The telescope you are using is a complex instrument, commanded by a sprawling software. Like an old couple, when both of them interact the output is substentially dependent of their current mood. In a bad day, this may result in a series of cryptic errors and crashes that are hard to decipher.

In such cases, the first thing to do is to follow the advice written on a sticker glued on the operation desk:

 “Don’t Panic”

The goal of this page is to help you with the most common problems you might encouter when observing lenses with WFI. If you don’t find what you need here, neither in the troubleshooting section of the operation manual it means you encountered an undocumented error (congratulations !) – please share it with us, especially if you managed to resolve it.

The OB execution crashed between two science exposure. What should I do ?

Click on “reset status” on the “Bob” window to reset the OB. Then click on “Interface – engineering mode”. This will allow you to edit the OB exposures on the fly. Click on the arrow on the left of the OB name to open it and access the exposures.

  • If the guiding is still active, then turn off the acquisition exposure by right-clicking on the arrow until you see a thumb down icon. Turn off the science exposures that have already been acquired in the previous execution of the OB. Then start the OB.
  • If the guiding is turned off, edit the acquisition exposure and look for the “PRESET.NEW” line, that should indicate “T”. By clicking on the “T”, you should be able to edit it and put “F” instead. This will prevent the telescope to move to its original position when you re-execute the OB. Turn off the science exposures that have already been acquired in the previous execution of the OB, by right-clicking on the arrow on the left of the exposures until you see a thumb down icon. Then start the OB. When the acquisition exposure asks you if you want to refine the pointing, say no.

I can’t find a good guiding star, it keeps drifting away from the box I selected

Try to adapt the size of the box on the fly. Even with the guiding activated, you can always pick a new guiding star and click on “Box to star” to readjust the guiding.

I can’t find no guiding stars at all, looks like the guiding CCD is dead !!

Well, it is either waiting for reanimation or dead for good. In both cases, you won’t be able to use the guiding for the night. To avoid too big drifts during the exposure, use the OBs with shorter exposure times if available. For example, instead of using DES0408_4x640_adjusted, use DES0408_12x220_adjusted. Note that this will slightly increase the total running time of the OB.

The automatic focus is going nuts, I see big donuts instead of stars on the images

Set the automatic focus to “False” on the “statemanager” desktop of the “BOB – Wide Field Imager” monitor. Then, move the focus manually to the theoretical prediction indicated in the “M2 Focus” section of the “TCS control panel” window, using the “Preset” field just below.

Using short test exposures that can be taken from the “e2p2 OS GUI” window in the desktop of the same name on the “BOB – Wide Field Imager” monitor, try different values for the focus around the theoretical predition. In the “rtd” window, you can measure the full width at half maximum (FWHM) of stars in these test exposures by clicking on “View – pick object” and clicking on stars. Compare the value of the FWHM you get with the actual seeing from the meteo monitor (there is a paper conversion table on your left). If you get similar values, this means you are close to the best focus you can get, and you can proceed with the science exposures.

The manual focus is going nuts as well ! What the…

If you used another instrument during the night, typically GROND, it might be that the theoretical prediction stays adapted to that instrument, and not to WFI. You should then apply an “unknown” offset from the theoretical prediction, i.e. manually explore many offsets and try to pick the best one (as explained in the previous error). Try starting with a focus 460 pts below the theoretical value, and let me know if it works or not.

I aborted an OB in BOB, but I cannot relaunch the next exposure, I keep getting a stupid error message saying enigmatic stuff about some WAIT command

There are three things you can try. In order of decreasing speed:

  1. Close the “bob” window, and reopen it from the terminal on the “startup” desktop, simply by typing “bob &”
  2. Click on “abort” on the “WFI General state” window, and/or on “abort seq./exp.” on the “e2p2 OS GUI” window in the desktop of the same name on the “BOB – Wide Field Imager” monitor. Do it multiple times, wait a few seconds, then click on “refresh” on the “bob” window. Multiple times. And try to re-execute your OB.
  3. Do a daily reboot of WFI (~10min), and if it doesn’t work reboot the TCS software (~15min) AND do a daily reboot of WFI. How to do this is described somewhere in the operation manual.

I couldn’t take night evening sky flats because of whatever the reason is. I would like to replace this with morning sky flats, but the OB stops after on exposure

This is a known bug in the morning sky flat sequence, that affects all the filters. The solution is to re-execute the OB at least three times (five times would be better), AND to manually dither the telescope between each execution. To do so, in the “TCS Control Panel” window look for the manual offset commands (on the right of the window), and apply a 20” offset both in RA. and DEC. before re-executing the sky flats OB

I observed with GROND, was nice and all but now that I try to come back to WFI, the mirror is stuck: typing “grondM3” does not work

This is a known issue that appears more often than you think, so the excerpt from the 2m2 operation manual is copied here :