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), ∊ 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.
Astronomy and Astrophysics
- Pub Date:
- June 2010
- stars: oscillations;
- stars: individual: ∊ Ophiuchi;
- stars: individual: η Serpentis;
- stars: individual: δ Eridani;
- stars: individual: β Hydri;
- line: profiles;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- Accepted for publication in Astronomy and Astrophysics, 9 pages, 10 figures and 3 tables. A version with figure 1 in full resolution can be obtained upon request from first author