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FITS File Formats

The table below summarizes the different FITS formats used for data sets archived within MAST. The notation used for the "format" column is described below. For more information on file formats, click on the mission names.

Mission File Type Sample Filename Format* Description / Comments
BEFS Extrcted Spectral Files befs2223.spc1 1-2Bf 12 columns, fluxes given in both photons & ergs/cm2/... units
Photon-list Files befs2223.lst1 B 6715226 rows! Not widely used.
Copernicus Raw c084.pep Bv Binary table containing variable-length vectors, with each row containing data from one scan.
Coadded Scans c084-001.bu1 Bf Binary table with fixed-length vectors.
Spectral Atlas Files alphacma2.fts B Binary table with scalar fields; each row contains data for one wavelength.
EUVE Image hz_43__9303101242N_img.fits 1-4I,1-5B Images and filter limits for one EUVE observation.
Event hz_43__9303101242N_evt.fits 5-11B Event and monitor data for one EUVE observation.
FOS Calibrated Wavelengths y3lg0107t_c0f.fits PA 2064xn primary array of wavelength vectors (A)
Calibrated Fluxes y3lg0107t_c1f.fits PA Primary array of fluxes (ergs/cm2/s/A)
Calibrated Sigmas y3lg0107t_c2f.fits PA Primary array of sigmas (ergs/cm2/s/A)
GHRS Calibrated Wavelengths z0ex021vt.c0f PA 2000x1 primary array of wavelengths (A)
Calibrated Fluxes z0ex021vt.c1f PA Primary array of fluxes (ergs/cm2/s/A)
Calibrated Sigmas z0ex021vt.c2f PA Primary array of Sigmas (ergs/cm2/s/A)
HUT Flux Calibrated 0833p652_100_01_d_ph.fits Pnh non-homogeneous primary array of fluxes and sigmas
IUE Raw file swp12345.rilo P 8-bit 768x768 image.
Linearized image lwp12345.lilo P,I 16-bit 768x768 array.
Resampled low dispersion swp12345.silo P,I 16-bit 640x80 primary array, and a 16-bit 640x80 image extension
Resampled high dispersion lwr97095.sihi P,Bf,2I 16-bit 768x768 primary array, and auxillary data.
Merged extracted spectral files lwp12345.mxlo Bf binary table with fixed-length vectors containing fluxes and wavelengths (in high dispersion, each row is one echelle order)
NICMOS mosaiced image n43u050_mos.fits P
2-d spectra .fits I
STIS Preview Spectra o4qa91929_p.fits B wavelengths in A, fluxes in ergs/cm2.. units.
1-d spectra o4mt02030_x1d.fits Bf 18 fields including wavelgenths & calibrated fluxes
summed 1-d spectra o4mt02030_sx1.fits Bf 18 fields including wavelgenths & calibrated fluxes
TUES Single order tues6003_3_ord40.fits B format similiar to BEFS, fluxes in both photons & ergs/cm2.. units.
Multiple Order tues6003_3_spectrum.fits B 20 row binary table, fluxes in both photons & ergs/cm2.. units.
UIT Raw density P 16-bit 2048x2048 (ASTRO-1) or 4096x4096 (ASTRO-2) image.
Linearized flat-fielded (e,f,fc) P 16-bit 2048x2048 (e,f) or 512x512 (fc) image.
Undistorted, rotated (g,gc) P 16-bit 2048x2048 (g) or 512x512 (gc) image.
Point-source (pph)/Aperture (aph) Photometry A ASCII Table of photometric measurements.
WUPPE Halfwave Level 1 Data ss-cyg_322731_1_hw.fits P,0-1B fluxes stored in primary array, polarimtery data in binary table

*Format Notation:
The following abbreviations are used for the various types of FITS header and data units (HDUs):

  • P- Primary array,
  • Pnh- Non-homogeneous primary array where each row of the array represents an independent vector (e.g., wavelength, flux, & error vectors),
  • B- Binary Table extension using only scalar fields,
  • Bf- Binary Table with fixed-length vector fields,
  • Bv- Binary Table with variable-length arrays,
  • I- Image extension,
  • A- ASCII Table extension.

If a number precedes the letter, it represents the number of occurrences of that particular HDU within the file. In some cases, the number of extensions may vary for a given file type. As an example, "P,Bf,2-4I" would describe a FITS file containing a primary HDU, followed by a binary table extension using fixed-length vector fields, followed by two to four image extensions.