Vortex Fiber Nulling (VFN) is a technique for suppressing starlight to observe exoplanets at small angular separations from their star, ≲ 1λ/D. This technique may enable the discovery and characterization of young giant planets at separations smaller than conventional coronagraphs can reach. A VFN mode was deployed to the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck II telescope in February 2022 and is now operational on-sky. This marks the first on-sky demonstration of VFN. The mode has achieved on-sky starlight rejection of ⪅ 1 × 10−2 in K-band and is primarily limited by residual wavefront error from the adaptive optics system. The current VFN performance enables KPIC to efficiently search for new companions at separations of 20 to 80 mas from their host star whereas the alternative observing mode requires precise, prior knowledge of the companion position. Here we present the latest results from the KPIC VFN mode. We also present the predicted performance improvement from an upcoming upgrade to switch the current charge two vortex mask with a new charge one which can target smaller separations and will double the planet throughput.
Psisim is a software suite that acts as a high-level simulation tool for the development and characterization of instrument performance in stellar and substellar observations. Psisim is capable of modeling science yields, generating simulated spectra, and acting as an exposure time calculator. Its modular framework allows for implementation of various instruments, including imagers and spectrographs. Currently models exist for KPIC, MODHIS, GPI, HISPEC, PSI-Blue and PSI-Red. One of the larger functionalities of psisim is the simulation of exoplanet observations behind adaptive optics systems. Utilizing instrument characteristics, such as Strehl ratio, throughput, etc., and pulling from models generated on the fly or from various common atmospheric grids, psisim is able to return simulated spectra and separate noise components from sky, photon, and thermal sources. We are then able to evaluate instrument performance and perform simulated science programs. We have recently upgraded psisim with a module for observations in polarized light. Manipulation of instrumental Mueller matrices mimics the effect optical components have on incoming light. Inversion of the instrumental Mueller matrices enables recovery of desired Stokes parameters, along with associated observational noise. Here we will provide an overview of psisim, highlighting key features and its adaptability for use with new instruments. We’ll demonstrate how psisim simulates observation with an example, describe a few use cases where it has proved useful, and provide some preliminary results of spectro-polarimetric observations using the new polarimetry mode.
Vortex fiber nulling (VFN) is a single-aperture interferometric technique for detecting and characterizing exoplanets separated from their host star by less than a diffracted beam width. VFN uses a vortex mask and single-mode fiber to selectively reject starlight while coupling off-axis planet light with a simple optical design that can be readily implemented on existing direct imaging instruments that can feed light to an optical fiber. With its axially symmetric coupling region peaking within the inner working angle of conventional coronagraphs, VFN is more efficient at detecting new companions at small separations than conventional direct imaging, thereby increasing the yield of on-going exoplanet search campaigns. We deployed a VFN mode operating in K band (2.0 to 2.5 μm) on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck II Telescope. We present the instrument design of this first on-sky demonstration of VFN and the results from on-sky commissioning, including planet and star throughput measurements and predicted flux-ratio detection limits for close-in companions. The instrument performance is shown to be sufficient for detecting a companion 103 times fainter than a fifth magnitude host star in 1 h at a separation of 50 mas (1.1 λ / D). This makes the instrument capable of efficiently detecting substellar companions around young stars. We also discuss several routes for improvement that will reduce the required integration time for a detection by a factor >3.
The High-resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC) is a diffraction limited, single-mode fiber fed spectrograph with R < 100, 000 in design for the Keck II telescope. It will also serve as part of the first light Multi-Object Diffraction-limited High-resolution Infrared Spectrograph (MODHIS) facility for the Thirty Meter Telescope (TMT). HISPEC will simultaneously observe from the y to K bands to explore transiting, non-transiting, and high-contrast sub-stellar companions, in addition to non-planetary science. For high-contrast planetary targets near the diffraction-limit, we perform echelle simulations using the latest HISPEC optical designs to model system performance with respect to anticipated scientific yields. Starting from the optical model, we propagate light through the system to generate a full-frame simulated echelle image. Noise sources are handled using modifications of existing software packages, including Pyechelle for optical aberrations and photon noise, our own PSISIM package for astrophysical, background, and throughput noise sources, and HxRG Noise Generator for detector noise. These simulated echelle images will serve as a test bed for the HISPEC data reduction pipeline in development from the existing Keck Planetary Imager and Characterizer (KPIC) instrument pipeline, a platform for trade studies in instrument design, and a validation of exoplanetary science goals in the high-contrast regime.
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