Capabilities
The table and plots below document the main characteristics of 4MOST.
Parameter | Design value | ||||||||||||||
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Field of view | Shape: hexagonal Size: 4.2 deg2 Diameter: 2.5 deg |
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Accessible sky (zenith angle < 55°) | 30,000 deg2 | ||||||||||||||
Multiplex fibre positioner | 2436 | ||||||||||||||
On-sky fibre aperture | Shape: circular Size: 1.65 arcsec2 Diameter: 1.45 arcsec |
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Minimum distance between fibres | 15 arcsec | ||||||||||||||
Expected on-target fibre-hours per year | LRS: 3.2 Mh/yr HRS: 1.6 Mh/yr |
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Overheads | 3.5 min for the field acquisition (telescope preset), 4.4 min for each science exposure including attached calibrations | ||||||||||||||
Detectors | Readout noise: < 2.3 e- Readout modes: normal (100 kHz), fast (400 kHz) Binning modes (cross-dispersion × spectral): 1×1, 2×1, 1×2, 2×2, 1×4 |
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Low-resolution spectrographs | |||||||||||||||
Multiplex | 812 (× 2) | ||||||||||||||
Wavelength range | 370 – 950 nm | ||||||||||||||
Spectral resolving power | 4000 – 7700 (see figure below) | ||||||||||||||
Spectral sampling | ≥ 2.5 pixel/FWHM | ||||||||||||||
Radial velocity accuracy | < 1 km/s | ||||||||||||||
Sensitivity | Limiting AB magnitudes for S/N = 10 Å-1, 6 × 20 min exposures, mean seeing, new moon (also see figure below):
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High-resolution spectrograph | |||||||||||||||
Multiplex | 812 | ||||||||||||||
Wavelength range | 392.6 – 435.5, 516 – 573, 610 – 679 nm | ||||||||||||||
Spectral resolving power | 18,000 – 21,000 (see figure below) | ||||||||||||||
Spectral sampling | ≥ 2.5 pixel/FWHM | ||||||||||||||
Radial velocity accuracy | < 1 km/s | ||||||||||||||
Sensitivity | Limiting AB magnitudes for S/N = 100 Å-1, 6 × 20 min exposures, mean seeing, 80% moon (also see figure below):
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