Prof.
Gerald
Handler
Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
For stars to exhibit pulsations, a mechanism driving the oscillations is required. Several such mechanisms are known and are associated with certain properties of the oscillating star. As a consequence, different groups of pulsating stars occur in specific regions in the HR Diagram: their instability strips. However, there have been reports of pulsating stars outside of the known instability strips. Perhaps the most (in)famous ones have been named the "Maia variables", a group of late B to early A type stars that apparently show pressure mode oscillations, but are located outside any known instability strips. The existence of such variables has been controversial since the 1950s and it has meanwhile been demonstrated that Maia itself does not show detectable pulsations. Nevertheless, in recent years some reports of related objects have appeared in the literature, mostly based on highly accurate space photometry. To investigate the nature of these objects, we have obtained and analysed high resolution spectra of 31 of these objects as well as examined their TESS photometric data. According to our results, many of these stars are normal pulsators of the Beta Cephei and Delta Scuti types, but some objects remain outside of any known instability strip. We have checked those for contamination in the large TESS pixels, possible binarity and rapid rotation. In this presentation, we discuss how many of those stars can indeed be considered to be pulsators "without a cause" (if any) and why, and whether there is substantial evidence for a class of "Maia variables".
This is an online event only:
Online: Zoom Link, (Passcode: 134595, Meeting ID: 823 8038 0442)
