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Fireball Spectrum
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Tue Oct 21, 2014 7:33 pm    記事の件名: 引用付きで返信

You were in the yellow submarine lift!, excellent! Very Happy

Talking to some of the other IMC-ers afterwards it seems we were lucky in getting the best tour.

I've been a member of the IMO for a long time but never went to the IMC's until the one in Armagh. Being only ~120km away from my home I had no excuse. I hope you enjoyed Giron. They are quite unique events. At Armagh I was really surprised as to how much was going on. Shocked

But once you get to know a few people they become great fun. I'm looking forward to Vienna already!

Yes, over sampling is very risky as it can introduce non existing artifacts but you clearly have a lot of experience in this. One of the most frustrating elements of meteor spectroscopy is the variablity. Working around this is a challenge.

From my own observations I get some sort of spectrum almost nightly (when it's clear). These are usually faint and not useable. About once a week I'll get a "good" one with decent detail and a fireball every couple of months. So you need patience. A lot of people get put off by this when they're used to collecting many meteor trails per night.

As an experiment I have started to use a plastic grating on one of my camera's to compare how it performs to the glass blazed gratings. The diffraction efficiency looks to be much poorer but they transmit a lot more light so it might be a compromise between getting spectra and a decent number of trails.

I look forward to seeing your next fireball spectrum.

cheers,
Bill.
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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 31, 2014 8:15 am    記事の件名: 引用付きで返信

Hi,
They just keep coming (and getting better!).... Very Happy Shocked

This was a fireball from last night.

cheers,
Bill.



M20141029_010423_KILWINNING_P.jpg
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M20141029_010423_KILWINNING_P.jpg



spec14_1-_28_29_corrected.png
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spec14_1-_28_29_corrected.png


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APODman



登録日: 2011.01.08
記事: 34

記事日時: Tue Nov 04, 2014 1:31 am    記事の件名: 引用付きで返信

Amazing mr. Bill !!!!

Congrats ! Very Happy
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Tue Nov 04, 2014 4:47 am    記事の件名: 引用付きで返信

Hello,
Thanks!
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Tue Nov 04, 2014 7:34 am    記事の件名: 引用付きで返信

Bill,

as you said: you need some patience. With this and a big portion of luck I caught a fireball spectrum recently, see here: http://www.meteorastronomie.ch/images/M20141031_030349_MAI_Spekt.mov On the same webpage http://www.meteorastronomie.ch/ergebnisse.html you also find some more results for this event. Look for "31. Okt. 2014, 03:03 UT" near the top of the page. The analysis of the spectrum is not easy, the flight path was almost parallel to the spectrum, in addition it broke apart and the spectrum was overexposed. I'll see what I can do with it. The meteor was quite fast, the triangulation gave about 70 km/sec and it exploded in a height of about 75 km. The data I received from the Swiss meteor database, which works quite efficient and successful. Thanks to all my colleagues who contributed.

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: Wed Nov 05, 2014 6:16 am    記事の件名: 引用付きで返信

Hi Martin,

I had a look at the web pages. Thats a great spectrum. Very Happy It's a good site too.

Luck is the key factor when it comes to sporadic fireballs. Sometimes you get lucky with the geometry but mosty you don't Wink

cheers,
Bill.
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Mon Nov 17, 2014 1:31 am    記事の件名: 引用付きで返信

Hi All,

Caught this one with the low res system (300lpm grating).
What's interesting is the very bright sodium emission from this one.
The video even showed a brief sodium train. (much like the brief 5577nm emission from fast meteors in appearence)

cheers,
Bill.



M20141115_051157_KILWINNING_P.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 Dec 19, 2014 5:25 am    記事の件名: Fireball spectra 引用付きで返信

Hi,

Unfortunately only caught one really bright Geminid. It was also only a bit of the spectrum.
I've done the usual processing and it's interetsing to compare it to the Perseid in the first post and the really nice sporadic fireabll.

Cheers,
Bill.



spectrum comparison (uncr-ed).jpg
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spectrum comparison (uncr-ed).jpg


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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Thu Dec 25, 2014 7:35 am    記事の件名: 引用付きで返信

Hello Bill,

maybe you can help me. I recorded a nice spectrum of a bright fireball (-5m), but unfortunately I looked in the wrong direction, so I captured only orders two two five if my calibration is correct. The arrows in the image point to Na-D lines in different orders. The tentative assignment was made for a linearized spectrum with known dispersion and the equal spacing of these lines. Equipment Tamron lens 12VG412ASIR, Watec 902H2 ultimate, grating Thorlabs 300L/mm, dispersion 40.0 A/pixel. With the overlap of the orders I have difficulties of assigning other lines. Maybe you can help me.
I think the next thing is to buy a grating with higher dispersion, this would make life easier.
More images of this Urside you can find on the webpage of our meteor group:
http://www.meteorastronomie.ch/ergebnisse.html

Regards, Martin



M20141222_212209_MAI_2P.jpg
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raw spectrum, M20141222_212209
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M20141222_212209_MAI_2P.jpg



M20141222_212209spectrum.JPG
 説明:
calibrated spectrum, M20141222_212209
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M20141222_212209spectrum.JPG


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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Thu Dec 25, 2014 8:09 am    記事の件名: 引用付きで返信

WOW, that is an interesting spectrum!
With respect to the orientation of your camera did the meteor happen to the left hand side or the right hand side of the frame?
Merry Christmas,
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Thu Dec 25, 2014 6:16 pm    記事の件名: 引用付きで返信

Hi Bill,

the meteor appeared on the right side (Azimut 205°, from survey camera, right edge of spectro image around Azimut 183°, from UFO Analyzer). The spectrum is oriented the same way as the image, wavelengths are actually wavelength*order, first order on the right of Zero order. Therefore the spectrum is reversed to normal view.
Hope this makes it clear. Do you know where I can find a reference spectrum of an Urside meteor? I'll try to figure out the approximate efficiencies for negative orders.

Merry Christmas,

Martin
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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Sat Dec 27, 2014 9:14 am    記事の件名: 引用付きで返信

Hi,
Been having another look at your spectrum. I'm not sure the lines you've marked are sodium lines. If this is an image of higher orders then as the dispersion increases, order to order, these lines would not be evenly spaced.

If you have a look at the very first image in this thread, the first order is to the left, then you can see the same pattern extended by the second order at twice the dispersion. At the right there are a few lines from the UV part of the tihird order overlapping with the IR part of the red. It gets complicated very quickly. But the point is the spacing between the same line in different orders is not the same. At very high orders this will be become confused but I still don't think the spacing would be uniform.

I can't fit any of the regular meteor spectral features I've recorded so far to your image so I do not have any idea!

However this made me think.... At the ACM conference in Niigata, Japan 2012. There was a paper presented about the spectrum from a re-entering space craft. It looked very complex with lots of synthetics and unusual metals from it's construction. So the only other thing I can think of is maybe it's not an Ursid. Perhaps it was a piece of re-entering space debris. Maybe it's orbit was coincidental to the apparent path of an Ursid. If you do a search you should be able to find the conference paper. I'm sorry I cannot remember the authors name.

I'm afraid that's all I can think of.

Have a happy new year (everyone).

cheers,
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Sat Dec 27, 2014 9:23 pm    記事の件名: 引用付きで返信

Hi Bill,

you raise some interesting comments on this fireball spectrum, however I do not fully agree with you.
Quote:
If this is an image of higher orders then as the dispersion increases, order to order, these lines would not be evenly spaced.

This is true if the incident light is at zero angle. For dispersion however the angle of the diffracted ray is important, dispersion varies as cos(beta), almost constant for a grating mounted perpendicular to the axis. For my setup dispersion varies from 37 to 41 A/pixel across the whole image. This has been corrected in the calibrated spectrum, so it is no surprise that the Na? Lines are evenly spaced. From the spacing I calculate a dispersion of 39.96 A/pixel,close to 40.12A/pixel as determined from a calibration with a HgAr lamp.
About Ursid spectra I found very little. These ones
http://leonid.arc.nasa.gov/leonidnews30.html
http://ursid.seti.org/Ursidspectrum-thumb.jpg
show lines of Na, Mg, Ca, Fe and O
Below I plotted the spectrum again, for clarity with the scale adjusted to the second order spectrum. For the 3rd order you would have to multiply the wavelength by a factor 2/3 etc.
The reason I do not see some lines has to do with the grating efficiency for these negative orders, which should not show up at all for a blazed grating. I calculated the grating efficiency for a 300 L/mm blazed grating with 17.5° blaze angle and adjusted the refractive index to n = 1.52 to get good agreement with the published efficiency of the Thorlab grating. Of course I do not know the actual shape of the grooves.
Next I calculated the grating efficiency of this grating for the incidence angle of approx. 50° of the meteor spectrum, which shows that efficiency drops to zero at different wavelengths around 350 to 550 nm for the different negative orders. That would explain why I do not see some expected lines.
Quote:
At the ACM conference in Niigata, Japan 2012. There was a paper presented about the spectrum from a re-entering space craft. It looked very complex with lots of synthetics and unusual metals from it's construction. So the only other thing I can think of is maybe it's not an Ursid

I have checked the observations of this meteor and everything points to an Ursid, the radiant, velocity and time of appearance. The velocity I measured at v0 = 35.5 km/sec, vg = 33.6 km/sec, compared with a literature value of vg = 33km/sec. I do not know of any spacecraft entering the atmosphere at this velocity and I could not find the reference at the ACM 2012 conference website. The unknown material could also point to an UFO out of control.
So I am afraid I also cannot explain everything. In order to avoid such problems in the future I ordered a 600L/mm grating, which simplifies the analysis.

Happy holidays to everybody,

Martin



2122trans_add40-50-d6_2ndzoom.png
 説明:
2nd order spectrum 4000 to 6000 A calibrated with higher orders overlapping
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2122trans_add40-50-d6_2ndzoom.png



300L_mm efficiency calculation.JPG
 説明:
comparison Thorlab data with calculated efficiency (light blue curve)
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300L_mm efficiency calculation.JPG



grating efficiency negative orders.jpg
 説明:
grating efficiency for negative orders at incidence angle of 50°
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grating efficiency negative orders.jpg



M20141222_212209map_pair.JPG
 説明:
map of flight path from Swiss Meteor Network
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M20141222_212209map_pair.JPG


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Bill W



登録日: 2012.02.13
記事: 157
所在地: Glasgow

記事日時: Sat Dec 27, 2014 10:29 pm    記事の件名: 引用付きで返信

Hi,

If you are using a normal Watec camera with a sony chip your graph cannot be correctly scaled.
This is due to the fundamental limit placed on the response by the physics of the photodiode sites.

Silicon has a long wavelength cut off of 1100nm. It is physically impossible to detect anything longer. The photons just do not have sufficient energy to cause electons to get across the bandgap. So the features you have longer than 1100nm (11000A) just cannot at thatwavelength. The graph must be re-scaled somehow.

You can double check this online as it is basic to the function of all silicon detectors.

I had completely forgotten about the "early sodium release" spectrum of the Ursid from the SETI site. Although there are differences spectrum to spectrum they have the same basic features. Your spectrum is completely different to the two from the other sites.

I'm afraid we'll just need to disagree on this one but I still think you've caught something other than an Ursid. (or a very unique Ursid!)

You have something truly unique no matter what!

cheers,
Bill.
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Martin Dubs



登録日: 2014.03.04
記事: 47

記事日時: Sun Dec 28, 2014 12:01 am    記事の件名: 引用付きで返信

Hi Bill,

I am afraid I did not express myself clear enough. I am fully aware of the spectral limit of the Watec camera, I even multiplied it it with the spectral efficiency of the different grating orders to explain what I see and to sort out the orders. I also checked with a spectrum of Sirius but the S/N was not overwhelming. The calibrated diagram shows the second order spectrum between 4500 and 6000A, the third order spectrum around 7000 to 9000A --> 5000 to 6000A rescaled and the fourth order spectrum above 9000A (real wavelength > 4500A), with the fourth order spectral line of Na at 11800A/2 = 5900A. What surprises me is the absence of lines between 6000 and 7000A. There you should have good sensitivity of the CCD and fairly high grating efficiency, if my calculations are correct. At third order and higher the overlap betweeen the orders makes it impossible for me to assign the lines. You are right, not everything makes sense with this explanation, the absence of series of lines with higher spacing at higher order is quite mysterious.
Quote:
Silicon has a long wavelength cut off of 1100nm

I know this, I used to coat Si lenses for IR optics, it becomes transparent above that wavelength. I also used Silicon as a thin film material for all kinds of coatings. One application was for a semitransparent layer for the double layer DVD-18, which has been replaced by the blu Ray disc.. But this gets a little off topic.

Regards, Martin
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