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Data Structures

MIDAS tables and keywords are used to store most the information created and/or used by the MOS context. The tables \fbox{{\small \tt MOS}}, \fbox{{\small \tt LINPOS}}, \fbox{{\small \tt LINFIT}}, and \fbox{{\small \tt WINDOWS}} are created by the MOS commands; the table \fbox{{\small \tt LINECAT}} is available in the MIDAS data base. A short description of the tables is given below; a detailed description of their contents can be found in Table L.6.

\fbox{{\small \tt MOS}}.tbl
is created by LOCATE/MOS and used during the whole reduction process. It contains the limits of the slitlets.

\fbox{{\small \tt LINPOS}}.tbl
is created by SEARCH/MOS and updated by CALIBRATE/MOS. It contains the pixel-positions of the calibration lines, the row and the slitlet they belong to, their identifications and their intensities.

\fbox{{\small \tt LINFIT}}.tbl
is created by CALIBRATE/MOS and used by REBIN/MOS. It contains the fit coefficients for the dispersion relations of each row scanned by SEARCH/MOS.

\fbox{{\small \tt WINDOWS}}.tbl
is created by DEFINE/MOS and used by FITSKY/MOS and by EXTRACT/MOS. It contains the positions of the objects and the sky regions.

\fbox{{\small \tt LINECAT}}.tbl
contains the wavelength calibration lines. There will be several line-catalogs available in the instrument related system area, adapted for the use with the FORS grisms.

Table L.2: Table MOS
Table MOS
Label Unit Description
SLIT - sequential number of slitlet
YSTART PIXEL first row of slitlet
YEND PIXEL last row of slitlet
XOFFSET PIXEL offset of slitlet

Table L.3: Line positions table
Label Unit Description
X PIXEL x-position of calibration line
Y - world coordinate of row in which the line was found
PEAK - Peak intensity of calibration line
SLIT - number of slitlet in which the line was found
WAVE Angstroem identification of the line (Å)
WAVEC Angstroem fitted wavelength (Å)
REJECT - Rejection code (-5: line has been rejected due to too large residual)

Table L.4: Line catalog table
Label Unit Description
WAVE ANGSTROEM wavelength of calibration lines

Table L.5: Line fit table
Label Unit Description
SLIT - number of slitlet in which the dispersion relation was determined
ROW PIXEL row in which the dispersion relation was determined
Y - world coordinate of ROW
RMS Angstroem r.m.s. error of dispersion relation (Å)
COEF_i - dispersion coefficients

Table L.6: Windows table
Label Unit Description
OBJ_SLIT - number of slitlet in which the object was found
OBJ_STRT - first row of the object's spectrum (world coordinates)
OBJ_END - last row of the object's spectrum (world coordinates)
NET_INTENS - net peak intensity the object's spectrum
SKY_STRT - first row of sky regions (world coordinates)
SKY_END - last row of sky regions (world coordinates)
SKY_SLIT - number of slitlet in which the sky was found

Table L.7: Standard star table
Label Unit Description
MAGNITUDE - magnitude

Table L.8: Keywords used in context MOS
Name Default value Contents
Keywords for flat-field related commands
FLATLIM/R/1/3 0,0,0 detection parameters for slitlet location (detection threshold, median width, lower limit)
FFORD/I/1/1 3 order of fit for the FF normalization
NORMMET/C/1/20 POLY method for FF normalization
ISLIT/I/1/1 0 counter for slitlets
NSLIT/I/1/1 0 total number of slitlets
SCAN_POS/D/1/1 0. scan position and width for slitlet location
Keywords for wavelength calibration related commands
SEAPAR/C/1/20 200,5 detection threshold and width
YBIN/C/1/20 3,3 Step and Binning in Y
CENTMET/C/1/16 GRAVITY centering method for calibration lines
XPOS/D/1/50 0. Positions of identified lines (pixels)
LID/D/1/50 0. Positions of identified lines (Angstroems)
WLCMET/C/1/2 FC Wavelength calibration method (Ident/Linear/ Fors) and (Constant/Variable/Fit)
POLTYP/C/1/10 CHEBYSHEV type of polynomials used for fitting (Polynom, Legendre or Chebyshev)
TOL/R/1/1 2.0 tolerance for autom. wavel. ident. (< 0 Å, > pix)
TOLWIND/I/1/1 4 tolerance window for interact. wavel. ident.
WLCORD/I/1/2 2,1 order of fit used to compute the dispersion
ALPHA/R/1/1 0.2 Rejection parameter for lines matching [0,.5]
SHIFTTOL/I/1/1 10 tolerance for line identification from one slitlet to next
YSTART/I/1/1 0 Starting row for calibration (pixel value)
WLCNITER/I/1/2 3,20 Minimum, Maximum number of iterations
MAXDEV/R/1/1 10. Maximum deviation (pixels)
WCENTER/D/1/1 0. Central wavelength
AVDISP/R/1/1 0. Average dispersion per pixel
PLOTC/C/1/1 N Plot residuals of wavelength calibration
CAL/I/1/100 0 Results of moscalib (+1 dispersion relation fitted, -1 no dispersion relation fitted)
DISP/I/1/1 0 amount of intermediate display for CALIB/MOS
GRISM/I/1/1 1 No. of grism used
REJTHRES/R/1/1 3. rejection threshold

Table L.9: Keywords used in context MOS (cont'd)
Name Default value Contents
Keywords for rebinning commands
REBSTRT/D/1/1 0. Starting wavelength for rebinning
REBEND/D/1/1 0. Final wavelength for rebinning
REBSTP/D/1/1 0. Wavelength step for rebinning
Keywords for object extraction and sky subtraction related commands
THRESH/R/1/1 -0.04 detection threshold for object search
WIND/I/1/1 5 detection window for object search
XBIN/I/1/1 20 Binning in X for object search
SCAN_POS/D/1/1 0. center for scan (define/mos) in world coordinates
INT_LIM/D/1/1 0.001 fraction of central intensity where object limits shall be defined
NOBJ/I/1/1 0 number of objects found by define/mos
NSKY/I/1/1 0 number of sky-regions found by define/mos
SKYMET/C/1/16   method used to fit sky
SKYPAR/I/1/6 0 order of fit for polynomial or width of window for median
EXTPAR/C/1/60   extraction parameters (order, iter)
Keywords for frame names
OBJ/C/1/60   object frame
EXTOBJEC/C/1/60   extracted object frame
CALOBJEC/C/1/40   extracted object frame
SKYFRAME/C/1/60 sky sky frame
WLC/C/1/60 wlc calibration frame
FLAT/C/1/60 flat flat-field
NORMFLAT/C/1/60 normflat normalized flat-field
Keywords for table names
MOS/C/1/60 mos table with slitlets' positions
LINFIT/C/1/60 coerbr table with dispersion coefficients
LINPOS/C/1/60 linpos table with wavelength positions
LINECAT/C/1/60 hear table with wavelength positions
WINDOWS/C/1/60 windows table with sky and objects positions

Table L.10: Keywords used in context MOS (cont'd)
Name Default value Contents
Keywords for CCD parameters
STEP/D/1/2 0.,0. step-size of raw frame
START/D/1/2 0.,0. start values of raw frame
NPIX/I/1/2 0,0 size of raw frame
CCDPAR/C/1/60   read-out-noise and conversion factor of CCD

next up previous contents
Next: MOS Cookbook - A Up: Multi-Object Spectroscopy Previous: Extraction of objects
Petra Nass