Hi Colleagues,
Recently I started variable stars observations using my Canon EOS 600D and put my results to AAVSO database (as PMAK).
Today, while entering another individual observation (through WebObs) I stuck with Check star magnitude field. Help states that "The instrumental magnitude of the check star that you used" should be entered.
So I dare to ask, what is the reason to enter "instrumental magnitude", which could be completely different for different software/observers? (I'm currently using IRIS) Why not estimated the standardized magnitude of the checkstar, for example?
Sincerely yours,
Maksym
P.S. In "AAVSO DSLR Observing manual", V.1.4, page 79: "In the Check Mag field enter
the transformed (not instrumental) magnitude as calculated by the spreadsheet". So there is a discrepancy between WebObs input form help and the manual (and probably the manual is correct while WebObs help is not). So I have an additional question: if I do not use transformation (I enter TG magnitudes), should I also enter standardized (without transformation) magnitude for the check star?
Hi Maksym,
If you are doing traditional varible-comparison-check photometry, then the comparison and check star submitted magnitudes are supposed to be instrumental. This is so that researchers can use these values for quality checking, such as seeing how the atmospheric transmission changes during a time series.
If you are doing ensemble photometry, the comp star magnitude is omitted (since there is no single comp star), and the check star magnitude is estimated using the same ensemble as you used for the target star. This is so that researchers can look at the calculated check star magnitude, and if its calibrated magnitude changes (say, a new release of APASS), then they can use the difference between your calculated value and the new "true" value to obtain an offset for the target's stars magnitude.
So the comp and check fields have two different submissions, depending on whether you are using traditional or ensemble techniques. I don't know which method you were using for submission, but maybe this description will help.
Arne
Thank you very much for the answer. So, in case of ensemble photometry (which I use), I should report both Variable and Check star magnitudes, estimated using the same approach (TG standardized magnitudes in my case), am I correct? [I will edit my last observations to enter estimated Check-star magnitudes]
Hi Maksym,
You have it right. For ensemble, enter the check star magnitude as estimated using the same approach as you used for the target variable.
Arne
Thank you, Arne!