Evidence for a sharp structure variation inside a red-giant star
Abstract
Context. The availability of precisely determined frequencies of radial and non-radial oscillation modes in red giants is finally paving the way for detailed studies of the internal structure of these stars.
Aims: We look for the seismic signature of regions of sharp structure variation in the internal structure of the CoRoT target HR 7349.
Methods: We analyse the frequency dependence of the large frequency separation and second frequency differences, as well as the behaviour of the large frequency separation obtained with the envelope auto-correlation function.
Results: We find evidence for a periodic component in the oscillation frequencies, i.e. the seismic signature of a sharp structure variation in HR 7349. In a comparison with stellar models we interpret this feature as caused by a local depression of the sound speed that occurs in the helium second-ionization region. Using solely seismic constraints this allows us to estimate the mass (M = 1.2-0.4+0.6 M_⊙) and radius (R = 12.2-1.8+2.1 R_⊙) of HR 7349, which agrees with the location of the star in an HR diagram.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2010
- DOI:
- 10.1051/0004-6361/201015442
- arXiv:
- arXiv:1009.1024
- Bibcode:
- 2010A&A...520L...6M
- Keywords:
-
- asteroseismology;
- stars: interiors;
- stars: oscillations;
- stars: fundamental parameters;
- stars: individual: HR 7349;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 4 pages, 5 figures, accepted in A&