RE: Fwd: [Aavso-photometry] pipeline

[Thomas Droege <tdroege2@earthlink.net>]

Michael and all,

One thing that I have learned is that if you try to be perfect, nothing
will come out of the end of the pipeline.  So you have to pick the most
critical things and work on them.  Lots of compromises have to be made. 
Then in the end, you need an independent way to evaluate what has been
measured.  Since I am now trying to write a paper, this is what I have been
working on.  

The real problem is that there is not very much stuff that you can use to
compare the result.  This leads to a not very satisfactory "bootstrap"
comparison.

There is also a lot of "folklore" to combat about what is important.  
There is a lot of ritual related to darks and flats and the like.  This has
been worked out over time as being appropriate when you are looking at a
field a few arc minutes across.  When the field is 4 degrees in the tass
case and 8 degrees (?) in the ASAS case, there may be a different set of
problems to consider.  There is no one around to tell you what makes sense,
so one has to work it out as you go.  

It is not very hard to detect that the result is not perfect.  (Perfect is
defined as electron statistics noise limited.)  The question is "what to do
about it?"  Take more flats?  Take more darks?  Focus more often?  Track
better?  Sort out "bad" nights?  How does one figure out what is a "bad"
night?  

I have run a year now and taken 160M or so measurements.  Now I am looking
at them.  So far, I see nothing that I can relate to "conventional" wisdom
about such things.  For example, I don't think taking more darks or flats
will change anything but the amount of measurements taken.  Moving to
Hawaii or some such place might help, but I doubt it.  I see some of the
same problems in the ASAS data that I see in my own, and ASAS is at as good
a location as can be imagined.  One possibility is that the better tass
optics compensate for the improved location of ASAS which is using a camera
lens whose field is not nearly so flat.  But I just don't know.

Where we stand now, the data is of some value.  In fact, over the region of
real interest - mag 10-13 - the data is mostly electron statistics limited.
This is encouraging.  There is some frustration that the data is not as
good as it should be at the brighter mags.  Sigh!  

Tom Droege   


> [Original Message]
> From: Michael Koppelman <lolife@bitstream.net>
> To: Tass <tass@listserv.wwa.com>
> Date: 1/1/2004 11:40:36 PM
> Subject: Fwd: [Aavso-photometry] pipeline
>
> Now I understand how hard this TASS type of thing is -- to automate 
> this whole process is no small trick. Now that I've learned it the hard 
> way I should probably look around at what I could use where someone 
> else did the hard work!
>
> Cheers,
> Michael
>
>
> Begin forwarded message:
>
> > From: Michael Koppelman <lolife@bitstream.net>
> > Date: January 1, 2004 11:37:23 PM CST
> > To: aavso-photometry@mira.aavso.org
> > Subject: [Aavso-photometry] pipeline
> >
> > I spent the last two days working on my astrometry. You can't combine 
> > multiple nights of observations unless you get that figured out. 
> > WCSTools is pretty cool but it took a lot of tinkering to get it 
> > figured out.
> >
> > I've also been working on my pipline. When you are doing a normal 
> > time-series run, you can just process it in Mira or similar and be 
> > done with it. With this sequence business it is much more complicated. 
> > Check out this flow chart:
> >
> > http://www.lolife.com/astronomy/pipeline.png
> >
> > This assumes you already have your transformation coefficients and 
> > zeropoints. I also assumes you have your images reduced and ready to 
> > be processed with phot in IRAF. A combination of IRAF, WSCTools, perl 
> > scripts and some command line hackery has reduced a lot of the work 
> > involved, but it still takes quite a lot of time.
> >
> > It seems to me as a beginner in this all-sky stuff that the hard part 
> > is after you close the dome and boot up the computer!
> >
> > Cheers,
> > Michael Koppelman
> > http://www.lolife.com/astronomy/
> >
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