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12.8 Low-Dispersion Merged Extracted Image FITS File (MXLO)

The data extracted from the low-dispersion SI are stored in the MXLO using a binary table extension with fixed-length floating point vectors to contain the extracted fluxes and associated $\nu$ flags. Since no primary data are included, the extension header immediately follows the primary header. Each row of the binary table includes the following columns:

Wavelengths are linearly sampled to a uniform step size and measured in vacuum. Double aperture low-dispersion spectra will contain two rows in the above format, with one row for each aperture (LARGE first, then SMALL). Note the NAXIS1 keyword in the Binary table extension defines the number of bytes per row in the table and is equal to 15+18*640, or 11,535 bytes.

The absolute calibration covers the range of 1150-1980Å for short-wavelength spectra and 1850-3350Å for long-wavelength spectra. Since the NEWSIPS software extracts data over a slightly larger wavelength range, data points outside this wavelength range are set to 0 in the absolutely-calibrated flux vector and -1 in the sigma vector. The net and background vectors are not affected. The uncalibrated data points are also flagged in the $\nu$ flag vector with the value of -2. Table 12.10 shows the basic FITS Keywords for the MXLO.


 
 
Table 12.10:  MXLO - Basic FITS Keywords
Keyword and value Description
SIMPLE = T Standard FITS Format
BITPIX = 8 8 bits ASCII
NAXIS = 0 No image data
EXTEND = T Extensions are present
TELESCOP= 'IUE ' International Ultraviolet Explorer
DATE = 'dd/mm/yy' Date file is written
ORIGIN = 'VILSPA ' Institution generating the file
XTENSION= 'BINTABLE' Table extension
BITPIX = 8 Binary data
NAXIS = 2 Two-dimensional table array
NAXIS1 = 11535 Bytes per row (15+18*NPOINTS)
NAXIS2 = n Number of apertures (1-single, 2-both)
PCOUNT = 0 Number of bytes following data matrix
GCOUNT = 1 Only one group
TFIELDS = 9 Number of columns in the table
TFORM1 = '5A ' Count and data type of field 1
TTYPE1 = 'APERTURE' Aperture type (large or small)
TUNIT1 = ' ' Unitless
TFORM2 = '1I ' Field 2 has one 2-byte integer
TTYPE2 = 'NPOINTS ' Number of points
TUNIT2 = ' ' Unitless
TFORM3 = '1E ' Count and data type of field 3
TTYPE3 = 'WAVELENGTH' 3rd field is starting wavelength
TUNIT3 = 'ANGSTROM' Unit is angstrom
TFORM4 = '1E ' Count and data type of field 4
TTYPE4 = 'DELTAW ' 4th field is wavelength increment
TUNIT4 = 'ANGSTROM' Unit is Angstrom
TFORM5 = '640E ' Count and data type of field 5
TTYPE5 = 'NET ' 5th field is net flux array
TUNIT5 = 'FN ' Unit is IUE FN
TFORM6 = '640E ' Count and data type of field 6
TTYPE6 = 'BACKGROUND' 6th field is background flux array
TUNIT6 = 'FN ' Unit is IUE FN
TFORM7 = '640E ' Count and data type of field 7
TTYPE7 = 'SIGMA ' 7th field is the sigma
TUNIT7 = 'ERG/CM2/S/A' Unit is erg/cm2/sec/Angstrom
TFORM8 = '640I ' Count and data type of field 8
TTYPE8 = 'QUALITY ' 8th field is the data quality flag
TUNIT8 = ' ' Unitless
TFORM9 = '640E ' Count and data type of field 9
TTYPE9 = 'FLUX ' 9th field is the calibrated flux
TUNIT9 = 'ERG/CM2/S/A' Unit is erg/cm2/sec/Angstrom
FILENAME= 'AAAnnnnn.MXLO' Filename (camera)(number).MXLO
EXTNAME = 'MXLO ' Name of table


next up previous contents
Next: 12.9 High-Dispersion Merged Extracted Up: 12 Final Archive Data Previous: 12.7 High-Dispersion Resampled Image
Karen Levay
12/4/1997