Header when summing spectra in ISIS

[Robin Leadbeater]

If you sum a series of spectra in ISIS, using "Tools" "Spectra Processing 2" remember to change the header details.

ISIS uses the header from the LAST spectrum in the series for the result so DATE-OBS and JD-OBS are incorrect and need be replaced with those from the first in the series.

It does not calculate the total exposure or JD-MID for the whole series either so these also need to be corrected.

Robin

[Peter Somogyi]

Since I'm doing per-exposure calibration for correcting the LHires moves (since "wavelength registration" not always working for me trustworthy), I'm also using this sum tool as a final step, and noticed this same problem. I fix it by opening headers and correcting values manually (then save the loaded fits - all in ISIS).

Of course, the major question here, for what purpose this serie sum is being meant for - is it meaningful to touch the header at all? If not, which fits file should be picked the header from? (my cleanest answer was at least pick it from the 1st, not the last one)

But as I saw, simple multiplication by const already touches exposure time (which indeed was unexpected for me, when combined 2 master darks to improve my darklib quality...noticed only when spectrum was noisy in the end - master dark's exposure time changed).

- Peter