Zeta Sagitarii is a short period binary, orbit taking 21 years. There's also a wide optical companion of mag 10.6. The binary is resolvable with middling apertures when widest, nearly equal stars at 0.6". They were near that separation a few years ago, but the system is now closing. The ephemeris gives 0.42" (interpolated) at the present date. So a C11 might give a Dawes split in good seeing. An 8-inch at high power in good seeing should give a rod effect; Dawes for an 8-inch is 0.57". Elongation can be detected down to 0.5-Rayleigh, sometimes closer; 0.5-R is 0.34" for an 8-inch.
My first observation of Zeta Sgr was decades ago with a 6-inch Newtonian, at a time when the separation was 0.6", around the maximum. At 400x it was an elongated notched pair. A revolution and a bit later with a 7-inch apo it was seen as a figure-8 pairing at 330x.
It will be a number of years before we see it get back to 0.5" or 0.6" and therefore reasonably accessible to medium apertures. Mid last year it was at 0.50". It won't get back to that separation until 2034. It will be in the 0.5" to 0.6" separation range from then until 2039.
The discovery designation is HDO 150, and the discovery was made in 1867 by Joseph Winlock with the Harvard 15-inch refractor.
Incidentally the stars are Sirian type (A), so both are white, but may look pale yellow to older eyes or through dust or haze.