially with velocities of 1000,
2000, 3000, 4000, and 5000 km/s. A solution of the radiative transfer
equation is presented. The changes in mean intensities are dependent
on the geometrical and optical thickness and in particular depend on
the ratio T/(B/A), where T is the maximum optical depth and B and A
are the outer and inner radii of the spherical shell, respectively.
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Title: Effects of Aberration and Advection on Line Transfer in Plane
Parallel Geometry
Authors: Peraiah, A.; Varghese, B. A.
1991BASI...19....9P Altcode:
We have investigated the effects of aberration and advection on line
formation in a plane-parallel medium. We have considered velocities
of the order of V = l000, 2000, 3000, 4000, 5000 km s<SUP>-1</SUP>
in a plane parallel medium in which the line centre optical depths are
500 and 1200. We consider a two-level atom approximation and find that
the line source (S<SUB>L</SUB>) changes considerably depending on the
optical depth, and S<SUB>L</SUB> for V = 0 km s<SUP>-1</SUP> differ
from that at V = 5000 km s<SUP>-1</SUP> by a factor of 10<SUP>3</SUP>.
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Title: Polarization in binaries
Authors: Barman, S. K.; Peraiah, A.
1991BASI...19...37B Altcode:
Theoretical models are computed for estimating linear polarization
from the extended dusty outer layers of the components of a close
binary system whose surfaces are distorted by rotation and mutual
tidal effects. Plane-parallel layers of the dusty atmospheres of the
components are assumed. A wavelength-dependent scattering coefficient
and a Rayleigh phase function is used in solving the equation of
radiative transfer. Polarization increases with decreasing wavelength
and increasing particle size. Polarization for uniform rotation is
larger than that for nonuniform rotation. Polarization for single
stars is always less than that for a binary component, dependent on
the position of the observer.
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Title: Radiative Transfer with Compton Scattering in Spherically
Symmetric Shells
Authors: Peraiah, Annamaneni; Varghese, Baba A.
1990PASJ...42..675P Altcode:
We have solved the equation of radiative transfer with Compton
scattering in spherically symmetric shells. The specific intensity was
expanded by a Taylor series and the first three terms were retained
in solving the transfer equation. We assumed optical depths of 2 and 5
in a spherical shell whose outer radii (B) and inner radii (A) are in
the ratio of 2 and 5. Multiple Compton scattering redistributes the
initial energy over a range of 1 to 10 Compton wavelengths. A good
fraction of the incident radiation is transferred across the shell,
the radiation being redistributed in wavelength, the percentage of
which depends on the optical thickness of the medium.
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Title: Abhyankar - the Scientist
Authors: Peraiah, A.
1990BASI...18..119P Altcode:
No abstract at ADS
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Title: Radiation transfer in fast moving fluids
Authors: Peraiah, A.
1990BASI...18..149P Altcode:
Various factors influencing the formation of spectral lines are
described, emphasizing the physics of stellar atmospheres. Broadening
mechanisms, photon or partial frequency redistribution, the role
of chemical species are briefly addressed. Emphasis is given to a
discussion of geometrical and dynamical aspects, including plane
parallel and spherical symmetry, the rest and the comoving frames,
and aberration and advection.
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Title: Effects of stimulated emission on radiative transfer with
partial redistribution.
Authors: Rangarajan, K. E.; Mohan Rao, D.; Peraiah, A.
1990A&A...235..305R Altcode:
The authors study the non-LTE line transfer with stimulated
emission. Stimulated emission is important for red transitions
in hot stars and infrared transitions in cool stars. The authors
investigate the deviation of the absorption and emission profiles
from each other for a two-level atomic model with the line scattering
described by the angle-averaged redistribution functions. The partial
redistribution formalism has been used while solving the radiative
transfer equation. The correct expression for the source function
derived by Baschek, Mihalas and Oxenius (1981) has been employed to
obtain the emission profile and the radiation field. From this study,
the authors have obtained the following results: the redistribution
function R<SUB>III</SUB> gives the emission profile same as that of
the absorption profile (like complete redistribution) in the core and
also in the wings but with a small enhancement at the intermediate
frequency points whether stimulated emission is present or not. The
emergent emission profile is different from the absorption profile by
several factors in the wings for R<SUB>II</SUB>.
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Title: Effect of the Time Spent by the Photon in the Absorbed State
on the Time-dependent Transfer of Radiation
Authors: Rao, D. Mohan; Rangarajan, K. E.; Peraiah, A.
1990ApJ...358..622R Altcode:
The time-dependent transfer equation is derived for a two-level atomic
model which takes both bound-bound and bound-free transitions into
account. A numerical scheme is proposed for solving the monochromatic
time-dependent transfer equation when the time spent by the photon in
the absorbed state is significant. The method can be easily extended
to solve the problem of time-dependent line formation of the bound-free
continuum. It is used here to study three types of boundary conditions
of the incident radiation incident on a scattering atmosphere. The
quantitative results show that the relaxation of the radiation field
depends on the optical depth of the medium and on the ray's angle
of emergence.
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Title: Equivalent widths of hydrogen Lyman alpha line in an expanding
spherical atmosphere
Authors: Peraiah, A.; Ingalgi, M. F.
1990JApA...11..209P Altcode:
The profiles of hydrogen Lyman-alpha line in an expanding spherical
atmosphere containing dust and gas were calculated. The variation of
equivalent widths with velocities of expansion of the atmosphere,
together with the amount of dust present in the medium is being
investigated. Curves of growth have been drawn for different velocities
and dust optical depths.
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Title: Radiative transfer with Compton scattering in plane parallel
geometry
Authors: Peraiah, A.
1990JApA...11..193P Altcode:
The equation of radiative transfer with Compton scattering is
solved. The specific intensity has been expanded by Taylor series with
respect to wavelength and the first three terms have been retained in
solving the transfer equation. It is noted that, in a medium stratified
in plane parallel layers, the multiple Compton scattering redistributes
the initial energy over a range of 3 to 5 Compton wavelengths. A good
fraction of the incident radiation is transferred across the layer
with redistribution in wavelength, the actual value depending on the
optical thickness of the medium.
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Title: Effects of dust on equivalent widths of spectral lines formed
in expanding spherically symmetric shells
Authors: Peraiah, A.; Ingalgi, M. F.
1990BASI...18...17P Altcode:
A study is made of the effects of the presence of dust and radial
expansion of the spherical shells around stars on the equivalent
widths of the lines formed in such shells. A non-LTE, two-level atom
approximation is considered, and it is assumed that the dust scatters
isotropically; 30 shells and an optical depth of 300 are considered. Two
types of expanding shells are treated: with velocity gradients and
without velocity gradients. Depending upon the parameters used, the
equivalent widths change considerably.
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Title: The Effects of Aberration and Advection in Plane-Parallel
and Absorbing Media
Authors: Peraiah, A.
1989Ap&SS.159..339P Altcode:
We have calculated the changes that would occur in mean intensity due to
the presence of aberration and advection terms in radiative transfer
equation. We have considered an absorbing medium with velocities
1000, 2000, 3000, 4000, and 5000 km s<SUP>-1</SUP> (β-0.0033, 0.017,
where β=V/C,V is the velocity of the medium andC is the velocity
of the light). Calculations have been done in a comoving frame with
monochromatic radiation field. We have calculated the deviation in mean
intensity defined asbar J = \{ [J(V = 0) - J(V > 0)]/J(V = 0)],
whereJ is the mean intensity. We have taken two types of absorbing
media (1) with a source of constant emission and (2) with emission
source. As the emission decreases as 1/n <SUP>2</SUP> wheren is the
number of layer, wheren=1 corresponds to τ<SUB>max</SUB> and n=N
corresponds to τ=0 We find that for a total optical depth of one,
the maximum change is about 2% whenB(r)=1 and about 6%, whenB(r)∝1/n
<SUP>2</SUP> whereB(r) is the Planck function. When the optical depth
increases to 5 the maximum change in the case of the constant source
function falls to 1.5%, where as in the other case in which the Planck
function changes as 1/r <SUP>2</SUP> the maximum changes remains at
6%. Further increase of the optical depth will reduce the changes
to less than 2%. The amplification factor in the case of the Planck
function varying as 1/r <SUP>2</SUP> is more than when the emission
sources are constant.
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Title: Effects of Aberration and Advection in a Partially Scattering
Medium
Authors: Peraiah, A.; Srinivasa-Rao, M.
1989BASI...17...14P Altcode:
We have investigated the effects of aberration and advection terms,
which are of order ν/c (where ν is the velocity of gas and C is
the velocity of light) on the solution of the radiative transfer
equation. We have employed a plane-parallel medium which is moving
with velocities 1000, 2000, 3000, 4000 or 5000 km s<SUP>-1</SUP> (β =
0.0033, - 0.07 where (β = ν/c). The calculations have been done in the
fluid frame, with monochromatic radiation field. We introduce emission
sources inside the medium. We assume equal contribution from internal
emission and from isotropic and coherent scattering to the radiation
field. We have estimated the effects of aberration and advection on
the mean intensities and on outward fluxes for different velocities
and different optical depths. The effects are found in terms of the
mean intensity barJ { = [J(ν = 0) - J(ν > 0)] × 100/J (ν = 0)
and the outward flux barF { = [F(ν = 0) - F(ν > 0)] × 100/F (V
= 0)}. We set ω (albedo for single scattering) equal to 0.5 and the
Planck function equal to B(n) == 1 (case i) and B(n) ∼ 1/n<SUP>2</SUP>
(case ii). In case (i), the values of barJ and barF are not spectacular
and the maximum changes are in the range of 2 to 3%. In case (ii)
the changes are in the range of 5 to 6%.
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Title: On the coronal lines λ5303 Å and λ6374 Å
Authors: Peraiah, A.; Varghese, B. A.
1989SoPh..124...53P Altcode:
We present theoretical calculations of the observed coronal emission
line profiles of FeXIV (5303 Å) and Fex (6374 Å) ions, which are
observed at the time of total solar eclipse. Baumbach's relation
(Allen, 1973) of electron density has been employed to compute the full
width at half maximum FWHM. We have employed several other electron
density distributions and found that the calculated differences in the
FWHM are within 0.5% of one another. We have used the ion densities
N<SUB>i</SUB>/N<SUB>E</SUB> given by Jordan (1969). To explain the
observed FWHM, we have assumed that the corona is expanding spherically
symmetrically with a velocity of one or two mean thermal units and
no turbulence is included. With these highly simplified assumptions,
we have reproduced qualitatively the profiles and FWHM's of the above
lines. However, to explain quantities of FWHM's, we should take into
account the inhomogeneities in the structure of the corona. It is thus
shown, that turbulence is not necessary to explain the observed FWHM.
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Title: Some physical processes influencing the polarization of
continuum and line radiation
Authors: Nagendra, K. N.; Peraiah, A.
1987A&A...181...71N Altcode:
Some physical mechanisms which affect the continuum and line
polarization are studied. The physical conditions of the plasma
selected for this purpose represent different astrophysical situations
of interest, particularly the magnetic stars. The pure absorption
polarization transfer equation is solved individually taking these
effects into account.
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Title: Aberration and Advection Effects in a Plane-parallel Medium
in Motion
Authors: Peraiah, A.
1987ApJ...317..271P Altcode:
The effects of aberration and advection terms in the fluid-frame
steady-state radiative-transfer equation are evaluated by means of
numerical computations for plane-parallel media moving at velocities
1000, 2000, 3000, 4000, and 5000 km/s. A monochromatic radiation field,
no internal emission, and coherent isotropic scattering are assumed;
the results are presented graphically and briefly characterized. The
inclusion of aberration and advection is shown to produce substantial
changes in the mean intensities and outward fluxes, even when time
dependency is neglected. Application of the results to models of light
propagation through the rapidly expanding outer layers of supergiants,
novae, supernovae, QSOs, etc. is recommended.
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Title: Effects of dust on the formation of lines in an expanding
spherical medium
Authors: Peraiah, A.; Varghese, B. A.; Rao, M. S.
1987A&AS...69..345P Altcode:
A series of line profiles formed in a spherically symmetric and radially
expanding atmosphere in which dust is present are computed, assuming
that the dust scatters radiation isotropically. Two cases of dust
distribution are employed: (1) uniform distribution of dust throughout
the medium and (2) density increasing with radius. The density and the
velocity of expansion of the gaseous component are assumed to satisfy
the equation of continuity for a model of a two-level atom in a non-LTE
approximation with complete redistribution. The calculations are done
in the comoving frame of the fluid and later transformed to a point
at infinity.
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Title: Transmission and reflection operators of radiative transfer
equation with aberration and advection terms. II - Line radiation
in spherical symmetry
Authors: Peraiah, A.
1987BASI...15...70P Altcode:
A formal solution of the equation of radiative transfer is presented
with aberration and advection terms corresponding to the lines
included. The operators of reflection and transmission in a radially
expanding spherically symmetric shell are derived. This solution
is valid in a medium moving with velocity v such that v/c is about
0.0167. Complete or partial frequency redistribution of photon
frequencies can be incorporated if desired.
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Title: Transmission and Reflection Operators of Radiative
Transfer Equation with Aberration and Advection Terms - Part One -
Monochromatic Radiation Field with Spherical Symmetry
Authors: Peraiah, A.
1987BASI...15....1P Altcode:
Integration of the radiative transfer equation, with the aberration and
advection terms included, is described, assuming coherent and isotropic
scattering. The operators of transmission and reflection derived in
this paper are applicable to situations in which v/c = 0.0167 where
v and c are the velocities of the gas and light respectively. These
operators can be applied to a spherically symmetric medium in which
matter scatters or absorbs and emits monochromatic radiation.
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Title: An Integral Operator Technique of Radiative Transfer in
Spherical Symmetry
Authors: Peraiah, A.
1987nrt..book..305P Altcode:
No abstract at ADS
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Title: Effects of Temperature and Velocity Gradients on Doppler Widths
Authors: Peraiah, A.; Varghese, B. A.
1986Ap&SS.126..295P Altcode:
We have investigated how the gradients of temperature and expansion
velocities will change the emergent profiles from an extended medium
in spherical symmetry. Variation of the source function and expansion
velocities are assumed. The following variations of temperature are
employed: <P />(1) <P />T(r) ; T<SUB>0</SUB> (isothermal case) <P />(2)
<P />T(r) ; T<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>1/2</SUP> <P />(3) <P
/>T(r) ; T<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>-1</SUP> <P />(4) <P />T(r)
; T<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>-2</SUP> <P />(5) <P />T(r) ;
T<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>-3</SUP> The profiles calculated
present an interesting feature of broadening.
---------------------------------------------------------
Title: Relativistic effects on radiative transfer equation: order
of magnitude study.
Authors: Peraiah, A.
1986KodOB...5..141P Altcode:
The author has analyzed how the high gas velocities which are observed
in objects such as the atmospheres of supergiant stars, novae,
supernovae, accretion discs around high density objects would change
the coefficients of different terms in the transfer equation which is
solved in a comoving frame. Velocities as low as 5000 km s<SUP>-1</SUP>
are enough to show the relativistic effects in different terms in the
transfer equation. It is suggested that the relativistic effects must
be taken into account in almost all the cases where the line profiles
are studied in the expanding atmospheres.
---------------------------------------------------------
Title: Discretization of the equation of radiative transfer with
Compton scattering.
Authors: Peraiah, A.
1986KodOB...5...61P Altcode:
The author has attempted to solve the equation of radiative transfer
by including Compton and inverse Compton scattering. He expanded the
specific intensity by Taylor series. The resulting equation has been
discretized for obtaining the solution.
---------------------------------------------------------
Title: Integral operator technique of line transfer.
Authors: Peraiah, A.
1986KodOB...5..113P Altcode:
The author presents details of a new technique of obtaining a numerical
solution of the radiative transfer equation in spherical symmetry in
a polychromatic system. He employed the integral operators together
with an interpolation formula of the specific intensity defined on
radius-angle-frequency grid. The author finds that the method is quite
stable and employs a large stepsize in all the variables on the grid.
---------------------------------------------------------
Title: Some Aspects of the Solution of Vector Transfer Equation in
a Magnetized Medium
Authors: Nagendra, K. N.; Peraiah, A.
1985Ap&SS.117..121N Altcode:
A simplification of the numerical method of solving the vector transfer
equation, given earlier by Nagendra and Peraiah (1985a), is described
for problems which involve only absorption. This allows us to attempt
to solve under realistic conditions and with reduced computing efforts,
the important problems of polarization of light emerging from magnetized
stars. For the purpose of illustration, the equations described are
used for solving the continuum and Zeeman line transfer problems.
---------------------------------------------------------
Title: Numerical solution of the radiative transfer equation in a
magnetized medium
Authors: Nagendra, K. N.; Peraiah, A.
1985MNRAS.214..203N Altcode:
A numerical method of solution based on the discrete space theory of
radiative transfer as applied to the transfer problems in an anisotropic
medium is discussed. Two simple applications, namely the scattering
in the atmosphere of a hot magnetic white dwarf and in a plasma slab
immersed in a superstrong magnetic field are discussed. The normal wave
transfer equations for the scattering and absorption of radiation are
used for this purpose. The solutions are compared with those obtained
for the non-magnetic Thomson scattering in the same media. A comparative
study is made of the normal wave and Stokes vector equations for a
Zeeman active gas.
---------------------------------------------------------
Title: Radiative transfer equation in spherical symmetry
Authors: Peraiah, A.; Varghese, B. A.
1985ApJ...290..411P Altcode:
A numerical solution of the radiative transfer equation in spherically
symmetric geometry is presented using integral operators within the
framework of the discrete space theory and expressing the specific
intensity in terms of the nodal values of the radius-angle mesh. The
solution obtained satisfies the following tests: (1) the invariance
of the specific intensity in a medium in which radiation is neither
absorbed nor emitted, (2) the continuity of the solution in both
angle and radial distribution, (3) a numerical proof showing the
uniqueness of the solution, and (4) the condition of zero net flux in
a scattering medium with one boundary having a specular reflector,
and global conservation of energy. The solution is found to satisfy
the above tests to the machine accuracy.
---------------------------------------------------------
Title: Solution of Radiative Transfer Equation with Spherical Symmetry
in Partially Scattering Medium
Authors: Peraiah, A.; Varghese, B. A.
1985Ap&SS.108...67P Altcode:
We have solved the equation of radiative transfer in spherical
symmetry with scattering and absorbing medium. We have set the albedo
for single scattering to be equal to 0.5. We have set the Planck
function constant throughout the medium in one case and in another
case the Planck function has been set to vary asr <SUP>-2</SUP>. The
geometrical extension of the spherical shell has been taken as large
as one stellar radius. Two kinds of variations of the optical depth
are employed (1) that remains constant with radius and (2) that varies
asr <SUP>-2</SUP>. In all these cases the internal source vectors and
specific intensities change depending upon the type of physics we have
employed in each case.
---------------------------------------------------------
Title: P Cygni type profiles.
Authors: Peraiah, A.; Srinivasa Rao, M.
1985KodOB...5...45P Altcode:
The authors present a series of P Cygni type profiles of spectral
lines computed by employing different velocity laws of expansion in a
spherically symmetric atmosphere. A comparison has been made with those
of Beals classification. They have employed the line transfer equation
in comoving frame in certain test cases, to obtain the source function
which is being used to calculate the profiles observed at infinity.
---------------------------------------------------------
Title: Radiative transfer equation in spherically-symmetric
non-scattering media.
Authors: Peraiah, A.; Varghese, B. A.
1984Ap&SS.107..177P Altcode:
We solved the equation of radiative transfer in spherically-symmetric
shells with arbitrary internal sources. We integrated the equation
of transfer on the discrete grid of angle and radius given by
[μ<SUB>j-1</SUB>, μ<SUB>j</SUB>] [r<SUB>i-1</SUB>, r<SUB>i</SUB>]. The
size in the angle coordinates is determined by the roots of a quadrature
formula where as the size in the radial coordinate is determined by
the non-negativity of the reflection and transmission operators. We
considered two cases of variation of the Planck function. (1) Constant
throughout the medium and (2) varying as 1/r <SUP>2</SUP>. We find
that in the inner shells, the radiation directed toward the centre
of the sphere is more than that directed away from the centre of the
sphere. In the outer shells the converse is true.
---------------------------------------------------------
Title: The interaction principle in radiative transfer.
Authors: Peraiah, A.
1984Ap&SS.105..209P Altcode:
We describe the interaction principle which is of fundamental importance
to the theory of radiative transfer in one-, two-, and three-dimensional
geometry. We also describe the practical difficulties associated with
this principle in these geometries.
---------------------------------------------------------
Title: Polarization of Continuum Radiation in Magnetic Atmospheres
Authors: Nagendra, K. N.; Peraiah, A.
1984Ap&SS.104...61N Altcode:
A numerical solution is presented for the problem of continuum radiative
transfer in a magnetoactive medium. The continuum opacities are
calculated in the presence of a strong magnetic field (H=10<SUP>7</SUP>
G) typical of magnetic white dwarfs. The L.T.E. pure absorption model
is assumed for calculating the polarized radiation field emitted by a
realistic model atmosphere in the plane parallel approximation. The
wavelength dependence of the linear and circular polarizations are
calculated for both uniform and dipole field configurations.
---------------------------------------------------------
Title: Effects of partial frequency redistribution functions R(II),
R(III) and R(V) on source functions
Authors: Mohan Rao, D.; Rangarajan, K. E.; Peraiah, A.
1984JApA....5..169M Altcode:
The effects of partial frequency redistribution on the formation of
spectral lines have been studied. The angle-averaged R(II), R(III)
and R(V) types of redistribution with isotropic phase function have
been considered. Transfer equation with plane-parallel geometry is
solved in isothermal atmospheres. For an atmosphere with constant
thermal sources, the frequency-dependent source function S/L/(R/V/)
lies below S/L/(R/III/) but above S/L/(R/II/) in the line wings.
---------------------------------------------------------
Title: Reflection effect in close binaries.
Authors: Peraiah, A.
1984bims.symp...27P Altcode:
The author describes an initial attempt of how the radiation field is
calculated from the irradiated surface of the component in a binary
system.
---------------------------------------------------------
Title: Discrete space theory of radiative transfer.
Authors: Peraiah, A.
1984mrt..book..281P Altcode: 1984mrt..conf..281P
This contribution describes a general numerical method for solving
the equation of radiative transfer in inhomogeneous media with curved
geometries. The method is based on the interaction principle and the
star product algorithm. It is applied to line formation in expanding
media.
---------------------------------------------------------
Title: Reflection effect in close binaries. IV. Limb darkening of
the reflected radiation incident from an extended surface of the
secondary.
Authors: Peraiah, A.; Rao, M. S.
1983JApA....4..175P Altcode:
The law of limb darkening has been calculated when the atmosphere
of the primary component is illuminated by the extended surface of
the secondary component in a binary system. The specific intensities
calculated at infinity show marked changes when the plane-parallel
approximation is replaced by the assumption of spherical symmetry. The
middle portions of the illuminated surface reflect maximum radiation
while the innermost and outermost layers show lesser amount of reflected
radiation.
---------------------------------------------------------
Title: Reflection Effect in Close Binaries. V. Effects of reflection
on spectral line formation
Authors: Peraiah, A.; Rao, M. S.
1983JApA....4..183P Altcode:
The effects of reflection on the formation of spectral lines is
investigated. The authors have assumed a purely scattering atmosphere
and studied how the equivalent widths change due to irradiation from
the secondary. Generally, the flux in the lines is increased at all
frequency points, the cores of the lines receiving more flux than the
wings. Moreover, the proximity of the secondary component changes the
equivalent widths considerably. The further away the secondary is from
the primary the higher are the equivalent widths.
---------------------------------------------------------
Title: Density dependence of the line source functions in scattering
media.
Authors: Peraiah, A.
1983Ap&SS..95..117P Altcode:
We have calculated source functions in a scattering medium in which the
density changes according to the law ofN <SUB> e </SUB> (r)∼r <SUP>
n </SUP> wheren takes the value from -3 to +3(1) andN <SUB> e </SUB>
(r) is the electron density. We have assumed that the media consist
of electrons and we have also considered a geometrically extended
media in which the outer radii are 2, 3, 5 times the inner radius. The
source functions obtained are completely due to electron scattering. It
is found that the source function varies considerably for different
variations of density changes fromn=-3 to +3. In the case of density
variation withn=-3 and -2, the source functions do not increase with
optical depth considerably, but whenn=-1, 0, they rise slowly with
the increase in optical depths and whenn=1 to 3 there is a steep rise
in the source functions with the optical depth increasing towards the
center of the star.
---------------------------------------------------------
Title: Reflection effect in close binaries. III - Distribution of
radiation incident from an extended source
Authors: Peraiah, A.
1983JApA....4..151P Altcode:
The effects of irradiation from an extended surface of the secondary
component on the atmosphere of the primary are studied. Consideration
is given to an isothermal and purely scattering medium. The resultant
radiation field due to irradiation from an extended surface and
self-radiation is different from that due to irradiation from a point
source and self-radiation. In the case of the point source the middle
layers of the exposed part of the atmosphere show maximum reflection,
while in the former case the reflection gradually decreases from the
center of the component towards the surface of the outermost layers of
the atmosphere. The reflection effect appears to be strongly dependent
on the density distribution of the electrons.
---------------------------------------------------------
Title: Reflection effect in close binaries. II - Distribution of
emergent radiation from the irradiated component along the line
of sight
Authors: Peraiah, A.
1983JApA....4...11P Altcode:
The author has calculated the effects of irradiation from a point
source observed at infinity. Plane-parallel approximation and
spherically-symmetric approximations are employed in calculating
the self-radiation field for the sake of comparison. It is found
that there are considerable changes in the radiation received at
infinity between the approximation of plane-parallel stratification
and spherical symmetry.
---------------------------------------------------------
Title: Effects on partial prequency redistributionR II on the level
population ratios in a resonance line
Authors: Peraiah, A.; Nagendra, K. N.
1983Ap&SS..90..237P Altcode:
Angle-averaged partial frequency redistributionR II has been employed
in obtaining a simultaneous solution of radiative transfer equation
in the comoving frame and the statistical equilibrium equation for
a non-LTE two level atom. We have obtained the ratios of population
densities of the upper and lower levels of the resonance line of PV by
utilizing the data given in Bernacca and Bianchi (1979). Line source
functions are also obtained for different types of variations of density
and velocity of the expanding gases. We have considered the atmosphere
to be 11 times as thick as the stellar radius. The first iteration was
started by putting the density of the upper level (N <SUB>2</SUB>) equal
to zero. However, the convergent solution shows a substantial increase
inN <SUB>2</SUB> although it is still much less than the equilibrium
value. The line source function and the ratio of the densities of the
particles in the upper and lower levels fall sharply from a maximum at
τ=τ<SUB>max</SUB> to minimum at τ=0. We have studied the scattering
integralint {_{ - infty }^{ + infty } J_x φ _x } dx and found that
this quantity also varies quite similar to the ratioN <SUB>2</SUB>/N
<SUB>1</SUB> and the line source functionS <SUB>L</SUB>.
---------------------------------------------------------
Title: Radiative Transfer Effects due to Curvature and Expansion in
a Dusty Planetary Nebulae
Authors: Peraiah, A.
1983IAUS..103..516P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Limb darkening due to the incidence of a parallel beam of
radiation.
Authors: Peraiah, A.
1983KodOB...3..120P Altcode:
The author has investigated how the radiation is distributed from
the centre to the limb when the atmosphere receives a parallel beam of
radiation from infinity. He considers a purely reflecting surface at the
bottom of the atmosphere when the outer layers are illuminated uniformly
from all directions. The atmosphere under question is half the radius of
the star itself. Although the extension of the atmosphere is quite small
the differences in the laws of limb darkening are considerable. The
differences are further accentuated when the radiation is assumed to
be totally reflected from the bottom of the atmosphere. The situation
can be very similar to that of a planetary atmosphere.
---------------------------------------------------------
Title: Reflection effect in close binaries. I - Distribution of
radiation from a point source
Authors: Peraiah, A.
1982JApA....3..485P Altcode:
The radiation field along an irradiated surface of a component in a
binary system is calculated. The source of irradiation is assumed to
be a point source. This is done primarily to understand easily how
the incident radiation will get changed after it is being scattered
by the atmosphere. It is noticed that the maximum radiation comes from
intermediate points of the atmosphere, the reason being that here there
exists the combined radiation due to the star and incident radiation
from the point source outside the star although both are diluted.
---------------------------------------------------------
Title: On the Balmer progression in the expanding shell of PLEIONE
Authors: Peraiah, A.
1982JApA....3..297P Altcode:
The Balmer progression in velocities seen in Pleione and other shell
stars is investigated without undertaking the complicated calculations
of non-LTE radiative transfer and hydrodynamics of the shells. The
equations of the conservation of mass and momentum are simultaneously
solved using assumptions which simplify the calculations of the
solution. The radiation pressure due to the lines and continuum are
examined. It is found qualitatively that the high excitation Balmer
lines of hydrogen are formed in a region where the velocity gradients
are high and therefore these lines show high radial velocities.
---------------------------------------------------------
Title: Effects of Partial Frequency Redistribution on the Level
Population Densities in a Resonance Line
Authors: Peraiah, A.; Rao, D. M.
1981Ap&SS..80..437P Altcode:
We have obtained a simultaneous solution of the statistical equilibrium
equation for a non-LTE two-level atom and the radiative transfer
equation in the comoving frames by employing the angle-averaged partial
frequency redistribution.R <SUB> i </SUB> with isotropic scattering. In
the first iteration we have set the population density of the upper
level equal to zero and allow it to be populated in the subsequent
iterations. The solution converges within two to four iterations. The
process of iteration is terminated when the ratios of population
densities in two successive iterations at each radial point, attain
an accuracy of 1%. The effects of partial frequency redistribution
is to increase the population density of the upper level. Radial gas
motions do not seem to have significant effects, although in highly
extend geometries, velocity gradients change the population densities
considerably.
---------------------------------------------------------
Title: Optical depth effects on the formation of spectral lines in
rotating and expanding spherical atmospheres
Authors: Peraiah, A.; Raghunath, G.; Nagendra, K. N.
1981JApA....2..277P Altcode:
The effect of high optical depths and large rotational velocities on
the spectral lines in rotating and radial expanding spherical shells is
investigated. It is assumed that the outer radius of the shell is three
times the inner radius and that there are no velocity gradients in the
shell; the radial optical depths are 10, 50, 100, and 500. The shell
rotates with velocities varying as 1/p, where p is the perpendicular
distance from the axis of rotation. Two expansion (radial) velocities,
V = 0 and V = 10 mean thermal units, are considered, with maximum
rotational velocities of 0, 5, 10, and 20. In the shell with no radial
motions, symmetric lines with emission in the wings were obtained for
rotational velocities = 0 and 5, while for rotational velocities greater
than or equal to 10, symmetric absorption lines were formed. Lines
with central emission were obtained in the case of an expanding shell.
---------------------------------------------------------
Title: Effects of redistribution with dipole scattering on line
source functions
Authors: Peraiah, A.; Rangarajan, K. E.
1981JApA....2..245P Altcode:
The partial frequency redistribution function for zero natural line
width and dipole scattering is used to obtain a simultaneous solution
of the statistical equilibrium and line transfer equations in the
comoving frame of an expanding gas. A non-LTE, two-level atom in an
expanding spherical medium is considered, and the population ratio of
the two levels, N2/N1, is calculated. The upper level population (N2),
initially set equal to zero, is found to be enhanced significantly
from its initial value. Variation in the velocity gradient had little
effect on the N2/N1 ratio when the geometrical thickness of the medium
was three or ten times the stellar radius; when the thickness was
increased to twenty times the central radius, however, the velocity
gradients changed this ratio considerably in the region where log T
is less than or equal to two, T being the total optical depth.
---------------------------------------------------------
Title: Radiative Transfer in the Co-Moving Frame
Authors: Peraiah, A.
1981Ap&SS..77..243P Altcode:
Solution of line-transfer equation in the co-moving frame, obtained on
the basis of discrete space theory, has been employed to calculate the
lines emerging from a rapidly expanding stellar atmosphere. The solution
is found to be highly stable for large velocities of expansion with both
positive and negative velocity gradients. We have presented profiles
of spectral lines that are translated along the line of sight of the
observer at infinity. We have treated a Non-LTE two-level atom in a
medium scattering isotropically with line and continuum emission. P
Cygni-type profiles noticed in a purely scattering medium.
---------------------------------------------------------
Title: Photon escape probabilities in expanding atmospheres
Authors: Peraiah, A.; Rangarajan, K. E.; Rao, D. M.
1981JApA....2...81P Altcode:
A comparison of mean number of scatterings and escape probabilities
has been made in isotropic scattering and dipole scattering by using
the angle-averaged partial frequency redistribution function. The
equations of radiative transfer and statistical equilibrium have
been solved simultaneously in a spherically symmetric expanding
atmosphere. Two cases of atmospheric extension where the ratios of
outer to inner atmospheric radii are 3 and 10 have been treated. It
is found that the partial frequency redistribution gives a larger
mean number of scatterings compared to that given by complete
redistribution. Velocities tend to reduce the mean number of scatterings
and increase the mean escape probabilities.
---------------------------------------------------------
Title: Effects of velocities on Ca II H and K lines.
Authors: Rangarajan, K. E.; Mohan Rao, D.; Peraiah, A.
1981KodOB...3...75R Altcode:
With a chosen model atmosphere, the authors find double peaked emission
for H and K lines in the static medium. The results show that the
systematic velocity fields do play a significant role in determining
the shape of the H and K profiles.
---------------------------------------------------------
Title: Transient solution of equations of hydrodynamics in gas clouds.
Authors: Peraiah, A.
1981KodOB...3...86P Altcode:
The author presents numerical results of transient phenomena in
incompressible fluids. This has been obtained by solving the equations
of conservation of momentum, energy and mass.
---------------------------------------------------------
Title: Formation of spectral lines with the redistribution function
R<SUB>I</SUB> along the line of sight.
Authors: Peraiah, A.
1981KodOB...3...84P Altcode:
The author studies the formation of spectral lines at infinity with
the redistribution function R<SUB>I</SUB>. The radial optical depths
considered are .5, 5, 10, 50 and 100. A linear law of velocity is
assumed in these calculations. Profiles clearly show the P Cygni nature
of asymmetry.
---------------------------------------------------------
Title: An Iterative Simultaneous Solution of the Equations of
Statistical Equilibrium and Radiative Transfer in Comoving Frame
Authors: Peraiah, A.
1980JApA....1..101P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effects of High Velocities on Photoionization Lines
Authors: Peraiah, A.; Raghunath, G.
1980JApA....1..113P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comoving Frame Calculations of Spectral Lines formed in
Rapidly Expanding Media with the Partial Frequency Redistribution
Function for Zero Natural Line Width
Authors: Peraiah, A.
1980JApA....1....3P Altcode:
Comoving frame calculations have been used to compute the spectral
lines formed in rapidly expanding spherical media. We have employed the
angle-averaged partial frequency redistribution function R(I) with a
two-level atom model in non-LTE atom approximation. A linear velocity
law increasing with radius has been employed with maximum velocity at
tau=o being set equal to 30 mean thermal units. It is found that one
obtains almost symmetric emission line profiles at large velocities
similar to those found in quasars.
---------------------------------------------------------
Title: Lines formed in Rotating and Expanding Atmospheres
Authors: Peraiah, A.
1980JApA....1...17P Altcode:
Spectral lines formed in a rotating and expanding atmosphere have
been computed in the frame of the observer at infinity. Two kinds of
velocity laws are employed: (i) a uniform radial velocity of the gas
and (ii) velocity increasing with radius (i.e. velocity gradients). The
atmosphere has been assumed to be rotating with constant velocity. We
have considered maximum radial and rotational velocities to be 10 and 3
thermal units respectively in an atmosphere whose geometrical thickness
is 10 times the stellar radius. The total radial optical depth at line
centre is taken to be about 100. In all cases, Doppler profile and a
source function which is varying as 1/r**2 have been used. Generally,
the lines are broadened when rotation is introduced. However, when
radial motion is also present, broadening becomes asymmetic and the
red emission and blue absorption are enhanced.
---------------------------------------------------------
Title: Effects of high radial velocities on line transfer in extended
atmospheres
Authors: Peraiah, A.
1980AcA....30..525P Altcode:
The equation of radiative transfer in a comoving frame has been
solved for rapidly expanding gaseous medium in spherically symmetric
extended stellar atmospheres. A non-LTE two-level atom with Voigt
profile function is assumed. The comoving terms in the radiative
transfer are discretized in the framework of the discrete space
theory of Grant. These terms are simply reduced to a tri-diagonal
matrix. The boundary conditions for the frequency derivative can be
introduced through the elements of the first and last rows of this
matrix. This seems to be quite stable for arbitrary velocities in the
medium. Maximum velocities up to 60 units of mean thermal velocities
have been considered.
---------------------------------------------------------
Title: Lines formed in a slowly expanding thin spherical shell.
Authors: Peraiah, A.; Raghunath, G.; Nagendra, K. N.
1980KodOB...3...30P Altcode:
The authors have investigated how an optically thin spherical shell
with small velocities change the profiles and equivalent widths of
the lines. They have employed several types of variations in density,
velocity of expansion and source functions. In all the cases they
find that the line centres are shifted to the blue side almost in
proportion to the velocity of expansion. The shells moving with constant
velocities shift the line centre the most, irrespective of the density
variation. The velocity gradients shift the line centre the least.
---------------------------------------------------------
Title: Flux vector splitting of the inviscid radiation gas dynamic
equations.
Authors: Peraiah, A.
1980KodOB...3...49P Altcode:
The author has analysed various schemes for the iterative simultaneous
solution of the inviscid gas dynamic equations. He considers the problem
from the point of view of the stellar atmospheres. The difference
between conservative and quasi-conservative systems has been analysed
by using the flux vector splitting process. The radiation pressure in
the atmosphere (due to continuum and resonance lines) has been included
in flux vector splitting analysis to obtain best difference schemes.
---------------------------------------------------------
Title: Rotational effects on line source function.
Authors: Peraiah, A.; Raghunath, G.
1980KodOB...3...21P Altcode:
The effects of rotation are investigated on the source functions
in an expanding atmosphere. The authors have considered a non-LTE
two-level atom in an extended atmosphere. They have also made use
of von Zeipel's theorem in giving the incident radiation at τ =
τ<SUB>max</SUB>. Uniform rotation is assumed and the values of the
ratios of the centrifugal force and gravity force at the equator
are taken to be 0.1, 0.4, 0.8 corresponding to a uniform rotational
velocity of 1, 4 and 8 mtu. It is found that rotation will dilute the
radiation field which is similar to the effects of expansion.
---------------------------------------------------------
Title: Simultaneous solution of radiative transfer equation in
the comoving frame and the statistical equilibrium equation with
complete redistribution.
Authors: Peraiah, A.
1980KodOB...3...17P Altcode:
Complete redistribution with Voigt profile function has been employed
in obtaining the simultaneous solution of line transfer and the
statistical equilibrium equation for a non-LTE two level atom in an
extended stellar atmosphere expanding with spherical symmetry.
---------------------------------------------------------
Title: Line Formation in Spherical Media with Partial Frequency
Redistribution. II. Expanding Media with Redistribution Function
R<SUB>I</SUB>
Authors: Peraiah, A.
1979Ap&SS..63..267P Altcode:
Lines formed in a differentially expanding atmosphere have been
calculated by using the angle averaged redistribution functionR
<SUB>I</SUB> (Hummer, 1962). We have compared these lines, in a few
cases, with those formed by complete redistribution in the observer's
frame of reference. We have considered an atmosphere whose ratios
of inner to outer radii are 2 and 10, and it is assumed that the
gas in the atmosphere is expanding uniformly with a maximum velocity
of 3 mean thermal units. We have presented lines formed in spherical
symmetry and those obtained by integrating over the apparent disc. Three
types of physical situations are considered with a 2-level atom with
non-LTE approximation (1) ɛ=10<SUP>-4</SUP>, β=10<SUP>-4</SUP>, (2)
ɛ=10<SUP>-4</SUP>, β=0 and (3) ɛ=β=0, where ɛ is the probability
per scatter that a photon is destroyed by collisional de-excitation,
and β is the ratioKc/Kl of absorption in the continuum per unit
frequency interval to that in the line centre. It is found that there
are noticeable differences between the profiles formed by partial
redistribution (PRD) and complete redistribution (CRD). The profiles
integrated over the stellar disc from the first type of the media
are box type with flat top, which are similar to those observed in WC
stars and those from the second type of media show emission peaks on
red and blue sides with emission on the red side larger than the one
on the blue side. The profiles from the third type of media with pure
scattering, show some emission on the red side and deep absorption
on the blue side. Large geometrical extensions of the atmosphere and
higher gas velocities seem to enhance these two effects.
---------------------------------------------------------
Title: Formation of the hydrogen Lyman alpha line in expanding
spherical planetary nebulae.
Authors: Wehrse, R.; Peraiah, A.
1979A&A....71..289W Altcode:
The radiation field in the hydrogen Lyman-alpha line is calculated for
an optically thick nebula, which is in uniform or accelerated expansion
(velocity increasing to the surface). The radiative-transfer equation
is solved for a spherical configuration using the discrete space theory
with partial redistribution. The computations were performed for a
nebula with a ratio of outer to inner radius of 3.3 and an optical
depth at line center of about 1000. Velocities up to 26 km/s are
considered. In all cases strongly asymmetric profiles are found with a
high emission peak at the red side of the line center and a low one at
the blue side. Inside the nebula the mean intensities are much smaller
than in the static case. The calculations also show that the transverse
velocity gradients induced by the sphericity are very important.
---------------------------------------------------------
Title: R<SUB>II</SUB> partial frequency redistribution function
and its effects on the formation of lines in expanding spherical
atmospheres.
Authors: Peraiah, A.
1979KodOB...2..203P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solution of the radiative transfer equation in spherically
symmetric media with spherical harmonic approximation.
Authors: Peraiah, A.
1979KodOB...2..230P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comoving frame calculations with Lorentz profiles in radially
expanding media.
Authors: Peraiah, A.; Raghunath, G.
1979KodOB...2..240P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiation pressure in resonance lines.
Authors: Peraiah, A.
1979KodOB...2..260P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of the Hydrogen Lyman ~ Line in Expanding Spherical
Nebulae with Dust
Authors: Peraiah, A.; Wehrse, R.
1978A&A....70..213P Altcode:
Summary. The radiation field in the hydrogen Ly line is calculated for a
dust fflled spherical gaseous nebula. It is assumed that the nebula with
a ratio of inner to outer radius of 3.3 has an optical depth at the line
center of about 1000 and is either static or expands uniformly with 26
km s '. For the solution of the radiative transfer equation the discrete
space theory with partial redistribution is used. It is found that the
dust gives only rise to small changes if it purely scatters. However,
if it absorbs it is very effective in reducing the mean intensities
j in the whole nebula, e.g. for an optical depth in the dust of =1
decreases J by about a factor of 7. The results also show that for
dust filled nebulae the effects of velocities are of minor importance
in contrast to dust-free configurations. Key words: gaseous nebulae -
dust - H Ly line - spherical radiative transport - expansion
---------------------------------------------------------
Title: Line Formation in Spherical Media with Partial Frequency
Redistribution I: Solution of the Line Transfer
Authors: Peraiah, A.
1978Ap&SS..58..189P Altcode:
The effects of partial redistribution of frequency on the formation of
spectral lines in a static and spherically symmetric media have been
investigated. The partial redistribution functionsR <SUB>I</SUB> andR
<SUB>II</SUB> (Hummer, 1962) have been employed to calculate the lines
for a two-level atom in non-LTE in a spherically symmetric medium with
homogenous physical characteristics whose ratiosB/A (of outer to inner
radii) are equal to 2 and 10. These results are compared with those
formed in a plane-parallel medium withB/A=1. Two types of atmosphere
are treated: (1) a pure scattering medium with ɛ=0 and β=0, and (2)
an atmosphere with a constant source of emission ɛ=10<SUP>-4</SUP>
and β=0, where ɛ is the probability per scatter that a photon
will be destroyed by collisional de-excitation and β is the ratioK
<SUB>c</SUB>/K <SUB>l</SUB> of opacity due to continuous absorption
per unit interval of frequency to that in the line. Lines formed in
complete redistribution also have been calculated for the sake of
comparison, and the total optical depth in all cases has been taken
to be 10<SUP>3</SUP> at the line centre. Vast differences have been
found between the lines formed by complete and partial redistribution
functions (which, for the sake of simplicity, we shall hereafter refer
to as CRD and PRD, respectively). In the case of a purely scattering
medium, a small amount of emission is observed in the wings for all
cases of scattering functions in the spherical medium as a result of the
combined effects of curvature and physical scattering. In the scattering
medium, more photons are scattered into the cores of the lines by PRD
than in the case of CRD. The lines formed in the medium with internal
sources show emission in all cases with small absorption in the cores,
except those lines formed by the angle-dependent PRD functions which
again depend on the geometrical extension of the medium.
---------------------------------------------------------
Title: Formation of the H Lyalpha line in an expanding spherical
planetary nebula with dust.
Authors: Wehrse, R.; Peraiah, A.
1978BASI....6...50W Altcode:
No abstract at ADS
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Title: On negative intensities in discrete space theory in spherical
medium.
Authors: Peraiah, A.
1978KodOB...2..180P Altcode:
No abstract at ADS
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Title: Effects of partial frequency redistribution with dipole
scattering on the formation of spectral lines in expanding media.
Authors: Peraiah, A.
1978KodOB...2..115P Altcode:
No abstract at ADS
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Title: Geometry effects on the formation of the hydrogen Ly alpha
line in planetary nebulae.
Authors: Peraiah, A.; Wehrse, R.
1977A&A....61..719P Altcode:
Summary. In order to study the effects of sphericity on the radiative
transfer in the hydrogen Ly oc line of planetary nebulae, the radiation
field in this line is calculated for static pure hydrogen models
with ratios of outer to inner radiis approximately equal to 2,4 and
8. For r0 r 2 the transfer equation is also solved in plane parallel
approximation for comparison. Both reflecting and open inner boundaries
are considered. The transfer equation has been solved in the framework
of the discrete space theory. In the spherical calculations the
profiles of the emergent radiation are not found to be very different
in their shapes (one from another) while there are large differences
in the internal radiation fields. Substantial changes occur for most
quantities, when the spherical approximation is replaced by the plane
parallel one. Key words: spherical radiative transfer hydrogen Ly cc
planetary nebulae
---------------------------------------------------------
Title: Linear Polarization from Rotating Extended Atmospheres of Stars
Authors: Peraiah, A.
1976A&A....46..237P Altcode:
Summary. Linear polarization from the extended atmospheres of
rotating stars has been calculated. Two types of atmospheres have
been considered: (1) the atmospheres of early type supergiants with
electron scattering (Thomson scattering) and (2) the atmospheres of
late type supergiants with scattering due to H2 molecules (Rayleigh
scattering). In both cases, the density at any point in. the atmosphere
is assumed to vary as the inverse square of the distance from the
centre of the star. In the latter type of atmosphere, the wavelength
dependence of linear polarization has been calculated and it appears
to be in accordance with the observational result (Kruszeski et al.,
1968; Dyck and SandfordII, 1971) that the polarization increases with
decreasing wavelength. It is also shown that, in the case of an electron
scattering atmosphere, polarization always increases with the size of
the atmosphere, while this need not be so in the case of an atmosphere
with molecular scattering. Keywords: linear polarization extended
atmospheres atmospheres of supergiant stars - Thomson scattering -
Rayleigh scattering
---------------------------------------------------------
Title: Numerical solution of radiative transfer equation in extended
spherical atmospheres with Rayleigh phase function.
Authors: Peraiah, A.
1975A&A....40...75P Altcode:
No abstract at ADS
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Title: Curvature Effects in Extended Stellar Atmospheres - Absorption
and Scattering
Authors: Peraiah, A.
1973Ap&SS..23..159P Altcode:
The numerical solution of radiative transfer equation including
curvature with both absorption and scattering has been developed in the
frame work of Discrete Space Theory. Two cases have been considered:
(A) irradiation of the atmosphere at τ=T and (B) no irradiation on
either side of the atmosphere. Isotropic scattering has been assumed. It
is found that the emergent luminosities (defined by ∫r <SUP>2</SUP>
I(r, μ) đμ) from scattering dominated atmospheres are smaller than
those from absorption dominated atmospheres.
---------------------------------------------------------
Title: Temperature Difference between Pole and Equator of the Sun
Authors: Peraiah, A.
1973SoPh...30...29P Altcode:
No abstract at ADS
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Title: Curvature effects in extended stellar atmospheres — Pure
absorption
Authors: Peraiah, A.
1973Ap&SS..21..223P Altcode:
The effects of curvature in an atmosphere with pure absorption are
investigated. Numerical solution of the transfer equation has been
obtained in the framework of the Discrete Space Theory of Radiative
Transfer. Two cases have been considered: (a) the atmosphere is
irradiated at the bottom and there is no incident radiation at the
top of the atmosphere; and (b) no radiation is incident on either
side of the atmosphere. It is found that the thermal sources inside
the atmosphere dominantly influence the emergent radiation and this is
very much so, in the spherical case and for large optical thickness. The
emergent luminosities increase with the geometrical thickness although
the emergent specific intensities are reduced and the former seems to
be because of the larger surface area and later seems to be because
of the effects of curvature.
---------------------------------------------------------
Title: Spectral line formation in extended atmospheres-II
Authors: Peraiah, A.
1973MNRAS.162..321P Altcode:
Line profiles have been computed for a model of two-level atom both
for plane parallel and spherically symmetric geometry assuming both
LTE and non-LTE.
---------------------------------------------------------
Title: Numerical solution of the radiative transfer equation in
spherical shells.
Authors: Peraiah, A.; Grant, I. P.
1973JIMA...12...75P Altcode:
No abstract at ADS
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Title: Effect of atmospheric curvature on spectral line profiles in
extended stellar atmospheres.
Authors: Peraiah, A.; Grant, I. P.
1972css..conf..211P Altcode: 1971css..conf..211P
No abstract at ADS
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Title: Spectral line formation in extended stellar atmo-spheres
Authors: Grant, L. P.; Peraiah, A.
1972MNRAS.160..239G Altcode:
A method of numerical solution of the equation of radiative transfer
for spectral line formation in extended spherically symmetric stellar
atmospheres is described. A simple Non-LTE two-level atom model is
assumed. Results are presented for the cases b/a 2 where a is the
inner and b the outer radius of the atmosphere.
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Title: Theoretical Light Changes in Close Binaries
Authors: Peraiah, A.
1970A&A.....7..473P Altcode:
A general expression for the gravity darkening of the tidally and
non-uniformly rotating Roche components of close binary systems has been
derived. This expression has been used to ealculate the temperatures
and spectral distributions on the surfaces of these components and to
compute their luminosities with limb-darkening taken into account. The
effects of uniform and non-uniform rotation have been considered
together with a few cases of synchronous rotation. The distributions,
especially that of temperature are relatively insensitive to the
amount of non-uniformity of the rotation. The laws of darkening tend
to converge as the mass ratio increases. The results for synchronous
rotation of the components a not very different from those found for
nonsynchronous systems. Luminosities can be reduced by as much as
40 to 50 percent of the total luminosities in different directions
depending upon the line of sight.
---------------------------------------------------------
Title: Gravity Darkening in the Components of Close Binary Systems
Authors: Peraiah, A.
1969A&A.....3..163P Altcode:
The variation of temperature and brightness on the surface of the
components of close binary systems has been investigated taking
account of non-uniform rotation and tidal effects of the other
component considered as mass pomt. The equations for such surfaces
had been developed in terms of the mass ratio of the two components
(m3/m1); ratio of the equatorial radius of the primary to the distance
between the centers of gravity of the two components (re/B); ratio
of centrifugal to gravity forces at the equator (1); and the ratio of
angular velocities at the equator and the pole (x). When these equations
are used to compute the temperature and brightness distributions by
using different values for the above mentioned parameters, it has been
observed that temperature and brightness fall very rapidly between 45
colatitude and the equator. Higher temperatures tend to reduce gravity
darkening due to tidal effect. The fall in brightness is steeper than
that of temperature. These results are compared with those of Ireland
by putting m3 = 0.
---------------------------------------------------------
Title: Apsidal Motion in Close Binary Systems
Authors: Peraiah, A.
1966ZA.....64...27P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotation of the Components in Close Binary Systems
Authors: Peraiah, A.
1965ZA.....62...48P Altcode:
No abstract at ADS
