Something weird is going on around the SP77 40-9 star near the LMC Other · Alexandr Zaytsev · ... · 4 · 470 · 5

Hi All,

There is some peculiar "double wall elliptical asterism" that looks like a very strangely shaped open cluster is first spotted around the SP77 40-9 star using @chilescope T3 (D=0.5m) system:

[1] https://www.astrobin.com/h5fb0p/

[2] https://www.astrobin.com/h5fb0p/L/



and then confirmed using @chilescope T1 (D=1m) system here later (there are more analysis details in the description of [3]):

[3] https://www.astrobin.com/8a27if/

[4] https://www.astrobin.com/8a27if/P/



Surprisingly, instead of dissipating under observation with larger aperture as one would expect from an accident of geometrical arrangement of random objects it appeared more well defined. This makes me wonder what it would looks like if even larger system could target it. Gaia wasn't of much help of making sense out this object, so at this stage I'm not at all sure if the point-like sources forming this elliptical structure are stars and not distant galaxies or components of an unusually complex gravitational lensing image (lifting the restrictions on fantastical scenarios a little ).

Dear @Gary Imm , @Marcel Drechsler , @Xavier Strottner , @Wolfgang Promper , have you ever seen anything similar in your images or in the literature?  @Wolfgang Promper , I was also wondering if you still have access to that ASA AZ1500 system in Chile that might be able to get a better look on this target (at least the pixel scale was smaller for it than that of that of Chilescope T1 system in deep sky configuration)?

This, of course, could be just a stellar remnant of a small HII region embedded into a molecular cloud sitting at the distance to the LMC ("a boring scenario"), but perhaps it is something far more interesting!

Thanks for looking in advance!

Cheers,
Alexandr Zaytsev.

Thanks, @Gary Imm for looking into this puzzle!

I agree that the central yellow star is indeed likely just an overlap, and it looks like it's a part of an association of stars of similar brightness and color sitting above the asterism in those images. Since the central star is sitting at a distance of about 67 kly by Gaia parallax measurements, that association is situated much closer than the LMC. The positioning of the central star is peculiar in itself, as it is very close to the longer axis of the outlined ellipses, but it's not in a focal point of either of them, so no hint of physical connection to the asterism there.


Yet, even with the central star suppressed, the brain has enough to pop that "double wall" structure easily. It even pops up on the DSS2 color low resolution images as a "dark void" surrounding SP77 40-9 (though now I know where to look for it, so this could also be a trick of the brain=):


This may be an indication of the presence of some low surface brightness component in this "ellipse" that gets nearly lost in the images taken with larger aperture / focal length instruments such as Chilescope T1 - at least at the level of ~24h exposure integral.

Thanks @Wolfgang Promper , that would be great!