Re: OGIP/93-013 - A list of standard strings for HE missions,instruments & filters.

["Jonathan McDowell" <jcm@urania.harvard.edu>]

To follow up on Ian's comments on Jeff's Alexis questions:

  2 (Filter keywords): This *is* a tricky one. On Einstein we only
had one filter of each type so there was no need to distinguish
between, say, several Al filters. I take Ian's point that post-launch
there is no absolute need to distinguish as long as the detector
is also specified, but I think I would come down on the side of
being explicit: either "Al-Si-C 03479 #1", or better, establish
a simpler official post-launch naming scheme of "Al/Si/C-1" for
telescope AF01, etc. with a separate calibration file giving the
correspondence between the as-flown filter Al/Si/C-1 and the
actual serial number 03479 #1. This will make it clear to the
user that different calibrations are needed for filters
Al/Si/C-1 and Al/Si/C-2. (The point of having such a file
is that for a yet-to-fly mission such as AXAF we can change the
filter just before launch and only have one place to change the mapping.)

  3 (Detectors): I agree with Ian that the extra spec is not necessary.
I think this sort of information is best stuck in a small calibration
file (even if it is also hardcoded in the s/w system): a little table
giving       Detector   Photocathode  Another-Quantity
             AF01       MgFl          Magenta   ...
             AF02     ...

  4:  We stuck to upper case for these strings for Einstein
because it retained the antiquarian flavor of the mission :-)
I would suggest that case-*sensitivity* be unimportant where
possible, so don't
have distinct detector names AF02 and Af02 referring to different
detectors, but these days (/pace/ Ian) we're using email more than
the phone so we might as well use the extra clarity gained by
mixed case. This is particularly true for chemical element combinations
such as MgFl. (e.g. is the CU filter a carbon-uranium compound or
a copper filter?) 

To echo Ian's disclaimer, these are my prejudices and not official
AXAF Science Center opinions.

   - Jonathan McDowell