We employ a state-of-the-art asteroseismological model of G117 - B15A , the archetype of the H-rich atmosphere ( DA ) white dwarf pulsators ( also known as DAV or ZZ Ceti variables ) , and use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to derive a new constraint on the mass of axion , the still conjectural non-barionic particle considered as candidate for dark matter of the Universe .
Assuming that G117 - B15A is truly represented by our asteroseismological model , and in particular , that the period of the dominant mode is associated to a pulsation g -mode trapped in the H envelope , we find strong indications of the existence of extra cooling in this star , compatible with emission of axions of mass m _ { a } \cos ^ { 2 } \beta = \left ( 17.4 ^ { +2.3 } _ { -2.7 } \right ) meV .