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Home > Astronomy > Telescope Operator Notes > Working with SAURON


SAURON is an Integral Field Spectrograph using a lenslet array. It's a private instrument, developed in Lyon in cooperation with Leiden and Durham astronomers.


The cryostat must be filled with the telescope off zenith, by at least 20 degrees (EL < 70 deg).

  • Zeroset ROT, AZ and ALT (as usual)
  • USER> FOCUS 97.9-97.95 (2012)

Use the standard uDAS autoguider for CASS with AUTOFOCUS 1500-2500.
Use GSS2 to find guide stars and select instrument WHTCASSOwn from the configuration menu. Sauron has a small field of view, so guide stars with any value of autoradial can be used. To move the probe, login in to Taurus as whtobs and then do "obssys" followed by e.g.:

  • TO> prag 15000 50000.

First Night

Rotator centre and Calibrate:
After an instrument change you are supposed to determine the rotator centre and to run the 7 star calibrate procedure, which takes about 20 minutes. However, if the first night with Sauron is not a S/D night, this can be omitted.

To measure the rotator centre, use the direct viewing TV mirror, this is the top surface of the comparison mirror (i.e. AGCOMP). Measure the star position on the TV screen (x,y) at some sky PA, then rotate 180 degrees and measure again. Calculate the midpoint, which is the rotator centre.

Calibrate is done on the rotator centre with the rotator tracking turned off (USER> ROT MOUNT xxx). Use the reference point determined as above and AGCOMP direct view to acquire CAL stars.

Determine orientation of fields:
IMPORTANT:The sky PA must be set to 0 for this part, with instrument OWN in the TCS.
On the first night of a Sauron run, the orientation on the sky of the detector (i.e. the angle between the RA and Dec axes and the detector columns/rows) should be determined accurately as this is an important parameter for the custom acquisition program. This is all done by the observer. As with the pointing Calibrate, this need not be repeated on subsequent nights (unless the detector was refitted).


Sky Flats:
These need to be taken around sunset at latest, although Sauron's light requirements are not as extreme as for OASIS. Be prepared for long nights, with sky flats often taken at the end of the night until after sunrise too!

Telescope focus:
Finding the best telescope focus for use with Sauron is not trivial since the instrument forms no direct images and the width of the individual spectra are determined by the lenslets rather than the input image size. The overall width of the spectral pattern and the peak brightness will be influenced by seeing and focus but you will need a cloud-free sky and stable seeing to use these to adjust the telescope focus. Therefore, the telescope focus may not be checked (but it can be done by checking the focus for ACAM?). The nominal focus is close to that used for ISIS or ACAM: 97.95 mm but as with these instruments there may be long term variation.

Because a given target (generally a galaxy) is usually followed for a few hours, when slewing to a new object watch out for limits (rotator, azimuth) and if necessary use:


Acquisition is done with ACAM: the astronomer takes an image with ACAM and then uses the custom program to calculate an offset in RA/DEC (usually of the order of 5-10 arcsec) to center the objects in the center of the SAURON (30x40 arcsec) field. After this offset, start guiding. If further offsets are needed, use the Handset in (A)POFF mode.

Arcs are also taken on arrival at a new position, as much to determine flexure effects as to make wavelength calibration. Small telescope offsets in RA/Dec are usually made between successive galaxy exposures.

Several standards may be observed, at the start and end of the night, probably with short exposure times so that guiding is not required, and limits will not be an issue. The acquisition procedure is the same as for the main targets.

Data Handling

On DVD as usual.

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Last modified: 05 April 2013