FOS/BLUE Wavelength-Zeropoint Correction Procedure Summary: A significant time-dependent systematic shift of up to 7 quarter-stepped pixels (1.75 diodes) in the zero-point of the FOS/BL wavelength scale has been confirmed in FOS Instrument Science Report (ISR) CAL/FOS-149 (Rosa, Kerber, and Keyes). ... Figures 1 and 2 (PDF - 14 Kbytes) illustrate the magnitude of the observed shifts and the effectiveness of the quick-fix algorithm provided here. ... Obtain the FOS ISR: CAL/FOS-149 (PDF - 53 Kbytes) . ...
... 172, Astronomical Data Analysis Software and Systems VIII, eds. D. M. Mehringer, R. L. Plante, & D. A. Roberts (San Francisco: ASP), 395 . ... We have investigated the internal zero-points of the HST's Faint object spectrograph (FOS) on-orbit wavelength calibration between 1990 (launch) and 1997 (de-commissioning). ... For BLUE systematic shifts of the zero-points are present, which amount to a maximum offset of 7 pixels (1.75 diodes) over the entire period. ...