Abstract
We recently discovered an apparently new class of pulsating Extreme Horizontal Branch (EHB) star in ω Cen. Tightly clustered around ∼50,000 K, these H-rich sdO stars exhibit rapid, multi-periodic oscillations on a timescale of 100 s. While four such objects have been detected in ω Cen, no counterparts have yet been found among the field population. Conversely, the rapid sdB pulsators around 31,000 K that are well-studied in the Galactic field have yet to be found in a globular cluster. We discuss the implications of this and also report the discovery of a fifth EHB pulsator in ω Cen.
Highlights
INTRODUCTIONSystematic differences in the observed binary properties of field and globular cluster Extreme Horizontal Branch (EHB) stars point towards different evolutionary scenarios dominating the EHB formation in the two stellar environments [5]
The study of pulsating Extreme Horizontal Branch (EHB) stars in globular clusters is a new field of research that is only just opening up
We know of just 5 EHB pulsators in Cen, which is by no means a typical globular cluster
Summary
Systematic differences in the observed binary properties of field and globular cluster EHB stars point towards different evolutionary scenarios dominating the EHB formation in the two stellar environments [5] It was suggested [6] that this may be explained by a He-white dwarf merger channel becoming more important for older stellar populations, but this remains to be confirmed. One very promising way of testing the different evolutionary scenarios proposed is through asteroseismology, where the fundamental parameters of a star are determined to a high accuracy by modelling its oscillation spectrum. This has been done with great success in particular for the rapid sdB (sdBVr ) pulsators. We hope to use asteroseismology to compare the evolution of EHB stars in clusters and among the field population and determine if and how they differ
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