Dynamical Evolution of Viscous Disks around Be Stars. II : polarimetry

Abstract

Be stars exhibit variability for a great number of observables. Putting the pieces together of the disk dynamics is not an easy task and requires arduous modeling before achieving a good fit of the observational data. In order to guide the modeling process and make it more efficient, it is very instructive to investigate reference dynamical cases. This paper focuses on continuum polarimetric quantities and is the second of a series that aims to demonstrate the capacity of deriving the dynamical history and fundamental parameters of a classical Be star through the follow-up of various observables. After a detailed study of the different opacities at play in the formation of polarized spectra, we investigate predictions of polarimetric observables in the continuum for different dynamical scenarios. Our models are based on a coupling of a hydrodynamic viscous decretion simulations in a disk and a 3-D non-LTE radiative transfer code. Introducing the polarization color diagram (PCD), we show that certain combinations of polarimetric observables exhibit features that are characteristic of a mass loss history. This diagram also enables to estimate fundamental parameters such as the inclination angle, the disk density scale and the $\alpha$ viscous diffusion parameter. We present the PCD as a powerful diagnosis tool to track the dynamical phases of a Be star such as disk building-up, dissipation, periodic and episodic outbursts. Finally we confront our models with observations of 4 Be stars that exhibited long-term polarimetric activity.

13 pages, 17 figures, Accepted for publication in ApJ

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• The life cycles of Be viscous decretion discs: time-dependent modelling of infrared continuum observations
• ALMA Observations of the T Tauri Binary System AS 205: Evidence for Molecular Winds and/or Binary Interactions
• Outbursts and Disk Variability in Be Stars
• Growth and Dissipation of Be Star Discs in Misaligned Binary Systems
• A Multi-observing-technique Study of the Dynamical Evolution of the Viscous Disk around the Be Star $\omega$ CMa
• Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of $\nu$ Puppis (B7-8 IIIe)
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• Outbursts and stellar properties of the classical Be star HD 6226
• Warped disks during type II outbursts in Be/X-ray binaries: evidence from optical polarimetry
• Short-term variability and mass loss in Be stars VI. Frequency groups in $\gamma$ Cas detected by TESS
• Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star $\beta$ CMi
• Visible and near-infrared spectro-interferometric analysis of the edge-on Be star $o$ Aquarii
• 2.5D global-disk oscillation models of the Be shell star ζ Tauri I. Spectroscopic and polarimetric analysis
• High-spatial-resolution simulations of Be star disks in binary systems: I. Structure and kinematics of coplanar disks
• Investigating the Circumstellar Disk of the Be Shell Star 48 Librae
• The optical counterpart to the Be/X-ray binary SAX J2239.3+6116
• Fast time optical variability in Be/X-ray binaries. Pulsation and rotation
• Effect of Be Disk Evolution on Global One-Armed Oscillations
• Evidence of a Mira-like tail and bow shock about the semi-regular variable V CVn from four decades of polarization measurements
• The Complex Circumstellar and Circumbinary Environment of V356 Sgr
• Evolution and Explosion of Massive Stars Leading to IIP-IIL SNe with MESA and SNEC
• Long-term optical variability of high-mass X-ray binaries. III. Polarimetry