A comparison of theoreticalCIV emission line strengths with active region observations obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical line ratios involving 2s ² S - 3p ² P, 2p ² P - 3s ² S, and 2p ² S - 3d ² D transitions inCiv between 312 and 420 Å are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. The potential usefulness of theCIV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed.     

Al xii line ratios in the Sun

Recent calculations of electron impact excitation rates in He-like Alxii are used to derive the theoretical electron temperature and density sensitive emission line ratios G ( = (f + i)/r and R ( = f/i, where f, i, and r are the forbidden 1s ^{2 1} S – 1s2s ³ S, intercombination 1s ^{2 1} S – 1s2p ³ P and resonance 1s ^{2 1} S – 1s2p ¹ P transitions, respectively. These ratios are found to be significantly different from earlier calculations, and are in much better agreement with X-ray spectral data for two solar flares obtained with the SMM and P78-1 satellites.     

A comparison of theoretical line strengths for the 2s 22p 2 − 2s2p 3 transitions in Ne v with solar data

Results are presented for several theoretical line ratios in Nev involving transitions between multiplets in the 2s ²2p ² and 2s2p ³ configurations. A comparison of these with solar data from the S082A and S-055 instruments on board Skylab reveals generally good agreement between theory and experiment, especially in the case of the high-resolution (S082A) observations. However the 2s ²2p ^{2 1} D – 2s2p ^{3 1} P (365.6 Å) and 2s ²2p ^{2 3}P – 2s2p ^{3 3} S (359 Å) lines appear to be blended, possibly with transitions in Fex and Fexi/Fexiii, respectively. We note that the intensity ratio I(365.6 Å)/I(416.2 Å) should be a valuable calibration check for a high-resolution extreme ultraviolet instrument in the spectral range 360–420 Å.     

Wavelength predictions for the 1s 22s-1s2s3p satellite transitions

The experimentally known energies of the 1s ²2s 1s2s(¹ S, ³ S)3p transitions are considered for lithium to calcium. Their differences from the corresponding He-like resonances are fitted to the atomic number by means of a polynomial function and, through interpolation, the wavelengths for nitrogen to sodium are calculated.     

Emission line ratios for C III in the sun

Theoretical electron-density-sensitive C III emission line ratios are presented forR ₁ =I(2s2p ³ P – 2p ^{2 3} P)/I(2s2p ¹ P – 2p ^{2 1} S) =I(1176 Å)/I(1247 Å),R ₂ =I(2s2p ³ P – 2p ^{2 3} P)/I(2s ^{2 1} S – 2s2p ³ P ₁) =I(1176 Å)/I(1908 Å), andR ₃ =I(2s2p ¹ P – 2p ^{2 1} S)/I(2s ^{2 1} S – 2s2p ³ P ₁) =I(1247 Å)/I(1908 Å). These are significantly different from those deduced previously, principally due to the adoption of improved electron impact excitation rates in the present analysis. Electron densities deduced from the present theoretical line ratios, in conjunction with observed values ofR ₁,R ₂, andR ₃ measured from solar spectra obtained by the Naval Research Laboratory's S082B instrument on boardSkylab, are found to be generally compatible. In contrast, previous diagnostic calculations imply electron densities fromR ₁,R ₂, andR ₃ that differ by up to two orders of magnitude. These results provide observational support for the accuracy of the atomic physics adopted in the present calculations, and the methods employed in the derivation of the theoretical line ratios.     

Improved theoretical line ratios for Ciii in the Sun

The recent twelve-state R-matrix calculations of electron excitation rates in Ciii by Berrington are used to derive level populations applicable to the solar transition region. Line ratios R = I(2p ^{2 3} P ^e - 2s2p ³ P ^°)/I(2s2p ¹ P ^° - 2s ^{2 1} S ^e ) and R ₂=I(2p ^{2 1} S ^e - 2s2p ¹ P ^°)/I(2p ^{2 3} P ^e - 2s2p ³ P ^°) deduced from these data in conjunction with the relevent transition probabilities are found to be in much better agreement with the observed quiet Sun values than those determined from the level population calculations of Keenan et al.     

X-rays spectroheliograms in lines of Mg xi and Mg xii

Spectroheliograms in the L Mg xii line and in the Mg xi resonance (R) 1s ²¹ S ₀-1s2p ¹ P ₁ line, intercombination (I) 1s ²¹ S ₀-1s2p ³ P _1,2, line, and the forbidden (F) 1s ²¹ S ₀-1s2s ³ S ₁ line, have been obtained.Two Bragg crystal spectrometers were used mounted with mechanical collimators to obtain a spatial resolution of 1 × 3. The apparatus was launched on a sounding rocket on July 2nd, 1971. A particularly thorough study was made of the brightest active region (MC 11402).Variations in the F to I Mg xi line intensity ratio from one point to another in the active region did not reveal the presence of high electron densities.The observed intensities of the Mg xi R line, Mg xii L line and Mg x 1s ²2s ² S _1/2-1s2p ¹ P 2s × × ² P1_{1/2, 3/2} S line are not well explained by an isothermal model. Good agreement between computed and observed intensities is obtained using the non-isothermal model proposed here.     

Theoretical emission line strengths for the beryllium-like ion Sxiii compared to XUV observations of solar flares

A comparison of Skylab S082A observations for several solar flares with calculations of the electron temperature sensitive emission line ratio R ₁ = I(2s2p ¹ P – 2s ^{2 1} S)/I(2s2p ³ P ₁ - 2s ^{2 1} S) = = I(256.68 Å)/I(491.45 Å) in Be-like SXIII reveals good agreement between theory and experiment, which provides observational support for the accuracy of the adopted atomic data. However, observed values of the electron density sensitive ratio R ₂ = I(2s2p ¹ P – 2s ^{2 1} S)/I(2p ^{2 3} P ₂ - 2s2p ³ P ₂) = = I(256.68 Å)/I(308.96 Å) all lie below the theoretical high density limit, which is probably due to blending in the 308.96 Å line.     

Al xii line ratios in the Sun

Recent calculations of electron impact excitation rates in He-like Alxii are used to derive the theoretical electron temperature and density sensitive emission line ratios G ( = (f + i)/r and R ( = f/i, where f, i, and r are the forbidden 1s ^{2 1} S ? 1s2s ³ S, intercombination 1s ^{2 1} S ? 1s2p ³ P and resonance 1s ^{2 1} S ? 1s2p ¹ P transitions, respectively. These ratios are found to be significantly different from earlier calculations, and are in much better agreement with X-ray spectral data for two solar flares obtained with the SMM and P78-1 satellites.     

Fe XVIII EMISSION LINES IN SOLAR X-RAY SPECTRA

We have calculated intensity ratios for emission lines of Fexviii in the 13–94 Å wavelength range at electron temperatures characteristic of the solar corona, T _e = 2–10 x 10⁶ K. Our model ion includes data for transitions among the 2s ²2p ⁵ , 2s2p ⁶, 2s ²2p ⁴3l, and 2s2p ⁵3l (l = s, p, and d) states. Test calculations which omit the 2s2p ⁵3l levels show that cascades from these are important. We compare our results with observed ratios determined from four solar X-ray instruments, a rocket-borne spectrograph, and spectrometers on the P78–1, OV1–17 and Solar Maximum Mission (SMM) satellites. In addition, we have generated synthetic spectra which we compare directly with flare observations from SMM. Agreement between theory and observation is generally quite good, with differences that are mostly less than 30%, providing limited support for the accuracy of the atomic physics data used in our calculations. However, large discrepancies are found for ratios involving the 2s ²2p ^{5 2}P_3/2- 2s2p ^{6 2}S line at 93.84 Å, which currently remain unexplained. Our analysis indicates that the FeXVIII feature at 15.83 Å is the 2s ²2p ^{5 2}P_3/2 - 2s ²2p ⁴(³P)3s ⁴P_3/2 transition, rather than 2s ²2p ^{5 2}P_3/2 - 2s ²2p ⁴(³P)3s ²P_3/2, as suggested by some authors.     

Theoretical emission line ratios for Si XIII compared to solar observations

The electron collision excitation rates recently calculated for transitions in Si xiii by Keenan et al. (1987) are used to derive the electron temperature sensitive ratio G(=(f + i)/r and the density sensitive ratio R(=f/i), where i, f, and r are the intercombination (1s ^{2 1} S – 1s2p ³ P _{1, 2}) forbidden (1s ^{2 1} S – 1s2s ³ S), and resonance (1s ^{2 1} S – 1s2p ¹ P), transitions respectively. Also estimated are the values of R in the low-density limit (R ₀) as a function of electron temperature. The theoretical G ratio at the temperature of maximum emissivity for Si xiii, G(T _m) = 0.70, is in much better agreement with the observed G for the 1985, May 5 flare determined by McKenzie et al. (G = 0.60 ± 0.07) than is the earlier calculation of Pradhan, who derived G(T _m) = 0.85. The error in the observed R ₀ ratio is so large that both our result and Pradhan's fall within the acceptable limits of uncertainty and hence one cannot estimate which of the two is the more accurate.     

Variation in Ovii X-ray line-emission from the solar corona

The variation in intensity of the solar X-ray resonance (1s ^{2 1} S ₀ - 1s2p ¹ P ₁), intercombination (1s ^{2 1} S ₀ - 1s2p ³ P ₁), and forbidden (1s^{2 1} S ₀ - 1s2s ³ P ₁) lines of helium-like Ovii with 2800 MHz solar radio flux is presented for three solar rotations. A high correlation (r 0.80) exists between the intensities of all three X-ray lines and the 2800 MHz solar flux. The ratio of the forbidden to the intercombination line intensities is found to be essentially independent of long term solar activity. This ratio is used to determine upper limits on the coronal electron density and to make inferences concerning the change in density with solar activity.     

Observation of possible Fe xvii 2p 53p(1S0)-2p 53s(1 P 1, 3 P 1) transitions in spectra of a solar active region and flare

Expected wavelengths and relative intensities are obtained, from calculations of other workers, for the hitherto unobserved transitions 2p ⁵3p(¹ S ₀)-2p ⁵3s(¹ P ₁, ³ P ₁) in Fe xvii. A candidate pair of lines at 197.05 Å and 242.09 Å was found in laboratory spectra and appears to be present in the spectra of a solar active region observed by the OSO-7 Goddard spectroheliograph, and in the spectrum of a Skylab-observed solar flare.     

A Comparison of Theoretical mgvi Emission Line Strengths with Active-Region Observations From Serts

R-matrix calculations of electron impact excitation rates in N-like Mgvi are used to derive theoretical electron-density-sensitive emission line ratios involving 2s ²2p ³–2s2p ⁴transitions in the 269–403 Å wavelength range. A comparison of these with observations of a solar active region, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals good agreement between theory and observation for the 2s ²2p ^{3 4} S–2s2p ^{4 4} Ptransitions at 399.28, 400.67, and 403.30 Å, and the 2s ²2p ^{3 2} P–2s2p ^{4 2} Dlines at 387.77 and 387.97 Å. However, intensities for the other lines attributed to Mgvi in this spectrum by various authors do not match the present theoretical predictions. We argue that these discrepancies are not due to errors in the adopted atomic data, as previously suggested, but rather to observational uncertainties or mis-identifications. Some of the features previously identified as Mgvi lines in the SERTS spectrum, such as 291.36 and 293.15 Å, are judged to be noise, while others (including 349.16 Å) appear to be blended.     

The identification of Feix and Nixi in the solar corona

The levels of the configuration 3s ²3 _p ⁵3d of Fe ix have been experimentally determined from their combinations with 3s3 _p ⁶3d ³ D in the region 300–400 Å. Wavelengths can now be accurately predicted for all transitions within 3s ²3 _p 53^d, and eight of these can be identified with coronal lines from 2042 to 4585 Å. Also, identifications of solar lines from 171 to 245 Å with electric-dipole and magnetic-quadrupole transitions to the ground state, 3s ²3p ^{6 1} S, are confirmed and extended. Solar identifications with corresponding transitions in Ni xi, both within 3s ²3 _p ⁵3d and to the ground state, are proposed on the basis of a short extrapolation.     

Calcul des probabilités de transition pour divers états excités du Fe XII

Résumé On a calculé les probabilités de transition pour les raies interdites ou permises entre les états (3p²3d-3p³), (3p²4s-3p³), (3s3p⁴-3s²3p³), (3p²4d-3P³) du FeXII. Les niveaux d'énergie ²D_3/2, ²D_5/2, ²P_1/2, ²P_3/2 ont été obtenus par extrapolation le long de la séquence isoélectronique P1. On discute brièvement les effets d'un écart aux conditions de couplage L-S dus aux interactions spin-orbite et de configuration.

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Transition probabilities have been computed for forbidden or permitted lines within the (3p²3d-3p³), (3p²4s-3p³), (3s3p⁴-3s²3p³), (3p²4d-3p³) configurations in FeXII. Energy levels ²D_3/2, ²D_5/2, ²P_1/2, ²P_3/2 have been predicted by extrapolation along the isoelectronic sequence P1. The effects of departures from L-S coupling due to spin-orbit and configuration interaction are briefly discussed.

     

S xi Emission Lines in Active Region Spectra Obtained with the Solar euv Rocket Telescope and Spectrograph (Serts)

Theoretical electron density sensitive emission line ratios involving a total of eleven 2s ²2p ²–2s2p ³ transitions in Sxi between 187 and 292 Å are presented. A comparison of these with solar active region observations obtained during rocket flights by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals generally good agreement between theory and experiment. However, the 186.87 Å line is masked by fairly strong Fexii emission at the same wavelength, while 239.83 Å is blended with an unknown feature, and 285.58 Å is blended with possibly Niv 285.56 Å. In addition, the 191.23 Å line appears to be more seriously blended with an Fexiii feature than previously believed. The presence of several new Sxi lines is confirmed in the SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Å, in excellent agreement with laboratory measurements. In particular, the detection of the 2s ²2p ^{2 3} P ₁ –2s2p ^{3 3} P _0,1 transitions at 242.91 Å is the first time (to our knowledge) that this feature has been identified in the solar spectrum. The potential usefulness of the Sxi line ratios as electron density diagnostics for the solar transition region and corona is briefly discussed.     

Mg vii and Si ix line ratios in the sun

Recent R-matrix calculations of electron excitation rates for Mg vii and Si ix are used to determine the theoretical density sensitive emission line ratios R ₁= I(2s2p ^{3 1} D ⁰ - 2s ² 2p ^{2 1} D ^e )/I(2s2p ^{3 3} S ⁰ - 2s ² 2p ^{2 3} P ₂ ^e ) and R ₂= I(2s2p ^{3 1} P ⁰ - 2s ² 2p ^{2 1} D ^e )/I(2s2p ^{3 3} S ⁰ - 2s ² 2p ^{2 3} P ₂ ^e ). These are found to be quite similar to the earlier results of Mason and Bhatia. Electron densities derived using observed R ₁ and R ₂ ratios from Skylab NRL XUV spectra of solar flares and active regions are in good agreement, and compare favourably with those deduced from ions formed at similar electron temperatures to Mg vii and Si ix.     

Z-dependence of the level intervals in 2s 2 2p 2, 2s 2 2p 3 and 2s 2 2p 4

Values of the level intervals in the ground configurations 2s ² 2p ², 2s ² 2p ³ and 2s ² 2p ⁴ have been critically compiled from laboratory observations and from observations of nebular and coronal forbidden transitions. The data are represented within experimental errors by means of semi-empirical extrapolation formulae which contain from 3 to 5 adjusted parameters. The results provide means for checking laboratory and astrophysical identifications and measurements. Tables of best level values are given for the configurations concerned.     

Magnetic dipole transitions in the beryllium isoelectronic sequence

Configuration interaction wavefunctions are used to evaluate magnetic dipole transitions between the 2s ², 2s2p, and 2p ² states in the beryllium isoelectronic sequence. It is found that the contribution from the magnetic dipole transitions is negligible, even for moderately high Z and will not be an important process in any laboratory or astrophysical plasma. Some significant differences from previous calculations are obtained.