Section 3 Faint Object Spectrograph

The process of calibrating Faint Object Spectrograph (FOS) data consists of the following steps:

1. Bad or suspect data are identified using the data quality initialization file, <uniquename>.R5H.

2. Raw counts are converted to count rates by dividing each data point by the exposure time and correcting for disabled diodes. The default disabled diodes reference file is <uniquename>.R4H .

3. The spectrum of raw count rates is corrected for the geomagnetically induced image motion problem (GIMP). The table of GIMP-correction scale factors, <uniquename>.CY7 , has extension .CYZ.

4. Raw count rates are correcte d for saturation in the detector electronics. The table <uniquename>.CMG contains the dead time constants used to correct for the nonlinear channel response of each diode.

5. The background is subtracted from the sky and object spectra. If no background observation was made, the default reference background file, <uniquename>.R0H , is used. This background is scaled according to the background count rates table, <uniquename>.CY8, to account for geomagnetic position. The observed background is smoothed with a median, followed by a mean filter before subtraction. The filter widths are contained in the reference table, <uniquename>.CY3 . No smoothing is done to the reference file background (if it is used).

6. Scattered light is subtracted from the sky and object spectra. For detector/disperser combinations that contain regions of no sensitivity to dispersed light, the level of scattered light is calculated as the average flux within the region of no sensitivity and subtracted from the entire sky and object spectra. This process requires the reference table, <uniquename>.CY9 , containing the beginning and ending diode positions of the no-sensitivity region for each detector/disperser combination. If the detector/disperser combination does not contain a region of no sensitivity, this correction is not performed.

7. Diode-to-diode sensitivity variations and fine structure are removed by multiplying by the flat field response. This process requires the flat field response file, <uniquename>.R1H . A second flat field file is required for paired aperture or spectropolarimetry observations.

8. The sky can be subtracted from the object spectra. The emission line table, <uniquename>.CY2, gives regions where a sky spectrum should not be smoothed before subtraction from the object spectrum. The detector parameters table, <uniquename>.CY3 , contains the filter widths (mean and median) for smoothing the sky (or background) spectra. The sky shift parameter table, <uniquename>.CY5, gives an integer shift in pixels that is to be applied to the sky spectrum before subtraction. The aperture parameters table, <uniquename>.CY0 , contains aperture areas required to scale a sky spectrum taken in one aperture of a paired aperture before subtraction from the object spectrum taken in the other aperture. The aperture position parameters table, <uniquename>.CY1 , is used to determine which aperture of an aperture pair was used for observing an object or sky spectrum.

9. Wavelength scales are generated using the dispersion coefficients from the wavelength parameters table, <uniquename>.CY6 .

10. Object spectra are converted to absolute flux units by multiplying by the inverse sensitivity vector. Two methods of flux conversion are supported by calfos.

The first, and better, calibration method uses an average inverse sensitivity (AIS) file, <uniquename>.R8H. The average inverse sensitivity is scaled for the specific aperture by use of the data in the table selected by the relative throughput parameters table. Corrections based on time and OTA focus are applied based on the . CYA, . CYC, and .CYD tables. This method is not used for spectropolarimetry data.

The second, original calibration, required for polarimetry data, uses an aperture dependent inverse sensitivity from the <uniquename>.R2H file. Two inverse sensitivity files are required for spectropolarimetry observations.

11. The final step performs ground software mode dependent reductions for time-resolved, spectropolarimetry, and rapid-readout observations. The spectropolarimetry reductions require the Wollaston and waveplate parameter table, <uniquename>.CYa*4, and the retardation reference file, *<uniquename>.R3H. If the spectropolarimetry data were acquired during the post-COSTAR epoch as indicated by the science header keyword/value pair, KYDEPLOY = T, and a post-COSTAR calibration is available, the post-COSTAR polarimetry correction reference file, <uniquename>.R9H, is also required.

3.1 FOS Reference Files

The FOS reference files are composed of a FITS header file and a binary data file. Although the header files follow the FITS conventions, the header listings in this section do not adhere precisely to these conventions. In the header listings contained in this section, beware of the following:

The single quotes required around character strings have been omitted. Numerical values have not been right justified. The third column in the listing (denoting the variable type) is additional information, not part of the FITS header itself.

3.1.1 Background Files (BAC): <uniquename>.R0H

FOS background reference files contain the default background data used during background subtraction (spectroscopy ground software mode) for both object and sky spectra.

Format: Background data are stored in a single group with M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X-substeps. Background data are stored in REAL*4 format. Data are in units of counts per second.

Flags and Indicators: The default background data file is selected on the basis of DETECTOR and OVERSCAN.

Restrictions: The FOS calibration software will reject any inappropriately sized groups. The following listing shows a sample image header of a background file.

SIMPLE = F                     / image conforms to the fits standard                      L1
BITPIX = 32                    / bits per data value                                      I2
DATATYPE= REAL\*4              / datatype of the group array                              CHR
NAXIS = 1                      / number of data axes                                      I2
NAXIS1 =                       / number of elements ((chnls+scan-1)\*xsteps)              I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 1                     / number of groups                                         I2
PCOUNT = 0                     / number of group parameters                               I2
PSIZE = 0                      / bits in the group parameter block                        I2

                      / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= BACKGROUND           / default background reference file                        CHR
HEADNAME=                      / header filename                                          CHR
DATANAME=                      / data filename                                            CHR
DATE =                         / date this file was written                               CHR

                      / FOS CONFIGURATION KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
CHNL =                         / first channel processed: 0,2,...,510                     I2
NCHNLS =                       / number of channels processed: 2,4,...,512                I2
NXSTEPS =                      / number of x substeps: 1,2,4,8,16                         I2
OVERSCAN=                      / overscan number: 1-256                                   I2
USEAFTER=                      / use this file for obs. taken on/after this date          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                        [Listing Version 03 26-MAY-1994]

3.1.2 Flat Field Files (FLT): < uniquename>.R1H

FOS flat field reference files contain diode and photocathode sensitivity data used to remove detector granularity from observed spectra (spectroscopy ground software mode).

Format: Flat field data are stored in a single group with M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X-substeps. Flat field data are stored in REAL*4 format. Data are inverse of detector flat field and are applied as a multiplicative operator in processing.

Flags and Indicators: The flat field data file is selected on the basis of DETECTOR, OVERSCAN, APER_ID, POLAR_ID, FGWA_ID, APER_POS, and PASS_DIR.

Restrictions: Inappropriately sized groups will be rejected. The following listing shows a sample image header for a FOS flat field file (<uniquename>.R1H).

SIMPLE = F                     / image conforms to the fits standard                      LI
BITPIX = 32                    / bits per data value                                      I2
DATATYPE= REAL\*4              / datatype of the group array                              CHR
NAXIS = 1                      / number of data axes                                      I2
NAXIS1 =                       / number of elements ((chnls+scan-1)\*xsteps)              I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 1                     / number of groups                                         I2
PCOUNT = 0                     / number of group parameters                               I2
PSIZE = 0                      / bits in the group parameter block                        I2

                       / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= FLAT FIELD           / pixel-to-pixel sensitivity ref file (multiplicative)     CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written                               CHR

                       / FOS FLAGS AND INDICATORS KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
FCHNL =                        / first channel processed: 0, 2, ..., 510                  I2
NCHNLS =                       / number of channels processed: 2,4,...,512                I2
NXSTEPS =                      / number of x substeps: 1, 2, 4, 8, 16                     I2
OVERSCAN=                      / overscan number: 1-256                                   I2
APER\_ID =                     / aperture id: A-1, A-2 .. B-1, .. ANY                     CHR
POLAR\_ID=                     / polarizer id: A, B, C                                    CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, .. ANY                      CHR
PASS\_DIR=                     / pass direction: 0,1,2                                    I2
APER\_POS=                     / aperture position: UPPER, LOWER, SINGLE                  CHR
USEAFTER=                      / use this file for obs. taken on/after this date          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                             [Listing Version 03 26-MAY-1994]

3.1.3 Inverse Sensitivity Files (IVS): <uniquename>.R2H

FOS inverse sensitivity reference files contain data used to convert object data to an absolute flux scale (spectroscopy ground software mode).

Format: Inverse sensitivity data are stored in a single group with M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X-substeps. Inverse sensitivity data are stored in REAL*4 format. Data has units of (ergs cm-2 s-1 A*-1)/(counts s-

1).

Flags and Indicators: The inverse sensitivity data file is selected on the basis of DETECTOR, OVERSCAN, APER_ID, POLAR_ID, APER_POS, PASS_DIR, and FGWA_ID.

Restrictions: Inappropriately sized groups will be rejected. The following listing shows a sample header from a FOS inverse sensitivity file.

SIMPLE = F                     / image conforms to the fits standard                      L1
BITPIX = 32                    / bits per data value                                      I2
DATATYPE= REAL\*4              / datatype of the group array                              CHR
NAXIS = 1                      / number of data axes                                      I2
NAXIS1 =                       / number of elements ((chnls+scan-1)\*xsteps)              I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 1                     / number of groups                                         I2
PCOUNT = 0                     / number of group parameters                               I2
PSIZE = 0                      / bits in the group parameter block                        I2

                          / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= INV SENSITIVITY      / inverse sensitivity ref file (multiplicative)            CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written                               CHR

                          / FOS FLAGS AND INDICATORS KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
FCHNL =                        / first channel processed: 0, 2, ..., 510                  I2
NCHNLS =                       / number of channels processed: 2,4,...,512                I2
NXSTEPS =                      / number of x substeps: 1, 2, 4, 8, 16                     I2
OVERSCAN=                      / overscan number: 1-256                                   I2
APER\_ID =                     / aperture id: A-1, A-2, .. B-1, .. ANY                    CHR
POLAR\_ID=                     / polarizer id: A, B, C                                    CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, .. ANY                      CHR
PASS\_DIR=                     / pass direction: 0, 1, 2                                  I2
APER\_POS=                     / aperture position: UPPER, LOWER, SINGLE                  CHR
USEAFTER=                      / use this file for obs. taken on/after this date          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                    [Listing Version 02 26-MAY-1994]

3.1.4 Retardation Files (RET): <uniquename>.R3H

FOS retardation files contain values computed from the retardation of the waveplate used during spectropolarimetric calibration to create observation matrix f(w). In particular, values D(1), D(2), and D(3) are included, where

math::
D(1) = 0:5(1 + cos*(DELTA))*D(2) = 0:5(1 - cos(DELTA))D(3) = sin(DELTA)

and DELTA is the channel-dependent retardation.

Format: Retardation data are stored in separate groups corresponding to pass direction for polarizers A and B. Groups are two-dimensional. Stored in the first dimension are M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X- substeps. This data array is repeated through the second dimension for each of the values D(1), D(2), and D(3). Retardation data are stored in REAL*4 format.

Flags and Indicators: The retardation data file is selected on the basis of the keywords DETECTOR, OVERSCAN, POLAR_ID, and FGWA_ID.

Restrictions: The FOS calibration software will reject any inappropriately sized groups. The following listing shows a sample header from an FOS retardation data file.

SIMPLE = F                     / image conforms to the fits standard                      L1
BITPIX = 32                    / bits per data value                                      I2
DATATYPE= REAL\*4              / datatype of the group array                              CHR
NAXIS = 2                      / number of data axes                                      I2
NAXIS1 =                       / number of elements ((chnls+scan-1)\*xsteps)              I2
NAXIS2 = 3                     / number of elements (D(1), D(2), D(3))                    I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 2                     / number of groups                                         I2
PCOUNT = 1                     / number of group parameters                               I2
0PSIZE = 32                    / bits in the group parameter block                        I2

                        / GROUP PARAMETERS: PODPS CALIBRATION
PTYPE1 = PASS\_DIR             / pass direction: 1, 2                                     CHR
PDTYPE1 = INTEGER\*4           / datatype of parameter 1                                  CHR
PSIZE1 = 32                    / number of bits in parameter 1                            I2

                        / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= WAVE RETARDATION     / waveplate retardation                                    CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written                               CHR

                        / FOS FLAGS AND INDICATORS KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
FCHNL =                        / first channel processed: 0, 2, ... 510                   I2
NCHNLS =                       / number of channels processed: 2,4,...512                 I2
NXSTEPS =                      / number of x substeps: 1, 2, 4, 8, 16                     I2
OVERSCAN=                      / overscan number: 1-256                                   I2
POLAR\_ID=                     / polarizer id: A, B                                       CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, H27, .. ANY                 CHR
USEAFTER=                      / use this file for obs. taken on/after this date          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                    [Listing Version 02 26-MAY-1994]

3.1.5 Disabled Diode Files (DDT): <uniquename>.R4H

FOS disabled diode files contain a disabled diode table for use in the standard case reduction when the Unique Data Log (UDL) is not available.

Format: Disabled diode data are stored in a single group with 512 data values, one for each diode, with a value of 0 indicating a disabled diode and a value of 1 indicating an enabled diode. Disabled diode data are stored in short integer format (INTEGER*2).

Flags and Indicators: The disabled diode data file is selected on the basis of the keyword

DETECTOR.

Restrictions: The FOS calibration software will reject any inappropriately sized groups. A sample header from an FOS disabled diode table appears in the following listing.

GCOUNT = 1                     / number of groups                                         I2
PCOUNT = 0                     / number of group parameters                               I2
PSIZE = 0                      / bits in the group parameter block                        I2
INSTRUME= FOS                  / instrument                                               CHR

                   / FOS DATA DESCRIPTOR KEYWORDS
FILETYPE= DISABLED DIODE       / disabled diode reference file                            CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written                               CHR

                   / FOS FLAGS AND INDICATORS KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
USEAFTER=                      / use this file for obs.  taken on/after this date         CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                        Listing Version 02 26-MAY-1994]

3.1.6 Data Quality Initialization Files (QIN): <uniquename>.R5H

FOS data quality initialization reference files contain a priori information about the effect of the FOS’s diode arrays on the quality of output data values.

Format: Data quality initialization data are stored in a single group with M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X-substeps. Data quality initialization data are stored in single-precision real format (REAL*4).

Flags and Indicators: The data quality initialization file is selected on the basis of the keywords DETECTOR, OVERSCAN, APER_ID, POLAR_ID, FGWD_ID, APER_POS, and PASS_DIR.

Restrictions: The FOS calibration software will reject any inappropriately sized groups. The listing below shows a sample data quality initialization file’s header.

                    / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= DQ INIT              / data quality initialization file                         CHR
HEADNAME=                      / reference header file name                               CHR
DATANAME=                      / reference data file name                                 CHR
DATE =                         / date this file was written                               CHR

                    / FOS FLAG AND INDICATOR KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
FCHNL =                        / first channel processed: 0, 2, ..., 510                  I2
NCHNLS =                       / number of channels processed: 2,4,...,512                I2
NXSTEPS =                      / number of x substeps: 1, 2, 4, 8, 16                     I2
OVERSCAN=                      / overscan number: 1-256                                   I2
APER\_ID =                     / aperture id: A-1, A-2, .. B-1, .. ANY                    CHR
POLAR\_ID=                     / polarizer id: A, B, C                                    CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, .. ANY                      CHR
PASS\_DIR=                     / pass direction: 0, 1, 2                                  I2
APER\_POS=                     / aperture position: UPPER, LOWER, SINGLE                  CHR
USEAFTER=                      / use this file for obs. taken on/after this date          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
END
                                                        [Listing Version 02 26-MAY-1994]

3.1.7 Average Inverse Sensitivity Files (AIS): <uniquename>.R8H

FOS average inverse sensitivity reference files contain data used to convert object data to an absolute flux scale (spectroscopy ground software mode). The sensitivity data pertain to a particular reference aperture. Object data obtained with other apertures must be corrected for differences in aperture throughput using reference data contained in table .CYB.

Format: Average inverse sensitivity data are stored in a single group with M * N entries, where M is the number of diodes plus overscan minus one and N is the number of X-substeps. Average inverse sensitivity data are stored in REAL* 4 format. Data have units of (ergs cm-2 s-1 A*-

1)/(counts s-1).

Flags and Indicators: The average inverse sensitivity data file is selected on the basis of DETECTOR, OVERSCAN, POLAR_ID, and FGWA_ID.

Restrictions: Inappropriately sized groups will be rejected.

The following listing shows a sample header from a FOS average inverse sensitivity file.

SIMPLE = F                     / image conforms to the fits standard                      L1
BITPIX = 32                    / bits per data value                                      I2
DATATYPE= REAL\*4              / datatype of the group array                              CHR
NAXIS = 1                      / number of data axes                                      I2
NAXIS1 = 2064                  / number of elements                                       I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 1                     / number of groups                                         I2
PCOUNT = 0                     / number of group parameters                               I2
PSIZE = 0                      / bits in the group parameter block                        I2

                / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= INV SENSITIVITY      / inverse sensitivity ref file (multiplicative)            CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
USEAFTER=                      /                                                          CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written (dd/mm/yy)                    CHR

                / FOS FLAG AND INDICATOR KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
FCHNL =                        / first channel processed: 0, 2, ..., 510                  I2
NCHNLS =                       / number of channels processed: 2,4,...,512                I2
NXSTEPS =                      / number of x substeps: 1, 2, 4, 8, 16                     I2
OVERSCAN=                      / overscan number: 1,...,256                               I2
APER\_ID =                     / aperture id: A-1, A-2, .. B-1, .. ANY                    CHR
POLAR\_ID=                     / polarizer id: A, B, C                                    CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, .. ANY                      CHR
PASS\_DIR=                     / pass direction: 0, 1, 2                                  I2
APER\_POS=                     / aperture position: UPPER, LOWER, SINGLE                  CHR
WO\_OFFAV=                     / average wave offset in diodes                            R4
NUM\_OBS =                     / number of observations used to make AIS                  I2
HISTORY
END
                                            [Listing Version 01 26-AUG-1997]

3.1.8 Post-COSTAR Polarimetry Files (PCP): <uniquename>.R9H

The FOS post-COSTAR polarimetry files contain data to correct the computed Stokes vectors (Q, U, and V) and consequently the derived quantities of linear polarization, circular polarization, and polarization position angle for the post-COSTAR instrument configuration.The purpose and effect of the correction procedure implemented with the PCP reference file as well as methodologies for the generation of this file are thoroughly explained in FOS Instrument Science Report CAL/FOS-150, FOS Spectropolarimetry.

Format: The post-COSTAR polarimetry correction data are stored in a total of nine groups. The first three groups contain the Q corrections for pass 1, pass 2, and the combined pass; the next three groups contain the U corrections for the respective pass directions; the final three groups contain the V corrections for the respective pass directions. The data are stored in REAL* 8 format. The Q corrections stored in groups 1 -3 are unitless. The U corrections stored in groups 4-6 are unitless. The V corrections stored in groups 7-9 have units of degrees.

Flags and Indicators: The post-COSTAR polarimetry data file is selected on the basis of the keywords DETECTOR, FGWA_ID, POLAR_ID, APER_ID, and KYDEPLOY=T.

Restrictions: The FOS calibration software will reject any inappropriately sized groups. The following listing shows a sample header from an FOS post-COSTAR polarimetry file.

SIMPLE = F                     / image conforms to FITS standard                          L1
BITPIX = 64                    / bits per data value                                      I2
DATATYPE= REAL\*8              / datatype of the group array                              CHR
NAXIS = 1                      / number of data axes                                      I2
NAXIS1 = 2064                  / number of elements                                       I2
GROUPS = T                     / image is in group format                                 L1
GCOUNT = 9                     / number of groups                                         I2
PCOUNT = 6                     / bits in the group parameter block                        I2
PSIZE = 256                    / number of group parameters                               I2

                       / GROUP PARAMETERS
PTYPE1 = DATAMIN               / minimum data value in the group                          CHR
PDTYPE1 = REAL\*4              / datatype of parameter 1                                  CHR
PSIZE1 = 32                    / number of bits in parameter 1                            I2
PTYPE2 = DATAMAX               / maximum data value in the group                          CHR
PDTYPE2 = REAL\*4              / datatype of parameter 2                                  CHR
PSIZE2 = 32                    / number of bits in parameter 2                            I2
PTYPE3 = CRPIX1                / generated by IRAF STF kernel, def=0.                     CHR
PDTYPE3 = REAL\*4              / datatype of parameter 3                                  CHR
PSIZE3 = 32                    / number of bits in parameter 3                            I2
PTYPE4 = CRVAL1                / generated by IRAF STF kernel, def=0.                     CHR
PDTYPE4 = REAL\*8              / datatype of parameter 4                                  CHR
PSIZE4 = 64                    / number of bits in parameter 4                            I2
PTYPE5 = CTYPE1                / first coordinate type                                    CHR
PDTYPE5 = CHARACTER\*8         / datatype of parameter 5                                  CHR
PSIZE5 = 64                    / number of bits in parameter 5                            I2
PTYPE6 = CD1\_1                / generated by IRAF STF kernel, def=1.                     CHR
PDTYPE6 = REAL\*4              / datatype of parameter 6                                  CHR
PSIZE6 = 32                    / number of bits in parameter 6                            I2

                       / FOS DATA DESCRIPTOR KEYWORDS
INSTRUME= FOS                  / instrument                                               CHR
FILETYPE= PCP CORRECTION       / post-COSTAR polarimetry correction                       CHR
HEADNAME=                      / header file name                                         CHR
DATANAME=                      / data file name                                           CHR
DATE =                         / date this file was written                               CHR

                        / FOS FLAGS AND INDICATORS KEYWORDS
DETECTOR=                      / detector: AMBER, BLUE                                    CHR
APER\_ID =                     / aperture id: A-1, A-2, .. B-1, .. ANY                    CHR
POLAR\_ID=                     / polarizer id: A, B, C                                    CHR
FGWA\_ID =                     / disperser id: CAM, H13, H19, .. ANY                      CHR
USEAFTER=                      / use this file for obs. taken on/after this data          CHR
PEDIGREE=                      /                                                          CHR
DESCRIP =                      /                                                          CHR
HISTORY                        PCPHFILE                                                   V1.0
HISTORY                        ROOTNAME=                                                  /
HISTORY                        PROPID =                                                   /
HISTORY                        TITLE =                                                    / HISTORY TARGNAME= /
HISTORY                        PSTRTIME=                                                  /Date of observation
HISTORY                        PCPDATE =                                                  /Date this curve was generated
HISTORY                        Check ISR CAL/FOS-150 for details.
HISTORY                        new\_pcp.r9h renamed to xxxxxxxxx.r9h on date.
END

3.2 FOS Reference Relations and STSDAS Tables

3.2.1 Aperture Parameters Table: <uniquename>.CY0

The FOS aperture parameters table contains parameters used to describe the FOS apertures. The table is filled using data from the project data base tape.

Format: Records of aperture parameters are organized by detector and aperture ID.

Selection Scheme: Data records are selected based on the aperture ID.

An aperture parameters STSDAS table (<uniquename>.CY0 ) will have the structure shown in Table 3-1.

Table 3-1. FOS Aperture Parameters Table, <uniquename>.CY0

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
APER_NAME CH*10 Aperture name from PDB tape
APER_ID CH*3 Entrance aperture: A-1 through C-4
APER_POS CH*6 Arcsec2 Position in an aperture pair: UPPER, LOWER, SINGLE
APER_AREA D Aperture area associated with the aperture position

3.2.2 Aperture Position Parameters Table: <uniquename>.CY1

The FOS aperture position parameters table contains the two Y position values used to determine which of the apertures (upper or lower) was used for a given observation.

Format: Records of aperture position parameters are organized by detector and disperser.

Selection Scheme: Data records are selected on the basis of detector and disperser.

Table 3-2 shows the structure of an FOS aperture position STSDAS table (<uniquename>.CY1 ).

Table 3-2. FOS Aperture Position Parameters Table, <uniquename>.CY1

Column Name Data Type Units Description
DETECTOR CH*5 D Y deflection units
FGWA_ID CH*3 Y deflection units
YUPPER YLOWER D Detector ID: AMBER, BLUE

3.2.3 Emission Lines Table: <uniquename>.CY2

The FOS emission lines table contains the beginning and ending data point numbers of known emission line regions to be avoided during the smoothing of sky spectra.

Format: Records of emission line data points are organized by detector, disperser, first channel, and the number of X-substeps.

Selection Scheme: Data records are selected on the basis of detector, disperser, first channel to be processed, and number of X-substeps.

Table 3-3 shows the structure of an FOS emission lines STSDAS table, <uniquename>.CY2.

Table 3-3. FOS Emission Lines Table, <uniquename>.CY2

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
FGWA_ID CH*3 FGWA disperser: CAM, H13, H19, H27, H40, H57, H78, L15, L65, PRI
FCHNL I First channel to be processed
NXSTEPS I Number of X-substeps: 1, 2, 4, 8, 16
LINE_BEG D pixel Beginning emission line data point number
LINE_END D pixel Ending emission line data point number

3.2.4 Filter Widths Table: <uniquename>.CY3

The FOS filter widths table contains the mean and median filter spectra widths used to smooth the sky and background.

Format: Records of detector parameters are organized by detector.

Selection Scheme: Records are selected on the basis of detector.

Table 3-4 shows the structure of a sample FOS filter widths STSDAS table, <uniquename>.CY3.

Table 3-4. FOS Filter Widths Table, <uniquename>.CY3

Column Name Data Type Units Description
Description SKY_MN I pixel
DETECTOR CH*5 Detector ID: AMBER, BLUE
BCK_MD I pixel Median filter width used for background spectra smoothing
BCK_MN I pixel Mean filter width used for background spectra smoothing
SKY_MD I pixel Median filter width used for sky spectra smoothing

3.2.5 Wollaston/Wavelength Parameters Table: <uniquename>.CY4

FOS Wollaston/waveplate parameters are stored in this reference table, which contains the initial position of the waveplate and the measures of the angles of each of two pass directions with respect to the Q = 1 coordinate axis of the polarization reference frame.

Format: Records of the two pass direction angles and the initial waveplate position are organized by detector, disperser, and polarizer.

Selection Scheme: Records are selected on the basis of detector, disperser, and polarizer. Table 3-5 shows a sample FOS Wollaston/wavelength parameter table, <uniquename>.CY4 .

Table 3-5. FOS Wollaston/Wavelength Parameters Table, <uniquename>.CY4

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
FGWA_ID CH*3 Disperser: H13, H19, H27, H40, H57, H78, L15, L65, PRI
POLAR_ID CH*1 Polarizer element: A, B
ALPHA1 D radians First pass direction angle
ALPHA2 D radians Second pass direction angle
W1 D radians Initial waveplate position angle
COMBPX I pixel Pixel for wavelength offset determination
A R radians Å^1 Pol angle correction amplitude coefficient 1
B R radians Pol angle correction amplitude coefficient 2
C1 D radians Å^3 Pol angle correction phase coefficient 1
C2 D radians Å^2 Pol angle correction phase coefficient 2
C3 D radians Å Pol angle correction phase coefficient 3
C4 D radians Pol angle correction phase coefficient 4
C5 D radians Å^1 Pol angle correction phase coefficient 5

3.2.6 Sky Shift Parameters Table: <uniquename>.CY5

FOS sky shift parameters are stored in this table, which contains the parameters used to offset wavelength scales of sky data.

Format: Records of sky wavelength scale offsets are organized by detector, aperture, disperser, and the number of X-substeps.

Selection Scheme: Records for each of the two FOS detectors are selected on the basis of aperture, disperser, and the number of X-substeps.

Table 3-6 shows the structure of a sample FOS sky shift parameters table.

Table 3-6. FOS Sky Shift Parameters Table, <uniquename>.CY5

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
APER_ID CH*3 Entrance aperture: A-1 through C-4
APER_POS CH*6 Position in aperture pair: UPPER, LOWER, SINGLE
FGWA_ID CH*3 FGWA disperser: CAM, H13, H19, H27, H40, H57, H78, L15, L65, PRI
NXSTEPS I Number of X-substeps: 1, 2, 4, 8, 16
NSHIFT I pixel Smoothed sky spectrum wavelength offset

3.2.7 Wavelength Coefficients Table: <uniquename>.CY6

FOS wavelength coefficients are stored in this table, which contains the coefficients used to generate a wavelength scale for FOS spectral data.

Format: Records of wavelength coefficients are organized by detector, disperser, aperture, polarizer, and pass direction.

Selection Scheme: Records are selected on the basis of detector, disperser, aperture, polarizer, and pass direction.

Table 3-7 shows a sample FOS wavelength coefficients table.

Table 3-7. FOS Wavelength Coefficients Table, <uniquename>.CY6

Column Name Data Type Units Description
DETECTOR XZERO D Å pixel-3 or Å pixel3
APER_ID CH*5 D Å pixel-4 or Å pixel4
APER_POS CH*3 pixel
FGWA_ID CH*6 Detector ID: AMBER, BLUE
POLAR_ID CH*3 Entrance aperture: A-1 through C-4
PASS_DIR CH*1 Position in aperture pair: UPPER, LOWER, SINGLE
COEFF_0 I FGWA disperser: CAM, H13, H19, H27, H40, H57, H78,L15, L65, PRI
COEFF_1 D Polarizer element: A, B, C Polarization pass direction
COEFF_2 D Å Zeroth order wavelength coefficient†
COEFF_3 D Å pixel-1 or Å pixel First order wavelength coefficient†
COEFF_4 D Å pixel-2 or Å pixel2 Second order wavelength coefficient†

† Å pixel-n for grating and Å pixeln for prism.

3.2.8 GIMP Correction Coefficients Table: <uniquename>.CY7

FOS GIMP correction scale factors are stored in this table and are used to correct for the geomagnetically induced image motion problem.

Format: Records of the GIMP correction scale factors are organized by detector.

Selection Scheme: Records are selected on the basis of detector.

Table 3-8 shows the structure of the FOS GIMP correction coefficients STSDAS table, <uniquename>.CY7.

Table 3-8. FOS GIMP Correction Table, <uniquename>.CY7

Column Name Data Type Units Description
DETECTOR Detector ID: AMBER, BLUE diodes/gauss R
CH*5 X_FACTOR X scale factor Y deflection units/gauss
R Y_FACTOR Y scale factor

3.2.9 Background Count Rates Table: <uniquename>.CY8

FOS predicted mean background count rates are stored in this table as a function of geomagnetic latitude and longitude. The mean background count rate at the time and position of the observation is interpolated from the table and used to scale the reference background during calibration.

Format: Records of background count rates are organized by detector, latitude, and longitude.

Selection Scheme: Records are selected on the basis of detector.

Table 3-9 shows a sample table of FOS background count rates as a function of geomagnetic position, <uniquename>.CY8.

Table 3-9. FOS Scale Background Table, <uniquename>.CY8

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
M_LAT I degrees Geomagnetic latitude
GM_LONG I degrees Geomagnetic longitude
BACK_RATE R counts s-1 Mean background count rate

3.2.10 Scattered Light Parameters Table: <uniquename>.CY9

The FOS scattered light parameters table contains the beginning and ending diode positions of spectral regions that have no sensitivity to dispersed light, from which the level of scattered light is measured.

Format: Records of regions of no sensitivity are organized by detector and disperser.

Selection Scheme: Records are selected on the basis of detector and disperser.

Table 3-10 shows the structure of an FOS scattered light parameters STSDAS table, <uniquename>.CY9.

Table 3-10. FOS Scattered Light Parameters Table, <uniquename> .CY9

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
FGWA_ID CH*3 FGWA disperser: CAM, H13, H19, H27, H40, H57, H78, L15, L65, PRI
RANGE_BEG D diode Beginning no-sensitivity range diode number
RANGE_END D diode Ending no-sensitivity range diode number

3.2.11 OTA Focus Parameters Table: <uniquename>.CYA

The FOS OTA focus parameters table contains the OTA focus position (relative to a nominal focus position) as a function of MJD and is used to correct FOS spectra for variations in aperture throughput as a function of focus.

Format: Records of relative OTA focus position are organized on the basis of Modified Julian Date.

Selection Scheme: Records are selected on the basis of Modified Julian Date (MJD). Table 3-11 shows the structure of an OTA focus history STSDAS table, <uniquename>.CYA .

Table 3-11. FOS OTA Focus Parameters Table, <uniquename>.CYA

Column Name Data Type Units Description
MJD FOCUS microns
D Modified Julian Date D Focus position from nominal

3.2.12 Relative Throughput Parameters Table: <uniquename>.CYB

The FOS relative throughput parameters table contains aperture throughput coefficients for nominal OTA focus that are used to correct for the difference in aperture throughput relative to the aperture for which the average inverse sensitivity curve applies.

Format: Records of second-order polynomial throughput coefficients are organized on the basis of detector, disperser, and aperture.

Selection Scheme: Records are selected on the basis of DETECTOR, FGWA_ID, APER_ID, and APER_POS.

Table 3-12 shows the structure of an FOS throughput parameters STSDAS table, <uniquename>.CYB.

Table 3-12. FOS Relative Throughput Parameters Table, <uniquename>.CYB

Column Name Data Type Units Description
DETECTOR CH*5 Detector ID: AMBER, BLUE
FGWA_ID CH*3 FGWA disperser: CAM, H13, H19, H27, H40, H57, H78, L15, L65, PRI
APER_ID CH*3 Entrance aperture: A-1 through C-4
APER_POS CH*6 Position in an aperture pair: UPPER, LOWER, SINGLE
REF_APER CH*3 Reference aperture: A-1 through C-4
WMIN D _ Minimum wavelength
WMAX D _ Maximum wavelength
C0 D Dimensionless constant term
C1 D _ -1 Linear term
C2 D _ -2 Quadratic term
NUM_AVG I Number of datasets used to compute the coefficients

3.2.13 Focus Throughput Parameters Table: <uniquename>.CYC

The FOS focus throughput parameters table contains aperture throughput values as a function of wavelength and OTA focus deviation from nominal. The throughput values are used in conjunction with OTA focus position, derived from table <uniquename>.CYA , to correct the absolute flux calibration due to focus changes.

Format: Records of throughput are organized on the basis of detector and aperture.

Selection Scheme: Records are selected on the basis of DETECTOR and APER_ID.

Table 3-13 shows the structure of an FOS focus throughput parameters STSDAS table, <uniquename>.CYC .

Table 3-13. FOS Focus Throughput Parameters Table, <uniquename>.CYC

Column Name Data Type Units Description
DETECTOR THROUGHPUT D microns
APER_ID CH*5
WAVELENGTH CH*3 Detector ID: AMBER, BLUE Entrance aperture: A-1 through C-4
FOCUS D A* D

3.2.14 Time Dependent Throughput Parameters Table: <uniquename>.CYD

The FOS time dependent throughput parameters table contains correction factors for changes in inverse detector sensitivity as a function of wavelength and time.

Format: Records of throughput changes are organized on the basis of detector, disperser, and time.

Selection Scheme: Records are selected on the basis of DETECTOR, FGWA_ID, and

Modified Julian Date (MJD). Table 3-14 shows the structure of an FOS time dependent throughput parameters STSDAS table, <uniquename>.CYD .

Table 3-14. FOS Time Dependent Throughput Parameters Table, <uniquename>.CYD

Column Name Data Type Units Description
Description CORRECTION D
DETECTOR CH*5 Detector ID: AMBER, BLUE
FGWA_ID CH*3 FGWA disperser: CAM, H13, H19, H27, H40, H57, H78, L15, L65,PRI
MJD D Modified Julian Date
WAVELENGTH D Wavelength

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