Casassus, S., Carcamo, M., Hales, A., Weber, P., & Dent, B. (2022). The Doppler Flip in HD 100546 as a Disk Eruption: The Elephant in the Room of Kinematic Protoplanet Searches. Astrophys. J. Lett., 933(1), L4.
Abstract: The interpretation of molecular-line data using hydrodynamical simulations of planet-disk interactions fosters new hope for the indirect detection of protoplanets. In a model-independent approach, embedded protoplanets should be found at the roots of abrupt Doppler flips in velocity centroid maps. However, the largest velocity perturbation known for an unwarped disk, in the disk of HD 100546, leads to a conspicuous Doppler flip that coincides with a thick dust ring, in contradiction with an interpretation in terms of a greater than or similar to 1 M-jup body. Here we present new ALMA observations of the (CO)-C-12(2-1) kinematics in HD 100546, with a factor of 2 finer angular resolutions. We find that the disk rotation curve is consistent with a central mass 2.1 < M-*/M-circle dot < 2.3 and that the blueshifted side of the Doppler flip is due to vertical motions, reminiscent of the disk wind proposed previously from blueshifted SO lines. We tentatively propose a qualitative interpretation in terms of a surface disturbance to the Keplerian flow, i.e., a disk eruption, driven by an embedded outflow launched by a similar to 10 M-earth body. Another interpretation involves a disk-mass-loading hot spot at the convergence of an envelope accretion streamer.
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Casassus, S., Christiaens, V., Carcamo, M., Perez, S., Weber, P., Ercolano, B., et al. (2021). A dusty filament and turbulent CO spirals in HD 135344B-SAO 206462. Mon. Not. Roy. Astron. Soc., 507(3), 3789–3809.
Abstract: Planet-disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD 135344B disc revealed two rings in the thermal continuum stemming from similar to mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a two-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J = (2 – 1) CO isotopologue lines and in the adjacent continuum, with up to 12 km baselines. Angular resolutions of similar to 0 ''.03 reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggests that turbulence, or superposed velocity components, is particularly strong in the spirals. The (CO)-C-12(2-1) 3D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to similar to 5 per cent +/- 0.5 per cent Keplerian, which corresponds to an excessively large accretion rate of similar to 2 x 10(-6) M circle dot yr(-1) if all of the CO layer follows the (CO)-C-12(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.
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