Lambda Ophiuchi - close uneven double star

[Tinderboxsky]

Lambda Orphiuchi is a close, uneven double star and is one of the test pairs for Sissy Hass’ double star project. I had occasion to re-visit this pair back in July, when high in the sky, to test resolution of this pair at different apertures. You might be interested in the results.

Star magnitudes are 3.9 and 5.15 and the separation is 1.4”
Seeing was 5/5 and transparency 7/7. A good night. All of these observations are with my Vixen 140mm refractor stopped down with a set of aperture masks and an LVW 3.5mm eyepiece giving 228X

100mm aperture - clear, distinct separation.

90mm aperture- appearance of two stars “kissing”. It was apparent that there would be a gap between the two but it is was not showing. There were several fleeting moments where a gap appeared for an instant.

80mm aperture - two joined lobes, with one brighter than the other. No momentary gaps.

70mm aperture - distinctive oval shape with one end fainter than the other.

60mm aperture - slightly oval shaped star in comparison to pin point neighbouring stars. No distinguishing features. This slightly oval shape be missed in general observation if one did not know this was a close double star.

[jahnpahwa]

Interesting comparison of the outcomes with aperture masks! Thanks :)

Which mount are/were you using for this sort of session for a 140mm refractor?

JP

[Tinderboxsky]

Thanks for your feedback. It is an interesting exercise using a set of aperture masks. Some results are quite surprising.
My Vixen NA140SS was on my TRex alt-az mount sitting on a Myzox tripod. It has a set of extended flexible handles to simplify manual tracking.
I use an Argo Navis for push-to navigation with a SkyFi unit to run everything from an iPad.

Steve.

[Tropo-Bob]

A nice set of observations Steve. What was it like when using the full 140mm? Were U able to split it using a lower magnification?

[Tinderboxsky]

I did not try Bob. The Sissy Hass double star project is all about using specific test pairs to observe at varying apertures. The aim is to find the lowest aperture that splits the pair. There is a large matrix of test pairs for different separations and different magnitude differences.