POLICAN: A Near-infrared Imaging Polarimeter at the 2.1m OAGH Telescope

TL;DR

POLICAN is a newly developed near-infrared imaging polarimeter for the 2.1m OAGH telescope, enabling detailed polarization studies of star-forming regions with high accuracy.

Contribution

This paper introduces POLICAN, a novel near-infrared polarimeter with specific calibration and data reduction techniques for studying interstellar magnetic fields.

Findings

Instrumental polarization of 0.51% was measured.

Polarimetric accuracy better than 0.5% achieved.

Position angle errors less than 5 degrees for bright stars.

Abstract

POLICAN is a near-infrared imaging linear polarimeter developed for the Cananea Near-infrared Camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. POLICAN is mounted ahead of CANICA and consist of a rotating super-achromatic 1-2.7 micron half-wave plate (HWP) as the modulator and a fixed wire-grid polarizer as the analyzer. CANICA has a 1024 x 1024 HgCdTe detector with a plate scale of 0.32 arcsec/pixel and provides a field of view of 5.5 x 5.5 arcmin^2. The polarimetric observations are carried out by modulating the incoming light through different steps of half-wave plate angles 0, 22.5, 45, 67.5 deg, to establish linear Stokes parameters (I, Q, and U). Image reduction consists of dark subtraction, polarimetric flat fielding, and sky subtraction. The astrometry and photometric calibrations are performed using the publicly available data from the Two Micron All Sky Survey. Polarimetric calibration includes observations of globular clusters and polarization standards available in the literature. Analysis of multiple observations of globular clusters yielded an instrumental polarization of 0.51%. Uncertainties in polarization range from 0.1% to 10% from the brightest 7 mag to faintest 16 mag stars. The polarimetric accuracy achieved is better than 0.5% and the position angle errors less than 5 deg for stars brighter than 13 mag in H-band. POLICAN is mainly being used to study the scattered polarization and magnetic fields in and around star-forming regions of the interstellar medium.