Be stars: one ring to rule them all?

Aims. We report theoretical spectral energy distributions (SEDs), Br$\gamma$ line profiles and visibilities for two scenarios that can explain the disk dissipation of active hot stars an account for the transition from the Be to the B spectroscopic phase. Methods. We use the SIMECA code to investigate these two scenarios: the first one where the disk is formed by successive outbursts of the central star. A low-density region is developing above the star and slowly grows outward and forms a ring-like structure that will gradually excavate the disk. The second one, where a slowly decreasing mass loss, for instance due to a decrease of the radiative force through an opacity change at the base of the photosphere, may also be responsible for the vanishing of the circumstellar disk. Results. We obtain that a clear signature of the disk dissipation following the ring scenario will be the disappearance of the high velocity tails in the emission lines and a nearly constant peaks separation. Moreover, we found that following the ring-like scenario the visibilities must show an increasing second lobe, an increase of the value of the first zero and, assuming an unresolved central star, a first zero of the visibility curves that appends at shorter baselines as far as the disk is been excavate. We propose to use the AMBER instrument on the VLTI to probe if the the ring scenario is the one that rule the Be phenomenon.Comment: 10 page

Confirming HD 23478 as a new magnetic B star hosting an H\u3b1-bright centrifugal magnetosphere

In this paper, we report 23 magnetic field measurements of the B3IV star HD23478: 12 obtained from high-resolution Stokes V spectra using the ESPaDOnS (Canada-France-Hawaii Telescope) and Narval (T\ue9lescope Bernard Lyot) spectropolarimeters, and 11 from mediumresolution Stokes V spectra obtained with the DimaPol spectropolarimeter (Dominion Astronomical Observatory). HD23478 was one of two rapidly rotating stars identified as potential 'centrifugal magnetosphere' hosts based on IR observations from the Apache Point Observatory Galactic Evolution Experiment survey. We derive basic physical properties of this star including its mass (M = 6.1+0.8<inf>-0.7</inf>M 99), effective temperature (Teff = 20 \ub1 2 kK), radius (R = 2.7+1.6 <inf>-0.9</inf> R 99), and age (\u3c4<inf>age</inf> = 3+37 <inf>-1</inf> Myr). We repeatedly detect weakly variable Zeeman signatures in metal, He, and H lines in all our observations corresponding to a longitudinal magnetic field of (Bz) 48 -2.0 kG. The rotational period is inferred from Hipparcos photometry (Prot = 1.0498(4) d). Under the assumption of the Oblique RotatorModel, our observations yield a surface dipole magnetic field of strength Bd 65 9.5 kG that is approximately aligned with the stellar rotation axis. We confirm the presence of strong and broad H\u3b1 emission and gauge the volume of this star's centrifugal magnetosphere to be consistent with those of other H\u3b1 emitting centrifugal magnetosphere stars based on the large inferred Alfv\ue9n to Kepler radius ratio.Peer reviewed: YesNRC publication: Ye