研究目的
To describe the design, commissioning, and performance of WIRC+Pol, a low-resolution near-infrared spectropolarimeter, and to characterize its capabilities and systematics for astronomical observations.
研究成果
WIRC+Pol is an effective low-resolution near-infrared spectropolarimeter with high dispersion ef?ciency (93%) and polarimetric stability (0.2% rms over 30 minutes). It can measure polarization to within 0.5% of literature values for bright sources, but angle measurements have a constant offset of ～15° due to instrumental factors. Future upgrades, such as adding a modulator, are planned to reduce systematics and achieve better than 0.1% accuracy. The instrument demonstrates the utility of polarization gratings for compact and ef?cient spectropolarimetry.
研究不足
Polarization calibration is limited by systematics, such as gravity-dependent pointing effects and non-common path errors from ?lter transmission variations. The instrument requires observations of unpolarized standards for calibration, and the current design lacks a rotating modulator, which could improve accuracy. Spatial and temporal variations in instrumental polarization affect measurements, with uncertainties around 0.2-1%.
1：Experimental Design and Method Selection:
The study involves upgrading the Wide-?eld InfraRed Camera (WIRC) with a polarization grating (PG) and quarter-wave plate (QWP) to enable spectropolarimetry. The design allows simultaneous measurement of Stokes parameters I, Q, and U in one exposure. A data reduction pipeline was developed in Python for processing observations.
2：Sample Selection and Data Sources:
Observations include unpolarized standard stars (e.g., HD 93521, HD 109055) and known polarized stars (e.g., Elia 2–25, Schlute 14) from astronomical catalogs. Data were collected on-sky using the Hale Telescope at Palomar Observatory.
3：List of Experimental Equipment and Materials:
Equipment includes the Hale Telescope, WIRC camera, PG and QWP device, focal plane mask, HAWAII-2 detector, and various ?lters (J and H bands). Materials involve liquid crystal polymer for the PG.
4：Experimental Procedures and Operational Workflow:
Procedures include installing the PG/QWP device, taking ?at and dark frames, observing standard and science targets, guiding the telescope to maintain source position, and using the data reduction pipeline for spectral extraction and polarization computation.
5：Data Analysis Methods:
Analysis involves dark subtraction, ?at-?eld correction, source detection, optimal spectral extraction, wavelength calibration using atmospheric features, and polarization calculation with error propagation. Statistical methods include sigma clipping and median absolute deviation for bad pixel identification.
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