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Proceedings Paper

Achieving a spectropolarimetric precision better than 0.1% in the near-infrared with WIRC+Pol
Author(s): Samaporn Tinyanont; Maxwell Millar-Blanchaer; Nemanja Jovanovic; Dimitri Mawet; Gautam Vasisht; Jennifer W. Milburn; Eugene Serabyn; Michael Porter; Skyler Palatnick; Connor Hopkins
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Paper Abstract

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.

Paper Details

Date Published: 6 September 2019
PDF: 12 pages
Proc. SPIE 11132, Polarization Science and Remote Sensing IX, 1113209 (6 September 2019); doi: 10.1117/12.2529863
Show Author Affiliations
Samaporn Tinyanont, California Institute of Technology (United States)
Maxwell Millar-Blanchaer, California Institute of Technology (United States)
Jet Propulsion Lab. (United States)
NASA (United States)
Nemanja Jovanovic, California Institute of Technology (United States)
Dimitri Mawet, California Institute of Technology (United States)
Jet Propulsion Lab. (United States)
Gautam Vasisht, Jet Propulsion Lab. (United States)
Jennifer W. Milburn, California Institute of Technology (United States)
Eugene Serabyn, Jet Propulsion Lab. (United States)
Michael Porter, California Institute of Technology (United States)
Skyler Palatnick, Univ. of Pennsylvania (United States)
Connor Hopkins, Pasadena High School (United States)

Published in SPIE Proceedings Vol. 11132:
Polarization Science and Remote Sensing IX
Julia M. Craven; Joseph A. Shaw; Frans Snik, Editor(s)

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