The VLT/ERIS vortex coronagraph: design, pointing control, and on-sky performance

Abstract

The Enhanced Resolution Imager and Spectrograph (ERIS) is the new near-infrared instrument at the VLT-UT4. ERIS replaces and extends the observational capabilities formerly provided by SINFONI and NACO: integral field spectroscopy at 1 to 2.5μm, imaging at 1 to 5μm with several options for high-contrast imaging, and long-slit spectroscopy. In particular, a vortex coronagraph is now available for high contrast observations at L and M band. It is implemented using annular groove (or vortex) phase masks (one for each of the L and M bands) in a focal plane, and a Lyot stop in a downstream pupil plane. The vortex coronagraph has a discovery space starting already at ∼1λ/D, and works well in broadbands. However, to reach its optimal performance, it is critical to correct for slow pointing errors onto the vortex phase mask, which mandates a dedicated pointing control strategy. To do so, a control loop based on the QACITS algorithm has been developed and commissioned for ERIS. Good pointing stability is now regularly achieved with errors between 0.01 and 0.02 λ/D and a correction rate of 0.2Hz. In this contribution, we first review the design of the ERIS vortex coronagraph. We then detail the implementation of the QACITS algorithm describing the entire observing sequence, including the calibration steps, the initial centering, and the stabilization during the observing template. We then discuss performance based on commissioning data in terms of pointing accuracy and stability. Finally, we present post-processed contrast curves obtained during commissioning and compare them with NACO vortex data, showing a significant improvement of about 1 mag at all separations.

Authors 17

1. Gilles Orban de Xivry
2. Olivier Absil
3. Robert J. De Rosa

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory (Chile)

4. Markus J. Bonse

   ETH Zurich · Max Planck Institute for Intelligent Systems

   Affiliation as printed

   ETH Zurich (Switzerland)

   Max Planck Institute for Intelligent Systems (Germany)

5. Felix Dannert

   ETH Zurich

   Affiliation as printed

   ETH Zurich (Switzerland)

6. Jean Hayoz

   ETH Zurich

   Affiliation as printed

   ETH Zurich (Switzerland)

7. Paolo Grani

   Arcetri Astrophysical Observatory · National Institute for Astrophysics

   Affiliation as printed

   INAF, Osservatorio Astrofisico di Arcetri (Italy)

8. Alfio Timothy Puglisi

   Arcetri Astrophysical Observatory · National Institute for Astrophysics

   Affiliation as printed

   INAF, Osservatorio Astrofisico di Arcetri (Italy)

9. Andrea Baruffolo

   Osservatorio Astronomico di Padova · National Institute for Astrophysics

   Affiliation as printed

   INAF, Osservatorio Astronomico di Padova (Italy)

10. Bernardo Salasnich

    Osservatorio Astronomico di Padova · National Institute for Astrophysics

    Affiliation as printed

    INAF, Osservatorio Astronomico di Padova (Italy)

11. R. Davies

    Max Planck Institute for Intelligent Systems

    Affiliation as printed

    Max Planck Institute for Intelligent Systems (Germany)

12. Adrian Michael Glauser

    ETH Zurich

    Affiliation as printed

    ETH Zurich (Switzerland)

13. Elsa Huby

    Centre National de la Recherche Scientifique · Observatoire de Paris · Sorbonne Université · Laboratoire d’études spatiales et d’instrumentation en astrophysique

    Affiliation as printed

    LESIA, Observatoire de Paris, Univ. PSL, CNRS, Sorbonne Univ., Univ. de Paris (France)

14. Matthew A. Kenworthy Aachen Leiden Univ. (Netherlands)

    Leiden University

    Affiliation as printed

    Leiden Univ. (Netherlands)

15. Sascha P. Quanz

    ETH Zurich

    Affiliation as printed

    ETH Zurich (Switzerland)

16. William C. Taylor

    UK Astronomy Technology Centre

    Affiliation as printed

    UK Astronomy Technology Ctr. (United Kingdom)

17. G. Zins

    University of Liège

    Affiliation as printed

    Liège Univ. (Belgium)