What is the “Rule” on determining the “A” star (Primary Star) ?
I used to understand that the “primary” star of a double, was the “Largest Star”, which was also the “Brightest Star”. Not sure where I learned that. Having a hard time finding an authority on that. But I did find a couple of references.
“Visual Observing of Double Stars by Charles E. Worley, which was/is a reprint from the magazine Sky and Telescope, apparently published in 1961. In the article (a booklet), was a drawing explaining Position angle and Separation.“The brighter component is always chosen as the origin of coordinates.”
Also in a text “Observing and Measuring Visual Double Stars” (R.W. Argyle, 2nd Ed, 2004 and 2012), has this on page 2, when talking about “position angle”… “With the brighter of the two stars being taken as the origin……”
That seems to tie in with my understanding, but still, not sure of where the “authority” on that is. Anyone have a clue ?
By why do I ask this? Myself, and a few friends, where checking out this beautiful Double Star System.
South-437 (S-437 aka WDS 03463+2411) is a Double Star System (5 stars) located smack in the middle of M-047 (Pleiades).
My actual observation of this Double Star system appears here:
Now, granted, the AB pair is the primary pair, with “A” being Mag 8.13, and “B” being Mag 9.39
I’m not doing Speckle imaging quite yet, so AB shows as a single star in the obersation.
So at that point, all is well.
Now enters “C”, as in AB,C
Of the group of 5 stars in this “System”…. The biggest and brightest is definitely “C”.
Which makes me stop and ponder……
Anyone care to jump in here and clear up my head ??