Early High-contrast Imaging Results with Keck/NIRC2-PWFS: The SR 21 Disk

Creators: Uyama, Taichi; Ren, Bin; Mawet, Dimitri; Ruane, Garreth; Bond, Charlotte Z.; Hashimoto, Jun; Liu, Michael C.; Muto, Takayuki; Ruffio, Jean-Baptiste; Wallack, Nicole; Baranec, Christoph; Bowler, Brendan P.; Choquet, Élodie; Chun, Mark; Delorme, Jacques-Robert; Fogarty, Kevin; Guyon, Olivier; Jensen-Clem, Rebecca; Meshkat, Tiffany; Ngo, Henry; Wang, Jason J.; Wang, Ji; Wizinowich, Peter; Ygouf, Marie; Zuckerman, Benjamin

Abstract

High-contrast imaging of exoplanets and protoplanetary disks depends on wave front sensing and correction made by adaptive optics instruments. Classically, wave front sensing has been conducted at optical wavelengths, which made high-contrast imaging of red targets such as M-type stars or extincted T Tauri stars challenging. Keck/NIRC2 has combined near-infrared (NIR) detector technology with the pyramid wave front sensor (PWFS). With this new module we observed SR 21, a young star that is brighter at NIR wavelengths than at optical wavelengths. Compared with the archival data of SR 21 taken with the optical wave front sensing we achieved ~20% better Strehl ratio in similar natural seeing conditions. Further post-processing utilizing angular differential imaging and reference-star differential imaging confirmed the spiral feature reported by the Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch instrument polarimetric observation, which is the first detection of the SR 21 spiral in total intensity at L' band. We also compared the contrast limit of our result (10⁻⁴ at 0."4 and 2 × 10⁻⁵ at 1."0) with the archival data that were taken with optical wave front sensing and confirmed the improvement, particularly at ≤0."5. Our observation demonstrates that the NIR PWFS improves AO performance and will provide more opportunities for red targets in the future.

Additional Information

© 2020 The American Astronomical Society. Received 2020 September 27; revised 2020 October 29; accepted 2020 October 30; published 2020 November 23. The authors would like to thank the anonymous referee for the constructive comments to improve the clarity of the manuscript. We thank Christian Ginski for sharing the updated detection limit of the archival Keck/NIRC2 data. 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. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 1100.C-0481(Q). This research has made use of NASA's Astrophysics Data System Bibliographic Services. This research has made use of the SIMBAD database (Wenger et al. 2000), operated at CDS, Strasbourg, France. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi:10.26093/cds/vizier). The original description of the VizieR service was published in Ochsenbein et al. (2000). T.U. acknowledges JSPS overseas research fellowship. M.L. acknowledges funding from the National Science Foundation under grants AST-1518339. The Keck infrared pyramid wave front sensor was developed with support from the National Science Foundation under grants AST-1611623 and AST-1106391, as well as the Heising Simons Foundation under the Keck Planet Imager and Characterizer project. This research is partially supported by NASA ROSES XRP, award 80NSSC19K0294. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). We wish to acknowledge the critical importance of the current and recent Maunakea Observatories day crew, technicians, telescope operators, computer support, and office staff employees, especially during the challenging times presented by the COVID-19 pandemic. Their expertise, ingenuity, and dedication is indispensable to the continued successful operation of these observatories. The authors wish to 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. Facility: Keck:II (NIRC2). - Software: pyKLIP (Wang et al. 2015), IRDAP (van Holstein et al. 2017, 2020).

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