43 Ori

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43 Ori

Postby Albert Stiewing » Fri Mar 01, 2019 7:33 pm

I had added 43 Ori to my to do list after seeing it needed attention in the BE database. Unfortunately, I did not get to it until last night and was quit surprised by the results. I need a little help in explaining what I am seeing. At this point I'm not sure I was on the right star as I could not make out any typical Be signature around 6563a. When I saw the image displayed, I at first thought I had left the calibration lamp on because of the vertical lines running through the image. Realizing that was not possible because I had a 2D spectrum, I then thought it might be geosynchronous satellites or emission lines from the Orion Nebula itself.
43Ori_L_Image.png


I only had one 1500s exposure before the clouds once again moved in. I processed it to see if the background subtraction would remove the vertical lines and just to compare it to other 43 Ori BE submissions. To my surprise the emissions lines matched other recent submissions. However I was the only one also showing blue side absorption lines. Is this possible or an artifact of having a gap between the defined spectrum zone and the sky zone?
43_Ori_L_1D_Comp.png
43_Ori_L_1D_Comp.png (40.97 KiB) Viewed 1815 times
Albert Stiewing
 
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Re: 43 Ori

Postby Robin Leadbeater » Fri Mar 01, 2019 8:06 pm

Hi Albert,

I would say this is H alpha/[NII] contamination from the nebulosity around the star (in both your spectrum and in those in BeSS.) Assuming you are using ISIS, a quick check to see if the sky lines are being subtracted correctly is to check the processed 2D image that ISIS generates before binning the spectrum. (you may have to tick "No" under "settings" "delete intermediate files" to see it) If the subtraction is working correctly there should be nothing visible in the sky background zones even with the image gain turned up.

Exactly subtracting the contamination in this situation might be difficult though as it might be varying significantly around the star so the background subtraction zones do not represent the true sky background at the star (Note that in normal circumstances is actually a good idea to have a gap between the target and sky background binning zones as it is important to make sure the target binning zone includes all the light from the target but none of this leaks into the sky background zones, checked by turning up the gain on the image.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
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Robin Leadbeater
 
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Re: 43 Ori

Postby Robin Leadbeater » Fri Mar 01, 2019 8:13 pm

Note also that accurate removal of sky lines needs the geometric correction of the spectrum image (smile and slant) to be precise otherwise you can get residual emission/absorption artifacts

Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
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