Engineering topics

Dufton, P. L.

Publications and source records attributed to Dufton, P. L..

6 records

NASA NTRS1995

The O IV and S IV intercombination lines in solar and stellar ultraviolet spectra

New calculations of O IV electron density diagnostic emission-line ratios involving the 1399.8, 1401.2, 1404.8, and 14076.4 A transitions are presented. A comparison of these calculations with observational data from a quiet solar region, a sunspot, and an active region obtained with the High Resolution Telescope and Spectrograph (HRTS), two flares observed with the SO82B spectrograph on board Skylab, and Hubble Space Telescope (HST) observations by the Goddard High Resolution Spectrograph (GHRS) of Capella, gives good results using the ratio R(sub 1) = I(1407.4 A)/I(1401.2 A). However, the electron density obtained using the ratio R(sub 2) = I(1407.4 A)/I(1404.8 A) is often an order of magnitude smaller. The O IV 1404.8 A line is blended with the S IV 1404.8 A line, and we investigate whether this ratio may still be used as a density diagnostic if the S IV 1406.1 A line intensity is used to correct for the presence of S IV 1404.8 A, using previous S IV calculations by Dufton et al. We still find systematic differences compared to density determinations from line ratios that do not involve the O IV 1404.8 A line, which we suggest are due to errors in earlier theoretical calculations of the S IV atomic data, and also possibly to previously unconsidered fluorescent pumping of the upper level of the S IV 1404.8 A transition.

Cook, J. W.↗

NASA NTRS1992

Solar Si II line ratios from the high-resolution telescope and spectrograph

Theoretical emission-line ratios involving multiplets near 1262, 1306, and 1530 A are derived on the basis of new calculations of electron-impact excitation rates for allowed transition in Si II. A comparison of these line ratios with observational data from a quiet solar region, a sunspot, and an active region, obtained with the HIRTS on board a sounding rocket flight reveals that the 1530-A multiplet is optically thick, which is consistent with a calculation of the optical depth of these lines through a model atmosphere. The 1262- and 1306-A multiplets appear to be effectively optically thin. The average discrepancy between the theoretical and observed ratios is about 40 percent, which may not be significant, since the estimated uncertainties in both the calculated and experimental data are approximately 30 percent.

Keenan, F. P.↗

NASA NTRS1986

S V line ratios in the sun

In the present prediction of level populations and emission line intensity ratios for electron densities and temperatures appropriate to the sun, on the basis of new atomic data for S V, the electron impact collision rates for spin-forbidden transitions, and the intercombination transition spontaneous radiative rate, are noted to be substantially larger than previously ascertained. The S V intensity ratio is shown to be a useful electron density diagnostic for log N(e) greater than 11.5 ratios deduced from observations obtained with a slit spectrograph aboard Skylab generally agree with the theoretical values presented.

Dufton, P. L.↗

NASA NTRS1984

Interstellar magnesium abundances

An improved evaluation of the Mg II 1240 A doublet oscillator strength is used in conjunction with recently published Copernicus observations to derive accurate Mg II column densities toward 74 stars. These imply an average of 40 percent of interstellar magnesium is in the gaseous phase. Magnesium depletion is examined as a function of various interstellar extinction and density parameters, and the results are briefly discussed in terms of current depletion theories.

Murray, M. J.↗

NASA NTRS1983

Si III line ratios in the sun

New atomic data for Si III have been used to predict level populations and emission-line intensity ratios for electron densities and temperatures appropriate to the solar transition region. The electron impact collision rates used here are substantially larger than those previously published owing to delineation of the complex resonance structures in the low-energy collision strengths. This together with small changes in the spontaneous radiative rates produces significant changes in the calculated intensity ratios. Generally good agreement is found with observations obtained using the Naval Research Laboratory slit spectrograph aboard Skylab, electron densities from three Si III ratios and from other methods normally agreeing to 0.2 dex or better for a wide variety of solar features. For a fourth ratio, incorporating lines with a wide wavelength separation, the agreement is less satisfactory, possibly owing to uncertainties in the observational data.

Dufton, P. L.↗

NASA NTRS1982

S IV emission-line ratios in the sun

New atomic data are presented for transitions between the five lowest levels in S IV, taking into account the fine-structure rates between the individual J levels together with the electron impact mixing rates within the levels. The values are found to differ significantly from previously published values. Using the atomic data, ionic level populations are deduced for a range of electron temperatures and densities. The results are used to calculate theoretical line intensity ratios for S IV. Excellent agreement is found with intensity ratios for a variety of solar features observed with the NRL normal incidence spectrograph on Skylab.

Dufton, P. L.↗