References of "Floquet, M"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailStochastic gravito-inertial modes discovered by CoRoT in the hot Be star HD 51452
Neiner, C.; Floquet, M.; Samadi, R. et al

in Astronomy and Astrophysics (2012), 546

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of ... [more ▼]

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of iron-peak elements in the envelope of the star. In the Milky Way, p-modes are observed in stars that are hotter than or equal to the B3 spectral type, while g-modes are observed at the B2 spectral type and cooler. <BR /> Aims: We observed a B0IVe star, HD 51452, with the high-precision, high-cadence photometric CoRoT satellite and high-resolution, ground-based HARPS and SOPHIE spectrographs to study its pulsations in great detail. We also used the lower resolution spectra available in the BeSS database. <BR /> Methods: We analyzed the CoRoT and spectroscopic data with several methods: Clean-NG, FreqFind, and a sliding window method. We also analyzed spectral quantities, such as the violet over red (V/R) emission variations, to obtain information about the variation in the circumstellar environment. We calculated a stellar structure model with the ESTER code to test the various interpretation of the results. <BR /> Results: We detect 189 frequencies of variations in the CoRoT light curve in the range between 0 and 4.5 c d[SUP]-1[/SUP]. The main frequencies are also recovered in the spectroscopic data. In particular we find that HD 51452 undergoes gravito-inertial modes that are not in the domain of those excited by the κ-mechanism. We propose that these are stochastic modes excited in the convective zones and that at least some of them are a multiplet of r-modes (i.e. subinertial modes mainly driven by the Coriolis acceleration). Stochastically excited gravito-inertial modes had never been observed in any star, and theory predicted that their very low amplitudes would be undetectable even with CoRoT. We suggest that the amplitudes are enhanced in HD 51452 because of the very rapid stellar rotation. In addition, we find that the amplitude variations of these modes are related to the occurrence of minor outbursts. <BR /> Conclusions: Thanks to CoRoT data, we have detected a new kind of pulsations in HD 51452, which are stochastically excited gravito-inertial modes, probably due to its very rapid rotation. These modes are probably also present in other rapidly rotating hot Be stars. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD, and Science Programs), Germany, and Spain. This work uses observations partly made with the HARPS instrument at the 3.6-m ESO telescope (La Silla, Chile) in the framework of the LP182.D-0356, as well as data obtained with Sophie at OHP and from the BeSS database.Table 3 is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 31 (4 ULg)
Full Text
Peer Reviewed
See detailDetecting and modelling the magnetic field of the β Cephei star V 2052 Ophiuchi
Neiner, C.; Alecian, E.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2012), 537

<BR /> Aims: Following the indirect detection of a magnetic field in the β Cephei star <ASTROBJ>V 2052 Oph</ASTROBJ> by Neiner and collaborators in 2003 with the Musicos spectropolarimeter, we remeasured ... [more ▼]

<BR /> Aims: Following the indirect detection of a magnetic field in the β Cephei star <ASTROBJ>V 2052 Oph</ASTROBJ> by Neiner and collaborators in 2003 with the Musicos spectropolarimeter, we remeasured the magnetic field of this star to attempt to directly confirm the detection of a magnetic field and study its configuration in greater detail. <BR /> Methods: We used the Narval spectropolarimeter installed at TBL (Pic du Midi, France), which is about 20 times more efficient than the Musicos spectropolarimeter. We applied the least-squares deconvolution (LSD) technique to various groups of lines to measure the circular polarisation of the light coming from <ASTROBJ>V 2052 Oph</ASTROBJ>. We synthesized the measured Stokes V profiles with a centred and off-centred dipole model. <BR /> Results: For the first time, we clearly detect the Zeeman signature in the Stokes V profiles of <ASTROBJ>V 2052 Oph</ASTROBJ> and thus directly prove the presence of a magnetic field in this star. The modulation with the rotation period is also confirmed and reflects an oblique dipole field. Thanks to the small error bars on the measurements, we are able to study the behaviour of different groups of lines and the centring of the dipole in the star. We find that the dipole is most likely off-centred along the magnetic axis and that He spots are present at the surface next to the magnetic axis. <BR /> Conclusions: We conclude that <ASTROBJ>V 2052 Oph</ASTROBJ> is a magnetic He-strong β Cep star, with a dipole field, probably off-centred, with B[SUB]pol[/SUB] ~ 400 G and He patches close to the magnetic poles. Based on observations obtained with the Narval spectropolarimeter at the Télescope Bernard Lyot, Observatoire du Pic du Midi, France. [less ▲]

Detailed reference viewed: 12 (5 ULg)
Full Text
Peer Reviewed
See detailFirst asteroseismic results from CoRoT
Michel, Eric; Baglin, A.; Weiss, W. W. et al

in Communications in Asteroseismology (2008), 156

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first ... [more ▼]

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. [less ▲]

Detailed reference viewed: 44 (18 ULg)
Full Text
See detailThe Gaia satellite: a tool for Emission Line Stars and Hot Stars
Martayan, C.; Frémat, Y.; Blomme, R. et al

in SF2A-2008 (2008, November 01)

The Gaia satellite will be launched at the end of 2011. It will observe at least 1 billion stars, and among them several million emission line stars and hot stars. Gaia will provide parallaxes for each ... [more ▼]

The Gaia satellite will be launched at the end of 2011. It will observe at least 1 billion stars, and among them several million emission line stars and hot stars. Gaia will provide parallaxes for each star and spectra for stars till V magnitude equal to 17. After a general description of Gaia, we present the codes and methods, which are currently developed by our team. They will provide automatically the astrophysical parameters and spectral classification for the hot and emission line stars in the Milky Way and other close local group galaxies such as the Magellanic Clouds. [less ▲]

Detailed reference viewed: 25 (6 ULg)
Full Text
See detailThe Seismology Programme of CoRoT
Michel, Eric; Baglin, A.; Auvergne, M. et al

in Proceedings of "The CoRoT Mission Pre-Launch Status - Stellar Seismology and Planet Finding (2006, November 01)

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working ... [more ▼]

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution. [less ▲]

Detailed reference viewed: 55 (34 ULg)
Full Text
Peer Reviewed
See detailThe frequency of Ap-stars with long rotation periods
Hensberge, H.; Manfroid, Jean ULg; Renson, Pierre ULg et al

in Astronomy and Astrophysics (1984), 132

Light variability was observed over time intervals of months to years in the stars HD 55540, HD 71066, HD 94660, and HD 187474. The significance of these results is discussed in terms of the frequency of ... [more ▼]

Light variability was observed over time intervals of months to years in the stars HD 55540, HD 71066, HD 94660, and HD 187474. The significance of these results is discussed in terms of the frequency of chemically peculiar CP2 stars showing (light) variability with periods longer than one month. This frequency, relative to the whole CP2 population, must lie somewhere between 4 and 16 percent. Observations, properly distributed in time, of a small subgroup of CP2 stars will be sufficient to obtain an accurate ratio of the number of LP-CP2 stars to the total number of CP2 stars. These observations, when continued until the periodicity is detected, could contribute also to the discussion whether these long periods should be identified with the rotation period. [less ▲]

Detailed reference viewed: 3 (0 ULg)