NavList:

Antoine C.: A couple of weeks ago, you wrote:
"But ... I still do not feel quite comfortable with double stars either.
The former FK4 Catalog did publish elements for the components applicable to some of the stars gravity centers, which just by itself was already sufficient for CelNav purposes. This also permitted to accurately compute the individual component positions in the sky.
I have not studied how the "new catalogs" - HIP and GAIA - permit the accurate computation of each individual component - as locally affected by its companion gravity - since they seem to publish only their "standard"  individual data in which the relative distance and angular motions/rotations do not seem to be addressed at all. This lack of information - as I see it - is to necessarily degrade sooner or later the quality and reliability of the ensuing numerical computations over the centuries, if not the decades or maybe even the years."

Yes! It's a little disconcerting, isn't it? As you note, it's not really of much "practical" interest --certainly not for realistic celestial navigation purposes-- and yet it's right at that limiting level where it bothers us, right? 

For the star in question, STF 572, we can learn some useful things about it from the stelledoppie.it page for the star including many other designations for it: SAO 76682, HIP 21619, Tycho2 1838-01922-1, Gaia DR2 151588916504442624, HD 29364, HR 1470. Among those, HR 1470, should catch our attention because it's an ID in the Bright Star Catalogue, and it's another indication that this star has been studied for a long time.

From the same site, we can see that the current separation is very nearly north-south (position angle 188°), and that fairly well guarantees that either star separately or the common center of light of the pair would be lined up in a way that would not change the distance from the Moon, so it doesn't matter dealing with the case in question (it would matter if the two stars here were swapped however). 

Also, the site informs us that the stars are nearly identical. They are both listed as spectral type F2V, and they have very similar apparent magnitudes: 7.36 and 7.21. That means the relative motion for this system should be simple. The stars are nearly equal in mass, and their center of mass would be nearly the same as the center of light. Yet it's not really of any importance in this case since the orbital period is estimated to be some thousands of years (it says "5012.5342y  ± 2557.4478" ...great precision and high uncertainty!). So for this specific star, I would say we have nothing further to do.

What about other binary/multiple stars where the motion is faster, and the position shifts are larger? To meet those conditions, they have to be relatively nearby binary systems. Certainly alpha Centauri (Rigil Kentaurus), Sirius, and Procyon are stars to get right. After that? Maybe we shouldn't worry... 

Then again... a little worry might be healthy :). Where are those mass estimates that we need if we do decide to go further? They're easily found for those nearby three. Beyond them, there's at least one database that I'm aware of that tries to include that critical mass information. It's Andrei Tokovinin's MSC, "Multiple Star Catalog", specifically the new edition released in 2018. Here's a starting point, if you're interested. The "classic" double and multiple star catalogs (and yes, including this "MSC"), are looking "dusty" and nearing obsolescence. They might all be replaced soon... One big analysis of GAIA data could see them all washed away.

Frank Reed