CaltechAUTHORS
Published August 13, 2025 | Version Published
Journal Article Metadata-only

Fringing analysis and forward modeling of Keck Planet Imager and Characterizer (KPIC) spectra

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon University of California, San Diego
  • 3. ROR icon Northwestern University
  • 4. ROR icon University of California, Los Angeles
  • 5. ROR icon Jet Propulsion Lab
  • 6. ROR icon UK Astronomy Technology Centre
  • 7. ROR icon W.M. Keck Observatory
  • 8. ROR icon University of California, Santa Cruz
  • 9. ROR icon Pomona College
  • 10. ROR icon The Ohio State University

Abstract

Keck Planet Imager and Characterizer (KPIC) combines high-contrast imaging with high-resolution spectroscopy (R∼35,000 in K band) to study directly imaged exoplanets and brown dwarfs in unprecedented detail. KPIC aims to spectrally characterize substellar companions through measurements of planetary radial velocities, spins, and atmospheric composition. The dominant source of systematic noise for KPIC was fringing or oscillations in the spectrum as a function of wavelength. The fringing signal could dominate residuals by up to 10% of the continuum for high S/N exposures, preventing accurate wavelength calibration, retrieval of atmospheric parameters, and detection of planets with flux ratios less than 1% of the host star. To combat contamination from fringing, we identified its three unique sources and adopted a physically informed model of Fabry–Pérot cavities to apply to post-processed data. We find that this strategy can effectively model fringing in observations of A0V/F0V stars, reducing the residual systematics caused by fringing by a factor of 2. Beyond modeling the fringing signal, we wedged two of the transmissive optics internal to KPIC to eliminate two of the three sources of fringing and confirmed the third source as the entrance window to the spectrograph NIRSPEC. When applied to new data taken with the wedged optics, our previous model of the Fabry–Pérot cavity reduced the amplitude of the residuals by a factor of 10.

Copyright and License

© 2025 Society of Photo-Optical Instrumentation Engineers (SPIE).

Acknowledgement

K.H. is supported by the National Science Foundation Graduate Research Fellowship Program (Grant No. 2139433). J.X. is supported by the NASA Future Investigators in NASA Earth and Space Science and Technology (FINESST) (Grant No. 80NSSC23K1434). Funding for KPIC has been provided by the California Institute of Technology, the Jet Propulsion Laboratory, the Heising-Simons Foundation (Grant Nos. 2015-129, 2017-318, 2019-1312, and 2023-4598), the Simons Foundation, and the NSF (Grant No. AST-1611623). An earlier version of this work was presented in the Proceedings of SPIE.46

The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We also wish to recognize the very important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain, and K.H. wishes to acknowledge that the astronomical observations in this paper were only possible because of the dispossession of Maunakea from the Kanāka Maoli.

Funding

K.H. is supported by the National Science Foundation Graduate Research Fellowship Program (Grant No. 2139433). J.X. is supported by the NASA Future Investigators in NASA Earth and Space Science and Technology (FINESST) (Grant No. 80NSSC23K1434). Funding for KPIC has been provided by the California Institute of Technology, the Jet Propulsion Laboratory, the Heising-Simons Foundation (Grant Nos. 2015-129, 2017-318, 2019-1312, and 2023-4598), the Simons Foundation, and the NSF (Grant No. AST-1611623). An earlier version of this work was presented in the Proceedings of SPIE.

Additional details

Related works

Is new version of
Journal Article: 10.1117/12.3018020 (DOI)
Discussion Paper: arXiv:2408.10173 (arXiv)

Funding

National Science Foundation Graduate Research Fellowship Program
2139433
National Aeronautics and Space Administration
80NSSC23K1434
California Institute of Technology
Jet Propulsion Laboratory
Heising-Simons Foundation
2015-129
Heising-Simons Foundation
2017-318
Heising-Simons Foundation
2019-1312
Heising-Simons Foundation
2023-4598
Simons Foundation
National Science Foundation
AST-1611623
W. M. Keck Foundation

Dates

Accepted
2025-07-30

Caltech Custom Metadata

Caltech groups
Astronomy Department, Division of Geological and Planetary Sciences (GPS), Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published