[daip] POSSM velocity calculation

[Mayumi Sato]

Dear Eric,

Thank you for your reply.
We did not do ALTDEF for either of multi-source and SPLIT files.
Clearly the IMHEAD I sent you show that ALTSW fails for the
multi-source file saying "USE ALTDEF" but ALTSW went through for SPLIT
file (however, which got a wrong velocity).

To check this, I re-ran SPLIT for the multi-source file and ran POSSM
on both files without doing anything with ALTDEF or ALTSW, but there
still remains the same velocity difference.
I suspect the 64 channel shift / ALTDEF problem occurs either in
SPLITting the files (without ALTDEF on multi-source file) or in POSSM.

When we imaged from the SPLIT files, the ISPEC spectra (with ALTSW but
without ALTDEF) showed the right velocity as in multi-source POSSM -
only SPLIT+POSSM got the wrong velocity.

Thank you very much for your help.
Please let me know any file/parameters of data you need to look at.

Many thanks,

Mayumi