Found!
Despite the 300 thousand things I have to do this week, the whole day was spent on one single, but solution was found and an elegant one :-)I was worried about the FORS calibration for my images. When I plot a color-color diagram and overplot Harris (1996) Galactic globular clusters on it they are not where my supposed population is.
Option 1 - There's a calibration error. Small errors can't be seen in magnitudes, but popup in colors!
So part of the day was a recalibration effort. FORS transformation equations, surface brightness profiles, very old FORS equations ... confirmed my values. If it's wrong, it's a serious problem ...
Option 2 - Filter differences. Johnson-Cousins to FORS-Bessel filters are supposed to be very close to each other ...
Couldn't find "colors" from Johnson-Cousins to FORS-Bessel filters, so solution was using a SSP model with output in both systems.
Not used to SSP models. Learning how to use Bruzual & Charlot (2003) or any other model would take too much time.
GALEV (Kotulla et al, 2009) turns out to have a great web interface that works very well, at least for simple uses such as my need. Managed to get my magnitudes for a GC with different metallicities and a large range of ages. All that without having to spend time learning details. Of course for something more sophisticated you probably have to really get into it, but for this filter transformation it has worked perfectly.
Got a mean color shift for a 15 Gyr population in metallicities ranging from [Fe/H] = -1.7 to 0.3, applied it to Harris (1996) GCs and VOILA, it all falls into place :-)
One problem less! Now let's move on and with minimal damage (bad calibration would require several modifications, once the right value was found).
Labels: hcg_gcs
posted by Cris Da Rocha @ 11:14 PM
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