Radial-velocity variations in pulsating Ap stars: Pr III and Nd III lines in the spectrum of gamma Equ

Based on high-resolution CCD spectrograms obtained at the Coude focus of the 2.6-m Crimean Astrophysical Observatory telescope on 13 nights from August through November 1998, we study radial-velocity variations in the roAp star gamma Equ. The largest amplitude of the periodic radial-velocity variations (up to 0.8 km/s) has been found using the spectral lines identified with NdIII 6145.07 A and PrIII 6160.24 A. The power spectra for the data on each night exhibit a peak at a frequency of 1.35 +/- 0.05 mHz, which corresponds to a pulsation period of about 12.35 min. The other identified lines in the spectral range under study show no variability that exceeds appreciably the accuracy of our measurements. The total power spectrum for PrIII 6160.24 A during the observations from August through November 1998 reveals the three most significant oscillation frequencies of 1349, 1355, and 1365 microHz. Only one of the four frequencies found by Martinez et al. (1986) when analyzing photometric data roughly coincides with our peak at 1365 microHz.