[Aavso-photometry] IRAF photcal -- worth it?

[Chuck Pullen]

Use the Force, Michael!

If you use my guide, and use the on-board Landolt '92 catalog, and don't 
ask for anything that is of the wall (Like V-I), it's not that hard.  Most 
of the tasks you are looking at are very fine adjustments, like aperture 
corrections between different nights data (use the same aperture...), or 
configuring your own catalog of standard stars from scratch.

However, remember that PHOTCAL is not just for transformation coefficients, 
it will calculate them and your extinction coefficients for all filters, 
then transform your unknown fields to the standard system of your 
calibration fields.  So, it's major reason for being is to calibrate 
unknown fields from known fields at different airmass, on photometric nights.

Chuck

At 10:52 2/6/05 -0600, Michael Koppelman wrote:

>Since I am pretty comfortable with IRAF I thought maybe I'd start using 
>photcal to do my transformation coefficients. Chuck P. has mentioned this 
>in the past. A quick look at the help terrified me:
>
>--> help photcal
>digiphot.photcal:
>        mkapfile - Prepare  aperture corrections file from apphot/daophot 
> output
>       mkcatalog - Type in a standard star catalog or observations file
>        mkimsets - Prepare an image set file for input to (mk)(n)obsfile
>    mk(n)obsfile - Prepare an oservations file from apphot/daophot output
>      mkphotcors - Prepare the photometric corrections files
>          apfile - Prepare an aperture corrections file from a text file
>         obsfile - Prepare an observations file from a text file
>
>        mkconfig - Prepare a configuration file
>       chkconfig - Check the configuration file for grammar and syntax errors
>       fitparams - Compute the parameters of the transformation equations
>         evalfit - Compute the standard indices by evaluating the fit
>       invertfit - Compute the standard indices by inverting the fit
>
>This looks nightmarishly complex. Currently I use IRAF to do the ccd 
>reductions and photometry and then just use perl and Excel to compute my 
>coefficients and do transformations on observations.
>
>Do I really want to go through the pain of learning photcal? I reread 
>Chuck's Zen of IRAF on the subject and it seems doable but...
>
>Thanks!
>
>Cheers,
>Michael Koppelman
>http://www.lolife.com/astronomy/
>
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>




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