Axions from Betelgeuse: Probing Axion Couplings with $^{23}\rm{Na}$ and $^{55}\rm{Mn}$
We investigate axion-like particle (ALP) production in the interior of Betelgeuse via nuclear de-excitation of thermally populated excited states of $^{23}$Na and $^{55}$Mn. As these ALPs propagate to Earth, they can produce photons either through their conversion in the Galactic magnetic field or through their decay. Using INTEGRAL-ISGRI and NuSTAR observations, we search for these photon signals, find no significant excess, and derive 95% CL exclusion limits on the ALP couplings. For magnetic-field conversion of ALPs, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI constrains $|g_{aγ}g_{ap}| < 4.1\times10^{-21}$ ($6.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ for $m_a < 10^{-10} \mathrm{eV}$. For ALP decays, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI (NuSTAR) constrains $|g_{aγ}g_{ap}|$ down to $3.0\times10^{-22}$ ($2.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ at $m_a \simeq 400$ ($83$) keV, weakening in both cases as $m_a^{-3/2}$ for lower ALP masses, and as $m_a^{-2}$ for $^{23}$Na below $m_a \sim 1$ keV, with sensitivity extending to $m_a \simeq 440.2$ ($124$) keV. Although our $^{23}\mathrm{Na}$-based limits are the strongest for both channels, their larger transition energy makes them more sensitive to the precise evolutionary stage of Betelgeuse, whereas the $^{55}\mathrm{Mn}$-based limits are considerably more robust against such uncertainties.