Gemini Planet Imager Observational Calibrations VIII: Characterization and Role of Satellite Spots

TL;DR

This paper details the calibration techniques for satellite spots in the Gemini Planet Imager, enabling precise measurement of the host star's properties despite the coronagraph blocking direct light, crucial for exoplanet imaging.

Contribution

It introduces and evaluates new methods for measuring satellite spot astrometry and spectrophotometry, improving calibration accuracy in high-contrast imaging.

Findings

Astrometric precision of 0.05 pixels in H-band data

Satellite spot flux stability within 7%

Spectral shape varies by 2%

Abstract

The Gemini Planet Imager (GPI) combines extreme adaptive optics, an integral field spectrograph, and a high performance coronagraph to directly image extrasolar planets in the near-infrared. Because the coronagraph blocks most of the light from the star, it prevents the properties of the host star from being measured directly. Instead, satellite spots, which are created by diffraction from a square grid in the pupil plane, can be used to locate the star and extract its spectrum. We describe the techniques implemented into the GPI Data Reduction Pipeline to measure the properties of the satellite spots and discuss the precision of the reconstructed astrometry and spectrophotometry of the occulted star. We find the astrometric precision of the satellite spots in an $H$-band datacube to be $0.05$ pixels and is best when individual satellite spots have a signal to noise ratio (SNR) of $> 20$. In regards to satellite spot spectrophotometry, we find that the total flux from the satellite spots is stable to $\sim 7\%$ and scales linearly with central star brightness and that the shape of the satellite spot spectrum varies on the $2\%$ level.