Tau Ophiuchi -- Multiple Star System in Ophiuchus
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Tau Ophiuchi – A Four Star System
Tau Ophiuchi (also called 69 Ophiuchi) is a triple star in amateur telescopes.  The main
star “A” has a smaller star that is a spectroscopic binary that is so close to the main star
that they cannot be separated in the telescope. This spectroscopic binary circles the main
star every 186 days.  These two stars are designated as “AA” in the drawing.

With a separation of only 1.7 arcseconds the “B” component is a good optical test for the
110mm refractor requiring high magnification and reasonably stable skies.  The “B” and
“A” stars circle each other every 257 years.  I find both the “A” and “B” stars as light yellow
in color.

The “C” star shines only at magnitude 9.3 and resides at a distant 100 arcseconds from
the “AA/B” stars.  Its orbital period around the “AA/B” stars likely takes thousands of years.