Rodrigo G. Vieira

High-resolution Br γ spectro-interferometry of the transitional Herbig Ae/Be star HD 100546 : a Keplerian gaseous disc inside the inner rim

We present spatially and spectrally resolved Br γ emission around the planet-hosting, transitional Herbig Ae/Be star HD 100546. Aiming to gain insight into the physical origin of the line in possible relation to accretion processes, we carried out Br γ spectro-interferometry using AMBER/VLTI from three different baselines achieving spatial and spectral resolutions of 2–4 mas and 12 000. The Br γ visibility is larger than that of the continuum for all baselines. DifferentialphasesrevealashiftbetweenthephotocentreoftheBr γ line–displaced ∼0.6mas (0.06au at 100 pc) NE from the star – and that of the K-band continuum emission – displaced ∼0.3 mas NE from the star. The photocentres of the redshifted and blueshifted components of the Br γ line are located NW and SE from the photocentre of the peak line emission, respectively. Moreover, the photocentre of the fastest velocity bins within the spectral line tends to be closer to that of the peak emission than the photocentre of the slowest velocity bins. Our results are consistent with a Br γ-emitting region inside the dust inner rim (0.25au) and extending very close to the central star, with a Keplerian, disc-like structure rotating counter-clockwise, and most probably flared (∼25 ◦ ). Even though the main contribution to the Br γ line does not come from gas magnetically channelled on to the star, accretion on to HD (1)

Be discs in binary systems I. Coplanar orbits

Be stars are surrounded by outflowing circumstellar matter structured in the form of decretion discs. They are often members of binary systems, where it is expected that the decretion disc interacts both radiatively and gravitationally with the companion. In this work we study how various orbital (period, mass ratio and eccentricity) and disc (viscosity) parameters affect the disc structure in coplanar systems. We simulate such binaries with the use of a smoothed particle hydrodynamics code. The main effects of the secondary on the disc are its truncation and the accumulation of material inwards of truncation. We find two cases with respect to the effects of eccentricity: (i) In circular or nearly circular prograde orbits, the disc maintains a rotating, constant in shape, configuration, which is locked to the orbital phase. The disc is smaller in size, more elongated and more massive for low viscosity parameter, small orbital separation and/or high mass ratio. (ii) Highly eccentric orbits are more complex, with the disc structure and total mass strongly dependent on the orbital phase and the distance to the secondary. We also study the effects of binarity in the disc continuum emission. Since the infrared and radio SED are sensitive to the disc size and density slope, the truncation and matter accumulation result in considerable modifications in the emergent spectrum. We conclude that binarity can serve as an explanation for the variability exhibited in observations of Be stars, and that our model can be used to detect invisible companions.

The pseudo-photosphere model for the continuum emission of gaseous discs

We investigate the continuum emission of viscous decretion discs around Be stars in this paper. The results obtained from non-LTE (local thermodynamic equilibrium) radiative transfer models show two regimes in the disc surface brightness profile: an inner optically thick region, which behaves as a pseudo-photosphere with a wavelength-dependent size, and an optically thin tenuous outer part, which contributes with about a third of the total flux. The isophotal shape of the surface brightness is well described by elliptical contours with an axial ratio

The life cycles of Be viscous decretion discs: time-dependent modelling of infrared continuum observations

b/a=\cos i

Multitechnique Testing of the Viscous Decretion Disk Model. 1. The Stable and Tenuous Disk of the Late-Type Be Star Beta CMi

for inclinations

Distinguishing post-AGB impostors in a sample of pre-main sequence stars

i<75^{\circ}

Revealing the structure of the outer disks of Be stars

. Based on these properties, a semi-analytical model was developed to describe the continuum emission of gaseous discs. It provides fluxes and spectral slopes at the infrared within an accuracy of

The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars

10\%

The life cycles of Be viscous decretion discs: The case of ω CMa

and

The Outer Disk of the Classical Be Star ψ Per

5\%