A sensitive search for methanol line emission toward evolved stars

TL;DR

This study conducted a sensitive search for methanol masers in evolved stars, specifically post-AGB stars and planetary nebulae, but found no detections, suggesting different chemical conditions compared to young stellar objects.

Contribution

First targeted search for methanol masers in evolved stars, providing insights into chemical processes and maser occurrence in these objects.

Findings

No methanol masers detected in the sample.

Methanol production in dust grains is less efficient in evolved stars.

More evolved planetary nebulae might host Class II masers.

Abstract

We present a sensitive search for methanol line emission in evolved stars at 1 cm, aiming to detect, for the first time, methanol masers in this type of objects. Our sample comprised post-AGB stars and young planetary nebulae (PNe), whose mass-loss processes and circumstellar structures resemble those of young stellar objects (YSOs), where methanol masers are detected. Class I masers were searched for in 73 objects, whereas Class II ones were searched in 16. No detection was obtained. The non-detection of Class I methanol masers indicated that methanol production in dust grains and/or the enhancement of its gas-phase abundance in the shocked regions of evolved objects are not as efficient as in YSOs. We suggest that relatively more evolved PNe might have a better probability of harboring Class II masers.