A WISE view on extreme AGB stars

TL;DR

This study analyzes WISE light curves of about 2000 AGB stars to identify long-period variables with high mass-loss rates, providing new insights into their variability, dust properties, and contribution to galactic dust return.

Contribution

It introduces a method to identify and characterize reddest AGB stars and LPVs using WISE data, including new long-period variables and detailed dust mass-loss estimates.

Findings

Identified approximately 750 candidate LPVs, including 145 with periods over 1000 days.

Separated C-rich and O-rich extremely red objects through SED fitting.

Estimated the dust return rate in the solar neighborhood from AGB stars.

Abstract

(abridged) Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate (MLR) of the star. Long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. However, the reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Our goal is to obtain a sample of LPVs with large MLRs by analysing WISE W1 and W2 light curves (LCs) for about 2000 sources, photometrically selected to include known C-stars with the 11.3 mu silicon carbide dust feature in absorption, and Galactic O-stars with periods longer than 1000 days. Epoch photometry was retrieved from the AllWISE and NEOWISE database and fitted with a sinus curve. Photometry from other variability surveys was also downloaded and fitted. For a subset of 316 of the reddest stars, spectral energy distributions (SEDs) were constructed, and, together with mid-infrared (MIR) spectra when available, fitted with a dust radiative transfer programme in order to derive MLRs. WISE based LCs and fits to the data are presented for all stars. Inspired by a recent paper, a number of non-variable OH/IRs are identified. Based on a selection on amplitude, a sample of about 750 (candidate) LPVs is selected of which 145 have periods over 1000 days, many of them being new. For the subset of the stars with the colours of C-rich extremely red objects (EROs) the fitting of the SEDs (and available MIR spectra) separates them into C- and O-rich objects. The number of Galactic EROs appears to be complete up to about 5~kpc and a total dust return rate in the solar neighbourhood for this class is determined. Based on the EROs in the Magellanic Clouds, a bolometric period luminosity is derived.