Two's a crowd? Characterising the effect of photometric contamination on the extraction of the global asteroseismic parameter $\nu_{\text{max}}$ in red-giant binaries

Abstract

Theoretical scaling relations for solar-like oscillators and red giants are widely used to estimate fundamental stellar parameters. The accuracy and precision of these relations have often been questioned in the literature, with studies often utilising binarity for model-independent validation. However, it has not been tested if the photometric effects of binarity introduce a systematic effect on the extraction of the seismic properties of the pulsating component(s). In this paper, we present an estimation of the impact of a contaminating photometric signal with a distinct background profile on the global asteroseismic parameter $\nu_{\text{max}}$ through the analysis of synthetic red-giant binary light curves. We generate the pulsational and granulation parameters for single red giants with different masses, radii and effective temperatures from theoretical scaling relations and use them to simulate single red-giant light curves with the characteristics of Kepler long-cadence photometric data. These are subsequently blended together according to their light ratio to generate binary red-giant light curves of various configurations. We then perform a differential analysis to characterise the systematic effects of binarity on the extraction of $\nu_{\text{max}}$. We find that the $\nu_{\text{max}}$ extraction for red-giant power spectra featuring overlapping power excesses is unreliable if unconstrained priors are used. Outside of this scenario, we obtain results that are nearly identical to single-star case. We conclude that i) the photometric effects of binarity on the extraction of $\nu_{\text{max}}$ are largely negligible as long as the power excesses of the individual components do not overlap, and that ii) there is minimal advantage to using more than two super-Lorentzian components to model the granulation signal of a binary red-giant.