NEW OBSERVATIONS AND A FREQUENCY-ANALYSIS OF THE EXTREMELY PECULIAR RAPIDLY OSCILLATING AP STAR HD 101065

We present 138 hr of new high-speed photometric observations of HD 101065 obtained with the 1-m telescope of the South African Astronomical Observatory. These observations reveal that HD 101065 pulsates with at least three frequencies near 1.37 mHz which cannot all be identified with consecutive overtones. These frequencies completely describe the oscillations down to the 0.40 mmag level. There is very strong evidence of many more frequencies below the 0.35 mmag level, but the complexity of the spectrum is such that we are unable to determine any of these frequencies securely. Definitive mode identifications and a straightforward application of the oblique pulsator model to HD 101065 are not yet possible. A tentative application of the techniques of asteroseismology indicates that HD 101065 is only slightly off the zero age main sequence and suggests that its radius, mass and luminosity are similar to those of the other Ap stars. There is also evidence which suggests that the second-order quantity in the asymptotic relation for pulsation in high-overtone p-modes, δν, is 3-7 times lower in the rapidly oscillating Ap stars than current theoretical expectations. We find a significant secular variation in the principal frequency using two independent techniques and we argue that it cannot be interpreted as arising from evolutionary effects in HD 101065. We then examine the possibility that an unresolved frequency is involved and we show that a binary star model in which a low-mass companion orbits about HD 101065 is consistent with the available observations. We have also detected the presence of two secondary frequencies which describe the long-term amplitude modulation of the principal frequency. These frequencies indicate that the amplitude of the dominant frequency may not be completely stable. Finally, we propose that a multi-site observing campaign may offer the best hope of further deciphering the frequency spectrum of HD 101065. © Royal Astronomical Society.