Last modified: 14 December 2012


Observation Selection

There are many filters that determine which data sets are included or excluded from each release of the Chandra Source Catalog.

Release 1


Public ACIS timed-exposure mode observations in FAINT, VFAINT, or FAINT_BIAS exposure modes are included.

The following ACIS observations are excluded:

  • any other exposure modes (including GRADED)
  • ACIS continuous-clocking mode observations
  • ACIS subarrays with <= 128 rows (there are too few rows to guarantee identifying source-free-regions for the streak map background algorithm).

Public HRC-I observations are included in Release 1.1.


HRC-S is excluded from Release 1, due to background features that get detected as false sources with the existing algorithms.

Other exclusions

All grating observations are excluded.

Moving target (solar system) observations are excluded.

Selection Criteria

There are also a number of criteria that an observation interval (OBI) must meet in order to be selected for catalog processing: