Fast-moving features in the debris disk around AU Microscopii

Journal name:
Nature
Volume:
526,
Pages:
230–232
Date published:
DOI:
doi:10.1038/nature15705
Received
Accepted
Published online

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 source1. 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 disk2, 3, 4, 5. 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 units6, 7, 8, 9. 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.

At a glance

Figures

  1. High-contrast images of the AU Mic debris disk.
    Figure 1: High-contrast images of the AU Mic debris disk.

    Images are shown for the three epochs (2010.69, 2011.63 and 2014.69) at the same spatial scale; the location of AU Mic is marked with a yellow star symbol. In a and b, the HST/STIS data were processed with multi-roll point spread function (PSF)-template subtraction and unsharp mask. SPHERE/IRDIS images are displayed in c, d and e, for three differential imaging techniques (average profile subtraction, KLIP and LOCI) (see Methods). The intensity maps are multiplied by the square of the stellocentric distance to counteract the high dynamic range of the data and to make the disk structures A–E visible at all separations.

  2. Extraction of disk substructure from the southeastern side.
    Figure 2: Extraction of disk substructure from the southeastern side.

    ac, The images from Fig. 1a–c after unsharp masking, subtraction of the smooth main body of the disk, and stretching in the vertical direction by a factor of two (see Methods). The same persistent pattern is recovered in all three epochs, though at shifted locations, implying motion away from the star. d, A contour plot of the two HST epochs after more aggressive spatial filtering (Methods), which produces sharp residual features highlighting the differential motion of each feature.

  3. Disk features across three epochs.
    Figure 3: Disk features across three epochs.

    Precise registration of the disk spine in the southeast side reveals vertical excursions (a) and intensity variations (multiplied by the square of the separation from the star, b). The SPHERE profile is an average of three data reductions (ADI, KLIP and subtraction of azimuthally averaged profile). Error bars are 1σ dispersion. The profiles are shifted vertically in proportion to the time intervals between epochs. Disk features are identified as five local maxima (A–E). Dashed orange lines roughly illustrate the possible trajectory of each feature. Feature A is undetected in 2010, being too close to the star. a.u., arbitrary units.

  4. Projected speeds of the disk features.
    Figure 4: Projected speeds of the disk features.

    The projected speeds of the five features A–E (green, red, orange, blue and magenta) are plotted against the projected separation from the star. Several orbits are shown for different mass assumptions (0.4, 0.6 and 0.8 solar masses) and two eccentricities: e = 0 (dotted lines), e = 0.9 (dashed lines). The solid lines stand for the maximum local system escape speed. Horizontal bars correspond to the range of projected separations between two epochs, while the vertical dotted lines stand for the projected speed uncertainty (peak-to-valley).

  5. Limit of detection to point sources.
    Extended Data Fig. 1: Limit of detection to point sources.

    The contrast is measured at 5σ using fake planets introduced to the data at discrete positions (circles) along the disk midplane to account for the self-subtraction of the ADI/KLIP algorithm. The dashed line defines the edge of the coronagraphic mask at 0.09″.

  6. Comparison of IRDIS and ZIMPOL images.
    Extended Data Fig. 2: Comparison of IRDIS and ZIMPOL images.

    a and b show zoomed-in regions of the KLIP and LOCI reductions of the IRDIS infrared data, whereas c is taken from the conservative LOCI reduction of the ZIMPOL optical data. Features A and B are reproduced accurately in the ZIMPOL data. An additional substructure between feature B and the midplane is also detected, as indicated by arrows. The yellow star symbol indicates the position of the star.

  7. Spine of the disk measured in SPHERE IRDIS data.
    Extended Data Fig. 3: Spine of the disk measured in SPHERE IRDIS data.

    The spine is measured using several reductions (noADI, ADI, KLIP) of the SPHERE IRDIS 2014 data. Average values and dispersions (error bars) are plotted as a blue line. For each region where a local maxima is identified, a Gaussian + first-order polynomial model is fitted in order to register precisely the five features.

  8. Central part of the SPHERE IRDIS image.
    Extended Data Fig. 4: Central part of the SPHERE IRDIS image.

    a shows a 12″ field of view of the SPHERE IRDIS image processed with the KLIP algorithm and b is a magnified version to indicate the bow-like deviation of the disk to the southeast in the central area (for separations shorter than ~0.7″). The horizontal dotted lines indicate the disk midplane.

  9. Positions of the disk features over time.
    Extended Data Fig. 5: Positions of the disk features over time.

    The positions of the features measured in the SPHERE and HST images are plotted as circles together with peak-to-valley error bars (in some cases, the errors are smaller than the symbol size). Linear fits on these three epochs illustrate the possible track of each feature. The black symbols show the location at which various inhomogeneities were reported in the literature, on the basis of older data6, 7, 8, 9. The colour coding is the same as in Fig. 4.

Tables

  1. Registration of features
    Extended Data Table 1: Registration of features

References

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  15. Schneider, G. et al. Probing for exoplanets hiding in dusty debris disks: disk imaging, characterization, and exploration with HST/STIS multi-roll coronagraphy. Astron. J. 148, 59 (2014)
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Author information

Affiliations

  1. LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, Université Pierre et Marie Curie, 5 place Jules Janssen, 92190 Meudon, France

    • Anthony Boccaletti
  2. ETH Zürich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich, Switzerland

    • Christian Thalmann,
    • Natalia Engler,
    • Michael R. Meyer &
    • Hans Martin Schmid
  3. Université Grenoble Alpes, IPAG, F-38000 Grenoble, France

    • Anne-Marie Lagrange,
    • Jean-Charles Augereau,
    • David Mouillet &
    • Jean-Luc Beuzit
  4. CNRS, IPAG, F-38000 Grenoble, France

    • Anne-Marie Lagrange,
    • Jean-Charles Augereau,
    • Julien Milli,
    • David Mouillet,
    • Jean-Luc Beuzit,
    • Julien H. Girard &
    • Markus Kasper
  5. Department of Astronomy, Stockholm University, SE-106 91 Stockholm, Sweden

    • Markus Janson
  6. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

    • Markus Janson,
    • Thomas Henning,
    • Joseph Carson,
    • Markus Feldt,
    • Johan Olofsson &
    • Joshua Schlieder
  7. Steward Observatory, 933 North Cherry Avenue, The University of Arizona, Tucson, Arizona 85721, USA

    • Glenn Schneider
  8. European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile

    • Julien Milli,
    • Julien H. Girard,
    • Arthur Vigan &
    • Zahed Wahhaj
  9. Eureka Scientific, 2452 Delmer, Suite 100, Oakland, California 96002, USA

    • Carol Grady
  10. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA

    • John Debes &
    • Dean Hines
  11. Centre de Recherche Astrophysique de Lyon, (CNRS/ENS-L/Université Lyon 1), 9 avenue Charles André, 69561 Saint-Genis-Laval, France

    • Maud Langlois
  12. Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France

    • Maud Langlois,
    • Kjetil Dohlen,
    • Thierry Fusco,
    • Claire Moutou,
    • Jean-Francois Sauvage,
    • Arthur Vigan &
    • Zahed Wahhaj
  13. University of Amsterdam, Anton Pannekoek Institute for Astronomy, Science Park 904 1098 XH Amsterdam, The Netherlands

    • Carsten Dominik
  14. INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

    • Anne-Lise Maire &
    • Massimo Turatto
  15. Department of Physics and Astronomy, College of Charleston, South Carolina, 29424, USA

    • Joseph Carson
  16. ONERA—The French Aerospace Laboratory, 92322 Châtillon, France

    • Thierry Fusco &
    • Jean-Francois Sauvage
  17. Sterrewacht Leiden, PO Box 9513, Niels Bohrweg 2, NL-2300RA Leiden, The Netherlands

    • Christian Ginski
  18. European Southern Observatory (ESO), Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany

    • Markus Kasper
  19. Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, California 91125, USA

    • Dimitri Mawet
  20. UMI-FCA, CNRS/INSU France (UMI 3386), and Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Correo Central, Santiago, Chile

    • François Ménard
  21. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington DC 20015, USA

    • Timothy Rodigas
  22. NASA Ames Research Center, Space Science and Astrobiology Division, MS 245-6, Moffett Field, California 94035, USA

    • Joshua Schlieder
  23. Observatoire de Genève, University of Geneva, 51 Chemin des Maillettes, 1290 Versoix, Switzerland

    • Stephane Udry
  24. Laboratoire J.-L. Lagrange, Observatoire de la Côte d’Azur (OCA), Université de Nice-Sophia Antipolis (UNS), CNRS, Campus Valrose, 06108 Nice Cedex 2, France

    • Farrokh Vakili
  25. Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, Oklahoma 73019, USA

    • John Wisniewski

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.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Limit of detection to point sources. (92 KB)

    The contrast is measured at 5σ using fake planets introduced to the data at discrete positions (circles) along the disk midplane to account for the self-subtraction of the ADI/KLIP algorithm. The dashed line defines the edge of the coronagraphic mask at 0.09″.

  2. Extended Data Figure 2: Comparison of IRDIS and ZIMPOL images. (738 KB)

    a and b show zoomed-in regions of the KLIP and LOCI reductions of the IRDIS infrared data, whereas c is taken from the conservative LOCI reduction of the ZIMPOL optical data. Features A and B are reproduced accurately in the ZIMPOL data. An additional substructure between feature B and the midplane is also detected, as indicated by arrows. The yellow star symbol indicates the position of the star.

  3. Extended Data Figure 3: Spine of the disk measured in SPHERE IRDIS data. (141 KB)

    The spine is measured using several reductions (noADI, ADI, KLIP) of the SPHERE IRDIS 2014 data. Average values and dispersions (error bars) are plotted as a blue line. For each region where a local maxima is identified, a Gaussian + first-order polynomial model is fitted in order to register precisely the five features.

  4. Extended Data Figure 4: Central part of the SPHERE IRDIS image. (321 KB)

    a shows a 12″ field of view of the SPHERE IRDIS image processed with the KLIP algorithm and b is a magnified version to indicate the bow-like deviation of the disk to the southeast in the central area (for separations shorter than ~0.7″). The horizontal dotted lines indicate the disk midplane.

  5. Extended Data Figure 5: Positions of the disk features over time. (223 KB)

    The positions of the features measured in the SPHERE and HST images are plotted as circles together with peak-to-valley error bars (in some cases, the errors are smaller than the symbol size). Linear fits on these three epochs illustrate the possible track of each feature. The black symbols show the location at which various inhomogeneities were reported in the literature, on the basis of older data6, 7, 8, 9. The colour coding is the same as in Fig. 4.

Extended Data Tables

  1. Extended Data Table 1: Registration of features (70 KB)

Additional data