Hello everyone,
Concerning photometry, is it possible to take 2 different images , one for the target and the other for the comp star ? Even if the conditions (gain , pose ) and sky are the same , there is Always an Airmass difference which can be corrected by a coefficent. Is it correct ?
But I don’t think it’s healthy to treat the target and the comparison star differently: intuitively, I think the error must increase: so in this case, do we need to increase the number of stacked photos to reduce the standard error?
Exemple, the magnitude of T CrB is now 10, so it’s easy to find close comp star in the same image.
But When it will reach 2 , i would have to change the lens of my DSLR to capture target and comp together (and adjust airmass to compare them, if sky pollution is not too different…) , but How can i do with a seestar S50 with a fix focal : take a second image to capture a star comp ? But in this case we add another error?
Thanks a lot !
I’ll put my two cents worth in here since it seems no one else has yet replied.
What you are describing is similar to the procedure used in photoelectric photometry (PEP), where the target star and the comp star may be 10 degrees (or more) apart on the sky. Back during the epsilon Aurigae eclipse in 2009-2011, I did infrared PEP using an SSP-4 photometer-- its been a while so I may have forgotten a detail or two but here is how that typically worked.
The pattern was: sky-comp-sky (swing to target star) sky-variable-sky (swing to comp star) sky-comp-sky. Normally, you would then repeat this pattern three times and average the results (of all the steps) to get one reading.
I removed the sky counts from the star counts using Excel, but I would think that if you are using some sort of photometry software to reduce your data, it would do that part since it does it for single star images.
We did have to correct for the differences in airmass differences between the comp and target stars and also for any color differences between them (since that will also have an extinction effect). We also had to determine those correction factors every night that we got data since they would change from night to night (PEP is very time consuming which is why so few people do it.
I think on the surface that what you have proposed would be doable, although I’m sure someone else will be along soon who as done PEP more recently than I and who might have some info that I have forgotten.
Firstly , thanks a lot for your interesting the answer!
If I well understand the PEP measures vs photometry : sky-comp-sky is a like an comp star aperture photometry and sky-target-sky (10° away ,in your exemple) is like target aperture photometry .
Patern Sky->comp->Sky , Sky->target->Sky , Sky->comp->Sky : I imagine that the reason to make a second serie Sky->comp->Sky is to average variations with the first serie to have close target conditions.
So ,practically, for photometry, I would have to alternate this patern 3 times (or I imagine n>3 if possible) and stack in one part n target and other part 2n comp , without forgetting to correct aimass and color before the target magnitude evaluation.
It’s really more complicated than the standard method! ;-))
Perhaps its possible to schedule easyly the patern with the Plan Mode of the Seesstar S30 or S50 ,exemple: 10s for Comp and after10s for Target and after 10s Comp and so on n times? But i don’t have it , perhaps a day…
Concerning T CrB when magnitude will be 2, i thing , helas, that the signal will be completly saturated with 10s pose Seestar…The PEP method is good but the Seestar not in this case, but it’ s another problem!
