ka5sma
Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 10/27/2023 - 22:11
Does anyone know if there is such a thing as a conversion constant or figure
for converting Clear Channel CCD images to V Mag?
Michael:
If you are using a Clear filter for photometry because a target is very faint or you don't have a V filter (get one!), you can report your magnitudes as CV. You should measure your target magnitude by comparison to the V magnitudes of your comps per your normal process. Do not report the magnitude as V BUT CV. It is an acceptable/appropriate filter name in an AAVSO Report.
HTH, Ken
thanks but this is for producting a light-curve..Photometry data....not pretty pictures....
If you are indeed using a monochrome CCD without a filter, then CV is the choice. If the object's magnitude is changing, you will get a light curve when you plot it vs time.
Ray TRE
If you are not using a filter, shouldn't it be reported as unfiltered? The CV filter choice is for data taken through the green channel of a DSLR (or other color camera)-- I don't think unfiltered data would fit there.
WebObs gives you a choice of "unfiltered with V zero point" which would be for unfiltered data using v magnitudes for your reference stars (as I understand it).
Tom
Tom:
A magnitude from the green channel of the Bayer array in a DSLR/OSC camera should be reported as TG (tri-color green) not CV. The green channel filter is certainly not a 'clear' filter. This TG magnitude is calculated by comparison to the catalog V magnitude of your comparison stars.
Ken
In the AAVSO International Database, 'CV' means that an observation was made without a filter and reduced to a V zeropoint using Johnson V-magnitude comparison stars (not v magnitude comp stars). The C stands for 'clear' - that is, no filter - and the V stands for the V zeropoint.
Similarly, if an observation were made without a filter and reduced to a Cousins R zeropoint using Cousins R-magnitiude comparison stars, it would be tagged as 'CR'.
This is how these types of observations are generally referred to in current astronomical publications.
Good observing,
Elizabeth Waagen, AAVSO HQ