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Aller, L. H.

Publications and source records attributed to Aller, L. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

An analysis of the planetary nebula NGC 2867

Spectroscopic observations made with the Anglo-Australian Telescope are combined with IUE data to provide material for a theoretical analysis of NGC 2867. Except for the S II forbidden line, line intensities in the optical region can be represented reasonably well by a simple theoretical model based on Balick's (1975) work. The model is used to assess temperatures in strata of higher ionization where no good spectroscopic diagnostic criteria are available and to derive ionization correction factors to account for unobserved stages of ionization. The derived chemical composition is compared with that of the sun and other planetaries. NGC 2867 shows no significant abundance peculiarities or abnormalities.

Aller, L. H.↗
NASA NTRS1981

The abundances of neon, sulfur, and argon in planetary nebulae

New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.

Beck, S. C.↗
NASA NTRS1981

A spectroscopic study of the high excitation nebula NGC 6302

The wonderfully intricate irregular gaseous nebula NGC 6302 shows a great range of excitation from the S I to Fe VII forbidden lines. Data obtained with the International Ultraviolet Explorer (IUE) covering the spectral range of wavelengths 1200-3203 and with the image-photon counting system at the Anglo-Australian telescope emphasizing the region of wavelengths 3200-4880 are used for a new determination of the chemical composition of this object. No simple theoretical model can represent the observed intensities. Helium and nitrogen are enhanced in abundance, as noted by previous observers, but the enrichment of nitrogen is a whole order of magnitude. Carbon and oxygen are decreased in abundance, neon and heavier elements show a 'normal' abundance pattern, but calcium and possibly silicon are depleted; presumably they are concentrated in grains.

Aller, L. H.↗
NASA NTRS1981

The optical and ultraviolet spectrum of the planetary nebula NGC 2440

New measurements of the optical and ultraviolet emission-line intensities of the high-excitation planetary nebula NGC 2440 in the wavelength range 1240-8578 A are analyzed with the aid of photoionization models. The observed O III and N II forbidden-line temperatures (13,800 K and 10,000 K, respectively) differ by more than the models predict. Inclusion of charge-transfer reactions at published rates improves agreement between calculated and observed abundances of many ions, but worsens the agreement for several highly ionized ions. Nitrogen shows a larger overabundance N(N)/N(O) approximately equal to 1.0, whereas ultraviolet lines give a carbon abundance close to the solar value. The refractory elements magnesium, calcium, and iron have similar gas-phase depletions of approximately 1.5 dex. The abundances of oxygen, neon, sodium, sulfur, chlorine, potassium, and argon are rougly solar.

Shields, G. A.↗
NASA NTRS1981

Analysis of high excitation planetary nebulae

Combination of extensive ground-based spectroscopic observation of high excitation planetary with IUE data permit determination not only of improved diagnostics but also better abundances for elements such as C and N that are well represented in the ultraviolet spectra and also C, Ar and metals Na, Ca and K whose lines appear in the wavelength 3200-8100 A region.

Aller, L. H.↗
NASA NTRS1974

Forbidden-line excitation data for certain coronal lines

Some new data pertinent to forbidden transitions for coronal lines of S XII, Ca XIII, K XI, Mn XIII, Fe XIV, Co XV, Ni XVI, N XV, Cr IX, Fe X, and Ni XII are presented. We include additional calculations of collision strengths for a number of ions and then set up and solve the equations of statistical equilibrium in the limiting approximations in which contributions to level population by cascade from higher levels are neglected. We then calculate volume emissivities per ion as a function of density and temperature.

Czyzak, S. J.↗
NASA NTRS1974

The solar abundance of beryllium

The solar abundance of beryllium is deduced from high-resolution Kitt Peak observations of the 3130.43- and 3131.08-A lines of Be II interpreted by the method of spectrum synthesis. The results are in good agreement with those previously obtained by Grevesse (1968) and by Hauge and Engvold (1968) and indicate that in the photospheric layers, beryllium is depleted below the chondritic value by a factor of about two. It is found that the beryllium abundance is equal to logN(Be)/N(H) + 12 = 1.08 plus or minus 0.05.

Ross, J. E.↗
NASA NTRS1974

The solar abundance of thulium

Consideration of one relatively unblended line of the solar spectrum, namely, the 3131.258-A line of Tm II, which yields a thulium abundance of 0.80 plus or minus 0.10 with the Corliss and Bozman (1962) f-value. The uncertainty of this figure is discussed in conjunction with the contradictory findings of some other investigators. The need for further detailed study of the lanthanides by the method of spectrum synthesis is pointed out.

Ross, J. E.↗
NASA NTRS1974

The solar abundance of germanium

Spectral scans of the wavelength regions around 3039 A and 3269 A were used as a basis for the determination of the solar abundance of germanium. A solar model similar to the one given by Elste (1968) was used in the analysis of the data. The germanium abundance values obtained are presented in a table. Taking into account an abundance compilation for the solar system conducted by Cameron (1973), it is concluded that the 'solar system' and solar atmospheric abundances of germanium are in accord.

Ross, J. E.↗
NASA NTRS1973

A photometric study of the counterglow from space.

Photometric observations of the region of the counterglow (Gegenschein) made from OSO-6 are examined. The observations were made during the September to October 1970 period when the counterglow was between the Milky Way arms at a relatively high (negative) galactic latitude. The lines of sight included a slice across the antisun region at an inclination of 48 degrees to the ecliptic. A comparison is made between the photometric gradients as measured from the spacecraft and similar gradients deduced from ground-based observations.

Roach, F. E.↗
NASA NTRS1973

A photometric perturbation of the counterglow.

An example of photometric variability of a counterglow region in the antisolar direction is discussed. A speculative interpretation of its significance leads to the suggestion that the weakened radiance of the counterglow may in this case be due to a dust cloud of scattering material in the general region of the earth-moon system.

Roach, F. E.↗
NASA NTRS1972

The solar abundance of silver.

Low noise, high resolution spectral scans have been obtained for the resonance lines of silver (3280.7 and 3382.9 A), observed at the center of the solar disk. The data are analyzed by the method of spectral synthesis, wherein we employ a model atmosphere resembling Elste's (1968) model, and checked by limb-darkening observations. The present kinematical model adopts a macroturbulent velocity of 2.2 km/sec and no microturbulence. With this model line profiles can be reproduced without invoking implausibly large collisional damping constants. The silver abundance turns out to be a factor of four under the value found from the Type I carbonaceous chondrites.

Ross, J. E.↗
NASA NTRS1972

Surface photometry of celestial sources from a space vehicle - Introduction and observational procedures.

Consideration of the possibility of studying diffuse celestial sources of relatively low surface brightness such as the Milky Way, zodiacal light, and gegenschein from above the earth's atmosphere with equipment flown in artificial satellites. The techniques used for this purpose are reviewed, and some of the difficulties encountered in daytime observations from satellites by the use of a special photometer and polarimeter flown in the orbiting skylab observatory, OSO-6, are cited.

Roach, F. E.↗
NASA NTRS1972

The solar abundance of gold.

Thirteen spectral scans (in the direction of increasing and decreasing wavelength) obtained with a new double-band pass monochromator system put into operation with the Michigan spectrometer at the Snow telescope at Mount Wilson are interpreted by the method of spectral synthesis. The intensity profile of the 3122.79 line, attributable to gold, is interpreted, and a representation of the solar spectrum in the neighborhood of the AU 3122.79 line is given in tabular form.

Ross, J. E.↗
NASA NTRS1972

The abundances of the elements.

For the immediate cosmic environs, there are three traditional sources of element abundance data, including chondritic meteorites, the solar atmosphere, and a certain type of average of stars near the sun. Cosmic ray material, or at least the particles that were accelerated to very high energies, includes contributions from great distances in the Galaxy, and perhaps from outside the Milky Way system itself. Problems in the determination of solar system abundances are discussed together with some factors affecting the profiles of spectral lines, the abundances of some elements in the solar atmosphere, young stars and the interstellar medium, the helium to hydrogen ratio, the helium isotopes, and abundances of light elements in the Galaxy and in neighboring galaxies.

Aller, L. H.↗