Abstract
Betelgeuse is a well known bright red supergiant that shows semi-regular
variations with four approximate periods of 2200, 420, 230, and 185 days. While
the longest period was customarily regarded as LSP (long secondary period) of
unknown origin, we identify the ~2200-d period as the radial fundamental mode,
and the three shorter periods as the radial first, second, and third overtones.
From a nonadiabatic pulsation analysis including the pulsation/convection
coupling, we have found that these radial pulsation modes are all excited in
the envelope of a model in a late stage of the core-carbon burning. Models with
similar pulsation property have masses around 11M_(19M_at ZAMS)
with luminosities (log L/L_=5.27~5.28) and effective temperatures (log
T_eff3.53) that are consistent with the range of the observational
determinations. We also find that a synthetic light curve obtained by adding
the fundamental and the first-overtone mode qualitatively agrees with the light
curve of Betelgeuse up to the Great Dimming. We conclude that Betelgeuse is in
the late stage of core carbon burning, and a good candidate for the next
Galactic supernova.
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