Absolute dimensions of the eccentric eclipsing binary V541 Cygni

TL;DR

This study precisely measures the physical properties of the eccentric eclipsing binary V541 Cygni, confirming stellar evolution models and GR predictions for periastron advance with high accuracy.

Contribution

It provides the first detailed, high-precision measurements of the component masses, radii, and temperatures of V541 Cygni, and confirms the relativistic contribution to periastron advance.

Findings

Component masses and radii are determined to better than 1% precision.

The periastron advance rate matches General Relativity predictions within uncertainties.

The stellar properties agree with current evolution models at an age of about 190 million years.

Abstract

We report new spectroscopic and photometric observations of the main-sequence, detached, eccentric, double-lined eclipsing binary V541 Cyg (P = 15.34 days, e = 0.468). Using these observations together with existing measurements we determine the component masses and radii to better than 1% precision: M1 = 2.335 +0.017/-0.013 MSun, M2 = 2.260 +0.016/-0.013 MSun, R1 = 1.859 +0.012/-0.009 RSun, and R2 = 1.808 +0.015/-0.013 RSun. The nearly identical B9.5 stars have estimated temperatures of 10650 +/- 200 K and 10350 +/- 200 K. A comparison of these properties with current stellar evolution models shows excellent agreement at an age of about 190 Myr and [Fe/H] approximately -0.18. Both components are found to be rotating at the pseudo-synchronous rate. The system displays a slow periastron advance that is dominated by General Relativity (GR), and has previously been claimed to be slower than predicted by theory. Our new measurement, dw/dt = 0.859 +0.042/-0.017 deg/century, has an 88% contribution from GR and agrees with the expected rate within the uncertainties. We also clarify the use of the gravity darkening coefficients in the light-curve fitting program EBOP, a version of which we use here.