We present a detailed spectroscopic and photometric analysis of DA and DB white dwarfs drawn from the Sloan Digital Sky Survey with trigonometric parallax measurements available from the Gaia mission .
The temperature and mass scales obtained from fits to ugriz photometry appear reasonable for both DA and DB stars , with almost identical mean masses of \langle M \rangle = 0.617 ~ { } M _ { \odot } and 0.620 ~ { } M _ { \odot } , respectively .
The comparison with similar results obtained from spectroscopy reveals several problems with our model spectra for both pure hydrogen and pure helium compositions .
In particular , we find that the spectroscopic temperatures of DA stars exceed the photometric values by \sim 10 % above T _ { eff } \sim 14 , 000 K , while for DB white dwarfs , we observe large differences between photometric and spectroscopic masses below T _ { eff } \sim 16 , 000 K. We attribute these discrepancies to the inaccurate treatment of Stark and van der Waals broadening in our model spectra , respectively .
Despite these problems , the mean masses derived from spectroscopy — \langle M \rangle = 0.615 ~ { } M _ { \odot } and 0.625 ~ { } M _ { \odot } for the DA and DB stars , respectively — agree extremely well with those obtained from photometry .
Our analysis also reveals the presence of several unresolved double degenerate binaries , including DA+DA , DB+DB , DA+DB , and even DA+DC systems .
We finally take advantage of the Gaia parallaxes to test the theoretical mass-radius relation for white dwarfs .
We find that 65 % of the white dwarfs are consistent within the 1 \sigma confidence level with the predictions of the mass-radius relation , thus providing strong support to the theory of stellar degeneracy .