We present a study of Chandra's optical distortions by
examining the positional accuracy of observed sources on the HRC-I.
We investigate the Chandra mirror and detector models' ability to reproduce the detector locations of observed sources by simulating ~160 calibration observations of AR Lac, HR 1099, and LMC X-1. To study the optical distortions of the mirrors more directly, we compare a 63 ksec observation of the Orion Nebular Cluster (ONC) with positions based on the well-determined optical astrometry of the cluster. We simulate observations of 100 reasonably bright sources from the Hillenbrand 1997 catalog of the ONC and compare the simulated positions with their observed positions. Offsets between the optical positions and the observed X-ray positions help determine a map of the optical distortions of the Chandra
Chandra X-ray Observatory (CXO) -- the third of NASA's Great
Observatories -- has now been successfully operated for four years and has brought us fruitful scientific results with many exciting
discoveries. The major achievement comparing to previous X-ray
missions lies in the heart of the CXO -- the High Resolution Mirror
Assembly. Its unprecedented spatial resolution and well calibrated
performing characteristics are the keys for its success. We discuss
the effective area of the CXO mirrors, based on the ground calibration measurements made at the X-Ray Calibration Facility in Marshall Space Flight Center before launch. We present the derivations of both on-axis and off-axis effective areas, which are currently used by Chandra observers.