Axion cooling of white dwarfs

To investigate the effect of axions in the cooling process of white dwarfs, their luminosity function was computed in the way described by Isern et al. (1991), but neglecting the sedimentation induced by solidification which can introduce a considerable delay in the cooling process. It was found that the luminosity function is only modified in the region of luminosities, -2.8 to -0.6 long(L/solar luminosity), remaining compatible with the observations, and that the total cooling time is shortened by 0.8 Gyr, a quantity that is not negligible but that is small compared with the delay introduced by solidification. Neutrino emission, which scales as T exp 7, is dominant at high luminosities (or central temperatures), and photon luminosity, which roughly scales as T exp 2.5, is dominant at low luminosities. Axion emission, which scales as T exp 4, is only dominant in the above-mentioned short luminosity interval, and the time spent by white dwarfs in this interval is only 0.85 Gyr.