Obscore Subtleties

[Arnold Rots]

We recently ran into a case where Obscore parameters are
either insufficient or ill-defined.
So, the question is: is this an issue that merits doing something
about or should we live with the ambiguity?

The case was a Chandra calibration observation taken pretty
far off-axis; we have quite a few of these and I don't expect us
to be the only ones engaging in this kind of thing.
The obvious purpose was to collect information on off-axis
behavior and PSF.

The first issue is that it would be helpful for unsuspecting users
to know that this was a calibration observation. Our database
knows that, but Obscore does not have a parameter that allows
communicating the type of observation. In addition to calibration,
one could think of observing modes, like pointed or scanning,
objective prism, grating, ...
Should Obscore be extended with information of this kind?
If so, how and to what extent?

The second issue concerns the coordinates, and is a question
of ambiguity.
The standard says "center of the observation".
Is that the pointing position (i.e., the tangent point) or the center
of the field of view? Both have their merits.
In the case at hand the tangent point fell well outside the FOV.

Just some more issues to mull over.
Cheers,

  - Arnold

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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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