A New Diagnostic of the Radial Density Structure of Be Disks
Zachary H. Draper (1), John P. Wisniewski (1,2), Karen S. Bjorkman (3), Xavier Haubois (4), Alex C. Carciofi (4), Jon E. Bjorkman (3), Marilyn R. Meade (5), Atsuo Okazaki (6)
((1) University of Washington, (2) NSF Astronomy & Astrophysics Postdoctoral Fellow, (3) University of Toledo, (4) Universidade de São Paulo, (5) University of Wisconsin, (6) Hokkai-Gakuen University)
We analyze the intrinsic polarization of two classical Be stars in the process of losing their circumstellar disks via a Be to normal B star transition originally reported by Wisniewski et al. During each of five polarimetric outbursts which interrupt these disk-loss events, we find that the ratio of the polarization across the Balmer jump (BJ+/BJ-) versus the V-band polarization traces a distinct loop structure as a function of time. Since the polarization change across the Balmer jump is a tracer of the innermost disk density whereas the V-band polarization is a tracer of the total scattering mass of the disk, we suggest such correlated loop structures in Balmer jump-V band polarization diagrams (BJV diagragms) provide a unique diagnostic of the radial distribution of mass within Be disks. We use the 3-D Monte Carlo radiation transfer code HDUST to reproduce the observed clockwise loops simply by turning ``on/off'' the mass decretion from the disk. We speculate that counter-clockwise loop structures we observe in BJV diagrams might be caused by the mass decretion rate changing between subsequent ``on/off'' sequences. Applying this new diagnostic to a larger sample of Be disk systems will provide insight into the time-dependent nature of each system's stellar decretion rate.
Reference: ApJL, in press
Status: Manuscript has been accepted