Monochromatic images in Hα, Hβ, (NII) λ 6584, (SII) λ 6717 and (OIII) λ 5007 lines are presented for morphological study of planetary nebulae. Narrow bandpass (Δλ = 5 to 10 Å) interference filters are generally used in order to discriminate peculiar structures existing in different emission lines. However, large bandwidths (Δλ = 50 Å) along with long exposures, are also necessary in searching for faint nebulosities associated with planetaries.

We have obtained seeing limited spectra of the (OIII) λ 5007 Å line at a velocity resolution of 18 km s−1 over the envelope of Abell 30.

From five spectrograms obtained at five different positions in the nebula, relative ionic concentrations have been derived with respect to the nucleus. They show that the degree of excitation generally decreases with distance from the nucleus. But there are also areas with locally enhanced or attenuated excitation. Taurus data, a series of two-dimensional monochromatic images centered on (OIII) λ 5007, have been used to construct a two-dimensional velocity map. It shows a large-scale structure similar to the one of direct images with the biconical pattern being at least partly present. Areas of locally lower radial velocity which seem to be inversion symmetrically distributed with respect to the centre, are also distinguished. They do not have pronounced counterparts on direct images. The cavity model suggested by Barral et al. (1982, MNRAS 199, 95) for NGC 6302 and Icke's biconical flow model (1981, Ap. J. 247, 152) are discussed.

Observations of HI in absorption made with the Very Large Array towards the thermal radio emission of the planetary nebula NGC 6302 show two velocity components at 6 and −40 km s−1 (radial velocity with respect to the local standard of rest). The 6 km s−1 component is almost certainly due to a line-of-sight cloud, but the −40 km s−1 component is most probably associated with NGC 6302. We interpret this absorption component as coming from the neutral, outer part of an expanding (~ 10 km s−1) ring whose inner part is ionized and produces the thermal continuum. The mass in atomic hydrogen of the outer (neutral) part of the ring is ~ 0.06 M⊙. NGC 6302 is in an evolutionary stage intermediate to those of protoplanetary nebulae such as GL 2688 and evolved planetary nebula such as NCG 7293. This is the first detection of neutral hydrogen associated with a planetary nebula.

Both nebulae are of similar appearance consisting of a central core and two highly symmetrical, elongated lobes. Using the large vertical Coude spectrograph of the 2.2-m telescope on Calar Alto, Spain, we obtained long-slit spectra in the red of high spectral (12 km s−1 FWHM) and spatial (2″) resolution from various positions within the nebulae. Our data indicate high similarity in the kinematical structure of both nebulae. The central cores are dominated by very broad emission lines. The Hα profiles (width ≈ 1600 km s−1 at 5% level in M2-9) exhibit an absorption feature blue-shifted by ≈ 20 km s−1 relative to the emission maximum, similar to profiles observed in some Herbig-Be-stars.

Up to now, the geometrical and kinematical structure of the well-known bizarre nebula NGC 7026 has not been discussed in the literature. Using the large vertical Coude spectrograph of the 2.2 m telescope on Calar Alto, Spain, we obtained long-slit spectra covering the nebula at 5 different position angles, in the ranges from 4730 to 5050 Å and from 6470 to 6770 Å. The high spectral (up to 6 km s−1 FWHM) and spatial resolution (seeing-limited ≲ 2″) reveals a rather complex structure in the lines of Hα, Hβ, (OIII) λλ 4959, 5007, HeI 6678, HeII 6560, (NII) λλ 6548, 6583, and (SII) λλ 6716, 6731. Generally, the lines exhibit a double “bowed” appearance; both components consist of several condensations of small angular extent. The velocity field suggests a non-spherical expansion of an elongated thin shell structure. The observations can be explained by an ovoidal or “bipolar” configuration of the nebula consisting of an expanding equatorial toroid (Vexp = 54 km s−1 in (SII)) and two blobs moving at higher velocities outwards along the polar axis (inclination angle with respect to the line-of-sight: 75°). The geometrical and kinematical structure observed in the lines of various excitation degrees indicates a pronounced ionization stratification and allows to derive the dependence of the expansion velocities on the radial distance inside the nebulae. No noticeable extinction within the nebula has been found. The bipolar structure of NGC 7026 resembles that of some other planetary nebulae and might be caused by an equatorial concentration of the circumstellar material lost during the late phase by the progenitor asymptotic giant-branch star. Using distances and interstellar extinctions of 48 stars within 1° of the planetary, we determined a distance of 2180 (≈ ± 700) pc for the nebula.

The Kuiper Airborne Observatory has been used to make measurements of the infrared forbidden lines of (SIII) 18.72μm, (NeV) 24.28μm and (OIV) 25.87μm in eight planetary nebulae. In all cases the beam was larger than the emitting region. The observed line fluxes are used to determine ionic abundances under the assumption of constant density throughout the relevant volume as determined by optical observations. In some cases the NeV near UV lines are used in conjunction with the infrared measurements to determine the electron temperature in the NeV emission regions. The (SIII) 33.47μm line can be used with the (SIII) 18.72μm line flux to characterize the clumping within the nebulae.

Absolute fluxes of the 3.3μm features were measured for 12 planetary nebulae. Both narrow-band photometry and low resolution spectrophotometry were used. Photometry was performed with narrow bandpass filters centered at 3.28μm and 3.72μm(λ/Δλ = 14). Using a CVF spectrophotometer, the 3.1μm – 3.8μm spectra of four nebulae (IC 418, IC 2149, NGC 6543, NGC 6572) were obtained. The values of the fluxes measured with the two different methods agree well.

Dielectronic recombination coefficients have been calculated for some ions of C, N and O by Storey (1981, Mon. Not. R. astr. Soc., 195, 27P). Using the same approach, we have extended those calculations to all other ions of C, N and O for which a dielectronic contribution to the total recombination coefficient might be expected at nebular temperatures. Recombination coefficients have been calculated in the temperature range from 5000 K up to the temperature at which the Burgess general formula becomes valid. The total dielectronic recombination coefficients are fitted to a simple function of the electron temperature.

The lines of the transitions between the subordinate levels of the CIII, NIII etc. ions are observed in the spectra of planetary nebulae (PN) (1). Their theoretical intensities may be found by solving the stationarity equations and accounting for both the recombination and cascade radiative transitions. It is possible to calculate the recombination spectra in various approaches: the single- or multi-configuration approximations (SCA and MCA) making use of both the superposition of configurations (SC) or the multiconfigurational Hartree-Fock-Jucys equations (2), taking into consideration the contribution of the dielectronic recombination to the intensities of the recombination lines. The energy spectra, the transition probabilities etc., as a rule ought to be calculated in the intermediate coupling scheme (2). Both analytical or numerical (e.g. Hartree-Fock) wave functions may be adopted.

We have investigated the effects due to curvature and radial expansion in a planetary nebula, with hydrogen and helium. We have solved the radiative transfer equation with spherically symmetric approximation in the rest frame. We have included dust in static as well as in expanding media. The effects on the internal sources and the mean intensities at the internal points have been calculated. It is found that the effect due to the presence of dust is to reduce the mean intensities, and curvature effects on the internal sources are more pronounced than the effects due to radial expansion of the gas.

The C IV resonance doublet at λ1548, 1550 is an important diagnostic tool in the study of planetary nebulae. The predicted theoretical intensity ratio of 2:1 is, however, rarely observed in high dispersion IUE spectrograms. The observed values for a sampling of 15 objects of differing excitation class range from a low of 0.74 to a high of 1.99. Variations in optical thickness, extinctions due to nebular dust, and interstellar absorption have been proposed as the cause for the deviation. Line profiles for the C IV doublet vary for different nebulae, encompassing a wide range of shapes which include: 1) narrow symmetric (Gaussian) profiles, 2) wide symmetric, 3) asymmetric with steep blue edge and extended red wing, 4) asymmetric with steep red edge and extended blue wing, 5) P Cygni profiles, 6) split peaks due to expansion velocities, and 7) multiple peaked or chaotic line structure. In addition to the main features, occasionally weak (subsidiary or ghost?) features occur that do not agree in intensity with the main line ratios but are not attributable to lines of other ions. Ultraviolet radial velocity displacements are in good agreement with optical data. Similar diversity in profiles and intensity ratios have been observed in protoplanetary nebulae and symbiotic stars. (Paper to appear in Astron. Astrophys.)

Our results are based on SWP 3215, a 120 min large aperture exposure. The electron density derived from N IV), Si III) and C III) ratios are log Ne < 4.3, 5.0 and 3.5. The measured resonance line ratio 1239/1243 of N V is 1.2 ± 0.1 and 1549/1551 of C IV is 1.9 ± 0.2. Both ratios are expected to be 2.0. Furthermore, it had already been reported that the C IV and N V resonance lines are fainter than predicted from models by factors from ~ 4 to ~ 6 (Torres-Peimbert et al., 1980, The First Two Years of IUE, NASA CP-2171, 641). Internal dust cannot account for any significant deviation from 2 for the resonance doublet ratio of N V (Hummer and Kunasz, 1980, Ap. J., 236, 609). However, the anomalous ratio of N V could be explained by a generally distributed hot ionized medium compatible with the C IV absorption found in approximately the same direction by Cowie et al. (1981, Ap. J., 248, 528).

Ionization models for NGC 6210, 7009, 3242 and II 2003 have been constructed from optical and IUE spectroscopic data. The CIV 155 nm resonance line is predicted about ten times stronger than observed. Radiative transfer calculations of the CIV lines in a spherical nebula, assuming partial frequency redistribution, were made to investigate the effects of dust absorption and an additional depopulation of the upper level.

The radiation field for a resonance line is calculated for a gaseous nebula which consists of a dust-free and a dust filled layer (1/2 or 1/4 of the total volume). For comparison we compute also the line profiles for corresponding homogeneous configurations, with and without dust.

The planetary nebula Hb 12 has recently been observed at infrared (Aitken et al., 1979) and radio (Purton et al., 1982) wavelengths. The detection of a silicate emission feature in the 8-13 μm region suggests that the nebula is oxygen rich. A high emission measure is derived from the radio spectrum, implying a high intrinsic density.

Sw St 1 is a compact and possibly young planetary nebula which has been recently observed at infra red (Aitken et al., 1979) and radio (Kwok et al., 1981) wavelengths. In the 8-13 μm region, a silicate emission feature is observed, suggesting that the nebular envelope is oxygen rich. The high emission measure determined from the radio observations implies a large value for the electron density.

The planetary nebula NGC 40 has a WC8 central star. From analysis of IUE spectra of the star, Benvenuti, Perinotto and Willis (1981, IAU Symposium 99) obtain the remarkable abundance ratio C/He ~ 0.2 and probably no hydrogen. The question arises as to whether the nebular shell has abnormal abundances.

Measurements of line intensities over a spectral range generally as great as 1300 Å to 11,000 Å have been made in four positions in the Ring Nebula and eight positions in NGC 7009. Ionic abudances determined from optical and UV lines are in good agreement, except that the C2+ abundance inferred from the optical 4267 Å recombination line is as much as 10 times higher than that measured from the 1906, 1909 Å CIII) lines. In both nebulae, this discrepancy is greatest nearest the central star. At the present time the most attractive explanation seems to be that the 4267 Å line is affected by resonance fluorescence due to light from central stars of planetaries.

YM29 is a nearby, filamentary, low surface brightness nebula whose spectrum exhibits lines of both high and low excitation. Johnson and Rubin (1971, Ap. J. 163, 151) observed YM29 as a weak radio source; despite uncertainties as to the thermal nature of the radio spectrum and their lack of a good optical spectrum, they classified YM29 as a peculiar planetary nebula. Based on photographic spectra, Liebowitz (1975, Ap. J. 196, 191) has reported that in YM29 the (N II) lines at λλ 6548, 6584 are several times the strength of Hα.