674 research outputs found
Influence of temperature fluctuations on continuum spectra of cosmic objects
The presence of convective and turbulent motions, and the evolution of
magnetic fields give rise to existence of temperature fluctuations in stellar
atmospheres, active galactic nuclei and other cosmic objects. We observe the
time and surface averaged radiation fluxes from these objects. These fluxes
depend on both the mean temperature and averaged temperature fluctuations. The
usual photosphere models do not take into account the temperature fluctuations
and use only the distribution of the mean temperature into surface layers of
stars. We investigate how the temperature fluctuations change the spectra in
continuum assuming that the degree of fluctuations (the ratio of mean
temperature fluctuation to the mean temperature) is small. We suggest the
procedure of calculation of continuum spectra, which takes into account the
temperature fluctuations. As a first step one uses the usual model of a
photosphere without fluctuations. The observed spectrum is presented as a part
depending on mean temperature and the additional part proportional to quadratic
value of fluctuation degree. It is shown that for some forms of absorption
factor the additional part in Wien's region of spectrum can be evaluated
directly from observed spectrum. This part depends on the first and second
wavelength derivatives, which can be calculated numerically from the observed
spectrum. Our estimates show that the temperature dependence of absorption
factors is very important by calculation of continuum spectra corrections. As
the examples we present the estimates for a few stars from Pulkovo
spectrophotometric catalog and for the Sun. The influence of temperature
fluctuations on color indices of observed cosmic objects is also investigated.Comment: 22 pages, 5 tables. Accepted for publication in Astrophysics & Space
Scienc
Intensity and polarization of radiation reflected from accretion disc
We consider the reflection of non-polarized radiation from the point-like
sources above the accretion discs both the optically thick and optically thin.
We investigate the dependence of the polarization of reflected radiation on the
aperture angle of incident radiation. The aperture angle is determined by the
radius of accretion disc and the height of the source above the disc. For
optically thick accretion discs we show that, if the aperture angle is smaller
70 grad, then the wave electric field oscillations of reflected radiation are
parallel to the accretion disc plane. For aperture angle greater than 70 grad
the electric field oscillations are parallel to the plane "normal to accretion
disc - the line of sight". The latter also holds for reflection from the
optically thin accretion disc independent of the aperture angle value.Comment: 11 pages, 4 figures.This is a pre-print of an article published in
Astrophysics and Space Scienc
Depolarization of multiple scattered light in atmospheres due to anisotropy of small grains and molecules. II. The problems with sources
In the previous paper we considered two classic problems - the diffuse
reflection of the light beam from semi-infinite atmosphere, and the Milne
problem. For both problems we used the technique of invariance principle. In
this paper we consider the solution of the problem when in semi-infinite
atmosphere the sources of unpolarized radiation are exist. Here we used the
technique of the Green matrices. We consider only continuum radiation.Comment: 9 pages. In submission to Astrophysics and Space Scienc
Depolarization of multiple scattered light in atmospheres due to anisotropy of small grains and molecules
Freely oriented small anisotropic grains and molecules depolarize radiation
both in single scattering and in the process of multiple scattering. Especially
large depolarization occurs for resonant scattering corresponding to the
electron transitions between the energy levels with very different quantum
numbers. The existence of light absorption also changes essentially the angular
distribution and polarization of radiation, outgoing from an atmosphere. In the
present paper we consider these effects in detail both for continuum radiation
and for resonant lines. Because the term describing the depolarization deals
with isotropic radiation, we consider the axially symmetric part of radiation.
We derived the formulas for observed intensity and polarization using the
invariance-principles both for continuum and resonant scattering. We confine
ourselves to two problems - the diffuse reflection of the light beam from
semi-infinite atmosphere, and the Milne problem.Comment: 18 pages, 2 table
Radiative transfer in scattering stochastic atmospheres
Many stars, active galactic nuclei, accretion discs etc. are affected by the
stochastic variations of temperature, turbulent gas motions, magnetic fields,
number densities of atoms and dust grains. These stochastic variations
influence on the extinction factors, Doppler widths of lines and so on. The
presence of many reasons for fluctuations gives rise to Gaussian distribution
of fluctuations. The usual models leave out of account the fluctuations. In
many cases the consideration of fluctuations improves the coincidence of
theoretical values with the observed data. The objective of this paper is the
investigation of the influence of the number density fluctuations on the form
of radiative transfer equations. We consider non-magnetized atmosphere in
continuum.Comment: 11 pages. Has been accepted for publication in Astrophysics and Space
Scienc
A Laboratory Study of Absorbing Capacity of Water Vapor at the Wavelengths from 6500 TO 10500 {\AA}
We obtained laboratory spectra of absorption by water vapor at the
wavelengths 6500-10500 {\AA} with the multipass cell. The water vapor content
along the line of view varied from 0.1 to 3.0 cm of precipitated water, the
pressure from 0.1 to 1.0 atm. The spectra were taken with the width of the exit
slit of the spectrophotometer 25, 50, 100, and 150 {\AA}. To match these
spectra, we selected empirical functions, which approximate the observed
absorption within the indicated interval of water vapor content and pressure
with the accuracy about 1%. For the water vapor band at the wavelengths regions
7200, 8200, and 9300 {\AA}, with the step 25 {\AA}, we determined the
parameters necessary for the calculation of empirical transmission functions.
The presented data make it possible to select the parameters for taking into
account the radiation attenuation in the spectral region of telluric water
vapor under the conditions of real astronomical observations for a specific
place and spectrophotometer. The suggested set of empirical parameters may
provide correction of observed stellar spectra for the extinction in the
atmosphere with the accuracy 0.m01-0.m02.Comment: 7 pages, 7 figures, and 2 tables. English version of russian pape
Radiation intensity and polarization from accretion discs with progressive increasing height
The article considers the optically thick accretion discs with the
progressive increasing height. The surface is assumed to be the conical form.
The radiation with considered wavelength emerges from an ring on the cone and
is described by the Milne problem for the intensity and polarization. The
inclination angles of the rings are taken 15 and 30 grad. The inclination
angles between the line of sight and the normal to the central accretion disc
plane are taken 30, 45, 60 grad for every value of the ring inclination. For
the continuum radiation the polarization of the emerging light is less than
that in the case of the plane accretion disc. The polarization position angles
of radiation emerging from the right and left parts of the ring are opposite
one another. They are determined by the geometry of the problem. The position
angle of the observed continuum radiation is parallel to the central plane of
the accretion disc. Our theory gives the new explanation of that the position
angles in "red" and "blue" wings of a spectral line are opposite one another.
This behavior exists in many Seyfert galaxies.Comment: 7 pages, 3 figure
The Determination of the Water Vapor Content in the Pulkovo VKM-100 Multipass Vacuum Cell Using Polymer Sensors of Humidity
In spectral studies of water vapor under laboratory conditions (determination
of molecular constants, measurement for spectral transmission functions), the
amount of water vapor in the time of the measurements is one of the most
essential parameters, which should be determined accurately. We discuss the
application for this purpose of polymer sensors of humidity manufactured by
Praktik-NC (Moscow) and used in the Pulkovo VKM-100 multipass vacuum cell.
These sensors were examined in the laboratory of Lindenberg Meteorological
observatory (Germany) by comparison between their readings and those of
standard measuring devices for various values of relative humidity, pressure,
and temperature. We also carried out measurements of relative humidity in boxes
with saline solution, in which the relative humidity that corresponds to a
given solution is guaranteed with the accuracy of several tenths of percent.
The analysis of the results of the laboratory examination of the sensors and
extended sets of measurements made with the Pulkovo cell made it possible to
conclude that in measurements in the interval of relative humidity 40-80%, the
~5% accuracy of the measurements for the water vapor content is reached.
Further paths are indicated for the increase of the accuracy of measurements
and extending the interval of the relative humidity, in which accurate
measurements may be carried out.Comment: 12 pages, 12 figures. English version of russian pape
Accuracy of the Water Vapour Content Measurements in the Atmosphere Using Optical Methods
This paper describes the accuracy and the errors of water vapour content
measurements in the atmosphere using optical methods, especially
starphotometer. After the general explanations of the used expressions for the
star-magnitude observations of the water vapour absorption in section 3 the
absorption model for the water vapour band will be discussed. Sections 4 and 5
give an overview on the technique to determine the model parameters both from
spectroscopic laboratory and radiosonde observation data. Finally, the sections
6 and 7 are dealing with the details of the errors; that means errors of
observable magnitude, of instrumental extraterrestrial magnitude, of
atmospheric extinction determination and of water vapour content determination
by radiosonde humidity measurements. The main conclusion is: Because of the
high precision of the results the optical methods for water vapour observation
are suited to validate and calibrate alternative methods (GPS, LIDAR,
MICROWAVE) which are making constant progress world-wide in these days.Comment: 29 pages, 21 figure
Resonance line in rotating accretion disc
We study the resonance line emission from the rotating plane optically thick
accretion disc, consisting of free electrons and resonant atoms. We use the
standard assumption that the source of continuum radiation is located near
central plane of the accretion disc, where the temperature is the highest. This
corresponds to the Milne problem consideration for continuum. We shortly
discuss the impossibility of the Milne problem for the resonance radiation. We
assume that the resonant atoms are located in a thin layer of an accretion disc
near the surface. In this case the resonance line emission arises due to
scattering of a continuum on the resonant atoms. In thin layer we can neglect
the multiple scattering of the resonance radiation on the resonant atoms. We
consider the axially symmetric problems, where the Stokes parameter U =0. We
take into account the Doppler effect for the frequencies of the resonance line.
The three types of the resonant atom sources are considered (see Figs.1-3). The
first source is the axially symmetric continuous distribution of the resonant
atoms along the circular orbit. The second spot-like source rotates in the
orbit. The third type presents two spot-like sources located in the orbit
contrary one to another. In the first and third cases the shape of the emitting
resonance line is symmetric, i.e. the right and left wings have the similar
shapes. In the second case the resonance line has asymmetric shape. The shape
of the emerging line depends significantly on the ratio of the rotation
velocity value to the velocity, characterizing the Doppler width. It also
depends on the ratio of the electron number density to the number density of
resonant atoms. The results of the calculations characterize the different
observational effects of H radiation in the accretion discs and can be
used for estimations of the parameters mentioned above.Comment: 14 pages, 9 figures. In press to Astrophysics and Space Scienc
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