Hello! I started re-imaging R LMI after several years. (B-V) is about 1.18 while the catalog value is 1.32. Several years ago, the (B-V) I obtained were close to catalog, sometimes a little higher.
I started looking at this because another observer was getting B values a magnitude less than me, with (B-V) close to 2.
What could be the reason for my (B-V) shift and the difference with the other observer?
1. Could the 20-year-old B filter start to show a red leak? If possible, how would I check this.
2. Could updated comps do this? I updated comps from 7 years ago, and all but one comps in my 20x20 arc-min FOV have (B-V) close to 0.6 (one 0.9), so not a good match for this red Mira.
Thank you for your guidance. Best regards.
Mike
The comps are the same.
The difference is that I’m using a bright check star this time - 000-BBQ-737 instead of 000-BBQ-742.
I’m not sure if this brightness difference is significant when the variable’s B magnitude is at minimum? Anyway, when I selected the same check star, the B magnitude was the same. Best regards.
Mike
Hi Mike.
Actually there is not a “catalogue value” for the B-V of a mira since their colors change during their cycle.
There are some values in the GCPD:
V= 7.35; B-V= 1.32 (when the star was bright)
V= 9.42; B-V= 1.70 (when the star was getting fainter)
V= 11.06; B-V= 1.85 (close to minimum, transformed from WBVR)
So it all depends on when in its cycle you measured it. B-V= 1.18 looks a bit too blue, but if it was exactly at maximum, it is not impossible. Without knowing the actual magnitude, comparing single color datapoints years apart will not make sense.
Cheers,
Sebastian
1 Like
Thanks! I appreciate the guidance.
Mike
Here is B-V for R LMI from AAVSO observations, distributed by phase.
Thank you! I appreciate the guidance.
Mike
