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Calibration Database System

STIS Reference File Tables

Reference files used by the STIS calibration pipeline (CALSTIS) are updated on a regular basis. Current reference files files can be retrieved from the HST archive, or downloaded directly from the oref directory.



STIS Bias Images (BIA)

The bias reference image consists of an image of the additive stationary pattern in the electronic zero point of the UVIS CCDs. The structure of the electronic bias is removed from science images by subtracting the bias reference image.




STIS Dark Images (DRK)

The dark current reference image file consists of an image of the dark signal (i.e. the signal detected in the absence of photons from the sky). The dark reference image is subtracted from science images to remove the dark signal.




STIS Pixel-to-Pixel Flats (PFL)

The PFLTFILE represents the relative variations in pixel-to-pixel sensitivity of the detector. These images contain the wavelength-dependent, high spatial frequency information about the uniformity of the detector response.




STIS Delta Flats (DFL)

The delta flats consist of an image containing changes to the small scale flat field contained in the pixel-to-pixel flat file.




STIS Low Order Flats (LFL)

The low order flats consist of a map of the large scale variations in the sensitivity across the detector. This image contains the wavelength-dependent, low spatial frequency information about the uniformity of the detector. As such, this reference image usually gets stored as a subsampled image and expanded to match the science data when being applied by calstis.




STIS Shutter Shading Images (SSC)

The shutter shading correction file consists of an image with exposure time correction (in seconds) used to correct for shading caused by the CCD shutter during very short exposures. Each pixel in the image gives the additional time that a given pixel was exposed above the nominal exposure.




STIS Small-Scale Distortion Correction Images (SSD)

The small scale distortion correction file contains correction deltas to be applied to the detector positions to correct for small scale detector distortions that are not adequately modeled by the mapping from the detector coordinates system to calibrated wavelength and spatial position.




STIS Bad Pixel Tables (BPX)

The bad pixel table contains the location of known problematic pixels and the codes indicating the nature of the problem. The pixel locations refer to the full-frame, unbinned image. The data quality codes are 16-bit signed integers with each bit representing a specific problem.




STIS CCD Parameters Tables (CCD)

The CCD parameters table contains various CCD operating parameters and is indexed on the amplifier used for readout, as well as the commanded gain and bias level. Each row of the table contains the CCD amplifier, commanded gain, number of unbinned detector pixels in a bin, commanded offset, actual gain, average bias level, read noise, and saturation threshold.




STIS Linearity Correction Tables (LIN)

The MAMA linearity table contains the global and local count rate limits for the MAMA detectors and the value for the time constant t , in the nonlinearity correction:

Counts_obs = (counts_act)x(e^(-t*counts_act))

The count rate limits are used to assign data quality values to individual pixels or to the entire exposure. The time constant is used to correct for the nonlinearity in counting. Each row contains the detector name, the global and local count rate limits, the value for the time constant, and the value for the radius in pixels of the region around a flagged pixel that should also be flagged. The reference pedigree and description are also provided per row.




STIS Analog-to-Digital Tables (A2D)

The A-to-D correction table contains corrected data number (DN) values that will replace the input DN values that were assigned by the analog-to-digital conversion during readout. The correction will compensate for any bias in the assignment of certain DN numbers. Each row consists of the CCD amplifier in use, the commanded gain, a reference keyword, the value of the reference keyword, the number of elements in the array of DN corrections, and the array of DN corrections. The reference pedigree and description are also provided per row.




STIS Photometric Conversion Tables (PHT)

The photometric conversion table contains the throughput of the instrument configuration as a function of wavelength assuming an infinite aperture centered on the detector. The table contains the photometric correction for a point source. Effects such as vignetting and echelle blaze function are folded into this table. Each row contains the optical element, the central wavelength and spectral order (if a spectroscopic mode observation), the number of array elements, and arrays for the transmissions and corresponding wavelengths. The reference pedigree and description are also provided per row.




STIS Aperture Throughput Tables (APT)

The aperture throughput table consists of wavelength-dependent transmissions for each aperture with respect to a reference aperture. This table is used in conjunction with PHOTTAB to convert observed counts to absolute flux.




STIS Cal Lamp Spectra Tables (LMP)

The template calibration lamp spectra table contains spectra of the calibration lamps obtained at each of the operating currents. These spectra are used to create templates, which in turn are used to determine the wavelength corrections from which automatically generated or user-requested WAVECALs are to be applied to the default dispersion solutions.




STIS Aperture Description Tables (APD)

The aperture description table contains the geometric description of the apertures and their offsets (in arcseconds) from a reference aperture. The aperture name, size (length and width), offsets from the center of the aperture to the center of a reference aperture (which is named in the header), offsets from the aperture center to the center of the occulting bars, and the widths of the occulting bars are given.




STIS Image Distortion Correction Tables (IDC)

The image distortion correction table consists of a set of world coordinate information and fits to a distortion function that are used to construct the rectified, linearized 2-D image. Each row of the table contains the aperture, optical element, WCS information that defines the output rectified image, and the coefficients to the fits to the distortion functions. Possible function types include CHEBYSHEV, LEGENDRE, and POWER_SERIES.




STIS Photometry Keyword Table (IMPHTTAB)

This table removes the dependency on SYNPHOT libraries in determining such photometric parameters as PHOTFLAM, PHOTBW, and PHOTPLAM with pre-computed values. The use of this table is triggered by the PHOTCORR keyword switch.




STIS Spectrum Distortion Correction Tables (SDC)

The 2-D spectrum distortion correction table consists of a set of world coordinate information used to construct rectified, linearized 2-D spectra. One corrected image is produced per spectral order. Each row of the table contains the optical element, central wavelength, spectral order, the nominal axis 2 position of the center of the spectrum, and the WCS information that defines the output rectified spectra.




STIS Incidence Angle Correction Tables (IAC)

The incidence angle correction table contains coefficients to fits of the change in two dispersion coefficients (the zero-point and the first-order terms) as a function of angular offset from the reference position. These corrections are applied to the default dispersion coefficients. Each row consists of the optical element employed, the observation type, the central wavelength, spectral order, the number of coefficients, and the two coefficients used to derive the corrections to each of the zero-point and first-order terms in the dispersion relation.




STIS Dispersion Coefficients Tables (DSP)

The dispersion coefficients table consists of the coefficients to the nominal dispersion solution to be applied to extracted 1-D spectra. Each row consists of grating, central wavelength, spectral order, the reference aperture name, and the coefficients to one of the dispersion functions (gratings or prism).




STIS Spectrum Trace Tables (1DT)

The 1-D spectrum trace table consists of displacements of spectra along Axis2 for determining the location of a spectrum prior to extracting the 1-D spectrum. Each row of this table consists of an array of the y-displacements of the center of the spectrum from the nominal center, tabulated by position along the slit (Axis2).




STIS 1-D Extraction Parameter Tables (1DX)

The 1-D extraction parameter table describes the extraction apertures (or "boxes") and methods used in the extraction of 1-D spectra. Each row of the table describes the size and orientation of the target extraction aperture and the sizes, locations, and orientation of background extraction regions. The orientations of the spectrum and the background boxes are expressed as coefficients to a low-order polynomial that specifies each orientation as a function of position along the order. The orientation angles are with respect to axis 2, in units of degrees. Also included are the order of the polynomial to be used in fitting the background for each wavelength bin, the algorithm to be used in extracting the order, and the maximum search extent for locating the orders (relative to the expected location).




MAMA Offset Correction Tables (MOC)

The MAMA offset correction table contains coefficients to fits of the change in the dispersion coefficients as a function of commanded offset from the reference position. These corrections are applied to the default dispersion coefficients.

Each row consists of the optical element employed, the central wavelength, spectral order, and the number of coefficients plus two arrays of coefficients that are used to derive the corrections to each of the terms in the dispersion relation.




STIS Cosmic Ray Rejection Tables (CRR)

The cosmic ray rejection table contains the parameters used in the cosmic ray rejection algorithm.

Each row of the table contains the value for the number of CRSPLIT images, the mean exposure time of the splits, the method used for the initial guess at the CR-rejected solution, the method for subtracting the sky, the statistical rejection thresholds, the rejection propagation radius and relative threshold, the data quality bit mask that designates bad input pixels, and a switch to control whether the data quality values are set for CR-rejected pixels in the input data.




STIS Photometric Correction Tables (PCT)

The purpose of the photometric correction table (PCT) can best be understood in the context of the photometric conversion table (PHT). The photometric conversion table (PHT) contains the throughput of the instrument configuration as a function of wavelength assuming a fixed height extraction aperture centered on the spectrum of the point source. This aperture height is currently (as of 23 Oct 97) 11 pixels for the MAMAs and 7 pixels for the CCD. To calibrate diffuse source spectra properly to absolute surface brightness and to allow for optional extraction apertures for point sources, a correction factor must be applied to the standard photometric point source calibration. The calibrated point source fluxes calculated must be divided by the correction factors in the PCT table for either of these two cases.




STIS Wavecal Parameters Table (WCP)

The wavecal parameters table (WCP) contains parameters that control the wavecal processing.




STIS Cross-Disperser Scattering Table (CDS)

Contains area-normalized scattering profiles for STIS cross-dispersers, as a function of offset measured in low-resolution MAMA pixels. Profiles must have an odd number of pixels with the midpoint of the profile corresponding to an offset of zero pixels. Each row corresponds to a particular cross-disperser. Each row contains the optical mode (OPT_ELEM) which is used during row selection, the number of data points (NELEM) in the scattering profile, the scattering profile itself (CDSCAT), PEDIGREE and DESCRIP.




STIS Echelle Scattering Table (ECH)

Contains area-normalized scattering profiles for STIS echelle gratings, as a function of offset measured in low-resolution MAMA pixels. Profiles must have an odd number of pixels with the midpoint of the profile corresponding to an offset of zero pixels. Each row corresponds to a particular echelle grating (OPT_ELEM) and echelle order (SPORDER). Each row contains the columns used during selection (OPT_ELEM and SPORDER), the number of data points (NELEM) in the scattering profile, the scattering profile itself (ECHSCAT), PEDIGREE and DESCRIP.




STIS Echelle Cross-Dispersion Scattering Table (EXS)

Contains area-normalized profiles describing smearing of echelle scattered light in the cross-dispersion direction. This is distinct from scattering by the cross-dispersing grating itself, which precedes the echelle grating in the optical path and is described in the CDS reference file. The physical origin of this component of scattering is not understood. Nonetheless, the scattering profile is given as a function of offset measured in low-resolution MAMA pixels. Profiles must have an odd number of pixels with the midpoint of the profile corresponding to an offset of zero pixels. Tables were initially constructed from the STIS IDT reference files named ech_xdisp_*.fits. Each row corresponds to a particular cross-disperser and hence a particular echelle grating. Each row contains the optical mode (OPT_ELEM) which is used during row selection, the number of data points (NELEM) in the scattering profile, the scattering profile itself (EXSCAT), PEDIGREE and DESCRIP.




STIS Detector Halo Table (HAL)

Contains volume-normalized detector halo images at one or more reference wavelengths for each echelle grating. Images have a maximum size of 1024 by 1024 MAMA low-resolution pixels. Each row corresponds to a particular combination of optical mode (OPT_ELEM) and reference wavelength (HALOWAVE). Each row contains columns used during row selection (OPT_ELEM and HALOWAVE), number of pixels along an edge of the square halo image (HALDIM), the halo image itself (HALO), PEDIGREE and DESCRIP.




STIS Echelle Ripple Table (RIP)

Contains peak-normalized ripple (or blaze) functions for STIS echelle gratings, as a function of wavelength, for each allowed echelle tilt (CENWAVE) and order (SPORDER). Tables were initially constructed from the STIS IDT reference files named ripple_*.fits. Each row corresponds to a unique combination of echelle grating (OPT_ELEM), tilt (CENWAVE), and order (SPORDER). Each row contains columns used during row selection (OPT_ELEM, CENWAVE, SPORDER), the number of wavelength points at which each ripple function is specified (NELEM), the wavelengths (in Angstroms) for each ripple function (WAVELENGTH), the actual ripple functions (RIPPLE), PEDIGREE and DESCRIP.




STIS Scattering Reference Wavelength Table (SRW)

Contains list of halo reference wavelengths (HRWLIST) and PSF reference wavelengths (PRWLIST) to use when correcting for the two-dimensional effects of scattered light. Each row corresponds to a unique combination of optical element (OPT_ELEM) and grating tilt (CENWAVE). Each row contains columns used during selection (OPT_ELEM and CENWAVE), the number of reference wavelengths for the given configuration (NHRW), the list of halo reference wavelengths (HRWLIST) in Angstroms, the list of PSF reference wavelengths (PRWLIST) in Angstroms, PEDIGREE and DESCRIP.




STIS Dark Correction Table (TDC)

The dark subtraction for the NUV-MAMA requires a special, time- and temperature-dependent characterization of the global rate of dark counts. This correction is distinct from the application of the DRK image, which corrects for the spatial distribution of the dark counts. This table contains the parameterization of this function.




STIS Telescope Point Spread Function Table (TEL)

Contains volume-normalized telescope PSF images at several reference wavelengths. Images have a maximum size of 196 by 196 pixels. NOTE: The PSF pixels need not have the same plate scale as STIS MAMA pixels! The actual plate scale (in arcsec per PSF pixel) for the PSF image is given in the PSCALE column. Each row corresponds to a particular reference wavelength (REFWAVE). Each row contains a reference wavelength (REFWAVE) used during row selection, plate scale (PSCALE) for the PSF image, number of pixels along an edge of the square telescope PSF image (PSFDIM), the telescope PSF image itself (TELEPSF), PEDIGREE and DESCRIP.




STIS Grating-Aperture Correction Table (GAC)

STIS spectroscopic flux depends on the grating and apertures combinations. The GACTAB reference file contains the needed correction vectors as a function of wavelength. They are selected by the OPT_ELEM/APERTURE/CENWAVE combination. The correction vector for a 52X2 observation at the standard position is assumed to have a value of unity.

This file contains correction vectors for the 52X* and 52X*E1 apertures when used with the G230LB, G430L, and G750L gratings. The final row of this file contains an "ANY" row set to a unit correction vector which will catch all other cases.




STIS Time Dependent Sensitivity Files (TDS)

Measures the change in the sensitivity of the detectors with time.