NON-EVOLUTIONARY SECULAR PERIOD INCREASE IN PULSATING DA WHITE-DWARFS

We show that the proper motion of a pulsating white dwarf results in a secular change of the radial velocity of the star and consequently co ntributes to the observed P. The proper motion term is always positive and for a typical DAV white dwarf it is of the order of 10(-14) divid ed by 10(-15) ss(-1). This effect is thus comparable with the expected evolutionary period change in these stars due to their cooling, which also produces a positive period derivative, and has to be taken into account when the intrinsic P is to be properly determined from the obs erved period change.