Substructures in protoplanetary disks imprinted by compact planetary systems
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2022
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Abstract
The substructures observed in protoplanetary disks may be the signposts of embedded planets carving gaps or creating vortices. The inferred masses of these planets often fall in the Jovian regime despite their low abundance compared to lower-mass planets, partly because previous works often assume that a single substructure (a gap or vortex) is caused by a single planet. In this work, we study the possible imprints of compact systems composed of Neptune-like planets (~10-30 Mearth) and show that long-standing vortices are a prevalent outcome when their inter-planetary separation (Delta a) falls below ~8 times Hp, the average disk's scale height at the planets locations. In simulations where a single planet is unable to produce long-lived vortices, two-planet systems can preserve them for at least 5000 orbits in two regimes: i) fully-shared density gaps with elongated vortices around the stable Lagrange points L4 and L5 for the most compact planet pairs (Delta a < 4.6 Hp); ii) partially-shared gaps for more widely spaced planets (Delta a ~ 4.6 - 8 H_p) forming vortices in a density ring between the planets through the Rossby wave instability. The latter case can produce vortices with a wide range of aspect ratios down to ~3 and can occur for planets captured into the 3:2 (2:1) mean-motion resonances for disk's aspects ratios of h >0.033 (h > 0.057). We suggest that their long lifetimes are sustained by the interaction of spiral density waves launched by the neighboring planets. Overall, our results show that distinguishing imprint of compact systems with Neptune-mass planets are long-lived vortices inside the density gaps, which in turn are shallower than single-planet gaps for a fixed gap width. Those interpretations can reproduce the shallow gap in the gas measured by the MAPS program and the crescent continuum emission reported in the inner gap of the HD 163296 disk. Building on previous works arguing for outer planets at 86 and 137 au, we provide with a global model of the disk that best reproduces the data and show that all four planets may fall into a long resonance chain, with the outer three planets having periods in the 4:2:1 sequence. We show that this configuration is not only an expected outcome from disk-planet interaction, but it can also help constraining the radial and angular position of the planet candidates.
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Tesis (Master in Astrophysics)--Pontificia Universidad Católica de Chile, 2022