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Home > Astronomy > Telescope Operator Notes > Working with PAUCAM


The PAU (Physics of the Accelerating Universe) project succesfully saw first light at the prime focus of the WHT on June 3rd 2015. PAUCam is an advanced imager comprising a mosaic of 18 state-of-the-art, fully-depleted, red-sensitive Hamamatsu CCDs, and a field of view with a diameter of about one degree (or about 11 times the sky area covered by the WHT's current prime-focus imager), of which 40 arcminutes are unvignetted. PAUCam was designed and built by a consortium of Spanish institutions (IFAE, ICE-CSIC/IEEC and PIC from Barcelona; CIEMAT and IFT-UAM/CSIC from Madrid).

PAUCam was built to carry out the PAU Survey, designed to study the existence and properties of dark energy using galaxy Redshift Space Distortions and Weak Lensing Magnification as cosmological probes. For this purpose, PAUCam will image up to 2 square degrees per night in 40 narrow-band and 5 broad-band filters to iAB~23, providing low-resolution (R~50) photometric spectra for around 30,000 galaxies, 5000 stars and 1000 quasars per night.


  • Zeroset AZ, ALT and ROT
  • USER> FOCUS 82.30 (May 2019)
Check that the telescope is at zenith and the petals closed and move the Nasmyth flat to the stow position by pressing the CASS button. On the TCS it will show that the optical configuration is "Prime (Nasmyth flat stowed)".

Filling the cryostat:

The cryostat will be filled by the PAUCAM team (only the first night PAUCAM is mounted). It is at prime focus so it is necesary to park the telescope at 10 degrees elevation (or use AP2).

In wet conditions, move the dome and telescope to these positions:

  • USER>DOME 298
  • USER>AZ 298
  • USER>EL 10

Rotator centre and Calibrate procedure:

As of Apr 2016, this has never been done (not needed since the pointing is good and it has a large FOV).


PAUCAM autoguiding was comissioned in April 2016 although with 100s exposures they find the tracking adequate so it won't be used for the PAU Survey, although it could be used for non-survey PAU observations.

If guiding will be used, the Autoguider to TCS selection switch should be in position PAUCAM (position no. 9). When autoguiding is used the PAUCAM system will send autoguiding packets to the TCS. This should be visible on the encoders page. There is no need to find a guide star as it is self-guided. There is no need to start the guiding either unless they want to do some corrections in their scripts.

To start guiding:

  • USER> AUTO ON 50 50


The OSA should remind PAUCAM observers that they should check the instrument (at ELEVATION 10 or AP2 position) and make sure Cryotiger-lines are sufficiently dry before going on sky and/or at the end of the night. In reality it's only needed when the humidity is moderate or high as ice will not be a problem at very low humidities.

Orientation: To get North pointing up on the detectors, set sky PA (the observers can also do this):


Movement of target using XY HANDSET keys: It will move as shown in the keyboard, but check next time it's mounted since they still have to define the global X and Y coordinates for their detector (each detector of the array has different X and Y orientations) and their display is arbitrary rotating 180 degrees. However, this will be hardly used because the PAUCAM system will normally go to different pointings between exposures (Apr 2016, ins_ad_xy2mount(16)=0.26843163 has been included with GSEXAM but Frank still has to set it to the instrument PAUCAM and update the documentation)

Acquisition: The observers will usually do the GOCAT (actually GOTO), often taking short exposures with a small offset inbetween. This can go on for many hours on the same field.

It is important to be sure that the rotator doesn`t reach the limit switch because the MOUNT PA range is only 357 degrees in total (limits: -163.37,193.63). Hitting the limit you can't simply unwrap, you have to wait a certain time until you get past the 3 'forbidden' degrees, which may take a while, depending where the object is on the sky, therefore watch carefully what the limits are each time they move to a new field and warn the observers if necessary.

To check if a rotator limit will be hit, see the AF2 rotator limits section

End of night: In the morning after observing, the telescope can be left at zenith as usual (this way the CASS instrument may be filled). It can also be left in dome flats position if required, as long as the CASS instruments are maintained cold if needed).

Dome Flats: The observers almost always need the telescope in dome flats position in the afternoon. On working days, put in a fault report and this will be done by ops. At weekends the telescope can be left in dome flats position before the OSA leaves, as long as the CASS cryostats are kept cold if needed. The PAUCAM system will control the dome flat lamps, open and close the petals and will take the exposures.

Data Handling

The data are handled by the PAUCAM team and do not appear in ING logs.

See also

PAUCAM instructions (last updated: 20160328).

In case any more TCS adjustments are needed (GSEXAM), please follow the links below:

PAUCAM guiding commissioning instructions for TCS users-OSAs (BSCW link, password protected).

PAUCAM commissioning instructions for TCS users-OSAs (BSCW link, password protected).

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Contact:  (Observing Support Assistant)
Last modified: 27 May 2019