Browsing by Author "Marsh, T. R."

Now showing 1 - 7 of 7
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    A DUSTY COMPONENT TO THE GASEOUS DEBRIS DISK AROUND THE WHITE DWARF SDSS J1228+1040
    (2009) Brinkworth, C. S.; Gansicke, B. T.; Marsh, T. R.; Hoard, D. W.; Tappert, C.
    We present Infrared Spectrometer And Array Camera (ISAAC) spectroscopy and ISAAC, UKIDSS, and Spitzer Space Telescope broadband photometry of SDSS J1228+1040-a white dwarf for which evidence of a gaseous metal-rich circumstellar disk has previously been found from optical emission lines. The data show a clear excess in the near- and mid-infrared (IR), providing compelling evidence for the presence of dust in addition to the previously identified gaseous debris disk around the star. The IR excess can be modeled in terms of an optically thick but geometrically thin disk. We find that the inner disk temperatures must be relatively high (similar to 1700 K) in order to fit the spectral energy distribution in the near- IR. These data provide the first evidence for the coexistence of both gas and dust in a disk around a white dwarf, and show that their presence is possible even around moderately hot (similar to 22,000 K) stars.
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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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    Once in a blue moon: detection of 'bluing' during debris transits in the white dwarf WD 1145+017
    (2017) Hallakoun, N.; Xu, S.; Maoz, D.; Marsh, T. R.; Ivanov, V. D.; Dhillon, V. S.; Bours, M. C. P.; Parsons, S. G.; Kerry, P.; Vanzi, Leonardo; Sharma, S.; Su, K.; Rengaswamy, S.; Pravec, P.; Kusnirak, P.; Kucakova, H.; Armstrong, J.; Arnold, C.; Gerard, N.
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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....