Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae

Abstract

High spectral resolution spectroscopy has proved to be very useful for the advancement of chemical abundances studies in photoionized nebulae, such as H II regions and planetary nebulae (PNe). Classical analyses make use of the intensity of bright collisionally excited lines (CELs), which have a strong dependence on the electron temperature and density. By using high resolution spectrophotometric data, our group has led the determination of chemical abundances of some heavy element ions, mainly O++, O+ and C++ from faint recombination lines (RLs), allowing us to deblend them from other nearby emission lines or sky features. The importance of these lines is that their emissivity depends weakly on the temperature and density structure of the gas. The unresolved issue in this field is that recombination lines of heavy element ions give abundances that are about 2-3 times higher than those derived from CELs -in H II regions- for the same ion, and can even be a factor of 70 times higher in some PNe. This uncertainty puts into doubt the validity of face values of metallicity that we use as representative not only for ionized nebulae in the Local Universe, but also for star-forming dwarf and spiral galaxies at different redshifts. Additionally, high-resolution data can allow us to detect and deblend faint lines of neutron capture element ions in PNe. This information would introduce further restrictions to evolution models of AGBs and would help to quantify the chemical enrichment in s-elements produced by low and intermediate mass stars. The availability of an echelle spectrograph at the E-ELT will be of paramount interest to: (a) extend the studies of heavy element recombination lines to low metallicity objects, (b) to extend abundance determinations of s-elements to planetary nebulae in the extragalactic domain and to bright Galactic and extragalactic H II regions.

6 pages, 6 figures, Accepted for publication in Astronomische Nachrichten

References in corpus (10)

• Resolving the electron temperature discrepancies in HII Regions and Planetary Nebulae: kappa-distributed electrons
• Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
• On the abundance discrepancy problem in HII regions
• The localized chemical pollution in NGC 5253 revisited: Results from deep echelle spectrophotometry
• Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
• Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603
• NGC 2579 and the carbon and oxygen abundance gradients beyond the solar circle
• Enrichment of the ISM by metal-rich droplets and the abundance bias in HII regions
• Properties of the ionized gas in HH202. I: Results from integral field spectroscopy with PMAS
• Temperature Variations and Chemical Abundances in Planetary Nebulae

Cited by in corpus (6)

• Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution
• Carbon and oxygen abundance gradients in NGC300 and M33 from optical recombination lines
• Density biases and temperature relations for DESIRED HII regions
• Carbon, nitrogen and oxygen abundance gradients in M101 and M31
• The chemical composition of Galactic ring nebulae around massive stars
• HOMERUN a new approach to photoionization modelling. I -- reproducing observed emission lines with percent accuracy and obtaining accurate physical properties of the ionized gas