The salty emission of the intermediate-mass AGB star OH 30.1 -0.7

TL;DR

This study uses ALMA observations to analyze the dust and molecular emissions of the intermediate-mass AGB star OH 30.1 -0.7, revealing a secondary dust feature, possible binary companion influence, and recent high-rate mass loss.

Contribution

First detailed ALMA analysis of OH 30.1 -0.7's dust and molecular emissions, identifying a secondary dust feature and constraining the nature of its binary companion.

Findings

Detection of a secondary dust feature 1.8 x 10^4 au from the star.

Evidence of a binary companion influencing molecular emission patterns.

Recent high-rate mass loss likely started around 2800 years ago.

Abstract

We analyse continuum and molecular emission, observed with ALMA, from the dust-enshrouded intermediate-mass AGB star OH 30.1 -0.7. We find a secondary peak in the continuum maps, "feature B", separated by 4.6" from the AGB star, which corresponds to a projected separation of $1.8 \times 10^4$ au, placing a lower limit on the physical separation. This feature is most likely composed of cold dust and is likely to be ejecta associated with the AGB star, though we cannot rule out that it is a background object. The molecular emission we detect includes lines of CO, SiS, CS, SO$_2$, NS, NaCl, and KCl. We find that the NS emission is off centre and arranged along an axis perpendicular to the direction of feature B, indicative of a UV-emitting binary companion (e.g. a G-type main sequence star or hotter), perhaps on an eccentric orbit, contributing to its formation. However, the NaCl and KCl emission constrain the nature of that companion to not be hotter than a late B-type main sequence star. We find relatively warm emission arising from the inner wind and detect several vibrationally excited lines of SiS (3 = 1), NaCl (up to 3 = 4) and KCl (up to 3 = 2), and emission from low energy levels in the mid to outer envelope, as traced by SO$_2$. The CO emission is abruptly truncated around 3.5" or 14,000 au from the continuum peak, suggesting that mass loss at a high rate may have commenced as little as 2800 years ago.