A guide to IRCS grism spectroscopy exposure times
Even with the 0.15'' slit, the spectral resolution of the IRCS grisms
is not high enough to work effectively between the OH
lines. Good removal of these lines is an essential part of obtaining
high quality scientific data, and this is usually performed by nodding
the target along the slit on a timescale no longer than the typical variability
timescale of the OH lines.
There is no autoguider available for the instruments on Infrared-Nasmyth focus of Subaru telescope. IRCS, one of IR-Nasmith instruments of Subaru telescope, relies on AO188 for guiding.
Therefore, targets without suitable AO188 guide stars, either, NGS, or TTGS, relies on the telescope tracking only.
Any exposure longer 300 seconds on targets without suitable AO guide stars should be avoided.