Location Table Product

Data product name

LocationTable

Data product custodian

SIR

Data model tag

R-1.6.6

Name of the Schema file

euc-test-sir-LocationTable.xsd

Schema documentation tag

No documentation element was found in schema file! Data Model custodian: even minimal information can be helpful

Data product elements

Header of type: sys:genericHeader

Data of type: sir:genericSirCollection

Parameters of type: ppr:genericKeyValueParameters

Processing Element(s) creating/using the data product

This data product is produced by the SIR_SpectraLocation PE.

It is used by SIR_BackgroundSubtraction, SIR_SpectraDecontamination and SIR_SpectraExtraction PEs.

Processing function using the data product

This is an internal data product. It is used only by SIR-PEs.

Detailed description of the data product

The main purpose of the LocationTable is to gather information to locate and extract spectra on the detectors. LocationTable is an hierarchical organization of LocationSpectra, AstronomicalObjects and LocationObjects.

Each object in the field of view produces spectra of different orders. The LocationSpectrum describes every spectral trace (of every orders) produced on the detectors. A single spectrum can involve multiple detectors; in this case one LocationSpectrum for each detector is created. The LocationSpectrum is the atomic component of the LocationTable.

LocationSpectra which refer to the same target are collected into the LocationObject. The LocationObject contains also the AstronomicalObject which describes physical properties of the target.

The LocationTable data product is the hierarchical collection of LocationObject of all available targets.

Each one of these objects (LocationSpectrum, LocationObject, AstronomicalObject and LocationTable) is serialized as HDF5 group into the HDF5 file. These 4 objects will be described in details in the next paragraphs.

../../_images/LocationTableGlobal.png

Fig. 19 : Location Table HDF5 file structure.

Location Spectrum group

Due to optical distortions and uncertainty in grism alignment, dispersed spectra are curved and not perfectly aligned with the dispersion direction. Since this curvature changes moving around the the FOV, each spectrum has it own curvature and it own inverse wavelength solution. These 2 properties are different spectrum by spectrum. For this reason the SIR_Pipeline has to produce one LocationSpectrum (green box in Fig. 19) for each spectrum in the FOV.

The LocationSpectrum group contains information about geometry of the spectrum and it is used to locate spectral wavelengths on the detector. This is performed by:

  1. Setting a lambda reference value

    • this value is defined by the attribute Offset of the IDSX and IDSY groups.

  2. Identifying the positions on the detector of this lambda reference value along the cross-dispersion direction

    • these positions are defined by The Reference lambda dataset. This dataset is a n by 2 matrix, each row defines the pixel where the reference lambda is. Number of rows changes object by object according with object size and angle.

  3. Applying polynomial solutions: along X and Y directions.

    • the IDSX and IDSY groups contain the Coeffs dataset: the polynomial coefficients of the wavelength solution. Each row is a set of polynomial coefficients; the number of rows of this dataset must be identical to the number of rows of the Reference lambda dataset.

Finally the LocationSpectrum contains attributes used to uniquely identify the spectrum:

  • the target ID

  • the Order of the spectrum itself

  • the Grism Position: 0, 90 or 180

  • the Detector involved by the spectrum

  • the Exposure ID

  • the Field ID

Astronomical Object group

The AstronomicalObject (yellow box in Fig. 19) gathers the astronomical properties of the target using the attributes:

  • Angle of the object in the sky

  • Bulge fraction of the target

  • Y-H Color

  • Dec and RA coordinates

  • object ID

  • Major axis and Minor axis of the object

  • object Type; at the moment only star (1) and galaxy (2) are implemented

Beside these values the AstronomicalObject also contains infrared magnitudes of the objects. The Magnitudes complex type table has 3 columns:

  • the magnitude Band

  • Vega flag: 1 if the magnitude is in the Vega system, 0 if not

  • the magnitude Value

Location Object group

The LocationObject (purple box in Fig. 19) collects together spectra with the same target ID; it combines one AstronomicalObject and several LocationSpectra.

Location Table group

The LocationTable (cyan box in Fig. 19) data product gathers LocationObjects and organizes them according with 2 different criteria:

  1. In the Detector_n groups LocationObjects are organized detector by detector (blue box in Fig. 20). Each LocationObject in one of these groups contains only spectra produced on the n-th detector.

  2. In the Location Objects group LocationObjects are organized by ID (red box in Fig. 20). LocationObject in this group gathers all spectra in the FOV with the same target ID.

../../_images/LocationTableHierarchy.png

Fig. 20 : Different hierarchy in the Location Table.

Finally the Reduction Recipes group contains one attribute for each input parameter of the SIR_Pipeline task used to create the LocationTable itself.