Fibre Configuration

af2_configure is the program used to create a fibre configuration. You should start the preocess of creating configuration files well in advance of your run, and send your configuration files to your SA for checking at least one week before your run.

The af2_configure user manual.

The af2_configure source code and executables.

AF2_configure needs two input files:

The file small_fibres.dat

The file wht_prime.dat .

The versions of these files used to generate the configuration files should be the same as the system versions used to perform the physical setup; the versions linked above are synchronised with the system versions.

Please take the following points into consideration when generating your configuration fields:

• As AF2 arranges 1.6-arcsec fibres over a near 1-degree field it is imperative your astrometry is of the highest accuracy obtainable. In the past, observers have used data from APM, COSMOS, Sloan and USNO, leading to good results.
• Astrometry of bright sources from photographic plates will have lower accuracy, and bright stars are also liable to display proper motion.
• If possible, astrometric material should be less than about 10 years old (again because of proper motion effects on acquisition stars).
• Do not underestimate how long it will take to produce the configuration files. We strongly prefer to receive all configurations at least one week before the run so we can test them in the AF2 observing system. A wise observer would also arrange to arrive at the telescope at least one day in advance of their observing as configurations may have to be re-done at short notice due to unforeseen circumstances (e.g. the loss of a fibre).
• At least 3 acquisition (fiducial) stars are required; to be safe we suggest >= 4. There should be some fiducial stars in the centre of the field, and some in the outer areas around 20-arcminutes from the centre.They should all be bright enough (V≤15) and, if possible, of similar brightness. Ideally fiducial stars would be between 13th and 15th magnitude.
• Always check your fiducial stars for proper motion; the science fibres are 1.6-arcsecs in diameter, so astrometry must be of the highest accuracy.
• Always make sure to have the most up-to-date versions of files small_fibres.dat and wht_prime.dat .
• Using a buffer size of 1.5 is mandatory, otherwise your setup will likely be rejected by the AF2 system computer. Even if such a configuration is accepted, the risk of the fibre-positioning mechanism losing a fibre rises significantly for smaller buffer sizes, leading to potential mechanical problems which could take hours to fix, or, even worse, could cause permanent damage to the fibres.
• Remember to set the parameter FIBRES SMALL in your field configuration file (.fld)
• If you have more than one field it's best to use one of fibres 82 and 84 consistently in all configurations if you can (in the event that they are needed). This is because the system is setup with either fibre 82 or 84 in the butted region of the detector mosaic. Changing this requires a (simple) re-configuration of the slit-unit.
• Note that no more than 99 "spare" fiducial stars should be contained in the output file (.cfg) ("spare" fiducials are those listed at the end of the file and numbered starting from 901), or the setup command given at the Instrument Control System (ICL) may fail.
• It's not necessary to provide distinct configuration files for a range of hours angles. For a given configuration, the appropriate sidereal time is input when the field is configured at the telescope; this overrides the hour angle specified in the configuration file.

The coherent fiducial bundles, allow one to see, in the acquisition/guiding camera, stars as faint as magnitude V~16 with a nearly full moon, good seeing (1~arcsec), and some integration. However, you should select stars a bit brighter than this limit (V≤15), to account for possible poor weather conditions, ideally 13th to 15th magnitude.

Your configurations should be checked by the telescope observing system software in advance of your observations to avoid any risk to the fibres. Send your configuration files to your SA for checking at least one week in advance of your run, so that there's sufficient time to fix any problems that may occur.

Instructions on how to check a configuration file:

This is a brief set of instructions on how to check configurations at the telescope, e.g. should you wish to make changes to, or create new, configurations.

1. In the WHT control room, log in as whtobs (your SA will provide you with the password) at the machine labeled as whtdrpc1 (or whtdrpc2).

2. Open a terminal and create a directory corresponding to the PI's surname, as follows:

   >mkdir /home/whtobs/AF2/PI_NAME/

3. Copy your configuration files using scp. For example, if you brought your files in a flash drive, and it is mounted as /media/flashdrive/, do:

   >cd /media/pendrive/
   >scp configuration_files* whtobs@whtdrpc1.ing.iac.es:/home/whtobs/AF2/PI_NAME/"
   

4. Connect to lpss42 (or, alternatively, lpss39) using ssh:

   >ssh -X whtobs@lpss42 (or, alternatively, >ssh -X whtobs@lpss39)

5. Once logged in, type

   >obssys

   and then

   >cd /home/whtobs/AF2/PI_NAME/

   You can now check your configuration files by typing:

   >af2 checkt configuration_file.cfg xx:xx:xx

   where xx:xx:xx is the sidereal time (the average) you are planning to observe the given configuration (you can check this at http://catserver.ing.iac.es/staralt/).