purple/blue shadow
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Budgieye
moderator
What is it? A good question, it is not visible in SDSS.
http://talk.galaxyzoo.org/#/subjects/AGZ000ayu8/help/discussions/new
http://skyserver.sdss.org/dr8/en/tools/explore/obj.asp?id=1237678617940722072
Possibly a variable star, or a comet, asteroid or ice world detected on the blue expsoure that moved between exposures for the other colours?
EDIT: see
8.3 asteroids, ice worlds, TransNeptunian Objects http://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000wrb?page=8&comment_id=53d8bc1e0d43f776b00010bb
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sat666leg
i've seen a few of these on the same frame when you zoom out..?
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Budgieye
moderator
I can see some blue-white stars, but I can't see any ghostly blue objects.
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JeanTate
in response to Budgieye's comment.
What is it?
Some kind of ghost?
Possibly a variable star, or a comet, asteroid or ice world detected on the blue expsoure that moved between exposures for the other colours?
What's the time interval between DECaLS three images of the same field? In SDSS asteroids etc are easily spotted because of the way it 'scanned' ... only ~a minute between each filter's 'view' of a field/position ...
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KWillett
scientist, admin, translator
It can vary by quite a lot; I don't believe there's any requirement that images are on the same night, for example.
http://legacysurvey.org/status/
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KWillett
scientist, admin, translator
Interesting - it's a transient feature only appearing in g-band. No sharp edges or anything that would indicate a camera defect for me.
I'm not immediately sure how far apart these images in different bands were observed in.
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Without data on the object's observation times, I can't confirm the object is an asteroid or not, but I can say that that situation is unlikely. Most asteroids are roughly spectrally neutral, and as you get further from the Sun, they often appear reddish, in distinct contrast with the blue-purple color of this object. It additionally does not show up in WISE, GALEX, or DSS images, or any other survey of a similar nature. While I don't have a definite confirmation any particular way on this, my most likely guess would be an observational artifact. In the DECaLS image, a similar object is visible at 328.1396, +1.2626.
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vrooje
admin, scientist
in response to KWillett's comment.
@KWillett, do you have a sense of whether this smudge is bright enough to definitely be picked up by SDSS had it been present at the time of observation?
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JeanTate
in response to planetaryscience's comment.
The blue-purple color is what a monochrome (present in a single filter/band) object of this magnitude/flux/intensity looks like, in DECaLS images; it does not, by itself, in any way suggest what the object's SED (spectral energy density/distribution, a.k.a. broadband spectrum) might be.
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JeanTate
in response to KWillett's comment.
I'm not immediately sure how far apart these images in different bands were observed in.
Are the date and time (and duration) of the observation (each band) in the FITS headers?
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KWillett
scientist, admin, translator
in response to JeanTate's comment.
They're definitely available, but not in the version of the FITS files I have right now (they're stacked for multiple observations, when present, and have very stripped down metadata). It'll take a bit of digging to find the original exposures.
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KWillett
scientist, admin, translator
in response to vrooje's comment.
Yes, although it'd be quite faint. It's a 21 mag object in DECaLS, compared to the 22.5 r-band limit of SDSS.
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KWillett
scientist, admin, translator
FITS files are here, if anyone wants to look at them.
https://www.dropbox.com/sh/7vhx2ixpcb0rvnz/AAAfr641jK1nKjKGXhA8CxxBa?dl=0
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sat666leg
found another one this time theres a green one close to it but a bit more pronounced.. might just be a coincidence..
RA,DEC..122.5171, 25.8890.. any ideas..Posted
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Budgieye
moderator
Here is a green and blue together, but I don't see a red.
http://imagine.legacysurvey.org/?ra=244.7845&dec=7.3887&zoom=16&decals-dr1j
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Budgieye
moderator
in response to sat666/leg's comment.
http://imagine.legacysurvey.org/?ra=328.10385391364&dec=1.236&zoom=14&layer=decals-dr1j
Here is another
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Ghost_Sheep_SWR
in response to sat666leg's comment.
Although i think most are probably now seen as asteroids, especially the blue + green ones, there are indeed more around the frame.
But in DECaLS, not SDSS. Here and here for example. And for me the first ever DECaLS blue, green AND red;
Any particular reason why the red image of an asteroid is so rare in DECaLS?
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Budgieye
moderator
Good question. Why the red image of an asteroid is so rare in DECaLS? anyone know?
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Redirected to sticky DECaLS thread, seems a better place
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