Are we witnessing ongoing planet formation in AB Aurigae?

Anthony Boccaletti, Emmanuel DiFolco, Anne Dutrey, Eric Pantin, Stephane Guilloteau, Ya-Wen Tang, Vincent Pietu, Emilie Habart, Julien Milli, Tracy Beck, Anne-Lise Maire, Sylvestre Lacour

While many exoplanets have been detected little is known about their formation. Most surveys are focusing on old systems, but observing planet when they form are relevant to establish the initial conditions.

In that context, AB Aur occupies a special place. At sub-millimeter wavelengths, ALMA has detected two molecular spiral arms at less than 100 au, together with a suspicion of a protoplanet candidate at 90 au (Tang et al. 2017), echoed by a recently claimed protoplanet candidate at this very same location (Currie et al. 2020).
Since Decembre 2019 we have been monitoring AB Aur with SPHERE at the VLT in the near IR. Polarimetric and non-polarimetric images identified a wealth of structures in scattered light at many scales, in particular two spiral arms clearly overlapping with the one from ALMA. The gain in angular resolution has allowed us to discover a bright feature at 0.18’’ (about 30 au) from the star, reminiscent of the connection between the inner and outer spiral arms as expected by the theory of wave density (Boccaletti et al. 2020). This is plausible evidence of a protoplanet signature. This « twist » feature has moved with respect to ALMA observations, consistent with Keplerian rotation. From the latest SPHERE observations, we confirmed this structure and we measured that the disk follows a Keplerian rotation, possibly at odd with respect to the common understanding of density waves. Three near IR bands JHK are now obtained from which we can study the disk colors either globally, or feature by feature, as well as the degree of polarization. Finally, Halpha imaging with SPHERE for identifying accretion signatures as well as interferometric data are also available.

We will discuss the dynamics of the system as well as the relevance of various protoplanet candidates in the AB Aur system.