Data description

In order to help the user in understanding the different execution steps of the MEGARA DRP, we describe in this section the characteristics of the main products, including input raw images and pipeline products (images and tables).

Raw Data

Raw data includes all FITS frames delivered to the user by GTC. These FITS images are 4196 x 4212 pixels in size have two extensions, the first one including the data themselves and the second one providing all the information about the fibers (positions in the sky, bundle to which they belong and whether they are devoted to the observation of target or sky). Among these images one can find bias frames (as they are obtained with the MegaraBiasImage observing mode they include the name of this mode it their filename), fiber-flat images (obtained with either the MegaraTraceMap or the MegaraFiberFlatImage observing modes), ThAr or ThNe HCL lamp spectra (obtained with the MegaraArcCalibration observing mode) and scientific observations with either the LCB (MegaraLcbImage or MegaraLcbAcquisition; this latter mode is commonly used when the target is a bright star, normally a spectrophotometric standard star) or the MOS (MegaraMosImage).

Pipeline Products

There are multiple types of products generated by the MEGARA DRP although they can be grouped in full-frame FITS images of 4096 x 4112 pixels in size (after the overscan+prescan regions are removed from the raw images), RSS images of 4300 x 623 (for LCB) or 4300 x 644 (for MOS) pixels, and structured data, which is in most cases are given in files of JSON format. Below we list the different products within these three groups along with the recipe that generates them.

Full-frame FITS image products

  • master_bias.fits (MasterBiasImage): Final image of the MasterBiasImage recipe.

  • reduced_image.fits (MegaraDarkImage, MasterTraceMap, MegaraModelMap, MegaraFiberFlatImage, MegaraArcCalibration, MegaraTwilightFlatImage, MegaraLcbStdStar, MegaraLcbAcquisition, MegaraLcbImage, MegaraMosImage, MegaraArcCalibration): Final image after all individual exposures have been processed and combined.

  • master_slitflat.fits (MegaraSlitFlat): Image obtained by observing a continuum-lamp light with the spectrograph out of its optimal focus. The level of de-focusing should be enough to ensure a uniform illumination through the entire CCD but keeping the wavelength of the light approximately the same at each given pixel that when the instrument is well focused.

  • fwhm_image.fits (MegaraArcCalibration): Voronoi map of the FWHM derived from the fits to the Gaussian profiles of all spectral lines identified in the arc-lamp image.

RSS FITS image products

  • master_fiberflat.fits (MegaraFiberFlatImage): Image to be applied to correct for variations in sensitivity in between fibers and from blue-to-red within each fiber.

  • master_twilightflat.fits (MegaraTwilightFlatImage): Image to be applied to correct for the effect of illumination introduced by the fiber-flat image when this was obtained through the FC-F ICM and differences between the pupil of the ICM and the GTC pupil when the object was observed. The values of the twilight-flat image are identical for all wavelengths but different from fiber to fiber (blue-to-red sensitivity variations were corrected with the fiber-flat image).

  • reduced_rss.fits (MegaraLcbAcquisition, MegaraLcbStdStar, MegaraLcbImage, MegaraMosImage, MegaraArcCalibration): Processed image prior to the subtraction of the sky spectrum.

  • sky_rss.fits (MegaraLcbAcquisition, MegaraLcbStdStar, MegaraLcbImage, MegaraMosImage, MegaraArcCalibration): RSS image showing signal only in the valid sky fibers. All other pixels are set to zero.

  • final_rss.fits (MegaraLcbAcquisition, MegaraLcbStdStar, MegaraLcbImage, MegaraMosImage, MegaraArcCalibration): Processed image after the subtraction of the sky spectrum is performed. In the case of the MOS, this image includes an extension of 92 rows by 4300 columns where all 7 fibers of each minibundle have been added together.

Structured products

  • master_wlcalib.json (MegaraArcCalibration): File with the information on the wavelength calibration solution for every fiber.

  • master_traces.json (MasterTraceMap): File with the tracing information.

  • master_model.json (MasterModelMap): File with the information on how to account for the cross-talk between adjacent fibers in the detector.

In the case of the MegaraLcbStdStar recipe, the MEGARA DRP also generates two different 1D spectra, that of the standard star obtained after extracting the 37 spaxels around the centroid identified in the observation-result file (star_spectrum.fits) and also the resulting sensitivity function (master_sentivity.fits).

In addition to all these files, the results directory of every recipe includes also a file named task.yaml (file with the description of the execution of the recipe), the file result.yaml (names of the files resulting from the recipe and some quality-control information) and the processing.log logging file.

Besides ds9/SAOimage or similar software packages, the FITS products generated by the MEGARA DRP can be also visualized using the tool numina-ximshow distributed as part of numina.