  We perform ground based photometric observations of 22 DA white dwarf stars,
10 already known ZZ Cetis and 12 candidates with atmospheric parameters inside
the classical instability strip. We report on the discovery of four new
variable DA white dwarf stars. Two objects are near the middle of the
instability strip, SDSS J082804.63+094956.6 and SDSS J094929.09+101918.8, and
two red edge pulsators, GD 195 and L495-82. In addition, we classified four
objects as possible variables, since evidence of variability was detected in
the light curve, but the S/N was not sufficient to establish a definite
detection. Follow-up observations were performed for 10 know ZZ Ceti stars to
verify period stability and search for new periodicities. For each confirmed
variable, we perform a detailed asteroseismological fit and compare the
structural parameters obtained from the best fit models with those obtained
from spectroscopy and photometry from Gaia. Finally we present a study of the
asteroseismological properties of a sample of 91 ZZ Ceti stars.
