Michele Floquet

Discovery of a magnetic field in the Slowly Pulsating B star ζ Cassiopeiae

ζ Cas is a B2 IV star with v sini = 17 km s −1 . Time-resolved circular spectropolarimetric observations of ζ Cas obtained in 2001 and 2002 with the Musicos ´ echelle spectropolarimeter at th e2mTBernard Lyot (TBL) show a sinu- soidally varying longitudinal magnetic field with a strength between 10 G and −46 G for the averaged line-of-sight component, corresponding to Bpol = 335 +120 −65 G. The period corresponds very accurately with the 5.37045 day period as derived from stellar wind variations observed in the ultraviolet. The epoch of the positive maximum field corresponds in phase with the maximum emission in the UV wind lines. This gives compelling evidence for a magnetic rotator model for this star, with an unambiguous rotation period of 5.37 days. We searched for periodicity in line-profile variations (lpv), radial velocity and minimum intensity curves in the ∼400 optical spectra. We found a non-radial pulsation mode with l = 2 ± 1 at the frequency f = 0.64 c d −1 . From this periodicity and from stellar parameters derived from model fits, we propose to classify ζ Cas as a Slowly Pulsating B (SPB) star. This is the third detection of a magnetic field in an early B-type pulsating star and the first one in a SPB star.

Effects of metallicity, star-formation conditions, and evolution in B and Be stars. II: Small Magellanic Cloud, field of NGC 330.

We search for effects of metallicity on B and Be stars in the Small and Large Magellanic Clouds (SMC and LMC) and in the Milky Way (MW). We extend our previous analysis of B and Be stars populations in the LMC to the SMC. The rotational velocities of massive stars and the evolutionary status of Be stars are examined with respect to their environments. Spectroscopic observations of hot stars belonging to the young cluster SMC-NGC 330 and its surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We determine fundamental parameters for B and Be stars with the GIRFIT code, taking into account the effect of fast rotation, and the age of observed clusters. We compare the mean vsini obtained by spectral type- and mass-selection for field and cluster B and Be stars in the SMC with the one in the LMC and MW. We find that (i) B and Be stars rotate faster in the SMC than in the LMC, and in the LMC than in the MW; (ii) at a given metallicity, Be stars begin their main sequence life with a higher initial rotational velocity than B stars. Consequently, only a fraction of B stars that reach the ZAMS with a sufficiently high initial rotational velocity can become Be stars; (iii) the distributions of initial rotational velocities at the ZAMS for Be stars in the SMC, LMC and MW are mass- and metallicity-dependent; (iv) the angular velocities of B and Be stars are higher in the SMC than in the LMC and MW; (v) in the SMC and LMC, massive Be stars appear in the second part of the main sequence, contrary to massive Be stars in the MW.

Rotation and magnetic field in the Be star omega Orionis

Ori is a B2IIIe star for which rotational modulation and non-radial pulsations (NRP) have been recently investi- gated from two independent observational campaigns in 1998 and 1999. Putting the data of these 2 campaigns together, and adding data obtained in 2001, we search for multiperiodicity in the line profile variations and evidence for outbursts. From new spectropolarimetric data obtained at the Telescope Bernard Lyot (TBL, Pic du Midi, France) in 2001 we also measure the Stokes V parameter in the polarised light. We find evidence for the presence of a weak magnetic field in ! Ori sinusoidally varying with a period of 1.29 d. The equivalent widths (EW) of the wind sensitive UV resonance lines also show a variation with the same period, which we identify as the rotational period of the star. We propose an oblique rotator model and derive Bpol = 530 230 G to explain the observations. Moreover, we carry out an abundance analysis and find the star to be N- enriched, a property which is shared with other magnetic stars. We propose! Ori as the first known classical Be star hosting a magnetic field.

Rotation, pulsations and magnetic field in V 2052 Ophiuchi: A new He-strong star

V 2052 Oph is a β Cep star with v sini ∼ 60 km s −1 . The behavior of its stellar wind was studied in the ultraviolet wavelength region with the IUE satellite. It revealed periodic variations in the equivalent widths (EW) of the resonance lines of wind-sensitive ions with a period of 3.638833 d, which is identified as the rotational period. These variations are typical of magnetic stars. Therefore time-resolved circular spectropolarimetric observations were obtained with the Musicos ´ spectropolarimeter at the 2-m Telescope Bernard Lyot (TBL) to search for a magnetic field in the star. Stokes V patterns were observed, the inclination and magnetic angles were derived and a value was determined for the polar magnetic field (250 ± 190 G) using an oblique rotator dipole model. The spectroscopic information was used to search for periodicity in line-profile variations (lpv), radial velocity and minimum intensity curves. Multiperiodicity was found, corresponding to radial (f1 = 7.15 c d −1 ) and non-radial (f2 = 6.82 c d −1 , l = 3 or 4) pulsation modes. The rotation period is also detected in rotationally modulated observables because of the magnetic poles passing through the observers line of sight. We determined the stellar parameters of the star, which was found to be chemically peculiar, in particular He-enriched. This makes V 2052 Oph the first magnetic He-strong early B star with known pulsational properties.

Non-radial pulsation, rotation and outburst in the Be star omega Orionis from the MuSiCoS 1998 campaign

w Ori (HD 37490, HR 1934) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (Ha, Hδ, HeI 4471, 4713, 4921, 5876, 6678, CII 4267, 6578, 6583, MgII 4481, SiIII 4553 and Sill 6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi Site Continuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity (v sin i = 179 kms - 1 ) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsini for several lines, as well as Violet and Red components of photospheric lines affected by emission (red He I lines, Sill 6347, CII 6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with l = 2 or 3, ‖m‖ = 2 with frequency 1.03 cd - 1 . It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 cd - 1 , in relation to the outburst.

Variability and pulsations in the Be star 66 Ophiuchi

Oph is a Be star seen under a moderate inclination angle that shows strong variability from UV to IR wavelengths. A concise review of long-term variability history is given. High resolution, high S /N spectroscopic observations obtained in 1997, 1998 and 2001 and spectropolarimetric observations obtained in 2000 are presented. These observations occurred during a long-term decrease of Hα intensity. Fundamental parameters of the star have been revisited from Barbier-Chalonge-Divan (BCD) calibrations. New V sini values are obtained using Fourier transforms applied to observed helium lines and a rotational frequency frot = 1.29 cd −1 is determined. Time series analysis and Fourier Doppler Imaging (FDI) of Hei lines (4713, 4921, 5876 and 6678 A) lead for the first time to the detection of multi-periodicity in 66Oph. The two main frequencies found are f = 2.22 cd −1 and f = 4.05 cd −1 . They are attributed to non-radial pulsations and can be associated with mode degree � = 2a nd� = 3, respectively. Inspection of Stokes V profiles suggests the presence of a weak Zeeman signature but further observations are needed to confirm the detection of a magnetic field in 66 Oph.

A study of the B and Be star population in the field of the LMC open cluster NGC 2004 with VLT-FLAMES

Observations of hot stars belonging to the young cluster LMC-NGC 2004 and its surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA mode. 25 Be stars were discovered; the proportion of Be stars compared to B-type stars is found to be of the same order in the LMC and in the Galaxy fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5 of these are found to be eclipsing systems from the MACHO database, with periods of a few days. About 75% of the spectra in our sample are polluted by hydrogen (H

Rotation, pulsations and outbursts in the Be star

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