Browsing by Author "Alonso, M. L."

Now showing 1 - 6 of 6
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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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    A survey of hot subdwarf pulsators in ω Cen
    (2013) Randal, S. K.; Calamida, A.; Fontaine, G.; Green, E. M.; Monelli, M.; Alonso, M. L.; Catelan , Marcio; Bono, G.; Dhillon, V. S.; Marsh, T. R.
    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....
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    Erratum to: A survey of hot subdwarf pulsators in ω Cen
    (2013) Randall, S. K.; Calamida, A.; Fontaine, G.; Green, E. M.; Monelli, M.; Alonso, M. L.; Catelan, Márcio; Bono, G.; Dhillon, V. S.; Marsh, T. R.
    Erratum for: "The name of the first author should be S. K. Randall".
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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....
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    The soundtrack of RR Lyrae in omega Cen at high-frequency.
    (2015) Calamida, A.; Randall, S. K.; Monelli, M.; Bono, G.; Buonanno, R.; Strampelli, G.; Catelan, Marcio; Van Grootel, V.; Alonso, M. L.; Stetson, P. B.; Stellingwerf, R. F.
    We present preliminary Sloan u',g'-band light curves for a sample of known RR Lyrae variables in the Galactic globular cluster omega Cen. Results are based on the partial reduction of multi-band time series photometric data collected during six consecutive nights with the visitor instrument ULTRACAM mounted on the New Technology Telescope (La Silla, ESO). This facility allowed us to simultaneously observe in three different bands (Sloan u',g',r') a field of view of ∼ 6×6 arcminutes. The telescope and the good seeing conditions allowed us to sample the light curves every 15 seconds. We ended up with a data set of ∼ 6,000 images per night per filter, for a total of more than 200,000 images of the selected field. This data set allowed us to detect different kind of variables, such as RR-Lyraes, SX Phoenicis, eclipsing binaries, semi-regulars. More importantly, we were able for the first time to sample at high-frequency cluster RR Lyraes in the u',g'-band and to show in detail the pulsation phases across the dip located along the rising branch of RR-Lyraes. Based on data collected with ULTRACAM@NTT (La Silla, ESO, PID: 087.D-0216)...