Fundamental effective temperature measurements for eclipsing binary stars - VII. The solar twin in LL Aquarii

TL;DR

This study precisely measures the fundamental parameters and effective temperatures of the binary star system LL Aqr, confirming its solar twin status and providing benchmark data for stellar astrophysics calibration.

Contribution

The paper presents high-precision, model-independent measurements of stellar radii, masses, and temperatures for LL Aqr, enhancing the benchmark sample of well-characterized solar-type stars.

Findings

Measured stellar radii and masses with high precision.

Derived effective temperatures consistent with solar twin characteristics.

Confirmed low magnetic activity levels in LL Aqr.

Abstract

The eclipsing binary LL Aqr is a bright V = 9.32, detached system consisting of two solar-type stars in an eccentric orbit (P = 20.2 d). The secondary component, LL Aqr B, was previously found to have physical and atmospheric parameters very similar to the Sun. Using high-precision photometry from TESS along with previously published orbital solutions, we obtain updated model-independent stellar radii and masses: $R_A = 1.3180 \pm 0.0013~R_{\odot}$, $R_B = 0.9927 \pm 0.0008~R_{\odot}$, $M_A = 1.1947 \pm 0.0009~M_{\odot}$, and $M_B = 1.0334 \pm 0.0006~M_{\odot}$. We derive the bolometric flux and fundamental effective temperature for each component using observed magnitudes, flux ratios from light curves in multiple bands and angular diameters derived from the radii and parallax from long baseline interferometry, measuring the following values: $T_{\rm eff,A} = 6242 \pm 50$ K, $T_{\rm eff,B} = 5839 \pm 44$ K, with an additional 9 K systematic error from the flux scale zero-point. We confirm that LL Aqr displays low stellar activity by obtaining $2\sigma$ upper limits on the mean surface magnetic field strengths of 78 G and 96 G. Our results suggest an age of 2.67 - 3.01 Gyr, which is consistent with previous studies. LL Aqr now joins an ever-growing sample of well-characterised benchmark stars that can be used to test and calibrate a wide variety of methods and techniques in stellar astrophysics.