Twilight fiber-flat

Mode:

Twilight fiber-flat

Usage:

Offline, Online

Key:

MegaraTwilightFlatImage

Product:

MasterTwilightFlat

Recipe:

TwilightFiberFlatRecipe

Recipe input:

megaradrp.recipes.calibration.twilight.RecipeInput

Recipe result:

megaradrp.recipes.calibration.twilight.RecipeResult

Depending on the final performance of the ICM (provided by the GTC) at F-C the twilight fiber-flat mode (proposed in this section) might be offered as optional to the observer or a must should a proper data reduction be required. In any case this must be always available as an observing mode.

The twilight fiber-flat observing mode should include the actions required to calibrate the low-frequency sensitivity variation in the spatial direction of the detector. In principle, the lamp fiber-flat should suffice to correct the change in sensitivity along both the spatial (fiber-to-fiber relative transmission) and the spectral direction of the system. The latter only combined with flux standard-star observations since the spectral shape of the ICM lamps is not known with enough accuracy.

The twilight fiber-flat is based on the observation of the blank twilight sky. This can safely assume to homogeneously illuminate the entire MEGARA field of view (3.5 arcmin x 3.5 arcmin).

Requeriments

The focal plane should be uniformly illuminated with twilight-sky light. As the illumination conditions change during twilight, each image set has a different exposure time. The purpose is to obtain a similar (linear) level of DUs at the detector (counts) under different illumination conditions.

This mode requires having the focal-plane cover configured (at least one of the sides should be open), the instrument shutter open, the telescope tracking, to move the pseudo-slit to that of the instrument mode of choice, 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 take a series of exposures with different exposure times and to readout the detector for this series of exposures, being these series the twilight image set, each with a different exposure time, but with similar level of counts.

Procedure

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

Products

Twilight-sky fiber-flat image sets are expected to be obtained as part of the routine calibration activities performed by the observer since are needed for processing any scientific-valid data. Therefore, this observing mode should be considered as part of the “Daily Calibration Modes”.

A RSS master illumination 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.twilight.RecipeInput(*args, **kwds)

RecipeInput documentation.

Attributes:

continuum_regionListOfType, requirement, optional, default=[1900, 1900]

Subtract this region before normalize the flat-field

extraction_offsetListOfType, requirement, optional, default=[0.0]

Offset traces for extraction

master_aperturesMultiType, requirement

Apertures information for extraction

master_biasMasterBias, requirement

Master BIAS image

master_bpmMasterBPM, requirement, optional

Master Bad Pixel Mask

master_darkMasterDark, requirement, optional

Master DARK image

master_fiberflatMasterFiberFlat, requirement

Master fiber flat calibration

master_slitflatMasterSlitFlat, requirement, optional

Master slit flat calibration

master_wlcalibWavelengthCalibration, requirement

Wavelength calibration table

normalize_regionListOfType, requirement, optional, default=[1900, 2100]

Region used to normalize the flat-field

obresultObservationResultType, requirement

Observation Result

class megaradrp.recipes.calibration.twilight.RecipeResult(*args, **kwds)

RecipeResult documentation.

Attributes:

master_twilightflatMasterTwilightFlat, product

reduced_imageProcessedFrame, product

reduced_rssProcessedRSS, product

class megaradrp.recipes.calibration.twilight.TwilightFiberFlatRecipe(*args, **kwargs)

Process TWILIGHT_FLAT images and create MASTER_TWILIGHT_FLAT product.

This recipe process a set of continuum flat images obtained in Twilight Fiber Flat mode and returns the master twilight flat product The recipe also returns the result of processing the input images up to slitflat correction. and the result RSS of the processing up to wavelength calibration.

See also

megaradrp.types.MasterTwilightFlat

description of MasterTwilightFlat product

Notes

Images provided in obresult are trimmed and corrected from overscan, bad pixel mask (if master_bpm is not None), bias and dark current (if master_dark is not None) and corrected from pixel-to-pixel flat if master_slitflat is not None. Images thus corrected are the stacked using the median.

The result of the combination is saved as an intermediate result, named ‘reduced_image.fits’. This combined image is also returned in the field reduced_image of the recipe result.

The apertures in the 2D image are extracted, using the information in master_apertures and resampled according to the wavelength calibration in master_wlcalib. Then is divided by the master_fiberflat. The resulting RSS is saved as an intermediate result named ‘reduced_rss.fits’. This RSS is also returned in the field reduced_rss of the recipe result.

To normalize the master_twilight_flat, each fiber is divided by the average of the column range given in normalize_region. This RSS image is returned in the field master_twilightflat of the recipe result.

class MegaraBaseRecipeInput(*args, **kwds)

MegaraBaseRecipeInput documentation.

Attributes:

obresultObservationResultType, requirement

Observation Result

class RecipeInput(*args, **kwds)

RecipeInput documentation.

Attributes:

continuum_regionListOfType, requirement, optional, default=[1900, 1900]

Subtract this region before normalize the flat-field

extraction_offsetListOfType, requirement, optional, default=[0.0]

Offset traces for extraction

master_aperturesMultiType, requirement

Apertures information for extraction

master_biasMasterBias, requirement

Master BIAS image

master_bpmMasterBPM, requirement, optional

Master Bad Pixel Mask

master_darkMasterDark, requirement, optional

Master DARK image

master_fiberflatMasterFiberFlat, requirement

Master fiber flat calibration

master_slitflatMasterSlitFlat, requirement, optional

Master slit flat calibration

master_wlcalibWavelengthCalibration, requirement

Wavelength calibration table

normalize_regionListOfType, requirement, optional, default=[1900, 2100]

Region used to normalize the flat-field

obresultObservationResultType, requirement

Observation Result

class RecipeResult(*args, **kwds)

RecipeResult documentation.

Attributes:

master_twilightflatMasterTwilightFlat, product

reduced_imageProcessedFrame, product

reduced_rssProcessedRSS, product

set_base_headers(hdr)

Set metadata in FITS headers.