Increasing science yield with a twilight observing program with the SCALES instrument at Keck

Isabel J. Kain; Carlos Alvarez; John M. O'Meara; Marc Kassis; Peter Wizinowich; Antonin Bouchez; Jim Lyke; Randy Campbell; Avinash Surendran; Imke de Pater; Katherine de Kleer; Ned Molter; Erin Redwing; Rosalie McGurk; Steph Sallum; Andrew Skemer

arXiv · 2509.13143

Increasing science yield with a twilight observing program with the SCALES instrument at Keck

Isabel J. Kain·Carlos Alvarez·John M. O'Meara·Marc Kassis·Peter Wizinowich·Antonin Bouchez·Jim Lyke·Randy Campbell·Avinash Surendran·Imke de Pater·Katherine de Kleer·Ned Molter·Erin Redwing·Rosalie McGurk·Steph Sallum·Andrew Skemer

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Abstract

While astronomical twilight closes the observing window for optical astronomers, the infrared sky remains dark even through sunrise, allowing IR astronomers to observe through twilight. The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument is a 2-5 micron coronagraphic integral field spectrograph scheduled to arrive at Keck in early 2026. SCALES has the potential to execute exciting science and support the astronomical community and upcoming NASA missions through a dedicated cadenced twilight observing program. We estimate that the current twilight observing program on Keck conducts 18+-1 hours per year of science observations; a facilitized twilight observing program that is prioritized by the observatory could yield 151+-2 hours of science time per year. This work presents the scientific motivation and high-level feasibility of two primary SCALES twilight science cases, monitoring of Solar System objects and a high-contrast imaging search for exoplanets around bright nearby stars, taking lessons from the existing NIRC2 and OSIRIS Twilight Zone program and considering increases in program scope. We also consider technical and operational challenges to overcome before the SCALES instrument begins its twilight observing program.

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Isabel J. Kain, Carlos Alvarez, John M. O'Meara, Marc Kassis, Peter Wizinowich, Antonin Bouchez, Jim Lyke, Randy Campbell, Avinash Surendran, Imke de Pater, Katherine de Kleer, Ned Molter, Erin Redwing, Rosalie McGurk, Steph Sallum, Andrew Skemer. 2025-09-16. Increasing science yield with a twilight observing program with the SCALES instrument at Keck. https://arxiv.org/abs/2509.13143

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