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Achieving a spectropolarimetric precision better than 0.1% in the near-infrared with WIRC+Pol

Tinyanont, Samaporn and Millar-Blanchaer, Maxwell A. and Jovanovic, Nemanja and Mawet, Dimitri and Vasisht, Gautam and Milburn, Jennifer W. and Serabyn, Eugene and Porter, Michael and Palatnick, Skyler and Hopkins, Connor (2019) Achieving a spectropolarimetric precision better than 0.1% in the near-infrared with WIRC+Pol. In: Polarization Science and Remote Sensing IX. Proceedings of SPIE. No.11132. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 1113209. ISBN 9781510629578.

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WIRC+Pol is a near-infrared low-resolution spectropolarimeter on the 200-inch Telescope at Palomar Observatory. The instrument utilizes a polarization grating to perform polarimetric beam splitting and spectral dispersion simultaneously. It can operate either with a focal plane slit to reduce sky background or in a slitless mode. Four different spectra sampling four linear polarization angles are recorded in the focal plane, allowing the instrument to measure all linear polarization states in one exposure. The instrument has been on-sky since February 2017 and we found that the systematic errors, likely arising from flat fielding and gravity effects on the instrument, limit our accuracy to ~1%. These systematic effects were slowly varying, and hence could be removed with a polarimetric modulator. A half-wave plate modulator and a linear polarizer were installed in front of WIRC+Pol in March 2019. The modulator worked as expected, allowing us to measure and remove all instrumental polarization we previously observed. The deepest integration on a bright point source (J = 7.689, unpolarized star HD65970) demonstrated uncertainties in q and u of 0.03% per spectral channel, consistent with the photon noise limit. Observations of fainter sources showed that the instrument could reach the photon noise limit for observations in the slitless mode. For observations in slit, the uncertainties were still a factor of few above the photon noise limit, likely due to slit loss.

Item Type:Book Section
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URLURL TypeDescription Paper
Tinyanont, Samaporn0000-0002-1481-4676
Millar-Blanchaer, Maxwell A.0000-0001-6205-9233
Mawet, Dimitri0000-0002-8895-4735
Vasisht, Gautam0000-0002-1871-6264
Additional Information:© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
Group:Astronomy Department
Subject Keywords:spectropolarimetry, polarization grating
Series Name:Proceedings of SPIE
Issue or Number:11132
Record Number:CaltechAUTHORS:20190909-093503549
Persistent URL:
Official Citation:Samaporn Tinyanont, Maxwell Millar-Blanchaer, Nemanja Jovanovic, Dimitri Mawet, Gautam Vasisht, Jennifer W. Milburn, Eugene Serabyn, Michael Porter, Skyler Palatnick, and Connor Hopkins "Achieving a spectropolarimetric precision better than 0.1% in the near-infrared with WIRC+Pol", Proc. SPIE 11132, Polarization Science and Remote Sensing IX, 1113209 (6 September 2019);
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98513
Deposited By: George Porter
Deposited On:09 Sep 2019 20:35
Last Modified:19 Nov 2019 18:57

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