C/O Abundance Ratios, Iron Depletions, and Infrared Dust Features in Galactic Planetary Nebulae

Abstract

We study the dust present in 56 Galactic planetary nebulae (PNe) through their iron depletion factors, their C/O abundance ratios (in 51 objects), and the dust features that appear in their infrared spectra (for 33 objects). Our sample objects have deep optical spectra of good quality, and most of them also have ultraviolet observations. We use these observations to derive the iron abundances and the C/O abundance ratios in a homogeneous way for all the objects. We compile detections of infrared dust features from the literature and we analyze the available Spitzer/IRS spectra. Most of the PNe have C/O ratios below one and show crystalline silicates in their infrared spectra. The PNe with silicates have C/O < 1, with the exception of Cn 1-5. Most of the PNe with dust features related to C-rich environments (SiC or the 30 μm feature usually associated to MgS) have C/O 0.8. Polycyclic aromatic hydrocarbons are detected over the full range of C/O values, including 6 objects that also show silicates. Iron abundances are low in all the objects, implying that more than 90% of their iron atoms are deposited into dust grains. The range of iron depletions in the sample covers about two orders of magnitude, and we find that the highest depletion factors are found in C-rich objects with SiC or the 30 μm feature in their infrared spectra, whereas some of the O-rich objects with silicates show the lowest depletion factors.

s-process enrichment in the planetary nebula NGC 3918. Results from deep echelle spectrophotometry

“…We adopt C/O=0.87±0.25 from C ii and O ii recombination lines (see Fig 8 and the ICFs given by Kingsburgh & Barlow 1994). C/O ratios from ORLs generally agree with those derived from UV/optical CELs Delgado-Inglada & Rodríguez 2014) and, additionally, they are not affected by aperture corrections and extinction uncertainties, which can potentially affect C/O ratios derived from CELs. Additionally, we also include some data from García-Rojas et al We use PySSN to deblend this line from the charge transfer feature, the telluric emission lines and a close He i line (see Fig.…”

“…For highly ionized Fe ions, we adopt the data recommended by Delgado-Inglada & Rodríguez (2014), and for neutron-capture elements we use the atomic data references compiled by Sharpee et al (2007). Errors in the line fluxes and the physical conditions were propagated via Monte Carlo simulations.…”

Physical Properties of the Very Young PN Hen3-1357 (Stingray Nebula) Based on Multiwavelength Observations

“…Obviously, the abundances in both IC4846 and Hen3-1357 are in excellent agreement even in the RL ǫ(C,N,O) and the Fe-depletion. So far, the ǫ(Mg) and ǫ(Fe) measurements have been performed only by Hyung et al (2001) using the IUE UV-spectrum and only by Delgado-Inglada & Rodríguez (2014) using the optical spectra, respectively. The largely depleted [Mg/H] = -1.69 in IC4846 might indicate that most of the Mg-atoms are captured by silicate grains.…”

C/O ratios in planetary nebulae with dual-dust chemistry from faint optical recombination lines

“…This problem is well known in nebular physics and consist in the fact that, for a given ion, ORLs provide systematically higher abundances than those obtained using CELs; this difference is generally parametrized by the abundance discrepancy factor (ADF), which is the ratio between ORLs and CELs abundances. Wang & Liu (2007) and Delgado-Inglada & Rodríguez (2014) showed that when computed simultaneously, ADFs given by N, O and C ions show an overall agreement that translates in very similar N/O and C/O when computed from both CELs and ORLs. With this method we avoid the biases discussed by Rola & Stasińska (1994) as we have computed the abundances from high-signal-to-noise optical spectra and used the same type of lines to compute C and O abundances.…”