VAMPIRES:Observing:Calibrations

VAMPIRES Calibrations

VAMPIRES Calibrations should be taken during the CHARIS calibration sequence, if CHARIS is in use. If not, the following actions can be taken directly.

PDI Flats

If the polarizing beamsplitter is in, when CHARIS is finished doing its PDI flats, increase the AO188 flat lamp to 2.4 amp. This should be enough light to take exposures with 300 EM gain. Set the data type to "FLAT" in vControl.

Braodband flats

If the nonpolarizing beamplitter or single-cam modes will be used, move the beamsplitter wheel and repeat the flat procedure from PDI flats. Set the data type to "FLAT" in vControl.

Pinholes

When CHARIS is finished doing its pinhole frames, increase the source amplitude to 2.4 amp. For each focus position (i.e., at 16 mm with a beamsplitter, 21 mm in single-cam mode, 14 mm in coronagraphic mode), take a set of pinhole frames. Set the data type to "COMPARISON" in vControl.

⚠️ VAMPIRES is non-telecentric

so any change in focus will change the plate scale. This is why each focus position needs to be recorded with the pinholes for accurate astrometric calibration

Darks

You can optionally put the Mirror into the pupil wheel, but sometimes scattered light still finds its way into the cameras. Take darks for each combination of EM gains, at least, and optionally for each exposure time. Set the data type to "DARK" in vControl. The actual dark current is quite low in the EM-CCDs, so it's more important to match EM gains than exposure times.

‼ Make sure to get all the darks

At the end of an observation, use the find_dark_settings script to parse through the night's data files and make sure to take any darks for EM gains used on-sky throughout the night.

Skies

Skies are generally not necessary since the sky is roughly 18 mag per square arcsecond in the visible, which is way below the read noise. Skies can be used as a substitute for darks as a convenience, especially if you are already taking skies for CHARIS. Set the data type to "SKY FLAT" in vControl and keep the EM gain and exposure settings the same as for the target.