NICMOS DQE Adjustment
pysynphot countrate calculations for NICMOS must be adjusted by a relative DQE correction factor. The “raw” countrate values reported in the ETC output have already been adjusted by this factor.
This value is a function of wavelength (w) and detector temperature (T) and is calculated relative to a base wavelength wb and temperature Tb. In imaging modes of the ETC, the effective wavelength is used. In spectroscopy, the actual wavelength is used.
The formula used does not have a term for the wavelength. There are coefficient values supplied at two different wavelengths for each detector. The DQE correction factor is calculated at each of the supplied wavelengths and then the final value is linearly interpolated or extrapolated from those values.
The basic formula for this calculation is:
Where:
|
Detector |
Tb |
wb |
ao |
a1 |
a2 |
|
NIC1 |
61.33 |
1.1μm |
3.9455511 |
-186.70592 |
103.90907 |
|
|
|
1.6μm |
2.6654824 |
-63.895348 |
-2559.7390 |
|
NIC2 |
61.33 |
1.1μm |
3.5951707 |
-175.70822 |
797.29513 |
|
|
|
1.6μm |
2.6047840 |
-80.939203 |
-1247.3214 |
|
NIC3 |
61.99 |
1.1μm |
3.4162172 |
-109.427348 |
-2660.3730 |
|
|
|
2.2μm |
1.3069482 |
39.966863 |
-3721.5676 |