We present analysis of the physical conditions and chemical abundances in NGC 6453, the Cat's Eye Nebula. Using archival HST images in conjunction with ground-based long-slit scanning spectra, we have produced an [O III] forbidden line temperature map of the nebula, which shows that the temperature remains constant at around 8000 K across the nebula. From the long-slit spectra, we have determined abundances both from collisionally excited lines (CELs) and optical recombination lines (ORLs). The ORL abundances are higher than the CEL abundances by a factor of approximately two.

Abell 30 is one of a small number of PN known as born-again PN, which appear to be old nebulae whose central star has undergone a further ejection of highly processed material. It consists of a large, faint, spherical shell, in which several bright knots are embedded. The knots were first noted by Jacoby (1979), and analysis of their abundances by Hazard et al (1980) and Jacoby & Ford (1983) showed that they are extremely hydrogen-deficient.

We have derived C, N and O abundances, relative to H, using optical recombination lines (ORLs), for a number of galactic planetary nebulae and for three Magellanic Cloud PNe (LMC N66, N141, SMC N87) and compared them with the corresponding abundances derived from collisionally-excited lines (CELs). Our goal was to investigate the fact that PNe ORL abundances are in most cases larger than those obtained from CELs. Our scanning, long-slit observations were combined with large-aperture IUE, IRAS and ISO data to yield integrated abundances for more than half of our target objects.

Ratag et al (1997) determined the chemical abundances of He, O, N, Ne, S, Ar, and Cl in ~110 planetary nebulae which are likely to be in the Galactic Bulge. The abundances are derived by employing theoretical nebular models as interpolation devices in establishing the ICFs. The overall agreement between the abundances obtained by employing the model-ICFs and those derived from the theoretical models is reasonably good. Based on this, it is of interest to study the reliability of various ICFs as well as to derive some alternative ICFs. The focus of the present study is sulphur.

We report the results of spectrophotometric determinations of chemical abundances for a planetary nebulae sample located outside the solar circle, with galactocentric distances between 8 and 14 kpc. Our results show a decreasing gradient for R>10 kpc and a possible dependence of the gradient with the age of the progenitors (Work supported by FAPESP).

We have constructed photoionization models of NGC 6153, M 2–36, and M1–42. These planetary nebulae show large differences, both, in the CNO and Ne abundances as derived from recombination lines and collisionally excited lines, as well as, in the electron temperature determined from Balmer jump and [OIII] lines. The model nebulae have low mass (about 1% of the total nebular mass) inclusions where the CNO and Ne abundances are enhanced by a factor of 200 or so.

In a sample of 30 young planetary nebulae, proto-PNe and other emission line objects we have found 11 young PNe and 2 symbiotic stars that show very broad wings of the emission Hα line (from 800 km s-1 and up to 5100 km s-1). For 7 objects, their first report was in Arrieta & Torres-Peimbert (2002).

Liu et al. (1995) and Luo, Liu & Barlow (2001) determined the CNONe abundances in NGC 7009 using optical recombination lines (ORLs) and found that they are all approximately a factor of five higher than the corresponding values derived from collisionally excited lines (CELs). We have obtained new deep high resolution long-slit spectra of NGC 7009. The data have been used to map the electron temperature, density and element abundances across the nebula, using both CELs and ORLs. While the electron temperature derived from the [O III] forbidden line ratio, Te([O III]), is found to be largely constant, that derived from Balmer jump of H I recombination spectrum, Te(BJ), shows large amplitude complicated variations. The ratios of the heavy element abundances derived from ORLs to those deduced from CELs are found to be correlated with the difference between the difference between Te([O III]) and Te(BJ) – a relation previously known to exist from analyses of the integration spectra of individual nebulae (Liu et al. 2001).

Using CFHT/SIS Fabry-Perot interferograms of the planetary nebula NGC 40, we present an investigation of the statistical properties of fluctuating gas motions using structure functions traced by Hα emission-line centroid velocities (Grosdidier et al. 2002). We consider the structure functions 〈|Δv(r)|p〉 of order p, i.e. the spatially averaged moments of order p of the spatial velocity increments at projected spatial scale r of NGC 40's velocity field. In this poster, we test for i) Structure-function scaling related to turbulence in the nebula, 〈|Δv(r) |p〉 ~ rχ(p),ϛ and ii) Nonlinearity of the observed scaling exponents χ(p)s, as expected for intermittent turbulent flows. The first order structure function is indeed found to scale at the smallest scales with χ(1) = H ≈0.68. This value is larger than the value expected in the case of incompressible or compressible turbulence, for which one would obtain H = 1/3 or 1/2, respectively. This result suggests that the Hα layer is thick compared to the projected spatial separations (O'Dell & Castañeda 1987, and references therein). We can give a more quantitative description of the turbulent status of the PN NGC 40 through the examination of the structure function for different orders. Additionally we can discuss the nature of the turbulence in terms of Universal Multifractals, a continuous-scale limit of multiplicative cascades (Schertzer & Lovejoy 1987) and derive the level of intermittency in the nebula. The function χ(p) is indeed found to be nonlinear and well reproduced with the following Universal Multifractal parameters: α ≈ 1.90–2 (the field is highly multifractal with a gaussian generator) and C1 ≈ 0.08 (the field suffers significant intermittency, which is incompatible with monofractal additive stochastic models usually introduced in similar studies): ϛ(p) = p × H − C1(pα - p)/(α - 1). Fig. 1 shows the hierarchy of exponents χ(p) along with its best Universal Multifractal fit. Our results on the Wolf-Rayet ring nebula M 1–67 (Grosdidier et al. 2001) led to the same level of multifractality (α ≈ 1.9) but with smaller intermittency (C1 ≈ 0.04). Preliminary results on the Orion nebula (Grosdidier 2002) reveal a turbulent status relatively similar to that of the PN NGC 40. On the whole, such a study provides a way to quantify turbulence in PN, and more generally in other HII regions (with potential implications for the estimation of temperature fluctuations) and give insight on astrophysical turbulence for its own sake.

A three-dimensional self-consistent photo-ionisation code is developed using Monte Carlo techniques in order to build realistic models of photoionised nebulae of arbitrary geometry and density distribution. The code's results are benchmarked against those of estabilished codes. Two models are computed for the planetary nebula NGC 3918 using two different density distributions. The results of the two models are compared with the observations.

In the spectrum of the young bipolar planetary nebula M2-9, we detected the He II Raman scattered feature at 6545 Å. However, in the same spectrum the He II emission lines at 6527 Å and 6560 Å are absent, which implies that the He II emission region is hidden from our line of sight and that the H I scattering region is pretty much extended not to be obscured entirely. We perform photoionization computations to estimate the physical size of the He II emission line region ≲ 1015 cm in the presence of hot luminous star with T ≳ 105 K and L ≲ 103L⊙.

With strategically important diagnostic lines of, e.g., [O II], [O III] and [S II], secured with the Keck I HIRES, we obtained electron densities and temperatures, while retaining 3-D spatial information for the well-known elliptical nebula NGC 7009: we found that the temperature fluctuations exceeded those reported in the HST imaging study, i.e. Te ~9500 – 11500 K; we also found large velocity dispersions in the [S II] maps (with extremely high density fluctuations, i.e. log Ne = 3.8 – 4.5), but not in the [O II] ones. The [S II] map indicates that this emission is from numerous small-scale blobs of size ~ 1″ spread over a wider region, while [O II] shows no such evidence. The [S II] emission is likely to be due to shock excitation, while the [O II] emission is perhaps due to photoionization.

Péquignot et al. (1997) reported the discovery of a broad spectral feature to the blueward of Hβ, centred at a wavelength of 4852Å, in NGC 7027. This was conclusively shown to arise from the Raman scattering of He++ (2–8) UV photons by neutral H, and was the first detection in a planetary nebula. Raman scattering features had previously been observed in symbiotic stars: Raman scattering of O VI by neutral H was discovered by Schmid (1992) and also found for He II by van Groningen (1993). The large width of the resulting feature is mainly due to the conservation of the line width in frequency during the scattering process.

The Far Ultraviolet Spectroscopic Explorer (FUSE)> satellite provides a unique opportunity to obtain high-resolution far-UV spectra of a wide variety of astronomical objects, including planetary nebulae. Most FUSE observations of PNe to date have concentrated on the hot central star, providing a very effective way to study the atmosphere of the central star, the surrounding nebula through the absorption features from circumstellar gas. FUSE has found evidence of hot molecular hydrogen in several planetary nebulae, including M27 and BD+30° 3639. Central star spectra also reveal new information about stellar winds, mass loss, and photospheric abundances.

Long slit spectra of astronomical objects either contain point sources, characterized by a known Point Spread Function (PSF), which is often wavelength dependent, and extended sources, such as nebulae, whose spatial extent is not a priori known. The analysis of long slit spectra consists in separating the spectrum into either: the point source(s), free of the background (“extraction”); or the extended source(s), free of contaminating point source spectra. Depending on the scientific aim, one or both of these data are of interest, such as the spectrum of the central star of a planetary nebula AND the line and continuum spectrum of the nebula with the star removed. In the simple case of a point source with a background gradient, the spectrum of the point source can be simply extracted by subtracting a background fit by a low order function and summing (perhaps with weights, as in optimal extraction) the point source signal at each spectral element in the cross-dispersion direction. When the background is complex or there are many point sources, there is no guide as to how to fit the extended source spectrum beneath the point sources. Simple methods can give a poor estimate of the spectra of point sources and the spectrum of the background in the vicinity of the stars. The application of image restoration algorithms to the spatial component of long slit spectra offers a potential solution.

During the ORFEUS-SPAS II mission (November 19th - December 7th 1996, aboard the space shuttle Columbia), the elliptical planetary nebulae NGC 6543 and NGC 6826 have been studied with the Echelle spectrometer. The instrumental wavelength range and resolution are 900Å - 1400Å and 0.1Å, respectively (R = 10000), which provides detailed information about emission and absorption lines which are inaccessible for ground-based observations. We present a new analysis of the absorption lines imposed on the spectra of the central stars.

The interior of a planetary nebula (PN) is expected to be filled with shocked fast wind from the central star. This hot gas plays the most important role in the dynamical evolution of the PN; however, its physical conditions are not well-known because useful X-ray and far-UV observations were not available until the advent of Chandra, XMM-Newton, and FUSE. This paper reviews X-ray observations of the hot gas in PN interiors and far-UV observations of the interfaces between the hot gas and the dense nebular shells.

We report the discovery of a correlation between X-ray luminosity of PNe and bolometric luminosity of central stars from CHANDRA data and discuss briefly its interpretation.

XMM-Newton EPIC observations of the planetary nebula NGC 7009, the Saturn Nebula, have detected extended X-ray emission from its central cavity. The diffuse X-ray emission must originate in the shocked fast stellar wind. Spectral analyses show that the temperature of the hot gas is 1.7 x 106 K. The RMS density derived from the volume emission measure is a few tens H-atom cm-3. The hot gas does not appear over-pressurized with respect to the nebular shell. The Saturn Nebula may represent an evolutionary stage at which the dynamic effects of the hot gas in the central cavity on the cold nebular shell starts to decline due to the diminishing strength of the fast stellar wind and the expansion of the central cavity.

The morphology of a complete sample of 255 northern planetary nebulae (PNe) was studied and correlated with the nebular parameters. PNe were classified according to the following scheme: round (R, 25%), elliptical (E, 58% of the sample), and bipolar (B, 17%). Bipolars include the quadrupolar subsample. A subclass of pointsymmetric and multiple shell PNe was also found. Nine per cent of ellipticals and 46% of bipolars were found to be pointsymmetric. Thirty-five per cent of the round and 22% of the elliptical PNe were found to be multiple shell PNe (MSPNe). Galactic latitude was found to be different for each morphological class (|b| = 8°, 5° and 2° for types R, E, and B, respectively). Galactic height was also found to vary: 〈z〉 = 647, 276, and 100 pc for categories R, E, and B, respectively. Segregation according to the chemical abundances was also found, with helium abundances of 0.10, 0.12, and 0.14 and N/O of 0.21, 0.31, and 1.33 for types R, E, and B, respectively. Both galactic distribution and chemical abundances point to a different stellar population for each morphological class, the round and bipolar types being the result of low and high stellar mass progenitor evolution, respectively.