Slit-flat

Mode:

Slit-flat

Usage:

Offline, Online

Key:

MegaraSlitFlat

Product:

MasterSlitFlat

Recipe:

SlitFlatRecipe

Recipe input:

SlitFlatRecipeInput

Recipe result:

SlitFlatRecipeResult

In the case of fiber-fed spectrographs the correction for the detector pixel-to-pixel variation of the sensibility is usually carried out using data from laboratory, where the change in efficiency of the detector at different wavelengths is computed and then used to correct for this effect for each specific instrument configuration (VPH setup in the case of MEGARA).

Requeriments

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.

The quality of present-day CCDs leads to a rather small impact of these pixel-to-pixel variations in sensitivity on either the flux calibration and the cosmetics of the scientific images, especially considering that not one but a number of pixels along the spatial direction are extracted for each fiber and at each wavelength. Therefore, we anticipate that this correction might not be needed or that, as a maximum, a first-order correction based on laboratory data might suffice. However, before the results of the analysis of the pixel-to-pixel variations in sensitivity planned using our CCD230 e2V test CCD are obtained we will consider this observing mode as TBC.

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 but offset by 3mm and to expose a certain time and to readout the detector a series of exposures, being this series the slit-flat image set.

Procedure

The “User” processes an observing block obtained in the observing mode Slit-flat. This mode includes the required actions to obtain a master slit-flat field. The master slit-flat field generated is used in other stages of the data processing.

Products

Slit-flat image sets are to be obtained both as part of the activities related to the verification of the instrument status (such as for evaluating the status of the MEGARA spectrograph) and also for processing data for scientific exploitation (correction for the pixel-to-pixel variation in sensitivity). The frequency at which these detector flat images should be acquired is TBC. Although defined in this document as a mode to be considered part of the “Daily Calibration Modes” if it is finally used only sporadic it should be considered as part of the “System Calibration Modes” instead.

A bidimensional master slit flat field, QA flag, a text log file of the processing and a structured text file containing information about the processing.

Recipe, inputs and results

class megaradrp.recipes.calibration.slitflat.SlitFlatRecipe(*args, **kwargs)

Process SLIT_FLAT images and create MasterSlitFlat.

RecipeInput

alias of SlitFlatRecipeInput

RecipeResult

alias of SlitFlatRecipeResult

class SlitFlatRecipeInput(*args, **kwds)

SlitFlatRecipeInput documentation.

Attributes:

master_biasMasterBias, requirement

Master BIAS image

master_bpmMasterBPM, requirement, optional

Master Bad Pixel Mask

master_darkMasterDark, requirement, optional

Master DARK image

obresultObservationResultType, requirement

Observation Result

class SlitFlatRecipeResult(*args, **kwds)

SlitFlatRecipeResult documentation.

Attributes:

master_slitflatMasterSlitFlat, product

reduced_imageProcessedFrame, product

set_base_headers(hdr)

Set metadata in FITS headers.