WIRC+Pol: a low-resolution near-infrared spectropolarimeter. (arXiv:1811.03138v1 [astro-ph.IM])

WIRC+Pol: a low-resolution near-infrared spectropolarimeter. (arXiv:1811.03138v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tinyanont_S/0/1/0/all/0/1">Samaporn Tinyanont</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Millar_Blanchaer_M/0/1/0/all/0/1">Maxwell A. Millar-Blanchaer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nilsson_R/0/1/0/all/0/1">Ricky Nilsson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mawet_D/0/1/0/all/0/1">Dimitri Mawet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knutson_H/0/1/0/all/0/1">Heather Knutson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kataria_T/0/1/0/all/0/1">Tiffany Kataria</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vasisht_G/0/1/0/all/0/1">Gautam Vasisht</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henderson_C/0/1/0/all/0/1">Charles Henderson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matthews_K/0/1/0/all/0/1">Keith Matthews</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Serabyn_E/0/1/0/all/0/1">Eugene Serabyn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milburn_J/0/1/0/all/0/1">Jennifer W. Milburn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hale_D/0/1/0/all/0/1">David Hale</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Roger Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vissapragada_S/0/1/0/all/0/1">Shreyas Vissapragada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Santos_L/0/1/0/all/0/1">Louis D. Santos Jr</a>

WIRC+Pol is a newly commissioned low-resolution (R~100), near-infrared (J and
H band) 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 February 2017. 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%.

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