EU Del: Exploring the onset of pulsation-driven winds in giant
stars
I. McDonald (Manchester), A.A. Zijlstra (Manchester), G.C. Sloan (Cornell),
E. Lagadec, (Obs. de la Cote d'Azur), C.I. Johnson (Harvard-Smithsonian CfA),
S. Uttenthaler (Univ. Vienna), O.C. Jones (STScI), C.L. Smith (York Univ.)
2016, MNRAS, 456, 4542
Full manuscript available locally (PDF)
or from the arXiv
(1512.04695).
We explore the wind-driving mechanism of giant stars through observations of
the nearby (117 pc), intermediate-luminosity (L ~ 1600 Lsun) giant
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 +/- 0.02 km
s, a 12C/13C ratio of
14+9-4, and a mass-loss rate of a few x 10-8
Msun yr-1. Published spectra suggest it may be
marginally metal-poor: [Fe/H] = -0.27 +/- ~0.3 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 puslation properties. We suggest
the much stronger mass loss from EU Del is driven by long-period stellar
pulsations, which may in turn be initiated by the potentially lower mass of
EU Del.
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