ESTIMATING Be STAR DISK RADII USING Hα EMISSION EQUIVALENT WIDTHS

摘要

We present numerical models of the circumstellar disks of Be stars, and we. describe the resulting synthetic Hα emission lines and maps of the wavelength-integrated emission flux projected onto the sky. We demonstrate that there are monotonic relationships between the emission-line equivalent width and the ratio of the angular half-width at half-maximum of the projected disk major axis to the radius of the star. These relationships depend mainly on the temperatures of the disk and star, the inclination of the disk normal to the line of sight, and the adopted outer boundary for the disk radius. We show that the predicted Hα disk radii are consistent with those observed directly through long baseline interferometry of nearby Be stars (especially once allowance is made for disk truncation in binaries and for dilution of the observed Hα equivalent width by continuum disk flux in the V band).