Diagnostics of solar ions: Ne VI,Mg VI,Si VIII and Mg VIII observed by SERTS

Diagnostics of solar ions Nevi, Mgvi, Siviii, and Mgviii in an active region observed by SERTS have been presented. Density, temperature, and electron pressure in the emitting source have been derived from theoretical line-ratio curves and its EUV spectrum obtained by SERTS. The variation of neon-to-magnesium and silicon-to-magnesium abundances has been discussed in the interpretation of the active region spectrum obtained by SERTS.     

The symbiotic stellar lines at 6830 Å, 7088 Å; An origin in optically thick fluorescence

The question of the origin of the symbiotic stellar lines at 6830 Å and 7088 Å, recently proposed to arise from Raman scattering of ultraviolet Ovi lines by hydrogen, is examined quantitatively by comparing line intensities expected from this process with the intensity of an Feii line photoexcited by one of the same Ovi lines. It appears that Raman scattering does not yield sufficient intensity to account for the symbiotic lines. An alternative mechanism for producing the lines exists, however, in off-line-center photoexcitation of optically thick hydrogen by the Ovi lines. This gives intensities which are higher than Raman intensities, and which are more consistent with the Feii fluorescent line intensity. Observed further redward shifts are also explained by the mechanism. It is therefore suggested that the proposed hypothesis of Ovi–Hi interaction may be valid, but that the process involved is probably not second-order Raman scattering but first-order fluorescent scattering.     

WR stars with the Ovi λλ3811, 3834 emission doublet

The catalog of the classical WR stars which have the emission doublet Ovi 3811, 3834 in their optical spectra (the catalog of the WR-Ovi stars) and the results of the spectroscopic investigations of the WR-Ovi stars HD 16523, HD 17638, and HD 192103 are presented. Rapid spectral variability of the emission doublet Ovi 3811, 3834 in the spectra of WR-Ovi stars HD 16523, HD 17638, and of the emission band 3680-3780 Å in the spectra of the WR-Ovi star HD 16523 is observed. It is shown that spectral sub-types of the stars HD 16523 and HD 17638 as estimated from different criteria are uncertain. We argue that the WR-Ovi stars HD 16523 and HD 17638, the optical spectra of which display emission doublet Ovi 3811, 3834, may be considered as WO5 stars. The sub-type WO5 is proposed for the first time. Classification criteria of the WO5 sub-type are represented. The possible contribution of the ions Heii to the emission at 3811 Å and 3834 Å is investigated. Thez-distributions of WR-Ovi stars and WR stars with the probable relativistic companions are found to be similar.     

The interpretation of XUV rocket measurements of intensity ratios of solar spectral lines of the lithiumlike ions O vi,Ne viii,and Mg x

A rocket borne spectrometer was flown to measure absolute intensities of extreme ultraviolet spectral lines from the three ions O vi, Ne viii, and Mg x present in the Sun. From these measurements, intensity ratios of lines from O vi, ratios of lines from Ne viii, and ratios of lines from Mg x were formed. These experimental ratios were compared with ratios calculated by using specific theoretical values of the ionization equilibrium in which dielectronic recombination was included in the processes establishing ionization balance. The effects of the electron density and temperature gradient on the temperature distribution of the flux of the spectral lines in the solar atmosphere have been taken into account in the calculations of the ratios. The agreement between the experimental and calculated ratios is good for the ions Ne viii and Mg x and satisfactory for the ion O vi for which the calculated ratio is subject to large uncertainties. A reliable measurement of the electron temperature in the lower corona was obtained from the experimental ratios for Mg x. This experimental temperature is in good agreement with the emission temperature of the spectral lines of Mg x predicted from the theoretical values of the ionization equilibrium. The design and photometric calibration of a new rocket spectrometer developed to measure the intensity ratios over the broad spectral region 50 to 1250 Å are also described.     

Excitation equilibrium for low lying levels in Cii,Niii, Oiv,Nevi, Mgviii,Six, and Siii

The populations of the excited state ² P _3/2 relative to the ground state ² P _1/2 have been investigated in C ii, N iii, O iv, Ne vi, Mg viii, Si x, and Si ii by considering all the radiative and collisional processes including the collisional transitions to the higher states which cascade to the upper level. The relative populations are used for the calculation of the line emissivities. The intensities of 76 320, 30 258 and 14 302 lines of Nevi, Mgviii, and Six ions respectively in the chromosphere-corona transition region are also calculated.     

Ovi and Heii emission lines in the spectra of quasars

The plasma-laser star model for quasars, which is based on the hypotheses that there is no red shift in the spectra of quasars and that the strength of the emission lines is due to laser action, is further developed. Continuity is shown to exist between the spectra of Ovi sequence planetary nuclei, Sanduleak stars, and 10 quasars. The Ovi 3811, 3834 and Heii 4686 emission lines in the spectra of these 10 quasars are identified. Candidate identifications for other quasar lines are also suggested. Making use of the similarity between the spectra of Ovi sequence planetary nuclei and those of the 10 quasars, absolute magnitudes, temperatures, and masses of these quasars are estimated. The distribution of quasars in galactic coordinates is also discussed. Three predictions are made.     

O VI (λ = 1032 Å) profiles in and above an active region prominence,compared to quiet Sun center and limb profiles

O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s^–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s^–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 10⁶ K, and a non-thermal velocity (NTV) of 49 km s^–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines.     

Solar XUV limb brightening observations

OSO-IV observations of the equatorial limb brightening of XUV resonance lines of Nv, O vi, Ne viii, Mg x and Si xii are interpreted with a modified version of a coronal model developed by Dupree and Goldberg (1967). Good agreement is obtained between the observed limb brightening and that predicted by the model. The sensitivity of the predicted limb-brightening curves to changes in parameters describing the model is discussed. Coronal abundances for N, O, Ne, Mg, and Si are obtained.     

Area variation with temperature of supergranule network features in the solar transition zone

Areas of network emission features in C ii 1135, C iii 977, O iv 544 and O vi 1032 were measured in and out of coronal holes. In the quiet Sun these areas, on the average, showed a 20% increase between C ii and O vi. In the coronal holes there was no significant average variation, but a number of the features showed an interesting decrease in area at intermediate temperatures.     

Observed heights of EUV lines formed in the transition zone and corona

The heights of formation of a number of extreme ultraviolet lines in active regions have been measured from OSO-IV spectroheliograms. Using the Lyman continuum at 2000 km above the white light limb as a reference, we find heights for Hei, Heii, Ciii, Niii, Oiv, Ovi, Neviii, Mgx, Sixii, Fexv and Fexvi that are in approximate agreement with models based on analysis of EUV emission intensities. The height of Cii is anomalously high. The accuracy of measurement is typically about 2000 km. The data suggest that the transition zone is less steep than calculated from EUV emission intensities; however, higher resolution observations are necessary to resolve the discrepancy.     

Structure and physics of solar faculae

Taking into account the effect of roughness (or local departures from sphericity) of the emitting layers in the chromosphere-corona transition zone (CCT) allows one to determine the optical depths of layers responsible for resolved structures in Cii, Ciii, Oiv, and Ovi lines. The result, at the top of the irregularities, is of the order of respectively ₁ 3.5,2.0, 1.6,0.5, and for the bottom of these irregularities, ₂ = 0.7, 0.4, 0.3, 0.25. The characteristic angle of these irregularities is, respectively, of the order of 35 °, 33 °, 35 °, and 41 °. For unresolved structures of Civ and Ovi (already analyzed in the spherical symmetry hypothesis in Paper III), one finds ₁ 0.6; 0.9 and ₂ 0.12; 0.2 in the case of quiet areas; in the case of active areas, the range is broader for Civ and Ovi, from 1.0 to 1.7 for ₁ and from 0.2 to 0.9 for ₂. The values obtained from Ovi are in reasonable agreement with each other for resolved and unresolved structures. And the obtained values of ₁ and ₂ correspond not too badly with the determinations made in Paper III, by methods not exceedingly influenced by the spherical symmetry hypothesis.     

The O VI emission from the sun

The ionization equilibrium of oxygen is calculated for various temperatures. A peculiarity in the dielectronic recombination leads to a considerable fraction of Ovi in the corona. Thus, the Ovi lines may be emitted from the corona rather than the transition region.     

EUV observations of the chromospheric network

Extreme ultraviolet observations of a quiet region of the Sun on August 18, 1969, with the Harvard spectroheliometer on OSO 6 indicate that the chromospheric network can be observed in lines of the chromosphere and transition region (T = 8.4 × 10⁵ K) with almost identical structure. At coronal heights, the network changes but some residual structure can still be discerned in Mgx and perhaps Sixii (T = 2.3 × 10⁶ K), although there is little or no evidence remaining in Fexvi (T = = 3.5 × 10⁶ K).     

Spectral evolution of Nova V400 Per (1974) and Nova V373 Sct (1975)

Photographic and spectroscopic observations of the two galactic novae, V400 Per and V373 Sct, which appeared in 1974 and 1975, have been carried out at Asiago. The light curves of the two novae were characterized by the presence of brightness oscillations during the early decline. The spectral evolution was quite normal: the spectra showed at first, over a relatively strong continuum, wide emission bands of moderate excitation, accompanied by blueshifted absorptions, with radial velocities of –1760 km s^–1 (Nova Per) and –1260 km s^–1 (Nova Sct). Later, after the novae entered the nebular stage, the continuum weakened, the absorption disappeared and the novae displayed the usual emission spectrum, with permitted and forbidden lines of high excitation ([Oiii], Niii, Hei, Heii). Forbidden lines of Fevi and Fevii-and in Nova Sct, also Fex and Ax-were present for a time, but they soon disappeared, so that at the end the spectrum was dominated by the [Oiii] nebular lines, even stronger than H.     

Intensity of lines from low-lying levels in C ii,N iii,O iv,Ne vi,Mg viii,Si x,and Si ii

The intensities of the lines for the transition ² P ₃ ^2/0 -² P ₁ ^2/0 in C ii, N iii, O iv, Ne vi, Mg viii, Si x, and Si ii in the chromosphere-corona transition region are investigated. The populations of the excited state ² P _f3/2 ^p0 relative to the ground state ² P _f1/2 ⁰ are obtained by considering all the radiative and collisional transition processes including the collisional transitions to the higher states which cascade to the upper level. It is found that in the transition region the intensity (which may be expressed as a function of temperature only) increases with the charge on the ion for a sequence.On leave from D.N. College, Gulaothi 245 408, India.     

Structure and physics of solar faculae

The OSO-8 satellite enabled us to study various characteristics of the profiles of Si ii, Si iv, C iv, and O vi lines above active areas of the Sun, as well as above quiet areas, and to derive some physical properties of the transition region between chromosphere and corona (CCT): (i) The study of the lines shows a general tendency for the microvelocity fields on the average to be nearly constant for the heights corresponding to T > 10⁵ K; however they seem to slightly increase with height in quiet areas, and decrease in active areas. (ii) A multicomponent model of the CCT is however quite necessary, and its geometry is far from being a set of plane-parallel columns. It is similar to an association of moving knots within the non-moving principal component of the matter. (iii) The proportion of mass, in the knots relative to that in the non-moving component, is several times larger in active regions than in quiet regions. (iv) In the knots, the non-thermal microvelocity fields are smaller in active regions and seem to decrease for T increasing above 10⁵ K, contrary to what happens in the steady principal component. Of course, we consider that microturbulence and Doppler shift are two aspects of the same distribution of velocity.     

EUV analysis of polar plumes

Three polar plumes were studied using Skylab Mg x and O vi data. The plumes lie within the boundaries of a polar coronal hole. We find that the mean temperature of the plumes is about 1.1 × 10⁶ K and that they have a small vertical temperature gradient. Densities are determined and found consistent with white light analyses. The variation of density with height in the plumes is compared with that expected for hydrostatic equilibrium. As is the case for other coronal features, polar plumes will be a source of solar wind if the magnetic field lines are open. On the basis of the derived plume model and estimates of the numbers of plumes in polar coronal holes, it appears that polar plumes contain about 15% of the mass in a typical polar hole and occupy about 10% of the volume.Skylab Solar Workshop post-doc appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.     

Combined Analysis of Ultraviolet and Radio Observations of the 7 May 2004 CME/Shock Event

We report results from the combined analysis of UV and radio observations of a CME-driven shock observed on 7 May 2004 above the southeast limb of the Sun at 1.86 R _⊙ with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The coronal mass ejection (CME) was first detected in white-light by the SOHO’s Large Angle and Spectrometric Coronagraph (LASCO) C2 telescope and shock-associated type II metric emission was recorded simultaneously by ground-based radio spectrographs. The shock speed (∼ 690 km s⁻¹), as deduced from the analysis of the type II emission drift in the radio spectra and the pre-shock local electron density estimated with the diagnostics provided by UVCS observations of the O vi λλ 1031.9, 1037.6 doublet line intensities, is just a factor ∼ 0.1 higher than the CME speed inferred by means of the white-light (and EUV) data in the middle corona. The local magnetosonic speed, computed from a standard magnetic field model, was estimated as high as ∼ 600 km s⁻¹, implying that the CME speed was probably just sufficient to drive a weak fast-mode MHD shock ahead of the front. Simultaneously with the type II radio emission, significant changes in the O vi doublet line intensities and profiles were recorded in the UVCS spectra and found compatible with abrupt post-shock plasma acceleration and modest ion heating. This work provides further evidence for the CME-driven origin of the shocks observed in the middle corona.     

Medium resolution EUV observations and network structure

Medium resolution observations have been used to find the fractional emitting area in three transition region lines. It is found that is given by DI _{mg x} ^k where k varies from 0.78 to 0.51 in the temperature range 2 × 10⁵ to 7 × 10⁵ K. The average emitting area in O vi deduced by this method is in good agreement with the results from ATM observations. The fractional emitting areas at different values of the Mg x intensity and at different temperatures are combined to find the variation of the areas with height. This variation is in good agreement with Giovanelli's model of the fractional area of cross-section of a magnetic tube of force in the transition region.     

Evolution du spectre de la Nova Delphini 1967 en 1971 et 1972

Continued spectroscopic observations of Nova Del 67 during 1971 and 1972 show a general decrease of the nebular and coronal emission with respect to the local continuum. The continuous spectrum exhibits a strong Balmer emission (figure 1). Equivalent widths of Hi, Hei, Heii, Oi, [Oi], Oii, [Oii], Oiii, [Oiii], Niii, [Sii], [Aiii], [Neiii], [Nev], [Fevi], [Fevii], [Fex], [Fexi], [Fexiv], [Nixvi], [Nixv] are listed in tables 1 and 2.Figures 5 to 10 show several line profiles, which can be interpreted in terms of a model proposed by Hutchings (1972). Kinematical properties of the nova envelope do not seem to have changed in the 1968–1972 time interval. However, a study of the [Oiii] (4959 Å) line indicates that the physical conditions in the polar blobs in 1972 (T _e=10 660 K,N _e=5,5×10⁵ cm^–3) are different from those prevailing in equatorial rings (T _e=9×100 K,N _e=7×10⁵ cm^–3).

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Le matérial d'observation utilisé pour cette étude a été obtenu à l'aide de téléscopes de 120 cm, 152 cm et 193 cm de l'Observatoire de Haute-Provence (CNRS).