PHYSICAL AND CHEMICAL PROPERTIES OF PLANETARY NEBULAE WITH WR-TYPE NUCLEI

Ashkbiz Danehkar,Roger Wesson,Amanda I Karakas,Quentin A Parker

doi:10.5303/pkas.2015.30.2.159

Abstract

We have carried out optical spectroscopic measurements of emission lines for a sample of Galactic planetary nebulae with Wolf-Rayet (WR) stars and weak emission-line stars (wels). The plasma diagnostics and elemental abundance analysis have been done using both collisionally excited lines (CELs) and optical recombination lines (ORLs). It is found that the abundance discrepancy factors (ADF=ORL/CEL) are closely correlated with the dichotomy between temperatures derived from forbidden lines and those from He I recombination lines, implying the existence of H-deficient materials embedded in the nebula. The H$\beta$ surface brightness correlations suggest that they might be also related to the nebular evolution.

Highlights

Observations of planetary nebulae (PNe) are used to determine the composition of the interstellar medium (e.g. Kingsburgh & Barlow, 1994), and to probe the physics of AGB stars (e.g. Karakas et al, 2009)
It is found that the abundance discrepancy factors (ADF≡optical recombination lines (ORLs)/collisionally excited lines (CELs)) are closely correlated with the dichotomy between temperatures derived from forbidden lines and those from He i recombination lines, implying the existence of H-deficient materials embedded in the nebula
The electron temperatures of high-excitation PNe are typically higher than low-excitation PNe, which can be explained by the radiation from the central stars

Summary

INTRODUCTION

Observations of planetary nebulae (PNe) are used to determine the composition of the interstellar medium (e.g. Kingsburgh & Barlow, 1994), and to probe the physics of AGB stars (e.g. Karakas et al, 2009). Excited lines (CELs) have been extensively used to derive the abundances of heavy elements Kingsburgh & Barlow, 1994; Liu et al, 2004). Optical recombination lines (ORLs) have a much weaker dependence on temperature, resulting in more reliable abundance analyses. Wesson et al (2005) found that Te([O iii]) > Te(BJ) > Te(He i) > Te(O ii), which was predicted by the two-phase models (Liu et al, 2004), containing some cold (Te ∼ K) Hdeficient materials, embedded in the warm (Te ∼ K) gas of normal abundances. Suitable sky windows were selected from the science data for sky subtraction

PLASMA DIAGNOSTICS

ABUNDANCE ANALYSIS

CONCLUSIONS