# Eclipsing binaries as standard candles: HD 23642 and the distance to the Pleiades

## TL;DR

This paper reanalyzes the eclipsing binary HD 23642 in the Pleiades to determine its distance using a new infrared surface brightness method, finding results consistent with some methods but conflicting with Hipparcos measurements.

## Contribution

It introduces a new infrared surface brightness calibration method for eclipsing binaries to accurately measure stellar distances.

## Key findings

- Distance to Pleiades: 139.1 +/- 3.5 pc
- Infrared methods yield more precise distances
- Results conflict with Hipparcos parallax measurements

## Abstract

We present a reanalysis of the light curves of HD 23642, a detached eclipsing binary star in the Pleiades open cluster, with emphasis on a detailed error analysis. We compare the masses and radii of the two stars to predictions of stellar evolutionary models and find that the metal and helium abundances of the Pleiades are approximately solar. We present a new method for finding distances to eclipsing binaries, of spectral types A to M, using the empirical calibrations of effective temperature versus surface brightness given by Kervella et al. (2004). We use the calibration for K-filter surface brightness to determine a distance of 139.1 +/- 3.5 pc to HD 23642 and the Pleiades. This distance is in excellent agreement with distances found from the use of theoretical and empirical bolometric corrections. We show that the determination of distance, both from the use of surface brightness relations and from the use of bolometric corrections, is more accurate and precise at infrared wavelengths than at optical wavelengths. The distance to HD 23642 is consistent with that derived from photometric methods and Hubble Space Telecscope parallaxes, but is inconsistent with the distance measured using Hipparcos parallaxes of HD 23642 and of other Pleiades stars.