Variable Star Polarimetry with PICSARR-2
Volume 54 number 2 (2026)
- Daniel V. Cotton
- Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933; dc@mira.org; ORCID: 0000-0003-0340-7773
- Jeremy Bailey
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia, and Western Sydney University, Locked Bag 1797, Penrith-South DC, NSW 2751, Australia; j.bailey@unsw.edu.au; ORCID: 0000-0002-5726-7000
- Logan Barrett
- Mountain View High School, 3535 Truman Avenue, Mountain View, CA 94040, and Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933; mail@loganb.me; ORCID: 0009-0000-7505-9072
- Glenn Henderson
- Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933; glenn@montereymakers.org
- Kim Sumagang
- Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933; ks2@mira.org
- Eric C. Haase
- Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933; eh@mira.org; ORCID: 0009-0004-7192-0055
Abstract
We present the upgraded Polarimeter using Imaging CMOS Sensor and Rotating Retarder 2 (PICSARR-2), describe its applications, and characterize its performance for stellar polarimetry on a 36-inch and 14-inch telescope. On the larger telescope in the SDSS g', r', and i' filters a precision of σ<SUB>p = 5.7 ppm on bright stars is recorded using a fast modulation rate corresponding to frame exposures of 12 ms; accounting for the internal errors in the individual observations gives a limiting precision of e<SUB>p = 1.3 ppm. Longer frame rates are required for stars with m > 5, but the recorded errors only underperform a photon shot noise derived extrapolation for m > 8, when even longer frame exposures are required. Stars as faint as m = 11 were observed. The position angle precision is measured as 0.0845 degree, and there is very good agreement between observations made by both the PICSARR-2 and HIPPI-2 polarimeters. On the smaller telescope the instrument’s performance approaches similar levels, and there is good cross-platform stability in the observation of standard stars. PICSARR-2 is therefore an excellent instrument to explore stellar variability due to a range of phenomena; examples from our ongoing pulsating star campaign and other variable star programs are presented.