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Interesting view of Wirtanen in UV Cyanogen band - no rotation evident

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#1 freestar8n

freestar8n

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Posted 07 December 2018 - 03:13 AM

Comet 46P/Wirtanen has a known rotation rate of about 8 hours and recently it was observed directly in the UV Cyanogen band around 388nm:

 

http://wirtanen.astr...6P_status.shtml

 

I was hoping to capture some indication of this rotation, first with Sloan filters and recently with a UV CN filter - but it has not worked out.

 

The comet is now moving to the north so northern hemisphere observers will have a chance to image rotation - but I am giving up and will switch to wide field.

 

My Sloan filter images were fairly high res. at 0.4" per pixel and well guided - but I could not see evidence of rotation over 4 hours.

 

So I switched to CN imaging, as used in the recent professional work that captured rotation, but the signal was extremely faint and I was barely able to see the comet at all in each 10m exposure. 

 

The end result of 5x10m exposures is here:

 

get.jpg?insecure

 

and my accompanying text is:

 

This is an interesting but non-impressive view of comet 46P/Wirtanen in the UV passband of the CN, "Cyanogen" emission line around 388nm. I was hoping to capture some detail in the CN emission, but it is very faint and the camera/optics are not optimized for UV sensitivity.

 

This is 5x10m exposures oag guided using MetaGuide shift guiding. Shift guiding was essential here for the 10m exposures since the comet is moving so fast.

 

It is often said that the green color of comets is due to cyanogen - but that is incorrect and the green is due mostly to diatomic carbon, C2, emission. "Cyanogen" or CN is often present, but emits mostly in the UV around 388nm and not in the green.

 

Details can be found here:

https://www.cloudyni...ot-cn-cyanogen/

 

Recently images of rotation in this comet were obtained in the CN band as reported here:

http://wirtanen.astr...6P_status.shtml

 

The rotation period is about 8 hours and can be observed with professional equipment but I was unable to detect it either with Sloan or CN filters.

 

I have imaged other comets with a CN filter as shown here:

https://www.cloudyni...-bicolor-image/

 

but that was with a 300 f/4 dlsr lens - and this image of 46P is with EdgeHD11 at f/7 and 0.4" per pixel.

So - good luck to anyone who might be able to capture this thing spinning.

 

Frank




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