An observational study of dust nucleation in Mira (<i>o</i> Ceti)

Abstract

Context. Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Observations of key aluminum bearing molecules around evolved stars has enabled us to investigate the nucleation of alumina (Al 2 O 3 ) dust in the gas. Aims. We aim to identify and characterize aluminum bearing species in the circumstellar gas of Mira (o Ceti) in order to elucidate their role in the production of Al 2 O 3 dust. Methods. We used multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA that probe the gas distribution in the immediate vicinity of the star at 30 mas; observations with ALMA, APEX, and Herschel in 2013-2015 for studying cycle and inter-cycle variability of the rotational lines of Al-bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features that constrain the physical parameters of the gas.