L2 — Instrument requirements

The L2 requirements allocate instrument capabilities and performance across eight categories. Quantities still marked TBD or TBC in the requirements workbook remain open allocations.

Spectroscopy

ZSpec must provide overlapping channel boundaries for spectral stitching, with gaps confined to permitted atmospheric intervals. The resolving-power requirements are a mean R≥18,000 with a 0.7″ slit in median natural seeing and R≥40,000 with a 0.3″ slit under supported seeing enhancement. Internal image quality is specified by an EE80 diameter ≤0.3″. Spectral and spatial sampling, slit selection, trace separation, readout modes, throughput, detector and thermal backgrounds, and OH-line scatter complete the spectroscopic allocations.

Imaging

ZImager must support simultaneous u, z, and a selectable intermediate band over at least 4 square arcminutes. Changing the intermediate filter must preserve acquisition and fixed-band imaging. A 0.15″ image must span at least 2.5 pixels, with high-speed read noise ≤0.3 electrons RMS per pixel per frame. The requirements also cover throughput, image quality, calibratable response, and user-selectable full-frame and subarray exposure modes.

Field, acquisition, and tracking

ZImager, the slit viewers, and the spectrograph apertures require calibrated coordinate transforms across a 30″ common field. Slit-viewing cameras interface with MAGIQ for fine acquisition. ZSpec must support slit-relative offsets of at least 1.5″ in all directions, field de-rotation, facility guiding and focus feedback, and acquisition and observation at WMKO-supported non-sidereal rates.

Overhead time

The overhead allocations cover instrument readiness, prepared-ToO calibrations, changes among science, calibration, and neighboring-instrument light paths, and target acquisition. Acquisition budgets distinguish direct slit placement from acquisition using ZImager. The numerical time allocations remain marked TBC in the workbook.

Calibration system and products

The internal calibration system sits upstream of the ZImager/ZSpec light-path selection. It illuminates the noddable spectroscopic field on every imager detector and spectrograph slit and provides an on-axis point source. Engineering calibrations must be possible with dome lights on; science calibrations must be possible during daytime with the dome closed and lights off. Wavelength accuracy, flat-field uniformity, illumination brightness, and reproducible spectrograph configurations support reusable calibrations. Spectroscopic standards and imaging zero points establish a common relative flux scale and absolute normalization.

Data and archive

The pipeline and Keck Observatory Archive receive raw data, calibration products, and associated metadata. Standard ZSpec products are optimally extracted, sky-subtracted spectra with wavelength and relative-flux calibration and identified OH contamination. Standard ZImager products are WCS-calibrated images, aperture photometry, and time-series light curves. Standard reduced products are required within two minutes of input availability; quicklook processing within five seconds. A standalone package supports local science-ready reduction.

The requirements also cover cross-channel flux calibration, sky and telluric correction, statistically optimal rejection or down-weighting of contaminated samples, exposure timing, ToO script and alert interfaces, and a common version-controlled simulation model for spectroscopy and imaging.

Instrument control software

The control system provides remote commands, status, configuration, sequencing, and acquisition through a unified interface for one-person remote operation. It accepts observatory target coordinates, program identifiers, non-sidereal rates, and prepared configurations or sequences. Laboratory, independent-subsystem, degraded, and simulated-device operation are required. Hazard detection, safe states, inhibited unsafe commands, operator diagnostics, engineering APIs and tools, and time-correlated logs support operation and maintenance.

Interface and operational

The instrument must meet the approved observatory interfaces, tracking and environmental envelopes, and allocations for volume, mass, power, glycol, compressed air, and networking. Requirements cover heat removal and other emissions, qualification for the environments each component encounters, and recoverable facility-service interruptions. Installation, routine servicing at RNAS, module exchange, spares, tools, drawings, procedures, and engineering notebooks support maintenance. Hazard control and the observatory’s three seismic cases define personnel and equipment protection.