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

[Jeff Hopkins]

Hello Steve,

I'm confused on what you are doing. Can you please elaborate on your procedure?

You should have 5 (the R-I is not needed as it can be derived from 
the other values) color transformation coefficients:
mu (for B-V)
epsilon for V
alpha for (V-R)
beta for (V-I)
gamma for (R-I)

Note: the alpha, beta and gamma are terms I use, but mu and epsilon 
are standard.

for extinction you should also have only 4/5 values
k'bv, k'v, k'vr, k'vi

These are what they are for your location and vary nightly.

and the same for the zero points
Zbv, Zv, Zvr, Zvi

Did you get the color data near the meridian (one or multiple images 
with the data averaged) and extinction at various air masses using a 
single star or the same stars and average the extinction data?

Jeff


At 12:02 -0700 09/01/2007, Steven Orlando wrote:
>Hello All,
>
>A couple of nights ago, I imaged two Landolt fields at different 
>airmasses. I took 5X1 min of BVRI, for the two fields. I used MPO 
>PhotoRed to analyze the data. This are the results:
>
>V-R:
>B: Transform = 0.328, k' = 0.458, ZP = 17.724
>V: Transform = -0.145, k' = 0.525, ZP = 19.062
>R: Transform = -0.196, k' = 0.635, ZP = 19.266
>I: Transform = 0.007, k' = 0.411, ZP = 18.406
>
>B-V:
>B: Transform = 0.173, k' = 0.428, ZP = 17.567
>V: Transform = -0.078, k' = 0.538, ZP = 19.132
>R: Transform = -0.105, k' = 0.383, ZP = 19.361
>I: Transform = 0.002, k' = 0.410, ZP = 18.403
>
>V-I:
>B: Transform = 0.17, k' = 0.421, ZP = 17.531
>V: Transform = -0.073, k' = 0.541, ZP = 19.148
>R: Transform = -0.101, k' = 0.387, ZP = 19.383
>I: Transform = 0.005, k' = 0.410, ZP = 18.402
>
>Are these good ballpark figures, I think the k' are way too high. I 
>really don't know about the trans and the ZP.
>
>If you're capturing a timed event like an exoplanet transit, how do 
>you transform the mags if you only shot the transit with one filter. 
>Do I just take some images of the transit star with another filter, 
>like R for example? I ask this because I don't understand how you 
>can calculate k' and ZP each night, if you are using one filter.
>
>Steve

-- 
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