2016MNRAS.456.4542M

We explore the wind-driving mechanism of giant stars through the nearby (117pc), intermediate-luminosity (L ~ 1600 L_☉) star EU Del (HIP 101810, HD 196610). Atacama Pathfinder Experiment observations of the CO (3-2) and (2-1) transitions are used to derive a wind velocity of 9.51±0.02 km/s, a 12C/13C ratio of 14^+9_-4 and a mass-loss rate of a fewx10^–8M_☉/yr. Analysis of published spectra show the star has a metallicity of [Fe/H] = -0.27± ∼ 0.30 dex. The star's dusty envelope lacks a clear 10-µm silicate feature, despite the star's oxygen-rich nature. Radiative transfer modelling cannot fit a wind acceleration model which relies solely on radiation pressure on condensing dust. We compare our results to VY Leo (HIP 53449), a star with similar temperature and luminosity, but different pulsation properties. We suggest the much stronger mass-loss from EU Del may be driven by long-period stellar pulsations, due to its potentially lower mass. We explore the implications for the mass-loss rate and wind velocities of other stars.