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Published January 10, 2021 | Accepted Version + Published
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Spiral Arm Pattern Motion in the SAO 206462 Protoplanetary Disk


Spiral arms have been observed in more than a dozen protoplanetary disks, yet the origin of nearly all systems is under debate. Multi-epoch monitoring of spiral arm morphology offers a dynamical way to distinguish two leading arm formation mechanisms: companion-driven and gravitational instability induction, since these mechanisms predict distinct motion patterns. By analyzing multi-epoch J-band observations of the SAO 206462 system using the SPHERE instrument on the Very Large Telescope in 2015 and 2016, we measure the pattern motion for its two prominent spiral arms in polarized light. On one hand, if both arms are comoving, they can be driven by a planet at 86₋₁₃⁺¹⁸ au on a circular orbit, with gravitational instability motion ruled out. On the other hand, they can be driven by two planets at 120₋₃₀⁺³⁰ au and 49₋₅⁺⁶ au, offering tentative evidence (3.0σ) that the two spirals are moving independently. The independent arm motion is possibly supported by our analysis of a re-reduction of archival observations using the NICMOS instrument on board the Hubble Space Telescope (HST) in 1998 and 2005, yet artifacts including shadows can manifest spurious arm motion in HST observations. We expect future re-observations to better constrain the motion mechanism for the SAO 206462 spiral arms.

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 3; revised 2020 December 7; accepted 2020 December 8; published 2021 January 11. We thank the anonymous referee for suggestions that increased the clarity and robustness of this Letter, and Jaehan Bae for useful discussions. T.F. and C.X. are supported by the National Key R&D Program of China No. 2017YFA0402600, project S202010384487 XMU Training Program of Innovation and Enterpreneurship for Undergraduate, and NSFC grants No. 11525312, 11890692. R.D. acknowledges financial support provided by the Natural Sciences and Engineering Research Council of Canada through a Discovery Grant, as well as the Alfred P. Sloan Foundation through a Sloan Research Fellowship. This research is partially supported by NASA ROSES XRP, award 80NSSC19K0294. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 095.C-0273 (A), 097.C-0702 (A), 097.C-0885 (A), and 297.C-5023 (A). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. 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: VLT:Melipal (SPHERE) - , Keck:II (NIRC2) - , HST (NICMOS). - Software: IRDAP (van Holstein et al. 2020), diskmap (Stolker et al. 2016b), scipy (Virtanen et al. 2020).

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Accepted Version - 2012.05242.pdf

Published - Xie_2021_ApJL_906_L9.pdf


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August 22, 2023
August 22, 2023