Predicting Stellar Angular Diameters from $V$, $I_C$, $H$, $K$ Photometry

TL;DR

This paper develops empirical relations to accurately predict stellar angular diameters using photometric color indices, aiding in microlensing event analysis with minimal uncertainty.

Contribution

It introduces calibrated relations for stellar angular diameters based on visible and near-infrared colors, applicable to a wide range of star types, with negligible metallicity effects.

Findings

Angular diameters measured with ≤2% uncertainty.

Single relations fit both dwarfs/subgiants and giants.

Metallicity does not significantly affect size predictions.

Abstract

Determining the physical properties of microlensing events depends on having accurate angular sizes of the source star. Using long-baseline optical interferometry we are able to measure the angular sizes of nearby stars with uncertainties $\leq 2\%$. We present empirically derived relations of angular diameters that are calibrated using both a sample of dwarfs/subgiants and a sample of giant stars. These relations are functions of five color indices in the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on the color used. We find that a combined sample of both main-sequence and evolved stars of A-K spectral types is well fit by a single relation for each color considered. We find that in the colors considered, metallicity does not play a statistically significant role in predicting stellar size, leading to a means of predicting observed sizes of stars from color alone.