2019/08/27 by Samaporn Tinyanont, Maxwell A. Millar‐Blanchaer, Tinyanont, Samaporn +17 · 1 citation
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.1908.10409
openalex publication_date 2019/08/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
WIRC+Pol is a near-infrared low-resolution spectropolarimeter on the 200-inch\nTelescope at Palomar Observatory. The instrument utilizes a polarization\ngrating to perform polarimetric beam splitting and spectral dispersion\nsimultaneously. It can operate either with a focal plane slit to reduce sky\nbackground or in a slitless mode. Four different spectra sampling four linear\npolarization angles are recorded in the focal plane, allowing the instrument to\nmeasure all linear polarization states in one exposure. The instrument has been\non-sky since February 2017 and we found that the systematic errors, likely\narising from flat fielding and gravity effects on the instrument, limit our\naccuracy to ~1%. These systematic effects were slowly varying, and hence could\nbe removed with a polarimetric modulator. A half-wave plate modulator and a\nlinear polarizer were installed in front of WIRC+Pol in March 2019. The\nmodulator worked as expected, allowing us to measure and remove all\ninstrumental polarization we previously observed. The deepest integration on a\nbright point source (J = 7.689, unpolarized star HD 65970) demonstrated\nuncertainties in q and u of 0.03% per spectral channel, consistent with the\nphoton noise limit. Observations of fainter sources showed that the instrument\ncould reach the photon noise limit for observations in the slitless mode. For\nobservations in slit, the uncertainties were still a factor of few above the\nphoton noise limit, likely due to slit loss.\n