Fri, 08/11/2023 - 15:14

So, I only have Johnson-Cousins V and B photometric filters. I transform my LPV magnitude measurements when possible using these two colors. Many LPVs are red to very red and at times the B magnitude is deeper than my setup can sufficiently record.

For transforming LPVs should I have obtained a R photometric filter to mate with the V filter?

Jamey (JENJ)

American Association of Variable Star Observers (AAVSO)
LPV Transformations

You can indeed calculate the R magnitude and V-R color index using a Johnson-Cousins R filter. However, you need first to have the R filter transformation coefficient (as for the V and B filters) for your entire optical train and instrumentation package to take into account differences between your individual equipment response and the standard magnitude system. See the AAVSO Handbook on CCD/CMOS photometry for guidance here. And you will need to look around a small bit to get the R standard magnitudes for the comparison stars of your variables.