2006A&A...448.1165S

A new continuous 3.5h series of high-resolution spectroscopic observations of the roAp star γ Equ, with about 12 points per pulsation cycle, is presented to study the mean magnetic field modulus variability with the pulsation period. Radial velocity variations with amplitudes of up to approximately 400m/s are clearly detected in the rare earth lines present in the covered spectral range. Two frequencies are resolved in their analysis, which are consistent with frequencies previously observed in the star. No significant radial velocity variation is detected for the line FeIIλ6149.2. The mean magnetic field modulus derived from measurement of the wavelength separation of the magnetically resolved components of this line does not show any variation, with a 3σ upper limit of ∼10G. While our results are consistent with the conclusion of the previous studies, difficulties to reconcile this result with those of other works may be attributed, in part at least, to the use of different diagnostic lines in different works and to the failure of all studies so far to fully resolve all the pulsation frequencies of γ Equ.