Oblique Pulsation: New, Challenging Observations with TESS Data

Abstract

A major result from the first cycle of the TESS mission shows that the well-studied roAp star HD 6532 has a completely different mode geometry when compared to the published extensive ground-based B observations taken in 1984, 1985 and 1994. This is a major challenge to the widely used and theoretically explored oblique pulsator model. There are three prime hypotheses: (1) The oblique pulsator model is wrong. If that is shown, 40 years of work on these stars will need reinterpretation. (2) The star has dramatically changed pulsation axes. No pulsating star has previously even been suspected of doing this. We do not know if a pulsating star can do this. (3) Theory and extensive spectroscopic observations show that the pulsation mode geometry in roAp stars is sensitive to atmospheric depth. Subsequently, in these stars, we can see pulsation amplitude, phase and geometry in 3D. It is possible that the ground-based B observations and the TESS red bandpass observations are seeing a very different pulsation structure at different depths. If this can be shown, it will be novel and unexpected with implications for stellar pulsation in general. The test of these hypotheses requires simultaneous ground-based observations in UBV at the time of new observations of HD 6532 by TESS. This problem is novel, has wider implications for asteroseismology, and is testable by our method