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1.
We have investigated the effects of increasing optical depths on spectral lines formed in a rotating and expanding spherical
shell. We have assumed a shell whose outer radius is 3 times the inner radius, with the radial optical depths equal to 10,
50, 100, 500. We have employed a constant velocity with no velocity gradients in the shell. The shell is assumed to be rotating
with velocities varying as 1/ρ, whereρ is the perpendicular distance from the axis of rotation, implying the conservation of angular momentum. Two expansion (radial)
velocities are treated: (1)V = 0 (static case) and (2)V = 10 mean thermal units. The maximum rotational velocities areV
rot = 0, 5, 10 and 20. In the shell where there are no radial motions, we obtain symmetric lines with emission in the wings forV
rot = 0 and 5 while forV
rot ≥ 10 we obtain symmetric absorption lines. In the case of an expanding shell, we obtain lines with central emission. 相似文献
2.
The partial frequency redistribution function for zero natural line width with dipole scattering (RI) has been considered in obtaining the simultaneous solution of the statistical equilibrium and line transfer equations in
the comoving frame of the expanding gas. We have considered a non-LTE two level atom in an expanding spherical medium whose
outer radii are 3, 10 and 20 times the stellar radius with a total optical depthT ≃ 2 × 103. In all the cases, we have calculated the population ratio of the two levels N2/N1 and compared these results with those obtained by using different expansion velocities and geometrical extensions. Initially,
the upper level population (N2) is set equal to zero. The converged simultaneous solution shows that the upper level population is enhanced considerably
from the initial value. Variation in velocity gradients seem to have little effect on the ratio N2/N1 when the geometrical thickness of the medium is 3 or 10 times the stellar radius. However, when the thickness is increased
to 20 times the central radius, the velocity gradients change the ratio N2/N1 considerably in the region where log T ≤ 2. The effect of variation of geometrical thickness is to reduce the N2/N1 ratio atτ = 0. 相似文献
3.
Radiative transfer (RT) problems in which the source function includes a scattering-like integral are typical two-points boundary
problems. Their solution via differential equations implies making hypotheses on the solution itself, namely the specific
intensity I (τ; n) of the radiation field. On the contrary, integral methods require making hypotheses on the source function S(τ). It seems of course more reasonable to make hypotheses on the latter because one can expect that the run of S(τ) with depth is smoother than that of I (τ; n). In previous works we assumed a piecewise parabolic approximation for the source function, which warrants the continuity
of S(τ) and its first derivative at each depth point. Here we impose the continuity of the second derivative S′′(τ). In other words, we adopt a cubic spline representation to the source function, which highly stabilizes the numerical
processes. 相似文献
4.
A. Peraiah 《Journal of Astrophysics and Astronomy》1980,1(1):17-23
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 mean 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
asymmetric and the red emission and blue absorption are enhanced. 相似文献
5.
6.
V. A. Sheminova 《Solar physics》2009,254(1):29-50
The properties of solar magnetic fields on scales less than the spatial resolution of solar telescopes are studied. A synthetic
infrared spectropolarimetric diagnostic based on a 2D MHD simulation of magnetoconvection is used for this. Analyzed are two
time sequences of snapshots that likely represent two regions of the network fields with their immediate surroundings on the
solar surface with unsigned magnetic flux densities of 300 and 140 G. In the first region from the probability density functions
of the magnetic field strength it is found that the most probable field strength at log τ
5=0 is equal to 250 G. Weak fields (B<500 G) occupy about 70% of the surface, whereas stronger fields (B>1000 G) occupy only 9.7% of the surface. The magnetic flux is −28 G and its imbalance is −0.04. In the second region, these
parameters are correspondingly equal to 150 G, 93.3%, 0.3%, −40 G, and −0.10. The distribution of line-of-sight velocities
on the surface of log τ
5=−1 is estimated. The mean velocity is equal to 0.4 km s−1 in the first simulated region. The average velocity in the granules is −1.2 km s−1 and in the intergranules it is 2.5 km s−1. In the second region, the corresponding values of the mean velocities are equal to 0, −1.8, and 1.5 km s−1. In addition the asymmetry of synthetic Stokes V profiles of the Fe i 1564.8 nm line is analyzed. The mean values of the amplitude and area asymmetry do not exceed 1%. The spatially smoothed
amplitude asymmetry is increased to 10% whereas the area asymmetry is only slightly varied. 相似文献
7.
The mechanisms of absorption formation in the cosmic microwave background (CMB) spectrum at the frequency of the 21-cm line of the transition between the ground-state hyperfine sublevels of the hydrogen atom are analyzed. We show that a strong nonlinearity at the compression stage of primordial matter density fluctuations can give rise to a significant (in depth) absorption even before the explosions of the first stars. In this case, the main effect is due to the heating of matter in a certain narrow range of temperatures under cloud compression. We consider a steady-state radiative transfer in the 21-cm line in a medium that represents a contracting primordial matter density fluctuation at a given redshift z modeled by a homogeneous spherically symmetric cloud in the state of collapse with an adiabatic change in the gas temperature. For a sequence of cloud states with different degrees of compression we have calculated the frequency profiles of the line in the flux of radiation emerging from the cloud. In the initial state we specify the cloud radius r0, while the gas density is assumed to be equal to the mean cosmological density for a given redshift. We show that for a separate cloud at z = 20, r0 = 1 kpc, and a degree of radius compression of 1.9 the absorption depth in the line center can reach 0.9 K. When averaged over an ensemble of clouds, the central frequency of the line and its width are determined by the details of the fluctuation evolution dynamics.
相似文献8.
A self-consistent method has been evolved to infer physical parameters like density, radiation field and abundances using
line and continuum radiations as diagnostics. For that purpose, we first calculate the temperatures of graphite and silicate
grains using the model of Li and Draine (Astrophys. J. 554:778, 2001) by solving self-consistently the energy balance for G
0 (1–104) times the radiation field following Weingartner and Draine (Astrophys. J. Suppl. Ser. 134:263, 2001). Consequently, infrared emission fluxes are also obtained. To keep it simple, this is presented in the empirical form of
parameters T
D
and wavelength. The same model of the grain is adopted for photoelectric heating of gas using the formalism of Weingartner
and Draine (Astrophys. J. Suppl. Ser. 134:263, 2001) (hereafter referred to as WD) and Bakes and Tielens (Astrophys. J. 427:822, 1994) (hereafter referred to as BT) for radiation field cited above in the range (6<hν≤13.6 eV). Temperature and abundances are determined using our own code for PDR very similar to cloudy code. All the possible
sources of heating and cooling are considered for setting up the thermal balance. For the gas phase abundances that vary with
depth in the cloud due to dust, self- and mutual shielding, chemical balance is solved. Most of the photoionization, photodissociation
or chemical reaction rates are taken from UMIST database. We present an analysis of the cooling lines of singly ionized carbon
[CII] at 158 μm and neutral oxygen [OI], at 63 μm and far infrared (FIR) continuum for a variety of star forming galaxies.
Method of analysis of observational data is different from that of Malhotra et al. (Astrophys. J. 561:766, 2001). The radiation field G
0, density N
h
and abundance of carbon are obtained through best fit of observed and calculated intensities for lines and continuum radiations. 相似文献
9.
The radio recombination line intensities of heavy elements of helium, carbon and oxygen are calculated with accounting for
dielectronic recombination. Dielectronic recombination rates are determined accurate to the second order of a perturbation
theory and the rates are described as function of principal quantum number for helium-like atom or ion. Balance equations
are solved for the departure coefficients from LTE bn. The collision and spontaneous transition rates are accounted for the balance equations, in which non-equilibrium distribution
source is dielectronic recombination. Non-equilibrium amplification coefficients are found as functions of a medium temperature,
density and ion charge z = 1–3 for radio recombination lines.
Optical depths are calculated for the heavy element low-frequency lines with the numbers 300 > n > 1200. For the chosen electronic temperatures and densities Te = 0.8× 104–10× 104 K, Ne = 0.05–0.1 cm−3 the line optical depth is determined by the values τL∼ 0.1× 10−4–100× 10−4. Calculated for free-free transition rates, the optical depth is given by using the value τff∼ 10−2τL. 相似文献
10.
A. D. Kaminker D. G. Yakovlev A. Y. Potekhin N. Shibazaki P. S. Shternin O. Y. Gnedin 《Astrophysics and Space Science》2007,308(1-4):423-430
We model thermal evolution of magnetars with a phenomenological heat source in a spherical internal layer and compare the
results with observations of persistent thermal radiation from magnetars. We show that the heat source should be located in
the outer magnetar’s crust, at densities ρ≲5×1011 g cm−3, and the heating rate should be ∼1020 erg cm−3 s−1. Heating deeper layers is extremely inefficient because the thermal energy is mainly radiated away by neutrinos and does
not warm up the surface to the magnetar’s level. This deep heating requires too much energy; it is inconsistent with the energy
budget of neutron stars.
相似文献
11.
Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline fromV 9.0 to ≃10.2 (compared to a value of ∼ 8.0 at recorded maximum). The spectrum and its evolution compare well with a typical
nova, though the principal absorption (∼ −750 km s−l) was very weak in comparison with the diffuse-enhanced absorption (∼ −1300 km s−1). The principal absorption could be identified only in the lines of O I λλ7774, 8446, and in moderate-resolution observations
of Hα. The salient features of spectral evolution follow: The near-infrared triplet of Ca n continuously weakened. O I λ8446
was always brighter than O I λ 7774, indicating continued importance of Lyman Β fluorescence. The lines due to [O I], [N II]
and N n brightened considerably near the end of our observations (37 days from maximum). The Hα emission line was asymmetric
all through with more emission towards the red. Its emission profile showed considerable structure. Based on the individual
peaks in the Hα line profile, a kinematical model is proposed for the shell of LW Ser. The model consists of an equatorial
ring, and a polar cone on the side away from the earth. The nearer polar cone did not show significant emission of Hα during
our observations. The polar axis of the shell is inclined at a small angle (∼ 15‡) to the line of sight. 相似文献
12.
We have theoretically studied the influence of a far-infrared radiation (FIR) field from Hπ region on the cooling by C and O atoms, C+ ion and CO molecule in a photodissociation region, and a molecular cloud associated with Hπ region (hereinafter referred as HI region) at low temperatures (T
k≤200 K). Comparisons have been made for cooling with and without FIR for two extreme abundances (10−4 and 10−7) of the mentioned species for temperatures ranging between 10 and 200K and an hydrogen particle density range 10 cm−3≤n
o≤ 107 cm3.
The cooling by the species with low line-splitting (CI, Cπ and CO) is significantly influenced by the radiation field for temperaturesT
k < 100 K while the effect of radiation field on cooling by OI is significant even at higher temperatures (T
k > 100 K). The effect of FIR field on the cooling of CO from low rotational transitions is negligibly small, whereas it is
considerable for higher transitions. In general, the cooling terms related to the short-wavelength transitions are more affected
by FIR than those related to longer wavelengths.
It is also demonstrated here that in the determination of thermal structure of an HI region the dust grains play an important role in the heating of gas only through photoelectron emission following irradiation
by far-ultraviolet (FUV) radiation, as the infrared radiation from the dust is too small to have substantial effect on the
cooling. It is found that in the Hπ /HI interface the FIR field from grains in the Hπ region is not capable of modifying the temperature of the warmest regions but does so in the inner part where the temperature
is low enough. 相似文献
13.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse
of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole
no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical
accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric
luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and
bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M
BH
≃(1.1⋅106
÷4.2⋅109) M
⊙ give the values of PRTs varying in the range of about T
BH
≃(4.3⋅105
÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present,
some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for
accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion. 相似文献
14.
A. Peraiah 《Journal of Astrophysics and Astronomy》1980,1(1):3-16
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 functionR
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 Τ=0 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. 相似文献
15.
Slow magnetohydrodynamic (MHD) standing wave oscillations in hot coronal loops for both strong (i.e. τd/P∼ 1) and weak (i.e. τd/P≥ 2) damping are investigated taking account of viscosity, thermal conductivity and optically thin radiation. The individual
effect of the dissipative terms is not sufficient to explain the observed damping. However, the combined effect of these dissipative
terms is sufficient to explain the observed strong damping, as well as weak damping seen by SUMER. We find that, the ratio
of decay time (τd) and period (P) of wave, i.e., τd/P (which defines the modes of damping, whether it is strong or weak) is density dependent. By varying density from 108 to 1010 cm−3 at a fixed temperature in the temperature range 6 – 10 MK, observed by SUMER, we get two sets of damping: one for which τ
d/P∼ 1 corresponds to strong damping that occurs at lower density and another that occurs at higher density for which τd/P ≥ 2 corresponds to weak damping. Contrary to strong-damped oscillations, the effect of optically thin radiation provides
some additional dissipation apart from thermal conductivity and viscosity in weak-damped oscillations. We have, therefore,
derived a resultant dispersion relation including the effect of optically thin radiation. Solutions of this dispersion relation
illustrate how damping time varies with physical parameters of loops in both strong and weak damping cases. 相似文献
16.
This is a study of optical emission lines of the nucleus of the Seyfert galaxy NGC 3227. This work is based on 53 spectrograms
obtained with the 6-m telescope at the brightness maximum of this galactic nucleus on January 12–15, 1977. A set of profiles
of the hydrogen Hα, and Hβ lines and the equivalent widths (EWλ) of six emission lines and blends averaged over series of observations are presented. Broadening of the hydrogen line profiles
was observed over the three days. At a level of 0.50 times the peak brightness the hydrogen line profiles were broadened by
12%, 35%, and 44%, respectively. The broadening of the Hβ line was accompanied by a reduction in its equivalent width (EW
;
). It is suggested that a flare was observed in the nucleus of the galaxy on a time scale of 3 days, possibly caused to a
shock wave in long-lived flows from the galaxy nucleus.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 499–510 (November 2006). 相似文献
17.
N. C. Rana 《Astrophysics and Space Science》1980,67(1):201-204
The absorption effects at the soft X-ray and hard ultraviolet wavelengths due to some model abundance of intergalactic carbon
material have been investigated for different cosmologies. Even though the local density, 2 × 109 <ϱ
0 = 1.0 × 10−34 g cm−3 of the absorbing component of the intergalactic material in the form of carbon is not adequate for the thermalization of
the discrete background radiation, the amount of absorption in the X-rays up to the Hubble radius is not negligible. 相似文献
18.
R. & R. Griffin 《Journal of Astrophysics and Astronomy》1986,7(3):195-223
Composite-spectrum binary stars generally consist of a late-type giant and a main-sequence star of type A or B. Their spectra
are therefore rather confusing; but by a technique of digital subtraction of the spectra of appropriate single late-type giants,
composite spectra can be split into their individual components. In favourable cases the radial velocities of both components
can be measured and the mass ratio determined. The procedures are illustrated by reference to HR 6902, a fifth-magnitude composite-spectrum
binary. Its components are shown to have spectral types of G9 II and B8 V, with a mass ratio of 1.31, and its orbit is determined.
There is some evidence that the system shows eclipses. If it does, the masses of the components are 3.9 and 3.0M⊙ respectively, and HR 6902 becomes the sixth known member of the important class ofζ Aur binaries. 相似文献
19.
A quiescent filament was observed near the center of the disk (N5, W5) with the MSDP spectrograph of the 50 cm refractor of
the Pic-du-Midi Observatory on June 17, 1986. We focus our study on the statistical moments of the Dopplershift,V
1, and the intensity,I
1, at the center of a chord of the Hα profile (±0.256 Å), versus the minimum intensityI
0. We use a statistical model simulating a numbern
max of threads (of optical thicknessτ
0 and source functionS
0), seen over the chromosphere. The threadsj along the same line-of-sighti are identical except for the velocityv
j (gaussian distributionv
0,σ
v). We search for the best fit between the observed and simulated quantities:V
1,σ (V
1),I
1,σ(I
1), and the histogram of theI
0 values over the field of view. A good fit is obtained with: (a) threads characterized byτ
0 = 0.2,S
0 = 0.06 (unit of the continuum at disk center), mean upward velocityv
0 = 1.7 km s−1 and gaussian-type velocity distributionσ
v = 3.5 km s−1. Other possible values ofτ
0 andσ
v are discussed; (b) underlying chromosphere deduced from observed quiet Sun (outside the filament) by modifying the chromospheric
velocities: additional mean upward velocity 0.7 km s−1, standard deviation reduced by a factorF
c ∼ 0.7. The results are discussed in connection with the values deduced from prominence observations. 相似文献
20.
A fraunhofer line profile depends on various parameters, partly related to the photospheric structure (T, P
g, P
e, v
conv, v
turb), partly to the atom or ion involved (such as oscillator strength, energy levels), partly also resulting from the interaction of the relevant kind of particles with the photosphere, and the photospheric radiation field. In this paper we shall mainly pay attention to the determination of: the macroturbulent (convective) velocities, v
conv (); the damping constant (); the abundance, A
el; the distribution function (v
conv, ) of the convective velocities at each depth ; the source function, S (); the microturbulent velocities, v
turb ().The particular difficulty with these unknowns is that they are, as a rule, coupled in the resulting line profiles, that is: the shapes and intensities in these profiles are determined by the combined influence of these unknowns (together with the other above-given parameters).In this paper we describe a method to determine these six unknowns empirically by separating them, in analysing accurate high-resolution observations of line profiles of a multiplet. The unknown functions and quantities are consecutively determined in the above given succession. For each determination another, appropriate part of the line profile is used. In some cases the influence of the mutual coupling of the various parameters cannot be completely eliminated, and an iterative method has to be used.The method is summarized in Table II and section 2, and is further explained in sections 3 to 8. It is applied to an infrared Ci multiplet. The main results are the following: 相似文献