The solar-type eclipsing binary system LL Aquarii

TL;DR

This study precisely measures the physical properties of the LL Aquarii binary system, demonstrating that its characteristics align well with theoretical models due to its lack of magnetic activity and tidal effects.

Contribution

It provides detailed measurements of a solar-type eclipsing binary with minimal magnetic activity, supporting models that predict stellar properties without magnetic inflation effects.

Findings

Primary star: 1.167 Msun, 1.305 Rsun

Secondary star: 1.014 Msun, 0.990 Rsun

No signs of stellar activity or magnetic effects

Abstract

The eclipsing binary LL Aqr consists of two late-type stars in an eccentric orbit with a period of 20.17 d. We use an extensive light curve from the SuperWASP survey augmented by published radial velocities and UBV light curves to measure the physical properties of the system. The primary star has a mass of 1.167 +/- 0.009 Msun and a radius of 1.305 +/- 0.007 Rsun. The secondary star is an analogue of the Sun, with a mass and radius of 1.014 +/- 0.006 Msun and 0.990 +/- 0.008 Rsun respectively. The system shows no signs of stellar activity: the upper limit on spot-induced rotational modulation is 3 mmag, it is slowly rotating, has not been detected at X-ray wavelengths, and the calcium H and K lines exhibit no emission. Theoretical stellar models provide a good match to its properties for a sub-solar metal abundance of Z = 0.008 and an age of 2.5 Gyr. Most low-mass eclipsing binary systems are found to have radii larger than expected from theoretical predictions, blamed on tidally-enhanced magnetic fields in these short-period systems. The properties of LL Aqr support this scenario: it exhibits negligible tidal effects, shows no signs of magnetic activity, and matches theoretical models well.