When observers want to use fast read mode, we should first make sure it is reasonable to use. First, fast read mode is not compatible with cadenced observing – an RV taken by KPF in fast read mode will have an arbitrary offset to and RV taken of the same star in normal read mode. Thus, fast read mode really only makes sense for observations which are complete within a single night (or small number of nights) such as astroseismology or RM measurements.

Split Nights: Fast and Normal

We need to develop a policy for split nights. Changing modes induces a thermal transient which affects subsequent RV measurements, so we should avoid this unless it is well motivated scientifically.

Procedures

The SA for the night is responsible for making sure that the read mode gets switched to fast for the appropriate section of the night and for switching it back to normal when appropriate. Even if a night (or portion of a night) is fast read mode, we must to take the normal set of daily calibrations in normal read mode to maintain our knowledge of the instrumental drift and wavelength solution.

In addition to the normal calibrations we need to switch in to fast read mode and take a set of fast read mode calibrations (primarily biases, but also darks if time allows). This is probably best done after regular scheduled cals are finished (usually around 5:30pm HST) and before sunset. This can be a very narrow time window at some times of year.

After Automated Afternoon Cals Finish

To change mode to fast run: kpfSetReadModeFast

Then run the cals using: kpfRunCalOB -f /kroot/rel/default/data/obs/kpf/FastReadoutCals.yaml

This OB executes 22 biases (to match our normal daily set) and 1 dark (we’d like more, but we likely won’t have time). The dark frame can be canceled if needed in favor of observing (using the usual methods for stopping an OB in progress).

After Fast Read Mode Observations are Done

To change mode back to normal run: kpfSetReadModeNormal

This must be done before the normally scheduled cals begin at 7am HST.