The circumstellar envelope of ζ Tauri through optical interferometry

We present optical interferometric observations of the Be star zeta Tauri obtained using the Navy Prototype Optical Interferometer (NPOI). The multichannel capability of the NPOI allows a high-quality internal calibration of the squared visibilities corresponding to the Halpha emission from the circumstellar environment. The observations suggest a strong departure from circular symmetry and thus are described by an elliptical Gaussian model. We use a nonlinear least-squares fit to the data to obtain the likeliest parameters, and the corresponding uncertainties are determined using a Monte Carlo simulation. We obtain 3.14 +/- 0.21 mas for the angular size of the major axis, -62.degrees3 +/- 4.degrees4 for the position angle, and 0.310 +/- 0.072 for the axial ratio. By comparing our results with those already in the literature, we conclude that the model parameters describing the general characteristics of the circumstellar envelope of zeta Tau appear to be stable on timescales of years. We also compare our results with the known parameters describing the binary nature of zeta Tau, and we conclude that the envelope surrounds only the primary component and is well within its Roche lobe.