Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS

SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integralfield spectrograph CHARIS. The spectropolarimetric capability of CHARIS is enabled by a Wollaston prism and is unique among high-contrast imagers. We present a detailed Mueller matrix model describing the instrumental polarization effects of the complete optical path, thus the telescope and instrument. From measurements with the internal light source, we find that the image derotator (K-mirror) produces strongly wavelength-dependent crosstalk, in the worst case converting ∼95% of the incident linear polarization to circularly polarized light that cannot be measured. Observations of an unpolarized star show that the magnitude of the instrumental polarization of the telescope varies with wavelength between 0.5% and 1%, and that its angle is exactly equal to the altitude angle of the telescope. Using physical models of the fold mirror of the telescope, the half-wave plate, and the derotator, we simultaneously fit the instrumental polarization effects in the 22 wavelength bins. Over the full wavelength range, our model currently reaches a total polarimetric accuracy between 0.08% and 0.24% in the degree of linear polarization. We propose additional calibration measurements to improve the polarimetric accuracy to <0.1% and plan to integrate the complete Mueller matrix model into the existing CHARIS post-processing pipeline. Our calibrations of CHARIS’ spectropolarimetric mode will enable unique quantitative polarimetric studies of circumstellar disks and planetary and brown dwarf companions.

[1]  M. Lequime,et al.  Exploitation of multiple incidences spectrometric measurements for thin film reverse engineering. , 2012, Optics express.

[2]  M. Majewski,et al.  Optical properties of metallic films for vertical-cavity optoelectronic devices. , 1998, Applied optics.

[3]  Julien H. Girard,et al.  Combining angular differential imaging and accurate polarimetry with SPHERE/IRDIS to characterize young giant exoplanets , 2017, Optical Engineering + Applications.

[4]  Kjetil Dohlen,et al.  The infra-red dual imaging and spectrograph for SPHERE: design and performance , 2008, Astronomical Telescopes + Instrumentation.

[5]  D. Fantinel,et al.  The polarimetric imaging mode of VLT/SPHERE/IRDIS II: Characterization and correction of instrumental polarization effects. , 2019 .

[6]  C. A. Grady,et al.  DISCOVERY OF SMALL-SCALE SPIRAL STRUCTURES IN THE DISK OF SAO 206462 (HD 135344B): IMPLICATIONS FOR THE PHYSICAL STATE OF THE DISK FROM SPIRAL DENSITY WAVE THEORY , 2012, 1202.6139.

[7]  Joel Nothman,et al.  SciPy 1.0-Fundamental Algorithms for Scientific Computing in Python , 2019, ArXiv.

[8]  K. Murakawa.  Polarization disks in near-infrared high-resolution imaging , 2010 .

[9]  Andrew W. Serio,et al.  First light of the Gemini Planet Imager , 2014, Proceedings of the National Academy of Sciences.

[10]  Gorachand Ghosh,et al.  Dispersion-equation coefficients for the refractive index and birefringence of calcite and quartz crystals , 1999 .

[11]  Mark S. Marley,et al.  Probing the physical properties of directly imaged gas giant exoplanets through polarization , 2011, 1106.0492.

[12]  Julien H. Girard,et al.  Three Radial Gaps in the Disk of TW Hydrae Imaged with SPHERE , 2016, 1610.08939.

[13]  M. Schmid.  Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light , 2016 .

[14]  Dimitri Mawet,et al.  POINT SOURCE POLARIMETRY WITH THE GEMINI PLANET IMAGER: SENSITIVITY CHARACTERIZATION WITH T5.5 DWARF COMPANION HD 19467 B , 2016, 1601.01353.

[15]  Dmitry Savransky,et al.  POLARIMETRY WITH THE GEMINI PLANET IMAGER: METHODS, PERFORMANCE AT FIRST LIGHT, AND THE CIRCUMSTELLAR RING AROUND HR 4796A , 2014, 1407.2495.

[16]  M. Rodenhuis,et al.  Data-reduction techniques for high-contrast imaging polarimetry - Applications to ExPo , 2011, 1105.2961.

[17]  Glenn Schneider,et al.  THE CASE OF AB AURIGAE’S DISK IN POLARIZED LIGHT: IS THERE TRULY A GAP? , 2009, 0911.1130.

[18]  Sascha P. Quanz,et al.  Disks around T Tauri Stars with SPHERE (DARTTS-S). I. SPHERE/IRDIS Polarimetric Imaging of Eight Prominent T Tauri Disks , 2018, The Astrophysical Journal.

[19]  Anthony Boccaletti,et al.  Three Years of SPHERE: The Latest View of the Morphology and Evolution of Protoplanetary Discs , 2017 .

[20]  B. A. Skiff.  VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2014) , 2014 .

[21]  Frantz Martinache,et al.  SCExAO, an instrument with a dual purpose: perform cutting-edge science and develop new technologies , 2018, Astronomical Telescopes + Instrumentation.

[22]  Julien Lozi,et al.  First light of the CHARIS high-contrast integral-field spectrograph , 2017, Optical Engineering + Applications.

[23]  Shane Jacobson,et al.  HiCIAO: the Subaru Telescope's new high-contrast coronographic imager for adaptive optics , 2008, Astronomical Telescopes + Instrumentation.

[24]  G. Perrin,et al.  The Subaru Coronagraphic Extreme Adaptive Optics System: Enabling High-Contrast Imaging on Solar-System Scales , 2015, 1507.00017.

[25]  Russell A. Chipman,et al.  Polarization Aberrations in Astronomical Telescopes: The Point Spread Function , 2015 .

[26]  C. U. Keller,et al.  The polarimetric imaging mode of VLT/SPHERE/IRDIS I: Description, data reduction and observing strategy , 2019 .

[27]  Jason J. Wang,et al.  β PICTORIS’ INNER DISK IN POLARIZED LIGHT AND NEW ORBITAL PARAMETERS FOR β PICTORIS b , 2015, 1508.04787.

[28]  Jason J. Wang,et al.  Debris Disk Results from the Gemini Planet Imager Exoplanet Survey's Polarimetric Imaging Campaign , 2020, The Astronomical Journal.

[29]  Julien H. Girard,et al.  SPHERE: the exoplanet imager for the Very Large Telescope , 2019, Astronomy & Astrophysics.

[30]  E. Kokubo,et al.  DIRECT IMAGING OF FINE STRUCTURES IN GIANT PLANET-FORMING REGIONS OF THE PROTOPLANETARY DISK AROUND AB AURIGAE , 2011, 1102.4408.

[31]  Olivier Guyon,et al.  Performance of Subaru adaptive optics system AO188 , 2010, Astronomical Telescopes + Instrumentation.

[32]  Julien H. Girard,et al.  A Search for Polarized Thermal Emission from Directly Imaged Exoplanets and Brown Dwarf Companions to Nearby Stars , 2020, The Astronomical Journal.

[33]  R. Lenzen,et al.  The instrumental polarization of the Nasmyth focus polarimetric differential imager NAOS/CONICA (NACO) at the VLT - Implications for time-resolved polarimetric measurements of Sgr A* , 2010, 1010.4708.

[34]  Frank Schmidt,et al.  Numerical Methods in Photonics , 2014 .

[35]  Julia J. Bryant,et al.  Ground-based and Airborne Instrumentation for Astronomy VIII , 2021 .

[36]  R. J. de Kok,et al.  CHARACTERIZING EXOPLANETARY ATMOSPHERES THROUGH INFRARED POLARIMETRY , 2011, 1108.1290.

[37]  C. Pinte,et al.  Nonazimuthal linear polarization in protoplanetary disks , 2015, 1509.06745.

[38]  Romain Laugier,et al.  Status of the SCExAO instrument: recent technology upgrades and path to a system-level demonstrator for PSI , 2020, Astronomical Telescopes + Instrumentation.

[39]  M. J. Dodge,et al.  Refractive properties of magnesium fluoride. , 1984, Applied optics.

[40]  Craig Loomis,et al.  Data reduction pipeline for the CHARIS integral-field spectrograph I: detector readout calibration and data cube extraction , 2017, 1706.03067.

[41]  J. Milli,et al.  A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS , 2021, Astronomy & Astrophysics.