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Submitting via webobs and 'Comp Mag'

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dokeeffe's picture
Submitting via webobs and 'Comp Mag'


I've been submitting a few CCD observations now via webobs and have a question on the fields for the comparison stars.

Comp Label: *
Comp Mag: *
Check Label: *
Check Mag: *

It says to enter the 'instrumental magnitude' to these fields so thats what I've been doing. So this is -2.5*log10 total flux. So I'm submitting numbers like -12.358758 etc etc.

However, from looking at other people's observations. I think that other people are puting in the actual measured magnitude of the comparsion stars....

Could someone clarify and let me know if I'm entring the wrong data?





HQA's picture
magnitude fields

Hi Derek,

For comp mag and check mag, when doing the traditional variable-comparison-check differential photometry, you should enter instrumental magnitudes.  The names are usually the AUIDs of the two stars.  Those magnitude fields are not used by any HQ software, but are there to help the researcher work with your submitted data.  You should not place the Photometry Table values for those two stars in their magnitude fields, as that gives no new information (the researcher can use the AUID to call up the star's magnitude).  Otherwise, I'm not clear what you mean by "actual measured magnitude".

For ensemble photometry, since there can be dozens of "comparison stars", the procedure is to measure the check star with the same ensemble you used for the target star; that is, like it was another target star.  So in that case, its reported magnitude might be very similar to what is found in the Photometry Table, rather than a "negative" instrumental magnitude.


dokeeffe's picture


Thanks for your fast reply! Yes when I said "actual measured magnitude" I meant when using ensemble photometry and then feed the check star's flux back into the ensemble.

I'll continue to fill in the instrumental mag.

Thanks again.



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