Compton effect and solar spectral lines

A scenario for the evolution of the Martian atmosphere consistent with various data of the Viking 1 and 2 and the Mariner 9 has been presented: Mars was formed from Renazzo-type meteorites polluted by the products of supernova explosion. A dense ancient Martian atmosphere has been swept away by the solar wind and the present tenuous atmosphere was supplied recently by the volcanic gas from the Tharsis region, after the occurrence of the magnetic field.     

Empirical NLTE analyses of solar spectral lines

The center-to-limb behaviour of the Ba ii 4554 resonance line is analyzed together with data from the extreme limb, flash intensities and profiles of other Ba ii lines. An empirical NLTE method is employed in which the observed profiles are compared with synthesized profiles based on a standard one-dimensional model atmosphere, with the line source function, the barium abundance, the collisional damping and the atmospheric turbulence as free parameters.The line profiles from the extreme limb furnish considerable constraints on the formation of Ba ii 4554. Its wings reverse into emission well inside the solar limb, a phenomenon which cannot be explained by any frequency-independent line source function. Accounting for effects of partially coherent scattering in the line source function is a necessary and adequate step to reproduce the observations both over the disk and near the limb. The form of the empirically derived frequency-dependent line source function is discussed.Results are given for various parameters (gf-values, solar barium abundance and isotope ratios, collisional damping, microturbulence and macroturbulence).The 4554 profile of disk center shows a depression in its blue wing resembling asymetries found in various stellar spectral lines.     

Empirical NLTE analyses of solar spectral lines

A method is suggested for empirical NLTE analyses of solar spectral lines. Special depthdependent departure coefficients (x) are introduced and the formulas are given for further application. From test calculations it is shown that the separation of the departure coefficients for the upper and the lower level from each other and from the uncertainties in several input parameters (oscillator strength times abundance, turbulent velocities and damping constant) is greatly facilitated when spectral lines are analysed on the disk, around the limb, as well as in the flash spectrum. Therefore it is necesssary that all accessible line data are used, from accurate line profiles to equivalent widths or integrated intensities. To reduce the number of independent variables the analysis should include many multiplets between a few spectroscopic terms.We discuss the advantages of translating the departure coefficients into a set of temperatures. Some published LTE and NLTE analyses are compared in terms of these temperatures. The results do not show inexplicable contradictions. For several atomic spectra the departures from LTE seem large enough to be established quantitatively by the detailed method suggested in this paper.     

Interferometric studies of spectral lines in the solar corona

A photographic Fabry-Perot interferometer was used to measure the breadth and wavelength of the Fexiv spectral line at 5303 Å in the solar corona, during the eclipse of 7 March, 1970, in Mexico. The observations were consistent with a possible large-scale vortex structure in a bright streamer, in which cooler gases revolved about a hotter core.Work supported by the United States National Science Foundation and by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under Grant AF-AFOSR-68-1496.     

On a possible explanation of chromospheric line asymmetries of solar flares

We discuss the relationship between the chromospheric downward motions and the line asymmetries in solar flares by using a simple model. It is found that both the blue asymmetry and red asymmetry of the H line can be caused by downward motions, as long as the moving material is confined to different heights in the chromosphere. The Ca ii K line, however, mainly shows a red asymmetry. The results can qualitatively explain some observations.     

On the broadening and shift of spectral lines

The Van der Waals interaction between a radiator and a light neutral perturber explains the broadening and shift of spectral lines only partly satisfactorily. Comparison with solar observations suggests that these theoretical damping constants are systematically too low. Moreover, the theoretically predicted shifts of the lines agree only incidentally with those obtained in laboratory experiments. We used a combination of a Smirnov-Roueff (S-R) interaction potential and a Van der Waals (VdW) potential. The damping constants, thus obtained, are always somewhat higher than those obtained by a VdW potential alone. The agreement between theory and experiment for the shift of the line is - although not completely satisfactory - better than the very poor agreement resulting from a VdW potential. However, the S-R potential may not be used in the case that heavy perturbers are involved. In that case the VdW potential yields the better results. Fairly good agreement is found between theoretically and empirically determined values ofγ for the solar centre.     

Effect of progressive Alfvén waves on the profiles of solar spectral lines

Progressive Alfvén waves set the atoms in oscillatory motion. The radiation will be absorbed (emitted) at a Doppler-shifted wavelength; the Doppler shift is determined by the velocity given to the atoms by the wave. The effect of the waves on the line profile, integrated over one period, is given for a few simple cases. A brief discussion of the possible application to sunspots is presented.     

On the polarization of the solar coronal emission lines

The results of the spectrophotometrical measurements of the polarization in the coronal lines Fe xiv 5303 Å and Fe × 6374 Å are given. Polarization spectrograms were obtained by two spectrographs (prism and echelle types) during the solar eclipse in Mexico on 7 March, 1970 near the region of the second contact at the heights 0.06 to 0.12 R above the limb. The polarization in the green line is about 30% (for averaged height 1.08 R ). The polarization in the red line is close to the errors of the measurement and does not exceed 6%. A brief discussion of the results is also given.     

A study on the asymmetries in flare lines

We calculate the H and CaII K profiles under different velocity models with chromospheric condensations and investigate the effect of the velocity in different layers on the profiles from a semi-empirical standpoint. The results show that the short-time, H blue asymmetry in the early stage of the flare can be caused by condensations in the transition zone, that the subsequent red asymmetry is the result of the downward motion of matter in the upper chromosphere, while the later CaII K asymmetries can be explained by downward velocities of 10–20 km/s in the middle and lower chromosphere.     

Polarization in spectral lines

The general formalism, presented in a previous paper of this series (Landi Degl'Innocenti, 1983a), is particularized to deduce the radiative transfer equations for polarized radiation and the statistical equilibrium equations for a multi-level atom in the zero-magnetic field, collisionless regime. The formulae are developed both in the standard representation and in the representation of the statistical tensors. For resonance scattering in a two-level atom, in the limiting case of complete depolarization of the ground level, we recover the classical results for Rayleigh scattering and we derive the expression of the phase matrix in terms of ordinary rotation matrices. The law of scattering is then generalized to take properly into account the influence of the anisotropy of the radiation field on the atomic polarization of the ground level (depopulation pumping).     

Polarization in spectral lines

A unifying theoretical approach is presented to derive from the general principles of Quantum Electrodynamics both the radiative transfer equations for polarized radiation and the statistical equilibrium equations for an atomic system interacting with a polarized radiation field. The radiation field is described by means of Stokes parameters while the atomic system is described in terms of its density-matrix operator. The non-diagonal terms of the density matrix are fully accounted for so that this formalism can be suitably employed to describe a wide variety of physical phenomena like resonance scattering, the Hanle effect and the Zeeman effect, either in optically thin or optically thick atmospheres, together with all the possible intermediate situations.The general formulae derived in the first sections of the paper are subsequently particularized introducing the dipole approximation in the relevant matrix elements describing the interaction between the atomic system and the radiation field. The final equations assume a quite compact expression by the introduction of suitable spherical tensors connected with the components of the polarization unit vectors associated with each direction of the radiation field. The general expressions and the main properties of these tensors are discussed in the Appendix.     

North-south asymmetries of solar particle events in upper stratospheric ozone

Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on 4 August 1972 and 25 January 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the Earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flow in summer; (4) topographic asymmetry between Northern and Southern Hemispheres.These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively.     

On model predictions of the power spectral density of radial solar p modes

We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect.     

On the nonthermal excitation and polarization of X-ray lines during solar flares

The energy distributions of nonthermal electrons are derived from hard X-ray spectra taken during the impulsive phase of two 2B flares in February 1969. They are used to calculate the fluxes of nonthermally excited X-ray lines of hydrogen-like and helium-like ions. These fluxes are compared to the total line fluxes observed at the same time with crystal spectrometers. The nonthermal excitation is found to give only small contributions to the total line intensities. This implies that the impact polarization which is to be expected for anisotropic velocity distributions of the energetic electrons, will be low. Nevertheless it should be feasible to detect line polarization during the impulsive phase of strong X-ray flares.NAS/NRC Research Associate.     

On the identification of Fe ix and Ni xi lines from coronal spectral

Identifications of coronal lines with transitions of Fe ix and Ni xi, as proposed by Wagner and House, and Svensson, Ekberg and Edlén, are checked by means of line intensity ratios, from observations obtained at the 1965 eclipse. All the suggestions of Svensson, Ekberg and Edlén are suitable.     

Limb effect of solar absorption lines

Low-noise limb-effect observations of the non-magnetic line Fei 557.6 nm are presented. Separate measurements along the solar equator and the meridian have been carried out and have been corrected for scattered light. The limb-effect line shifts at the pole and at the equatorial limb are found to be equal. The detailed shape of the limb effect along the meridian is found to differ significantly from that along the equator. This difference can be explained by the presence of a meridional circulation pattern, with horizontal flows < 50 m^–1 from both the equator and poles toward ± 45° latitude. Alternatively the meridian/equator difference may be caused by a combination of latitude dependence of the granular parameters. An increase with latitude of the granular velocity scale height, contrast, or mean sizes could explain the observations.     

Correction of observational profiles of spectral lines

The profiles obtained from radial-velocity observations of the Rosette Nebula with a Fabry-Pérot (F.P.) interferometer (Meaburn andSmith, 1968) had to be corrected, for the spreading action of the instrumental function, and for motion of the observer. Two current methods are compared and a method devised for fitting a sum of Gaussians to a noisy output profile.     

On the depth dependence of the solar rotation velocity determined from fraunhofer lines

From 63 mostly unblended Fraunhofer lines measured along the solar east-west diameter the rotation velocity has been determined. The mean value is 1986 km s^#X2212;1. The velocity decreases with the optical depth in the photosphere. Over a range of 700 km the difference of the velocities is 41 m s^#X2212;1 for the Holweger-Müller atmosphere or 34 m s^#X2212;1 for the Harvard Smithsonian reference atmosphere.