The spectrum of the Cr star epsilon ursae majoris

Fourteen coudé spectrograms (eight with dispersion 12.4 Å mm^–1 and six 7 Å mm^–1) of the Cr star UMa (Ap) have been studied. The observations were made at the Haute Provence Observatory. The radial velocities of the various ions have been measured. The existence of Balmer progression in radial velocity is doubtful. The variability of some lines is in the opposite sense of K of Caii. Both a rough and a fine analysis have been made. The results of these analyses are compared and found to be in good agreement. The results of the fine analysis indicate a defect of Al, Si and Ca; Sc, Ti, Fe and Sr are normal, Mg and Ni are in slight excess. V, Cr and Mn are in excess by factors of 3, 12, 19; Y, Zr and Ba are in excess by factors of 9, 15, 30. Rare earths are in excess by factors ranging between 100–1000. These results are compared with the majority of the Cr–Eu–Sr stars.The observations have been made at the 152 cm coudé telescope of the Haute Provence Observatory.     

Correlation and variability of the HeI 4471 and MgII 4481 absorption lines in Be stars: A possible diagnostic tool for nonradial pulsations

In a total of 181 photographic spectrograms, obtained at the Manuel Foster Observatory of the Catholic University in Santiago (Chile), the equivalent widths of the absorption lines HeI 4471 and MgII 4481 have been determined for 10 selected southern Be stars and 4 normal B-type stars. The mean equivalent widths of each star are compared to published mean values from largers samples of B stars. On the average, Be stars coincide with normal B-type stars in their equivalent width. However, a striking difference between rapidly and slowly rotating stars in their line ratios (HeI/MgII) was found, which is probably an artifact due to a systematic misclassification of spectral types of rapidly rotating B stars (v sini>200 km s^–1). Six of the ten Be stars show evidence for variability in HeI and/or MgII with time-scales shorter than a few days and amplitudes up to a factor 2 in equivalent width. Line variability occurs in the entire range of projected rotation velocity (70 km s^–1<v sini<350 km s^–1), but seems to be restricted to spectral types B2-B4. In addition, variations at longer time-scales (years) were observed in two cases. Three of the variable stars (HR 4074, HR 4537, and Ara) present correlated variations in both lines, one ( Cen) anti-correlated variability. We interpret our results in terms of nonradial pulsations and stress the importance to study the HeI/MgII lines and their variability in a larger sample of Be, Bn, and normal B stars, including archival material in order to follow-up line variability for several decades in the past.     

Coronal density and temperature gradients

Mean density models of the solar corona show evidence for two distinctive density regimes characterized by different density gradients. High density gradients are identified with regions of predominantly open magnetic lines of force and low density gradients are identified with regions of predominantly closed magnetic lines of force. Spectroscopic data yielding equivalent widths of forbidden lines of Fe x and Fe xiv strongly suggest that the coronal temperature for r > 2.5 R decreases considerably less rapidly in equatorial regions than r ^–2/7, which is the decrease predicted by conduction models with open field lines.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Physical parameters of reflection nebulae in the galaxy

We show how, given observed equivalent widths of Mgii and Mgi absorptions due to an interstellar cloud in which a late-B star is embedded, the basic physical parameters: kinetic temperature, mean density, electron density, and radius can be constrained. Hydrogen ionization by means of cosmic rays and the effect of the stellar radiation field on the magnesium ionization equilibrium are taken into account.The method is applied to the reflection nebula surrounding the star HD 26676. The resulting solutions for the radius and temperature of the nebulosity are comparable to the typical values derived for diffuse interstellar clouds from optical and 21-cm measurements, if a cosmic-ray ionization rate 10^–16s^–1 — in agreement with recent determinations — is assumed. The results are not strongly dependent on the gas pressureP forP varying in a range of values typical of interstellar clouds.     

Solar flare X-ray spectra

Results are presented of an investigation of solar flare X-ray spectra in the region 1.70–1.95 Å, obtained aboard the Intercosmos-4 satellite during the maximum of solar activity (October–November, 1970). With the use of 6 high resolution spectra in the region 1.85–1.87 Å the identification of lines due to 18 transitions of 2p 1s type, consisting of the resonance, intercombination and forbidden Fe xxv ion lines and the satellite Fe xxiv lines has been performed. With the use of the recent laboratory data the averaged wavelengths of the lines were obtained confirming the theoretically calculated ones with an accuracy about ± 0.0004 Å. A variable Doppler shift of the Fe xxv resonance lines was observed for the flare of November 16, 1970, which points to hot plasma motions with velocities up to 400 km s^-1.     

Radial velocity and profile variations of the ultraviolet circumstellar lines in ζ tauri

The radial velocity and profile variations of UV lines of the shell star Tau have been examined in the IUE spectra obtained in 1978–1982. The neutral atoms, and once or twice-ionized ions (exceptCii, Aliii, Siiii resonance lines) follow the same velocity variations as in the visual spectra, while the Siiv andCiv resonance lines show a constant negative velocity (–50 km s^–1 at the core). The Aliii,Cii resonance lines and probably Feiii (mult. No. 34) are formed in both regions, i.e., in lowly-ionized and highly-ionized regions and the Siiii resonance line is formed in a highly-ionized region.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

‘Prominences’ of RY Tauri

High-resolution spectroscopic monitoring of the Nai D lines in the T Tau-type star RY Tau results in the discovery of relatively cool gas clouds ascending and descending inside the stellar wind on a time-scale of few days and co-rotating with the star. Radial velocity of the clouds varies from –100 to +100 km s^–1, which is twice as large as thev sini of the star.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

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.     

Wave propagation in the photosphere

Using a 32 minutes sequence of observation, brightness and velocity fluctuations in the wings of the Mgi line at 5172.7 Å and Fe ii line at 5197.578 Å are analysed. The analysis of phase shifts and amplitude ratios leads to the following conclusions:

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.     

Fabry-Pérot observations of the Rosette Nebula

The results of observations of the Rosette Nebula using the equipment described byMeaburn andSmith (1968) and the reduction procedures outlined inSmith andWalker (1968) are reported. The results and conclusions differ markedly from an earlier report (Flynn, 1965), of detailed radial-velocity observations of this nebula. The peak positions of the H-line profiles have now been shown not to vary greatly. The mean of 37 measurements at different points gives, for the heliocentric velocity of the Rosette nebula, +35±5 km sec^–1. The widths of the lines are consistent with a model of randomly directed streaming motions of order 15 to 25 km sec^–1.     

Multiple loop activations and continuous energy release in the solar flare of June 15, 1973

The spatial and temporal evolution of the high temperature plasma in the flare of 1973 June 15 has been studied using the flare images photographed by the NRL XUV spectroheliograph on Skylab.The overall event involves the successive activations of a number of different loops and arches bridging the magnetic neutral line. The spatial shifts and brightenings observed in the Fe xxiii–xxiv lines are interpreted as the activation of new structures. These continued for four or five minutes after the end of the microwave burst phase, implying additional energy-release unrelated to the nonthermal phase of the flare. A shear component observed in the coronal magnetic field may be a factor in the storage and release of the flare energy.The observed Fe xxiii–xxiv intensities define a post-burst heating phase during which the temperature remained approximately constant at 13 × 10⁶ K while the Fe xxiv intensity and 0–3 Å flux rose to peak values. This phase coincided with the activation of the densest structure (N _e = 2 × 10¹¹ cm^–3). Heating of higher loops continued into the decay phase, even as the overall temperature and flux declined with the fading of the lower Fe xxiv arches.The observed morphology of individual flaring arches is consistent with the idea of energy release at altitude in the arch (coincident with a bright, energetic core in the Fe xxiv image) and energy flow downward into the ribbons. The Doppler velocity of the Fe xxi 1354 Å line is less than 5 km s^–1, indicating that the hot plasma region is stationary.The relation of this flare to the larger class of flares associated with filament eruptions and emerging magnetic flux is discussed.     

High-dispersion spectroscopy of the symbiotic star AX Per: A binary model with rapid mass accretion

Results of high-dispersion spectroscopy (10 Å mm^–1) of the symbiotic star AX Per carried out in the years from 1979 to 1987 are reported. The emission line [FeVII] 6086 consists of a narrow and a broad component; the radial velocity of the narrow one varies according to the photometric period 681.6 days. This variation (K=30.6±1.5 km s^–1) seems to be due to the orbital motion of the hot star. The radial velocity of absorption lines varies with an inverse phase dependence and a much smaller amplitude (K=5.6±2 km s^–1), which may reflect the orbital motion of the red giant. The variation of the radial velocity of the emission lines of FeII, ect. (K=6.7±1.5 km s^–1) might be due to the rotation of the red giant. The profile of H emission line suddenly changed around the phase of the photometric minimum, which could be explained as a result of an eclipse of the emitting region by the red giant. On the other hand, some problems remain open in the behaviour of the radial velocities of H and HeI 5876.The observed results support a binary model of AX Per consisting of a rather massive (3M ) M-type giant and a Main-Sequence star (0.6M ). AX Per seems to be in an early stage of the Case C mass transfer, and the estimated very high mass accretion rate (10^–4 M yr^–1) is consistent with the theoretical models. The narrow component of the emission line of [FeVII] 6086 might be emitted in radiatively driven polar jets on the hot star of which luminosity is close to the Eddington limit.A new identification as ZrII at 6106.47 Å is proposed for the emission line at 6106 Å.     

The impulsive and gradual phases of a solar limb flare as observed from the solar maximum mission satellite

Simultaneous observations of a solar limb flare in the X-ray and ultraviolet regions of the spectrum are presented. Temporal and spectral X-ray observations were obtained for the 25–300 keV range while temporal, spectral, and spatial X-ray observations were obtained for the 30–0.3 keV range. The ultraviolet observations were images with a 10 spatial resolution in the lines of O v (T _e 2.5 × 10⁵ K) and Fe xxi (T _e 1.1 × 10⁷ K). The hard X-ray and O v data indicate that the impulsive phase began in the photosphere or chromosphere and continued for several minutes as material was ejected into the corona. Impulsive excitation was observed up to 30 000 km above the solar surface at specific points in the flare loop. The Fe xxi observations indicate a preheating before the impulsive phase and showed the formation of hot post-flare loops. This later formation was confirmed by soft X-ray observations. These observations provide limitations for current flare models and will provide the data needed for initial conditions in modeling the concurrent coronal transient.     

The soft X-ray polychromator for the Solar Maximum Mission

The 1.4–22.4 Å range of the soft X-ray spectrum includes a multitude of emission lines which are important for the diagnosis of plasmas in the 1.5–50 million degree temperature range. In particular, the hydrogen and helium-like ions of all abundant solar elements with Z > 7 have their primary transitions in this region and these are especially useful for solar flare and active region studies. The soft X-ray polychromator (XRP) is a high resolution experiment working in this spectral region. The XRP consists of two instruments with a common control, data handling and power system. The bent crystal spectrometer is designed for high time resolution studies in lines of Fe i-Fe xxvi and Ca xix. The flat crystal scanning spectrometer provides for 7 channel polychromatic mapping of flares and active regions in the resonance lines of O viii, Ne ix, Mg xi, Si xiii, S xv, Ca xix, and Fe xxv with 14 spatial resolution. In its spectral scanning mode it covers essentially the entire 1.4–22.5 Å region.This paper summarizes the scientific objectives of the XRP experiment and describes the characteristics and capabilities of the two instruments. Sufficient technical information for experiment feasibility studies is included and the resources and procedures planned for the use of the XRP within the context of the Solar Maximum Mission is briefly discussed.     

On the fine structure of the evershed effect

The fine structure of the Evershed effect was studied using spectrograms obtained on 3 July 1969 at the Pulkovo Observatory. The results of the study of Fei and Cai lines show that the outward motion in the penumbra is concentrated only in dark filaments. It is supposed that interfilamentary spaces are parts of the photosphere not covered by dark filaments. The velocity variation along a few dark filaments shows that maximum velocity is at a distance 0.8 Rs from the center of the sunspot. The mean velocity in the interfilamentary elements is of the same order as that in the photosphere directly adjoining the penumbra. The results of measurement in Ti ii, Fe ii and CH lines show that in the colder upper part of the penumbra (CH) the velocity is greater than the velocity measured in the deeper layers (Feii and Tiii). The mean velocity at the outer boundaries of the dark filaments (Tii) is 1.5–2.0 km/s.     

Diagnostic application of highly ionized iron lines in the XUV spectrum of a solar flare

Recent atomic data have been used to analyze a solar flare spectrum obtained with the Goddard Space Flight Center's grating spectrometer on the OSO-5 satellite. There exist in the wavelength region 90–200 Å strong lines from each of the ions Fe xviii-Fe xxiv. The Fe xxi lines can be used as an electron density diagnostic for the 10⁷ K plasma. From our analysis of a particular flare, we find a steep positive slope in the emission measure between 10^6.5 and 10^7.2 K and an electron density of 4 × 10¹¹ cm^–3 at 10⁷ K. We emphasise the need for high spectral and spatial resolution observations of solar flares in this wavelength region, which has to date been largely neglected.     

On the continuum and the absolute magnitude of eta Carinae

The excitation temperature, colour excess and continuum of Car in the visible and near ultraviolet have been determined from the study of the excitation of the ionized iron emission lines. The excitation temperatures of Feii and [Feii] are about 8000K, value which is very much lower than the mean ionization temperature of the elements in Car.E _B-V is about 1^m.1; the absolute visual magnitude is presently –10^m.5±1^m. From the equivalent widths of the emission lines the true continuum between 1.5 and 3.0 ^–1 has been derived. The correspondingB-V is –0^m.14, while the Balmer jump is less than 0^m.5. The continuum appears mainly nebular in origin with a strong contribution of the two-photon emission from the 2s-level of hydrogen in the blue.     

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.     

Sub-iron to iron nuclei in low-energy (50–200 MeV nucl−1) cosmic rays as observed in the Skylab experiment

In this paper we present our most recent results on the sub-iron (Sc to Cr) to Fe nuclei abundance ratios in the low-energy cosmic rays of 50 to 250 MeV nucl.^–1 and their implications as observed in theSkylab experiment. In view of the importance of this ratio in determining the cosmic-ray pathlength in interstellar medium, we have obtained additional data in the same detector module and the results of final analysis are reported. Charge determinations in the Lexan detector were made from an average of about four independent measurements ofZ for each of the cosmic-ray events and the mean charge resolution is obtained asZ/Z0.2. From about 100 events of calcium to nickel in low-energy cosmic rays, sub-iron (Sc to Cr) to Fe–Co ratio is determined as 1.43±0.40 in 50–250 MeV nucl.^–1. This shows a large energy dependence of the ratio as compared to the value of 0.4–0.8 in 200–1000 MeV nucl.^–1 as measured by many investigators. The origin of this large enhancement of the ratios in low-energy cosmic rays is not known at present. Some possible suggestions are briefly mentioned.