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Kastner, S. O.

Publications and source records attributed to Kastner, S. O..

At least 37 records · Page 2
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NASA NTRS1988

Spatial probing of nebular properties via Bowen pumping

On the basis of detailed calculations of O III line intensities under optically thin and optically thick conditions, an analysis is proposed for spatially resolved observations of the Bowen lines which could yield the local photoexcitation rate and an estimate of the local optical depth, more specifically the local mean escape probability associated with the line of sight. The importance of such newly defined escape probabilities is emphasized. An illustrative application is made to the data of Barker for the planetary nebula NGC 6720. The far-infrared line ratio I (88 microns)/I(52 microns) is also sensitive to Bowen pumping at low optical depths, and interpretation of the ratio may need to take this effect into account in some H II regions. It is noted that the S III far-infrared line ratio could provide an independent check on whether the effect is present.

Bhatia, A. K.↗
NASA NTRS1988

Discrete fluorescent saturation regimes in multilevel systems

Using models of multilevel atoms, the fluorescent process was examined for the ratio of the photooxidation rate, Pij, to the collisional oxidation rate, Cij, in the pumped resonance transition i-j. It is shown that, in the full range of the parameter Pij/Cij, there exist three distinct regimes (I, II, and III) which may be usefully exploited. These regimes are defined, respectively, by the following conditions: Pij/Cij smaller than about 1; Pij/Cij much greater than 1 and Pij much lower than Cki; and Pij/Cij much greater than 1 and Pij much higher than Cki, where Cki is the collisional rate populating the source level i. The only regime which is characterized by the sensitivity of fluorescent-fluorescent line intensity ratios to Pij is regime I. If regime III is reached, even fluorescent-nonfluorescent line ratios become independent of Pij. The analysis is applied to the resonant photoexcitation of a carbonlike ion.

Kastner, S. O.↗
NASA NTRS1987

Atomic parameters for carbon-like S XI

Calculations of radiative rates and collision strengths of S XI for 46 levels of the six configurations 2s2 2p2, 2s 2p3, 2p4, 2s2 2p 3s, 2s2 2p 3p, and 2s2 2p 3d are presented concurrently so that all the atomic data are self-consistent. Collision strengths are calculated at an incident electron energy of 25 Rydbergs above the ground level 2p2(3P0) in order to include collisional excitation to the highest level considered. Good agreement with previous results is found, and it is suggested that the given electric dipole rates are accurate to within at least 20 percent.

Bhatia, A. K.↗
NASA NTRS1986

Electron collisional excitation and resonant photoexcitation of solar S XI

The line emission of carbon-like S XI is predicted using a comprehensive 46-level model including the configurations 2p2, 2s2p3, 2p3s, 2p4, 2p3p, 2p3d. Relative intensities of allowed, intercombination, and forbidden lines are computed for quiet and active solar conditions. The process of photoexcitation by the Fe XIII 191.26 A line is included to study its effect on EUV lines and the infrared forbidden lines at 1.92 and 1.39 microns. It is concluded that an observation of the 1.92-micron line by Olsen, Anderson, and Stewart (1971) is consistent with quiet solar conditions in the absence of photoexcitation.

Kastner, S. O.↗
NASA NTRS1985

Expected intensities of solar neon-like ions

A study of the expected intensities of the stronger solar neon-like ion emission lines, some not yet observed, is carried out to compare with the observational situation. The potential usefulness of the 2p5 3s(3P2) - 2p6 forbidden line as a density diagnostic is discussed, and new electric quadrupole lines in the soft X-ray range are noted. 'Observability diagrams' are presented as a convenient overview of the known and unobserved lines. The S VII resonance lines appear to have anomalous intensities.

Bhatia, A. K.↗
NASA NTRS1984

On Bowen enhancement of the N III spectrum under solar and nebular conditions

Expected enhancement of the N III emission-line spectrum by the Bowen He II to O III to N III resonant photoexcitation process is computed using a six-configuration model. Preliminary comparisons with available solar and nebular observations indicate that the process may play only a small role, although photoexcitation quenching of the N III and O III far-infrared fine-structure lines is noted as a possibly important mechanism. Some features are discussed in connection with the nebular emission at 1750 A, which is suggested as an indicator of excitation class for planetary nebulae.

Kastner, S. O.↗
NASA NTRS1984

Wavelength coincidence of allowed and intercombination multiplets in N III and O IV - A density and/or temperature diagnostic

Two multiplets of N III with different intensity dependence on source conditions fall in the same wavelength interval near 1750 A, and the analogous multiplets in O IV also lie close together. It is suggested that the multiplet pair can be useful for diagnostic purposes. The calculated ratios are consistent with available observations. A preliminary inspection of solar flare spectra shows the presence of the higher-density-indicating allowed multiple in O IV.

Kastner, S. O.↗
NASA NTRS1984

Diagnostic application of highly ionized iron lines in the XUV spectrum of a solar flare

Recent atomic data have been used to analyze a solar flare spectrum obtained with the Goddard Space Flight Center's grating spectrometer on the OSO-5 satellite. There exist in the wavelength region 90-200 A strong lines from each of the ions Fe XVIII-Fe XXIV. The Fe XXI lines can be used as an electron density diagnostic for the 10 to the 7th K plasma. From an analysis of a particular flare, a steep positive slope in the emission measure between 10 to the 6.5th and 10 to the 7.2th K and an electron density of about 4 x 10 to the 11th per cu cm at 10 to the 7th K is found. The need is emphasized for high spectral and spatial resolution observations of solar flares in this wavelength region, which has to date been largely neglected.

Mason, H. E.↗
NASA NTRS1983

A spectroscopic method for calibration of solar extreme ultraviolet instrumentation

A method of calibrating solar extreme ultraviolet spectrographs in space using coronal emission lines of known relative intensity is presented and demonstrated. This approach is useful for recalibrating orbiting instruments that may be subject to degradation during extended periods of operation. The calibration results are insensitive to the physical distribution of emitting plasma in any likely solar coronal source. It is suggested that this technique may be useful for calibration of spectrographs used in the study of laboratory plasmas.

Neupert, W. M.↗
NASA NTRS1983

The solar O III spectrum. II - Longer wavelengths, line widths, and the He II Lyman alpha radiation field

The solar O III spectrum above 900 A is analyzed, including several visible and infrared lines which are important in nebular studies. The dependence of the line intensities on the rate of photoexcitation by He Ly-alpha is determined, and the observability of these lines in the solar spectrum is studied. The impact approximation is employed to calculate the expected line widths of the stronger solar O III lines. The photoexciting field at 304 A calculated from the observed intensities of the O III lines below 900 A (Bhatia et al., 1982) is compared with the field predicted by a recent model (Avrett et al., 1976). It is shown that additional radiation trapping must be present beyond that given by this model.

Kastner, S. O.↗
NASA NTRS1983

Expected intensities of solar forbidden lines emitted from 2p(k) (k = 2, 3, 4) configurations

Predicted intensities of all significant transitions within the ground configurations of six-, seven-, and eight-electron ions are tabulated for solar conditions, on a common scale. Some applications of the table entries to line identification and emission measure analysis are presented, including proposed Mg VI classifications for the coronal lines 3488.5 A and 3502.5 A.

Kastner, S. O.↗
NASA NTRS1983

On the observability of forbidden lines

The disappearance of forbidden lines for O III at intermediate plasma densities may be due to background wing emission of the stronger allowed lines, rather than to Stark broadening of the forbidden lines as suggested recently. The general conclusion is supported that the classical explanation of quenching is erroneous, at least for O III.

Kastner, S. O.↗
NASA NTRS1982

The solar spectrum of O IV, including photoexcitation by Fe IX 171.07 A

The extreme and far ultraviolet doublet spectrum of O IV, emitted from the solar transition region, is calculated taking account of expected photo-excitation by Fe IX at the wavelength 171.07 A. Four multiplets are shown to be sensitive to such photoexcitation, of which two in particular are potentially observable and could provide an estimate of the local Fe IX radiation field.

Kastner, S. O.↗
NASA NTRS1981

Exact random walk definition of the collisional-radiative ionization and recombination coefficients

The collisional-radiative ionization and recombination coefficients are shown to be expressible in terms of the 'total probability', from initial level i to final level j, which excludes intermediate returns to the initial level. Applications are made to three-level and four-level systems to illustrate the method of calculation and compare with an approximation currently used.

Kastner, S. O.↗
NASA NTRS1981

Evaluation and universal curves of the photon loss probability

In the transfer of radiation in a plasma, an important parameter (which measures the coupling between the radiation field and the electron gas) is the photon loss probability per scattering epsilon, defined as the ratio of collisional de-excitation to total de-excitation. The evaluation of epsilon requires normally knowledge of specific collisional excitation rates and radiative transition rate coefficients. In the considered investigation a general formula for epsilon is obtained which depends only on electron density, temperature, and line wavelength. Use is made of a simple Bethe-Coulomb expression recently derived by Kastner (1980) for the collisional excitation rate coefficient. Epsilon is obtained as a function of the three variables, and universal curves of it can be constructed with one of the variables as parameter. As an example of the application of the considered procedure, the variation of epsilon with height h in the solar atmosphere is shown in a graph for several solar lines.

Kastner, S. O.↗