American Association of Variable Star Observers (AAVSO)
Sat, 05/13/2023 - 11:54


Risking being repetitive, let me ask you all a simple question, please:

If a group of amateurs assembling a minimalist setup for variable star photometry in general, from O-B stars to red giants, were to choose between V & B, and V & Ic J-C filters, which one would be a more sensible option? 

I see experienced people indicating either one but I never learned the rationale subjacent to this subject.

Thank you for any comments.


American Association of Variable Star Observers (AAVSO)
filter choice

The two choices have about the same astrophysical value.  B&V is usually the preferred choice, IF you are observing stars that aren't so red that the B exposures get longer than you can reasonably take.  There is more published data, especially from the PEP era, that used B&V.  The older photomultiplier tubes had little I-band response, and it took a while before the professionals settled on an I-band filter (the Cousins Ic) for those systems that could work in the red.  It also matches the APASS catalog.

However, many observers monitor LPVs, where the B-band is hard, especially when the star reaches minimum.  So for those stars, Ic may be a better choice as the second filter.  In addition, not all fields have good Ic comps, though you can form a pretty good Ic from the APASS BVg'r'i' catalog.

So the choice is yours!