An independent limit on the axion mass from the variable white dwarf star R548

Abstract

Abstract. Pulsating white dwarfs with hydrogen-rich atmospheres, also known as DAV stars, can be used as astrophysical laboratories to constrain the properties of fundamental particles like axions. Comparing the measured cooling rates of these stars with the expected values from theoretical models allows us to search for sources of additional cooling due to the emission of weakly interacting particles. In this paper, we present an independent inference of the mass of the axion using the recent determination of the evolutionary cooling rate of R548, the DAV class prototype. We employ a state-of-the-art code which allows us to perform a detailed asteroseismological fit based on fully evolutionary sequences. Stellar cooling is the solely responsible of the rates of change of period with time (Π) for the DAV class. Thus, the inclusion of axion emission in these sequences notably influences the evolutionary timescales, and also the expected pulsational properties of the DAV stars. This allows us to compare the theoreticalΠ values to the corresponding empirical rate of change of period with time of R548 to discern the presence of axion cooling. We found that if the dominant period at 213.13 s in R548 is associated with a pulsation mode trapped in the hydrogen envelope, our models indicate the existence of additional cooling in this pulsating white dwarf, consistent with axions of mass m a cos 2 β ∼ 17.1 meV at a 2σ confidence level. This determination is in agreement with the value inferred from another well-studied DAV, G117−B15A. We now have two independent and consistent estimates of the mass of the axion obtained from DAVs, although additional studies of other pulsating white dwarfs are needed to confirm this value of the axion mass.

White Dwarf Stars

“…126 Refs. [127][128][129][130][131][132] show white dwarf pulsations and luminosity function are consistent with extra cooling caused by axions of masses around 17 ± 4 mev.…”

Pulsating white dwarfs

“…[69][70][71][72][73][74] show white dwarf pulsations and luminosity function are consistent with extra cooling caused by axions of masses around 17 ± 4 meV.…”

The quest for an intermediate-scale accidental axion and further ALPs

“…The same parameter range is preferred to explain the anomalous size of the observed period decrease of the pulsating WDs G117-B15A and R548 by additional axion/ALP losses [102,103]. A third independent hint of anomalous stellar losses has recently been found in the red-giant branch of the globular cluster M5, which seems to be extended to larger brightness than expected within the Standard Model.…”