On the Interpretation of Echelle Diagrams for Solarlike Oscillations Effect of Centrifugal Distortion
Abstract
This work aims at determining the impact of slow to moderate rotation on the regular patterns often present in solarlike oscillation spectra, i.e., the frequency spacings. We focus on the wellknown asteroseismic diagnostic echelle diagrams, examining how rotation may modify the estimates of the large and small spacings, as well as the identification of modes. We illustrate the work with a real case: the solarlike star ηBootis. We study a mainsequence 1.3 M _{sun} star as a typical case. The modeling takes into account rotation effects on the equilibrium models through an effective gravity and on the oscillation frequencies through both perturbative and nonperturbative calculations. We compare the results of both type of calculations in the context of the regular spacings (like the small spacings and the scaled small spacings) and echelle diagrams. We show that for echelle diagrams the perturbative approach remains valid for rotational velocities up to 4050 km s^{1}. We show that for the rotational velocities measured in solarlike stars, i.e., vsin i up to 2030 km s^{1}, rotation effects must be taken into account in the modeling for a correct interpretation of the observed oscillations. In particular, theoretical oscillation frequencies must be corrected up to the second order in terms of rotation rate, including near degeneracy effects. For rotational velocities of about 16 km s^{1} and higher, diagnostics on large spacings and on modal identification through echelle diagrams can be significantly altered by the presence of the m ≠ 0 components of the rotationally split modes. We found these effects to be detectable in the observed frequency range. Analysis of the effects of rotation on small spacings and scaled small spacings reveals that these can be of the order of or even larger than surface effects, typically turbulence, microscopic diffusion, etc. Furthermore, we show that scaled spacings are significantly affected by stellar distortion even for small stellar rotational velocities (from 10 to 15 km s^{1}) and therefore some care must be taken when using them as indicators for probing deep stellar interiors.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2010
 DOI:
 10.1088/0004637X/721/1/537
 arXiv:
 arXiv:1009.0123
 Bibcode:
 2010ApJ...721..537S
 Keywords:

 stars: evolution;
 stars: individual: eta Bootis;
 stars: interiors;
 stars: oscillations;
 stars: rotation;
 stars: solartype;
 stars: variables: general;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 10 pages,5 figures, accepted for publication in ApJ