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 L_sun) 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 M_sun 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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