Preparing an UCLES Proposal

Signal to Noise Calculator

Please use the UCLES Signal to Noise calculator to estimate the exposure time for your observing program.

Gratings

UCLES provide high resolution as set by the slit width and detector used. The spectral resolution is measured as Lambda / delta_Lambda, where delta_Lambda = FWHM of unresolved lines (usually 2 pixels). With the EEV, Rmax ~ 100,000, and with the MITLL, Rmax ~ 80,000. Typically 1 arcsec slit width corresponds to R ~ 45,000. 

The wavelength coverage is set by the choice of grating, where the 31/6 lines/mm grating gives almost continuous wavelength coverage at the bluer wavelengths with a shorter slit length, while the 79 lines/mm grating gives 2.5 times longer slit but less complete wavelength coverage. Both gratings produce almost identical dispersion and resolution, and the primary difference is in the free spectral range and order separation.

Detectors

1. Blue sensitive E2V 2K x 4K (13.5 micro pixels)

Image scale: 0.16 arcsec per spatial pixel

On chip binning in both spatial and spectral direction is possible.

SPEED READ OUT TIME (s) GAIN (e-/ADU) READ OUT NOISE (e-) SATURATION (e-) NON-LINEARITY (ALPHA x10-6)
SLOW 445 (403) 0.37 2.45 (2.3) 24,000 (ADC) 0.14
NORMAL 178 (158) 1.30 3.15 (3.2) 85,000 (ADC) 0.60
FAST 132 (132) 2.80 5.27 (5.35) 183,000 (ADC) 0.78
NONASTRO 89 (74) 6.67 9.74 (9.8) 437,000 (ADC) 1.92

2. Red sensitive MITLL3 2K x 4K (15 micro pixels)

Image scale: 0.18 arcsec per spatial pixel

No binning possible.

SPEED READ OUT TIME (s) GAIN (e-/ADU) READ OUT NOISE (e-) SATURATION (e-) NON-LINEARITY (ALPHA x10-6)
XTRASLOW (936) 0.074 (1.16) 5,000 (ADC) -0.23
SLOW 300 (296) 0.37 1.84 (1.7) 24,000 (ADC) 0.23
NORMAL 163 (154) 1.1 2.38 (2.4) 72,000 (ADC) 0.36
FAST 127 (120) 2.2 3.47 (3.3) 141,000 (ADC) 0.19
NONASTRO 85 (75) 4.5 6.55 (6.3) 178,000 0.02

Notes:
READOUT TIME:
 Lab measurements are given in parentheses.
READOUT NOISE:
 Lab measurements are given in parentheses.

 

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