[Comm2011] Fwd: PPRS-049927-Closed-VST-OMEGACAM-Possible drift of IA donuts during IA loop - centering algoriithm robust?-Science Operations

[Konrad Kuijken]

Begin forwarded message:

> From: Paranal_AREmail <esoarspl at eso.org>
> Subject: PPRS-049927-Closed-VST-OMEGACAM-Possible drift of IA donuts during IA loop - centering algoriithm robust?-Science Operations
> Date: December 13, 2013 14:52:39 GMT+01:00
> To: kuijken at strw.leidenuniv.nl
> Reply-To: Paranal_AREmail <esoarspl at eso.org>
> 
> Ticket PPRS-049927 in the Paranal PRS has now been closed.
> A description of the problem, including its resolution, is listed below.
> 
> 
> Problem Number  : PPRS-049927
> 
> Creation Date   : 2013-03-23 18:31:07  by Steffen Mieske  (vst at eso.org)
> Type            : Problem
> Keywords        : Possible drift of IA donuts during IA loop - centering algoriithm robust?
> Priority        : Necessary
> Deadline        : 
> Status          : Closed
> 
> -----  Minor Change Section ---------------------
> 
> -------------------------------------------------
> 
> Location             : VST
> Area/Instrument Type : INSTRUMENTS
> System/Instrument    : OMEGACAM
> Sub-system           : SOFTWARE
> 
> Assigned to Group    : Science Operations
> Assigned to Person   : smieske
> CC List              :
> kuijken at strw.leidenuniv.nl
> tszeifer at eso.org
> smieske at eso.orgVst_Omega_Notification 
> uweilenm at eso.org 
> msterzik at eso.org 
> vst at eso.org
> par-vst at eso.org 
> acarlier at eso.org 
> akaufer at eso.org 
> par-tios at eso.org 
> Vst_all 
> tios-omega at eso.org 
> pietro.schipani at oacn.inaf.it 
> tios-vst at eso.org
> 
> Telescope Downtime   : 00:00
> Workload (hrs.)      : 2
> Detailed Description :
> Dear Ricardo,
> 
> could you verify please how the (re-)centering algorithm of the boxes of the IA CCD works? We have seen a few times either a jump of the donut from the center a bit towards the outskirts of the box, or a slow drift. The drift was apparently happending during guiding, but it is not 100% clear. [it was an observation from Konrad Kuijken who did the photo I sent you, but he did not 100% clearly remember whether it was during science or during aquisition]
> 
> As a first step it would be good to verify at which places in the SW the OS actually changes the box position of the IA star, for a recentering. I was up to now only aware of a recentering that happens after the very first box readout in the aquisition. At least this is where one typically sees a recentering: the pick object in aquisition may have been a bit inaccurate and thus the first box readout is used to re-center correctly the box.
> 
> In other places of the IA sequences, my interpretation of a motion of the IA donut would have been that the telescope is actually moving. Now we got a bit suspicious whether there is a continuous recentering of the box running that may not be robust.
> 
> Thanks for your help in this first step of analysis,
> Steffen
> 
> PS: I include Konrad in CC who found the occurences.
> 
> -----  Worklog & Comments Section ---------------
> 
> Worklog and Comments : 
>   2013-07-18 23:45:02   rschmutz
>      The IA star centers are obtained with the CENTROI command.
>      This command is only executed by the acquisition template, during the IA acquisition step.
> 
>      The IA box positions are also updated:
> 
>      1) In the acquisition template, during the IA acquisition step, after the user made a manual selection
>      of the IA stars (the manual selection is done after the CENTROI command).
> 
>      2) Between exposures, when the IA stars are manually re-selected.
> 
>      3) During offsets (with the OFFSAD command sent to ociaServer):
>      Note that the offset is specified in RA,Dec coordinates, which have to be converted into
>      detector coordinates according to the current telescope position and pixel scale, to so
>      compute the offset in pixels (in x,y coordinates).
>      If this conversion is not 100% correct, then you could evtl. see a shift of position of the
>      IA stars within the box.
>      The accuracy of this conversation could evtl. be verified on-sky performing offsets always
>      in the same direction.  While doing this, the IA star should stay on the center of the box.
>   2013-08-16 21:20:06   rschmutz
>      Ticket assigned back to the OmegaCAM IS.
>      Assignee changed: smieske 
>      Assigned to Group Changed: Science Operations 
>      Modified By: rschmutz 
>      Modified Date: 2013-08-16 21:20:05 
>      Assignee changed: smieske 
>      Assigned to Group Changed: Science Operations 
>      Modified By: rschmutz 
>      Modified Date: 2013-08-16 21:20:05 
>   2013-09-07 21:22:16   smieske
>      I would like to do some tests of this in my next shift starting Sept. 30.
> 
>      Steffen
>   2013-12-13 13:48:54   smieske
>      We could not reproduce this. At most, one can have a shift between the first click and the start of the longer iterations due to the centering algorithms. However, during IA integrations we could not really witness this. Relative offsets are performed with very high accuracy.
> 
>      I close the ticket.
> 
>      Thanks,
>      Steffen
> 
>      Status Changed: Closed 
>      Modified By: smieske 
>      Modified Date: 2013-12-13 13:48:54 
>      Status Changed: Closed 
>      Modified By: smieske 
>      Modified Date: 2013-12-13 13:48:54 
> 
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