1,304 research outputs found

    Discovery of a very weak magnetic field on the Am star Alhena

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    Alhena (γ\gamma Gem) was observed in the frame of the BRITE (BRIght Target Explorer) spectropolarimetric survey, which gathers high resolution, high signal-to-noise, high sensitivity, spectropolarimetric observations of all stars brighter than V=4 to combine seismic and spectropolarimetric studies of bright stars. We present here the discovery of a very weak magnetic field \textbf{on} the Am star Alhena, thanks to very high signal-to-noise spectropolarimetric data obtained with Narval at T\'elescope Bernard Lyot (TBL). All previously studied Am stars show the presence of ultra-weak (sub-Gauss) fields with Zeeman signatures with an unexpected prominent positive lobe. However, Alhena presents a slightly stronger (but still very weak, only a few Gauss) field with normal Zeeman signatures with a positive and negative lobe, as found in stronger field (hundreds or thousands of Gauss) stars. It is the first detection of a normal magnetic signature in an Am star. Alhena is thus a very interesting object, which might provide the clue to understanding the peculiar shapes of the magnetic signatures of the other Am stars.Comment: letter accepted by MNRA

    Observations of magnetic fields in hot stars

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    The presence of magnetic fields at the surfaces of many massive stars has been suspected for decades, to explain the observed properties and activity of OB stars. However, very few genuine high-mass stars had been identified as magnetic before the advent of a new generation of powerful spectropolarimeters that has resulted in a rapid burst of precise information about the magnetic properties of massive stars. During this talk, I will briefly review modern methods used to diagnose magnetic fields of higher-mass stars, and summarize our current understanding of the magnetic properties of OB stars.Comment: Proceedings of IAUS272: Active OB stars, review talk (11 pages

    Combining seismology and spectropolarimetry of hot stars

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    Asteroseismology and spectropolarimetry have allowed us to progress significantly in our understanding of the physics of hot stars over the last decade. It is now possible to combine these two techniques to learn even more information about hot stars and constrain their models. While only a few magnetic pulsating hot stars are known as of today and have been studied with both seismology and spectropolarimetry, new opportunities - in particular Kepler2 and BRITE - are emerging and will allow us to rapidly obtain new combined results.Comment: proceedings of the IAU Symposium 307 held in Geneva in June 201

    Stochastic excitation of gravity waves in rapidly rotating massive stars

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    Stochastic gravity waves have been recently detected and characterised in stars thanks to space asteroseismology and they may play an important role in the evolution of stellar angular momentum. In this context, the observational study of the CoRoT hot Be star HD 51452 suggests a potentially strong impact of rotation on stochastic excitation of gravito-inertial waves in rapidly rotating stars. In this work, we present our results on the action of the Coriolis acceleration on stochastic wave excitation by turbulent convection. We study the change of efficiency of this mechanism as a function of the waves' Rossby number and we demonstrate that the excitation presents two different regimes for super-inertial and sub-inertial frequencies. Consequences for rapidly rotating early-type stars and the transport of angular momentum in their interiors are discussed.Comment: 2 pages, 1 figure, IAU 307 symposium proceedings, 'New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry', Eds. G. Meynet, C. Georgy, J.H. Groh & Ph. Ste

    Wind tunnel evaluation of YF-12 inlet response to internal airflow disturbances with and without control

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    The response of terminal-shock position and static pressures in the subsonic duct of a YF-12 aircraft flight-hardware inlet to perturbations in simulated engine corrected airflow were obtained with and without inlet control. Frequency response data, obtained with inlet controls inactive, indicated the general nature of the inherent inlet dynamics, assisted in the design of controls, and provided a baseline reference for responses with active controls. All the control laws were implemented by means of a digital computer that could be programmed to behave like the flight inlet's existing analog control. The experimental controls were designed using an analytical optimization technique. The capabilities of the controls were limited primarily by the actuation hardware. The experimental controls provided somewhat better attenuation of terminal shock excursions than did the YF-13 inlet control. Controls using both the forward and aft bypass systems also provided somewhat better attenuation than those using just the forward bypass. The main advantage of using both bypasses is in the greater control flexibility that is achieved
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