Delta Sct pulsation in magnetic Ap stars: the discovery of delta Sct pulsations in HD218994AB and measurement of the magnetic fields of HD218994A and HD21190

KURTZ, D. W.; HUBRIG, S.; GONZÁLEZ, J.F.; VAN WYK, F.; MARTINEZ, P.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2008 vol. 386 p. 1750 - 1755

0035-8711

We have discovered that at least one component of the visual binary star HD218994AB is a delta Sct star. The primary star of this system is a known rapidly oscillating Ap (roAp) star; therefore, it is possible that it is both an roAp star and a delta Sct star - a hybrid. There are no confirmed such hybrid roAp-delta Sct stars, and they are predicted theoretically not to exist. More probably, HD218994B is the delta Sct star, as it is 0.54mag fainter than the primary and also lies in the delta Sct instability strip. It then offers the potential to determine Teff and L for the primary which appears to be one of the more evolved roAp stars and an important test the theoretically calculated roAp star instability strip. In this case, the system also is important since the stars are a co-eval pair of very similar mass, yet one is a magnetic roAp star and the other is probably a non-magnetic delta Sct star with a normal spectrum. We detect a significant longitudinal magnetic field strength of 440 +/- 23G in the roAp star HD218994A. We also present the first measurement of the longitudinal magnetic field strength for the δSct star HD21190, the most-evolved Ap star known. We obtain a formally significant value of 47 +/- 13G. If confirmed, this will make HD21190 the first magnetic δSct star known.