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arXiv · 1512.04695

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

I. McDonald·A. A. Zijlstra·G. C. Sloan·E. Lagadec·C. I. Johnson·S. Uttenthaler·O. C. Jones·C. L. Smith
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Abstract

We explore the wind-driving mechanism of giant stars through the nearby (117 pc), intermediate-luminosity ($L \approx 1600$ L$_\odot$) star EU Del (HIP 101810, HD 196610). APEX observations of the CO (3--2) and (2--1) transitions are used to derive a wind velocity of 9.51 $\pm$ 0.02 km s$^{-1}$, a $^{12}$C/$^{13}$C ratio of 14 $^{+9}_{-4}$, and a mass-loss rate of a few $\times$ 10$^{-8}$ M$_\odot$ yr$^{-1}$. From published spectra, we estimate that the star has a metallicity of [Fe/H] = --0.27 $\pm$ $\sim$0.30 dex. The star's dusty envelope lacks a clear 10-$μ$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.

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I. McDonald, A. A. Zijlstra, G. C. Sloan, E. Lagadec, C. I. Johnson, S. Uttenthaler, O. C. Jones, C. L. Smith. 2015-12-15. EU Del: exploring the onset of pulsation-driven winds in giant stars. https://doi.org/10.1093/mnras%2Fstv2942

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