Spectrophotometry of five planetary nebulae

The results of a spectroscopic investigation of five planetary nebulae are given. The relative intensities of emission lines observed in them were determined. The electron density and electron temperature of the central region of the nebula KjPn 8 were determined. It was shown that the gas in this region is very highly excited. Translated from Astrofizika, Vol. 41, No. 3, pp. 367–375, July–September, 1998.     

Dynamical structure of planetary nebulae in three dimensions

The interacting of two winds model and a nonspherical density functionin three dimensions is introduced to study the dynamical structure ofplanetary nebulae. A fast wind with a mechanical energy interacts with asuper wind mass-loss rate of 2 × 10^-10 M yr and avelocity of 10 km s^-1. As a result it produces a dense and luminosmedium.Taking into account the above assumptions, we introduce the code(DS3D),and numerically we calculate the following physical quantities:the shell velocity, the shell radious and thickness, and other physicalquantities throughout the entire nebula.     

Far infrared emission from three new planetary nebulae

As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10^-6 to 3.7 × 10^-5 forM _dust /M _bd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.     

Hydrogen-poor planetary nebulae

Five planetary nebulae are known to show hydrogen-poor material nearthe central star. In the case of A58, this gas was ejected following alate thermal pulse similar to Sakurai's Object. In this paper I will reviewthese five objects. One of them, IRAS 18333 –2357, may not be a truePN. I will show that there is a strong case for a relation to the [WC]stars and their relatives, the weak emission-line stars. The surfaceabundances of the [WC] stars are explained via diffuse overshoot intothe helium layer. The hydrogen-poor PNe do not support this: theirabundances indicate a change of abundance with depth in the heliumlayer. A short-lived phase of very high mass loss, the r-AGB, isindicated. Sakurai's Object may be at the start of such a phase, and mayevolve to very low stellar temperatures.     

Photoionization models and chemical abundances of three halo planetary nebulae

Abtracts Photoionization models have been constructed to explain the line emission of the three halo planetary nebulae: K 648, 49+88°.1 and 108–76°.1. The charge transfer reactions between neutral hydrogen and different ions were taken into account in ionization equations. Due to lack of observational information, radiation-bounded as well as matter-bounded models have been considered. Both these models indicate that He and C abundances are close to solar values whereas the heavier elements are depleted.Partially supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil.This paper was entirely written when I received a preprint of Peimbert and Torres-Peimbert (1979) whose results confirm a high abundance of carbon in the planetary nebula 49+88°.1.     

Magnetic fields in planetary nebulae and post-AGB nebulae

Magnetic fields are an important but largely unknown ingredient of planetary nebulae. They have been detected in oxygen-rich asymptotic giant branch (AGB) and post-AGB stars, and may play a role in the shaping of their nebulae. Here we present SCUBA submillimetre polarimetric observations of four bipolar planetary nebulae and post-AGB stars, including two oxygen-rich and two carbon-rich nebulae, to determine the geometry of the magnetic field by dust alignment. Three of the four sources (NGC 7027, 6537 and 6302) present a well-defined toroidal magnetic field oriented along their equatorial torus or disc. NGC 6302 may also show field lines along the bipolar outflow. CRL 2688 shows a complex field structure, where part of the field aligns with the torus, whilst an other part approximately aligns with the polar outflow. It also presents marked asymmetries in its magnetic structure. NGC 7027 shows evidence for a disorganized field in the south-west corner, where the SCUBA shows an indication for an outflow. The findings show a clear correlation between field orientation and nebular structure.     

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.     

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 3p ³ 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 3p ⁿ configurations.     

Theoretical models of planetary nebulae

Introduction of the O⁺⁺+H⁰O⁺+H⁺ charge exchange rate suggested by Butler, Bender and Dalgarno leads to theoretical nebular models that differ from those previously computed in several important respects. Different elemental abundances, bluer central star energy distributions, and truncated (material limited) models are required. If the argon abundance is fixed from the 7135 [Ariii] line intensity, 4740 [Ariv] is invariably predicted to be much too strong. Better atomic parameters, together with improved charge exchange rates for other ions, and more accurate dielectronic recombination rates may alleviate the situation.     

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.     

Theoretical models of planetary nebulae

Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN _H=100 cm^–3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as 4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and 4686 Heii.     

IRSPEC observations of planetary nebulae

We have obtained infrared spectra of planetary nebulae in the 3.0–3.8 m range using IRSPEC, the ESO grating infrared spectrograph, attached to the 3.6-m telescope. We find evidence of an evolution of the carriers of the unidentified emission bands in the 3 m region, and explain the observed behaviour in terms of ion irradiation from fast stellar wind.Based on observations collected at the European Southern Observatory, La Silla, Chile.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Univers, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Accurate coordinates of planetary nebulae

Accurate optical coordinates of 734 PNe, measured on the charts of the Digitized Palomar Sky Survey, are presented. As a result of the discussion about the external accuracy the constants –0.8″ in RA and +0.8″ in DEC should be added to the coordinates measured by us. They were used but rounded off already in CGPN(2000). The list and measurements of new 31 candidates of central stars are given which might be interesting for stellar evolution.     

Plasma diagnostics of planetary nebulae

Diagnostics for the rarefied plasmas in gaseous nebulae are reviewed, beginning with the pioneering papers of V. A. Ambartsumian. These papers, as well as the diagnostic techniques which have been developed on the basis of ideas contained in them, are discussed. Diagnostic techniques for homogeneous, as well as inhomogeneous, plasmas are described. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 363–383 (August 2008).     

Flows in clumpy planetary nebulae

The dynamics of clumps observed in planetary nebulae are considered. The possibility that SiO maser spots in evolved stars and the planetary nebula clumps are formed by the Parker instability behind shocks in pulsating stars' atmospheres is raised. Molecular observations of the clumps are suggested. The effects of the ablation of clumps on the global flow structure of a more tenuous plasma in which they are embedded are reviewed.     

Filamentary structures in planetary nebulae

We have studied small-scale, filamentary features in 14 planetary nebulae and found that some structures are recurrent and shaped like the letters V and Y, with the apex or stem pointing toward the central parts of the nebula. Two such filaments containing dust, one in NGC 3132 and one in NGC 7293, were investigated in more detail. The mass and density of the filaments were obtained from extinction measurements, and their physical properties were derived. We propose that the structures are confined by magnetic fields, and derive magnetic field strengths of about 10⁻⁸ T, in line with earlier estimates. We also estimate the magnitude of the electric currents that we expect are generated in these dynamic systems. We propose a theory where the magnetic fields control the sculpting and evolution of small-scale filaments. This theory demonstrates how the substructures may form magnetized flux ropes that are twisted around each other, in the shape of double helices. Similar structures, and with similar origin, are found in many other astrophysical environments.