Destructuring the disk of AB Aurigae: Dynamics and accretion

Abstract

In this paper, we present near-IR polarized images of the AB Aur disk at three epochs spanning 3.85 years with SPHERE/IRDIS, as well as Halpha images obtained with SPHERE/ZIMPOL at a single epoch. The purpose of this study is to analyze the dynamics of the entire disk and of the various structures in near-IR polarimetry, and to identify sources of Halpha emission to derive constraints on their mass accretion rate. The dynamical study in the near-IR shows that the disk globally follows Keplerian rotation, but we observe a departure from this behavior at radii smaller than ~60au. At the smallest radius of ~25au, we measure a deviation from Keplerian rotation as large as ~12deg over 3.85 years, demonstrating sub-Keplerian rotation. The two bright spirals within the millimeter cavity have different dynamic trends, and we discuss their possible link with the identified planet candidates. We also discuss the implications of the non-Keplerian behavior, and we posit that it could be related to interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits. Furthermore, the orbital analysis of the compact sources (labeled f1, f2, and f3) suggests that their orbital planes are significantly inclined with respect to the disk plane by several tens of degrees. The variability of the shadows suggests that they are produced by optically thick regions located within ~60au. For the photometric analysis in Halpha, we derive a flux of about 8.22x10^{-15} erg/s/cm^2 for the entire feature f1, but only 6.46x10^{-16} erg/s/cm^2 at the location of AB Aur b, consistent with non-detection. If f1 were a point source and the accretion remained constant for 1Myr, it would correspond to ~5-20 Jupiter masses according to the magnetospheric accretion model or ~6-10 Jupiter masses according to the boundary layer accretion model.