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.


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!