The dust content of planetary nebulae: a reappraisal

TL;DR

This study uses extensive photoionization models and IRAS data to analyze dust content in planetary nebulae, revealing that dust-to-gas ratios vary widely and are not necessarily reduced during nebula evolution.

Contribution

It introduces a new methodology using distance-independent diagrams and models to accurately assess dust properties, challenging previous claims of dust grain size reduction.

Findings

Dust-to-gas mass ratios vary widely among planetary nebulae.

No evidence found for decrease in dust-to-gas ratio during evolution.

Grain size reduction is an artifact of earlier analysis methods.

Abstract

We have performed a statistical analysis using broad band IRAS data on about 500 planetary nebulae with the aim of characterizing their dust content. Our approach is different from previous studies in that it uses an extensive grid of photoionization models to test the methods for deriving the dust temperature, the dust-to-gas mass ratio and the average grain size. In addition, we use only distance independent diagrams. With our models, we show the effect of contamination by atomic lines in the broad band IRAS fluxes during planetary nebula evolution. We find that planetary nebulae with very different dust-to-gas mass ratios exist, so that the dust content is a primordial parameter for the interpretation of far infrared data of planetary nebulae. In contrast with previous studies, we find no evidence for a decrease in the dust-to-gas mass ratio as the planetary nebulae evolve. We also show that the decrease in grain size advocated by Natta and Panagia (1981, ApJ 248,189) and Lenzuni et al. (1989, ApJ 345, 306) is an artefact of their method of analysis. Our results suggest that the timescale for destruction of dust grains in planetary nebulae is larger than their lifetime. Footnote: Table 1 is also accessible in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html