Affiliation
American Association of Variable Star Observers (AAVSO)
Sat, 05/13/2023 - 11:54
Hello,
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.
Ari
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!
Arne
Hello, Arne!
Thank you so much for your elucidating explanation.
Now I finally understood it.
Cheers,
Ari