Aspect Solution File (asol3.fits)
The aspect solution file consists of a single FITS format file describing the orientation of the telescope as a function of time—with fine astrometry corrections applied—which is used to accurately determine the celestial position of an X-ray event for an observation. Fine astrometry corrections are applied by determining an exposure weighted transformation matrix by cross-matching the full-field observation to a reference observation, where the reference observation is the observation in a stack—which the full-field observation is also a member of—with the highest signal-to-noise.
FITS HDUs (CXC Data Model blocks):
- ASPSOL: astrometry corrected aspect solution for the observation.
- xfm3: transformation matrix applied to the observation's aspect solution, resulting in the attached ASPSOL block.
The aspect solution FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_asol3.fits
where 〈i〉 is the instrument designation, 〈s〉 is the data source, 〈obs〉 is the observation identification, 〈obi〉 is the observation interval identification, 〈v〉 is the data product version number, and 〈c〉 is the cycle. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.