The innermost corona observed at the 1973 June 30 eclipse

Slitless flash spectrograms in heights below 8000 km above the solar limb were obtained by the University of Kyoto Expedition at Atar, Mauritania. The integrated intensities of Fexiv 5303, Fex 6374, Fexi 7892, and the continuum are measured as a function of height above the solar limb at eleven points (P.A. = 284–300°) around the third contact point. It is found that a significant amount of the emission in Fex 6374 originates in chromospheric levels well below 8000 km. This implies that the interspicular region of the chromosphere is occupied by coronal material. The average values of the electron temperature and the electron density in the interspicular region are derived from the Fex 6374 and the Fexi 7892 intensities on the assumption of spherical symmetry: T _e = 0.9–1.1 × 10⁶ K and N _e = 9–10 × 10⁸ cm^–3. The intensity variations of the coronal lines and the continuum with position angle are also studied. Strong correlations between Fexiv 5303 and the continuum and between Fex 6374 and Fexi 7892 are found. From the Fex 6374 intensities it is inferred that there is a density fluctuation in the innermost corona by at least a factor of two.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 271.     

Emission line ratios for Fexxi applicable to the XUV spectra of solar flares

Electron impact excitation rates for Fexxi, calculated with theR-matrix code, are used to determine theoretical electron density sensitive emission line ratios involving transitions in the 121–146 wavelength range. The observed ratios for a solar flare, obtained with a grazing spectrometer on board the OSO-5 satellite, imply electron densities which are consistent, with discrepancies that do not exceed 0.3 dex. In addition, the derived values ofN _e are similar to those estimated for the high temperature regions of other solar flares. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations.     

The UV spectrum of the binary system SZ Psc

In this paper we study the far-UV as well as the UV spectrum of the spectroscopic binary system SZ Psc in the wavelength ranges 1235–1950 Å and 2710–3090 Å, respectively, from spectra obtained with the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc is mainly an emission spectrum. The short wavelength region includes emission lines formed from the low chromosphere to the transition region (e.g., Siiv,Civ, andNv) and also a deep and broad absorption line of Feii.The Mgii[1] resonance doublet at about 2800 Å presents a P Cygni profile and a multiple structure with two emission and two absorption satellite components. We also present the emission measure diagram in the temperature region 4.4T _e <53.     

Ar XIII line ratios in solar flares

Theoretical ArXIII electron-density-sensitive emission line ratios, derived using electron impact excitation rates interpolated from accurateR-matrix calculations, are presented forR ₁ =I(242.22 )/I(236.27 ),R ₂ =I(210.46 )/I(236.27 ), andR ₃ =I(248.68 )/I(236.27 ). Electron densities deduced from the observed values ofR ₁,R ₂, andR ₃ for solar flares obtained with the NRL S082A slitless spectrograph on boardSkylab are in excellent agreement, and furthermore compare favorably with those determined from line ratios in CaXV, which is formed at a similar electron temperature to that of ArXIII. These results provide experimental support for the accuracy of the atomic data adopted in the analysis, as well as for the techniques used to calculate the line ratios.     

Mass-luminosity distribution and physical conditions of ionized gas in NGC 4575

Photographic photometry and spectroscopic observations of NGC 4575 suggest it to be a galaxy of reduced dimensionsD×d=14.4×13.5 kpc and of high luminosityM=–20.7. The rotation curve was also determined. Assuming a model of three homogeneous similar spheroids, we derived the density and mass distribution, and their total mass was found to be _T =2.33 × 10¹⁰.The mass luminosity ratio does not vary withinr=24, indicating that the stellar composition is similar within it, and the ratio _T / _T 1 suggests that this object contains a high proportion of young stars. From the emission lines it is found that the electronic density Ne100 cm^–3 is relatively low in the HII regions. The abundance ratiosN(N)/N(S) andN(N)/N(H) for the nucleus and two emission regions were also derived.     

On the coronal lines in the chromosphere at the 1970 eclipse

Spectrographic observations of the flash spectrum were made by the Kwasan Observatory at the total solar eclipse on 7 March, 1970. The integrated intensities of Fexiv 5303, Fex 6374, and the continuum were measured on the spectrograms as a function of height above the Sun's limb. It was found that a large amount of emission in the coronal lines originates in the interspicular regions of the chromosphere. Analysis of the data yielded that the interspicular regions consist of coronal material of T _e = 1.6 × 10⁶–1.2 × 10⁶ and log N _e = 8.5–9.5, and that a decrease in T _e and an increase in N _e occur with decreasing height.     

Transitions in highly ionized silicon

Configuration interaction wavefunctions are used to calculate energy levels, wavelengths, oscillator strengths, line strengths, transition probabilities, lifetimes and branching ratios for absorption transitions between the 2lnl [n = 2, 3;l l] states for Si xi. Comparison with recent beam-foil experimental data for the 2s2p ¹ P, 2p ^{2 1} D and 2p ^{2 1} S states is generally good, though in some cases cascade effects may be larger than had been expected.     

Ca X line ratios in solar flares

Theoretical Ca X electron temperature sensitive emission line ratios, derived using electron excitation rates interpolated from accurateR-matrix calculations, are presented forR ₁ =I(419.74 )/I(574.02 ,),R ₂ =I(411.65 )/I(574.02 ),R ₃ =I(419.74 )/I(557.75 ), andR ₄ =I(411.65 )/I(557.75 ). A comparison of these with observational data for three solar flares, obtained by the Naval Research Laboratory's S082A slitless spectrograph on boardSkylab, reveals good agreement between theory and observation forR ₁ andR ₃ in one event, which provides limited support for the accuracy of the atomic data adopted in the analysis. However, in the other flares the observed values ofR ₁ –R ₄ are much larger than the theoretical high-temperature limits, which is probably due to blending of the 419.74 line with Civ 419.71 , and 411.65 with possibly Ciii 411.70 .     

Electron densities above a polar coronal hole based on improved Si IX density diagnostics

Using new close-coupling excitation rates for the C-like ion Siix, density-diagnostic ratios based on Siix lines have been re-evaluated and applied to a sequence of CDS observations taken above a polar coronal hole. The derived electron densities are in excellent agreement with previous values of N_eestimated from the N-like ion Siviii for another coronal hole. The confirmed trend is for a fall-off of one order of magnitude within the first 0.3 Rabove the limb. These densities are well fitted with an analytic formula for the density profile out to at least 8 R, by which stage the electron density has fallen to 4×10³ cm^–3, from 1.5×10⁸ cm^–3at 1.0 R.     

The peculiarities of diffusion of the galactic cosmic rays at low energies

I give an interpretation of a result of Simpsonet al. (1988) on the variation with kinetic energyT _i of the mean pathlengthX _m (T _i ) of the galactic cosmic rays (CGRs) in the range 0.1T _i 10.0 GeV nucl^–1. I argue that the data onX _m (T _i ) may be interpreted in terms of a model of GCR diffusion on the one-dimensional Alfvén-wave turbulence, having a cutoff in the spectrum at frequencies _h , where _h is the proton gyrofrequency. The cutoff results in changing of the character of variation of the GCR diffusion coefficientD(T _i )T ^a in the rangeT _i 1 GeV nucl^–1 towards some more complicated variation at 0.1T _i 1.0 GeV nucl^–1 due to the peculiarities of the pitch-angle scattering at 90⁰.     

Extreme Ultraviolet Emission Lines of ca xv in Solar and Laboratory Spectra

New R-matrix calculations of electron impact excitation rates in Caxv are used to derive theoretical electron density diagnostic emission line intensity ratios involving 2s ²2p ²–2s2p ³ transitions, specifically R ₁=I(208.70 Å)/I(200.98 Å), R ₂=I(181.91 Å)/I(200.98 Å), and R ₃=I(215.38 Å)/I(200.98 Å), for a range of electron temperatures (T _e=10^6.4–10^6.8 K) and densities (N _e=10⁹–10¹³ cm^–3) appropriate to solar coronal plasmas. Electron densities deduced from the observed values of R ₁, R ₂, and R ₃ for several solar flares, measured from spectra obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, are found to be consistent. In addition, the derived electron densities are in excellent agreement with those determined from line ratios in Caxvi, which is formed at a similar electron temperature to Caxv. These results provide some experimental verification for the accuracy of the line ratio calculations, and hence the atomic data on which they are based. A set of eight theoretical Caxv line ratios involving 2s ²2p ²–2s2p ³ transitions in the wavelength range 140–216 Å are also found to be in good agreement with those measured from spectra of the TEXT tokamak plasma, for which the electron temperature and density have been independently determined. This provides additional support for the accuracy of the theoretical line ratios and atomic data.     

Echelle observations of C iii λ1909 and Si iii λ1892

Profiles of C iii 1909 and Si iii 1892 obtained on and near the limb during the 1976 flight of the University of Hawaii echelle rocket spectrograph were reduced and analyzed to determine electron densities and mass motions. The electron pressure derived (N _eT_e 4 × 10¹⁵ cm^–3) agrees well with that determined by Cook and Nicolas (1979) from ATM data. Nonthermal velocities in the region of formation of Si iii 1892 on the disk were found to be 10–12 km s^–1, somewhat lower than the values obtained by Doschek et al. (1976), also from ATM spectra. However, velocities derived at and above the limb were in closer agreement, about 17 km s^–1.Geosciences Systems Department, Computer Sciences Corporation, 8728 Colesville Road, Silver Spring, Md. 20910, U.S.A.     

Physical conditions of ionized gas and mass-luminosity distribution in NGC 7793

The physical state of ionized gas in NGC 7793 was studied by spectroscopical means: the electronic temperature isT _e10⁴K while the electronic density ranges fromN _e1400 cm^–3 in the nucleus toN _e1000 cm^–3 in the emission regions. There are also indications of an excess of nitrogen in the nucleus. TheM/L ratio suggests for NGC 7793, a high proportion of young objects quite uniformly distributed over its body, with a slight concentration towards the nuclear region.     

Correlation of He II lyman alpha with He I 10830 Å, and with chromospheric and EUV coronal emission

This paper describes the results of comparing SERTS-3 images obtained in the transition region line of Heii 304 with chromospheric Hei 10830 absorption, with strong coronal lines of Mgix 368 , Fexv 284 and 417 , and Fexvi 335 and 31 , with H, with Caii 8542 , and with magnetograms in Fei 8688H. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the Heii 304 and Hei 10830 images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 than in 304 . In active regions, the 304 line follows more closely the behavior of H and Caii 8542 than the 10830 line.     

Analysis of the hyades giant stars ε and γ Tau

Two hyades giant stars, and Tau, have been studied from an analysis of strong line profiles. We get for Tau,T _e =4750K and logg=2.7, and for Tau,T _e =4700K and logg=2.8. Hydrogen-to-metal ratio for the two stars is nearly the same as that of solar value.     

Extreme ultraviolet spectra of solar active regions and their analysis

Extreme ultraviolet spectra of several active regions are presented and analyzed. Spectral intensities of 3 active regions observed with the NRL Skylab XUV spectroheliograph (170–630 Å) are derived. From this data density sensitive line ratios of Mg viii, Si x, S xii, Fe ix, Fe x, Fe xi, Fe xii, Fe xiii, Fe xiv, and Fe xv are examined and typically yield, to within a factor of 2, electron pressures of 1 dyne cm^–2 (n _e T = 6 × 10¹⁵ cm^–3 K). The differential emission measure of the brightest 35 × 35 portion of an active region is obtained between 1.4 × 10⁴ K and 5 × 10⁶ K from HCO OSO-VI XUV (280–1370 Å) spectra published by Dupree et al. (1973). Stigmatic EUV spectra (1170–1710 Å) obtained by the NRL High Resolution Telescope and Spectrograph (HRTS) are also presented. Doppler velocities as a function of position along the slit are derived in an active region plage and sunspot. The velocities are based on an absolute wavelength scale derived from neutral chromospheric lines and are accurate to ±2 km s^–1. Downflows at 10⁵ K are found throughout the plage with typical velocities of 10 km s^–1. In the sunspot, downflows are typically 5 to 20 km s^–1 over the umbra and zero over the penumbra. In addition localized 90 and 150 km s^–1 downflows are found in the umbra in the same 1 × 1 resolution elements which contain the lower velocity downflows. Spectral intensities and velocities in a typical plage 1 resolution element are derived. The velocities are greatest ( 10 km s^–1) at 10⁵ K with lower velocities at higher and lower temperatures. The differential emission measure between 1.3 × 10⁴ K and 2 × 10⁶ K is derived and is found to be comparable to that derived from the OSO-VI data. An electron pressure of 1.4 dynes cm^–2 (n _e T = 1.0 × 10¹⁶ cm^–3 K) is determined from pressure sensitive line ratios of Si iii, O iv, and N iv. From the data presented it is shown that convection plays a major role in determining the structure and dynamics of the active region transition zone and corona.     

Measurement of the relative intensities of Heζ-H8 lines λ3889Å in the spectrum of the chromospheric spicules at various heights above the limb

A series of 31 large scale spectra of the spicules near H8-He lines 3889 Å has been photographed at different heights (1500–5000 km) with 53-cm coronagraph. The solar image was 121 mm in diameter, dispersion and spatial resolution were respectively 0.647 Å mm^–1 and 1–2. Equivalent widths of both lines have been measured and ratio R = EW_He/EW_H8 was obtained. T _e(h) distribution in the averaged spicule deduced differs from that in the recent spicule model by Beckers (1972): the spicules are colder greatly than it was accepted hitherto (T _e 10000 K). The electron temperature in the quiescent prominence which occurred in the spectra was also estimated: T _e 6000 K at h = 4000 and 5000 km.     

A model of impulsive loop flares revisited

A critical examination of the components of the recent impulsive loop flare model of Takakura is made. It is found that his analysis of the stability of the electron distribution resulting from anomalous heat conduction is in error and electron plasma waves would not be excited. Rather, in the regions where the electron/proton temperature ratioT _e/T _i 10, electrostatic ion-cyclotron waves would be excited and in the regions whereT _e 10, ion-acoustic waves would be excited. Ratios ofT _e/T _i 10 occur only in the late time development behind the conduction fronts. Since the anomalous resistivity due to electrostatic ion-cyclotron waves is fortuitously about 70% of the one used by Takakura, the general development will follow closely the one calculated by him. Because the anomalous resistivity due to ion-acoustic waves is about 95 times the one used by Takakura, the development in the parts of the loop whereT _e/T _i 10 for late times would be altered considerably.Also Guest Worker at NOAA Space Environment Laboratory, Boulder, Colorado, U.S.A.     

Solar X-ray spectra observed from the ‘Intercosmos-4’ satellite and the ‘Vertical-2’ rocket

Results are given of the detailed analysis of fourteen Fe xxv-xxiii lines ( = 1.850–1.870 Å) in the spectra of a solar flare on 16 Nov. 1970. The spectra were obtained with a resolution of about 4 × 10^–4 Å, which revealed lines not previously observed and allowed the measurement of line profiles. The measured values of the wavelengths and emission fluxes are presented and compared with theoretical calculations. The analysis of the contour of the Fe xxv line ( = 1.850 Å) leads to the conclusion that there is unidirectional macroscopic gas motion in the flare region with the velocity (projection on the line of sight) ± 90 km s^–1.Measurements of the 8.42 Å Mg xii and 9.16 Å Mg xi lines in the absence of solar flares indicate prolonged existence of active regions on the solar disk with T _e = 4–6 × 10⁶K and emission measure ME 10⁴⁸ cm^–3. The profile of the Mg xii line indicates a macroscopic ion motion with a velocity up to 100 km s^–1.     

On intensity ratios of helium and hydrogen lines in quiescent prominences

Observations of the lines He i 3888 and H8 in 80 quiescent prominences by the author, and in other prominences by Kubota et al. (1972) and Morozhenko (1971), have been used to derive the dependences of I(3888)/I(H8) on I(H8), N ₂ ³ _s on ₀ (H), and N ⁺ n _e on ₀(H) (Figures 1, 2, 3 and 4). The equations of ionization equilibrium and triplet system steady state for a helium atom (27 levels and continuum were considered) were solved together with the radiation transfer equation in the helium Lyman continuum. As given n _e () distribution with depth and T _e =7500 K were assumed. The 2³ S level population N₂ ³ s, helium emission measure N ⁺ n _e and the intensity ratios of the He i 3888 and H8 lines were calculated and compared with observation (Figures 2, 3 and 4, solid lines). The figures show that in bright prominences the observed values of N ₂ ³ s and N ⁺ n _e are systematically higher than the calculated ones. These deviations cannot be eliminated by decreasing n _e . One can make the calculations and observations agree for bright prominences by increasing the UV radiation which penetrates into the prominence.