A Decade of MWC 758 Disk Images: Where Are the Spiral-arm-driving Planets?

Abstract

Large-scale spiral arms have been revealed in scattered light images of a few protoplanetary disks. Theoretical models suggest that such arms may be driven by and co-rotate with giant planets, which has called for remarkable observational efforts to look for them. By examining the rotation of the spiral arms for the MWC 758 system over a 10-yr timescale, we are able to provide dynamical constraints on the locations of their perturbers. We present reprocessed Hubble Space Telescope (HST)/NICMOS F110W observations of the target in 2005, and the new Keck/NIRC2 L -band observations in 2017. MWC 758's two well-known spiral arms are revealed in the NICMOS archive at the earliest observational epoch. With additional Very Large Telescope (VLT)/SPHERE data, our joint analysis leads to a pattern speed of 0. • 6 +3. • 3 −0.• 6yr −1 at 3σ for the two major spiral arms. If the two arms are induced by a perturber on a near-circular orbit, its best fit orbit is at 89 au (0. 59), with a 3σ lower limit of 30 au (0. 20). This finding is consistent with the simulation prediction of the location of an arm-driving planet for the two major arms in the system.

Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms?

“…These predictions are broadly consistent with the observed rate of rotation of the spiral arms over the past decade (Ren et al 2018), which indicates that the perturbing companion has an orbital period 600 yr−placing it exterior to the spiral arms at a most likely separation of ∼0. 6.…”

Dust traps in the protoplanetary disc MWC 758: two vortices produced by two giant planets?

“…This is very close to the location of Clump 1 in the (sub)millimetre images (∼85 au), and it seems unlikely that a massive companion at about 95 au could form a dust-trapping vortex at the location of Clump 1. However, we stress that the uncertainty in the estimation of the pattern speed is large, as highlighted in Ren et al (2018), and that there is actually no constraint on the upper distance of the putative companion. The 3σ lower limit on the pattern speed goes to 0 indeed (that is, no rotation; Ren et al 2018), which would formally correspond to a companion at infinite distance.…”

“…However, we stress that the uncertainty in the estimation of the pattern speed is large, as highlighted in Ren et al (2018), and that there is actually no constraint on the upper distance of the putative companion. The 3σ lower limit on the pattern speed goes to 0 indeed (that is, no rotation; Ren et al 2018), which would formally correspond to a companion at infinite distance. The orbital distance that we assume for the outermost planet in our model (140 au) is therefore entirely consistent with the current measurement of the spirals pattern speed.…”

“…Recent high angular resolution observations have revealed stunning non-axisymmetric emission features in the MWC 758 disc. These asymmetries so far consist of multiple spiral arms and arcs in near-infrared scattered light (Grady E-mail: clement.baruteau@irap.omp.eu et al 2013;Benisty et al 2015;Reggiani et al 2018;Ren et al 2018), an asymmetric ring of emission at ∼0. 32 as well as a compact crescent-shaped structure at ∼0.…”

Pushing the limits of the coronagraphic occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph

“…17,18 Concurrently, postprocessing techniques that suppress speckle noise, such as the locally optimized combination of images (LOCI) algorithm, 19 the Karheunen-Loève image projection (KLIP) algorithm, 20 and non-negative matrix factorization 21 have been developed and shown to be successful at pushing contrasts closer to the photon noise limit of a given coronagraph. These techniques have been shown to be effective with archival NICMOS images [22][23][24][25] from its calibrated archive 26 and STIS 27 coronagraphic images.…”