¹ Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P. O. Box 4106, Atlanta, GA 30302-4106
² Department of Astronomy, University of Michigan, 500 Church Street, 917 Dennison Building, Ann Arbor, MI 48109-1042
³ Astronomy Department, Yale University, New Haven, CT 06520-8101
⁴ Kitt Peak National Observatory, National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732
⁵ Department of Astronomy, University of Texas, 1 University Station, C1400, Austin, TX 78712
⁶ Ritter Observatory, M. S. 113, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606-3390
⁷ Astronomical Institute, Academy of Sciences, Fricova 296, CZ-251 65 Ondrejov, Czech Republic

We present the first K'-band, long-baseline interferometric observations of the northern Be stars  Cas,  Per,  Tau, and  Dra. 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 fits of the four model parameters (disk base density, radial density exponent, disk normal inclination, and position angle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux and the resulting orientations generally agree with those from interferometric H and continuum polarimetric observations. We find that the angular size of the K' disk emission is smaller than that determined for the H emission, and we argue that the difference is the result of a larger H opacity and the relatively larger neutral hydrogen fraction with increasing disk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases of  Per and  Dra. We also present contemporaneous observations of the H H, and Br emission lines. Synthetic model profiles of these lines that are based on the same disk inclination and radial density exponent as derived from the CHARA Array observations match the observed emission line strength if the disk base density is reduced by  1.7 dex.

Accepted by ApJL
Preprints from gies@chara.gsu.edu
or on the web at http://arxiv.org/abs/astro-ph/0609501