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Fireball spectrum

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BillW's picture
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Fireball spectrum

A few hours ago I captured what is probably the highest resolution meteor spectrum ever taken from the UK, if not further afield.

I thought my Perseid spectrum was a lucky catch but this is simply extraordinary!

This image was secured with a ASI ZWO 174mm camera and a pretty mediocre 35mm f1.2 lens, I purchased just a few weeks back from ebay!, and 500 line/mm plastic grating material. Each "slice" is 45ms in duration and there are over 80 actual native lines present.

At the moment I have no idea what the wavelength calibration is as there are none of the usual recognisable groups. This is the first image I've obtained with this camera/lens/grating configuration.

This will probably keep me busy for a while. It is also conceivable it's space debris. If any of the the Nemetode group see this, check the times to see if you have this. It would be fantastic to get an orbit. Time stamp is on the bottom left of image.

Cheers,

Bill.

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Fireball spectrum

Hi Bill,

Spectacular!

I replied last night that I was sitting under cloud, unfortunately. I've sent an e-mail to the NEMETODE group, so fingers crossed that at least one of the meteor video cameras covering Scotland will have recorded it.

Cheers,

     Alex.

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What a result

An excellent observation. Luck plays a part but so does knowing what you’re doing!  Unfortunately like Alex I was under cloud. Hopefully there will be someone in the NEMETODE group with clear skies to provide data that will help will an orbit.

Very well done.

Peter

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Mmm, having tried a few

Mmm, having tried a few comparisons and matching existing spectra I have no clue as to what this thing is!

I found some spectra of the Hyubusa 1 probe re-entry which actually had some similarities but were of much lower resolution.

Rather re-enforces my suspicion it might be space debris. However an allsky shot has been secured of what might be the same object. A nice bright greenish coloured fireball. So I'd wager most of these lines will be iron or magnesium, magnesium alloy's are probably common in space frames I'd imagine.

Next plan is just a slog to try and match up library lines....

Cheers,

Bill.

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Fireball spectrum

Hi Bill,

I think it's now been designated as 3I/Ward.       :-)

     Alex.

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Indeed,  LOL!!! ; - ))

Indeed,  LOL!!! ; - ))

Been leafing through my optoelectronic texts. The cut of a si photodiode can be as low as 320nm but the glass will probably attenuate that heavily. I'm thinking the shortest wavelength have got to be of the order of 350nm.

I think I can see some pattern of Fe lines at the extreme left BUT if that's correct then there is nothing at the usual Ca wavelength. So it would need to be a pure Fe/Ni. Problem with that is I have never seen such diffuse bands before. This is usually the sign of multiple electronic bands overlapping from molecules.

Something to do on the weekend if it's raining I suppose....

cheers,

Bill.

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Molecular Bands

Yep assuming that blue is on the right, that central band looks just like a molecular band with a steep band head on the red side tapering down towards the blue.  Like C2 Swan bands in comets for example. (hydrocarbons from left over fuel?) If you are using coated lenses then the cut off will be around 3650A. Do you have a best guess wavelength calibrated spectrum to share?

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annotated comet spectrum
Robin Leadbeater's picture
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Finding the origin with zero order out of the field

I don't know if you can apply it here but sometimes if your zero order is outside the field and your spectrum is reasonably linear (low dispersion angle) you can estimate the location of the origin (zero order) using  common features in the first and second order spectra. (The distance from the zero order to a feature in the 1st order ~ the distance between the same feature in the two orders)

Cheers

Robin 

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Hi,

Hi,

Yes, I've tried all of these approaches and I still don't get anything I can make sense of. Checking against several cometary spectra was the first port of call since it doesn't match any meteor spectrum I've caught. In the 11 years I've been actively pursuing the video operations I've had one other like this. That has just been put in the "unknown" category.

I've got a few more strategy's to apply first. I'll figure it out eventually... maybe! ; - )

Cheers,

Bill.

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Orientation

I'm trying to orientate myself.  To make things easier, could you say (a) whether shorter wavelengths are to the left or the right of the image as shown here and (b) are the lighter colours bright emission lines (i.e. it's a positive image) or dark absorption lines on a negative continuum?

I'm almost certain that its the first in case (b) but it would be good to have it from the horse's mouth as it were.

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Yep, that's correct. near UV

Yep, that's correct. near UV towards left hand side and the whole thing is an emission spectrum.

Based on the sensitivity profile from other spectra, the wavelength span is around 360-650nm (ish!)

Continual failure with the usual elements in meteors is making me more convinced it is some sort of man made "stuff" re-entering.

No luck with an orbit so far, as that would at least help resolve the natural/man made issue.

However, if it is an artificial source there are not that many spectra of what's coming back in so it's still interesting in it's own right! 

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wavelength calibration

It is a bit difficult to tell from the scaled stretched image posted but with the configuration (35mm fl lens, 500 l/mm grating, 11.5mm wide sensor, rescaled to 640 pixels, the linear dispersion will be  ~10.3A/pixel in the posted image (small angle approximation)   The weak lines at the right hand edge are therefore likely to be the second order image of the group at the left hand edge.  With this information we can estimate the location of the zero order and produce a wavelength calibrated spectrum.The calculated calibration is also in agreement  with the quoted approx 3600-6500A response

(The small angle approximation will not hold precisely at the dispersion angles from a 500l/mm grating but the method could be finessed using angular dispersion in place of linear dispersion to produce an accurate wavelength calibration)

Cheers

Robin

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Hi,

Hi,

I Initially thought the line to the right were a second order also but I'm not sure. Careful examination reveals the separations don't quite tie up with twice the wavelength even correcting for the slight non linearity of the dispersion.

Checking through the NIST data base there are over 2000 Fe lines listed from 350-450nm. Looking at the "stronger" ones I still can't get a clean fit.

I'm sure I'm imposing am image scale bias, as this one is very large for a meteor spectrum. 35mm focal length is positively a telephoto lens in the meteor observing world.

I've chopped the spectrum into shorter sections from a single 45ms slice (it looks quite different when examined this way, a curious psychological effect.) 

It may or may not help....!  ; - )

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I'm giving myself a headache!

I'm giving myself a headache!!!

By trying to figure out what it can't be (in terms of "normal" meteor lines) I'm down to around 150 lines from and handful of metal elements (non Fe neutral and ions) plus around 100 main Fe lines.

Still seems kinda uphill... ; - )