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

[Konrad Kuijken]

Begin forwarded message:

> From: Paranal_AREmail <esoarspl at eso.org>
> Subject: PPRS-049927-Updated-VST-OMEGACAM-Possible drift of IA donuts during IA loop - centering algoriithm robust?-Software
> Date: July 19, 2013 1:48:54 GMT+02:00
> To: kuijken at strw.leidenuniv.nl
> Reply-To: Paranal_AREmail <esoarspl at eso.org>
> 
> Problem number PPRS-049927 in the Paranal PRS has now been updated.
> The new details of the ticket are listed below.
> This is for your information only.
> 
> 
> 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          : Assigned
> 
> -----  Minor Change Section ---------------------
> 
> -------------------------------------------------
> 
> Location             : VST
> Area/Instrument Type : INSTRUMENTS
> System/Instrument    : OMEGACAM
> Sub-system           : SOFTWARE
> 
> Assigned to Group    : Software
> Assigned to Person   : rschmutz
> 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.
> 
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