CHARA Array<i>K</i>′‐Band Measurements of the Angular Dimensions of Be Star Disks

Abstract

We present the first K'-band, long-baseline interferometric observations of\nthe northern Be stars gamma Cas, phi Per, zeta Tau, and kappa Dra. The\nmeasurements were made with multiple telescope pairs of the CHARA Array\ninterferometer, and in every case the observations indicate that the\ncircumstellar disks of the targets are resolved. We fit the interferometric\nvisibilities with predictions from a simple disk model that assumes an\nisothermal gas in Keplerian rotation. We derive fits of the four model\nparameters (disk base density, radial density exponent, disk normal\ninclination, and position angle) for each of the targets. The resulting\ndensities are in broad agreement with prior studies of the IR excess flux and\nthe resulting orientations generally agree with those from interferometric\nH-alpha and continuum polarimetric observations. We find that the angular size\nof the K' disk emission is smaller than that determined for the H-alpha\nemission, and we argue that the difference is the result of a larger H-alpha\nopacity and the relatively larger neutral hydrogen fraction with increasing\ndisk radius. All the targets are known binaries with faint companions, and we\nfind that companions appear to influence the interferometric visibilities in\nthe cases of phi Per and kappa Dra. We also present contemporaneous\nobservations of the H-alpha, H-gamma, and Br-gamma emission lines. Synthetic\nmodel profiles of these lines that are based on the same disk inclination and\nradial density exponent as derived from the CHARA Array observations match the\nobserved emission line strength if the disk base density is reduced by\napproximately 1.7 dex.\n