首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 328 毫秒
1.
Multiple resonance scattering of spectral line radiation is examined in atmospheres with uniformly distributed sources of unpolarized radiation. It is assumed that the profile of the absorption coefficient is lorentzian and that scattering involves complete frequency redistribution. The polarization characteristics of the emerging radiation are determined by iterative solution of a nonlinear Ambartsumyan-Chandrasekhar matrix integral equation. In particular, it is found that for pure scattering the maximum polarization at the limb of the disk is 5.421%. The polarization characteristics of the emerging radiation are compared for three different absorption profiles: Lorentz, Doppler, and rectangular (monochromatic radiation). __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 199–217 (May 2007).  相似文献   

2.
Dubrovich  V. K.  Grachev  S. I. 《Astronomy Letters》2019,45(11):701-709

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   

3.
H. Frisch 《Solar physics》1996,164(1-2):49-66
Resonance polarization, which is created by the scattering of an anisotropic radiation field in regions of zero or weak magnetic fields, is strongly dependent on the frequency redistribution taking place during the scatterings. Here we discuss the frequency redistribution matrix relevant to resonance lines, concentrating on linear polarization. First we analyze in detail the redistribution matrix in a zero magnetic field given by the theory of Omont, Smith and Cooper (1972), revisited by Domke and Hubeny (1988). We explain that the linear polarization maxima which may appear in the wings of the Stokes Q profiles of strong resonances lines such as the Ca I 4227 Å line are coherent frequency redistribution effects. Various approximate forms of the frequency redistribution matrix are also examined. For resonance polarization in a weak magnetic field, we suggest a new expression for the redistribution matrix which can be used at all line frequencies, and is consistent with the condition that the Hanle effect acts only in the line core.  相似文献   

4.
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.  相似文献   

5.
A multilayer radiative transfer, high-spectral-resolution infrared model of the lower atmosphere of Mars has been constructed to assess the effect of scattering on line profiles. The model takes into account aerosol scattering and absorption and includes a line-by-line treatment of scattering and absorption by CO2 and H2O. The aerosol complex indices of refraction used were those measured on montmorillonite and basalt chosen on the basis of Mars ir data from the NASA Lear Airborne Observatory. The particle sizes and distribution were estimated using Viking data. The molecular line treatment employs the AFGL line parameters and Voigt profiles. The modling results indicate that the line profiles are only slightly affected by normal aerosol scattering and absorption, but the effect could be appreciable for heavy loading. The technique described permits a quantitative approach to assessing and correcting for the effect of aerosols on lineshapes in planetary atmospheres.  相似文献   

6.
Absorption of solar radiation of wavelengths between 175 to 205 nm plays a fundamental role in the photochemistry of the middle atmosphere. Nitric oxide photodissociates in the δ(0-0) and δ(1-0) bands near 191 and 183 nm, respectively, initiating the primary mechanisms for NOx removal in the middle atmosphere. The spectrally rich Schumann-Runge (S-R) bands of O2 are the main source of atmospheric opacity at these wavelengths. A re-evaluation of O2 absorption has been made based on recent advances in understanding of S-R line shapes, leading to differences with conventional approaches assuming Voigt line profiles in line-by-line calculations of the O2 cross section. The new results are used to examine the impact of O2 transmission on the photodissociation of NO in the δ(0,0) and δ(1,0) bands.  相似文献   

7.
The behavior of profiles of the Na I D line and of the infrared Ca II triplet for the star R Coronae Borealis (R CrB) during shallow light minima of 1998-1999 is traced using high-resolution spectra. During a light maximum, the sodium lines had an absorption profile with a shift of —(2-4) km/sec. During a light minimum, a narrow emission feature, which has an almost constant absolute intensity and a shift of —(8-10) km/sec, and an intense circumstellar absorption feature, which has a variable profile and a variable relative shift corresponding to an increase to 220 km/sec in the velocity of mass ejection, appeared in the cores of absorption lines. For several days before the onset of a light minimum, all three calcium lines exhibited a narrow emission feature in the line core with a shift of —(1-5) km/sec. All the subsequent changes in a line involved mainly the shape of the absorption line profile. The narrow emission feature's absolute intensity and relative position were maintained during all our observations. The behavior of the Na I D line profiles can be described qualitatively within the framework of the model of a spherical dust shell.  相似文献   

8.
For the case of pure absorption lines (LTE) a method is described which enables the general computation of Zeeman-split line profiles. The magnetic field vector, the Doppler shift and the line absorption coefficient is permitted to vary arbitrarily with optical depth. Elliptical birefringence (e.g., Faraday rotation) of the solar atmosphere is taken into account. Some numerical examples are given and some interesting behaviors of the line profiles are discussed.  相似文献   

9.
Be stars show both emission and absorption profiles in the optical part of the spectrum, and these are found to vary with the time. Some of the shifts in profiles were earlier interpreted as Doppler shifts. However, some of the shifts of features in both emission and absorption line profiles may be artifacts due to superposition of an emission profile arising from an Hii region around a binary compact object, and a profile due to the Be star. This interpretation of shifts in line profiles has the advantage over the conventional Doppler-shift interpretation in so far as it does not need the oscillation of a large mass of circumstellar gas, and leads to the observed correlation between radial velocity (RV) variations and V/R variations.  相似文献   

10.
The causes of variability of line profiles in the spectra of O supergiants are analyzed. It is suggested that the main cause of the variability is the motion in the atmosphere of dense clumps of matter (inhomogeneities or clouds) along the Une of sight between star and observer. The profiles of C IV and Si IV UV resonance lines in the spectra of bright OB supergiants are calculated for spherically symmetric atmospheres and for atmospheres with inhomogeneity along the line of sight. The dependence of the line profiles on the distance of the inhomogeneity from the center of the star is investigated. It is shown that the formation and evolution with time of discrete absorption components (DACs) in the profiles of C IV and Si IV UV resonance lines can be explained within the framework of the proposed model of variability of line profiles. The parameters of the inhomogeneities moving in the atmosphere to produce DACs are estimated. Translated from Astrofizika, Vol. 41, No. 3, pp. 423–441, July–September, 1998.  相似文献   

11.
We consider resonant absorption in a spectral line in the outflowing plasma within several tens of Schwarzschild radii from a compact object. We take into account both Doppler and gravitational shifting effects and reformulate the theory of P Cygni profiles in these new circumstances. It is found that a spectral line may have multiple absorption and emission components depending on how far the region of interaction is from the compact object and what the distribution of velocity and opacity is. Profiles of spectral lines produced near a neutron star or a black hole can be strongly distorted by Doppler blue- or redshifting and gravitational redshifting. These profiles may have both red- and blueshifted absorption troughs. The result should be contrasted with classical P Cygni profiles, which consist of redshifted emission and blueshifted absorption features.
We suggest that this property of line profiles to have complicated narrow absorption and emission components in the presence of strong gravity may help researchers to study spectroscopically the innermost parts of an outflow.  相似文献   

12.
We have treated formation of spectral lines in a commoving frame where photoionization is predominant over collisional processes. We have assumed that the radiation field for causing photoionization is a function of Planck function. We have also considered the situation in which the continuum contributes to the radiation in the line. In all the models the quantityB/A (ratio of outer to inner radii) is kept equal to 10 and the total optical depth is taken to be 103. The velocity is assumed to be varying according to the lawdV/dτ ∼ < 1/τ whereτ is the optical depth (τ > 0) in the given shell. The velocities at the innermost radius (r =A) are set equal to 0 and at the outermost radius (r =B), the maximum velocities are taken to be 0, 1, 3 and 10 Doppler units. The calculated line profiles are those seen by an observer at infinity.P Cygni-type profiles are observed in the case of a medium with no continuum absorption. For a medium with continuum absorption double peaked asymmetric profiles are noticed when the velocities are small; the two emission peaks merge into a single asymmetric peak for larger velocities.  相似文献   

13.
The influence of the chromospheric condensation on H line profiles for the thermal model of a solar flare has been empirically studied in this paper. The so-called thermal model here means that there is no temperature increase relative to the quiet-Sun chromosphere but with a chromospheric condensation in the lower part of its transition region, which case is assumed to represent the early stage of the impulsive phase. The main results include: when the temperature within the condensation region is assumed to be equal to that in front of it, the influence is to create an additional absorption profile overlapping on the original one; by increasing the condensation strength, the H line profile changes from a little line-center increase to broadened red asymmetry, then to the reversed red asymmetry, and finally to two independent absorption profiles; the thickness of the condensation determines the absorption of the additional profile; descending the transition region has no obvious effect on the basic characteristic of the H line profile except a little increase in the line center. Assuming that the temperature within the condensation is higher than that ahead of the condensation, the calculated H line profiles may be strong enough to be comparable with the observations. This means that if the condensation in the purely thermal model can reach a higher temperature, we may also use only thermal origin to explain a chromospheric flare.Alexander von Humboldt Research Fellow, on leave from Purple Mountain Observatory, Nanjing, China.  相似文献   

14.
The He II → He I recombination of primordial helium plasma (z ? 1500–3000) is considered in terms of the standard cosmological model. This process affects the formation of cosmic microwave background anisotropy and spectral distortions. We investigate the effect of neutral hydrogen on the He II → He I recombination kinetics with partial and complete redistributions of radiation in frequency in the He I resonance lines. We show that to properly compute the He II → He I recombination kinetics, it is important to take into account not only the wings in the absorption and emission profiles of the He I resonance lines, but also the mechanism of the redistribution of resonance photons in frequency. Thus, for example, the relative difference in the numbers of free electrons for the model using Doppler absorption and emission profiles and the model using a partial redistribution in frequency is 1–1.3% for the epoch z = 1770–1920. The relative difference in the numbers of free electrons for the model using a partial redistribution in frequency and the model using a complete redistribution in frequency is 1–3.8% for the epoch z = 1750–2350.  相似文献   

15.
Aur binaries are particularly well suited for the study of the winds of late type supergiants. The analysis technique is based on theoretical modelling of flux profiles which are formed by resonance scattering in the expanding envelope. However, the hot B star ionizes the wind and can produce a considerable H II region around the B star. In order to investigate the influence of the Strömgren sphere on the line formation we have calculated theoretical P Cyg line profiles with an H II region. The line source function is solved with the Sobolev method followed by a correct formal integration (Hempe, 1982). The ionization of metals within the H II region is described by an ionization parameter which mimics the typical ionization fraction of the relevant ions. The resulting line profiles are dependent on the geometric shape of the H II region, the velocity distribution, and the opacity parameter. The reduced absorber density within the H II region produces weakened line profiles and the specific geometry of the H II region influences the emission and the absorption component in different ways. The careful analysis of model computations suggests that the region of the line formation is not only restricted to the vicinity of the B star, hence the outer integration boundary has to be taken to a sufficiently large radius in the calculation of line profiles.  相似文献   

16.
The temporal variations of the radial velocity and profile of the Hα line in the spectrum of α Cyg are analyzed based on 240 CCD spectra taken with the coude spectrograph attached to the 2-m telescope of Shamaha Astrophysical Observatory of the National Academy of Sciences of Azerbaijan in 1998–2000. The results obtained are inconsistent with the conclusion made by the Heidelberg group concerning the behavior of the variability of the Hα-line profile [1]. The observed pattern of radial-velocity variations is due to nonradial pulsations and differs for the blue and red halves of the absorption profile. The pulsation parameters differ for different levels of residual intensity for both halves of the absorption profile. The amplitude and period increase from the core toward the wing of the line for the red half of the absorption profile, and, on the contrary, decrease toward the line wing for the blue half of the profile. Absorption features are observed on the blue half of the absorption profile. Their emergence and disappearance, as well as minor migrations are indicative of the clumpy structure of the stellar envelope. The similarity of the variability behavior of the absorption and emission profiles indicates that the latter too owe their variability to nonradial pulsations. Thus the variability of the stellar wind in its formation regions is partly due to the nonradial pulsations of the underlying layers of the atmosphere. On the whole, the variability of the position and photometric parameters of the absorption and emission components of the profile is indicative of the nonstationary nature and asymmetric shape of the stellar wind.  相似文献   

17.
Spectroscopic data taken with a moderate resolution spectrograph in the region of the Hα and Hβ lines are presented for the Herbig B8e star MWC 419. The spectroscopic observations were accompanied by broad band BVR photometric measurements. The observations reveal a variability in the line profiles that is typical of Herbig Ae/Be stars with signs of a strong stellar wind. The greatest changes are observed in the region of the absorption components of the line profiles, which convert the profile from a type P CygII to P CygIII, as well as in the intensities of the central emission components. A model technique is used for quantitative interpretation of this variability and it shows that the P Cyg profile conversion of the absorption component can be explained in terms of a stellar wind model in which its distribution over latitude varies on a time scale of a few days. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 259–280 (May 2007).  相似文献   

18.
This paper presents some numerical results relative to a solution, based on the density matrix formalism, of the non-LTE, polarized radiative transfer problem for a two-level atom. The results concern the atomic upper level population and alignment, and the emergent radiation Stokes profiles, for a plane-parallel, static, isothermal atmosphere embedded in a magnetic field of intermediate strength, such that the Zeeman splitting has to be taken into account in the line profile. Zeeman coherences are neglected, whereas magneto-optical effects are taken into account, resulting in a full 4×4 absorption matrix. Induced emission is neglected and complete frequency redistribution, in the rest and laboratory frames, is assumed. Pure Doppler absorption profile (gaussian shape) has also been assumed. The presentation of the results is preceded by a brief discussion of their accuracy and of the numerical difficulties that were met in the solution of the problem.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia  相似文献   

19.
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (|b| > 15°) Galactic latitudes. The Declination coverage of the present survey is δ}> - 45°. With a mean rms optical depth of ∼ 0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components. A subsequent paper will discuss the interpretation of these results.  相似文献   

20.
Theoretical X-ray line profiles from colliding wind binaries   总被引：1，自引：0，他引：1  
We present theoretical X-ray line profiles from a range of model colliding wind systems. In particular, we investigate the effects of varying the stellar mass-loss rates, the wind speeds and the viewing orientation. We find that a wide range of theoretical line profile shapes is possible, varying with orbital inclination and phase. At or near conjunction, the lines have approximately Gaussian profiles, with small widths  (HWHM ∼ 0.1 v ∞)  and definite blueshifts or redshifts (depending on whether the star with the weaker wind is in front or behind). When the system is viewed at quadrature, the lines are generally much broader  (HWHM ∼ v ∞)  , flat-topped and unshifted. Local absorption can have a major effect on the observed profiles – in systems with mass-loss rates of a few times  10−6 M⊙ yr−1  the lower energy lines  ( E  ≲ 1 keV)  are particularly affected. This generally results in blueward-skewed profiles, especially when the system is viewed through the dense wind of the primary. The orbital variation of the linewidths and shifts is reduced in a low-inclination binary. The extreme case is a binary with   i = 0°  , for which we would expect no line profile variation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号