# Triple Range Imager and POLarimeter (TRIPOL) --- A Compact and Economical Optical Imaging Polarimeter for Small Telescopes

## TL;DR

TRIPOL is a compact, economical optical imaging polarimeter designed for small telescopes, capable of simultaneous imaging and polarimetry across three wavelength bands, enabling studies of time-variable and wavelength-dependent phenomena.

## Contribution

This paper introduces TRIPOL, a novel, lightweight polarimeter that combines simultaneous imaging and polarimetry in three bands for small telescopes, with demonstrated performance and applications.

## Key findings

- Achieved limiting magnitudes of g' ~ 19.0, r' ~ 18.5, i' ~ 18.0 mag with S/N=10.
- Instrumental polarization measured at ~0.3% across bands.
- Successful application to star-forming cloud IC 5146 and variable star GM Cep.

## Abstract

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.