Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 06/20/2012 - 23:20
I think one of Matthews more important topics from his blog post is:
"When you provide comparison and check magnitudes, they should be instrumental magnitudes, not the catalog magnitude that you assume for the comparison and check stars."
Hmmmm, I think I missed that point in my previous 8 years of observing variables. I will try to do better.
Hi Jerry,
That requirement for the extended format file has been confusing for a while (including us at headquarters in the beginning), but what the instrumental magnitude allows us to do is see how your variable, comparison, and check are all varying individually. Without it, we see the variation of variable+comp and check+comp (unless you provide the instrumental magnitude of the check star alone). This doesn't hurt the data per se, but having the extra information can let someone using the data try and understand the data better. The airmass is also useful in that regard.
If you've been providing the comparison's VSP magnitude up to now don't panic, the data are still completely useful and there's no need to revise them. The only time instrumental magnitudes are critical is if we find something we don't understand in the observations and need to figure out what's going on. But starting now, if you can modify your output files to use the instrumental magnitude, please do.
I'll add one last thing, namely that accurate transformation of your data can have an enormous impact on how effectively data from multiple observers can be combined. Arne's upcoming photometry book will cover that, and we're going to write some guidance and instructions on doing it for the website as well. You can find a link to Gordon Sarty's short offprint on transformation on our CCD Observing Manual page.
VPhot does AAVSO format report with instrumental magnitudes , isn´t it? I guess it does but I would need confirmation.
Regards
Miguel