We report the design concept and performance of a compact, light-weight, and economic imaging polarimeter, TRIPOL (the Triple Range Imager and POLarimeter), capable of simultaneous optical imagery and polarimetry. TRIPOL splits the beam from wavelength 400 to 830 nm into g'-, r'-, and i'-bands with two dichroic mirrors, and measures polarization with an achromatic half-waveplate and a wire-grid. The simultaneity makes TRIPOL a useful tool for small telescopes for photometry and polarimetry of time variable and wavelength dependent phenomena. TRIPOL is devised for a Cassegrain telescope of an aperture of ~1 m. This paper presents the engineering considerations of TRIPOL and compares the expected with the observed performance. Using the Lulin 1-m telescope and 100 seconds integration, the limiting magnitudes are g' ~ 19.0 mag, r' ~ 18.5 mag and i' ~ 18.0 mag with a signal-to-noise of 10, in agreement with design expectation. The instrumental polarization is measured to be ~ 0.3% at three bands. Two applications, one to the star-forming cloud IC 5146, and the other to the young variable GM Cep, are presented as demonstration.
@article{arxiv.1905.01845,
title = {Triple Range Imager and POLarimeter (TRIPOL) --- A Compact and Economical Optical Imaging Polarimeter for Small Telescopes},
author = {S. Sato and P. C. Huang and W. P. Chen and T. Zenno and C. Eswaraiah and B. H. Su and S. Abe and D. Kinoshita and J. W. Wang},
journal= {arXiv preprint arXiv:1905.01845},
year = {2019}
}