Line-profile variations of stochastically excited oscillations in four evolved stars *
1
School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK e-mail: saskia@bison.ph.bham.ac.uk
2
Instituut voor Sterrenkunde, Katholieke Universiteit Leuven,
Celestijnenlaan 200 D, 3001 Leuven, Belgium
3
Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
4
Department of Astrophysics, IMAP, University of Nijmegen, PO Box 9010,
6500 GL Nijmegen, The Netherlands
Received:
29
June
2009
Accepted:
8
February
2010
Context. Since solar-like oscillations were first detected in red-giant stars, the presence of non-radial oscillation modes has been debated. Spectroscopic line-profile analysis was used in the first attempt to perform mode identification, which revealed that non-radial modes are observable. Despite the fact that the presence of non-radial modes could be confirmed, the degree or azimuthal order could not be uniquely identified. Here we present an improvement to this first spectroscopic line-profile analysis.
Aims. We aim to study line-profile variations in stochastically excited solar-like oscillations of four evolved stars to derive the azimuthal order of the observed mode and the surface rotational frequency.
Methods. Spectroscopic line-profile analysis is applied to cross-correlation functions, using the Fourier parameter fit method on the amplitude and phase distributions across the profiles.
Results. For four evolved stars, β Hydri (G2IV), ϵ Ophiuchi (G9.5III), η Serpentis (K0III) and δ Eridani (K0IV) the line-profile variations reveal the azimuthal order of the oscillations with an accuracy of ±1. Furthermore, our analysis reveals the projected rotational velocity and the inclination angle. From these parameters we obtain the surface rotational frequency.
Conclusions. We conclude that line-profile variations in cross-correlation functions behave differently for different frequencies and provide additional information about the surface rotational frequency and azimuthal order.
Key words: stars: oscillations / stars: individual: ϵ Ophiuchi / stars: individual: η Serpentis / stars: individual: δ Eridani / stars: individual: β Hydri / line: profiles
The software package FAMIAS developed in the framework of the FP6 European Coordination Action HELAS (http://www.helas-eu.org) has been used in this research.
© ESO, 2010