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tokens: companions in the disk. Huang et al. (2018) and Dullemond et al. (2018) show that the rings frequently seen in continuum emission from (sub)millimeter grains are likely caused by dust trapping, perhaps due to embedded planets carving gaps in disks as opposed to being related to snow lines. In the case of SR 21 the possibility of a low-mass companion being responsible for carving out this cavity is further supported by the small grains seen in scattered light. These are expected to be closely coupled to the gas, tracing spiral arms confined to the millimeter cavity, as is frequently seen in hydrodynamical models. Azimuthal asymmetries in the outer ring. It is hard to tell from scattered light alone whether the asymmetry of the outer ring is caused by azimuthally localized overdensities in the gas and dust or if they are the product of shadowing by the inner spiral arms. This asymmetry looks different in all three ALMA bands available: Band 9 shows an asymmetry in the south, while Bands 7 and 3 show a ring-like structure with a bright asymmetry to the north. Pinilla et al. (2015b) have already suggested that the southern bright spot seen in Band 9 may be the result of a hotter region in the southern side of the disk. This is supported by Band 9 being optically thick (peak optical depth of τ ∼2.0, assuming a physical temperature of 20 K). Therefore, continuum emission in this band is not only sensitive to density variations, but also to temperature variations, which can produce structure in the emission. In Band 3, where the disk is optically thin (peak optical depth of τ = 0.17 assuming a physical temperature of 20 K), the asymmetry is reversed, with the southern bright spot disappearing and the northern one becoming prominent. This asymmetry, at this low optical depth, suggests that the northern bright spot seen in SPHERE and ALMA Bands 7 and 3 probably corresponds to a dust overdensity at this location of the ring. Band 7, with an intermediate estimated peak optical depth of τ = 0.5, shows both the overdensity and the hot region in the south. Such an overdensity could, for example, be produced in the apastron location of a slightly eccentric disk, where the lower velocity at apastron leads to higher gas densities that can also slow down drifting grains and replicate the overdensity in large grains ( Ataiee et al. 2013 ). The spiral arms pointing to the likely position of the planet. The “kinked spiral” feature we see to the north in the saturated cut of the H -band data (Fig. 1 ) is strongly reminiscent of the spirals arising in hydrodynamical models of planet-disk interaction (see, e.g., Nelson et al. 2000 ; Sándor et al. 2007 , or Pinilla et al. 2015b ). The position of the kink in the spiral, indicating the exact location of the planet in these hydrodynamical models, is found inside of the ALMA ring and in the gap between this ring and the two brighter inner spirals seen with SPHERE (Fig. 1 , right panel). This is consistent with a