The O IV and S IV Intercombination Lines in Solar and Stellar Ultraviolet Spectra
Abstract
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 R1 = I(1407.4 A)/I(1401.2 A). However, the electron density obtained using the ratio R2 = 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1995
- DOI:
- 10.1086/175664
- Bibcode:
- 1995ApJ...444..936C
- Keywords:
-
- Electron Density (Concentration);
- Emission Spectra;
- Mathematical Models;
- Oxygen Ions;
- Stellar Spectra;
- Ultraviolet Astronomy;
- Electron Energy;
- High Resolution;
- Hubble Space Telescope;
- Skylab Program;
- Spectral Resolution;
- Spectrographs;
- Astronomy;
- ATOMIC DATA;
- ATOMIC PROCESSES;
- SUN: UV RADIATION;
- ULTRAVIOLET: STARS