  We present the discovery of a long-period, rapidly oscillating Ap star,
HD177765. Using high-resolution time-series observations obtained with UVES at
the ESO VLT telescope, we found radial velocity variations with amplitudes
7-150 m/s and a period of 23.6 min, exceeding that of any previously known roAp
star. The largest pulsation amplitudes are observed for Eu III, Ce III and for
the narrow core of Halpha. We derived the atmospheric parameters and chemical
composition of HD177765, showing this star to be similar to other long-period
roAp stars. Comparison with theoretical pulsational models indicates an
advanced evolutionary state for HD177765. Abundance analyses of this and other
roAp stars suggest a systematic variation with age of the rare-earth line
anomalies seen in cool Ap stars.
