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Instrument & Calibration



Cycle 6 Information

GALEX Project at Caltech

The image fields [Smith, Cornett and Hill (1987) ApJ 320, 609, and (1990) ApJ 355, 746] are circular, 11.4 degrees in diameter, centered at RA 5h 17m 47s dec –68° 40’ 40”(1950), and have resolution ~50 arcsec at field center, increasing to ~2.5 arcmin at the field edge. The images [λeff=1495Å ; Δλ (FWHM) = 200Å and λeff=1934Å ; Δλ (FWHM) = 220Å] were made with a sounding rocket payload using a microchannel plate imaging onto film, and have been digitized, linearized and calibrated to ~15%. The FITS headers of the images contain complete calibration and astrometry information.

The following calibration constants are to be multiplied by the sum of the pixels in your aperture to yield a value in ergs cm-2 s-1 Å-1. These constants are for the provided exposure in each bandbass for 20 micron pixels (2048 x 2048 image).

The integer images' pixel units are linearized and are calibrated by the following constants. Additional comments and caveats follow.

Shorter Wavelength Exposure lmc1380a.fits
Nominal wavelength 1380 Å
Eff. Wavelength for OB association 1500 Å
Calibration for 20 micron pixels (2048x2048 image), exposure time of 80s 8.83 x 10-17erg cm-2 s-1 Å-1 / (image-unit pixel)
Download this image
Longer Wavelength Exposure lmc1909a.fits
Nominal wavelength 1909Å
Eff. Wavelength for OB association 1940Å
Calibration for 20 micron pixels (2048x2048 image), exposure time of 90s 2.06 x 10-17erg cm-2 s-1 Å-1 / (image-unit pixel)
Download this image

Calibration was done using ANS data of a region containing parts of associations LH 85 and 89 -- a continuous source from the sounding-rocket viewpoint. Since the shortest ANS band is around 1550 angstroms, the implied spectral energy distribution had to be extrapolated to shorter wavelengths; thus, calibration of the 1380 angstrom band is more uncertain than that of the 1909 angstrom band.


Responsible NASA Official: Susan G. Neff
J.D. Myers

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