Effect of seeing on roundness
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by eugenius
Depending on exposure time and telescope diameter, seeing can distort an image. How much of the non-roundness of many of the images is due to this effect? Most images are not exactly round. Perhaps "roundness" needs to be better defined.
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by lrebull scientist, translator, admin
You're right that it matters for DSS and 2MASS .. and even WISE! (though with no atmosphere, it's not seeing, but PSF variations as the pipeline combines multiple exposures.) By "not round", we're looking to weed out things that look more like a peanut, or a smear, or a rectangle.
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by eugenius in response to lrebull's comment.
OK, that's helpful, but consider the case of AWI0000c6m: the first image is distinctly non-round, with wings even.
The other bands are less asymmetric (although not centered on the cross-hair, another issue). Should we regard this
case as "round"?Posted
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by Kiarash
Thank you guys, I was confused too! it was really helpful.
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by lrebull scientist, translator, admin
Sorry, I missed your reply.. with respect to this guy, I agree that it is somewhat strange at the shorter bands. The smear, though, isn't in exactly the same direction at adjacent bands. We don't have a lot of help from the SED or from SIMBAD on this one. If this were just my own data, I might keep it as a marginal candidate.
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by Ivan_3
Sorry this object noted as good, maybe the influence of coma, the atmosphere, the error motion of the telescope.
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by Zooniverse99
Oh dear! now I am confused again. however round this example might be how can it be a marginal candidate when it extends so far out of the red circle on final frame?
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by abans scientist, moderator in response to Zooniverse99's comment.
Here is a blog post that answers your question
http://blog.diskdetective.org/2014/02/04/why-do-the-stars-seem-to-grow-at-longer-wavelengths/
Basically Wise 4 has the worst angular resolution, so we expect it to be blurry
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by Zooniverse99
Thanks the blog post helped some but I also went back to square one and reviewed the tutorial again. I think I need a bit more flexibility.
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by jdebes scientist, admin
Zooniverse99, don't worry too much about being exactly right every time. We're just looking for everyone to try their best. The nice thing is that each object will have multiple people looking at it, so if someone flubs here and there, it will all work out in the end. There's no such thing as bad data 😃
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by Zooniverse99
Encouraging thanks
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