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Fireball Spectrum
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SonotaCo
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登録日: 2004.08.07
記事: 10036
所在地: 139.67E 35.65N

記事日時: Tue Sep 10, 2013 8:00 am    記事の件名: two explosion? 引用付きで返信

Well. do you mean below?

1. This is a field de-interlaced image of PAL, means, 20msec exposure image.
2. Meteor moves along the red arrow direction, and this is the spectrum of final explosion part of a meteor.
3. There are two spectrum area A,B.
4. A is the earlier 10msec(almost) part, and B is the later 10msec part.
5. There are many luminous bands in B, but many of them does not exist in A.

If so....
There might be two different type explosions, or very bright explosion happens at the last of explosion.
Anyway, I have never recognized such very fast changing like this.



twoexpjpg.jpg
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a part of Bill's image
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Tue Sep 10, 2013 5:25 pm    記事の件名: 引用付きで返信

Hi,

In answer to your list of questions, Yes to them all. An excellent summary of the points!

My own theory is that as some iron bands disappear in the lower band but the Si line and very strong atmospheric lines are only in the lower section, this is a sign of a fragmentation in the very last moments and differences in the grain composition are being shown.

There are a few more video frames that show the upper line remains stationary and the lower line continues to move as if it is a kind of shock wave or explosion front so some vapour carrying the ions is being pushed forward.

As you note, this is happeneing in a very short interval of time. Assuming an emission time of 10msec, at approx 60km/sec entry speed the physical length of the emitting columns are ~600m.

Regards,
Bill.
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Wed Oct 08, 2014 6:49 pm    記事の件名: 引用付きで返信

Hi All,

I have been getting a regular stream of meteor spectra . Last night I caught the brightest since the Perseids of last year. (This one was ran right through Perseus!)

Unfortunately it ran at a shallow angle to the grating axis but a good number of lines are visible.

The image shows a rough examination of some of the lines/groups.

regards,
Bill.

PS. The broad line towards the bottom is scattered, overlapping spectra from the moon.



M20141007_212902_KILWINNING_w4P_annot.jpg
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Fri Oct 10, 2014 6:37 am    記事の件名: 引用付きで返信

Hi,
I have been developing my analysis skills.... Wink

Here is a.graph of the spectrum and a synthetic spectrum to show the colours. Unfortunately due to the shallow angle between the meteor and grating there are also artifacts that are not true spectral lines.

Cheers,
Bill.



tauridspec_corrected.png
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tauridspec_corrected.png



tauridspec_corrected-s.png
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SonotaCo
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登録日: 2004.08.07
記事: 10036
所在地: 139.67E 35.65N

記事日時: Fri Oct 10, 2014 6:59 am    記事の件名: 引用付きで返信

Wow Shocked Razz
beaautiful Surprised
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Lightningwizard



登録日: 2007.10.19
記事: 154

記事日時: Mon Oct 13, 2014 11:41 pm    記事の件名: 引用付きで返信

I will try to get meteor spectra with my Point Grey 1920x1200 camera. But,
1) I only have a 25mm F0.95 lens to use with the grating, so narrow view and lower chance of capture
2) The grating I have is an Edmund Optics 300 lines/mm - it seems to need a bright meteor before you can see any spectral lines.
3) The narrow view means the meteor and the spectrum may not fall both inside the image.
4) From a spectrum I obtained of a lightning channel it is clear that my lenses are far from apochromatic: the focus on infrared can be poor while it is sharp in visible light range.

I will post here if I get some result.

_________________
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http://www.lightningwizard.com
EuroSprite blog:
http://eurosprite.blogspot.com
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Wed Oct 15, 2014 12:28 am    記事の件名: 引用付きで返信

Lightning Wizard,

I have heard of but never used a Point Grey camera. Do they work well with normal UFO capture? Or do you use the HD version?

What kind of frame rates do you get with UFO Capture and these camera's?

Thanks,

Bill.
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Lightningwizard



登録日: 2007.10.19
記事: 154

記事日時: Sat Oct 18, 2014 4:40 am    記事の件名: 引用付きで返信

I got a meteor bright enough to see its spectrum. Remarkable is a lasting trail (>7 frames of 1/15th second) with one spectral line. I did some rough flat field subtraction to enhance contrast, but it does not look so nice because I used JPEG images dumped directly from UFOCaptureHD. I had to filter a bit to reduce noise on the spectrum. For calibration I added a HP sodium lamp. I would just have to work out the conversion between pixel distance and nanometers. See http://www.astrosurf.com/buil/us/spe2/calib2/suburb_1.gif
The lasting trail corresponds to the line left of the sodium maxima (green) at x=274, must be O(I) 557.7 nm?

This black and white Point Grey camera works with UFOCaptureHD2 v.4.10. I can get only 20 frames per second because some hardware in my laptop seems to limit the speed. Potentially I could reach 87 fps in Mono8 or 162 fps in Raw8 at full resolution.
Not sure yet if also their color cameras work with it.



spectrum_meteor.PNG
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spectrum_meteor.PNG



spectrum.PNG
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blue is meteor spectrum, orange sodium HP.
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Sun Oct 19, 2014 6:28 am    記事の件名: 引用付きで返信

Fantastic, You didn't have to wait very long!

Yes the 557.7nm line is very useful for line identification. As this is a forbidden transition it generaly only happens with fast moving meteors that start to ablate higher up where the pressure conditions allow it to occur before quenching occurs. I've seen a few (slower) meteors leaving similar trails form the bright metal lines of Sodium and Magnesium. So it is useful to have another wavelength calibration. Like your sodium light I use a laboratory mercury vapour lamp to do the same.

If you leave your system running you might pick up a spectrum every few nights. It is absolutely fascinating to see both the similarities and the differences between them all.

Thanks for the info about the camera.

Cheers,
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Sun Oct 19, 2014 8:25 am    記事の件名: 引用付きで返信

Hello Bill and Lightningwizard,

I can confirm your observations. I have started meteor spectroscopy recently with a Watec 902H2 ultimate and a F/1.2 approx 6.6mm fl. with a 300L/mm Thorlabs grating. I caught a nice meteor of about -4m with spectra in first and -1 and -2 order.
I also noticed the trail, which was well visible after I registered and stacked the meteor images. I had determined the dispersion of the grating with a HgAr calibration lamp, so the identification of the spectral lines should be OK. The strong O I line is visible also in the -1 and -2 orders of the blazed grating. For the processing of the spectrum I used IRIS (http://www.astrosurf.com/buil/us/iris/iris.htm)
I also attach the image showing the orientation in the sky with spectra of alp and bet Ori.
The focal length of 6.6 mm (Tamron 12VG412ASIR) is a compromise between resolution and field of view. I think for identification of the principal lines the resolution is sufficient. I was also able to determine the path and orbit with data from our new Swiss meteor network.

Regards, Martin



m012100calib.PNG
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wavelength calibrated spectrum with identified meteor lines
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m012100calib.PNG



18_0121_34-40crop.jpg
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registered and stacked image (7 frames)
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18_0121_34-40crop.jpg



m012100orientation.PNG
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view of sky area with Orion and raw meteor spectrum. first order and overview
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Lightningwizard



登録日: 2007.10.19
記事: 154

記事日時: Sun Oct 19, 2014 11:04 pm    記事の件名: 引用付きで返信

Thanks for your comments. I am not much knowledgable in emission/absorption spectral lines but indeed it is wonderful to be able to derive information about the differences in meteor composition from it.
From my spectrum with a 300 lp/mm grating on a 25mm lens on this camera, the spectral resolution is (819-467)/(1070-610) = 0.766 nm per pixel. With a wide lens like 8mm this system still would resolve 2 nm if a meteor trail would be only 1 pixel wide.

The peaks in my example meteor above a threshold of 100 should be approximately:
511, 516-519, 557, 574-577, 586, 591, 614, 622, 633, 641, 650, 659, 728-744, 760, 766, 776, 782 nm. If the blue part is not noise its peak wavelengths correspond to 384, 430 and 445 nm. I wouldn't know all their responsible sources, maybe you can name them Smile

I found new software by Christian Buil (http://www.astrosurf.com/buil/isis/isis_en.htm) but this stuff has quite a learning curve.

_________________
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EuroSprite blog:
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Mon Oct 20, 2014 2:33 am    記事の件名: 引用付きで返信

Hi Guys,

Well done Martin, thats a good capture. It's nicely focussed. You are correct about the issue of field of veiw and resolution. It's all a compromise!

LW your line ID's are great BUT they are almost impossible to identify with certainty Sad
The problem is the low resolution of all our systems! Even though we can get effectively sub nm/pix resolution so many of the lines caused by the various elements in the minerals produce a huge number of lines that are very closely spaced.

"Line blending" is an issue with all meteor spectroscopy. Also, there is the problem of lens distortion. Even with good quality lenses there is often sufficient distorion to give misleading results. Even with precise line calibration these distortions can make lines that are well known appear to have wavelengths that are incorrect. Modelling this is very difficult!

Using lines that we are certain of, such as the magnesium triplet and Sodium doublet (both of which are unresolved in most meteor spectra) we can at least identify basic types such as those are mostly stony or those which contain mostly iron.

It's not an easy thing to do but we now have better tools than ever before!

Yes, Cristians' software is very comprehensive! I use VSPEC which was written by one of his friends, Valerie Desnoux. It's a bit more straight forward for our lower resolution images.

I'm glad to see others are now doing meteor spectroscopy!

cheers,
Bill.

PS. There are a few more spectra on the Meteor Observers Forum at http://meteorobserver.proboards.com/

and a video from last years leonids showing the forbidden O line well.
https://www.youtube.com/watch?v=gfGsEQadYNY&list=UULl2pBJ9qzheyFDplXGcF6w
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Mon Oct 20, 2014 5:34 am    記事の件名: 引用付きで返信

Hi Bill,

thank you for your critical remarks. I liked very much the CERN video, nice memories of IMC2014 Smile
These are my first attempts, so the idea was to start at short focal length to get any spectrum at all. At a focal length of 4 mm the change of dispersion across the frame was quite bad, so I changed to a somewhat larger focal length, where the nonlinearity is not quite as severe. For these first attempts I used a linear calibration, but I have the tools to do a nonlinear calibration as well with IRIS, ISIS or some other software. I think the strong O I line in different orders might be quite helpful for that purpose. Also I am aware that the broad lines are blends of many lines. Once I get a few spectra I may well change to even longer focal length, but if half the spectrum or the zero order is missing, line identification gets complicated. Now I wait for the next fireball while the weather is still good.

Best regards, Martin
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Mon Oct 20, 2014 5:24 pm    記事の件名: 引用付きで返信

Hi Martin,

I thought I recognised your surname but wasn't sure. The IMC was good but unfortunately I was feeling unwell for most of it. CERN was great, the group I was with (those in the elevator) were in high spirits!

Were you at the IMC in Poland? There were some people from ESTEC at that one and we had some long conversations about dealing with all the spectroscopy problems.

It seemed to be if you solved one it generated another Wink

Cheers,
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Tue Oct 21, 2014 5:19 am    記事の件名: 引用付きで返信

Hi Bill,
yes I was in the same elevator at CERN and it was my first IMC, since I started meteor astronomy only this year, although I am doing spectroscopy for many years. Since there were no new fireballs, I analyzed the last one, applying a nonlinear calibration with the OI lines in Order -2, -1, 0 and +1. You also wanted higher resolution, so I applied an oversampling and some Richardson Lucy deconvolution (a method which I normally discourage people from using) with the following result. Maybe you can assist me in assigning some more lines. I used ISIS for the calibration and IRIS for thepreprocessing and processing of the spectra.

Regards, Martin



18_0121_normal-overs2x_cal.png
 説明:
spectrum of meteor 20141018 calibrated, without and with deconvolution
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