S. J. Czyzak

A spectroscopic study of moderately bright planetary nebulae

Spectroscopic results are presented for most of the nebulae observed in a programme involving some forty planetaries measured with an image tube scanner at Lick Observatory and with a photo-electric spectrum scanner at Mt. Wilson Observatory. The spectroscopic range normally covered, λ 3700 to λ 8700 is supplemented for a few objects with appropriate photographic data calibrated photoelectrically for the region λ 3120-λ 3800. Available published photoelectric data are also employed to improve the calibration of the finally adopted system of intensities.The main thrust of the programme is to investigate weaker lines, arising from less abundant ions, or due to less favorable excitation conditions. Information pertaining to additional ions gives further diagnostic data on the nebular plasma.For a given nebula, different diagnostics suggest different values of the electron temperature and density. These are believed to represent actual variations in physical conditions from point to point within the nebula, although in some instances, they may reflect inadequacies in atomic parameters, particularly collisional cross-sections. The spectroscopically most interesting nebulae show a wide variation in physical conditions, indicated by lines ranging in excitation from those of Mgi to [Fevii]. Relatively cool clouds of denser material appear to be immersed in a high excitation plasma excited by a hot central star.

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) 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)roughly-equal1.0, 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 approx.1.5 dex. The abundances of oxygen, neon, sodium, sulfur, chlorine, potassium, and argon are roughly solar.

Atomic structure calculations and nebular diagnostics

Consideration is given to the interpretation of the spectra of gaseous nebulae and extended stellar envelopes in terms of electron density and temperature, fluctuations of related parameters, ionic concentrations, and chemical compositions. The calculation of atomic structure, A-values, and other parameters is considered in relation to nebular diagnostics, and diagrams for diagnostic parameters are presented. Observational checks on the theory with respect to the p3 configuration are examined, and the p2 and p4 configurations are also discussed. 41 references.

On the presence of graphite in the interstellar medium

The justification for the presence of graphite in the interstellar medium is examined. The conditions necessary for growth of graphite (single crystals) and other structurally disordered carbons are discussed. The effect of structural imperfections on the mechanical, thermal, electrical, magnetic, optic and chemical properties is illustrated. From this information it is concluded that the existence of graphite (single crystals) in the interstellar medium is unlikely. While various forms of highly disordered carbon grains may exist, none would satisfy the physical properties necessary to explain both polarization and extinction simultaneously.

Spectrum of the high-excitation planetary Nebula NGC 6741 (33-2 deg 1)

Image tube observations carried out at the Lick and Mount Wilson Observatories were combined with IUE and infrared observations to study the spectra of the high-excitation planetary nebula NGC 6741. Plasma diagnostics were carried out and ion concentrations were calculated for ions from He I to Ca4(+). The ion densities and plasma diagnostics data were compared with theoretical nebular models to interpret the spectra and to obtain ionization correction factors. It is shown that the exciting star in NGC 6741 has an effective temperature near 160,000 K. The predicted abundance ratios for the lines at 5876/4686 A, 3426/3868 A, and 3727/5007 A conformed well to the observations. The derived logarithmic abundances in NGC 6741 are given in a table. 62 references.

The optical and ultraviolet spectra of the high excitation planetary nebula, CD -23 deg 12238 = Me 2-1

The bright, high-excitation planetary CD-23/sup 0/12238, Me 2-1 or (342+27/sup 0/1) has been studied in both optical and ultraviolet spectral regions with an image dissector scanner at the Shane 3 m telescope and with the IUE. Analysis is carried out with the aid of a theoretical model which is used as an interpolation device to obtain the nebular chemical composition. Carbon and nitrogen appear to be enhanced with respect to solar values, but probably not much, if any, compared with an average galactic planetary. The composition of Me 2-1 appears to differ from that of certain previously studied high-excitation objects that seem to be nitrogen-rich, notably NGC 2440 and NGC 6302. It is suggested that the precursor star may have had essentially a solar composition; C, N, O, and some Ne were manufactured and mixed to the surface layers prior to the development of a planetary shell.

Yttrium abundance in the sun.

Solar abundance of Y derived from Y II lines by computing transition probabilities and oscillator strength involving several configurations

A review of the forbidden transition probabilities of theCi sequence

For the forbidden transition of theCi sequence, the values obtained by several investigators are examined and reviewed. The differences and similarities in results obtained by several investigators are explained and are partly attributed to the method employed in calculating the atomic wave functions. These results are compared against the earlier work of Garstang (1951).

Theoretical models of planetary nebulae

Theoretical models are attempted for eight moderate excitation planetary nebulae which have been intensively observed with the image-tube scanner at Lick and in other investigations. The models are uniform density structures, often truncated, with central star energy distributions and chemical compositions so adjusted as to give an optimum fit with the observations. Although a satisfactory representation can be obtained for most of the stronger, usually observed lines, those arising from the 3p3 configuration, specifically the nebular transitions of [Sii], [Cliii], and [Ariv], often give difficulties. A comparison with results of model predictions with those from simple, traditional procedures generally shows a good agreement, except in those instances where different judgments are made in interpreting emissions of ions of 3pn configurations.

Monochromatic photographs of giantHii regions in the Magellanic Clouds

Narrow band-pass direct photographs have been secured of the central region of 30 Doradus and of several other nebulosities in the Magellanic Clouds. We have utilized an image tube camera attached to the Yale one-meter telescope at the Cerro Tololo Interamerican Observatory. Interference filters whose band passes were selected to allow for the radial velocities of the Magellanic Clouds have been utilized to record monochromatic images of [Nii] λ6584, Hα, Hei λ5876, and [Oiii] λ5007. In 30 Doradus the main filamentary structures appear to be very similar in Hα, Hei, [Nii], and [Oiii] at least in the inner regions where most spectroscopic measurements have been made. The features appear to be material bounded rather than radiation bounded and the excitation differences are very small. Likewise, in NGC 346 in the Small Magellanic Cloud the [Oiii] and Hα images are very similar, but in N44 in the Large Magellanic Cloud excitation differences do appear. The implications of these observations for chemical compositions of nebulosities in the Magellanic Clouds would appear to be that spectroscopic and scanner studies should be supplemented by monochromatic photographs. Some nebulosities can be handled by simple models while for others excitation differences must be taken into account.