Simultaneous Six-way Observations from the Navy Precision Optical Interferometer

TL;DR

This paper reports the first measurements of six stars' angular diameters using the Navy Precision Optical Interferometer's six-element mode since the early 2000s, revealing the smallest diameters measured with NPOI to date.

Contribution

It demonstrates the capability of the NPOI six-element mode to measure very small stellar diameters and discusses the challenges and future improvements in measurement accuracy.

Findings

Measured six stellar diameters, including the smallest with NPOI.

Identified flux imbalance and non-linearities as sources of measurement spread.

Plans to improve accuracy with the VISION beam combiner.

Abstract

We measured the angular diameters of six stars using the 6-element observing mode of the Navy Precision Optical Interferometer (NPOI) for the first time since the early 2000s. Four of the diameters ranged from 1.2 mas to 1.9 mas, while the two others were much smaller at approximately 0.5 mas to 0.7 mas, which are the two smallest angular diameters measured to date with the NPOI. There is a larger spread in the measurements than data obtained with 3- or 4- or 5-element modes, which can be attributed in part to the flux imbalance due to the combination of more than 2 siderostats in a single spectrograph, and also to cross talk between multiple baselines related to non-linearities in the fast delay line dither strokes. We plan to address this in the future by using the VISION beam combiner.