Log(gf) for singly-ionized elements of the iron group

Moderately accurate oscillator strengths are obtained by application of systematic corrections to Warner's-log(gf) for the once ionized elements of the iron group. Corrections are derived by comparison of Warner's values with those of Kurucz-Peytremann (Scii, Tiii,Vii, Crii, Mnii, Coii, and Niii) and Kurucz (Feii).K–P andK derived log(gf) by semi-empirical methods for many transitions using scaled Thomas-Fermi-Dirac potentials for the atoms of the elements from B to Ni. Although their individual values may be seriously in error, it has been shown that their mean scales are acceptable, being affected at most by rather small errors. It is known, for example, that when interacting terms are not properly accounted for in the semi-empirical method, very small values are derived for log(gf); these were dropped away in calculating mean corrections as they exhibited gross deviations.The relations loggf(KP)–loggf(W) vs , loggf(W), andE _u (energy of the upper level) have been investigated, and constant corrections, or weak dependences are found.Using Warner's corrected log(gf) for these elements, we have shown in a rather qualitative way that abundances consistent with the values accepted at present are found in the solar photosphere.Research supported in part by the SECYT.     

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.     

A numerical test of the quasi-equilibrium approximation for stellar silicon burning

A measure of the range of the validity of the nuclear quasi-equilibrium approximation, employed byBodansky, Clayton andFowler (1968) for the treatment of stellar silicon burning, is obtained by comparison of the predicted abundances with the results of a numerical solution of the equations for the time rates of change of the nuclear abundances. The results of these calculations, performed for a temperatureT=3×10⁹K, are compared with those obtained by Bodanskyet al. for a temperatureT=5×10⁹K. The time required for the realization of the quasi-equilibrium condition at high temperatures is found to comprise a more substantial fraction of the silicon burning lifetime. This behavior is found to be attributable to the relative temperature sensitivities of the nuclear photodisintegration rates which determine the silicon burning lifetime and the charged particle reaction rates (largely Ti⁴⁴(,p) V⁴⁷) which determine the rate of buildup of iron peak nuclei.     

On coronal Fe abundances and temperatures from XUV emission lines

Data obtained by the OSO-7 spectroheliograph on strong XUV lines of five, different Fe ions from the outer equatorial corona are presented. Interpretation of the data with a spherically symmetric model atmosphere gives average ion abundances for lines of sight at 0.3R from the limb. Fe xvi is usually more abundant than Fe xv, xiv, xii and ix, but there are times when Fe xii is more abundant than the other ions. The deviation of measured relative abundances of Fe xii, xiv, and xvi from predictions of ionization equilibrium at one temperature seems to indicate that there are appreciable temperature variations along lines of sight. Element abundances are very uncertain since they appear to depend so heavily on likely but unknown density irregularities along lines of sight.     

Carbon,nitrogen, and oxygen abundances in Procyon,Sun, and Arcturus

Ci, Ni, andOi permitted and forbidden lines in the near-infrared spectra of Procyon (F5 IV–V), Sun (G2 V), and Arcturus (K2 IIIp) have been analyzed to determine their carbon, nitrogen, and oxygen abundances. Procyon is found to have normal abundances while Arcturus is found to have an enhanced nitrogen abundance by a factor of 1.03 dex relative to the Sun. The dependence of the derived abundances on the effective temperature and luminosity is investigated.Much of the work reported here was contained in the Ph.D. thesis of the author submitted to the Istanbul University, Turkey, in 1986.     

Computation of oscillator strengths by a semi-empirical method for some elements of the iron-group and their solar photospheric abundance

Oscillator strengths calculated by the STF method for selected transitions of V i and Co i have permitted to deduce, from an LTE study of weak lines, photospheric abundances in agreement with those obtained from carbonaceous chondrites. A summary of results is also presented for all the iron-group elements.     

Theoretical models of planetary nebulae

Theoretical models are calculated for 15 planetary nebulae of medium-to-high excitation, following procedures previously described. Initial stellar energy distributions are adopted from Cassinelli (1971), but are subsequently modified to obtain the best representation of optical spectra for the selected objects. Other adjustable parameters include the stellar radius,R ^(*), the nebular density,N _H, the truncation radius,r _c, for the nebular shell, and the chemical composition. Excitationsensitive ratios are usually well-represented as are the actual observed intensities of spectral lines. Forbidden lines arising from 3p ³ configurations, e.g., those of [SII], [ArIV], and [ClIII] offer difficulties. For this sample of nebulae, the mean abundances seem to agree well with those found in an earlier study where the models were used as interpolation devices (Aller, 1978). Our objective is not to use the models to derive abundances explicitly, but rather to use them to find ionization correction factors. Some cautions and limitations of this procedure are described.     

Density and temperature diagnostics of solar emission lines from NeVI and MgVI

Line intensity ratios of NeVI lines with respect to a resonance line of MgVI have been considered for electron density and temperature determinations within the chromosphere-corona transition region. The electron pressure within the transition region has been assumed to be constant. In addition, these ratios would enable us to estimate the relative element abundances of neon to magnesium. An attempt has been made to explain the extreme ultraviolet intensities of NeVI and MgVI lines as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum. Theoretical intensities for NeVI and MgVI lines have been computed using a model solar atmosphere. Theoretical intensities obtained by using the values 3.98 × 10^–5 and 3.16 × 10^–5 for element abundance of Ne and Mg, respectively, seem to agree well with the expected intensities. The agreement between some of the expected and computed intensities suggests the need for future observations at higher spectral resolutions to resolve difficulties arising out of blending due to two or more lines.     

Density dependence of solar emission lines of boron-like ions

Steady state level density of 20 levels of boron-like ions, Mg viii and Si x, have been computed as a function of electron density and temperature. We have accounted for collisional and spontaneous radiative processes. Photo-excitation between the two levels of the ground term has also been considered. Using the computed level density, line intensities have been obtained as a function of electron density and temperature. In case of Mg viii, line intensity ratio I(430.47)/I(436.62) is found to be electron density sensitive. Likewise other pairs of lines namely, I(75.03)/I(74.86), I(315.02)/I(430.47), and I(315.02)/I(335.23) are also found to be density sensitive. Similar density sensitive line intensity ratios have been found for Si x. Absolute line fluxes from these ions at earth distance have been computed and are found to be comparable with values obtained, using various satellite and rocket measurements.Paper presented at the 5th Astronomical Society of India Meeting, held at Uttar Pradesh State Observatory, Naini Tal, India, 5–9 November, 1979.     

The identification of new forbidden coronal lines in the solar EUV spectrum

Identifications are proposed for twenty of the twenty-eight coronal lines observed in the spectra obtained during a rocket flight into the path of the 7 March, 1970 solar eclipse. The methods by which the lines have been identified are discussed. Most of the lines identified are from forbidden transitions between levels in the ground 2p ⁿ and 3p ⁿ configurations in high ions of magnesium, silicon, sulphur, iron, and nickel. The temperature range represented is from 6.9 × 10⁵ K to 2.5 × 10⁶ K. The classification of three lines of Fexii and two of Nixiv has led to a revised identification for the near ultraviolet ² D _3/2-² P _1/2 transition in Fe xii. This transition can be identified with the line at 3072 Å rather than that at 3021 Å as previously suggested in the literature.     

Charge composition of medium energy cosmic-ray nuclei from neon to iron

Charge composition of cosmic-ray nuclei from neon to iron has been studied in a stack of cellulose nitrate plastic detectors exposed in a balloon flight over Fort Churchill. 401 cosmic-ray nuclei of 10Z26 stopping in the detector system have been analysed. Fluxes of individual nuclei have been extrapolated to the top of the atmosphere. Relative abundances, obtained from these fluxes, have been compared with those obtained by other investigators.     

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.     

Solar flare line emission between 6 Å and 25 Å

A list of emission lines in the spectra of solar flares between 6 Å and 25 Å has been compiled using data obtained with a KAP crystal spectrometer on the OSO-5 satellite. The emission lines have been classified according to their sensitivity to flare activity. This classification provides a method for discriminating between iron in high stages of ionization (Fe xx-Fe xxv) and lower stages (Fe xvii- Fe xix), the lines of which are both present in the same spectral region during flares. Identifications consistent with these classifications are proposed. Anomalous intensities in the spectra of Fe xvii and Fe xx are pointed out, and implications of the observations for models of the X-ray emitting regions are discussed.     

Integration and Comparison of Clementine and Lunar Prospector Data: Global Scale Multielement Analysis1 (Fe,Ti, and Th) of the Lunar Surface

In this paper, we present (1) a statistical analysis, based on a systematic clustering method, of a dataset integrating the global abundance maps of the three elements iron, titanium, and thorium derived from Clementine and Lunar Prospector and (2) a comparison of iron abundances between Clementine and Lunar Prospector. Homogeneous geologic units are compositionally characterized and spatially defined in relation to the major rock types sampled on the Moon. With the lowest abundances of Fe, Ti, and Th found on the Moon, the lunar highland terrains are quite homogeneous with two major large feldspathic units, one being slightly more mafic than the other. Two distinct regions with unique compositions are unambiguously identified: the Procellarum KREEP Terrane (PKT) and the South Pole–Aitken (SPA). The PKT, which includes all the units with Th abundances higher than 3.5 ppm (KREEP-rich materials), is delimited by an almost continuous ringlike unit. In particular, it includes the western nearside maria, except for Mare Humorum. With concentrations in Fe, Ti, and Th enhanced relative to the surrounding highlands, the South Pole–Aitken basin floor represents a large mafic anomaly on the far side, suggesting wide deposits of lower crust and possible mantle materials. However, due to indirect residual latitude effects in the CSR (Clementine spectral reflectance) measurements, iron abundances might have been overestimated in SPA, thus implying that crustal materials, rather than mantle materials, might represent the dominant contributor to the mafic component exposed on the basin floor.     

Investigation of non-uniform heating during the decay phase of solar flares

We have analysed X-ray spectra of 13 solar flares as obtained by the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission. In particular, we have examined the observed ratio of T _Fe/T _Ca where T _Fe and T _Ca are the temperatures obtained from the Fexxv and Caxix spectra, respectively. In order to simplify the investigation we have analysed only flares which reach quasi-steady-state during the decay. It turned out that the observed ratios cannot be explained by a model consisting of a single, uniformly heated loop, with a constant or variable cross-sectional area. We propose that this problem may be solved by introducing some distribution of the heating function across the flaring loop. This model has been tested by detailed calculations.     

X-ray and extreme ultraviolet (1–400 Å) spectroscopy of the sun,from OSO-III

X-ray spectra of the sun have been obtained during solar flares. New emission lines are observed in the spectral range from 1.3 Å to 3 Å, and 8 Å–20 Å, the most intense of the new emission features being tentatively attributed to optical transitions in high stages of ionization of iron (Fexxv through Fexx). Studies of the variability of these lines during flares provide new information of the development of a hot plasma in the initial stages of the flare event.     

A comparison of solar EUV intensities and K-coronameter measurements

Characteristics of the emission observed above the solar limb in four EUV lines, Sixii 499, Mgx 625, Neviii 770, and Ovi 1032 are discussed. The mean temperature of the corona derived from the ratios of the intensities of Sixii 499 and Mgx 625 is 1.8 million K. There do not appear to be significant temperature differences in regions with low EUV intensities and those with high EUV intensities, suggesting that the EUV emission from the lithium-like ions depends primarily on the integral of n _e ² along the line of sight.The EUV data are compared with K-coronameter measurements in order to yield new estimates of the abundances of Si, Mg, Ne and O relative to hydrogen. Within the uncertainties of the analysis, these coronal abundances are in agreement with the corresponding photospheric values.     

A model atmosphere analysis of the binary 112 Herculis

Double-lined spectra have been obtained at 2 Å/mm for the Mn star 112 Herculis AB. The components are shown to be a B6.5V star and A2V star. Hydrogen-line-blanketed models are used to calculate atmospheric abundances. The best models appear to beT _e=13500 K, logg=4.0, _T =2.5 km/sec for the primary; andT _e=10000K, logg=4.2, _T =6 km/sec for the secondary. Both stars appear to have the same abundances. Helium, carbon, magnesium, aluminum, silicon, calcium, vanadium, and nickel appear to be considerably underabundant; phosphorus, scandium, titanium, manganese, iron, gallium, and mercury considerably overabundant; and chromium, strontium, and zirconium normal in abundance.     

Levitation

Some stars have outer layers which are sufficiently quiescent for diffusion to occur and to modify the relative abundances of the chemical elements. Levitation occurs when the forces due to radiation pressure are larger than those due to gravitation. The paper describes some recent work on the calculation of the radiative forces using atomic data obtained in the course of the work of the Opacity Project. Large abundance anomalies are observed for the HgMn stars, which lie on or close to the main sequence and have effective temperatures in the range 11000 to 15000 K. Some results are given for calculated abundances of elements of the iron group in the HgMn stars. levitate: Torise or cause to rise and float in the air, usually attributed to supernatural intervention. (Collins Dictionary of the English Language)     

Relative abundances of cosmic ray nuclei from neon to iron over Fort Churchill

The relative abundances of the nuclei from neon to iron in the energy interval 150–400 MeV/n have been estimated by using a balloon borne cellulose-nitrate plastic detector. The source abundances are obtained by extrapolating the near-earth abundances using leaky box model of cosmic ray propagation in the interstellar space. The results are compared with those of other investigators and a general agreement is obtained. However, a discrepancy arises especially in the case of Al which is not detected in the present investigation.