Fast-moving features in the debris disk around AU Microscopii

Abstract

In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These 'debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10–60 astronomical units, persisting over intervals of 1–4 years. All these features appear to move away from the star at projected speeds of 4–10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.

Additional Information

© 2015 Macmillan Publishers Limited. Received 23 January 2015; Accepted 28 August 2015; Published online 07 October 2015. SPHERE was built by a European consortium led by IPAG (France). SPHERE was funded by the ESO, with additional contributions from CNRS, MPIA, INAF, FINES and NOVA. SPHERE also received funding from the European Commission FP6 and FP7 programmes as part of OPTICON under grant numbers RII3-Ct-2004-001566 (FP6), 226604 (FP7) and 312430 (FP7). French co-authors are supported by ANR-14-CE33-0018. Part of this work has been carried out within the framework of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation. C.T. and M.R.M. acknowledge the financial support of the SNSF.This study is based on observations from program 60.A-9249(C) at ESO Very Large Telescope and from program number 12228 made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA Inc. under NASA contract NAS 5-26555. We are also grateful to the ESO for releasing the commissioning data for publication. Finally, we thank P. Zarka, N. Meyer-Vernet, B. Stelzer and Q. Kral for discussions. J.S. is a NASA Postdoctoral Program Fellow. Author Contributions: A.B. reduced and analysed IRDIS data and wrote the paper. C.T. reduced the IRDIS and ZIMPOL data and contributed to the manuscript writing. A.B., C.T., A.-M.L., M.J., J.-C.A., G.S., C.G., J.D., D.M., T.H., C.D., C.G., J.O. and J.S. worked on the interpretation of the results. G.S., C.G., J.D., D.H., T.R. and J.W. re-reduced HST data. J.M., M.L., D. Mouillet., D. Mawet, J.H.G. and Z.W. operated the instrument at the telescope. A.-L.M. worked on the astrometric calibration. A.B., A.-M.L, M.L., D. Mouillet, T.H., J.-L.B., K.D., M.F., T.F., M.K., F.M., M.M., C.M., J.-F.S, H.M.S, M.T., S.U, F.V. and A.V. contributed to the instrument conception. All authors commented on the manuscript. The authors declare no competing financial interests.

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