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Comet NEOWISE with the Star Analyser

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#1 robin_astro

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Posted 08 July 2020 - 06:44 AM

Comet 2020 F3 (NEOWISE) is now naked eye from the northern hemisphere low in the dawn sky  It does  not appear from behind some trees  for a few days yet from the observatory though so I rigged up a portable setup last night using a Star Analyser in front of a 50mm lens on an AS120mm camera, normally used as a guide camera on the ALPY spectrograph.

 

NEOWISE_SA_setup.jpg

 

 

There is not much contrast between the spectrum and the bright sky but the sodium emission is clear.

 

02_05_44_F3_spectrum_50pc_crop_annot.png

 

Cheers

Robin


Edited by robin_astro, 08 July 2020 - 06:45 AM.

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#2 BinoGuy

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Posted 23 August 2020 - 03:31 PM

Question for anyone,  I'll be getting the ASI120mm mono guide cam to use with an off-axis guider (presumably the ZWO entry level one) in about a month.  This will be primarily used on my WO Z73.  I am also very interested in doing a little astrophysics while I take the long exposures.  I've been poking at the calculator on the RSpec site and playing around with spacing but my lack of practical experience with guiding and OAGs means the picture isn't as clear as I'd like.  A little searching on the CN site also didn't immediately reveal an obvious answer.

 

So, my question is, do we think I can use the SA-100 filter screwed in to the front of the ASI120mm camera that I am using for guiding with the ASIAIR Pro?  Guiding on a bright star while also grabbing the spectrum of whatever-star-I-happen-to-be-guiding-with.  Based on what I see in the SA screenshots, it might work?!?  

 

Any and all input accepted, even if you say it is a wakadoodle idea,  If, however, a Nobel Prize is offered for this brilliant idea I will mention all of you in my acceptance speech.

 

ha ha ha  Matt



#3 robin_astro

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Posted 24 August 2020 - 06:32 AM

Hi Matt,

 

Yes you will get a spectrum of anything in the field of your guide camera so it should work in principle as long as your guider software is happy to guide on the slightly out of focus zero order guide star image. (The star image will be out of focus because the best focus in the spectrum is not the same as for the zero order). With a small sensor like the ASI120, the star image will need to be near the edge of the camera field to get the maximum length of spectrum so this could potentially also give issues with the guider software. Check how near the edge you can guide then chose the spacing so that you can fit the spectrum up to say 7000A between there and the opposite edge of the camera field (The on line calculator will give you the scale in A/pixel for a given spacing)

 

Cheers

Robin


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#4 robin_astro

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Posted 24 August 2020 - 07:18 AM

With a small sensor like the ASI120, the star image will need to be near the edge of the camera field to get the maximum length of spectrum so this could potentially also give issues with the guider software. 

Actually, with  your short telescope focal length you should be able to get a good result even with the star image centred. With a spacing of say 30mm say you could still fit the spectrum in the field

 

Cheers

Robin


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#5 BinoGuy

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Posted 25 August 2020 - 05:25 PM

Thank you Robin.  Seems simple enough to change focus and grab some images of the spectrum and then refocus to guide (Will that work??).  

Of course, this is all theoretical...  so far my first night out with the camera resulted in some fabulous 9MP pictures of a tree down the block.  Clouds moved in and made both Jupiter and Arcturus wink in and out of visibility so I wasn't able to find focus on a star.

 

i will probably pick up the SA grating and OAG in a month or so and report back.

 

clear skies




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