# On-sky performance analysis of the vector Apodizing Phase Plate coronagraph on MagAO/Clio2

## TL;DR

This paper evaluates the on-sky performance of a vector apodizing phase plate coronagraph installed on MagAO/Clio2, demonstrating improved contrast and robustness in high-contrast imaging at infrared wavelengths.

## Contribution

It introduces a novel achromatic vector apodizing phase plate coronagraph with a dual-PSF design for enhanced on-sky performance and ease of integration in existing telescopes.

## Key findings

- Achieved 1.46 mag contrast improvement at 3.5 λ/D through PSF subtraction.
- Delivered a 5σ contrast of 8.3 mag at 2 λ/D and 12.2 mag at 3.5 λ/D.
- Demonstrated robust on-sky performance over 1.5 hours of observation.

## Abstract

We report on the performance of a vector apodizing phase plate coronagraph that operates over a wavelength range of $2-5 \mu$m and is installed in MagAO/Clio2 at the 6.5 m Magellan Clay telescope at Las Campanas Observatory, Chile. The coronagraph manipulates the phase in the pupil to produce three beams yielding two coronagraphic point-spread functions (PSFs) and one faint leakage PSF. The phase pattern is imposed through the inherently achromatic geometric phase, enabled by liquid crystal technology and polarization techniques. The coronagraphic optic is manufactured using a direct-write technique for precise control of the liquid crystal pattern, and multitwist retarders for achromatization. By integrating a linear phase ramp to the coronagraphic phase pattern, two separated coronagraphic PSFs are created with a single pupil-plane optic, which makes it robust and easy to install in existing telescopes. The two coronagraphic PSFs contain a 180$^\circ$ dark hole on each side of a star, and these complementary copies of the star are used to correct the seeing halo close to the star. To characterize the coronagraph, we collected a dataset of a bright ($m_L=0-1$) nearby star with $\sim$1.5 hr of observing time. By rotating and optimally scaling one PSF and subtracting it from the other PSF, we see a contrast improvement by 1.46 magnitudes at $3.5 \lambda/D$. With regular angular differential imaging at 3.9 $\mu$m, the MagAO vector apodizing phase plate coronagraph delivers a $5\sigma\ \Delta$ mag contrast of 8.3 ($=10^{-3.3}$) at 2 $\lambda/D$ and 12.2 ($=10^{-4.8}$) at $3.5 \lambda/D$.