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Hubble Space Telescope
ACS Anomalies

SBC observations of bright objects may show optical ghosts possibly due to reflection between the back and front sides of the filter.

The brightness of the ghost is typically less than 1% of the star brightness. The displacement of the ghosts from the star image is filter dependent:

Filter Displacement (pixels)
F122M -50,+155
F125LP -30,+95
F150LP -28,+78

Note: Displacement from the center of the real object in the undistorted image.

The following images show two example for an isolated star:

FIG1: Ghost in F122M of star HS2027+0651, Program 9020, 400 sec, ROOTNAME= 'j8c102vzq'

and a cluster of stars(the ghost image is indicated with a red circle):

FIG2: Multiple ghosts in F150LP in NGC6681, Program 9023, 560 sec, ROOTNAME='j8c601sxq'