The Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory consists of a series of upgrades to the Keck II Adaptive Optics system and the NIRSPEC spectrograph to enable diffraction-limited, high-resolution (R∼35, 000) spectroscopy, originally in the K (∼2.0−2.5 μm) and L (∼3.2−3.7 μm) bands only. Phase I consisted of single-mode fiber injection/extraction units used in conjunction with an H band pyramid wavefront sensor. Using single-mode fibers provides a gain in stellar rejection, a substantial reduction in sky background, and a stable, well-defined line-spread function on the spectrograph. In 2022, Phase II brought a 1000-actuator deformable mirror, beam-shaping optics, a vortex fiber nulling mode, and more.
In this paper we present the results of the latest upgrades to the KPIC instrument. Among these upgrades, a second fiber bundle with related injection/extraction optics and new dichroics were added to extend KPIC’s science capabilities to y through H band, and to provide access to laser frequency combs for spectral calibration from y-K. Additionally, the charge 2 vortex mask for fiber nulling was supplemented with a charge 1 mask to enable spectroscopy of low mass companions at very small angular separations. Other upgrades included an atmospheric dispersion corrector, a new calibration source switching system, and an optimized tip/tilt control system. Here we show preliminary results of on-sky tests performed in the first few months of re-commissioning, along with the next steps for the instrument.
HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is an infrared (0.98 to 2.46 microns) cross-dispersed, R=100,000 single-mode fiber-fed diffraction-limited echellette spectrograph for the Keck II telescope’s adaptive optics (AO) system. MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph) shares similar specifications as HISPEC while being optimized for TMT’s first-light AO system NFIRAOS. Keck-HISPEC, currently in full-scale development and slated for first light in 2026, and TMTMODHIS, currently in conceptual design phase, will provide increasingly compelling science capabilities from exoplanet atmosphere characterization through both transit and direct high-contrast spectroscopy, to detection and mass measurements through infrared precision radial velocity (RV). The science cases include the precise RV measurements of stars orbiting the Galactic Center, Solar System studies, and the chemodynamical history of nearby dwarf galaxies and the galactic halo.
The High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC) is a new instrument for the W. M. Keck Observatory that enables R∼100,000 spectroscopy simultaneously across the y, J, H, and K astronomical bands (0.98-2.5 μm). The fiber delivery subsystem of HISPEC is responsible for routing science and calibration light throughout the observatory efficiently. It consists of high-performance single mode fibers, a photonic lantern, mechanical and MEMS-based fiber switchers that allow for the reconfiguration of light paths. To efficiently cover this large wavelength range, a silica fiber is used for the y&J bands and the 1×3 photonic lantern while a ZBLAN fiber is used for the H&K bands. The HK fiber is a custom design by Le Verre Fluore. The fibers route the science light from the focal point of the adaptive optics system to spectrographs in the basement ∼65 m away, hence, the fibers must be very efficient. To calibrate the instrument, several mechanical fiber switchers can be used to direct calibration light to the spectrograph or the front of the optical train. Some switchers must make over 800 cycles annually, while maintaining sub-3% coupling losses between fibers with core sizes of 4.4 μm. To achieve this, extensive testing was conducted, in which throughput and dust accumulation were monitored to determine how these parameters are impacted by switch preparation procedures and ambient environmental conditions. We developed systems to automatically and remotely clean and image fiber end faces in situ. We have created a protocol that allows us to achieve thousands of switch connections reliably. Additionally, through the 25,000+ switch cycles ran during testing, we identified shortcomings in the design of these mechanical fiber switchers which will be remedied for the final instrument.
Astrophysical research into exoplanets has delivered thousands of confirmed planets orbiting distant stars. These planets span a wide range of size and composition, with diversity also being the hallmark of system configurations, the great majority of which do not resemble our own solar system. Unfortunately, only a handful of the known planets have been characterized spectroscopically thus far, leaving a gaping void in our understanding of planetary formation processes and planetary types. To make progress, astronomers studying exoplanets will need new and innovative technical solutions. Astrophotonics – an emerging field focused on the application of photonic technologies to observational astronomy – provides one promising avenue forward. In this paper we discuss various astrophotonic technologies that could aid in the detection and subsequent characterization of planets and in particular themes leading towards the detection of extraterrestrial life.
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