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See detailX-ray spectroscopy of early-type stars: The present and the future
Rauw, Grégor ULg; Nazé, Yaël ULg; Oskinova, L. M.

in Astronomische Nachrichten (2008), 329(2), 222-225

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be ... [more ▼]

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be addressed in order to fully understand the X-ray spectra of these objects. Many of these issues require high-resolution spectroscopy or monitoring of a sample of massive stars. Given the moderate X-ray brightness of these targets, rather long exposure times are needed to achieve these goals. In this contribution, we review our current knowledge in this field and present some hot topics that could ideally be addressed with XMM-Newton over the next decade. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [less ▲]

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See detailThe effect of turbulent mixing on g-modes spectrum of MS stars
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Eggenberger, P. et al

in Astronomische Nachrichten (2008), 329

Understanding transport processes inside stars is one of the main goals of asteroseismology. Chemical turbulent mixing can affect the internal distribution of μ near the energy generating core, having an ... [more ▼]

Understanding transport processes inside stars is one of the main goals of asteroseismology. Chemical turbulent mixing can affect the internal distribution of μ near the energy generating core, having an effect on the evolutionary tracks similar to that of overshooting. This mixing leads to a smoother chemical composition profile near the edge of the convective core, which is reflected in the behavior of the buoyancy frequency and, therefore, in the frequencies of gravity modes. We describe the effects of convective overshooting and turbulent mixing on the frequencies of gravity modes in B-type main sequence stars. In particular, the cases of p-g mixed modes in β Cep stars and high-order modes in SPBs are considered. [less ▲]

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See detailGravity modes and mixed modes as probes of stellar cores in main-sequence stars: From solar-like to β Cep stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Eggenberger, P. et al

in Astronomische Nachrichten (2008), 329

We investigate how the frequencies of gravity modes depend on the detailed properties of the chemical composition gradient that develops near the core of main-sequence stars and, therefore, on the ... [more ▼]

We investigate how the frequencies of gravity modes depend on the detailed properties of the chemical composition gradient that develops near the core of main-sequence stars and, therefore, on the transport processes that are able to modify the \mu profile in the central regions. We show that in main-sequence models, similarly to the case of white dwarfs, the periods of high-order gravity modes are accurately described by a uniform period spacing superposed to an oscillatory component. The periodicity and amplitude of such a component are related, respectively, to the location and sharpness of the \mu gradient. We briefly discuss and interpret, by means of this simple approximation, the effect of turbulent mixing near the core on the periods of both high-order and low-order g modes, as well as of modes of mixed pressure-gravity character. [less ▲]

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See detailDiscovery of magnetic fields in three He variable Bp stars with He and Si spots
Briquet, Maryline ULg; Hubrig, S.; Schöller, M. et al

in Astronomische Nachrichten (2007), 328

It is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, non-pulsating chemically peculiar hot Bp stars and pulsating stars co-exist in the ... [more ▼]

It is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, non-pulsating chemically peculiar hot Bp stars and pulsating stars co-exist in the slowly pulsating B stars and β Cephei instability strips. We have conducted a search for magnetic fields in the four Bp stars HD 55522, HD 105382, HD 131120, and HD 138769 which previously have been wrongly identified as slowly pulsating B stars. A recent study of these stars using the Doppler Imaging technique revealed that the elements He and Si are inhomogeneously distributed on the stellar surface, causing the periodic variability. Using FORS 1 in spectropolarimetric mode at the VLT, we have acquired circular polarisation spectra to test the presence of a magnetic field in these stars. A variable magnetic field is clearly detected in HD 55522 and HD 105382, but no evidence for the existence of a magnetic field was found in HD 131120. The presence of a magnetic field in HD 138769 is suggested by one measurement at 3 σ level. We discuss the occurrence of magnetic B stars among the confirmed pulsating B stars and find strong magnetic fields of order kG and oscillations to be mutually exclusive. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO programmes 71.D-0308(A), 072.D-0377(A), and 073.D-0466(A)). [less ▲]

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