Direct Imaging Detection of the Protoplanet AB Aurigae b at Wavelengths Covering Pa$β$: Rebuttal to Biddle et al. (2024)

Abstract: Recently, Biddle et al. (2024) claimed a non-detection of the protoplanet AB Aurigae b in Keck/NIRC2 Pa$\beta$ imaging. I reprocess these newly-public data and compare them to data from the extreme AO platform (SCExAO/CHARIS) used to discover AB Aur b. AB Aur b is decisively imaged with SCExAO/CHARIS at wavelengths covering Pa$\beta$. The Biddle et al. non detection of AB Aur b results from a far poorer image quality that is non competitive with SCExAO/CHARIS. Their contrast limits and thus constraints on accretion are overestimated due to an inaccurate AB Aur b source model. Consequentially, the revised Pa$\beta$ 2-$\sigma$ upper limit from these data is about three times higher than previously reported. Irrespective of image quality, single-band Pa$\beta$ imaging is ill suited to conclusively identifying accretion onto AB Aur b. Instead, high-resolution H$\alpha$ spectroscopy may provide accretion signatures. Aside from PDS 70, AB Aurigae remains the system with the strongest evidence for having a directly-imaged protoplanet.