Combined Spectra Product

Data product name

DpdSirCombinedSpectra

Data product custodian

SIR

Data model tag

R-10.0

Name of the Schema file

euc-sir-CombinedSpectra.xsd

Last Edited for DPDD Version

2.0

Processing Elements Creating / Updating / Using the Product

Creators:

  • SIR_Combine_Spectra

Processing function using the data product

SPE

Proposed for inclusion in EAS/SAS

This product is proposed for inclusion in the SAS: yes.

Data product elements

Header:

object of type sys:genericHeader

Data:

object of type sir:sirCombinedSpectra

QualityFlags:

object of type dqc:sqfPlaceHolder

Parameters:

object of type ppr:genericKeyValueParameters

Detailed description of the data product

SIR_Combine_Spectra pipeline is triggered on a tile bases: there is 1 dpdCombinedSpectra for each dpdMerFinalCatalog. In the case where the MER catalog covers both a red and a blue field, we will have 2 CombinedSpectra: one RSG and one BGS.

A single MER tile is covered by several exposures, once all the exposures that intersect that tile have been reduced by the SIR_Extract_Spectra pipeline, the SIR_Combine_spectra pipeline can be triggered, and the dpdCombinedSpectra data are produced.

This product will contains a set of CombinedSpectrum, one for each object contained in the MER catalog. It is stored as a collection of fits files, each file contains 1000 CombinedSpectrum.

The primary header of these fits files contains generic information such as:

  • the number of CombinedSpectrum stored in the file

  • the tile ID

  • the lambda range of these spectra: RGS or BGS

  • the dictionary describing the bit mask

HDU PRIMARY: header

Name

Description

Value

Keywords

FITS_DEF

string = sir.combinedSpectra

FITS_VER

string = 0.2

TELESCOP

string = EUCLID

INSTRUME

or NISPsim for simulations

string = NISP

DATE

UT date when this file was created

string

ORIGIN

FITS file originator

string

SOFTVERS

Version of the processing function pipeline

string

VERSION

Data Release version

string

N_OBJ

Number of sources in file

integer

TILE_ID

MER tile index

integer

LRANGE

The grisms used in combination: BGS or RGS see definition simpleType = combinedGrism

string

MSK_FLAG_GOOD

Mask bit position

integer = 0

MSK_FLAG_NOT_USE

Mask bit position

integer = 1

MSK_FLAG_LOW_SNR

Mask bit position

integer = 2

MSK_FLAG_EXT_PRB

Mask bit position

integer = 4

MSK_FLAG_HIGH

Mask bit position

integer = 8

MSK_FLAG_LOW

Mask bit position

integer = 16

MSK_FLAG_REL_FLUX

Mask bit position

integer = 32

MSK_FLAG_ABS_FLUX

Mask bit position

integer = 64

CombinedSpectrum

A single CombinedSpectrum contains:

Each single CombinedSpectrum contained in the fits file is identified by an enumerative m and is stored as a collection of HDUs in the fits file. Each HDU associated to a give object starts with m.

../../_images/combined.png

Fig. 30 : In the figure a part of CombinedSpectra. The CombinedSpectrum m=995 (A) alongside the combined spectrum, it contains 5 dither extracted spectra and their respective contaminants. The CombinedSpectrum m=997 (B) is an example of empty CombinedSpectrum.

m_META

This is the content of the m_META HDU:

HDU m_META: header

Name

Description

Value

Keywords

N_DITH

Number of dither containing object, was DITH_NUM

integer

OBJ_ID

MER-specified identifier of the m-th object

integer

RA_OBJ

R.A. of the m-th object

double

DEC_OBJ

Declination of the m-th object

double

NOTE: if no spectra are extracted for a given object, the CombinedSpectrum is empty and it consists of this single extension. (See the B example in the figure Fig. 30)

m_DITH1D_n_SIGNAL

For each spectrum m, there is a variable number of m_DITH1D_n_SIGNAL spectra; the number of these spectra depends on the number of exposures containing the spectrum of object m. Each m_DITH1D_n_SIGNAL is identified by the pointing ID n. In the example A of the figure Fig. 30 n is: 3197, 3198, 3199, 3318, 3319.

The header of m_DITH1D_n_SIGNAL contains info about the origin of this spectrum:

HDU m_DITH1D_n_SIGNAL: header

Name

Description

Value

Keywords

EXTNAME

string

GWA_POS

GWA position (RGS270,RGS000,RGS180,BGS000,OPEN)

string

GWA_TILT

Commanded Grism Tilt Angle

integer

DITH_ID

The dither index

integer

PTGID

Pointing ID in the name

integer

EXPTIME

Exposure time

double

FSCALE

Scaling factor

double

WMIN

Minimum wavelength of the binning

double

BINWIDTH

Wavelength bin width

double

BINCOUNT

Wavelength bin count

double

DET_ID

The detector index

integer

DET_ID_2

Additional detector involved

integer

LSF_SIG

Standard deviation of the Gaussian Line Spread Function model

double

EXT_PROF

1D extraction profile used (NONE,OPT_THUMB,OPT_PSF)

string

If the spectrum was entirely contained in a single detector, the DET_ID_2 keyword will be missing; otherwise, if it is present, it means the extracted spectrum spanned across two detectors (part on DET_ID and part on DET_ID_2).

The m_DITH1D_n_SIGNAL is organized as binary table and it contains the following columns:

  • WAVELENGTH: the spectrum wavelengths bin [\(\mathring{A}\)]

  • SIGNAL: the spectrum fluxes bin [\({erg}\ {cm^{-2}} s^{-1} \mathring{A}^{-1}\)]. Fluxes stored in this column are scaled by the FSCALE factor written in Header.

  • MASK: the bit mask for the current flux bin. The definition of this bit mask is stored in the Primary Header (see MSK_* keywords).

  • VAR: the variances associate to the fluxes [\({erg^2} {cm^{-4}} s^{-2} \mathring{A}^{-2}\)]. (The FSCALE scaling factor must also be taken into account for this column).

  • QUALITY: each flux bin of an extracted 1D spectrum is obtained by combining different pixels from the input frame (2D extraction), and by combining different points of the 2D spectrum (1D extraction). During these two extraction processes, not all available pixels are used (bad pixels, cosmic rays, etc. are excluded). Moreover not all pixels are used with the same weights both in the 2D resampling and the 1D extraction. This quality value is a number between 0 and 1 that accounts for how many pixels were used to obtain this flux bin: it is the ratio between the weighted sum of the pixels actually used and the weighted sum of the pixels potentially available to obtain this bin. Quality 1 means all available pixels were used, 0 means no pixels were used.

m_DITH1D_n_CONTAMINANTS

These extensions are associated to m_DITH1D_n_SIGNAL extensions; this extension is a table which contains the list of contaminants of the m_DITH1D_n_SIGNAL spectra.

HDU m_DITH1D_n_CONTAMINANTS: header

Name

Description

Value

Keywords

EXTNAME

string

GWA_POS

GWA position (RGS270,RGS000,RGS180,BGS000,OPEN)

string

GWA_TILT

Commanded Grism Tilt Angle

integer

DITH_ID

The dither index

integer

PTGID

Pointing ID in the name

integer

HDU m_DITH1D_n_CONTAMINANTS: 1 columns table

Name

Description

Unit

Format

Columns

OBJ_ID

Object ID of contaminant, int 64

NA

FITS K

m_COMBINED1D_SIGNAL

This extension contains the combined spectrum obtained combining all the related m_DITH1D_n_SIGNAL; this spectrum is stored as Binary Table HDU.

HDU m_COMBINED1D_SIGNAL: header

Name

Description

Value

Keywords

EXTNAME

string

EXPTIME

Exposure time

double

FSCALE

Scaling factor

double

WMIN

Minimum wavelength of the binning

double

BINWIDTH

Wavelength bin width

double

BINCOUNT

Wavelength bin count

integer

LSF_SIG

Standard deviation of the Gaussian Line Spread Function model

double

EXT_PROF

1D extraction profile used (NONE,OPT_THUMB,OPT_PSF)

string

HDU m_COMBINED1D_SIGNAL: 6 columns table

Name

Description

Unit

Format

Columns

WAVELENGTH

Wavelength column, was WBIN

Angstrom

FITS E

SIGNAL

Fluxes column

erg/s/cm2/Angstrom

FITS E

MASK

Pixel mask column, int 32

Number

FITS J

VAR

Variance on fluxes

erg2/s2/cm4/Angstrom2

FITS E

QUALITY

Pixel quality flag column, float 32

Number

FITS E

NDITH

Number of spectra used in combination, int 16

Number

FITS I

This table contains all the columns of the m_DITH1D_n_SIGNAL plus the additional column NDITH.

This NDITH columns contains the number of spectra which contributed to obtain the current flux bin. By definition the values of this column are lower equal than N_DITH keyword: the N_DITH keyword gives a global information, NDITH columns gives this information for each bin.