We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf , HS 0507+0434B .
Using the wavelength dependence of observed mode amplitudes , we deduce the spherical degree , \ell , of the modes , most of which have \ell = 1 .
The presence of a large number of combination frequencies ( linear sums or differences of the real modes ) enabled us not only to test theoretical predictions but also to indirectly infer spherical and azimuthal degrees of real modes that had no observed splittings .
In addition to the above , we measure line-of-sight velocities from our spectra .
We find only marginal evidence for periodic modulation associated with the pulsation modes : at the frequency of the strongest mode in the lightcurve , we measure an amplitude of 2.6 \pm 1.0 kms ^ { -1 } , which has a probability of 2 % of being due to chance ; for the other modes , we find lower values .
Our velocity amplitudes and upper limits are smaller by a factor of two compared to the amplitudes found in ZZ Psc .
We find that this is consistent with expectations based on the position of HS 0507+0434B in the instability strip .
Combining all the available information from data such as ours is a first step towards constraining atmospheric properties in a convectionally unstable environment from an observational perspective .