Focusing on B-emission stars, we investigated a set of H$alpha$ equivalent widths calculated from observed spectra acquired over a period of about 4 years from 2003 to 2007. During this time, changes in equivalent width for our program stars were mon
itored. We have found a simple statistical method to quantify these changes in our observations. This statistical test, commonly called the F ratio, involves calculating the ratio of the external and internal error. We show that the application of this technique can be used to place bounds on the degree of variability of Be stars. This observational tool provides a quantitative way to find Be stars at particular stages of variability requiring relatively little observational data.
In anticipation of the possible collision between a circumstellar disk and the secondary star in the highly eccentric binary system Delta Scorpii, high angular resolution interferometric observations have been acquired aimed at revising the binary pa
rameters. The Navy Prototype Optical Interferometer (NPOI) was used to spatially resolve the binary components in 2000 and over a period between 2005 and 2010. The interferometric observations are used to obtain the angular separations and orientations of the two stellar components at all epochs for which data has been obtained, including 2005 and 2006, for which based on previous studies there was some uncertainty as to if the signature of binarity can be clearly detected. The results of this study represent the most complete and accurate coverage of the binary orbit of this system to date and allow for the revised timing of the upcoming periastron passage that will occur in 2011 to be obtained.
High spatial resolution observations of the Halpha-emitting wind structure associated with the Luminous Blue Variable star P Cygni were obtained with the Navy Prototype Optical Interferometer (NPOI). These observations represent the most comprehensiv
e interferometric data set on P Cyg to date. We demonstrate how the apparent size of the Halpha-emitting region of the wind structure of P Cyg compares between the 2005, 2007 and 2008 observing seasons and how this relates to the Halpha line spectroscopy. Using the data sets from 2005, 2007 and 2008 observing seasons, we fit a circularly symmetric Gaussian model to the interferometric signature from the Halpha-emitting wind structure of P Cyg. Based on our results we conclude that the radial extent of the Halpha-emitting wind structure around P Cyg is stable at the 10% level. We also show how the radial distribution of the Halpha flux from the wind structure deviates from a Gaussian shape, whereas a two-component Gaussian model is sufficient to fully describe the Halpha-emitting region around P Cyg.
We present a numerical model describing a circularly symmetric gaseous disk around the Be star chi Ophiuchi. The model is constrained by long-baseline interferometric observations that are sensitive to the H-alpha Balmer line emission from the disk.
For the first time our interferometric observations spatially resolve the inner region of the circumstellar disk around chi Ophiuchi and we use these results to place a constraint on the physical extent of the H-alpha-emitting region. We demonstrate how this in turn results in very specific constraints on the parameters that describe the variation of the gas density as a function of radial distance from the central star.
We have computed theoretical models of circumstellar disks for the classical Be stars $kappa$ Dra, $beta$ Psc, and $upsilon$ Cyg. Models were constructed using a non-LTE radiative transfer code developed by citet{sig07} which incorporates a number of
improvements over previous treatments of the disk thermal structure, including a realistic chemical composition. Our models are constrained by direct comparison with long baseline optical interferometric observations of the H$alpha$ emitting regions and by contemporaneous H$alpha$ line profiles. Detailed comparisons of our predictions with H$alpha$ interferometry and spectroscopy place very tight constraints on the density distributions for these circumstellar disks.
We present the results of an experiment to image the interacting binary star beta Lyrae with data from the Navy Prototype Optical Interferometer (NPOI), using a differential phase technique to correct for the effects of the instrument and atmosphere
on the interferometer phases. We take advantage of the fact that the visual primary of beta Lyrae and the visibility calibrator we used are both nearly unresolved and nearly centrally symmetric, and consequently have interferometric phases near zero. We used this property to detect and correct for the effects of the instrument and atmosphere on the phases of beta Lyrae and to obtain differential phases in the channel containing the Halpha emission line. Combining the Halpha-channel phases with information about the line strength, we recovered complex visibilities and imaged the Halpha emission using standard radio interferometry methods. We find that the results from our differential phase technique are consistent with those obtained from a more-standard analysis using squared visibilities (V^2s). Our images show the position of the Halpha emitting regions relative to the continuum photocenter as a function of orbital phase and indicate that the major axis of the orbit is oriented along p.a.=248.8+/-1.7 deg. The orbit is smaller than previously predicted, a discrepancy that can be alleviated if we assume that the system is at a larger distance from us, or that the contribution of the stellar continuum to the Halpha channel is larger than estimated. Finally, we also detected a differential phase signal in the channels containing HeI emission lines at 587.6 and 706.5nm, with orbital behavior different from that of the Halpha, indicating that it originates from a different part of this interacting system.
