Instrument Requirements

These design pressures drive ZShooter’s technical trades. The science team will continue to evaluate exact numbers throughout instrument design as technical trades arise. Here we capture design pressures clearly to show what capabilities the instrument is trying to protect.

Read this table as design point, rather than a frozen baseline.

Capability	Design point	Why	Science cases effectively lost without it
Spectral coverage	310-2480 nm in one visit through six science channels	One-shot optical-IR leverage is the whole point for a large fraction of the target set.	Kilonovae, TDEs, high-z SNe, solar system targets, broad-band transient follow-up
Nominal resolution	About R = 18k with a 0.7” slit	Keeps RV, abundance, and line-profile work alive without giving up workhorse throughput.	Binaries, primordial D/H, polluted white dwarfs, CGM / IGM absorption, detailed stellar work
Higher-resolution path	Narrower-slit (penalty-free with AO-enhancement)	Much of the instrument’s long-term value sits in not painting ourselves into a low-R corner.	D/H, lensed systems, future HIRES-replacement use, line-profile science
Lower-resolution path	Nominal or wider slit (narrow w/AO-enhanced) with a mix of on-chip and digital binning (5-20x total)	Rapid transient classification often needs only broad spectral classification	Faint TOO followup
Slit length	10 arcsec baseline	Gives room for sky subtraction, nodding strategy, and practical real-world acquisition.	Nebular SNe, solar system, binaries, faint point-source spectroscopy
Rapid response	Always-online on K1 RNAS with a low-overhead observing path; latency budget 5-min	Fast temporal-event science does not forgive slow setup.	Kilonovae, GRBs, LFBOTs, young SNe, early TDEs
Detector format	2k x 2k active area per science channel	Simplifies the instrument, removes mosaics from the baseline, and lowers maintenance pain.	Broadly everything; this is mostly about buildability and operational sanity
Imaging support	Simultaneous tri-band optical imaging, with final (1-3’) field still under active trade	Acquisition support, environmental context, fallback photometry, and fast-timing science all want this.	Kilonovae, binaries, solar system, very faint transients, context imaging
High-cadence imaging	Millisecond / sub-second with ZImager qCMOS	Some science cases are fundamentally timing-limited, not exposure-limited.	Ultracompacts, occultations, compact binaries, rapid optical variability
Quicklook + calibration support	Near-real-time reduction and usable calibration products are part of the operations plan	Observers need to decide on the fly whether to keep going, stop, or change tack.	ToO triage, faint transients, RV quality control, efficient classical observing

Science & Facility (L1) Requirements

The optical design is driven by five coupled requirements. ZShooter must cover the atmospheric near-UV cutoff through K band, preserve enough resolving power for stellar and circumstellar kinematics, remain sensitive enough for deep spectra after binning to low resolution, support sky subtraction, and avoid operational configurations that would slow ToO response.

The choice of a high native resolving power only pays off if the detectors keep low enough read noise that the spectra can be rebinned later without losing the S/N advantage. Likewise, the choice to keep ZShooter always-online on K1 RNAS only pays off if ZFront, ZImager, ZSpec, and the guide/WFS interface do not create a hidden acquisition or calibration bottleneck.

The design is optimized for dynamic range in spectral information: enough native resolution that stellar, CSM, absorber, and abundance programs are not compromised, and low enough detector/read-noise penalty that R≈1000 products remain efficient for faint transients. Moreover the use of

low/zero-noise detector technologies is expected to further mitigate the noise penalty

from high binning factors.

Subsystem (L2) Requirements

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Detailed (L3) Requirements

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