An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent

Abstract: In the era of precision cosmology it is essential to determine the Hubble Constant with an accuracy of 3% or better. Currently, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC) which as the second nearest galaxy serves as the best anchor point of the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to precisely and accurately measure stellar parameters and distances. The eclipsing binary method was previously applied to the LMC but the accuracy of the distance results was hampered by the need to model the bright, early-type systems used in these studies. Here, we present distance determinations to eight long-period, late- type eclipsing systems in the LMC composed of cool giant stars. For such systems we can accurately measure both the linear and angular sizes of their components and avoid the most important problems related to the hot early-type systems. Our LMC distance derived from these systems is demonstrably accurate to 2.2 % (49.97 +/- 0.19 (statistical) +/- 1.11 (systematic) kpc) providing a firm base for a 3 % determination of the Hubble Constant, with prospects for improvement to 2 % in the future.

• The paper demonstrates that using late-type eclipsing binaries yields a precise LMC distance of 49.97 kpc with ~2.2% accuracy.
• It employs 16 years of OGLE photometry combined with high-resolution MIKE and HARPS spectra to minimize systematic uncertainties.
• The improved distance measure strengthens the calibration of the cosmic distance scale and supports more accurate Hubble Constant determinations.

An Eclipsing Binary Distance to the Large Magellanic Cloud

This paper presents an evaluation of the distance to the Large Magellanic Cloud (LMC) using the eclipsing binary method, yielding a distance precise to approximately 2.2% (49.97 ± 0.19 (statistical) ± 1.11 (systematic) kpc). The work is a robust contribution to enhancing the precision of the cosmic distance scale, which is critical for accurate determinations of the Hubble Constant.

The study provides an empirical framework by focusing on binary systems composed of late-type giant stars, avoiding the complexities associated with early-type systems. Until now, the distances measured from early-type systems faced significant limitations due to flux calibration challenges and temperature-reddening degeneracies, resulting in accuracy hindrances between 5-10%. The present work circumvents these issues by targeting cool stars where the surface brightness-color relation (SBCR) is stable and well-characterized, permitting distance measurements without the dependency on theoretical stellar models.

Methodology and Observations

Leveraging extensive monitoring data from the Optical Gravitational Lensing Experiment (OGLE) spanning over 16 years, the researchers identified and studied eight long-period eclipsing binaries. They obtained high-resolution spectra using leading instruments such as the MIKE spectrograph at Las Campanas and HARPS at the European Southern Observatory’s La Silla facility. Additionally, near-infrared photometry was captured using the New Technology Telescope at La Silla. The primary data was analyzed using the Wilson-Devinney code, and refined through Monte Carlo simulations to estimate uncertainties.

The calibration of angular sizes based on SBCR and V-K color was central to the measurement. The systematic uncertainties arose primarily from the SBCR calibration and photometric zero points, contributing to a total systematic error of 2.1%.

Significant Outcomes and Implications

The obtained distance measurement aligns closely with recent estimates of the LMC, providing an improved modulus with empirical grounds (49.88 ± 0.13 kpc mean via weighted average). This validation suggests negligible impact from the LMC's geometrical structure, underpinning the LMC as a reliable anchor for cosmic distance calibrations. Furthermore, the work underscores the vital role of LMC-related measurements, leveraging LMC's substantial Cepheid population for Period-Luminosity Relation (CPLR) calibration, crucial for Hubble Constant derivation.

Significantly, the eclipsing binary method, through an empirical approach, shows promise in reducing uncertainties in distance measurements that rely on theoretical predictions of stellar parameters. The study advocates the potential for further improvements, particularly by refining the SBCR calibration for late-type stars to possibly reach a 1% accuracy goal.

Future Directions

As astronomical observation techniques evolve, this method of distance determination positions itself to complement future astrometric missions like GAIA. The authors propose further researches refining the SBCR, critical to meeting even more stringent accuracy requirements. This progress holds substantial implications not only for refining the Hubble Constant but also as a comparative benchmark against future high-precision satellite data.

The adoption of late-type eclipsing binaries, as advocated in this paper, may forge pathways toward innovations in stellar parameter determination, reaffirming the LMC’s instrumental role in precision cosmology. The study remarkably contributes by offering a framework reducing systematics, thereby enhancing the meta-analysis potential of LMC-related distance surveys ongoing and emerging in astrophysical research.