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1.
本文针对晚型星红外辐射的一些模型，讨论相应的拟合方法。对有拱星壳层的晚型星的双黑体模型，给出了具体的拟合方法──线性化方法。最后我们就拟合结果及拟合程序编制方面讨论了线性化方法的优缺点。  相似文献   

2.
梁雅琼  仲佳勇 《天文学报》2005,46(2):151-157
根据非局域热动平衡状态下谱线形成理论，利用相对论多组态原子程序软件包FAC模拟了类铍氧离子的X射线及EUV光谱．分析了间接过程对类铍氧离子X射线及EUV光谱形成的影响．在典型天体等离子体密度(ne=10加／立方厘米)情况下，采用了3种模型，在不同温度下模拟X射线及EUV光谱形成过程，分析比较了间接过程对谱线形成的贡献，并给出了它们的速率系数，得出了在谱线形成过程中，间接过程具有非常重要的作用．  相似文献   

3.
According to the theory of spectral line formation in the state of non-local thermodynamic equilibrium and by using the software package FAC for the relativistic multi-configuration atomic processes, the X-ray and EUV spectra of Be-like oxygen ions are simulated. The effects of indirect processes on the X-ray and EUV spectra of Be-like O ions are probed. In the situation of the typical cosmical plasma density (ne = 1010/cm3), three models are adopted. For different temperatures, the processes of formation of X-ray and EUV spectra are simulated, and the contributions of indirect processes to the formation of spectral lines are analyzed and compared. Besides, their rate coefficients are given. It is found that in the process of spectral line formation, the indirect processes have exceedingly important effects.  相似文献   

4.
The IRAS low-resolution spectra (LRS) of 29 symbiotic stars are presented in this paper. It is found that silicate dust is common material in the circumstellar shells of symbiotic stars. From the IRAS low-resolution spectra, IRAS colors, symbiotic types and spectral types, some physical properties of symbiotic stars with the LRS spectra are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
The uncertainty of the spectral transmission function due to the nonsphericity of cosmic dust particles is analysed for optically thick C-rich and O-rich dust shells. The transmission function directly prescribes the intensity of radiation that passes through a dust shell. It is shown that nonspherical particles affect the stellar spectra in a different way than a system of equally sized spherical particles. Discrepancies in the stellar spectra for both morphological models (spheres and irregular targets) grow with optical thickness of the dust shell and the spectral behaviour of the optical thickness depends on the particle size distribution function. In particular, two most frequently used distrubutions, a power law and Dirac’s delta function, are considered in the presented numerical runs. Light transmission through C-rich dust shells is strongly influenced by absorption which dominates in case of carbonaceous particles. Irregularly shaped carbonaceous particles reduce the intensity of stellar spectra more efficiently than spherical particles of the same composition (the difference is about 10–30%). MgO particles which may be present in O-rich dust shells are almost pure scatterers, thus the ratio of transmission functions for irregularly shaped particles and spherical ones show specific resonant features (especially at wavelengths below 0.4 μm).  相似文献   

6.
New, more detailed calculations of the emission spectra of the He-like Kα complex of calcium, iron and nickel have been carried out using data from both distorted-wave and R-matrix calculations. The value of the GD ratio (an extended definition of the G ratio that accounts for the effect of resolved and unresolved satellite lines) is significantly enhanced at temperatures below the temperature of He-like maximum abundance. Furthermore, it is shown that satellite lines are important contributors to the GD ratio such that   GD / G > 1  at temperatures well above the temperature of maximum abundance. These new calculations demonstrate, with an improved treatment of the KLn     satellite lines, that Kα satellite lines need to be included in models of He-like spectra even at relatively high temperatures. The excellent agreement between spectra and line ratios calculated from R-matrix and distorted-wave data also confirms the validity of models based on distorted-wave data for highly charged systems, provided the effect of resonances is taken into account as independent processes.  相似文献   

7.
Synthetic brightness profiles resulting from consistent dynamical models for circumstellar dust shells around long-period variables are presented and discussed with respect to a corresponding observation of IRC +10216.  相似文献   

8.
We present results for the spectral distortions of the cosmic microwave background (CMB) arising due to bound–bound transitions during the epoch of cosmological hydrogen recombination at frequencies down to  ν∼100 MHz  . We extend our previous treatment of the recombination problem now including the main collisional processes and following the evolution of all the hydrogen angular momentum substates for up to 100 shells. We show that, due to the low baryon density of the Universe, even within the highest considered shell full statistical equilibrium (SE) is not reached and that at low frequencies the recombination spectrum is significantly different when assuming full SE for   n > 2  . We also directly compare our results for the ionization history to the output of the recfast code, showing that especially at low redshifts rather big differences arise. In the vicinity of the Thomson visibility function the electron fraction differs by roughly −0.6 per cent which affects the temperature and polarization power spectra by ≲ 1 per cent. Furthermore, we shortly discuss the influence of free–free absorption and line broadening due to electron scattering on the bound–bound recombination spectrum and the generation of CMB angular fluctuations due to scattering of photons within the high shells.  相似文献   

9.
ISO-SWS spectra of two Mira variables (R Cas and T Dra), taken at two different pulsational phases, are presented. We describe the reduction of the data and the encountered problems. The dust features observed by ISO at different phases and with the Low Resolution Spectrometer of IRAS are compared. We briefly discuss the results in terms of current models for the circumstellar dust shells of AGB variables. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

10.
We analyse the line and continuum spectra of the symbiotic system CH Cygni. We adopt the colliding‐wind model to explain the symbiotic system at different phases. Peculiar observed features such as flickering, radio variation, X‐ray emission, as well as the distribution of the nebulae and shells throughout the system are investigated by modelling the spectra at different epochs. The models account consistently for shock and photoionization and are constrained by absolute fluxes. We find that the reverse shock between the stars leads to the broad lines observed during the active phases, as well as to radio and hard X‐ray emission, while the expanding shock is invoked to explain the data particularly during the transition phases (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
By a combination of radiative lifetimes measured using the fast-beam-laser method and experimental branching ratios deduced from Fourier transform spectrometer spectra, it has been possible to derive experimental f -values for Lu  ii lines observed in the visible and near-ultraviolet regions. These data are compared with relativistic Hartree–Fock calculations, taking core polarization effects into account, and a set of additional oscillator strengths of astrophysical interest is presented.  相似文献   

12.
Observations of ε Eri (K2 V) have been made with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope . The spectra obtained show a number of emission lines which can be used to determine, or place limits on, the electron density and pressure. Values of the electron pressure are required in order to make quantitative models of the transition region and inner corona from absolute line fluxes, and to constrain semi-empirical models of the chromosphere. Using line flux ratios in Si  iii and O  iv a mean electron pressure of P e= N e T e=4.8×1015 cm−3 K is derived. This value is compatible with the lower and upper limits to P e found from flux ratios in C  iii , O  v and Fe  xii . Some inconsistencies which may be because of small uncertainties in the atomic data used are discussed.  相似文献   

13.
A radiative transfer model for newly formed hot stars surrounded by optically thick dust shells is applied to a number of compact infrared sources. The model parameters are derived by fitting the synthetic spectra to the observed one between 8 and 13 m and used to derive additional properties of the shells and the embedded stars.  相似文献   

14.
Recent observations of long-period variable stars at spatial resolutions from approximately 1 arcsec to several milli-arcsecs have provided new insights into pulsation, dust formation, and mass-loss of AGB stars. These insights have come from long baseline interferometric observations obtained across a wide range of wavelengths, from the optical, through the infrared, to wavelengths as long as several millimeters. The present status and recent results from long baseline interferometry, particularly at optical and infrared wavelengths, are discussed. Such results include diameters and limb-darkening, surface features, mode of pulsation, location of SiO masers, inner radii of dust shells, physical conditions in the dust formation zone and of the inner regions of the dust shells. The results are interpreted in terms of present models of dust formation and mass-loss.  相似文献   

15.
A one-dimensional inhomogeneous cylindrical plasma model with the magnetic field, whose field lines are concentric circles and the equilibrium parameters of the magnetic field and a medium change across magnetic shells, has been considered. In the scope of this model, it has been indicated that Alfvén modes can have discrete spectra. Such modes originate when resonators exist across magnetic shells, which can be implemented in the ring current area or near the outer edge of the plasmapause. The characteristics of the implementation of the modes with discrete spectra have been studied. The results are compared with the satellite observations. It has been concluded that poloidallypolarized pulsations in the Earth’s magnetosphere are largely oscillations with discrete spectra. It has been shown that the proposed model, which does not consider many properties of the magnetosphere, makes it possible to explain the main features in the experimentally observed generation of azimuthal small-scale ULF oscillations in the near-Earth plasma. The results can be used to interpret the satellite and SuperDARN radar measurements.  相似文献   

16.
Recent advances in modelling the radiating character of dynamic laboratory and astrophysical plasmas are applied here in a new examination of the properties of the atmosphere of the classical T Tauri star BP Tau. We analyse archived International Ultraviolet Explorer ( IUE ) UV spectra of BP Tau. We adopt a collisional-radiative model and utilize emission measure (EM) and differential emission measure (DEM) techniques to try to constrain the distribution of emitting material in temperature in the atmosphere of this star. We use spectroscopic diagnostic techniques to probe atmospheric parameters such as electron density, and to set constraints on the volume of emission regions. This work is important for understanding the fundamental properties of BP Tau and other T Tauri stars, and for providing a more complete basis for models of their atmospheres.  相似文献   

17.
We present coefficients for the calculation of the continuous emission spectra of H  i , He  i and He  ii due to electron–ion recombination. Coefficients are given for photon energies from the first ionization threshold for each ion to the   n = 20  threshold of hydrogen  (36.5 μm)  , and for temperatures  100 ≤  T ≤ 105 K  . The emission coefficients for He  i are derived from accurate ab initio photoionization data. The coefficients are scaled in such a way that they may be interpolated by a simple scheme with uncertainties less than 1 per cent in the whole temperature and wavelength domain. The data are suitable for incorporation into photoionization/plasma codes and should aid with the interpretation of spectra from the very cold ionized gas phase inferred to exist in a number of gaseous clouds.  相似文献   

18.
M. Contini 《New Astronomy》2011,16(7):439-444
The visual magnitude profile of the symbiotic system Z And during the 1984–1986 activity period appears double peaked and the flux intensity is low compared to outbursts in other epochs. The detailed modeling of the observed spectra, accounting for the shells ejected by the red giant star, shows that the outburst is intrinsically single but distorted by the collision at different phases of the white dwarf wind with two close shells.  相似文献   

19.
The first theoretical transition probabilities are obtained for a set of 46 Pm  ii transitions of astrophysical interest. These data fill in a gap in astrophysics and will allow to establish, on a firmer basis, the presence of some lines of this radioactive element in the spectra of chemically peculiar stars and, consequently, a quantitative investigation of the stellar Pm abundance. A search for Pm  ii lines in Przybylski's star (HD 101065) and in HR 465 is reported and discussed, supporting the detection of this ion. A more detailed quantitative analysis is awaiting the availability of dedicated model atmospheres for these stars.  相似文献   

20.
The central engine causing the production of jets in radio sources may work intermittently, accelerating shells of plasma with different mass, energy and velocity. Faster but later shells can then catch up slower earlier ones. In the resulting collisions shocks develop, converting some of the ordered bulk kinetic energy into magnetic field and random energy of the electrons which then radiate. We propose that this internal shock scenario , which is the scenario generally thought to explain the observed gamma-ray burst radiation, can also work for radio sources in general, and for blazars in particular. We investigate in detail this idea, simulating the birth, propagation and collision of shells, calculating the spectrum produced in each collision, and summing the locally produced spectra from those regions of the jet which are simultaneously active in the observer's frame. We can thus construct snapshots of the overall spectral energy distribution, time-dependent spectra and light curves. This allows us to characterize the predicted variability at any frequency, study correlations between the emission at different frequencies, specify the contribution of each region of the jet to the total emission, and find correlations between flares at high energies and the birth of superluminal radio knots and/or radio flares. The model has been applied to reproduce qualitatively the observed properties of 3C 279. Global agreement in terms of both spectra and temporal evolution is found. In a forthcoming work, we will explore the constraints that this scenario sets on the initial conditions of the plasma injected in the jet and the shock dissipation for different classes of blazars.  相似文献   

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