SIMBAD references

We compute rates of period change (P{dot}) for the 215 s mode in G117-B15A and the 213 s mode in R548, first for models without axions, and then for models with axions of increasing mass. We use the asteroseismological models for G117-B15A and R548 we derived in an earlier publication. For G117-B15A, we consider two families of solutions, one with relatively thick hydrogen layers and one with thin hydrogen layers. Given the region of parameter space occupied by our models, we estimate error bars on the calculated P{dot} values using Monte Carlo simulations. Together with the observed P{dot} for G117-B15A, our analysis yields strong limits on the DFSZ axion mass. Our thin hydrogen solutions place an upper limit of 13.5 meV on the axion, while our thick hydrogen solutions relaxes that limit to 26.5 meV.