General ETC

We have several versions of the KCWI blue ETC available. It will calculate S/N for a given slicer, grating, type of object (point or extended), and object wavelength. The data used for this simulator is laboratory calibrations, updated with on-sky performance data in April-May 2017.

The on-line blue Python package is implemented at Blue online.

We have a new IDL version of a KCWI red ETC available. Similarly to the blue (below), it will calculate the simulated S/N for a given slicer, grating, object type, and object wavelength. The throughputs used for this are SIMULATED, and will be updated once we have on-sky data.

RED ETC version

IDL version

The original IDL version of the exposure time calculator is available here . More details of how to run the pipeline are listed below. Contact kcwi_info **_@_** keck.hawaii.edu for help.

Please be aware that both the blue and red IDL versions run via with a base program called "ketc.pro". Please make sure you run this from the red ETC directory and ".r ketc.pro" to use the red ETC, not the blue ketc.

The Red ETC runs identically to the Blue ETC, so see the blue example commands below. A sample Red start command for a S/N curve with the Medium Slicer, RL grating, peak wavelength 6563, seeing 0.75", 600 sec integration time, 2x2 binning, emission line flux as specified, is:
IDL> kcrm_etc,'M','RL',6563,0,0.75,600,'2x2',flux=1e-17
The command 'kcrm_etc,/h` will show the help info.

IMPORTANT NOTE: The generation of postscript files is currently not working unless you have a private copy of the appropriate library (PS_START), which has been retired from the coyote package.

BLUE ETC versions

Online Python Version

The Python version of the Blue ETC has been implemented for online use here.

Package Python Version

A downloadable Python version of the Blue ETC (and other Keck instrument ETCs) is here.

The Medium slicer setting does not work. We are working on it. In etc_kcwi.py, search for "0.69,seeing" and put it in brackets to make it work for you: "[0.69,seeing]".

IDL Version

The original IDL version of the exposure time calculator is available here . More details of how to run the pipeline are listed below. Contact kcwi_info **_@_** keck.hawaii.edu for help.

IMPORTANT NOTE: The generation of postscript files is currently not working unless you have a private copy of the appropriate library (PS_START), which has been retired from the coyote package.

Examples of IDL SNR Calculations

1. Point source
IDL> ketc, 'S', 'BL', 4500., 0.,0.75,3600.,'1x1',mag_AB=23.,plotout='mag_AB-23.0_a0.0_S_BL_0.75_3600_1x1'
f_lam ~ lam^      0.00000
reference wavelength =      4500.00
SLICER: S
GRATING: BL
SEEING:      0.750000 arcsec
Å/pixel:     0.625000
spectral pixels in 1 spectral resolution element =        2
Å/resolution element:      1.25000
Å/SNR bin:      1.25000
Pixels/Spectral SNR bin:      2.00000
SNR Spatial Bin [arcsec^2]:     0.562500
SNR Spatial Bin [pixels^2]:       14.5773
OBJECT mag:      23.0000 mag_AB

2.Point source 22AB Small slicer, BM grating
IDL> ketc, 'S', 'BM', 4500., 0.,0.75,3600.,'1x1',mag_AB=22.,plotout='mag_AB-22.0_a0.0_S_BM_0.75_3600_1x1'
f_lam ~ lam^      0.00000
reference wavelength =      4500.00
SLICER: S
GRATING: BM
SEEING:      0.750000 arcsec
Å/pixel:     0.280000
spectral pixels in 1 spectral resolution element =        2
Å/resolution element:     0.560000
Å/SNR bin:     0.560000
Pixels/Spectral SNR bin:      2.00000
SNR Spatial Bin [arcsec^2]:      0.562500
SNR Spatial Bin [pixels^2]:       14.5773
OBJECT mag:      22.0000 mag_AB
etc2

3. point source 20AB, Small slicer, BH2 grating
IDL> ketc, 'S', 'BH2', 4500., 0.,0.75,3600.,'1x1',mag_AB=20.,plotout='mag_AB-20.0_a0.0_S_BH2_0.75_3600_1x1'
% Compiled module: KETC.
f_lam ~ lam^      0.00000
reference wavelength =      4500.00
SLICER: S
GRATING: BH2
SEEING:      0.750000 arcsec
Å/pixel:     0.125000
spectral pixels in 1 spectral resolution element =        2
Å/resolution element:     0.250000
Å/SNR bin:     0.250000
Pixels/Spectral SNR bin:      2.00000
SNR Spatial Bin [arcsec^2]:      0.562500
SNR Spatial Bin [pixels^2]:       14.5773
OBJECT mag:      20.0000 mag_AB
àREAD NOISE BECOMING COMPARABLE TO SKY NOISE. 1x2 BINNING NOT YET IMPLEMENTED.
etc3

5. Extended object, flux=1e-17 erg cm^-2 s^-1 arcsec^-2, emission line with linewidth=10Å, Large slicer, BL grating, 3600 s, 2” x 2” bins.

IDL> ketc, 'L', 'BL', 4500., 0.,0.75,3600.,
flux=1.e-17,'2x2',emline_width=10.,spatial_bin=[2.,2.],
plotout='f1e-17_emw10_L_BL_0.75_3600_1x1'

f_lam ~ lam^      0.00000
reference wavelength =      4500.00
SLICER: L
GRATING: BL
SEEING:      0.750000 arcsec
Å/pixel:     0.625000
spectral pixels in 1 spectral resolution element =        8
Å/resolution element:      5.00000
Å/SNR bin:      5.00000
Pixels/Spectral SNR bin:      8.00000
SNR Spatial Bin [arcsec^2]:       4.00000
SNR Spatial Bin [pixels^2]:       10.0781
OBJECT Flux   1.00000e-17 erg cm^-2 s^-1 in 10.0 Å
EMISSION LINE OBJECT --> flux is not per unit Å
etc4

6. Same as #5 with Nod-and-shuffle.

IDL> ketc, 'L', 'BL', 4500., 0.,0.75,3600.,flux=1.e-17,'2x2',emline_width=10.,spatial_bin=[2.,2.],
plotout='f1e-17_emw10_L_BL_0.75_3600_1x1_NAS',nas=120.