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WIRC+Pol: A Low-resolution Near-infrared Spectropolarimeter

Tinyanont, Samaporn and Millar-Blanchaer, Maxwell A. and Nilsson, Ricky and Mawet, Dimitri and Knutson, Heather and Kataria, Tiffany and Vasisht, Gautam and Henderson, Charles and Matthews, Keith and Serabyn, Eugene and Milburn, Jennifer W. and Hale, David and Smith, Roger and Vissapragada, Shreyas and Santos, Louis D., Jr and Kekas, Jason and Escuti, Michael J. (2019) WIRC+Pol: A Low-resolution Near-infrared Spectropolarimeter. Publications of the Astronomical Society of the Pacific, 131 (996). Art. No. 025001. ISSN 0004-6280. http://resolver.caltech.edu/CaltechAUTHORS:20181213-132118775

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Abstract

WIRC+Pol is a newly commissioned low-resolution (R ~ 100), near-infrared (J and H bands) spectropolarimetry mode of the Wide-field InfraRed Camera (WIRC) on the 200 inch Hale Telescope at Palomar Observatory. The instrument utilizes a novel polarimeter design based on a quarter-wave plate and a polarization grating (PG), which provides full linear polarization measurements (Stokes I, Q, and U) in one exposure. The PG also has high transmission across the J and H bands. The instrument is situated at the prime focus of an equatorially mounted telescope. As a result, the system only has one reflection in the light path providing minimal telescope induced polarization. A data reduction pipeline has been developed for WIRC+Pol to produce linear polarization measurements from observations. WIRC+Pol has been on-sky since 2017 February. Results from the first year commissioning data show that the instrument has a high dispersion efficiency as expected from the polarization grating. We demonstrate the polarimetric stability of the instrument with rms variation at 0.2% level over 30 minutes for a bright standard star (J = 8.7). While the spectral extraction is photon noise limited, polarization calibration between sources remain limited by systematics, likely related to gravity dependent pointing effects. We discuss instrumental systematics we have uncovered in the data, their potential causes, along with calibrations that are necessary to eliminate them. We describe a modulator upgrade that will eliminate the slowly varying systematics and provide polarimetric accuracy better than 0.1%.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1088/1538-3873/aaef0fDOIArticle
https://arxiv.org/abs/1811.03138arXivDiscussion Paper
ORCID:
AuthorORCID
Tinyanont, Samaporn0000-0002-1481-4676
Nilsson, Ricky0000-0002-5408-4954
Mawet, Dimitri0000-0002-8895-4735
Knutson, Heather0000-0002-0822-3095
Kataria, Tiffany0000-0003-3759-9080
Vasisht, Gautam0000-0002-1871-6264
Additional Information:© 2018. The Astronomical Society of the Pacific. Received 2018 September 23; accepted 2018 November 7; published 2018 December 13. This work is supported by the National Science Foundation under grant No. AAG-1816341. The WIRC+Pol upgrade was in part supported by a grant from the Mt. Cuba Astronomical Foundation. We thank Paulo Miles-Páez for providing us polarized spectra of Elia 2–25 polarized standard star for comparison with our observations and for discussions on best practices in reducing near-IR spectropolarimetric data. We thank staff of Palomar Observatory for assisting our observations. Palomar Observatory is operated by a collaboration between California Institute of Technology, Jet Propulsion Laboratory, Yale University, and National Astronomical Observatories of China.
Funders:
Funding AgencyGrant Number
NSFAST-1816341
Mt. Cuba Astronomical FoundationUNSPECIFIED
NASA Hubble FellowshipUNSPECIFIED
Subject Keywords:instrumentation: polarimeters – methods: data analysis – methods: observational – techniques: polarimetric
Record Number:CaltechAUTHORS:20181213-132118775
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181213-132118775
Official Citation:Samaporn Tinyanont et al 2019 PASP 131 025001
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91767
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:13 Dec 2018 22:02
Last Modified:26 Mar 2019 17:29

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