Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA

The young intermediate-mass star AB Aurigae is surrounded by a transition disk whose cavity contains several proposed protoplanets, including the debated source “AB Aur b” at a projected separation of ≈ 0 . ″ 6 (≈93 au). To search for circumplanetary material associated with these candidates, we have obtained the most sensitive (∼20 μ Jy beam −1 rms) and highest angular resolution (∼30 mas) Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 (0.88 mm) observations of AB Aur to date. We recover the asymmetric dust ring in the continuum emission peaking at ∼ 0 . ″ 9 (∼140 au) and compact emission at the stellar position, but detect no point source at the location of AB Aur b or any of the other proposed protoplanet candidates down to a 3 σ limit of 60 μ Jy. For optically thin emission, this corresponds to a dust mass of ≲0.0059 M ⊕ (for a dust temperature of 40 K), comparable to the circumplanetary disk around PDS 70 c. The 12 CO emission fills the continuum cavity, revealing an inner spiral structure and a clear rotation pattern. The gas at the position of AB Aur b is smoothly connected to the ambient disk with no localized excess or obvious kinematic deviation. If any proposed candidates are accreting, their circumplanetary material must have a low dust mass, a small physical size, dust that is optically thick, or a dearth of large millimeter-emitting grains.