Volume 584, December 2015
|Number of page(s)||5|
|Published online||17 November 2015|
Relating turbulent pressure and macroturbulence across the HR diagram with a possible link to γ Doradus stars⋆
1 Argelander-Institut für Astronomie, Universität Bonn, auf dem Hügel 71, 53121 Bonn, Germany
2 Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
3 School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
Received: 1 September 2015
Accepted: 14 October 2015
A significant fraction of the envelope of low- and intermediate-mass stars is unstable to convection, leading to sub-surface turbulent motion. Here, we consider and include the effects of turbulence pressure in our stellar evolution calculations. In search of an observational signature, we compare the fractional contribution of turbulent pressure to the observed macroturbulent velocities in stars at different evolutionary stages. We find a strong correlation between the two quantities, similar to what was previously found for massive OB stars. We therefore argue that turbulent pressure fluctuations of finite amplitude may excite high-order, high-angular degree stellar oscillations, which manifest themselves at the surface an additional broadening of the spectral lines, i.e., macroturbulence, across most of the HR diagram. When considering the locations in the HR diagram where we expect high-order oscillations to be excited by stochastic turbulent pressure fluctuations, we find a close match with the observational γ Doradus instability strip, which indeed contains high-order, non-radial pulsators. We suggest that turbulent pressure fluctuations on a percentual level may contribute to the γ Dor phenomenon, calling for more detailed theoretical modeling in this direction.
Key words: turbulence / convection / line: profiles / stars: general / stars: variables: general / stars: low-mass
Appendices A and B are available in electronic form at http://www.aanda.org
© ESO, 2015
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