On the circumstellar envelopes of semi-regular long-period variables

TL;DR

This study investigates the properties of circumstellar envelopes around semi-regular long-period variables, revealing correlations in mass loss rates and unexpected SiO profile similarities, which could impact understanding of planetary nebula formation.

Contribution

The paper presents new high-resolution IRAM and Yebes observations of molecular lines in SRs, proposing a novel method for estimating mass loss rates and highlighting unusual SiO profile behaviors.

Findings

Moderate correlation between mass loss rates and CO intensity ratios.

Potential new method for estimating mass loss rates.

Unexpected similarity between SiO and CO profiles in some stars.

Abstract

The mass loss process along the AGB phase is crucial for the formation of circumstellar envelopes (CSEs), which in the post-AGB phase will evolve into planetary nebulae (PNe). There are still important issues that need to be further explored in this field; in particular, the formation of axially symmetric PNe from spherical CSEs. To address the problem, we have conducted high S/N IRAM 30m observations of 12CO J=1-0 and J=2-1, and 13CO J=1-0 in a volume-limited unbiased sample of semi-regular variables (SRs). We also conducted Yebes 40m SiO J=1-0 observations in 1/2 of the sample in order to complement our 12CO observations. We report a moderate correlation between mass loss rates and the 12CO(1-0)-to-12CO(2-1) intensity ratio, introducing a possible new method for determining mass loss rates of SRs with short analysis time. We also find that for several stars the SiO profiles are very similar to the 12CO profiles, a totally unexpected result unless these are non-standard envelopes.