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Poster contributions

Shock-Induced Polarized Hydrogen Emission Lines in omicron Ceti
N. Fabas, A. Lèbre, D. Gillet
(GRAAL - Universite Montpellier 2 - Montpellier)
We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with NARVAL instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi (France). We have detected time variable polarimetric signatures (on UQV Stokes spectra) associated to Balmer Hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We confirm the shockwave assumption which was one of the explanations proposed by McLean & Coyne (1978) to understand the linear polarization of the Balmer lines of Mira. In the future, we plan to extend this work initiated with omicron Ceti (M type Mira) to other Mira variables (C and S- spectral types Miras).

Similarity properties and scaling laws of radiating shocks and accreted column in magnetic cataclysmic variables: The POLAR Project
E. Falize, B. Loupias, A. Ravasio, C. D. Gregory, A. Dizière, M. Koenig, C. Michaut, C. Cavet, J.-P. Leidinger, X. Ribeyre

Search for cool brown dwarfs with the new optical and near-infrared whole sky surveys
B. Goldman, Th. Henning
The first brown dwarfs have been discovered 15 years ago, and the coolest ones have temperatures of about 500K, almost bridging very low mass stars to the Solar giant planets. Indeed some insolated exoplanets have temperatures typical of brown dwarfs. With a new generation of on-going and soon-to-start surveys such as PanSTARRS1, UKIDSS/VISTA and WISE, the prospects to find brown dwarfs in larger number, various flavours and cooler temperatures have never been so good. In this paper I describe our recent discoveries from the UKIDSS near-infrared survey, including one of the two coolest "benchmark" brown dwarfs. I also present the prospects of the optical PanSTARRS1 survey which started regular operation in May.

Long-term magnetic field monitoring of the Sun-like star ksi Bootis A
Morgenthaler A., Petit P., Aurière M., Dintrans B., Fares R., Gastine T., Lanoux J., Lignières F., Morin J., Ramirez J., Saar S., Théado S., Van Grootel V.
Phase-resolved observations of the solar-type star ksi Bootis A were obtained using the Narval spectropolarimeter at Telescope Bernard Lyot (Pic du Midi, France) during years 2007, 2008, 2009 and 2010. The data sets enable us to study both the rotational and the long-term evolution of various activity tracers. Here, we focus on the large-scale photospheric magnetic field (reconstructed by Zeeman-Doppler Imaging), the Zeeman broadening of the FeI 846.84 nm magnetic line, and the chromospheric CaII H and H$\alpha$ emission. We observe a global decrease of all magnetic proxies over the years, accompanied in the magnetic maps by a decreased fraction of magnetic energy stored in the toroidal field component.

Effective temperature scale of M dwarfs
Arvind Singh Rajpurohit, Céline Reylé, Mathias Schultheis, France Allard
(Observatoire de Besançon, Institut UTINAM)
We present a comparison of low-resolution spectra of 60 stars covering the whole M-dwarf sequence. Using the most recent PHOENIX stellar atmosphere models (Allard, Homeier & Freytag 2010, in preparation) we do a quantitative comparison to our observed spectra in the wavelength range 450-850 nm. We perform a first confrontation between models and observations by comparing the TiO band intensities and we assign effective temperatures. Teff-colour and Teff-spectral type relations will then be compared with the published ones.

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Samuel Boissier 2010-06-16