Seismically unresolved red-giant binary candidates

We selected stars from the APOKASC3 catalog that have at least one neighboring source within 20 arcsec and show oscillations in similar frequency ranges. We focus on the systems where the light curves from each star in AB candidates are available or can be extracted with a custom mask. From these star pairs, we identified 6 seismically unresolved AB candidates whose PDS morphologies change noticeably across light curves extracted with different apertures.

We determined asteroseismic parameters and derived masses and radii from the PDSs of both AB candidates and single stars to quantify the biases. Oscillations from two stars in a single PDS cause inaccurate mode identification and bias the seismic parameters. These biases propagate into stellar properties, with mass and radii for the 6 AB candidates investigated here differing by up to ~3 and ~2 times relative to the individual stars, respectively.

For the AB candidate with the most complex PDS, core properties such as period spacings and coupling factors become unreliable, with the coupling factor often being overestimated. We checked that all 6 AB candidates are chance alignments. Our results indicate that the inconsistencies in asteroseismic and stellar parameters across various studies on the stars with complex PDSs can be explained by potential seismically unresolved asteroseismic binaries.

These findings highlight the importance of identifying and accurately accounting for such systems in asteroseismic analysis.