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Galaxy Evolution Explorer

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Instrument & Calibration



Cycle 6 Information

GALEX Project at Caltech


Important information about observations made after May 4, 2010

After a "Coarse Sun Point" event on May 4th, 2010, it was noticed that point sources on the reduced NUV direct images were spread out (streaked) in the Y detector detection, resulting in a degradation of resolution of a factor of >5 in Y (the X direction was not affected).  This behavior is likely due to the partial failure of a capacitor associated with an A/D converter.

Fortunately, the photon position deviations were found to be correlated with the YA value (found in the raw photon position data).  After much testing and changes to the GALEX pipeline code, we have recovered the previous resolution of the reduced GALEX images to within 0.1 arcseconds FWHM on average.  (Note that the point source FWHM on any given GALEX image generally varies between 5.1 to 5.9 arcseconds.)

Unfortunately, we were unable to completely correct a small number of the photons, which results in 'ghost' images of bright sources amounting to less than 1% of the flux of the primary source.  The ghosts appear between 30 and 50 arcseconds above and below the primary source in the Y detector direction.  The detector X position of the primary and ghost are the same (within the error).  (See the 'nuv_det_x' and 'nuv_det_y' columns in the -mcat.fits file.)

Generally, the ghosts do not appear in the '-xd-mcat.fits' catalog, and are instead absorbed into the flux of the primary source.  A report on the details of the new GALEX performance will be available on the MAST GI web page in the near future


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

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