Arc

Mode:

Arc

Usage:

Offline, Online

Key:

MegaraArcCalibration

Product:

WavelengthCalibration

Recipe:

ArcCalibrationRecipe

Recipe input:

ArcCalibrationRecipeInput

Recipe result:

ArcCalibrationRecipeResult

This mode sequence includes the required actions to translate the geometrical position of each point in the detector into physical units of wavelength. The calibration is performed by means of using reference calibration lamps (arc lamps) that should be part of the Instrument Calibration Module (ICM) at F-C. Note that the optical distortions in the spectrograph will lead to different wavelength calibrations from each individual fiber, therefore the entire focal plane should be illuminated by the corresponding arc lamp of choice. Given the relatively high spectral resolution and broad wavelength coverage of MEGARA we anticipate that more than one arc lamp will be needed at the ICM. The lamps at ICM have to deliver enough bright spectral lines for calibrating the whole range of MEGARA spectral resolutions and wavelength ranges (for HR modes only two VPHs shall be provided by MEGARA but more gratings could come funded by GTC users). MEGARA has provided a whole review of the possible illumination systems in the document TEC/MEG/151, but the responsibility of the development of the ICM module is on the GTC side.

Requirements

The entire focal plane should be illuminated with light from the ICM arc lamp with the required input focal ratio. This mode requires having the ICM turned on, one of the arc lamps at the ICM also turned on, the focal-plane cover configured (at least one of the sides should be open), the instrument shutter open, 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 expose a certain time and to readout the detector a series of exposures, being this series the arc image set.

Procedure

The “User” processes an observing block obtained in the observing mode Arc. This mode includes the required actions to translate the geometrical position of each point in the detector into physical units of wavelength. The wavelength calibration generated is used in other stages of the data processing.

Products

Arc image sets are to be obtained both as part of the activities related to the verification of the instrument status and for processing data for scientific exploitation and are part of the “Daily Calibration Modes”.

A data structure containing information about wavelength calibrations (the format is TBD), a 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.arc.ArcCalibrationRecipe(*args, **kwargs)

Provides wavelength calibration information from arc images.

This recipes process a set of arc images obtained in Arc Calibration mode and returns the information required to perform wavelength calibration and resampling in other recipes, in the form of a WavelengthCalibration object. The recipe also returns a 2D map of the FWHM of the arc lines used for the calibration, the result images up to dark correction, and the result of the processing up to aperture extraction.

See also

megaradrp.products.WavelengthCalibration

description of WavelengthCalibration product

megaradrp.products.LinesCatalog

description of the catalog of lines

megaradrp.processing.aperture

aperture extraction

numina.array.wavecalib.arccalibration

wavelength calibration algorithm

megaradrp.instrument.configs

instrument configuration

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). 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_traces. the result of the extraction is saved as an intermediate result named ‘reduced_rss.fits’. This RSS is also returned in the field reduced_rss of the recipe result.

For each fiber in the reduced RSS, the peaks are detected and sorted by peak flux. nlines is used to select the brightest peaks. If it is a list, then the peaks are divided, by their position, in as many groups as elements in the list and nlines[0] peaks are selected in the first group, nlines[1] peaks in the second, etc.

The selected peaks are matched against the catalog of lines in lines_catalog. The matched lines, the quality of the match and other relevant information is stored in the product WavelengthCalibration object. The wavelength of the matched features is fitted to a polynomial of degree polynomial_degree. The coefficients of the polynomial are stored in the final master_wlcalib object for each fiber.

class ArcCalibrationRecipeInput(*args, **kwds)

ArcCalibrationRecipeInput documentation.

Attributes:

debug_plotint, requirement, optional

Save intermediate tracing plots

extraction_offsetListOfType, requirement, optional, default=[0.0]

Offset traces for extraction

lines_catalogMegaraLinesCatalog, requirement

Catalog of lines

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

nlinesListOfType, requirement, optional, default=[20]

Use the ‘nlines’ brigthest lines of the spectrum

obresultObservationResultType, requirement

Observation Result

polynomial_degreeListOfType, requirement, optional, default=[5]

Polynomial degree of arc calibration

store_pdf_with_refined_fitsint, requirement, optional

Store PDF plot with refined fits for each fiber

class ArcCalibrationRecipeResult(*args, **kwds)

ArcCalibrationRecipeResult documentation.

Attributes:

fwhm_imageDataFrameType, product

master_wlcalibWavelengthCalibration, product

reduced_imageProcessedFrame, product

reduced_rssProcessedRSS, product

RecipeInput

alias of ArcCalibrationRecipeInput

RecipeResult

alias of ArcCalibrationRecipeResult

calc_fwhm_of_line(row, peak_int, lwidth=20)

Compute FWHM of lines in spectra

model_coeff_vs_fiber(data_wlcalib, poldeg, times_sigma_reject=5)

Model polynomial coefficients vs. fiber number.

For each polynomial coefficient, a smooth polynomial dependence with fiber number is also computed, rejecting information from fibers which coefficients depart from that smooth variation.

run(rinput)

Execute the recipe.

Parameters:

rinputArcCalibrationRecipe.RecipeInput

Returns:

ArcCalibrationRecipe.RecipeResult