The angular size of dwarf stars and subgiants - Surface brightness relations calibrated by interferometry

TL;DR

This paper calibrates empirical surface brightness relations for dwarf and subgiant stars using interferometric measurements, enabling accurate angular diameter predictions from photometry or temperature, with high precision.

Contribution

It provides new calibrated relations for stellar angular diameters based solely on direct measurements, improving size estimates for a range of star types.

Findings

Surface brightness relations achieve <1% dispersion.

Relations based on K and L magnitudes are most precise.

Calibrations cover spectral types A0 to M2 for dwarfs and A0 to K0 for subgiants.

Abstract

The availability of a number of new interferometric measurements of Main Sequence and subgiant stars makes it possible to calibrate the surface brightness relations of these stars using exclusively direct angular diameter measurements. These empirical laws allow to predict the limb darkened angular diameters theta_LD of dwarfs and subgiants using their dereddened Johnson magnitudes, or their effective temperature. The smallest intrinsic dispersions of sigma < 1% on theta_LD are obtained for the relations based on the K and L magnitudes, for instance log theta_LD = 0.0502 (B-L) + 0.5133 - 0.2 L or log theta_LD = 0.0755 (V-K) + 0.5170 - 0.2 K. Our calibrations are valid between the spectral types A0 and M2 for dwarf stars (with a possible extension to later types when using the effective temperature), and between A0 and K0 for subgiants. Such relations are particularly useful to estimate the angular size of calibrators for long baseline interferometry from readily available broadband photometry.