α Centauri AB

Details α Centauri AB α Centauri AB

Mar 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...531..503g&link_type=abstract

The Astrophysical Journal, Volume 531, Issue 1, pp. 503-520.

Astronomy and Astrophysics

Astronomy

42

Stars: Binaries: Visual, Stars: Fundamental Parameters, Stars: Individual: Constellation Name: &Alpha, Centauri, Stars: Interiors, Stars: Oscillations

Scientific paper

Detailed models of α Centauri A and B based on the Hipparcos, Yale, and Söderhjelm parallaxes are compared. The consequences of the uncertainty in mass, luminosity, surface temperature, and composition on the structure and the p-mode pulsation spectrum of the models are presented. All of the models were constructed using the most current stellar structure physics available to us, including helium and heavy-element diffusion, OPAL (Lawrence Livermore Opacity Library) equation of state, and OPAL and Alexander opacities. Self-consistent models of α Cen A and B that satisfy the observational constraints have an initial helium mass fraction YZAMS=~0.28. The age of the system depends critically on whether or not α Cen A has a convective core. If it does (our best model), then α Cen AB is ~7.6 Gyr old, and if it does not, then the binary system is ~6.8 Gyr old. Both ages and YZAMS are accurate to +/-~10% owing to observational uncertainties. The Galactic enrichment parameter (ΔY/ΔZ) for our best model pair is less than 1. Pulsation analyses of our best models yield an average large and small spacing of 101+/-3 μHz and 4.6+/-0.4 μHz, respectively, for α Cen A, and 173+/-6 μHz and 15+/-1 μHz for α Cen B. Some methodologies that use p-mode frequency observations to constrain the system further are outlined. We include a simple test to determine whether or not α Cen A has a convective core and introduce a method to use the small frequency spacing to determine the age of system, overcoming the limitation that it is also sensitive to composition.

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