The high-contrast performance of the Keck Planet Imager and Characterizer

TL;DR

The paper evaluates the high-contrast imaging capabilities of the Keck Planet Imager and Characterizer (KPIC), demonstrating its sensitivity and performance in detecting faint exoplanets close to their host stars over four years of on-sky data.

Contribution

This work provides the first comprehensive on-sky sensitivity measurements of KPIC, highlighting its ability to reach extreme contrasts and identifying key noise sources affecting performance.

Findings

KPIC achieves contrasts of 1.3e-4 at 90 mas and 9.2e-6 at 420 mas.

KPIC can detect planets within the inner working angle of other high-contrast instruments.

Performance is close to the photon noise limit after mitigation of systematic noise.

Abstract

The Keck Planet Imager and Characterizer (KPIC), a series of upgrades to the Keck II Adaptive Optics System and Instrument Suite, aims to demonstrate high-resolution spectroscopy of faint exoplanets that are spatially resolved from their host stars. In this paper, we measure KPIC's sensitivity to companions as a function of separation (i.e., the contrast curve) using on-sky data collected over four years of operation. We show that KPIC is able to reach contrasts of $1.3 \times 10^{-4}$ at 90 mas and $9.2 \times 10^{-6}$ at 420 mas separation from the star, and that KPIC can reach planet-level sensitivities at angular separations within the inner working angle of coronagraphic instruments such as GPI and SPHERE. KPIC is also able to achieve more extreme contrasts than other medium-/high-resolution spectrographs that are not as optimized for high-contrast performance. We decompose the KPIC performance budget into individual noise terms and discuss limiting factors. The fringing that results from combining a high-contrast imaging system with a high-resolution spectrograph is identified as an important source of systematic noise. After mitigation and correction, KPIC is able to reach within a factor of 2 of the photon noise limit at separations < 200 mas. At large separations, KPIC is limited by the background noise performance of NIRSPEC.