Developing an instrumental polarization characterization routine for SCExAO VAMPIRES

The Visible Aperture Masking Polarimetric Imager for Resolved Exoplanetary Structures (VAMPIRES) is a visible light instrument on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. In a previous work, the instrumental polarization (IP) and crosstalk of VAMPIRES was characterized from measurements with a polarized internal calibration source. In this work, we use unpolarized standard star observations to estimate the polarization of Subaru's Nasmyth mirror (M3) and use polarized standard star observations to quantify the overall system Mueller matrix model's accuracy. We present an instrument matrix inversion routine that has returned stable results for all tested on-sky sources. With the current 675nm Mueller matrix model of VAMPIRES, the median residuals when retrieving the on-sky degree of linear polarization (DoLP) and angle of linear polarization (AoLP) of three polarized standards were 0.27% and 3.57% respectively.