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.     

Raies nébulaires et coronales dans le spectre infrarouge de la Nova Delphini

Nova Delphini 1967 has been observed in the red and photographic infrared at the Haute-Provence Observatory from September 7 to November 12, 1968. Dispersions range from 230 Å/mm to 4 Å/mm. The slope of the continuous spectrum in the region 1.3–1.7 ^–1 leads to a gradient of 3.06, which did not appear to vary during the observing period. This gradient is, however, very different from the value 1.71 measured on plates secured in August 1968. Lines ofHi, Hei, Heii, Feii,Oi,Cii and forbidden transitions due toOi,Oii, Fevii, Fex, Fexi,Siii,Aiii,Av,Axi and Nixv have been identified. Their intensities at various dates are given in Table II. Line profiles could be measured for a few lines taken on a 39 Å/mm spectrogram on October 3. Hei 6678 and 7065 are displayed on Figures 2 and 3. Figure 4 gives the [Oii] doublet at 7319–7330, while the H profile, obtained on October 4 can be seen on Figure 5. The line extends over more than 45 Å and narrow absorptions are seen at 6551.05; 6555.75; 6563.15; 6571.49; 6574.45. Due to the absence of published data on radial velocities of absorption lines in the visible spectrum at that time, it is not possible to give a clear identification for these features. Some of them may belong to H, while others are probably due to metals.     

The determination of physical parameters for circumstellar clouds

The possibility of the detection of circumstellar clouds around hot stars have been shown based on the analysis of observed equivalent widths of resonance line 2852 Mgi of interstellar origin. An attempt has been made to combine two methods, earlier suggested — Method of Doublet 2800 Mgii and Method of Depression — for the determination of the parameters of circumstellar clouds. The sequence of the determination of these parameters is illustrated on the application of this combined method for circumstellar clouds around five hot stars. The value of the mean absorption coefficientk ₀ for the system of resonance lines in the region of depression 2400 Å, is obtained. An application of the conception of spectral classification of circumstellar clouds has been realized.     

Narrow band CCD imagery of southern galaxies in strong lines and continua: NGC 613

CCD narrow band imagery of the southern barred spiral NGC 613 has been obtained in the light of H, H, [Oiii] 5007 Å, [Oii] (3726+29) Å and continua at 3765, 5230, and 6500 Å. Absolute fluxes have been obtained for the lines H and [Oiii] 5007 Å and continua at 5230 and 6500 Å. Distribution of ages, monochromatic colour vs absolute brightness and [Oiii]/H are discussed.     

Velocity measures in the sunspot Rome no. 7490 (July 5, 1979)

Material motions on the solar surface have been deduced from the wavelength shift of Fe i 6302.5 Å, measured over the umbra and inner penumbra of a spot for which the magnetic field configuration has already been established with some confidence. The two vector fields are considered together in detail and the results support the convective roll sunspot model (Spruit, Galloway). For the magnetic field regions, both material flow along the field lines and field line motions are derived. A small upward motion only is deduced for the field free regions.     

The structure of sunspots

Magnetic field strengths in small umbrae and pores are measured using the line Ti i 6064.6 Å, which is formed purely in umbrae. We find field strengths between 1900 and 2600 G in the darkest parts of small umbrae and of well established pores; the spread is partly intrinsic. The field strength in diffuse transient protopores amounts to 1500 ± 250 G.We demonstrate that usage ofthe well-known magnetic line 6173.3 Å and other Fe i lines yield systematically smaller magnetic field strengths than Ti i 6064.6 Å. This is due to blending ofthe components with the central component due to photospheric stray light and the component. Routine measurements are therefore unreliable for small spots 251-01Based on observations at Sacramento Peak Observatory, Sunspot, New Mexico, U.S.A.     

Fabry-Pérot line profiles in the λ5303 å and λ6374 å coronal lines obtained during the 1983 Indonesian eclipse

During the total solar eclipse of 11 June, 1983, an imaging dual-channel Fabry-Pérot interferometer was used to obtain line profiles simultaneously in the green 5303 Å [Fe xiv] and the red 6374 Å [Fe x] coronal lines at various positions in the corona. Extensive microdensitometry followed by multi-Gaussian curve-fitting analysis has resulted in the determination of coronal temperatures and velocity separations between different pockets of coronal gas in the line of sight over a large extent of the corona. Fewer high temperature zones are to be found in the corona of 1983 compared with our similar green-line measurements of the solar maximum corona of 1980. The data are consistent with a temperature maximum occurring at 1.2 R , as found at the 1980 eclipse, but our new data are insufficient to observe farther out than this radius and so determine the position of a maximum. The velocity field in the corona at the 1983 eclipse is less structured compared with that at the 1980 eclipse and is mainly confined to the zone 20–30km s^–1.     

Ultraviolet observations of β Persei, μ1 Scorpii and γ2 Velorum with the TD-1A satellite

This paper reports on the results of a study of S59 ultraviolet spectral scans of the spectroscopic binaries Persei, ¹ Scorpii and ₂ Velorum. In the case of ¹ Sco it was found that the Mgii doublet at 2800 Å undergoes intensity variations that may be indicative of variable emission in the photographic spectrum. The continuum in the 2490–2590 Å range deviates from the continuum of the comparison stars. In ₂ Vel, flux variations in the 2770–2870 Å region have been detected.Member of the Carrera del Investigador Cientifico, CONICET, Argentina. Guest Investigator of the S59 experiment on board the TD-1A satellite.     

Radio observations of compact solar sources located between sunspots

Data from SSRT form the basis for initiating a study of the properties of long-lived, compact microwave sources located outside sunspots. A step-like birth of such a source was detected and is described in this study. This sheds light on the relationship between the step-like phenomenon detected with SSRT and the peculiar source phenomenon observed at RATAN-600. Peculiar sources precede large flares and are projected onto the photospheric neutral line. It seems likely that the build-up of a large flare is also step-like in character. We also discuss a source overlying the neutral line which accompanied a large active region that did not produce any large flare.     

The He i 10 830 Å chromosphere and filament associated structures

Full disk, He I 10 830 Å solar spectroheliograms have been generated using the Haleakala Stokes polarimeter-spectrometer. The spectroheliograms, with spatial resolution of 10 × 16 arc sec and wavelength bandpass of 0.53 Å, were developed for the detection of coronal holes, and have been compared with nearly simultaneous H and Ca K flltergrams.Areas of reduced helium absorption have been noted in the neighborhood of filaments and neutral zones in the longitudinal solar magnetic field. The existence of these helium lanes is discussed in terms of their relationship to H filament channels or to the coronal cavities which surround prominences.     

Mass motions in a flare spray

High velocity H ejections were observed in association with an important solar flare on March 12, 1969, and simultaneously with Type II followed by Type IV radio emission detectable to 3–4 solar radii (R ) from the center of the Sun. From a sequence of H coronagraph photographs, trajectories and velocity determinations were made for fragments of the flare spray which was visible to a distance of 2 R . The temporal and spatial relationship between the optical and radio events is discussed. The mass motions appear to be controlled by the gravitational field while the fragments move in the direction of the open magnetic field lines.     

Monochromatic observations of planetary nebulae

Monochromatic images in H, H, [Nii] 6584, [Sii] 6717, and [Oiii] 5007 lines are presented for a morphological study of planetary nebulae. Narrow bandpass (=5 to 10Å) interference filters are generally used in order to discriminate peculiar structures existing in different emission lines. However, large bandwidths (=50 Å) along with long exposures, are also necessary in searching for faint nebulosities associated with planetaries.Three faint objects of the Abell's list of old planetary nebulae have been observed through narrow band filters, by means of an image tube (A33, A36 in Chile) or the image photon counting device (A79 at the Haute Provence Observatory). Following the H/[Nii] intensity ratio, a discussion is given about the distance previously derived with some assumptions concerning the measured red fluxes.     

Complete determination of the magnetic field vector and of the electron density in 14 prominences from linear polarizaton measurements in the HeI D3 and Hα lines

The present paper is devoted to the interpretation of linear polarization data obtained in 14 quiescent prominences with the Pic-du-Midi coronagraph-polarimeter by J. L. Leroy, in the two lines Hei D₃ andH quasi-simultaneously. The linear polarization of the lines is due to scattering of the anisotropic photospheric radiation, modified by the Hanle effect due to the local magnetic field. The interpretation of the polarization data in the two lines is able to provide the 3 components of the magnetic field vector, and one extra parameter, namely the electron density, because the linear polarization of H is also sensitive to the depolarizing effect of collisions with the electrons and protons of the medium. Moreover, by using two lines with different optical thicknesses, namely Hei D₃, which is optically thin, and H, which is optically thick ( = 1), it is possible to solve the fundamental ambiguity, each line providing two field vector solutions that are symmetrical in direction with respect to the line of sight in the case of the optically thin line, and which have a different symmetry in the case of the optically thick line.It is then possible to determine without ambiguity the polarity of the prominence magnetic field with respect to that of the photospheric field: 12 prominences are found to be Inverse polarity prominences, whereas 2 prominences are found to be Normal polarity prominences. It must be noticed that in 12 of the 14 cases, the line-of-sight component of the magnetic field vector has a Normal polarity (to the extent that the notion of polarity of a vector component is meaningful; no polarity can be derived in the 2 remaining cases); this may explain the controversy between the results obtained with methods based on the Hanle effect with results obtained through the Zeeman effect. A dip of the magnetic field lines across the prominence has been assumed, to which the optically thick H line is sensitive, and the optically thin Hei D₃ line is insensitive.For the Inverse prominences, the average field strength is 7.5±1.2 G, the average angle,, between the field vector and the prominence long axis is 36° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 29° ± 20°, and the average electron density is 2.1 × 10¹⁰ ± 0.7 × 10¹⁰ cm^–3. For the Normal prominences, the average field strength is 13.2±2.0 G, the average angle,, between the field vector and the prominence long axis is 53° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 0° ± 20° (horizontal field), and the average electron density is 8.7 × 10⁹ ± 3.0 × 10⁹ cm^–3.     

Extreme ultraviolet flashes of solar flares observed via sudden frequency deviations: Experimental results

Properties of solar-flare EUV flashes measured via a type of ionospheric event, called a sudden frequency deviation (SFD), are presented. SFD's are sensitive to bursts of radiation in the 1–1030 Å wavelength range. He ii 303.8 Å, O v 629.7 Å, HL 972.5 Å and C iii 977.0 Å have essentially the same impulsive time dependence as the 1–1030 Å flash responsible for SFD's. Soft X-rays (2–20 Å) and certain EUV lines have a much slower time dependence than the 1–1030 Å flash. Most SFD's have some fine structure, but marked quasi-periodicity in EUV flashes is quite rare. EUV flashes are closely associated with hard X-ray bursts, white-light emission, microwave radio bursts and small bright impulsive kernels in the H flare. The intensity of EUV flashes depends on the central meridian distance of the H flare location; the intensity decreases at the limb. The total energy radiated in the 10–1030 Å flash for the largest events observed is about 10³¹ ergs.     

The solar abundance of thorium and lead

Two new Th ii lines have been identified in the spectrum of the solar photosphere. The abundance derived from these lines together with the previously known Th ii line at 4019 Å, is log _Th = 0.85 ± 0.20 in the log _H = 12.00 scale. Analysis of three Pb i lines in the photospheric spectrum resulted in an abundance of log _pb = 1.90 ± 0.10. The solar Th/Pb ratio is: _Th/ _Pb = 0.09 _-0.005 ^0.09 .     

Observations of the infrared triplet of singly ionized calcium

Observations are presented of the Caii infrared triplet (8498 Å, 8542 Å, and 8662 Å) at three positions on the solar disk to make possible direct analyses of the lines and comparisons with theoretical computations. The source functions for the two strongest lines (8542 Å and 8662 Å) are equal at those heights corresponding to the wings of the lines (¦¦ > 0.4 Å) but not to those of the cores. We suggest that the apparent source function inequality in the cores is due to limb darkening caused by inhomogeneities in the chromosphere.Of the National Bureau of Standards and University of Colorado.     

Study of the post-flare loops on 29 July 1973

Bright and dark curvilinear structures observed between the two major chromospheric ribbons during the flare of 29 July 1973 on films from the Big Bear Solar Observatory are interpreted as a typical system of coronal loops joining the inner boundaries of the separating flare ribbons. These observations, made through a 0.25 Å H filter, only show small segments of the loops having Doppler shifts within approximately ± 22 km s^–1 relative to the filter passband centered at H, H -0.5 Å or H +0.5 Å. However, from our knowledge of the typical behavior of such loop systems observed at the limb in H and at 5303 Å, it has been possible to reconstruct an appoximate model of the probable development of the loops of the 29 July flare as they would have been viewed at the limb relative to the position of a prominence which began to erupt a few minutes before the start of the flare. It is seen that the loops ascended through the space previously occupied by the filament. On the assumption that H fine structures parallel the magnetic field, we can conclude that a dramatic reorientation of the direction of the magnetic field in the corona occurred early in the flare, subsequent to the start of the eruption of the filament and prior to the time that the H loops ascended through the space previously occupied by the filament.     

Chromospheres of flare stars

The present paper contains an attempt to formulate a theory, based on fast electrons hypothesis, of the chromospheres of flare stars. At the same time we shall undertake a survey of observations on the emission lines of flare stars and comparisons with the theory. The general discussion in the introduction concerning the civilian right of fast electron hypothesis is followed by sections in which the following problems are tackled: the anatomy of the light curve of the flare in UV Cet-type stars or its division into two components; the sources of radiation, ionizing hydrogen and other elements, and the estimation of their power in cold dwarf stars with emission lines; conditions for the excitation of emission lines in the chromospheres of those stars; the problem of duration of luminescence of flare stars in the emission lines (observations and theory); the electron temperature and electron concentration in the chromospheres of flare stars; the problem of the luminescence of emission lines in the quiescent star; the degree of ionization and the role of inelastic collisions of the electrons in the chromosphere of flare stars; the profiles of emission lines, their broadening and intensification during the flare; the dependence of the infensity of emission lines on the flare amplitude; the nature and peculiarities of two types of the Haro flares; the impact of radiation dilution and the spectral class of the star on the equivalent width of the emission lines; the possibility of exciting the forbidden lines; the problem of generation of the emission lines of neutral and ionized helium; the possibility of the Lyman-alpha emission in flare stars, the expected parameters of such emission — the radiation power, the equivalent width and profile of the Lyman-alpha line; the possibility of the presence of the strongest (after the -line) emission line — of doublet 2800 Mgii in the spectra of flare stars, the expected value of the intensity and equivalent width of that line.     

Ionized helium in prominences and in the chromosphere

Quiescent prominences It is found that Heii 4686 is emitted in the same cold region of 10000 K as hydrogen, metal and neutral helium emission lines. This conclusion is based on the finding that the observed width of 4686 is the same as the calculated width of 4686. The calculated width is derived from the observed widths of hydrogen and metallic lines. The large intensity of Heii 4686 in 10000 K can be explained by the ionization of Heii due to the UV radiation below 228 Å that comes from the corona and the transition region.Loop prominences The very broad width (30 to 50 km s^–1) of 4686 for two post-flare loop prominences shows that the Heii line is emitted in hot regions different from regions of hydrogen and metal emission. From the widths of the Balmer lines and many metallic lines the kinetic temperature for one loop is found to be 16000 K in one part and 7600 K in another part. The electron densities are 10^12.0 cm^–3 and less than 10^11.0 cm^–3 respectively.Chromosphere The intensity of 4686 in the chromosphere can be interpreted in terms of a temperature of 10000 K with the ionization due to UV radiation. But, since observations of the width of 4686 are not available, a definitive conclusion for the chromosphere cannot be reached.     

Small-scale motions over concentrated magnetic regions of the quiet Sun

We have used a 5.5 min time-sequence of spectra in the Fe i lines 5576 (magnetically insensitive), 6301.5 and 6302.5 (magnetically sensitive) to study the association of concentrated magnetic regions and velocity in the quiet Sun. After the elimination of photospheric oscillations we found downflows of 100–300 m s ^–1, displaced by about 2 from the peaks of the magnetic field; this velocity is comparable to downflow velocity associated with the granulation and of the same order or smaller than the oscillation amplitude. Quasi-periodic time variations of the vertical component of the magnetic field up to ± 40% were also found with a period near 250 s, close to the values found for the velocity field. Finally we report a possible association of intensity maxima at the line center with peaks of the oscillation amplitude.