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ADS astronomy entries on 2022-09-14
=author:"Cannon, Chris J." OR =author:"Cannon, C.J."
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Title: The Transfer of Spectral Line Radiation
Authors: Cannon, C. J.
2012tslr.book.....C Altcode:
Preface; 1. Basic theory for model 2-level atoms; 2. Exact solutions to
the transfer equation; 3. Numerical methods of solution; 4. Extension
to model multi-level atoms; 5. Radiation gas dynamics; 6. Quantum
mechanical emission and absorption profiles; 7. Frequency and angle
re-distribution; 8. A quantum electrodynamical radiative transfer
equation; Appendices; References.
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Title: Book-Review - the Transfer of Spectral Line Radiation
Authors: Cannon, C. J.
1986S&T....71S.579C Altcode:
No abstract at ADS
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Title: Book-Review - the Transfer of Spectral Line Radiation
Authors: Cannon, C. J.; Mihalas, D.
1986Obs...106...23C Altcode:
No abstract at ADS
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Title: Radiative gas dynamics in the transonic regime
Authors: Cannon, C. J.
1985ApJ...289..363C Altcode:
The three equations specifying conservations of mass, momentum,
and energy in radiating gases, coupled to the equation of radiative
transfer, are examined for flow velocities approaching the local speed
of sound. It is found that time-dependent terms are essential to any
analysis of this transonic regime. In particular, it is found that
wave-type perturbations start to amplify, rather than damp, when
the flow velocity exceeds a critical value v(crit), where v(crit)
is approximately 80 percent of the local thermal speed. These
amplifications exhibit an e factor increase over a time scale
of order 40 s for solar-type atmospheres, and eventually reach a
magnitude which invalidates the concept of a steady state gaseous
flow. Further, the work done by pressure forces during a cycle of
these wave disturbances generates a nonzero heating of the gas when
the temperature fluctuations lead the velocity fluctuations as is the
case when the gas radiates. This heating mechanism could explain some
aspects of stellar chromospheric temperature increases.
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Title: The transfer of spectral line radiation
Authors: Cannon, C. J.
1985tslr.book.....C Altcode:
No abstract at ADS
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Title: Non-local perturbation techniques in radiative transfer.
Authors: Cannon, C. J.
1984mrt..book..157C Altcode: 1984mrt..conf..157C
Perturbation techniques are presented for reducing the required
computing time and enhancoing the accuracy of calculations of energy
transfer in a radiating gas. The methods reduce the number of grid
points by treating a simplified problem and assuming a more manageable
redistribution. The effects of spurious sources and sinks are considered
only after a zero-th order solution is obtained, with its inherent
errors. The Feautrier, perturbed integral, and Scharmer perturbation
methods are discussed, noting techniques for incorporating them into any
current numerical scheme for solving the transfer equation. The main
benefit is faster computations for coupled gas-dynamic and radiative
transfer problems.
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Title: The origin of stellar winds: subatmospheric nonthermal storage
modes versus radiation pressure.
Authors: Cannon, C. J.; Thomas, R. N.
1977ApJ...211..910C Altcode:
Most current models of matter-flux in hot stars place its origin in
radiation pressure, and then model the flow explicitly to produce no
chromosphere-corona. Our model of the stellar atmosphere as a transition
zone between stellar interior and interstellar medium places the origin
of matter-flux, chromosphere-corona, and spectral 'emission classes'
in subatmospheric nonthermal kinetic energy storage, equally for all
stars, hot or cold. Current observations of both hot and cold stars
suggest chromospheres to be a universal phenomenon, correlated with
matter-fluxes, and enhanced in 'emission-class' stars. To clarify the
difference between the two kinds of models above, we reformulate the
wind-tunnel analogy to stellar winds, suggesting that stars satisfy an
'imperfect,' rather than 'perfect,' such model; i.e., transonic shocks
occur before the throat, corresponding to an imposed outward velocity
in the storage section, or subatmosphere. We then investigate the
stability of an arbitrary stellar atmosphere, hot or cold, to suggest
a cause for such an outward subatmospheric velocity.
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Title: Solutions of the Radiative Transfer Equation for LY cc, LY
fi, MG N H & k, CA II H & K Using Two-dimensional Geometry,
Macroscopic Velocity Fields, and Frequency and Angle Dependent
Redistribution
Authors: Cannon, C. J.
1976A&A....52..337C Altcode:
Summary. We discuss the general equations to be solved for an adequate
diagnostic analysis of stellar spectral lines. A numerical method
of solution to the equation of transfer for spectral line radiation
is then presented for the general problem in which multidimensional
geometry, multi-dimensional macroscopic velocity fields and angle and
frequency dependent redistribution are incorporated. In particular,
we present a perturbation solution, which converges rapidly, for
the multi-dimensional geometry problem and combine this method with
previously developed perturbation procedures to solve the fully coupled
case. The complete method is quite general and has the basic advantage
of ease in programming. Indeed, the extension of existing programs,
which solve the one-dimensional complete redistribution case, to
the present problem is somewhat straightforward. In demonstrating
the method, we orient our computations toward hydrogen Ly cc, Ly
fi, Mg h & k and Ca H & K to illustrate a) the many coupled
effects of multi-dimensional geometry and angle-frequency dependent
redistribution on a variety of different spectral lines, and b)
the extremely large variety of emergent line profiles which can be
obtained for a given fixed atmospheric geometrical configuration, this
variety being manifested in the shape, in the absolute magnitude, and
in the frequency displacement of the resulting emergent intensity. We
discuss in some detail the various mechanisms, and their relative
importance, which can possibly dominate in giving rise to the emergent
line intensity as seen by the observer, and emphasise, in this latter
respect, that one cannot associate any particular line profile shape,
intensity or frequency displacement with a corresponding particular
atmospheric geometrical configuration. We further discuss the spatial
averaging of the emergent intensities from the point of view of the
possible elimination of the need for the usual microturbulent velocity
parameter. Key words: radiative transfer diagnostic analysis
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Title: Non-isotropic redistribution in chromospheric-type stellar
atmospheres.
Authors: Vardavas, I. M.; Cannon, C. J.
1976A&A....53..107V Altcode:
Solutions to the equation of radiative transfer for spectral-line
formation are obtained using the full-angle and frequency-dependent
redistribution functions R II and R III in one-dimensional
chromospheric-type model stellar atmospheres. It is found that the
angle dependency of these redistribution functions plays a significantly
less important role than does the corresponding frequency dependence in
determining the emergent line profile for one-dimensional geometries. It
is further found that the results obtained using R III (both angle
dependent and angle averaged) are only slightly different from those
using complete redistribution. In contrast, the wing frequency coherency
of R II significantly affects the emergent line profile by drastically
reducing the wing intensities, yielding limb-darkening at almost all
frequencies, and enhancing the effect of the macroscopic velocity
field. More particularly, R II produces emission peaks in the emergent
line profile even for photoelectrically controlled spectral lines
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Title: Problems in theory of stellar atmospheres
Authors: Cannon, C. J.
1976MmSAI..47..627C Altcode:
No abstract at ADS
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Title: Redistribution perturbations in radiative transfer theory.
Authors: Cannon, C. J.; Lopert, P. B.; Magnan, C.
1975A&A....42..347C Altcode:
A method referred to as redistribution perturbation technique is
proposed for solving the transfer equation for spectral line radiation
involving the redistribution of both photon angle and frequency
at a photon scattering event. The technique is formulated for the
integrodifferential and integral representations of the transfer
equation. Essentially, the technique starts with a zero-order solution
obtained from the equation of radiative transfer where complete
redistribution holds, then the first- and higher-order terms are
derived from a perturbation series which is shown to converge very
quickly. The method allows a considerable saving in computer time and
storage for problems in which redistribution plays an important part.
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Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. V: The
Multi-Dimensional Structure of the Photosphere and Low Chromosphere
Authors: Altrock, R. C.; Cannon, C. J.
1975SoPh...42..289A Altcode:
The two-dimensional equation of transfer is solved for the case of
locally-controlled source function (LTE) and radiationally-controlled
ionization. Horizontal fluctuations in electron temperature and
macroscopic velocity fields are superposed on the basic one-dimensional
model (cf. Altrock and Cannon, 1972). Output intensities are compared
with observed rms intensity fluctuations and spatially-averaged
intensities in Mg I 4571 Å. We find that at least one model (with a
height-independent temperature fluctuation ΔT/T=±0.02 in the range
0⩽h⩽450 km) can predict the magnitude of the intensity fluctuations
in both the continuum and λ4571 Å. The asymmetry of the line can
be explained by adding a height-independent, temperature-correlated
flow of amplitude 1 to 2 km s<SUP>−1</SUP>. The relationship between
these results and other multi-dimensional analyses is discussed.
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Title: Mass flux in stars. The origin of stellar winds: subatmospheric
non-thermal storage modes vs radiation pressure.
Authors: Cannon, C. J.; Thomas, R. N.
1975MSRSL...9..231C Altcode: 1975assp.conf..231C; 1975apes.conf..231C
No abstract at ADS
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Title: The multi-dimensional structure of the photosphere and low
chromosphere of the sun.
Authors: Altrock, R. C.; Cannon, C. J.
1974BAAS....6..428A Altcode:
No abstract at ADS
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Title: The inversion of emission line spectra from Wolf-Rayet stars.
Authors: Cannon, C. J.
1974A&A....34..387C Altcode:
The investigation reported is concerned with the quantitative estimation
of the density, temperature, and velocity distributions on the basis of
a direct inversion of the observed emission line spectra. Emission line
profiles are computed with the aid of model Wolf-Rayet atmospheres of
specified density, temperature, and velocity. The inversion technique is
applied to the obtained data and the information content of the emission
line in question is examined, taking into account the manner in which
the computed distributions converge to the originally specified values.
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Title: The Multi-Dimensional Structure of the Photosphere and Low
Chromosphere of the Sun.
Authors: Cannon, C. J.
1974BAAS....6..428C Altcode:
No abstract at ADS
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Title: The temperature and velocity distribution in Wolf-Rayet stars.
Authors: Cannon, C. J.
1974A&A....32...79C Altcode:
Summary. A methodology for determining the qualitative features of
the physical parameters dominating the emission line spectra observed
from Wolf-Rayet stars is discussed. Although we use quite different
arguments to those presented by Kuhi (1973), we arrive at the same basic
conclusion, i.e. that the electron temperature in WC stars decreases
with increasing radius in the region in which the emission spectra
is formed. Key words: Wolf-Rayet stars - atmospheric structure -
temperature - velocity
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Title: The Effect of Redistribution on the Emission Peaks from
Chromospheric-type Stellar Atmospheres
Authors: Cannon, C. J.; Vardavas, I. M.
1974A&A....32...85C Altcode:
Summary. The equation of transfer for spectral line radiation is solved
for a physically idealistic model problem involving departures from
complete redistribution. In particular, we consider a two-level atom
one- dimensional atmosphere exhibiting a chromospherictype temperature
rise, and compute emergent absorption line profiles having emission
peaks similar to those observed in the core of Ca II and Mg ii H
and K lines. We also include a macroscopic velocity field, and show
that the corresponding emergent line profiles computed assuming
complete redistribution are markedly different to those obtained
using the angle-averaged redistribution function for the case of pure
Doppler broadening with isotropic scattering (i.e. in Hummer's, 1962
notation). In some cases, for example, the emission peaks obtained
using complete redistribution disappear altogether when using Rr ,
and thus we conclude that the effects of general must be taken into
account when analysing spectral `lines of this type. Key words:
redistribution - line profile - emission peaks - chromosphere
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Title: A Two-Dimensional Analysis of Intensity Fluctuations in MgI
4571 A on the Solar Disk
Authors: Altrock, Richard C.; Cannon, C. J.
1974BAAS....6Q.284A Altcode:
No abstract at ADS
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Title: The effect of velocity gradients on multi-level atom non-LTE
line source functions.
Authors: Vardavas, I. M.; Cannon, C. J.
1974AuJPh..27..157V Altcode:
No abstract at ADS
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Title: The velocity-dependent source function in radiative transfer
theory.
Authors: Cannon, C. J.; Cram, L. E.
1974JQSRT..14...93C Altcode:
No abstract at ADS
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Title: The temperature distributions of the electrons, atoms and
ions in aerodynamic radiative transfer.
Authors: Cannon, C. J.
1974JQSRT..14..761C Altcode:
No abstract at ADS
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Title: Time-dependent aerodynamic non-LTE radiative transfer.
Authors: Cannon, C. J.
1974JQSRT..14..745C Altcode:
No abstract at ADS
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Title: Frequency-Quadrature Perturbations in Radiative-Transfer Theory
Authors: Cannon, C. J.
1973ApJ...185..621C Altcode:
A new numerical method is presented for solving the equation of
radiative transfer for spectral- line formation. This method enables the
integral over frequency to be represented by a quadrature sum of lower
order than that previously used to obtain solutions of the required
accuracy. In particular, it is found that the method is best suited to
slab geometry where, using only one point quadrature over frequency,
results are obtained at least as accurate as those obtained from
other existing numerical methods. Although more frequency-quadrature
points are necessary in semi- infinite situations, the method gives
sufficiently accurate solutions for E( CuLl A UL) of order 10- ,
for example, with just three quadrature points. Thus, since at least
seven quadrature points have been required in the past for numerical
solution of even the most simple problem in spectral-line formation
theory, the computer time and storage required for this new method is
significantly reduced. Further, the technique is quite general and may
be used in any radiative-transfer problem involving integration over
frequency. It may also be used, if so desired, in conjunction with
other methods and may therefore be easily incorporated into existing
computer programs. Subject headings: line formation - radiative transfer
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Title: Erratum: "The formation of Mg I 4571 Å in the solar
atmosphere. II: The effect of one-dimensional macroscopic velocity
fields [Sol. Phys., Vol. 29, p. 275 - 286 (1973)].
Authors: Altrock, R. C.; Cannon, C. J.
1973SoPh...31..524A Altcode:
No abstract at ADS
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Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. II:
The Holweger Solar Model
Authors: Altrock, Richard C.; Cannon, C. J.
1973SoPh...30...31A Altcode:
No abstract at ADS
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Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. II:
The Effect of One-Dimensional Macroscopic Velocity Fields
Authors: Altrock, Richard C.; Cannon, C. J.
1973SoPh...29..275A Altcode:
An analysis of the 4571 Å line of neutral magnesium is presented in
which one-dimensional macroscopic velocity fields are included. It
is shown that gradients over restricted heights in the vertical
and horizontal components of the velocity field of order -0.005
s<SUP>−1</SUP> and -0.004 s<SUP>−1</SUP> (such that velocity towards
the observer decreases as height increases), respectively, result in
asymmetries in the computed line profile similar to those observed. The
heights in the solar atmosphere at which these velocity gradients exist
are shown to be very critical in reproducing the observations. It was
found that the best results were obtained when the gradients existed in
the height range from ∼ 200 km to ∼ 300 km below the temperature
minimum. The results indicate that for the Mg I 4571 Å line model
calculations that do not include one-dimensional flow velocities may
safely be compared with frequency-averaged observations.
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Title: A One-Dimensional Approximation to the Macroturbulent Velocity
Field in the Solar Atmosphere
Authors: Altrock, R. C.; Cannon, C. J.
1973BAAS....5R.268A Altcode:
No abstract at ADS
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Title: Angular quadrature perturbations in radiative transfer theory.
Authors: Cannon, C. J.
1973JQSRT..13..627C Altcode:
No abstract at ADS
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Title: An exact solution to the multi-dimensional line transfer
equation.
Authors: Cannon, C. J.
1973JQSRT..13.1011C Altcode:
No abstract at ADS
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Title: Erratum: The Minimum Temperature in the Solar Atmosphere.
Authors: Altrock, R. C.; Cannon, C. J.
1972BAAS....4..426A Altcode:
No abstract at ADS
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Title: The Formation of Mg I 4571 Å in the Solar Atmosphere. I:
A Model Analysis of a One-Dimensional Static Atmosphere
Authors: Altrock, Richard C.; Cannon, C. J.
1972SoPh...26...21A Altcode:
A one-dimensional analysis of the 4571 Å line of neutral magnesium is
presented. The Harvard-Smithsonian Reference Atmosphere (HSRA) and the
Bilderberg Continuum Atmosphere (BCA) are used to compute the emergent
line profiles at various positions on the solar disc. The resultant
profiles, when compared to the observations, indicate that the HSRA
electron temperature distribution is a more satisfactory representation
of the solar atmosphere in the region of the temperature minimum than is
the BCA. A slight modification to the HSRA is suggested which reduces
the minimum temperature to 4140K and enables an even more satisfactory
`fit' to the available data.
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Title: The Minimum Temperature in the Solar Atmosphere.
Authors: Altrock, R. C.; Cannon, C. J.
1972BAAS....4..310A Altcode:
No abstract at ADS
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Title: A general formulation of the transfer equation. II. Line
formation with general redistribution
Authors: Cannon, C. J.
1972AuJPh..25..177C Altcode:
No abstract at ADS
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Title: The Effect of Two-Dimensional Macroscopic Velocity Fields on
Models of the Lower Solar Chromosphere
Authors: Cannon, C. J.
1971SoPh...21...82C Altcode:
Two-dimensional macroscopic velocity fields are featured in
the calculation of two-dimensional models of the lower solar
chromosphere. Relative rms line centre intensity fluctuation data and
mean limb darkening data obtained in Mg b and Na D are used together
with values of the cross-correlation between line centre brightness and
`line of sight velocities'. It is found that the large scale fluctuation
data can be explained by models of the lower solar chromosphere in which
the inhomogeneous effects arise only from horizontal, two-dimensional
macroscopic velocity fields. It is also shown, however, that the
corresponding small scale fluctuation data cannot be explained in a
similar manner.
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Title: Line Transfer in the Presence of Two-Dimensional Velocity
Gradients
Authors: Cannon, C. J.; Rees, D. E.
1971ApJ...169..157C Altcode:
Feautrier's (1964) method is generalized to solve the equation of
radiative transfer for a spectral line in an atmosphere exhibiting
horizontal fluctuations in all physical parameters together with
multidimensional velocity gradients. odel two-dimensional velocity
problems are discussed.
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Title: A Fast Method for the Determination of Emergent Intensities
in Radiative Transfer Theory
Authors: Cannon, C. J.
1971PASA....2...42C Altcode: 1971PASAu...2...42C
One of the quantities usually required when solving the equation
of radiative transfer is the intensity of radiation emerging from
the surface of the medium under consideration. For multi-dimensional
situations however, the methods presented to date have been numerical,
and these first calculate the so-called source function S<SUB>v</SUB>
(r, Ω) as a function of position r, angle Ω and frequency v. This
is generally the most difficult part of the exercise since an
integro-difierential equation must be solved. The emergent intensity
is then determined by solving a relatively simple first order
differential equation by any of the well known numerical integration
schemes. However, if the emergent intensity is required at a large
number of angles, frequencies, and positions on the surface of the
medium, and this is usually the case, the amount of computing needed
may be considerable.
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Title: Center Limb Observations of Inhomogeneities in the Solar
Atmosphere. II: The Na D and Na 5688 Doublets and the MgI 4571 Line
Authors: Cannon, C. J.; Wilson, P. R.
1971SoPh...17..288C Altcode:
Center-limb observations of line-center intensity fluctuations in the Na
D and Na 5688 doublets and the Mg 4571 line are described. For small
scale structures the rms distributions for the photospheric lines
show maxima of 20% at a heliocentric angle of 40° (Mg4571) and 9%
at 20° (Na 5688). The rms values for Na D range between 10 and 13%
but show no significant maximum. Values for large scale structures
are somewhat less.
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Title: Calculations of Two-Dimensional Models of the Lower Solar
Chromosphere
Authors: Cannon, C. J.
1971SoPh...16..314C Altcode:
Several two-dimensional models of the lower solar chromosphere
are computed using relative RMS line centre intensity variations
and mean limb darkening curves observed in Mg b and NaD. These
calculations indicate that the small scale fluctuations observed
at line centre in these lines may result from density and electron
temperature fluctuations in the lower chromosphere, while the large
scale fluctuations may result from either fluctuations in the deeper
lying continuum or horizontal and vertical differential velocity fields.
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Title: Center-Limb Observations of Inhomogeneities in the Solar
Atmosphere. I: The Mg b Lines
Authors: Cannon, C. J.; Wilson, P. R.
1970SoPh...14...29C Altcode:
Center-limb observations of line-center intensity and velocity
fluctuations in the Magnesium b lines are described. Autocorrelation
and power spectral analyses indicate small scale brightness structures
having periodicities of 3000 km and 8000 km and large scale structures
of 22000 km. Corresponding velocity structures are 6000 km and 30000 km.
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Title: The Application of Feautrier’s Technique to Problems in
Radiative Transfer
Authors: Cannon, C. J.
1970PASA....1..386C Altcode: 1970PASAu...1..386C
There exists a large number of varying methods of solution in
radiative transfer theory. House and Avery have recendy published
an exposition of the Monte-Carlo technique and the very nature of
this solution makes it readily amenable, in theory, to the study
of any transfer problem. Grant and Hunt have developed a method
involving the invariant S<SUB>n</SUB> matrix transformation and this
also appears quite general in its application. Further, the Riccati
transformation technique, developed by Rybicki and Hummer, has already
been used in solving several different transfer problems. However,
these methods have certain disadvantages. The equations are of first
order and thus stability difficulties arise. Also, the finer details
of the method rely, to a large extent, on the particular problem under
consideration, and experience with such a method is required for the
efficient computation of solutions.
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Title: Line Transfer in Two Dimensions
Authors: Cannon, C. J.
1970ApJ...161..255C Altcode:
A method is presented for solving the equation of radiative transfer
for a spectral line formed in a multidimensional atmosphere. The
method generalizes the Feautrier solution in one dimension and allows
the study of atmospheres which exhibit horizontal fluctuations in all
parameters. Model two-dimensional problems are discussed.
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Title: Power Spectral Analysis of Chromospheric Inhomogeneities
Authors: Cannon, C. J.
1969PASA....1..197C Altcode: 1969PASAu...1..197C
In July 1967 and June 1968 observations of the central intensity
variation in several chromospheric lines were obtained by P. R. Wilson
and myself at Sacramento Peak Observatory, New Mexico using
the 16-inch coronagraph coupled with the high-dispersion Littrow
Spectrograph. Observations in the MgB lines (λ5184, 5173, 5167 Å)
were obtained the first summer whilst the NaD lines (λ5889, 5896 Å)
were studied in the second. Table I shows the mean heights in the
solar atmosphere at which it is thought these lines are formed.
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Title: The Structure of a Sunspot. III: Observations of the Wilson
Effect
Authors: Wilson, P. R.; Cannon, C. J.
1968SoPh....4....3W Altcode:
White-light photographs of a fairly regular sunspot have been obtained
for all but one day of its passage across the disk. From microphotometer
tracings across these photographs, intensity profiles across the spot
have been obtained at several heliocentric angles, θ.
