CO-SPATIAL LONG-SLIT UV/OPTIC AL SPECTRA OF 10 GALACTIC PLANETARY NEBULAE WITHHST/STIS. I. DESCRIPTION OF THE OBSERVATIONS, GLOBAL EMISSION-LINE MEASUREMENTS, AND CNO ABUNDANCES

Abstract

We present observations and initial analysis from an HST Cycle 19 program using STIS to obtain the first co-spatial, UV-optical spectra of ten Galactic planetary nebulae (PNe). Our primary objective was to measure the critical emission lines of carbon and nitrogen with unprecedented S/N and spatial resolution over the wavelength range 1150-10270Å, with the ultimate goal of quantifying the production of these elements in low-and intermediate-mass stars. Our sample was selected from PNe with a near-solar metallicity, but spanning a broad range in N/O based on published ground-based and IUE spectra. This study, the first of a series, concentrates on the observations and emission-line measurements obtained by integrating along the entire spatial extent of the slit. We derived ionic and total elemental abundances for the seven PNe with the strongest UV line detections (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, and NGC 7662). We compare these new results with other recent studies of the nebulae, and discuss the relative merits of deriving the total elemental abundances of C, N, and O using ionization correction factors (ICFs) versus summed abundances. For the seven PNe with the best UV line detections, we conclude that summed abundances from direct diagnostics of ions with measurable UV lines gives the most accurate values for the total elemental abundances of C and N (although ICF abundances often produced good results for C). In some cases where significant discrepancies exist between our abundances and those from other studies, we show that the differences can often be attributed to their use of fluxes that are not co-spatial. Finally, we examined C/O and N/O versus O/H and He/H in well-observed Galactic, LMC, and SMC PNe, and found that highly accurate abundances are essential for properly inferring elemental yields from their progenitor stars. Future papers will discuss photoionization modeling of our observations, both of the integrated spectra and spatial variations of the UV vs. optical lines along the STIS slit lengths, which are unique to our observations.

The Nucleus of the Planetary Nebula Egb 6 as a Post-Mira Binary*

“…However, the detected source is almost certainly too bright to be due to emission lines from the CEK. There are very few nebular emission lines in the F814W bandpass; see, for example, the I-band spectrum of the PN IC 2165 in Figure 4 of Dufour et al (2015). IC 2165 has a central star with parameters similar to that of the hot component of EGB 6, according to Henry et al (2015), so a similar nebular emission spectrum is expected.…”

The evolution of Galactic planetary nebula progenitors through the comparison of their nebular abundances with AGB yields

“…Note that the carbon abundance whose derivation is based on photoionisation models C/H = 8.13 (Henry et al 2015) is in much better agreement with our interpretation. NGC 7662 is a inhomogeneous PN, with a lot of stratification (see Dufour et al 2015). This may help to explain the disagreement between the carbon and other abundance indicators.…”

“…It is worth noting that all abundance references use the same ICF scheme (Kingsburgh & Barlow 1994), and are thus homogeneous, with the exception of the 7 PNe whose abundances are from Dufour et al (2015). We comment on possible use of the model abundances from Henry et al (2015), based on Dufour et al' s (2015) data, in specific cases in the following sections.…”

“…We also searched the literature for Galactic PNe whose spectra has been acquired with the HST. Henry et al (2015) and Dufour et al (2015) examined 7 carbon determinations in Galactic PNe (4 in common with the IUE samples described above). Furthermore, Henry et al (2008) observed the halo PN DdDm 1 (PN G061.9+41.3), and Bianchi et al (2001) observed a globular cluster PN (K648 in M15).…”

IFU Spectroscopy of Southern Planetary Nebulae V: Low-Ionisation Structures

“…The morphology of IC 2553 was described as elongated inner shell, surrounded by a group of knots, with almost a spherical outer shell (Corradi et al 2000). Finally, PB 6 reveals a relatively circular double shells in which internal structures appear as a set of knots (Dufour et al 2015).…”