HR 710 (HD 15144): an ultra-Sr-rich, magnetic Ap star with a close companion

The magnetic, chemically peculiar A-star HR 710 (HD 15144, ADS 1849A, AB Cet) has a close companion in a nearly circular orbit. Its 3-d period is unusually short for such stars. The system emits moderately hard X-rays, which likely come from a white dwarf secondary (ADS 1849Ab). The Sr II spectrum is very strong, and the resonance lines show similar core-nib structure to the stronger Ca K line. We place only loose constraints on a model. There are indications of a lower electron/gas pressure than expected from the star's parallax and brightness. Strong-line profiles and anomalous excitation/ionization indicate significant deviations from traditional models, fixed by T-eff, log g and abundances. Weak spectral-line profiles and wavelength shifts probably indicate abundance patches rather than the presence of a secondary (ADS 1849Ab) spectrum. Our UV-Visual Echelle Spectrograph (UVES) spectra are from only one epoch. Additional low-noise, high-resolution spectra are needed. We discuss the spectrum within the context of abundance stratification.