THE DETECTION OF CYCLIC FREQUENCY VARIABILITY IN THE RAPIDLY OSCILLATING AP STAR HD-134214

We have discovered cyclic variability in the pulsation frequency of th e rapidly oscillating Ap (roAp) star, HD 134214, at about the same tim e as similar frequency variability has been found in two other roAp st ars, HR 3831 and alpha Cir. We have obtained 74 hours of new high-spee d photometric data in 1991, 1992 and 1993. These new data, plus data o btained previously in 1985 and 1990, give us an accumulated data set s panning nine years. From an analysis of these data, we find a peak-to- peak variation in the pulsation frequency of HD 134214 of 0.42 muHz, o n a time-scale of about 248 days, which repeats well but not exactly. A lack of radial velocity variation rules out an explanation of this f requency variability as a Doppler shift caused by binary motion. As wi th HR 3831, we suggest that the cyclic frequency variability may be ca used by a modulation of the magnetic field, similar to such frequency modulations seen in global solar oscillations. HD 134214 shows a modul ation in frequency similar to the value detected in the Sun, and the l argest yet known for an roAp star.