A CHARA ARRAY SURVEY OF CIRCUMSTELLAR DISKS AROUND NEARBY Be-TYPE STARS

Abstract

We report on a high angular resolution survey of circumstellar disks around\n24 northern sky Be stars. The K-band continuum survey was made using the CHARA\nArray long baseline interferometer (baselines of 30 to 331 m). The\ninterferometric visibilities were corrected for the flux contribution of\nstellar companions in those cases where the Be star is a member of a known\nbinary or multiple system. For those targets with good uv coverage, we used a\nfour parameter Gaussian elliptical disk model to fit the visibilities and to\ndetermine the axial ratio, position angle, K-band photospheric flux\ncontribution, and angular diameter of the disk major axis. For the other\ntargets with relatively limited uv coverage, we constrained the axial ratio,\ninclination angle, and or disk position angle where necessary in order to\nresolve the degeneracy between possible model solutions. We also made fits of\nthe ultraviolet and infrared spectral energy distributions to estimate the\nstellar angular diameter and infrared flux excess of each target. The mean\nratio of the disk diameter (measured in K-band emission) to stellar diameter\n(from SED modeling) is 4.4 among the 14 cases where we reliably resolved the\ndisk emission, a value which is generally lower than the disk size ratio\nmeasured in the higher opacity Halpha emission line. We estimated the\nequatorial rotational velocity from the projected rotational velocity and disk\ninclination for 12 stars, and most of these stars rotate close to or at the\ncritical rotational velocity.\n