ALMA images of discs : are all gaps carved by planets?
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Protoplanetary discs are now routinely observed and exoplanets, after the numerous indirect discoveries, are starting to be directly imaged. To better understand the planet formation process, the next step is the detection of forming planets or of signposts of young planets still in their disc, such as gaps. A spectacular example is the Atacama Large Millimeter/submillimeter Array (ALMA) science verification image of HL Tau showing numerous gaps and rings in its disc. To study the observability of planet gaps, we ran 3D hydrodynamical simulations of a gas and dust disc containing a 5 MJ gap-opening planet and characterized the spatial distribution of migrating, growing and fragmenting dust grains. We then computed the corresponding synthetic images for ALMA. For a value of the dust fragmentation threshold of 15 m s−1 for the collisional velocity, we identify for the first time a self-induced dust pile-up in simulations taking fragmentation into account. This feature, in addition to the easily detected planet gap, causes a second apparent gap that could be mistaken for the signature of a second planet. It is therefore essential to be cautious in the interpretation of gap detections.
Gonzalez , J-F , Laibe , G , Maddison , S T , Pinte , C & Ménard , F 2015 , ' ALMA images of discs : are all gaps carved by planets? ' , Monthly Notices of the Royal Astronomical Society: Letters , vol. 454 , no. 1 , pp. 36-40 . https://doi.org/10.1093/mnrasl/slv120
Monthly Notices of the Royal Astronomical Society: Letters
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.1093/mnrasl/slv120