[Aavso-photometry] Calculation of Transforms, K' and ZP

[Jeff Hopkins]

Hello Brian,

Nice to hear from you.

I am not familiar with your book or PhotoRed.

I'm still of the old school I guess. The mu and epsilon are still 
standards for me. In my book(s) I discussed how to determine the 
coefficients for the (V-R), (V-I) and (R-I) color indexes. I have 
also written software to handle all the reduction. This get more 
complex, at least for me, as I do UBVRIJH band work. It is difficult 
to find "standards" on what the transformation coefficients are 
called. I guess like you and me we can name them whatever we wish. 
The psi, mu and epsilon are pretty standard, however.

One thing I warn people about is using someone else's software 
without having a very firm idea about what is happening. As such I 
always recommend going through the complete process at least once 
with pencil and paper (and calculator). Also, in addition to the 
least squares method to determine slopes and intercepts I recommend 
doing some actual plots. Sometimes the plots can show problems that 
might otherwise be missed. They also give a better feel for what is 
happening.

I have gone through this calibration many times and what I have 
discovered is it is highly unlikely with the same system and same 
season that if you do multiple calibrations they will be the same. 
They should be close, but I think anything beyond the second decimal 
place is pretty fuzzy. Getting transformations to just one decimal 
place will provide fairly good results. Averaging several from 
different calibrations may be even better.

I'm looking forward to getting past the high heat and monsoon here. 
It's 112 right now and has been close to or above 110 almost every 
day during July and August. I miss my nightly observing. Bob Stencel 
e-mailed me a week ago around mid-night from Mt. Evans, CO (14,000' 
+). I had just gotten from doing some high heat observing (95 at 
midnight) and he said it was a balmy 38 there. He's doing some JH 
infrared band work with my SSP-4 since there is no way I can use it 
in this heat.

Jeff


At 12:55 -0700 09/01/2007, Brian D. Warner wrote:
>Jeff,
>
>PhotoRed does not produce the "old standard" mu/epsilon, which 
>presume color-index
>transforms instead of single color (still based on color index 
>differences, however).
>My book covers the methods applied in PhotoRed, so I'm not going to 
>go into detail
>here.
>
>For one, Steve did not use the Landolt magnitudes for his 
>calculations but those
>based on J-K conversions which I developed for "close enough" work 
>to calibrate
>night-to-night work for asteroid lightcurves, i.e,. _internal_ system and not
>Johnson-Cousins standard.
>
>Second, there is considerable scatter in his data when applying the 
>Hardie method for
>first order extinction, probably due to using those conversions. 
>This lead to bad FOE
>values.
>
>I'm working with Steve to go through the tutorials in PhotoRed that 
>do use Henden
>fields for finding FOE and transforms, and then compare what's done 
>there to what
>he's trying to do with his own images and data. Something is getting lost in
>translation <g>
>
>Clear Skies,
>Brian D. Warner
>Palmer Divide Observatory/Space Science Institute
>http://www.MinorPlanetObserver.com
>
>Collaborative Asteroid Lightcurve Link (CALL)
>http://www.MinorPlanetObserver.com/astlc/default.htm

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
(623) 247-1190 (Fax)
www.hposoft.com