129 research outputs found

    Magnetic field detection in the B2Vn star HR 7355

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    The B2Vn star HR 7355 is found to be a He-rich magnetic star. Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory to measure the disk-averaged longitudinal magnetic field at various phases of the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z = -2200 and +3200G was found, with confidence limits of 100 to 130G. The field topology is that of an oblique dipole, while the star itself is seen about equator-on. In the intensity spectra the HeI-lines show the typical equivalent width variability of He-strong stars, usually attributed to surface abundance spots. The amplitudes of the equivalent width variability of the HeI lines are extraordinarily strong compared to other cases. These results not only put HR 7355 unambiguously among the early-type magnetic stars, but confirm its outstanding nature: With v sin i = 320 km/s the parameter space in which He-strong stars are known to exist has doubled in terms of rotational velocity.Comment: 6 pages, 5 figures, 1 Table. Accepted for publication in MNRAS Letter

    The (B0+?)+O6 system FN CMa: A case for tidal-pulsational interaction?

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    FN CMa is visually double with a separation of about 0.6arcsec. Sixty high-cadence VLT/UVES spectra permit the A and B components to be disentangled, as the relative contribution of each star to the total light entering the spectrograph fluctuates between exposures due to changes in seeing. Component A exhibits rapid line-profile variations, leading us to attribute the photometric variability seen by HIPPARCOS (with a derived P=0.08866d) to this component. From a total of 122 archival and new echelle spectra it is shown that component A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of 0.6 may result in tidal modulation of the pulsation(s) of component Aa.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution, Mass Loss and Critical Limit

    The magnetic field of zeta Orionis A

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    Zeta Ori A is a hot star claimed to host a weak magnetic field, but no clear magnetic detection was obtained so far. In addition, it was recently shown to be a binary system composed of a O9.5I supergiant and a B1IV star. We aim at verifying the presence of a magnetic field in zeta Ori A, identifying to which of the two binary components it belongs (or whether both stars are magnetic), and characterizing the field.Very high signal-to-noise spectropolarimetric data were obtained with Narval at the Bernard Lyot Telescope (TBL) in France. Archival HEROS, FEROS and UVES spectroscopic data were also used. The data were first disentangled to separate the two components. We then analyzed them with the Least-Squares Deconvolution (LSD) technique to extract the magnetic information. We confirm that zeta Ori A is magnetic. We find that the supergiant component zeta Ori Aa is the magnetic component: Zeeman signatures are observed and rotational modulation of the longitudinal magnetic field is clearly detected with a period of 6.829 d. This is the only magnetic O supergiant known as of today. With an oblique dipole field model of the Stokes V profiles, we show that the polar field strength is ~ 140 G. Because the magnetic field is weak and the stellar wind is strong, zeta Ori Aa does not host a centrifugally supported magnetosphere. It may host a dynamical magnetosphere. Its companion zeta Ori Ab does not show any magnetic signature, with an upper limit on the undetected field of ‚ąľ\sim 300 G

    Spatial distribution of stellar rotational axes from Be stars

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    Para conocer la distribuci√≥n de velocidades de rotaci√≥n de las estrellas Be, se utiliza la suposici√≥n est√°ndar que los ejes de rotaci√≥n se distribuyen uniformemente. En este trabajo usamos √°ngulos proyectados de polarimetr√≠a de casi 500 estrellas Be y realizamos un an√°lisis estad√≠stico. Adem√°s llevamos a cabo una simulaci√≥n Monte Carlo cuyos resultados explican las caracter√≠sticas observadas de los √°ngulos, confirmando que provienen de una distribuci√≥n uniforme, pero que sus √°ngulos proyectados poseen una estructura bimodal. Esta √ļltima caracter√≠stica podr√≠a cambiar las conclusiones acerca de la distribuci√≥n de velocidades de rotaci√≥n de estas estrellas.In order to know the distribution of rotational velocities of Be stars, a standard assumption is used, namely that the rotational axes are uniformed distributed. We use here polarimetric projected angles data from almost 500 Be stars and we make a statistical analysis. Furthermore we perform a Monte-Carlo simulation that explains the observed features of the angles, confirming that it is indeed uniform distributed, but the projected angles possess a bimodal structure. This last features may change the conclusion about the rotational velocity distribution of these stars.Fil: Cur√©, M.. Universidad de Valpara√≠so; ChileFil: Christen, A.. Universidad de Chile; ChileFil: Rivinius, Th.. European Southern Observatory; ChileFil: Rial, Diego Fernando. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Oficina de Coordinaci√≥n Administrativa Ciudad Universitaria. Instituto de Investigaciones Matem√°ticas "luis A. Santal√≥"; Argentina. Universidad de Valpara√≠so; Chil
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