Temperature Variations from HST Imagery and Spectroscopy of NGC 7009

Abstract

We obtained new HST/STIS long-slit spectra and WFPC2 imagery of the planetary nebula NGC 7009 in order to obtain high spatial resolution of the intrinsic flux ratio [O III] 4364/5008, which is a well-known diagnostic for electron temperature (Te). Our primary purpose was to quantify Te variations across the nebula. We address whether the observational data support the possibility that the [fractional] mean-square Te variation (t2) (Peimbert 1967) in NGC 7009 may be as large as ~0.1. Such large values are required to reconcile the “abundance dichotomy” by Te variations alone. The abundance dichotomy (discussed by Liu at greater length elsewhere in this volume) refers to the significantly higher heavy element abundances derived from optical recombination lines (e.g., a factor of ~5 for NGC 7009, Liu et al. 1995) compared with the corresponding values deduced from collisionally-excited lines.