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Neupert, W. M.

Publications and source records attributed to Neupert, W. M..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Solar coronal holes as sources of recurrent geomagnetic disturbances

Observations of the solar corona by Oso 7 have been used in a superposed epoch analysis to study the relationships between classes of coronal features and geomagnetic activity. Both bright coronal regions and regions of less than average brightness were investigated. It was found that for the period from January 1972 through January 1973, a significant enhancement in geomagnetic activity occurred 2-3 days after central meridian passage of large coronal holes that extended to within 5 deg of the solar subearth point when they were on the meridian. Large coronal holes appear to satisfy the requirements for 'M regions' which were hypothesized to be responsible for recurrent geomagnetic disturbances (Bartels, 1934). If solar wind high-speed streams originate preferentially in these regions, their velocity at the base of the corona will be substantially higher than that expected from an axisymmetric solar wind model.

Neupert, W. M.↗
NASA NTRS1974

Polarization results of solar X-rays from OSO-7

Polarization measurements of solar X-ray events that were obtained with an instrument on OSO-7 are presented. The results appear to be consistent with the results of Tindo et al. on the existence and magnitudes of polarization. A comparison with polarization predictions when X-rays are produced by radial beams of electrons gives two examples of deviations from such a model.

Nakada, M. P.↗
NASA NTRS1974

Solar-flare emission lines in the range from 66 to 171 A; 2sr 2pk - 2s/r-1/ 2p/k+1/ transitions in highly ionized iron

New emission lines found in several flare spectra obtained with the Goddard grating spectrometer on the OSO-5 satellite, in 1969, have been listed by wavelength and relative intensity. These new lines, including several as strong as normal quiet-sun lines, are extremely variable in intensity and have been assigned mainly to transitions of the type 2sr 2pk - 2s(r-1) 2p(k+1) in iron ions up to Fe XXIII.

Kastner, S. O.↗
NASA NTRS1974

Ionization equilibrium in soft X-ray-emitting solar flares

Studies of the 1.9-A line produced by highly ionized iron during a solar flare indicate that this emission occurs under conditions approaching a steady-state ionization equilibrium. Time-dependent and steady-state ionization equilibrium values are used for calculation of 1.9 A line fluxes per unit flare emission. The results are compared with those obtained by observations of some four solar flares, showing that the calculations from time-dependent equilibrium values approximate the observed line flux values with the same accuracy as the calculations from steady-state equilibrium values only when the electron densities are equal to or greater than 10 billion per cu cm.

Phillips, K. J. H.↗
NASA NTRS1974

On helium-like 1s2l-1snl prime transitions in solar flare spectra

Expected wavelengths and intensities are computed for 1s2l-1snl prime transitions in helium-like ions of the abundant elements from oxygen to iron under coronal conditions. Probable observations of some of these lines in the spectra of solar flares are discussed, and attention is called to a possible reversal of singlet and triplet intensities as compared to laboratory observations.

Kastner, S. O.↗
NASA NTRS1974

The GSFC EUV and X-ray spectroheliograph on OSO-7

The Goddard Space Flight Center instrument carried on the pointed section of the OSO-7 satellite is described. This instrument contains: an extreme-ultraviolet spectroheliograph using glancing incidence optics of Wolter's Type II to focus the sun's light on the entrance slit of a concave grating spectrometer; an auxiliary H-alpha system; two X-ray spectroheliographs using mechanical collimators for spatial resolution and Ross filters to isolate spectral bands of interest; and a flare polarimeter operating in the 15-40 keV X-ray region. The subsystems may be operated in a number of modes which, when combined with the spacecraft modes, give the instrument great flexibility for making solar observations. Representative results from each of the subsystems are presented.

Underwood, J. H.↗
NASA NTRS1973

K alpha line emission during solar X-ray bursts

The expected flux of K alpha line emission from sulfur, argon, calcium, and iron is calculated during both thermal and nonthermal solar X-ray events. Such emission is shown to be weak during the course of most of the nonthermal hard X-ray bursts that Kane and Anderson (1970) have observed. If Compton backscattering is significant at high energies, the flux is reduced still further for disk flares, but it is noted that the strong, near-limb burst of June 26 would have produced about 100 photons /sq cm/sec of sulfur and iron K alpha emission. The impulsive hard X-ray bursts may in general be too short-lived for much K alpha emission. It may be noted that sulfur K alpha emission in particular depends sensitively on the lower-energy limit of the nonthermal electron spectrum, assuming such a sharply defined boundary exists. During soft X-ray bursts, when temperatures of a few 10 to the 7th power K are obtained, K alpha emission from certain iron ions, specifically Fe XVIII-XXIII, may be important.

Phillips, K. J. H.↗
NASA NTRS1973

Solar flare line emission between 6 A and 25 A

A list of emission lines in the spectra of solar flares between 6 and 25 A 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.

Neupert, W. M.↗
NASA NTRS1973

K alpha line emission during solar X-ray bursts

Calculations of K alpha line emission from S, Ar, Ca and Fe are presented. It is reported that on the basis of data for hard X-ray bursts, the flux during most impulsive, non-thermal events is likely to be weak, though for a few strong bursts, a flux of approximately 100 photons/cm/s may be expected. The amount of S K alpha emission particularly is sensitively dependent on the value of the lower energy bound of the non-thermal electron distribution, offering a possible means of determining this. Thermal K alpha emission is only significant for Fe ions. The calculated thermal K alpha radiation is much less than that observed during an intense soft X-ray burst. It is concluded that a detailed temperature structure for the emission source is required in order to explain the discrepancy.

Phillips, K. J. H.↗
NASA NTRS1972

Results from the GSFC OSO 7 spectroheliograph

The capabilities of the pointed spectroheliograph on board the OSO 7 are discussed. The range and results of the instrument in recording the evolution of solar active regions and solar flares are considered.

Neupert, W. M.↗
NASA NTRS1972

Evidence for the 300-second oscillation from OSO-7 extreme-ultraviolet observations.

The detection and significance of 300-second oscillations in extreme-ultraviolet lines formed in the solar transition region are discussed. Detection was accomplished with the Goddard extreme-ultraviolet spectroheliograph and the Wolter type II grazing-incidence telescope. The Cooley-Tukey algorithm was used to compute the required Fourier transform of the discrete data. Presence of significant power in the observed lines around 262 sec seems to be the first observational evidence that periodic waves in this frequency range persist at heights where local kinetic temperatures are close to one million degrees K. The observed horizontal extent of the wave fronts appears to be much greater than the extent of coherent oscillating elements at chromospheric heights. Several implications are stated for the problem of heating of the transition region and low corona.

Chapman, R. D.↗
NASA NTRS1972

X-ray line emission associated with solar flares.

The characteristics of X-ray spectra associated with solar flare activity are examined on the basis of observation data obtained by means of OSO-III and OSO-V. Solar spectra immediately before and during flares are compared, and variation of X-ray line emission with time during an X-ray burst is studied for two emission lines of iron. These and other observations suggest that at any instant of time only a fraction of the eventual amount of flare plasma is being heated and ionized in a highly localized volume, and that the ionization takes place nearly instantaneously.

Neupert, W. M.↗
NASA NTRS1971

Solar flare X-ray spectra

Solar flare X ray spectrum analysis for lower corona physical conditions, discussing continuum and line emission

Neupert, W. M.↗
NASA NTRS1971

Glancing incidence optics for X-ray and ultraviolet astronomy.

Glancing incidence telescopes of the kind first described by Wolter have now been physically realized, so that it is possible to obtain high-resolution images of celestial objects at all wavelengths greater than about 3 A. The GSFC-MSFC X-ray telescope for the Apollo telescope mount uses Wolter type 1 optics and is capable of forming images of the sun in the 8-70 A region with spatial resolution of the order of one arc second. The GSFC extreme ultraviolet spectroheliometer for OSO H uses type 2 optics and can obtain images of the sun in spectral lines in the 170-400 A region with a spatial resolution of about ten arc seconds. Theoretical (ray trace) and laboratory data on these systems are presented.

Underwood, J. H.↗
NASA NTRS1971

X-ray spectroscopy of solar active regions and flares.

Review of some recent contributions of X-ray spectroscopy to knowledge about solar active regions and flares. As an example of the importance of X-ray spectroscopy, it is pointed out that, while there are no emission lines from highly ionized silicon in the visible spectrum, the XUV spectrum has emission lines from SiIX through SiXIV. Jordan's (1969) calculations of ionization equilibria for silicon and iron are illustrated by diagrams and discussed. The observation of SiXIV gives evidence for regions having electron temperatures from 5 to 20 million deg. The ability to record the corona against the disk of the sun has enabled Van Speybroeck et al. (1970) to identify many bright diffuse X-ray emitting regions with remnants of old active regions of the type giving rise to unipolar magnetic regions. The physical characteristics of the hot coronal plasma associated with chromospheric flares are outlined on the basis of current observations.

Neupert, W. M.↗