von Zeipel-Kozai-Lidov oscillations in nearby bright stars. I. Lambda Ophiuchi

TL;DR

This study analyzes the complex orbital dynamics of the nearby Lambda Ophiuchi system, revealing that ZKL oscillations are modulated by relativistic and tidal effects, with implications for understanding stellar evolution in multiple star systems.

Contribution

The paper provides a detailed semi-analytical solution for the full orbital architecture of Lambda Ophiuchi, incorporating relativistic, tidal, and rotational effects on ZKL oscillations.

Findings

Inner binary undergoes ZKL oscillations with significant eccentricity variation.

Relativistic and tidal precession modulate the oscillation amplitude.

Potential for complete dynamical characterization through observations.

Abstract

The challenge of constraining both the inner and the outer orbits in multiple stars has resulted in a growing abyss between the rich theoretical and the sparse observational studies of von Zeipel-Kozai-Lidov (ZKL) oscillations in stellar systems. Here we solve for the full orbital architecture of the bright intermediate-mass nearby system Lambda Ophiuchi based on astrometric measurements of the outer orbit (period of 129 years) compiled in the Sixth Catalog of Orbits of Visual Binary Stars and new VLTI/GRAVITY interferometric measurements that are used to determine the inner orbit (period of 42 days). The orbits are retrograde and misaligned by either $88.5\pm1.9^o$ or $113.5\pm1.9^o$, which in either case results in the inner binary currently undergoing ZKL oscillations. While pure Newtonian point source evolution would have predicted the stars in the inner binary to have merged long ago, in reality the eccentricity oscillations are significantly modulated by general relativistic, tidal and rotational bulge precession. We show that due to the effect of ``slaved'' precession the dynamics can still be solved semi-analytically. We find that the (currently unknown) inclination angles between the stellar spins axes and the inner orbital axis play a very important role in the amplitude of the ZKL oscillations, which is at a minimum $\Delta e = e_{\mathrm{max}} - e_{\mathrm{min}} \simeq 0.15$ and could be as high as $\Delta e \simeq 0.70$. We argue that currently feasible spectroscopic and interferometric observations could allow for a complete and unique dynamical solution for this system.