A B S T R A C TWe present deep, high-resolution optical spectra of two Galactic bulge planetary nebulae (PN), M 1-42 and M 2-36. The spectra show very prominent and rich optical recombination lines (ORLs) from C, N, O and Ne ions. Infrared spectra from 2:4-197 mm were also obtained using the Short and Long Wavelength Spectrometer (SWS and LWS) on board ISO. The optical and infrared spectra, together with archival IUE spectra, are used to study their density and thermal characteristics and to determine elemental abundances.We determine the optical and UV extinction curve towards these two bulge PN using observed H I and He II recombination line fluxes and the radio free -free continuum flux density. In the optical, the reddening curve is found to be consistent with the standard Galactic extinction law, with a total to selective extinction ratio R ; AðVÞ/ EðB 2 VÞ ¼ 3:1. However, the extinction in the UV is found to be much steeper, consistent with the earlier finding of Walton, Barlow & Clegg.The rich ORL spectra from C, N, O and Ne ions detected from the two nebulae have been used to determine the abundances of these elements relative to hydrogen. In all cases, the resultant ORL abundances are found to be significantly higher than the corresponding values deduced from collisionally excited lines (CELs). In M 2-36, the discrepancies are about a factor of 5 for all four elements studied. In M 1-42, the discrepancies reach a factor of about 20, the largest ever observed in a PN. M 1-42 also has the lowest Balmer jump temperature ever determined for a PN, T e ðBJÞ ¼ 3560 K, 5660 K lower than its [O III] forbidden line temperature.We compare the observed intensities of the strongest O II ORLs from different electronic configurations, including l4649 from 3s-3p, l4072 from 3p-3d, l4089 from 3d-4f, and l4590 and l4190 from the doubly excited 3s 0 -3p 0 and 3p 0 -3d 0 configurations, respectively. In all cases, in spite of the fact that the ratios of the ORL to CEL ionic abundances span a wide range from ,5-20, the intensity ratios of l4649, l4072, l4590 and l4190 relative to l4089 are found to be nearly constant, apart from some small monotonic increase of these ratios as a function of electron temperature. Over a range of Balmer jump temperature from 3500-8100 K, the variations amount to about 20 per cent for the 3s-3p and 3p-3d transitions and a factor of 2 for the primed transitions, and are consistent with the predictions of the current recombination theory. Our results do not support the claim by Dinerstein, Lafon & Garnett that the relative intensities of O II ORLs vary from nebula to nebula and that the scatter is largest in objects where the discrepancies between ORL and CEL abundances are also the largest.We find that the ORL to CEL abundance ratio is highly correlated with the difference between the temperatures yielded by the [O III] forbidden line ratio and by the H I Balmer jump, providing the strongest evidence so far that the two phenomena, i.e. the disparity between ORL and CEL temperature and abundance ...

In Paper I, we presented spectrophotometric measurements of emission lines from the ultraviolet (UV) to the far‐infrared for 12 Galactic planetary nebulae (PNe) and derived nebular thermal and density structures using a variety of plasma diagnostics. The measurements and plasma diagnostic results are used in the current paper to determine elemental abundances in these nebulae. Abundance analyses are carried out using both strong collisionally excited lines (CELs) and weak optical recombination lines (ORLs) from heavy element ions. Assuming electron temperatures and densities derived from H i recombination spectra (line and continuum), we are able to determine the ORL C abundance relative to hydrogen for all the PNe in our sample, N and O abundances for 11 of them and Ne abundances for nine of them. In all cases, ORL abundances are found to be systematically higher than the corresponding values deduced from CELs. In NGC 40, the discrepancy between the abundances derived from the two types of emission line reaches a factor of 17 for oxygen. For the other 10 PNe, the discrepancies for oxygen vary from 1.6 to 3.1. In general, collisionally excited infrared fine‐structure lines, which have excitation energies less than 103 K and consequently emissivities that are insensitive to electron temperature and temperature fluctuations, yield ionic abundances comparable to those derived from optical/UV CELs. For a given nebula, the discrepancies between the ORL and CEL abundances are of similar magnitude for different elements. In other words, relative abundance ratios such as C/O, N/O and Ne/O deduced from the traditional method based on strong CELs are comparable to those yielded by ORLs, for a wide range of ORL to CEL oxygen abundance ratios, varying from near unity to over a factor of 20. We have also determined ORL abundances relative to hydrogen for the third‐row element magnesium for 11 nebulae in our sample. In strong contrast to the cases for second‐row elements, Mg abundances derived from the Mg ii 3d–4f λ4481 ORL are nearly constant for all the PNe analysed so far and agree within the uncertainties with the solar photospheric value. In accordance with results from previous studies, the ORL to CEL abundance ratio is correlated with the difference between the electron temperatures derived from the [O iii] forbidden‐line ratio, on the one hand, and from the hydrogen recombination Balmer discontinuity, on the other. We find that the discrepancy between the ORL and CEL abundances is correlated with nebular absolute diameter, surface brightness, the electron density derived from [S ii] CELs, and excitation class. The results confirm that the dichotomy of temperatures and heavy elemental abundances determined from the two types of emission line, which has been widely observed in PNe, is a strong function of nebular evolution, as first pointed out by Garnett and Dinerstein. Our analyses show that temperature fluctuations and/or density inhomogeneities are incapable of explaining the large discrepancies between the ...

We present deep optical spectra of the archetypal young planetary nebula (PN) NGC 7027, covering a wavelength range from 3310 to 9160 Å. The observations were carried out by uniformly scanning a long slit across the entire nebular surface, thus yielding average optical spectra for the whole nebula. A total of 937 emission features are detected. The extensive line list presented here should prove valuable for future spectroscopic analyses of emission line nebulae. The optical data, together with the archival IUE and ISO spectra, are used to probe the temperature and density structures and to determine the elemental abundances from lines produced by different excitation mechanisms. Electron temperatures have been derived from the hydrogen recombination Balmer jump (BJ), from ratios of He  optical recombination lines (ORLs) and from a variety of diagnostic ratios of collisionally excited lines (CELs). Electron densities have been determined from the intensities of high-order H  Balmer lines and of He  Pfund lines, as well as from a host of CEL diagnostic ratios. CEL and ORL diagnostics are found to yield compatible results. Adopting respectively electron temperatures of T e = 12 600 and 15 500 K for ions with ionization potentials lower or higher than 50 eV and a constant density of N e = 47 000 cm −3 , elemental abundances have been determined from a large number of CELs and ORLs. The C 2+ /H + , N 2+ /H + , O 2+ /H + and Ne 2+ /H + ionic abundance ratios derived from ORLs are found to be only slightly higher than the corresponding CEL values. We conclude that whatever mechanism is causing the BJ/CEL temperature discrepanies and the ORL/CEL abundance discrepancies that have been observed in many PNe, it has an insignificant effect on this bright young compact PN. The properties of the central star are also discussed. Based on the integrated spectrum and using the energy-balance method, we have derived an effective temperature of 219 000 K for the ionizing star. Finally, we report the first detection in the spectrum of this bright young PN of Raman-scattered O  features at 6830 and 7088 Å, pointing to the existence of abundant neutral hydrogen around the ionized regions.

We have obtained deep optical spectra of medium resolution for a sample of 12 Galactic planetary nebulae (PNe). Optical recombination lines (ORLs) from carbon, nitrogen and oxygen have been detected in 11 of them and neon ORLs in nine of them. All spectra were obtained by scanning a long slit across the nebular surface, yielding relative line intensities for the entire nebula that are suitable for comparison with integrated line fluxes measured in other wavelength regions using space‐borne facilities, such as the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). For 11 PNe, ISO infrared spectra between 2.4 and 197 μm are available, most of them taken by ourselves, plus a Kuiper Airborne Observatory (KAO) infrared spectrum of NGC 6210. IUE ultraviolet (UV) spectra are available for all nebulae except one in our sample. The UV, optical and infrared spectra have been combined to study nebular thermal and density structures and to determine elemental abundances. We have determined UV to optical extinction curves towards these PNe by examining observed fluxes of H i and He ii recombination lines, radio free–free continuum flux density, and UV to optical nebular continua. For 11 PNe in our sample, the derived optical reddening curves are found to be consistent with the standard Galactic extinction law for a total‐to‐selective extinction ratio, R≡A(V)/EB–V= 3.1. However, the optical extinction curve towards Hu 1–2 yields R= 2.0. The UV extinction towards Hu 1–2 and NGC 6572 is also found to be much steeper than the standard Galactic reddening law. In contrast, the UV extinction curve along the sight lines towards NGC 6210 is found to be much shallower, although in the latter case the uncertainties involved are quite large. Electron temperatures and densities have been derived using a variety of diagnostic ratios of collisionally excited lines (CELs) in the UV, optical and infrared. The results show clear stratifications, both in temperature and density. Lines emitted by ions formed in regions of higher ionization degree yield higher temperatures than lines arising from regions of lower ionization degree, while densities deduced from ratios of infrared diagnostic CELs of low critical densities, such as the [O iii] 88‐μm/52‐μm ratio, are systematically lower than those derived from UV and optical diagnostic lines, which in general have much higher critical densities than the infrared fine‐structure lines. Electron temperatures have also been derived from the ratio of the nebular continuum Balmer discontinuity to H 11 for 11 PNe. For four of these, the Balmer jump temperatures are more than 1000 K lower than values derived from the [O iii] optical collisionally excited diagnostic line ratio. With a difference of 3580 K, NGC 40 has the lowest Balmer jump temperature relative to the [O iii] optical forbidden‐line temperature. High‐order Balmer line decrements have been used to determine electron densities. The results are consistent with values derived from forbidden‐line density‐dia...

We investigated the ultrafast proton migration and the Coulomb explosion (CE) dynamics of methyl chloride (CHCl) in intense femtosecond laser fields at the wavelengths of 800 nm (5.5 × 10 W/cm) and 400 nm (4 × 10 W/cm), respectively. Various fragment channels from molecular dication and trication were observed by coincidence momentum imaging through the measurement of their kinetic energy releases (KERs). The proton migration from different charged parent ions was analyzed from the obtained KER distributions. For the direct CE channel of CH + Cl and CH + Cl, the contribution of multiply excited electronic states and multicharged states is identified. In addition, the measurements of relative yields of the fragmentation channel at different laser wavelengths provide a selective control of proton migration for CHCl molecules in intense laser fields.