We measure apparent velocities ( v _ { app } ) of the H \alpha and H \beta Balmer line cores for 449 non-binary thin disk normal DA white dwarfs ( WDs ) using optical spectra taken for the ESO S N Ia P rogenitor surve Y ( SPY ; ) .
Assuming these WDs are nearby and co-moving , we correct our velocities to the Local Standard of Rest so that the remaining stellar motions are random .
By averaging over the sample , we are left with the mean gravitational redshift , \langle v _ { g } \rangle : we find \langle v _ { g } \rangle = \langle v _ { app } \rangle = 32.57 \pm 1.17 km s ^ { -1 } .
Using the mass-radius relation from evolutionary models , this translates to a mean mass of 0.647 ^ { +0.013 } _ { -0.014 } M _ { \odot } .
We interpret this as the mean mass for all DAs .
Our results are in agreement with previous gravitational redshift studies but are significantly higher than all previous spectroscopic determinations except the recent findings of .
Since the gravitational redshift method is independent of surface gravity from atmosphere models , we investigate the mean mass of DAs with spectroscopic T _ { eff } both above and below 12000 K ; fits to line profiles give a rapid increase in the mean mass with decreasing T _ { eff } .
Our results are consistent with no significant change in mean mass : \langle M \rangle ^ { hot } = 0.640 \pm 0.014 M _ { \odot } and \langle M \rangle ^ { cool } = 0.686 ^ { +0.035 } _ { -0.039 } M _ { \odot } .