Radio continuum properties of young planetary nebulae

TL;DR

This study uses high-resolution radio observations of young planetary nebulae to analyze their spectral properties, revealing their early evolutionary stages and structural features like bipolar shapes, with implications for understanding planetary nebula evolution.

Contribution

The paper provides new multi-frequency radio data and modeling of post-AGB stars, demonstrating their status as very young planetary nebulae and revealing diverse optical thickness and structural characteristics.

Findings

Some targets are optically thick at high frequencies.

Detection of flux increase over four years in IRAS 18062+2410.

Bipolar structures possibly due to circumstellar tori or jets.

Abstract

We have selected a small sample of post-AGB stars in transition towards the planetary nebula and present new Very Large Array multi-frequency high-angular resolution radio observations of them. The multi-frequency data are used to create and model the targets' radio continuum spectra, proving that these stars started their evolution as very young planetary nebulae. In the optically thin range, the slopes are compatible with the expected spectral index (-0.1). Two targets (IRAS 18062+2410 and 17423-1755) seem to be optically thick even at high frequency, as observed in a handful of other post-AGB stars in the literature, while a third one (IRAS 20462+3416) shows a possible contribution from cold dust. In IRAS 18062+2410, where we have three observations spanning a period of four years, we detect an increase in its flux density, similar to that observed in CRL 618. High-angular resolution imaging shows bipolar structures that may be due to circumstellar tori, although a different hypothesis (i.e., jets) could also explain the observations. Further observations and monitoring of these sources will enable us to test the current evolutionary models of planetary nebulae.