2.5D global-disk oscillation models of the Be shell star ζ Tauri I. Spectroscopic and polarimetric analysis

Abstract

Context. Various Be stars exhibit intensity variations of the violet and red emission peaks in their HI lines observed in emission. This so-called $V/R$ phenomenon is usually explained by the precession of a one-armed spiral density perturbation in the circumstellar disk. That global-disk oscillation scenario was confirmed, both observationally and theoretically, in the previous series of two papers analyzing the Be shell star ζ Tauri. The vertically averaged (2D) global-disk oscillation model used at the time was able to reproduce the $V/R$ variations observed in Hα, as well as the spatially resolved interferometric data from AMBER/VLTI. Unfortunately, that model failed to reproduce the $V/R$ phase of Br15 and the amplitude of the polarization variation, suggesting that the inner disk structure predicted by the model was incorrect. Aims. The first aim of the present paper is to quantify the temporal variations of the shell-line characteristics of ζ Tauri. The second aim is to better understand the physics underlying the $V/R$ phenomenon by modeling the shell-line variations together with the $V/R$ and polarimetric variations. The third aim is to test a new 2.5D disk oscillation model, which solves the set of equations that describe the 3D perturbed disk structure but keeps only the equatorial (i.e., 2D) component of the solution. This approximation was adopted to allow comparisons with the previous 2D model, and as a first step toward a future 3D model. Results. The new 2.5D formalism improves the agreement with the observed $V/R$ variations of Hα and Br15, under the proviso that a large value of the viscosity parameter, α = 0.8, be adopted. Nonetheless, it remains challenging for the models to reproduce consistently the amplitude and the average level of the polarization data, whatever formalism is adopted.

arXiv comment14 pages, 9 figures, 3 tables

References in corpus (12)

• A natural explanation for periodic X-ray outbursts in Be/X-ray binaries
• NLTE Monte Carlo Radiative Transfer: I. The Thermal Properties of Keplerian Disks around Classical Be Stars
• Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks
• The first determination of the viscosity parameter in the circumstellar disk of a Be Star
• Cyclic Variability of the Circumstellar Disc of the Be Star $\zeta$ Tau. II. Testing the 2D Global Disc Oscillation Model
• Cyclic variability of the circumstellar disk of the Be star zetaTau - I. Long-term monitoring observations
• Dynamical Evolution of Viscous Disks around Be Stars. II : polarimetry
• Toward Mapping the Detailed Density Structure of Classical Be Circumstellar Disks
• Drastic Spectroscopic Variability of the Be/X-ray Binary A0535+262/V725 Tau during and after the 2009 Giant Outburst
• Global Disk Oscillations in Binary Be Stars
• New activity in the large circumstellar disk of the Be-shell star 48 Lib
• Spectroscopic Variations of the Be-shell Star EW Lac in the V/R Variation Periods

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