Board Skylab Research Articles

C IV line ratios in the sun

Recent R-matrix calculations of electron impact excitation rates for transitions in C IV are used to derive the theoretical electron temperature-sensitive emission-line ratios R1 = I(312.43 angstrom)/I(419.74 angstrom), R2 = I(3 84.14 angstrom)/I(419.74 angstrom), R3 = I(312.43 angstrom)/I(419.49 angstrom), and R4 = I(384.14 angstrom)/I(419.49 angstrom). A comparison of these with solar observational data obtained with the Naval Research Laboratory's S082A slitless spectrograph on board Skylab reveals good agreement between theory and observation for R2 and R4, which provides experimental support for the accuracy of the atomic data adopted in the analysis. However, most of the observed values of R1 and R3 lie above the theoretical high-temperature limit, which is probably due to blending of the 312.43 angstrom line.

Improved line ratio calculations involving delta-n = 1 (2-3) transitions in O V and a reanalysis of SKYLAB observations of solar flares

New R-matrix calculations of electron impact excitation rates in O v are used to rederive theoretical electron density diagnostic emission-line ratios involving transitions between the n = 2 and 3 levels, which includes lines at 192.80, 192.90, 215.10, 215.25, 220.35, and 248.46 angstrom. A comparison of these diagnostics with observational data for two solar flares obtained with the Naval Research Laboratory's S-082A spectrograph on board Skylab reveals better agreement between theory and observation than was found previously. This provides experimental support for the improved accuracy of the atomic data employed in the present analysis.

The 3s2 3p 2P-3s3p2 4P intercombination lines of Fe XIV in the sun

We have examined EUV spectra of solar flares obtained with the Naval Research Laboratory's S082A slitless spectrograph on board Skylab and provisionally identified the five components of the Fe XIV 3s 2 3p 2 P-3s3p 2 4 P intercombination multiplet. A comparison of the observed Fe XIV line intensities with theoretical predictions reveals good agreement between theory and experiment, which tends to confirm our identifications and those made previously by Trabert, Hutton, and Martinson. The potential usefulness of the lines as electron density diagnostics is briefly discussed

Fe XII line ratios in solar flares

view Abstract Citations (16) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fe XII Line Ratios in Solar Flares Tayal, S. S. ; Henry, Ronald J. W. ; Keenan, F. P. ; McCann, S. M. ; Widing, K. G. Abstract Relative level populations and the density-sensitive emission-line ratios R1 = I(186.87 A)/I(193.51 A), R2 = I(196.64 A)/I(193.51 A), and R3 = I(191.05 A/I(193.51 A) are derived using the recent R-matrix calculations of electron impact excitation rates for Fe XII over a wide range of electron densities (10 to the 9th - 10 to the 12th/cu cm) and at an electron temperature of 1.5 x 10 to the 6th K. These results are applied to solar active region and flare spectra obtained by the Naval Research Laboratory's S082A slitless spectrograph on board Skylab. Excellent agreement is found with observations. The electron densities deduced from Fe XII line ratios are also in agreement with those determined from Fe XIII and Fe XIV. Publication: The Astrophysical Journal Pub Date: March 1991 DOI: 10.1086/169786 Bibcode: 1991ApJ...369..567T Keywords: Line Spectra; Metallicity; Solar Flares; Solar Spectra; X Ray Spectra; Atomic Energy Levels; Emission Spectra; Iron; Skylab Program; Solar Electrons; Solar Physics; ATOMIC PROCESSES; SUN: FLARES; SUN: SPECTRA; X-RAYS: SPECTRA full text sources ADS |

NE VII line ratios in the sun

Theoretical Ne VII electron density sensitive emission-line ratios, derived using electron impact excitation rates calculated with the R-matrix code, are presented for R1 = I(561.7 A)/I(465.2 A) and R2 = I(561.4 A)/I(465.2 A). A comparison of these with observational data for solar flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals excellent agreement between theory and observation, which confirms the usefulness of R1 and R2 as Ne diagnostics for solar flares, as well as providing experimental support for the accuracy of the atomic data adopted in the line ratio calculations. 36 refs.

NIV line ratios in the Sun

Theoretical Niv emission line ratios, which incorporate several improvements over previous estimates, are presented for R1 = I(923.2 A)/I(765.1 A) and R2 = I(1718.6 A)/I(1486.5 A), which are electron density and temperature sensitive, respectively. A comparison of R1 with observational data for several solar features obtained with the Harvard S-055 spectrometer on board Skylab reveals generally good agreement between theory and observation, except for the quiet Sun, which is probably due to the 923.2 A line being blended with an Feiii transition in this instance. The observed value of R2, determined from a quiet-Sun spectrum obtained by the S082-B spectrograph on board Skylab, implies an electron temperature in excellent agreement with that of maximum Niv fractional abundance in ionisation equilibrium, which provides observational support for the accuracy of the diagnostic calculations.

Argon XV line ratios in the sun

view Abstract Citations (13) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Argon XV Line Ratios in the Sun Keenan, F. P. ; Widing, K. G. ; McCann, S. M. Abstract Theoretical Ar XV emission-line ratios are presented for R1 = I(2s2p 1P-2s2 1S)/I(2s2p 3P1-2s2 1S) = I(221.12 A)/I(423.98 A) and R2 = I(2s2p 1P-2s2 1S)/I(2p2 3P2-2s2p 3P2) = I(221.12 A)/I(266.23 A), which are electron temperature and density sensitive, respectively. A comparison of these with observational data for solar flares obtained with the NRL S082A slitless spectrograph on board Skylab reveals that there is good agreement between theory and observation for R1, which provides experimental support for the accuracy of the atomic data adopted in the analysis. However the observed values of R2 all lie below the theoretical high-density limit, which may be due to blending of the 266.23 A transition with an unidentified line. Publication: The Astrophysical Journal Pub Date: March 1989 DOI: 10.1086/167218 Bibcode: 1989ApJ...338..563K Keywords: Argon; Line Spectra; Solar Flares; Solar Spectra; Stellar Composition; Atomic Energy Levels; Satellite-Borne Instruments; Skylab Program; Solar Spectrometers; Spectrum Analysis; Solar Physics; ATOMIC PROCESSES; SUN: FLARES; SUN: SPECTRA; ULTRAVIOLET: SPECTRA full text sources ADS |

A comparison of theoretical O iii line strengths with XUV solar observations from the S082A instrument on board Skylab

Relative level populations in Oiii, determined using R-matrix calculations of electron impact excitation rates, are used to derive the theoretical emission line ratios R1 = I(525.80 A)/I(599.62 A), R2 = I(507.41 A)/I(599.62 A), R3 = I(507.71 A)/I(599.62 A), and R4 = I(508.18 A)/I(599.62 A). Electron temperatures deduced from the observed values of these ratios for several solar features obtained with the NRL S082A slitless spectrograph on board Skylab are in good agreement, and also compare favourably with that of maximum Oiii fractional abundance in ionisation equilibrium, logTmax = 4.96. These results provide experimental support for the accuracy of the atomic data adopted in the line ratio calculations.

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 A) and 2s 22p 2 3P − 2s2p 3 3 S (359 A) lines appear to be blended, possibly with transitions in Fex and Fexi/Fexiii, respectively. We note that the intensity ratio I(365.6 A)/I(416.2 A) should be a valuable calibration check for a high-resolution extreme ultraviolet instrument in the spectral range 360–420 A.

Si III electron temperature diagnostics for the solar transition region

R-matrix calculations of electron impact excitation rates for transitions in Si iii are used to derive the electron-density-sensitive emission line ratios R 1 = I(1113.2 A)/I(1206.3 A), R 2 = I(1298.9 A)/I(1206.3 A), and R 3 = I(1296.7 A)/I(1206.3 A). A comparison of these with observational data for several solar features obtained with the Harvard S-055 spectrometer on board Skylab reveals that theory and experiment are compatible if the electron temperature of the Si iii emitting region of the solar atmosphere is log T e = 4.5, but not if log T e = 4.7. The implication of the choice of a lower temperature on the electron energy distribution function is also briefly discussed.

S vi line ratios in the Sun

R-matrix calculations of electron impact excitation rates in S vi are used to determine the theoretical temperature sensitive emission line ratios \(R1 = I(3d^2 D3/2,5/2 - 3p^2 P3/2)/I(3p^2 P1/2 - 3s^2 S1/2) = I(712.8{\AA})/I(944.5{\AA})\) and \(R1 = I(3d^2 D3/2,5/2 - 3p^2 P3/2)/I(3p^2 P1/2 - 3s^2 S1/2) = I(712.8{\AA})/I(933.4{\AA}),\) which are found to be up to 30% larger than the earlier results of Flower and Nussbaumer. A comparison of the present data with solar observations from the Harvard S-055 spectrometer on board Skylab implies that the 944.5 A transition may be blended with lines from species with relatively low ionization potentials, in contrast to the findings of Flower and Nussbaumer. The 712.8 A transition may also be similarly blended.

Theoretical Siiv line ratios compared to extreme ultraviolet solar observations

New theoretical electron temperature sensitive emission line ratios in Siiv involving the 3d2D − 3p2P and 4s2S − 3p2P multiplets at ∼1125 and 816 A, respectively, are derived using recent R-matrix electron excitation rate calculations. A comparison of these with observational data for a solar active region at the limb obtained with the Harvard S-055 spectrometer on board Skylab reveals that there is good agreement between theory and observation for ratios that include the 2D3/2, 5/2 − 2P3/2 transition at 1128.3 A. This is in contrast to the findings of Keenan, Dufton, and Kingston (1986) and provides support for the atomic data adopted in the calculations. However, the 2D3/2 − 2P1/2 line at 1122.5 A appears to be severely blended, as suggested previously by Burton and Ridgeley (1970) and Feldman and Doschek (1977), as it leads to electron temperature estimates that differ significantly from that expected in ionisation equilibrium. The fact that the I(1122.5 A)/I(1128.3 A) intensity ratios determined from several flare spectra are closer to theory than that for the active region indicates that the blending is probably due to species with relatively low ionization potentials, as noted by Flower and Nussbaumer (1975). Electron temperatures deduced for a sunspot are much lower than that predicted from ionisation balance calculations, in agreement with earlier results, and imply that a cooling flow may be present.

Euv Emission Line Ratios for Si IV in the Solar Transition Region

AbstractTheoretical electron temperature sensitive emission line ratios in Si IV involving the 3d2D − 3p2P and 4s2S - 3p2P multiplets at ~1125A and 816A respectively are derived using R-matrix electron excitation rate calculations. A comparison of these with observational data for a solar active region obtained with the Harvard S-055 spectrometer on board Skylab reveals that there is good agreement between theory and observation for the ratio that includes the2D3/2, 5/2 −2p3/2 transition at 1128.3A. This is in contrast to the findings of Keenan, Dufton and Kingston, and provides support for the atomic data adopted in the calculations. However the2D3/2 −2pl/2 line at 1122.5A appears to be severely blended, as it leads to electron temperature estimates that differ significantly from that expected in ionisation equilibrium. The fact that the I(1122.5A)/I(1128.3A) intensity ratios determined from several flare spectra are closer to theory than that for the active region indicates that the blending is probably due to species with relatively low ionisation potentials, such as an Fe III transition at 1122.53A, as suggested previously by Burton and Ridgeley, and Feldman and Doschek. Electron temperatures deduced for a sunspot are much lower than that predicted from ionisation balance calculations, in agreement with earlier results, and imply that a cooling flow may be present.

Theoretical Ne v emission line ratios compared to solar observations

The recent level population calculations for Ne v by Aggarwal are used to determine the theoretical emission line ratios R1 = I(2s2p31Do - 2s22p21De)/I(2s2p33D20- 2s22p23P1e) and R2 = I(2s2p31Do-2s22p21De)/I(2s2p33D30-2s22p23P2e). A comparison of these with observational data for a solar flare and erupting prominence obtained with the NRL XUV spectrograph on board Skylab reveals that R1 and R2 are in their predicted high density limits. Although the ratios cannot be used as density diagnostics for values of ne typical of the solar transition region, it is shown that they are temperature sensitive and hence may be employed to determine the electron temperatures of Ne v line emitting regions.

Physical properties of individual coronal loops in a solar active region observed in the XUV

The physical properties of individual coronal loops in a solar active region observed in the XUV by the slitless objective grating spectroheliograph on board Skylab are investigated. Spectroheliograms of the normal active loop region McMath 12378 reveal three distinctive structural groups of loops in different temperature ranges, namely (1) small compact and smaller loops at temperatures of about 2,000,000 K observed in Fe XV and Fe XVI; (2) large Ne VII and Mg IX loops at temperatures from 500,000 to 1,000,000 K; and (3) chromospheric ribbons in He II and H alpha. The temperature of the active region is found to be uniform at about 2,000,000 K in the loops and background while loop density is found to be 3.5 x 10 to the 9th/cu cm in the loops and 2.5 x 10 to the 9th/cu cm in the surrounding background. Significant changes in the active region are observed in 24 h, although the gross temperature density structures of many loops do not show changes in 7 min. Gas pressure within the coronal loops is found to be about 40% greater than that of the background plasma. The observed loop parameters are noted to be consistent with flux-limited models of density enhancement in magnetic flux tubes and thus no esoteric heating function is required.

A Model of Surge

This paper reports on the application of a siphon flow model to the late stage of a surge observed in the UV radiation by the S055 experiment on board Skylab. The MgX λ625 and OVI λ1032 emissions from the density distributions occurring in flows which become supersonic at the top of the loop agree with the observations, indicating a pressure drop, along the loop, of a factor of 4 for the plasma emitting the OVI line, and of a factor of 2 for the plasma emitting the MgX line.

Limb darkening 1945-3245 A for the quiet sun from SKYLAB data

Limb-darkening measurements of the quiet sun in the spectral range 1945-3245 A have been made using NRL's SO82B instrument on board Skylab. The spectral intensities have been averaged over 10 A wavelength bands, and coefficients for linear, quadratic, and logarithmic fits to the observed center-to-limb variations have been calculated and tabulated as a function of wavelength. The quadratic fits are found to represent the observations best, the observed and calculated values agreeing to better than plus or minus 15% on the average. Attention is drawn to the value of the results for ultraviolet photometry of eclipsing binaries.

A survey of soft X-ray limb flare images - The relation between their structure in the corona and other physical parameters

The data used in the investigation were obtained by the American Science and Engineering S-054 experiment on board Skylab. The instrument employed was a grazing incidence X-ray telescope which records images of the sun on film. The morphology of limb flares is investigated and the observed spatial structure is related with the other physical parameters of the region (temperature, density, characteristic times, and energy density). It is concluded that two physically distinct classes of flares exist that differ both in their morphology and in the physical properties which characterize the emitting regions.

A Discussion on the physics of the solar atmosphere - A.t.m. observations on the X u.v. emission from solar flares

Far ultraviolet spectroheliograms (190-465 A) and ultraviolet spectra (900-1900 A) of selected flares obtained on board Skylab by two instruments of the Naval Research Laboratory are presented. Time sequences of three events are discussed in detail; they are compared with simultaneous X-ray measurements from the N.R.L.’s Solrad 9 and from the OSO-7 X-ray spectrometer of the University of California, San Diego. In all events, where proper observational coverage was obtained, a small kernel seems to be the source of the prime energy release of a flare. The size of this kernel is determined by the spatial resolution of the spectroheliograph, which is approximately 2". Densities in this kernel exceed 3 x 1012 cm-3. Ion temperatures in a subflare kernel are determined to be larger than 20 MK. It is very likely, that these temperatures are much higher in the flare kernel of more energetic events. Hot clouds of coronal gas at 20 MK surround the kernel. These clouds are trapped below high magnetic structures, and subsequently seem to be the energy reservoir for heating the post flare loops. During the explosive phase, strong Doppler broadening can be seen, especially in transition zone lines of the brightened plages. These can be interpreted as impact of high energetic particles guided down to the solar surface along the loops. The observations suggest that high speed mass motions have their origin in the exploding flare kernel.

The large coronal transient of 10 June 1973

During the 8.5 month flight of the High Altitude Observatory's white light coronagraph on board Skylab, over 100 coronal transients were observed. In this paper we present a description of one well observed loop transient, that of 10 June 1973. The transient apparently resulted from the eruption of a quiescent prominence on the limb; the emergence of a new, bipolar active region near the prominence may have caused the eruptior. The transient's leading edge rose from 3.6 to 5.0 solar radii (R ⊙) from Sun center at approximately 500 km s−1 during the 32 min of coronagraph observations. Material in a pre-existing streamer was swept away by the transient, causing the streamer to disappear. The mass ejected into the corona above a projected height of 2 R ⊙ was ≈ 5.4 × 1015 g, the potential energy associated with the ejected transient material was ⩾7.0 × 1030 erg, and the kinetic energy of the ejected material is estimated as 1.7 × 1030 erg. The 10 June 1973 transient was, in most respects, typical of other loop transients observed by Skylab.