HelI line?

HelI line?

Postby pvelez » Thu Dec 13, 2012 5:30 am

Sadly, in Sydney I'm too far south to have a go at RR Lyrae. However, inspired by this campaign, I atempted a spectrum of SS Fornax last night. At Vmag 9.5 it was within reach of my LISA.

I'm presently at work so I can't present my profile at the moment. One thing I did notice was a prominent emission line at about 6680 A. Looking at VSpec, the likely explanation is either a HelI or FeI line. This puzzles me as I can't see any similar line in the spectra of RR Lyrae in this campaign. It may simply be noise (though that woudl surprise me as its quite prominent. Its the product of 5 x 600 seconds taken with an ST-10XME through a LISA on an RC8.

Does anyone have any thoughts on this?

Pete
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Re: HelI line?

Postby Thierry Garrel » Thu Dec 13, 2012 12:23 pm

Exellent observation !
6678 is HeI line.
It gets in emission in RR Lyr only at maximun of the blazkho effect and only for a few minutes, every 39d. Your observation is very interesting cause we known some other RR lyrae stars with He emission events but quite a few.
See Preston and al, for such examples, nearly the only ones we have detected.
HeII, 4686, maybe in emission too. But it is more difficult to see, the emission came only 5 percent above the continuum. Look at 5876 too, another HeI line, intense, allso in emission when HeI6678 is.
Send me your spectra as soon as possible for evaluation by a professional who is involved in RR Lyr shock waves study. You may have observe something who is called the grail from Blazkho chasers. Bravo.

Look at this presentation for physics http://thizy.free.fr/shelyak/ohp2012/OH ... s%20Gillet).pdf
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Re: HelI line?

Postby pvelez » Thu Dec 13, 2012 9:25 pm

Thierry

thanks for your post. Unfortunately its a false alarm I fear - a product of poor processing on my part. I didn't apply the cosmic ray filter in ISIS when first running the program. When I did, it was removed.

Here's the spectrum as first processed - you can see why I had thought I had a clear emission line.

I'll go back to the data at the weekend when I have time and see if I can polish up my processing skills.

Pete

PS the x axis numbering is a bit busy. I need to work on that too
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Re: HelI line?

Postby pvelez » Fri Dec 14, 2012 11:34 pm

I've reprocessed this data. Here is my revised spectrum - after applying flats, cosmetic file and the cosmic ray filter. The HeI line is gone but I do have 2 prominent emission lines - I think they are FeI lines. I'm not sure if they are a feature of the spectrum or simply a function of my processing.

Apologies for the false alarm on the HeI line.

Pete
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Re: HelI line?

Postby Robin Leadbeater » Fri Dec 14, 2012 11:48 pm

Hello Pete,

Looking at the images is the easiest way to check what are real spectrum features and what are artifacts.
Even (perhaps especially) with automatic processing programs like ISIS and SpcAudace, I always look at the individual images. There are many potential problems (hot pixels, cosmic ray hits, sky lines, etc, etc) which are obvious in the images (and can be dealt with there) but which are difficult to interpret in the final spectrum profile after summing the images and binning.

Cheers
Robin
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Re: HelI line?

Postby Thierry Garrel » Tue Dec 18, 2012 6:10 pm

Pete,
False alarm, is still an alarm and you were right to post it.
a second important point while observing RR Lyrae stars is to expose 5 minutes for individual images during 2h before maxima and half an hour after. Do not stack images, reduced it one by one.
They are pulsating star, going fast to the maxima and slowly to the minima. Typical 2h to go to maxima and 10h to minima. Emission lines came along the maxima phase. First balmer series, and in a second time HeI 5676, 6678, with nearly impossible to detect HeII4686. The second ones are those we are looking for to explain Blazkho effect, a century old mysterious effect !
If you stack your individual exposures you will see lines with different radial velocity red to blue superposing themselves in somewhat large band or double peak. Return to your individual images, reduce its one by one and look what going on emission and send here your new individual spectra.

Thierry
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Re: HelI line?

Postby pvelez » Wed Dec 19, 2012 5:50 am

Thanks Thierry

I'll have a play with this over the Christmas break - and take some new data if the weather plays nicely

Pete
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Re: HelI line?

Postby Thierry Garrel » Thu Dec 20, 2012 6:05 pm

Hope some Christmas surprises soon !
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