Abundances of Planetary Nebulae NGC3242 and NGC6369

TL;DR

This study reanalyzes the chemical compositions of planetary nebulae NGC3242 and NGC6369 using mid-infrared spectra from space telescopes, revealing new abundance measurements and insights into their stellar origins.

Contribution

It provides the first determination of phosphorus abundance in NGC3242 and compares nebular compositions with solar values, highlighting differences from previous studies.

Findings

Abundances from mid-infrared lines differ from earlier results.

Low helium and oxygen suggest low-mass progenitor stars.

Phosphorus abundance measured for the first time in NGC3242.

Abstract

The spectra of the planetary nebulae NGC3242 and NGC6369 are reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope and the Infrared Space Observatory (ISO). The aim is to determine the chemical composition of these objects. We also make use of International Ultraviolet Explorer (IUE) and ground based spectra. These elliptical PNe are interesting because they are well-studied, nearby, bright objects and therefore allow a reasonably complete comparison of this type of nebulae. Abundances determined from the mid-infrared lines, which are insensitive to electron temperature, are used as the basis for the determination of the composition, which are found to differ somewhat from earlier results. The abundances found, especially the low value of helium and oxygen, indicate that the central star was originally of rather low mass. The abundance of phosphorus has been determined for the first time in NGC3242. The electron temperature in both of these nebulae is roughly constant unlike NGC6302 and NGC2392 where a strong temperature gradient is found. The temperature of the central star is discussed for both nebulae. Finally a comparison of the element abundances in these nebulae with the solar abundance is made. The low abundance of Fe and P is noted and it is suggested that these elements are an important constituent of the nebular dust.