CHARA Array K'-Band Measurements of the Angular Dimensions of Be Star Disks

We present the firstK 0 -band,long-baseline interferometric observations of the northern Be starsCas,� Per,� Tau, andDra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fitsof thefourmodelparameters(diskbasedensity,radialdensityexponent,disknormalinclination,andpositionangle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux, and the resultingorientationsgenerallyagreewiththosefrominterferometricHandcontinuumpolarimetricobservations.We find that the angular size of the K 0 diskemissionis smaller thanthatdeterminedfor the Hemission, and weargue that thedifferenceisthe resultof a larger Hopacityandtherelativelylarger neutral hydrogenfractionwithincreasingdisk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases ofPer andDra. We also present contemporaneous observations of the H� , H� ,andBremissionlines.Syntheticmodelprofilesoftheselinesthatarebasedonthesamediskinclinationandradial densityexponentasderivedfromtheCHARA Arrayobservationsmatchtheobservedemissionlinestrengthif thedisk base density is reduced by � 1.7 dex.