No abstract

This paper describes the OI Exchange Format, a standard for exchanging calibrated data from optical (visible/infrared) stellar interferometers. The standard is based on the Flexible Image Transport System (FITS), and supports storage of the optical interferometric observables including squared visibility and closure phase -- data products not included in radio interferometry standards such as UV-FITS. The format has already gained the support of most currently-operating optical interferometer projects, including COAST, NPOI, IOTA, CHARA, VLTI, PTI, and the Keck Interferometer, and is endorsed by the IAU Working Group on Optical Interferometry. Software is available for reading, writing and merging OI Exchange Format files.Comment: 26 pages, 1 figur

Long-baseline interferometric observations obtained with the Navy Prototype Optical Interferometer of the H-emitting envelopes of the Be stars Tau and CMi are presented. For compatibility with the previously published interferometric results in the literature of other Be stars, circularly symmetric and elliptical Gaussian models were fitted to the calibrated H observations. The models are adequate for characterizing the angular distribution of the H-emitting circumstellar material associated with these Be stars. To study the correlations between the various model parameters and the stellar properties, the model parameters for Tau and CMi were combined with data for other Be stars from the literature. After accounting for the different distances to the sources and stellar continuum flux levels, it was possible to study the relationship between the net H emission and the physical extent of the H-emitting circumstellar region. A clear dependence of the net H emission on the linear size of the emitting region is demonstrated, and these results are consistent with an optically thick line emission that is directly proportional to the effective area of the emitting disk. Within the small sample of stars considered in this analysis, no clear dependence on the spectral type or stellar rotation is found, although the results do suggest that hotter stars might have more extended H-emitting regions.

We present optical interferometric observations of the Be star 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 H 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 AE 0:21 mas for the angular size of the major axis, À62: 3 AE 4: 4 for the position angle, and 0:310 AE 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 Tau appear to be stable on timescales of years. We also compare our results with the known parameters describing the binary nature of Tau, and we conclude that the envelope surrounds only the primary component and is well within its Roche lobe.

Interferometric observations of two well-known Be stars, Cas and Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H -emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H -emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ringlike structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations.