[Comm2011] report from Groningen

[helmich]

Hi Gijs,

Tilt:
-----

We need to discuss this with Koen. In principle the VST guys must try first
to better align M1,M2 or whatever else is needed to optimize the image.
Until now they've not had the luxury of having a huge measuring device to
sample the focal plane. Hopefully they can do something.

PSF:
----

Pietro & co are happy to use our PSF_Anisotropy tool. I've shown Thomas and
Fernando Selman how to use it (and Split.py) and sent instructions to the
three of them. Pietro has my email and skype for any support needed.
Perhaps there are a few things we can do to improve it. They had a small
issue two nights ago with it, simply because the plot turned completely
black because of crowding. We haven't included many filtering options to
make the plot sparser, other than using boxes, but I've only updated the
code that doesn't average in boxes. Maybe you can look further at adding
filtering. Also the legend showing example ellipticity and the actual size
of the bars in the plot may not scale appropriately. (The scaling of
pylab.quiver is a bit mysterious, and I've hacked in the legend).

Detector issues:
----------------
I am slightly concerned about the combination of detector issues

Saturation+Linearity+Readnoise+Gain (+Crosstalk?)

They are all related to some degree. Because of the Saturation at 57000ADU
(actually it varies from 57k-61k ish, depending on the skybackground), the
FIERA filtering was changed. The result of that has been an increase in RON
from 2.2 ADU to 2.8 ADU roughly. At the same time the gain has dropped
(unexpectedly) from ~2.2 to ~1.6 e/ADU.

Saturation at 57k ADU with gain 2.2 e/ADU = 125k electrons
Saturation at 65k ADU with gain 1.6 e/ADU = 104k electrons

Van de regen in de drup? One thing we should like to know is the behaviour
of the variable saturation at around 57k. How is the linearity at this
point; i.e. as the saturation level changes, or at this lower saturation
level, is the linearity curve shifted or cut off?

This morning Dietrich noted apparently rather high noise in images taken
last night of Saturn.

Olaf and Christoph are still working on the crosstalk issue.

Ewout


On Thu, 31 Mar 2011 15:05:51 +0200, Gijs Verdoes Kleijn
<verdoes at astro.rug.nl> wrote:
> Dear Ewout et al.,
> 
> A brief summary report for you from Groningen data analysis:
> Tilt: can we help (see John's email for details)?
> PSF distorsions :  can we help (see John's email for details)?
> Crosstalk: we will also look into effect of cable replacement here.
> Linearity: well within specs for all CCDs
> Saturation:     already at 57000 ADU
> Readnoise:    seems in spec: to be confirmed completely
> Bias: seem in spec: to be confirmd completey
> Hotpixels:     hot pixel counts look ok compared to ILT 2005 report.
> DomeFlats: patterns noted which were also seen in Fabrice's thesis.
> Effect on data reduction TBD.
> Coldpixels: counts look ok compared to ILT 2005 report
> Science Data: data reduction on-going. Quick look raw data so far:
> cosmetics: bad columns here and there, reflected light.
> 
> Feel free to off-load tasks on us when possible.
> 
> Best wishes, on behalf of team here, Gijs
> 
> --
> --------------------------------------------------------------------
> |dr Gijs Verdoes Kleijn         |   astronomer                     |
> |e-mail: verdoes at astro.rug.nl   |   OmegaCEN / Kapteyn Institute / |
> |www: www.astro.rug.nl/~verdoes |   Target                         |
> |tel: +31-50-3638326            |   University of Groningen        |
> |mobile: +31-654658050          |   postal address:                |
> |                               |   Kapteyn Astronomical Institute |
> |                               |   Postbus 800, 9700 AV, Groningen|
> |                               |   The Netherlands                |
> --------------------------------------------------------------------
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