Browsing by Author "Brassard, P."

Now showing 1 - 3 of 3
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    A Study of the Newly Discovered Rapid sdO Pulsators in ω Centauri
    (2012) Randall, S. K.; Fontaine, G.; Calamida, A.; Brassard, P.; Chayer, P.; Alonso, M. L.; Catelan , Marcio; Bono, G.; Green, E. M.; Dhillon, V. S.; Marsh, T. R.
    We summarise recent observational and modelling results obtained for the newly discovered rapid sdO pulsators in ω Centauri. At present, these variables have no counterpart among the field star population, and the extent and purity of the associated instability strip is not yet well defined. First non-adiabatic computations indicate that the pulsations observed are driven by the same κ-mechanism that has been invoked to explain the oscillations in the extensively studied field sdB pulsators. The ω Cen variables appear to show only a small number of independent modes down to the currently achievable detection threshold and there is evidence for significant amplitude variations over time. It remains to be seen whether these objects can be exploited for asteroseismology in the near future; this will certainly be challenging both from an observational and a modelling point of view....
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    Pulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch
    (2016) Randall, S. K.; Calamida, A.; Fontaine, G.; Monelli, M.; Bono, G.; Alonso, M. L.; Van Grootel, V.; Brassard, P.; Chayer, P.; Catelan, Márcio; Littlefair, S.; Dhillon, V. S.; Marsh, T. R.
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    Pulsating Hot Subdwarfs in Omega Centauri
    (2016) Randall, S. K.; Calamida, A.; Fontaine, G.; Monelli, M.; Bono, G.; Alonso, M. L.; Van Grootel, V.; Brassard, P.; Chayer, P.; Catelan , Marcio; Littlefair, S.; Dhillon, V. S.; Marsh, T. R.
    We recently discovered the first globular cluster hot subdwarf pulsators in Omega Centauri (ω Cen). These stars were initially thought to belong to the class of rapidly pulsating subdwarf B stars, which are well established among the field star population and have become showcases for asteroseismology. However, our spectroscopic analysis revealed the ω Cen variables to be significantly hotter than expected, indicating that they form a new class of subdwarf O pulsators clustered around 50 000 K, not known among the field star population. Non-adiabatic pulsation modelling suggests that the driver for the pulsations occurs via the same iron opacity mechanism that is at work in the rapidly pulsating subdwarf B stars....