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A ring around a red star

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Alan Snook's picture
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A ring around a red star

This image was taken by a friend a few days ago. He is a seasoned imager.  The field is the Squid Nebula.

Of the two brightest stars in his image, one of them is very red. When imaged with an OIII filter it appears to have a ring around it. The other, non-red star appears normal. He says both star images appear normal in Ha.

He has found another image online, captured in the same wavelength, and the star looks normal. This link is to an image which shows how red the star is.

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https://www.astrobin.com/315318/?nc=all

Has anybody an explanation for what's going on here please?  He is confident the ring must be some sort of artifact, but it would be super if he's got the discovery image of a red super-giant puffing off it's outer shell.

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Image icon Lee P Squid Nebula ringed star.jpg293.65 KB
djswan2002's picture
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V419 Cep - what's going on?

Hi Alan. Thanks for posting this. I'm browsing through images of the star on Aladin. The star is so bright that unfortunately the star image is associated with artifacts in all the plates. I'm not saying your colleague hasn't found something - we need further obs. But not from me I'm afraid - I'm at 55 degrees north and the summer solstice approaches!

BTW: North is left, East is down.

dgs
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Was the image captured with a

Was the image captured with a reflector or refractor? If the latter, the ring may have been caused by the star showing excess infrared emission hence out of focus with respect to other stars. Advise him to take another image of the same star field, but this time refocus on the star with the ring. If that sharpens then all the others will look like planetary nebulae - proving the point!

David

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[OIII] image

Hi David,

That was my first thought but this is reported to be a narrow band image in [OIII].  Though perhaps it is  possible that the filter leaks in the IR? 

Cheers

Robin

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examples of IR leaks in [OIII] filters

As here for example

http://www.astrosurf.com/buil/filters/curves.htm#Astronomik%20Visual%20OIII

OK for visual use but most of these would need an IR block with a CCD camera

Robin

Alan Snook's picture
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He used a refractor - a budget ED70.

Many thanks folks, I'll pass those comment back no and let you know what flows from that.

Sorry about all the rubbish lines in my first post. I don't know why it's done that.

Alan

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The OIII filter used

He's used a Baader 8.5nm CCD narrow band filter. The graph shows it is fairly transparent beyond 1,050nm.

Alan

Robin Leadbeater's picture
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Bright IR source

Well the sensor would not have much sensitivity that far into the IR but the star in question is the bright (V mag 6.6) star  V419 Cep / HD203380.  It is spectral class M2i which will be about 3x brighter at 1000nm compared with in the visual so pretty bright where the filter is transparent.  

Robin

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Baader Oxygen

I have a Baader Oxygen filter which seemed to leak. I gave up using it because of it.

There may have been a faulty batch at some point.