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arXiv · 2509.07138

An on-sky investigation into factors limiting the performance of Keck-NIRC2 for conducting infrared high-contrast imaging

Rachel Bowens-Rubin·Maïssa Salama·Jayke S. Nguyen·William Thompson·Philip Hinz
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Abstract

The most common instrument used by the exoplanet/brown dwarf direct imaging community at the W.M. Keck Observatory is currently the NIRC2 near-infrared imager. We performed on-sky testing to investigate three effects which may be limiting the performance of NIRC2 when conducting high-contrast imaging observations from $3-5\mu$m. First, we report the measurements of an on-sky test of the throughput of the L/M vector vortex coronagraph. We quantify the throughput and additional background flux penalties, noting that the performance effects of using the vector vortex coronagraph in the Ms-filter are greater than in the Lp-filter. Second, we utilize the recently commissioned NIRC2 electronics upgrade to measure the sky variability at sub-second speeds. We find that the background varies at timescales of less than 30s, indicating that the electronics upgrade may open an opportunity to improve the sky-background subtraction of future surveys. Third, we document the contribution of the image derotator to the spatial non-uniformity in the background flux. We conclude by giving a set of recommendations of how the Keck-NIRC2 high-contrast imaging community can adapt their observing strategies to improve the sensitivity of future surveys.

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Rachel Bowens-Rubin, Maïssa Salama, Jayke S. Nguyen, William Thompson, Philip Hinz. 2025-09-08. An on-sky investigation into factors limiting the performance of Keck-NIRC2 for conducting infrared high-contrast imaging. https://doi.org/10.1117/12.3018160

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