Stars as Laboratories for Fundamental Physics - MPP Theory Group

52 Chapter 2
They calculated the distribution for the temperature bins of Tab. 2.2
in analogy to the discussion of neutrino dipole moments in the previous
section. Their results are shown in Fig. 2.13 as a function of α 26 where
I have corrected from ⟨F ⟩ = 3, which they used in order to compare
with Raffelt (1986b), to the more appropriate value ⟨F ⟩ = 1.
Fig. 2.13. Relative number of 0.6 M ⊙ WDs in the hot and intermediate
temperature bins of Tab. 2.2 as a function of the “fine-structure constant”
α 26 = α ′ /10 −26 of pseudoscalar bosons (Blinnikov and Dunina-Barkovskaya
1994). I have corrected from ⟨F ⟩ = 3 to the more appropriate value 1. The
number of WDs in the temperature range 12,000−40,000 K is normalized to
unity. The shaded bands correspond to the observations (Tab. 2.2).
This temperature method is now relatively insensitive because axion
cooling leaves the shape of the luminosity function nearly unchanged,
except that the neutrino dip is washed out for strong cooling. In detail,
however, important changes occur. It is noteworthy that boson cooling
has a significant impact on the shape of the luminosity function
even for α 26 < 1. It appears that the possibility of residual hydrogen
burning in young WDs would make the present argument more conservative
because it has the same effect as boson emission, namely to
reduce or wash out the neutrino dip in the luminosity function.
2.2.5 Period Decrease of Variable White Dwarfs
The luminosity function allows one to determine the WD cooling speed
because one is looking at a large WD ensemble of different age. Recently
it has become possible for the first time to measure WD cooling directly
for a single object by virtue of the period change of a ZZ Ceti star.