The 99th orbital harmonic reproduces the reported 3952.19 microhertz peak in AA Doradus two-minute TESS data

Baran et al. (2021) reported a possible stellar pulsation in AA Doradus at 3952.19 microhertz. They also gave 4381.14 microhertz as a possible true frequency. We test a sampling alias from an orbital harmonic that their model did not include. Their orbital period gives harmonic 99 at 4381.106164 microhertz. A pure sinusoid at this harmonic, sampled at the selected original TESS times, gives an alias peak at 3952.1950 microhertz. Our measured residual peak is at 3952.1935 microhertz. Adding only harmonic 99 to a model with harmonics 1 through 93 reduces this peak from 60.3 to 4.0 parts per million. Our processing does not exactly repeat the reported 76 parts per million amplitude. Six later sectors with 20-second sampling show harmonic 99 at an exposure-corrected semi-amplitude of 86.4 plus or minus 12.5 parts per million. An independent fit removes both eclipse windows before it fits the harmonic and the two reported frequencies together. It gives approximate 95 percent amplitude bounds of 48.1 and 67.2 parts per million at the two reported frequencies. These bounds require constant frequency and phase across the selected later observations. The evidence supports an orbital sampling alias for the old peak. It does not exclude a transient pulsation or a pulsation fixed to orbital phase. The package contains selected public data, source hashes, code, figures, and reproduction instructions.

AA Doradus · TIC 425064757 · TESS · eclipsing binaries · hot subdwarfs · stellar pulsations · sampling aliases · orbital harmonics · public data