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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_\odot (19M_\odot at ZAMS) with luminosities (log L/L_\odot =5.27~5.28) and effective temperatures (log T_{eff}\approx 3.53) 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.
We have found carbon-burning models that excite the radial funda-mental mode, as well as the first, second, and third overtones. Theperiods excited pulsation modes agree with periods of 2190, 417,230, and 185 d that had been detected in Betelgeuse. On the HR dia-gram, these models are located within the allowed range of effectivetemperature and luminosity of Betelgeuse. Beginning with a massof 19 ⊙ at ZAMS (with a rotation velocity of 0.2 or 0.4 crit), themodels lose significant mass mainly in the core-He burning stage to have a mass of 11 ∼ 12 ⊙ in the core carbon-burning stage. A largeradius of about 1300 ⊙ (needed for the long-period fundamentalmode) is supported by interferometric measurements of the angulardiameter combined with the distance.
We conclude that Betelgeuseshould currently be in a late phase (or near the end) of the core car-bon burning. After carbon is exhausted in the core, a core-collapseleading to a supernova explosion is expected in a few tens years.
https://arxiv.org/pdf/2306.00287.pdf