PLOTS

The following plots are the differences between coordinates obtained from Chandra observations and those obtained from existing catalogs vs time in day of mission.

The following steps are taken to generate these plots

• All observations with grating are selected from a recent observation listNone grating observations with known point sources (e.g., previously observed objects)are also added to the list.
  
• Find coordinates for each observation from SIMBAD. If the coordinates information is given at three decimal accuracy, we use the observation. Otherwise it is dropped from the further process. These coordinates are converted into detector coordinates
  
• Using a cell detect function, find source positions in detector coordinates.
  
• Assuming the brightest object is the targeted source (this is true most of the time, because all observations are grating observations), compare those to the coordinates from the SIMBAD
  
• Convert the differences into arc sec, and plot the results

DATA Plotted (ASCII format)