Home > Data Centre > Data description



Data description

4 September 2017 ( maj : 8 February 2018 ), by Nadège Meunier

Description of the data available in the public workspaces

Please do not hesitate to contact us at sphere-dc-req at univ-grenoble-alpes.fr is you have any opinions, needsn ideas on the available data.

Reduced calibration files

Several types of reduced calibrations files are available. The complete description can be found in the ESO SPHERE pipeline use manual (latest version here). The available frametype are the following:

For the IRDIS instrument:

  • IRD_FLAT_FIELD
  • IRD_STATIC_BADPIXELMAP
  • IRD_MASTER_DARK

For the IFS instrument:

  • IFS_IFU_FLAT_FIELD
  • IFS_INSTRUMENT_FLAT_FIELD
  • IFS_WAVECALIB
  • IFS_SPECPOS
  • IFS_MASTER_DFF_LONG*
  • IFS_STATIC_BADPIXEL_MAP
  • IFS_MASTER_DARK

Level 1 reduced data : IFS and IRDIS output description

  • files *center_im.fits : master reduced cube in units in ADU per second, corrected for the filter and neutral density transmissions. The 4 dimensions are : X, Y (detector coordinates), number of frames(temporal dimension), number of wavelength channel (spectral dimension). The star is centered on 512.5,512.5, in image coordinates (starting from 1 and not from 0) at the center of a pixel.
    • Corresponding frametype: IFS_SCIENCE_REDUCED_SPECTRAL_MASTER_CUBE (for the IFS instrument) and IRD_SCIENCE_REDUCED_MASTER_CUBE (for the IRDIS instrument)
  • files *median_unsat.fits (for flux calibration) : units in ADU per second. Corrected for the filter and neutral density transmissions. The 4 dimensions are : X, Y (detector coordinates), number of PSF (often one before and one after science sequence), number of wavelength channel (spectral dimension)
    • Corresponding frametype: IFS_SCIENCE_PSF_MASTER_CUBE (for the IFS instrument) and IRD_SCIENCE_PSF_MASTER_CUBE (for the IRDIS instrument)
  • files *lam.fits: array containing the wavelength calibration for each spectral channel (IFS instrument) and the list of filter wavelengths (IRDIS instrument)
    • Corresponding frametype: IFS_SCIENCE_LAMBDA_INFO (for the IFS instruments) and IRD_SCIENCE_LAMBDA_INFO (for the IRDIS instruments)
  • files *rotnth. fits : array containing the parallactic angle to rotate each frame to have the true north UP. Corrected using true north calibration from Maire et al. 2016 SPIE 9908, id. 990834.
    • Corresponding frametype: IFS_SCIENCE_PARA_ROTATION_CUBE (for the IFS instrument) and IRD_SCIENCE_PARA_ROTATION_CUBE (for the IRDIS instrument)

Level 2 reduced data available at the CT

Several routines are used to produce a residual image whenever possible, for IFS and IRDIS observations. Each algorithm produces a series of files, described below.

Flux in the reduced images: The pixel values in the reduced images are the flux ratio between the residual flux in the coronagraphic image and the estimated maximum of the star PSF. Thus, it gives the contrast ratio in the reduced images. The maximum of the star PSF is derived from the best fit of the PSF by a function that reproduces the SPHERE PSF (close to a Gaussian function). The coronagraphic image results from the speckle intensity minimization. The normalization factors are saved in the normalization_vector.fits file.

Most files of interests are available in the *allcomb.tar file and after extraction in the Reduction_000/Images/allcomb/ directory. These files are the following:

  • reduced_image.fits: Final reduced image
  • reduced_image_corrthput.fits: Final reduced image corrected from throuput (files with throughput correction are only available for two of the algorithms below, cADI and TLOCI)
  • reduced_image_median.fits and reduced_image_median_corrthput.fits: same but using a median-combination instead of an average of the data cube
  • snrmap.fits and snrmap_unsharp13.fits: 2D SNR map before/after a 13x13 pixel unsharpened mask.
  • detection_map.fits: map of a local 1sigma standard deviation worked out in boxes of 2 FWHM radial size and a total area of 5 FWHM.
  • Note that the files cube_* contains the same images but one per wavelength instead of beeing stacked.

Other files of interests are in the *contrast_curves.tar file and include .eps files and the contrast curve (contrast versus the angular separation) in fits and ascii format.

The algorithms can be identified by the field "Reference" in the process brower (see FAQ) and in the directories after retrieval. They are:

  • NoADI: simple stacking of the master cubes
  • cADI : Classical Angular Differential Imaging (Marois et al. 2006, Lafrenière et al 2007)
  • TLOCI : Flavor of Angular Differential Imgaging based on Locally Optimised Combination of Images (Marois et al .20011, Galicher et al 2017)
  • RadProfile: Simple subtraction of the median flux at each given radius. Effectively removes the circularly symetric component of the PSF.

Level 2 reduced data available at the TDB

The files available at the TDB are a subset of those available at the CT (described above):

  • the final reduced image using a median-combination (equivalent to reduced_image_median.fits above)
  • the 2D SNR map after a 13x13 pixel unsharpened mask, stacked in wavelength (equivalent to the snrmap_unsharp13.fits above).