The Nearby Evolved Stars Survey III: First data release of JCMT CO-line observations

Abstract

Low- to intermediate-mass ($\sim$0.8$-$8 M${}_{\odot }$) evolved stars contribute significantly to the chemical enrichment of the interstellar medium in the local Universe, making accurate mass-return estimates in their final stages crucial. The Nearby Evolved Stars Survey (NESS) is a large multi-telescope project targeting a volume-limited sample of $\sim$850 stars within 3 kpc in order to derive the dust and gas return rates in the Solar Neighbourhood, and to constrain the physics underlying these processes. We present an initial analysis of the CO-line observations, including detection statistics, carbon isotopic ratios, initial mass-loss rates, and gas-to-dust ratios. We describe a new data reduction pipeline to analyse the available NESS CO data from the JCMT, measuring line parameters and calculating empirical gas mass-loss rates. We present the first release of the available data on 485 sources, one of the largest homogeneous samples of CO data to date. Comparison with a large literature sample finds that high mass-loss rate and especially carbon-rich sources are over-represented in literature, while NESS is probing significantly more sources at low mass-loss rates, detecting 59 sources in CO for the first time and providing useful upper limits. CO line detection rates are 81% for the CO (2--1) line and 75% for CO (3--2). The majority (82%) of detected lines conform to the expected soft parabola shape, while eleven sources show a double wind. Calculated mass-loss rates show power-law relations with both the dust-production rates and expansion velocities up to $\sim 5\times 10^{-6}$~\msunyr. Median gas-to-dust ratios of 250 and 680 are found for oxygen-rich and carbon-rich sources, respectively. Our analysis of CO observations in this first data release highlights the importance of our volume-limited approach in characterizing the local AGB population as a whole.

18 pages, 12 figures, accepted for publication in Astronomy & Astrophysics, data to be made available at https://evolvedstars.space

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