Date: Thu, 2 Dec 1999 13:15:15 -0500 (EST) From: Jeremy Drake Subject: point source HETG/LETG+ACIS-S SIM Z offsets and ACIS-S chips To: CXC From: Jeremy Drake Subject: point source HETG/LETG+ACIS-S SIM Z offsets and ACIS-S chips Date: 2/12/99 This memo is to clarify the current CXC Calibration recommendations regarding the FEP0 issue and the ACIS-S chips to use, and default SIM Z offset positions to use with LETG and HETG observations that use ACIS-S as the detector. FEP0 ---- While running ACIS-S with 5 chips the CXC Calibration recommended chips to use are S1-S5, dropping S0. SIM Z Offest ------------ The purpose of defining different SIM offsets is to place the source as near to the framestore as practicable in order to ameliorate the effects of CTI in ACIS-S FI chips. The offsets outlined here supersede those of the earlier memo on this topic (JJD, 28/10/99). The recommended offsets outlined in the earlier memo for the combination of LETG+ACIS-S in both TE and CC modes could not be implemented due to a FID light problem that is not easily solved. Only the LETG+ACIS-S offsets were affected; these are amended below. The revised set of CXC Calibration recommended off-sets for POINT SOURCES ONLY for all the combinations of HETG, LETG, ACIS-S and CC and TE modes are as follows: Configuration Mode SIM z (mm) SIM z (motor steps)* HETG+ACIS-S TE -3 -1193 HETG+ACIS-S CC -4 -1591 LETG+ACIS-S TE -8 -3182 LETG+ACIS-S CC -8 -3182 * Conversion from mm --> motor steps according to /data/ascmp2/eriksen/focus/zsim2motor IMPORTANT NOTES 1/ For cases in which the source is significantly extended relative to the instrument resolution, or when there are multiple sources of interest in the field, these offsets will not necessarily apply as some source photons of interest could fall off the active detector area. 2/ For the combination LETG+HRC-S, until further notice all observations, unless otherwise specified, are recommended to be performed with no SIM offset such that 0th order is acquired at the nominal aim point in the z centre of the detector.