Prospects of Constraining Tidal Dissipation in Low-Mass Binary Stars

The dynamical evolution of short-period low-mass binary stars (M < 1.5 Msun, P < 10 days) is strongly influenced by tidal dissipation. Despite its fundamental role in binary evolution, constraining the strength of tidal dissipation, typically parameterized by the tidal quality factor Q, has remained discrepant by orders of magnitude in the existing literature. New observational constraints from time-series photometry (i.e. Kepler, K2, TESS), as well as advancements in theoretical models that incorporate more realistic rheology of stellar structure are invigorating new optimism for the field. Two paths have emerged to leverage the new data sets to constrain Q: modeling individual systems or population inference. We examine the challenges and advantages of various model validation approaches by using numerical simulations of equilibrium tide model combined with stellar evolution and magnetic braking to predict binary dynamical evolution over Myr-Gyr timescales. We use sensitivity analysis to examine to what degree each unknown model input (the initial conditions and tidal Q) influences observables (the final orbital and rotation states). These techniques allow us to analyze the coupled nonlinear effects of the 18-dimensional phase space and systematically assess the limitations due to both inherent model degeneracies, as well as observational uncertainties. Our results show that even under the simplest and most tractable models of tides, the path towards validating Q is ill-posed: inherent degeneracies between tidal Q and model initial conditions severely limit the prospects of constraining tidal Q for individual binary systems, even when considering the strongest possible constraints (i.e. binaries with precise masses and ages). Alternatively we show that evolution states over a wide range of initial conditions tend to converge towards trajectories along a low-dimensional (orbital period, rotation period, eccentricity) manifold. This analysis suggests that a population approach based on equilibrium analysis may be a promising path forward for validating tidal theories.