Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 12/11/2014 - 02:00
I have an instrument magnitude file that I downloaded from VPhot for NGC 7790, but when I try to use it in PTGP, I get a message that I need at least one file for each filter. I only have a V filter - am I missing something on how to use it for just one filter?
Thanks!
Hi Meeka:
The process of transformation involves the use of multiple filters (at least two) to transform a magnitude from your system (v) to the Standard system (V). It is possible to transform one filter magnitude BUT ONLY with assumptions about the color of the target of interest. This is not a normal procedure. PTGP cannot calculate transformation coefficients with only one filter.
You should begin with a google search on transformation and a similar search of the AAVSO web site to understand the transformation process. Various articles and books discuss the process.
However, don't let this stop you from submitting untransformed magnitudes to the AAVSO. They are still valuable. At some point, you may want to invest in a second filter.
Ken (MZK)