Calibration Procedures
Procedures for VAMPIRES calibrations.
Nightly / Pre-observing Calibrations
The following calibrations should be taken with every observation for each readout mode and crop planned during the observation. For all of these calibrations we recommend taking 1000 frames, minimum. Even in multiband mode, a single 1000-frame cube is okay; it will be a large file, but you only need to open it once to make the master calibration file.
Flat frames
Flat frames are critical for calibrating CMOS images due to the variance in gain from pixel to pixel. Flat frames are not strictly necessary for polarimetric differential imaging because the frame differencing will remove the fixed pattern noise, but we still recommend taking them for all observations.
Coronagraph masks
Because we align the coronagraph masks by moving the mask in the focal plane, it is difficult to take useful flats with the coronagraph mask in. We recommend taking standard flats with the fieldstop in addition to well-centered coronagraph mask flats.
To take flat frames, make sure the NsIR cal source is in- we recommend using 14V and 3A for the lamp settings. At these settings, there should be plenty of signal in any filter with 100 ms exposure times
sonne $ set_tint 0.1
sonne $ vampires_datatype flat
then log the data to gen2.
Pinhole frames
Pinhole frames should be taken right after flats by inserting the pinhole mask
scexao2 $ src_fib pinhole &
and then defocusing the DM with manual_zernike
scexao2 $ manual_zernike &
To do this, manually adjust the focus slider to +60 nm (as a starting point)
The datatype for pinholes is COMPARISON
sonne $ vampires_datatype comparison
Dark frames
For dark frames just match the exposure time of the flats and pinholes
sonne $ set_tint 0.1
and set the datatype
sonne $ vampires_datatype dark
Post-observing Calibrations
Dark frames
🧪: Automatated script
There is a script for automatically logging all necessary dark frames AFTER an observation has completed. This is convenient to have a perfect match for all the science data, but be aware the script is somewhat experimental.
First, prepare VAMPIRES for darks by putting the visible block in
$ vis_block in
then on scexao5 activate the vampires_control environment
scexao5 $ conda activate vampires_control
and enter the night’s saved data directory
scexao5 $ cd /mnt/fuuu/ARCHIVED_DATA/$(date -u +%Y%m%d)
and run the vampires_autodarks script
scexao5 $ vampires_autodarks -n 1000 .
feel free to change the number of frames per dark with the -n flag. I recommend 1000 frames unless it will take prohibitively long (e.g., if your EXPTIME is 1 second then 1000 frames will take 1000 seconds, so maybe choose something smaller).
On-sky Calibrations
In general, on-sky calibrations are reserved for stellar calibrators and are up to the observer to specify since they ultimately come out of their time budget.
Sky Frames
Sky frames are not strictly necessary for all VAMPIRES observations– we estimate that the sky background at its brightest is ~18 mag/sq.arcsec, which is not the limiting noise term for exposure times less than 1 second. One may consider taking sky frames as a proxy for dark frames, though. Sky frames have the data type SKYFLAT
sonne $ vampires_datatype skyflat
Photometric Standards
We recommend scheduling a photometric standard for each filter used if you are concerned with photometric accuracy. If using a coronagraph with satellite spots, we recommend scheduling a “ladder sequence”, where the coronagraph mask is removed to calibrate the photometry of satellite spots. Flux standard stars and ladder sequences have the data type STANDARD
sonne $ vampires_datatype standard
Astrometric Standards
We recommend observing an astrometric standard if you are concerned with astrometric accuracy. We have a list of binary stars with high-precision orbital ephemerides which can be used for VAMPIRES observations. This calibration should only need to be done once per run, if desired. The data type for astrometric standards is the normal OBJECT
sonne $ vampires_datatype object