[Tinderboxsky (Steve)]

I spent some time last night observing HJ5188, a double star in Sagittarius to find the lowest aperture with which I could resolve the faint companion.

The companion is mag 10.13, the primary mag 6.63 and the separation is 3.3”. So, the challenge is resolving a close faint (relative to the primary) companion .

The seeing was reasonable and transparency good. Seeing limited the best useful magnification to 100X in my 140mm refractor. H5188 was at 72 degree altitude, so nice and high for observing. I had a series of simple cardboard aperture stops that could be slipped into a holder on the dew shield.

140mm aperture - straight forward with faint secondary clearly visible
120mm aperture - difficult observation with faint secondary still visible
100mm aperture - very difficult observation. Very faint secondary only visible in moments of better seeing
90mm aperture - failed to observe the faint secondary.

I have a feeling it might be possible to improve on these observations slightly on a night of good seeing.

Why this double star? Well, it is one of the test pairs in the Sissy Haas Double Star project. Sissy has put out a call for more observations for this pair.

Scope: Vixen NA140SS with LVW8 giving 100X.