Estimating Be Star Disk Radii using Hα Emission Equivalent Widths

We present numerical models of the circumstellar disks of Be stars, and wedescribe the resulting synthetic H-alpha emission lines and maps of thewavelength-integrated emission flux projected onto the sky. We demonstrate thatthere are monotonic relationships between the emission line equivalent widthand the ratio of the angular half-width at half maximum of the projected diskmajor axis to the radius of the star. These relationships depend mainly uponthe temperatures of the disk and star, the inclination of the disk normal tothe line of sight, and the adopted outer boundary for the disk radius. We showthat the predicted H-alpha disk radii are consistent with those observeddirectly through long baseline interferometry of nearby Be stars (especiallyonce allowance is made for disk truncation in binaries and for dilution of theobserved H-alpha equivalent width by continuum disk flux in the V-band).Comment: 12 pages, 2 figures, ApJL in pres