Dynamical Evolution of Viscous Disks around Be Stars. II: polarimetry.
X. Haubois1,2,3, B. C. Mota2, A.C. Carciofi2, Z. H. Draper4,5, J. P. Wisniewski6, D. Bednarski2, Th. Rivinius71 LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92195 Meudon, France
2 Instituto de Astronomia, Geofísica e Ciéncias Atmosféricas, Universidade de São Paulo, Brazil
3 Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia
4 Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd, Victoria, BC V8P 5C2 Canada
5 Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 Canada
6 H. L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks St Norman, OK 73019, USA
7 European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile
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.
Accepted in ApJ on 10/02/2014
or on the web at: arXiv:1402.1968