How much Is enough? Using the NPOI archive to characterize stellar diameter measurements

The Navy Precision Optical Interferometer (NPOI) has been in operation since 1996, building a substantial data archive. This provided the opportunity to determine how many data points are needed for a single star's angular diameter fit to become stable as more data points were included. In an iterative process, we calculated the diameters for an ever-increasing number of data points for 31 stars. We found that at approximately 1,000 data points, the scatter in the diameter fits fell below 2%. Assuming a 3-telescope triangle and using 15 channels across a range of wavelengths, 1,000 data points equates to 22 to 25 bracketed observations, which can usually be accomplished in 2 to 4 nights. This will be a useful rule-of-thumb when planning observations and gathering data on single, symmetrical stars.