EU Del: exploring the onset of pulsation-driven winds in giant stars

We explore the wind-driving mechanism of giant stars through the nearby (117 pc), intermediate-luminosity (L approximate to 1600 L-circle dot) 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(-1), a C-12/C-13 ratio of 14(-4)(+9) and a mass-loss rate of a few x 10(-8) M-circle dot yr(-1). Analysis of published spectra show the star has a metallicity of [Fe/H] = -0.27 +/- similar to 0.30 dex. The star's dusty envelope lacks a clear 10-mu m 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.