A distance determination to the Small Magellanic Cloud with an accuracy of better than 2 percent based on late-type eclipsing binary stars

TL;DR

This study uses late-type eclipsing binary stars in the Small Magellanic Cloud to measure its distance with an accuracy better than 2%, revealing its internal structure and a possible stellar core.

Contribution

It provides a highly precise distance measurement to the SMC using a new sample of eclipsing binaries and insights into its internal stellar structure.

Findings

Distance to SMC center is 62.44 kpc with <2% error.

Detected a possible spherical stellar core in the SMC.

Found a line-of-sight depth of up to 7 kpc in the SMC.

Abstract

We present a new study of late-type eclipsing binary stars in the Small Magellanic Cloud (SMC) undertaken with the aim of improving the distance determination to this important galaxy. A sample of 10 new detached, double-lined eclipsing binaries indentified from the OGLE variable star catalogues and consisting of F- and G-type giant components has been analysed. The absolute physical parameters of the individual components have been measured with a typical accuracy of better than 3%. All but one of the systems consist of young and intermediate population stars with masses in the range of 1.4 to 3.8 M_Sun. This new sample has been combined with five SMC eclipsing binaries previously published by our team. Distances to the binary systems were calculated using a surface brightness - color calibration. The targets form an elongated structure, highly inclined to the plane of the sky. The distance difference between the nearest and most-distant system amounts to 10 kpc with the line of sight depth reaching 7 kpc. We find tentative evidence of the existence of a spherical stellar sub-structure (core) in the SMC coinciding with its stellar center, containing about 40% of the young and intermediate age stars in the galaxy. The radial extension of this sub-structure is ~1.5 kpc. We derive a distance to the SMC center of D_SMC=62.44 +/- 0.47 (stat.) +/- 0.81 (syst.) kpc corresponding to a distance modulus (m-M)_SMC=18.977 +/- 0.016 +/- 0.028 mag, representing an accuracy of better than 2%.