
Delivered-To: oxborrow@dsri.dk
Date: Mon, 06 May 2002 16:10:20 +0200
From: Peter Kretschmar <peter.kretschmar@obs.unige.ch>
Subject: Re: ADD and bkg
To: Sami Maisala <smaisala@astro.helsinki.fi>
Cc: Niels Joergen Westergaard <njw@dsri.dk>, Stefan Larsson <stefan@astro.su.se>, Carol Anne Oxborrow <oxborrow@dsri.dk>
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  Hi Sami,

  sorry for not replying earlier - it still seems hard for me to find
a few minutes of time for anything at the moment.

  I've read your text over the weekend and it seemed generally fine
to me, with just one question: On p.113 you write under Processing:
"open 'blank' model from JMXi-SIDX-BKG-IDX". Why do you need to do
this, if you set one spectral parameter? Is it because the blank model
will effectively contain the detector shape?

  Now some comments on the discussion between Niels Jrgen and you:

Sami Maisala wrote:
> 
> yes I agree. The idea is to work in sub groups (blocks). I use term
> 'sub-group' to make difference between different type of models. In each
> sub-group we are using  only one decisive parameter - The others are set
> to the disregard values (-1)
>
  This is fully in line with what I remember from our discussion. The point
was to not use up too much of disk space by sampling the full 3D model.

  I should also mention that - hooray! - we do actually have a function
DALAUXgetPhase() for the orbital phase in DAL3AUX. Stphane had written
it already but not quite finished other updates when he handed over the
code to Bruce and during the handover the matter of this function 
dispappeared somehow. So, if I understand correctly, the function is
included in the latest delivered DAL3AUX, but the official documentation
coming with it is obsolete. Bruce will have an updated documentation for
us soon.
 
> I think this is misleading information.
>
  Now that you mention it: yes. If we have three models each predicting
a normalized level of 0.5 for a given spot, the result should not be
(0.5)^3 :-)
 
> In our case we should make  the
> combination by adding these models together and then make a normalization
> and the result is the final combined normalized bkg model.
> 
> Do you agree?
> 
  Yes.

> How about the diffuse bkg handling? I tried to put shortly together that
> what we discussed in our last meeting. Do you agree that?
>
  It seems correct to me.
 
> I have few missing pieces in this whole picture.
> Would you send me your ideas what you had in your mind in that meeting.
> There was few things I couldn't quite follow. I have questions like:
> 
> What we actually put in our galactical diffuse bkg catalogue?
> 
> How to use and calculate the tilt angle?
> 
  OK, we have to be specific now: Naively, I would think that at the
extreme points the flux is 1.0+-tan(tilt_angle) and for all other 
points the value is left as an exercise for the student :-) :-)
But before this is done, do you others agree?

> what was the model selection function?
> 
  ??? Of which function are you speaking now?

> What is the effect of the roll angle if we are using
> the same diffuse bkg model over the whole detector?
> 
  If it is tilted you need to rotate the tilt direction, right?

  Cheers,
  Peter
