[Comm2011] OCAM2 daily log day 2

[John P. McFarland]

Hi All,

Tonight started with better conditions than last night, but there were 
clouds around the horizon that quickly came over the observatory.  A full 
set of daily and weekly health checks and calibrations were successfully 
completed this morning.  This evening, the 4-angle sky flat in g was 
successfully performed.  On the agenda for tonight was the 32-CCD photometry 
of SA107.  r-band, g-band, and part of i-band were observed after the polar 
field, but they were plagued by trefoil PSFs due to mirror deformations. 
In an e-mail to Dietrich Baade from Pietro Schipani near the end of OCM1B 
(see below), it was recommended to use the SETPC command after presetting to 
new coordinates after an AO calibration.  This was only partially tested 
before the PULPO error that occurred with the VST people yesterday morning 
recurred.  This error prevented any further data taking.  Prior to this, a 
work-around of running a onecal and resetting the focus value in between 
exposures appeared adequate.  Given that the two persons responsible for 
fixing the PULPO problem last time were no longer on the mountain and that 
they left no report about it, and that the conditions were far from 
photometric, it was decided to call it a night.

Cheers,


-=John


========================================================================

-------- Original Message --------
Subject:    Re: triangular stars
Date:   Mon, 09 May 2011 14:32:22 +0200
From:   Pietro Schipani <pietro.schipani at oacn.inaf.it>
To: Dietrich Baade <dbaade at eso.org>
CC: Steffen Mieske <smieske at eso.org>

Dear Dietrich,

I think the following might have happened.

When you do a new preset, you shall normally execute ONECAL cmd; not 
only the first (open loop) calibrated AO correction is performed, but 
also the task which kills the trefoil in VST is activated. Then you do 
IA, etc.

If, afterward, you do a new preset, even on the same coordinates, and 
you do not execute ONECAL again (because you do not want to loose the 
differential correction just done with the Shack-Hartmann), the "killing 
trefoil" task is disabled! Therefore so far the workaround was to send 
another command (SETPC) to enable it again (I wrote it in my last 
report). I would guess this was not done and caused the trefoil on the 
image.

To make it much easier, we are going to implement another keyword for 
the preset (the code is already done, today I am supposed to install and 
test it), with which the instrument can control with its SETUP if both 
ONECAL  and "killing trefoil" task must be activated, or only the 
"killing trefoil" task. This will help in case we want to send a second 
preset on the same coordinates or to very close objects, where we guess 
the correction we have just done with the active optics is still ok and 
so we don't want ONECAL, but still we need to compensate the trefoil 
(that increases without this task because the axial supports are not 
astatic and so the fixed points weight tend to change, rapidly if we are 
at large zenithal angles).

Best regards,
Pietro





Il 09/05/2011 10:01, Dietrich Baade ha scritto:
> Dear Pietro,
>
> Tonight, at about UT 06:40 (or 06:05 ??), Edwin performed an IA.  We 
> also checked the forces on M1, the distribution of which did not 
> signal anything grossly anomalous.
>
> However, virtually all stellar images were very highly triangular in 
> shape; see the data on wocoff (astro:/diskb/data/raw/2011-05-08).
>
> On the other hand, it seems (I'm trying to reconstruct things ex post 
> facto) that before and after the IA (if it was around 06:05) different 
> filters were used (g after u), and something may have gone wrong as 
> part of the filter change.
>
> We repeated the IA at 07:25 (this time is certain).  This had the 
> desired effect, I think.
>
> This was not the first time that such strongly triangular stars have 
> been seen.
>
> Kind regards,
>
> Dietrich.
>
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