Dynamical Evidence of a Spiral Arm–driving Planet in the MWC 758 Protoplanetary Disk

Creators: Ren, Bin; Dong, Ruobing; van Holstein, Rob G.; Ruffio, Jean-Baptiste; Calvin, Benjamin A.; Girard, Julien H.; Benisty, Myriam; Boccaletti, Anthony; Esposito, Thomas M.; Choquet, Élodie; Mawet, Dimitri; Pueyo, Laurent; Stolker, Tomas; Chiang, Eugene; De Boer, Jozua; Debes, John H.; Garufi, Antonio; Grady, Carol A.; Hines, Dean C.; Maire, Anne-Lise; Ménard, François; Millar-Blanchaer, Maxwell A.; Perrin, Marshall D.; Poteet, Charles A.; Schneider, Glenn

Abstract

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion–disk interaction and gravitational instability (GI)—predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ~5 yr using the SPHERE instrument on the Very Large Telescope, we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0.°22 ± 0.°03 yr⁻¹, pointing to a driver at 172⁺¹⁸₋₁₄ au around a 1.9 M_☉ central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk.

Additional Information

© 2020 The American Astronomical Society. Received 2020 May 8; revised 2020 July 8; accepted 2020 July 8; published 2020 July 29. We thank the anonymous referee for comments that improved the clarity of this Letter, and Cassandra Hall for useful discussions. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 060.A-9389(A) and 104.C-0472(A). B.R. thanks Christian Ginski for discussions on shadowing effects, Rémi Soummer for initiating the Archival Legacy Investigations of Circumstellar Environments (ALICE) project that set up the stage for R18 and this Letter. T.E. was supported in part by NASA Grants NNX15AD95G/NEXSS, NNX15AC89G, and NSF AST-1518332. A.L.M. acknowledges the financial support of the F.R.S.-FNRS through a postdoctoral researcher grant. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Very Large Telescope (SPHERE) - , Keck:II (NIRC2). - Software: diskmap (Stolker et al. 2016), IRDAP (van Holstein et al. 2017, 2020), scipy (Virtanen et al. 2020).

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