Linearity tests¶
Mode: | Linearity tests |
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Usage: | Offline |
Key: | MEGARA_LINEARITY_TEST |
Product: | |
Recipe: | LinearityTestRecipe |
Recipe input: | LinearityTestRecipeInput |
Recipe result: | LinearityTestRecipeResult |
Although the linearity of the MEGARA CCD are well characterized at the LICA lab already, it might be advisable to generate linearity test frames both as part of the AIV activities and after changes in the MEGARA DAS.
The MEGARA e2V 231-84 CCD offers a full-well capacity of 350,000 ke-. Linearity tests carried out in instruments already using this type of CCD indicate a linearity better than ±0.4% at 100 kpix/sec in the range between 140 to 40,000 e- (Reiss et al. 2009 for MUSE@VLT). Given these good linearity results (up to 40,000 e-) and considering the fact that at the spectral resolutions of MEGARA we will rarely reach those signals from astronomical targets linearity can be considered negligible. Despite these facts, it is advisable to carry out this kind of tests both at the lab and at the telescope on the MEGARA CCD itself.
While Linearity tests will be generated as part of the characterization activities at the lab, the use of the ICM would also allow carrying them out as part of AIV activities and routinely as part of the “System Calibration Modes”. Therefore, we define here an observing mode that the observatory staff could use to generate updated Linearity tests should these be needed.
In the case of fiber-fed spectrographs the fiber flats (either lamp or twilight flats) are not optimal for carrying out Linearity tests as these leave many regions in the CCD not exposed to light. The whole CCD should be illuminated at different intensity levels in order for properly carrying out these tests.
Requirements¶
In the case of MEGARA we will offset the pseudo-slit from its optical focus position to ensure that the gaps between fibers are also illuminated when a continuum (halogen) lamp at the ICM is used. The NSC zemax model of the spectrograph indicates that by offsetting 3mm the pseudo-slit we would already obtain a homogenous illumination of the CCD. A series of images with different count levels would be obtained.
This mode requires having the ICM halogen lamp on, the instrument shutter open, to move the pseudo-slit to the open position, to configure the VPH wheel mechanism in order to select the grating to be used, to move the focusing mechanism to the position pre-defined for the specific VPH of choice and to expose a certain time and to readout the detector a series of exposures, being this series the slit-flat image set. Note that the Linearity test will be done using only one spectral setup as this is independent of the VPH of use. The specific choice for the VPH will depend on the actual color of the ICM halogen lamp and on the actual response of the VPHs. In principle, we should choose the VPH at the peak of the lamp spectral energy distribution but we
Procedure¶
Products¶
This Linearity-test observing mode will be used only sporadically as it is considered part of the “System Calibration Modes”.
Recipe, inputs and results¶
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class
megaradrp.recipes.calibration.linearity.
LinearityTestRecipe
(*args, **kwds)¶ Process LINTEST images and create LINEARITY_CORRECTON.
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class
MegaraBaseRecipeInput
(*args, **kwds)¶ MegaraBaseRecipeInput documentation.
Attributes
obresult (ObservationResultType, requirement) Observation Result
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class
LinearityTestRecipe.
MegaraBaseRecipeResult
(*args, **kwds)¶ MegaraBaseRecipeResult documentation.
Attributes
qc (QualityControlProduct, product)
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LinearityTestRecipe.
RecipeInput
¶ alias of
MegaraBaseRecipeInput
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LinearityTestRecipe.
RecipeResult
¶ alias of
MegaraBaseRecipeResult
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class