An asteroseismic constraint on the mass of the axion from the period drift of the pulsating DA white dwarf star L19-2

We employ an asteroseismic model of L19-2, a relatively massive ($M_{\star} \sim 0.75 M_{\sun}$)andhot($T_{\rm eff} \sim 12,100$ K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), and use the observed values of the temporal rates of period change of its dominant pulsation modes ($\mathrm{\Pi }\sim 113$ s and $\mathrm{\Pi }\sim 192$ s), to derive a new constraint on the mass of the axion, the hypothetical non-barionic particle considered as a possible component of the dark matter of the Universe. If the asteroseismic model employed is an accurate representation of L19-2, then our results indicate hints of extra cooling in this star, compatible with emission of axions of mass $m_{\mathrm{a}}{\cos }^2\beta \lesssim 25$ meV or an axion-electron coupling constant of $g_{\mathrm{a}\mathrm{e}}\lesssim 7\times {10}^{-13}$.