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Astron. Astrophys. 326, 177-186 (1997)

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Rapidly rotating stars with either H burning or He burning core

M. Shindo 1, M. Hashimoto 1, Y. Eriguchi 2 and E. Müller 3

1 Department of Physics, Kyushu University, Ropponmatsu, Fukuoka 810, Japan
2 Department of Earth Science and Astronomy, University of Tokyo, Komaba, Tokyo 153, Japan
3 Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Str.1, D-85740, Garching, Germany

Received 18 December 1996 / Accepted 28 March 1997

Abstract

We have succeeded in constructing structures of realistic models for rapidly rotating inhomogeneous stars in the nuclear burning stages. The nuclear reaction networks both for CNO cycle and for helium burning have been successfully included in the 2D numerical code. Concerning the equation of state and the opacity, we have used the same ones as used in calculations of spherical stellar structures. The rotation law in our computations covers uniform rotation and differential rotation with rapidly rotating cores. We have computed several equilibrium sequences of massive stars up to models just before the mass begins to shed from the equatorial surface (critical models).

We mainly discuss two critical sequences of models: 1) 18 [FORMULA] stars with hydrogen burning cores and 2) 5 [FORMULA] helium stars with helium burning cores. It is found that the effect of rotation on the structure is similar for both sequences. For uniformly rotating hydrogen burning stars the luminosity decrease is about 6.4% which is consistent with the results obtained by other authors. For models which have the angular momentum distribution concentrated toward the center, we get very flattened shapes of stellar surfaces. Compared with the non-rotating models, decrease of the luminosity is found to be 16% for the critical models if the total angular momentum is less than 1053 g cm2 s-1 and if a toroid-like structure of the density distribution does not appear. On the other hand, decrease of the luminosity becomes significant for stars with the toroid-like structure of the density distribution, i.e. for toroidal distribution of the energy source. It is remarkable that stars whose ratio of the polar radius to the equatorial radius is less than 0.25 have extended envelopes due to a delicate balance between the gravitational force and the centrifugal force.

Key words: nuclear reactions – accretion – stars:rotation

Send offprint requests to: M. Hashimoto

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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