  We measure apparent velocities (v_app) of absorption lines for 36 white
dwarfs (WDs) with helium-dominated atmospheres -- 16 DBAs and 20 DBs -- using
optical spectra taken for the European Southern Observatory SN Ia progenitor
survey (SPY). We find a difference of 6.9+/-6.9 km/s in the average apparent
velocity of the H-alpha lines versus that of the HeI 5876AA for our DBAs. This
is a measure of the blueshift of this He line due to pressure effects. By using
this as a correction, we extend the gravitational redshift method employed by
Falcon et al. (2010) to use the apparent velocity of the HeI 5876AA line and
conduct the first gravitational redshift investigation of a group of WDs
without visible hydrogen lines. We use biweight estimators to find an average
apparent velocity, <v_app>_BI, (and hence average gravitational redshift,
<v_g>_BI) for our WDs; from that we derive an average mass, <M>_BI. For the
DBAs, we find <v_app>_BI = 40.8+/-4.7 km/s and derive <M>_BI = 0.71 +0.04 -0.05
Msun. Though different from <v_app> of DAs (32.57 km/s) at the 91% confidence
level and suggestive of a larger DBA mean mass than that for normal DAs derived
using the same method (0.647 +0.013 -0.014 Msun; Falcon et al. 2010), we do not
claim this as a stringent detection. Rather, we emphasize that the difference
between <v_app>_BI of the DBAs and <v_app> of normal DAs is no larger than 9.2
km/s, at the 95% confidence level; this corresponds to roughly 0.10 Msun. For
the DBs, we find <v_app>^He_BI = 42.9+/-8.49 km/s after applying the blueshift
correction and determine <M>_BI = 0.74 +0.08 -0.09 Msun. The difference between
<v_app>^He_BI of the DBs and <v_app> of DAs is less than or equal to 11.5 km/s
(~0.12 Msun), at the 95% confidence level. The gravitational redshift method
indicates much larger mean masses than the spectroscopic determinations of the
same sample by Voss et al. (2007)...

Solar and Stellar Astrophysics