S. O. Kastner

The coronal spectra of Fe XV and Ni XVII

Predicted allowed and forbidden EUV line intensities of Fe xv and Ni xvii are presented in explicit graphical form, clarifying and extending the earlier treatment of Bely and Blaha (1968). In the case of the former ion a detailed comparison with available observations leads to questioning or rejection of some presently accepted line identifications (323.57 Å, 317.61 Å), and on the other hand suggests that a quiet Sun line at 304.853 Å is due to Fe xv. For the little known ion Ni xvii estimates of level structure and line wavelengths are given and a preliminary comparison is made with recent flare observations.

Observations of n = 3 → n′ = 4 transitions in the Mg i and Si i sequences for elements chromium through zinc

Extreme ultraviolet spectra of 3p2-3p4d and 3p3d-3p4f transition arrays in twelve- and fourteen-electron ions, which differ by only a closed 3s2 subshell, are investigated in more detail than hitherto obtained for the elements chromium through zinc. The spectra were obtained with a two-meter vacuum spectrograph using a high-voltage spark source. Single- and multi-configuration calculations were carried out to compare predictions obtained for different model assumptions, and for the two different sequences.

Solar flare line emission between 6 Å and 25 Å

A list of emission lines in the spectra of solar flares between 6 Å and 25 Å has been compiled using data obtained with a KAP crystal spectrometer on the OSO-5 satellite. The emission lines have been classified according to their sensitivity to flare activity. This classification provides a method for discriminating between iron in high stages of ionization (Fe xx-Fe xxv) and lower stages (Fe xvii- Fe xix), the lines of which are both present in the same spectral region during flares. Identifications consistent with these classifications are proposed. Anomalous intensities in the spectra of Fe xvii and Fe xx are pointed out, and implications of the observations for models of the X-ray emitting regions are discussed.

Prediction and Identification of Some Transitions Associated with 2pk and 2pk-13l Configurations in Six-, Seven- and Eight-electron Ions

Calculations of fine structure and transition probabilities, using the SUPERSTRUCTURE program developed at University College London, have been carried out for the 2pk and 2pk-13l configurations of ions with six, seven or eight electrons. The predicted line patterns are compared with existing observations for silicon, sulfur, argon and calcium to yield some new identifications in laboratory and solar spectra and to indicate some transitions, as yet unobserved, that may be of observational importance.

Image Construction for Concave Gratings at Grazing Incidence, by Ray Tracing

The images formed by a concave grating used at grazing incidence are constructed by a ray-tracing method. The method, equivalent to a recently developed procedure of Spencer and Murty, can be used for any configuration of grating and object. The results are compared with a third-order approximate theory for the case of rays parallel to the Rowland plane.

Aspheric grating for extreme ultraviolet astronomy.

A family of plane curves is developed which can diffract incident parallel rays to a point focus. These curves, termed diffractoidal curves, are rotated around an axis to produce surfaces of revolution correspondingly termed diffractoids, whose imaging properties for sources at infinity are studied by ray tracing in a few examples. The paraboloid emerges as a limiting case of the diffractoid. A comparison is made between the stigmatic focusing properties of the diffractoid and the toroidal grating.

Ray-tracing the convex curved crystal x-ray spectrograph

The calculation of ray paths through the convex defocusing crystal x-ray spectrograph is described for both localized and extended sources. Application is made to some actual experimental configurations to obtain resolution values and source sizes. Wavelength calibrations are also obtainable with the ray-trace method in advance of instrument construction if desired.

Spectra of ions in the fluorine I isoelectronic sequence from Sc XIII to Cu XXI.

In a study of the spectra of ions Sc xiii to Cu xxi in the fluorine isoelectronic sequence, lines of the 2p5–2p4 3s and 2p5–2p4 3d arrays have been observed and classified, as well as some lines of the 2s 2p6–2s2p5 3s array. Assignments were made on the basis of extrapolations and an intermediate-coupling calculation. The results are compared with those available in the literature.

Proposed Mg V, Fe XIV and forbidden Fe XVII line identifications in the EUV solar spectrum

Some line identifications in solar disk and limb spectra are proposed on the basis of recent laboratory and theoretical results reported in the literature, including allowed lines of Mgi and Fexiv in the EUV spectrum and an expected forbidden line of Fexvii near 1190 Å.

Level structure and predicted intercombination lines in magnesium-like V xii, Cr xiii, Mn xiv, and Co xvi

Improved energy levels for V xii, Cr xiii, Mn xiv, and Co xvi are obtained from comparison of observed values with results calculated by the Superstructure program. Predicted wavelengths of important intercombination lines are given and some probable misidentifications in the literature are noted.