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BillW's picture
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More meteor spectroscopy

Hi All,

With the general idea six years in the making I've finally been able to, sort off ;) , start to produce a meteor spectrum "family chart" like you see for stellar classifications.

 

 

It is utterly fascinating to see how they are all similar but different! The sporadic fireball has many iron lines in the blue and green whilst the Perseid has quite a strong Hydrogen line and several Silicon lines in the red and near IR.

The Geminid has very strong magnesium emissions.

Brill!

Cheers,

Bill.

 

 

 

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Meteor Spectroscopy

Hi Bill,

Excellent - really pleased to see you obtaining this quality of data. Obviously the different spectra are of different widths ... is this a reult of the use of different gratings for the different observations?

Best regards

William

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Hi William,

Hi William,

The size, that is span of wavelength, is just a consequence of what bit of the spectrum was in the field of view.

The actual dispersion is the same. The sporadic fireball was a bullseye. It went across the fov slightly diagonally but dead centre. So the whole range of the (silicon) detector was utilised and a full range spectrum was caught, from the UV cut off of the glass to nearly the edge of the silicon "band gap" at just over 1000nm. Actually that was a remarkably lucky catch!

You have a greater chance of catching the whole spectrum if one uses a lower dispersion grating. But then the resolution drops, it's all a compromise.

cheers,

Bill.

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Meteor Spectroscopy

Great work, Bill. Fascinating to see the results you are obtaining. Hopefully we'll soon get some multi-station captures of the same event, to tie in with your spectroscopy.

Go well!
Jeremy 

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Hi,

Hi,

Been working through some more spectra. This one looks really nice in the blue. Mostly Iron (Fe) lines here with some additional weak Magnesium lines in the near UV. Taken on 2014 11 15 : 051157UT but using a 300 groove/mm grating. However this shows the effect of "good" geometry even at relatively low dispertions. Looks like a stony iron sporadic.

 

Cheers,

Bill.

 

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Now for a plain old iron

Now for a plain old iron meteor....

With the exception of a couple of magnesium lines these are all probably iron lines.

 

 

Meteor 2014 04 19 : 235419UT

 

The family tree is growing....

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....and growing....

....and growing....

Another nice fireball spectrum.This is getting towards the highest resolution meteor spectrum taken using the WATEC generation of video cameras.

A 600 groove/mm fused silica grating but the meteor was caught in the second order so roughly equivalent of a 1200 groove/mm grating in the first order. The double line at the sodium wavelength is genuine. It can be seen evolving in the video but I haven't been able to identify what it is (yet) The system resolution, even in the second order, doesn't have the ability to split the sodium doublet so it's not that. Another interesting meteor mystery!

Fireball 2014 12 28 : 0450UT

 

Cheers,

Bill.

 

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Hi,

Hi,

I think this is quite an interesting little spectrum. 0508UT 15/3/15. Not very bright and very few lines visble. However it has exceptionally bright OI emission from the "forbidden" transision at 557.7nm. Looking at any other of my spectra here there is no comparable emission in  any of them!

 

Due to the quantum mechanics involved this is a meta stable state, the O atoms sit excited for 0.74 seconds before emitting the photon. So it only occurs with meteors that are very swift and start to or completely abalate above ~100-110km. Below this the atmosphere quenches the transition through collisional loss.

The usual strong Mg and Na so looks like a stony job but it must have been coming straight at us for a very fast effective impact speed. A fascinating addition to the diagnostic info available.

cheers,

Bill.

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Co-observed meteor

Hi,

A first (as far as I know) for UK meteor observing early this morning. Working with some of the Nemetode group I finally caught a meteor that was also captured with the Nemetode observers' camera (David, just outside Girvan). This is a great step forward as it means we can now have orbital AND compositional information for meteors.

Here is my capture frame:

 

And here is Davids image:

 

Doing the usual spectrum processing reveals very strong Magnesium and Sodium emmisions but there are also bands of iron in the spectrum. So it looks like this was a stony iron meteor, thus:

and the usual colour treatment:

There is the possibilty that it was caught from another location which would give a much better orbital fit. Hopefully Dennis will have re positioned his camera.

It's all good stuff :-))

cheers.

Bill.

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Co-observed meteor

Hi,

After a bit of messing around I managed to produce this sky track for the meteor in UFO Analyser. William will be doing the orbital analysis of myself and Dave's data (as well as hopefully Dennis's)

It seems that this might well be a Lyrid. However once the orbit has been determined we should have a better idea of the certainty of that.

 

(To his credit he came up with the highly imaginative name/acronym for my spectroscopy programme. Much better than what I had originally thought :-)))

Looking good.

Cheers,

Bill.

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co observed meteor

After some quick work by William, the orbit indicates a low inclination sporadic.

Bill.

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Hi,

Hi,

Another interesting spectrum to consider. I caught an usual spectrum on the morning of the 13th. Unusually it only had one bright line in the green. I initially assumed this would be magnesium. WRONG! The alarm was raised when the atmospheric lines (to the right hand side of the spectra) didn't fit. After trying a few lines from the NIST reference library the best candidate was from iron. Re calibrating using the atmospheric oxygen line,  the green line did seem to fit with an iron emission. So did the blue iron and calcium lines. So I'm confident this is a reasonable fit.

I've compared it to the spectro-orbital capture from the 4th to show the differences. The one from the 4th looks like a stony/stony iron with the rich Fe, Mg and Na lines. What this one is I don't know.

Yet another one for the zoo....

cheers,

Bill.

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....And another....

....And another....

A really well dispersed spectrum of a sporadic meteor captured on the night of the Lyrid shower peak.

The instrument corrected graph.

And of course the celestial art which just looks better....

cheers,

Bill.

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Perseids 2015

Hi,

Much to my surprise the night of the Perseid peak was clear all night. From22.00ut to 03.20ut I recorded 377 perseids and 51 others/sporadics. Out of these I captured 28 spectra, 8 of which were reasonably good.

One issue that has been problematic is correct "instrument correction" of the spectra. A flux corrected stellar spectrum can be used but what class of star to use? The temperatures that exist with the meteor head are high, several thousand kelvin but using a corresponding temperture of star/black body equivalent means that the shorter wavelength won't be right. Similalry the reverse is true, correct for short wavelength then the long wavelengths go awry. This is especially a problem as silicon based detectors are hugely more sensitive in the red/near IR than the blue.

I thought it might be interesting to do a instrument correction by dividing through by a nominal silicon photodiode response.

I got a curve from a large photodiode manufacturer and normalised the curve at ~700nm, about halfway between the lowest responsivity and the peak at 820nm. The actual curve varies slightly depending on how the juntion is biased but this mostly affects the longer wavelengths which are being lowered by the division so the errors are small over all (I think ;-) )

Anyway here are a couple of graphs from a spectrum of a Perseid from this years peak. The difference is huge!, they don't even look like the same spectrum the red has been lowered by that much. This actually shows how INsensitive silicon devices are to the far blue. (film was much better, who'd have thought....)

Uncorrected "raw" spectrum.

and the "corrected" spectrum

The red end may be a little over done as the original shows a rise in the graph caused by smoke wafting across the fov raising the backgroud level. However the blue end was reasonably dark and is fairly representative. This was the only spectrum of the night that had some blue lines to test the idea on. Its not a perferct example but demonstrates the point.

Having said all that acutal flux calibration is still subject to much uncertainty and is quite difficult to do in an easy manner for us amateurs.

Food for thought....

cheers,

Bill.

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Perseids 2015

Hi Bill,

I'm glad you had a successful night with the weather cooperating! That is a nice spectrum you have captured.

I'm not sure if there is any reason why you could not apply this to meteor spectroscopy, but when I am correcting for the instrument and atmospheric response I use an A type star. Ideally one with an easily available professionally corrected spectrum. The temperature of the star is not the important thing, it does not need to match the target. The instrument response will be calculated from my spectrum compared to the professional spectrum across all wavelengths. What matters is that A stars have very simple spectra so it is easy to smooth the response as there will just be a few blips for the hydrogen lines.

Best wishes,

Andy

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Hi Andy,

Hi Andy,

Thanks for the comments. Using a A0 star was exactly what I did to start with. By removing the hydrogen lines this left a nice continuum. But what I found was that at the blue end it produced some odd results because of the shape of the continuum in this regime. In the basic library with Visual Spec the spectrum of Vega, for example has a sharp cut off then some oscillating components. Smoothing this out leads to dips in the continuum which I believe is not reflective of whats going on with a meteor. I could be plain wrong about this of course but I've made the assumption that even though a meteor may not have a genuine continuum the spectrum would be superimposed on a hypothetical blackbody continuum of the meteor temperture.

So it might very well be a two step process in the end. Divide through by the si response then do another division with the appropriate black body curve. The plan is to sort out this years Perseid results then go back and try some comparisons with normalised spectra from the ones I've collected using both the stellar method and si curve to see how they look.

However this issue isn't of importance for basic line ID and wavelength calibrations but it's a necessary step to get a good handle on it for proper flux calibration and measurement. The scientific papers I seen on this seem to me to be VERY complex and need complicated modelling of various parameters. So it's possible to do but it might take someone with more computing and maths skills than me to crack!

Mmmm, tricky, very tricky but a fascinating challenge! ;-)

cheers,

Bill.

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Perseids 2015

Hi Bill,

That makes sense, in as much as something odd at the blue end in the reference spectra gives you trouble correcting the continuum. Do you know what the rough continuum shape should be for meteors? Any speculation on my part would more than likely be wrong.

I'm not sure if this will help, but sometimes I use BASS to process my spectra. This creates the response correction in a slightly different way. You still use your spectrum and a reference spectrum, but once you've done the division you use your mouse to select specific points on the divided spectrum. BASS then joins the dots to create a smooth response curve. I'm not sure if that would give you a way to create a response curve avoiding the dips or peaks.

Instrument and atmospheric correction is a tricky area. I've been struggling with it myself for the better part of this year, but I think I'm about there with my latest spectra.

Fascinating work you are doing. Like you say you can get lots of useful information even without the continuum correction.

Best wishes,

Andy

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Yes flux calibration of

Yes flux calibration of meteor spectra, even in relative terms is going to be tough.  The instrument response can be corrected for using a reference star and provided atmospheric conditions are stable, even the atmospheric extinction con be accounted for by taking reference stars at different elevations and applying a correction based on the elevation of the meteor (The usual simpler technique of chosing a reference  close in elevation to the target to cancel atmospheric extinction is problematic here of course !)  A big problem though is likely to be flat field effects which can be severe with these sorts of wide field systems.  A normal flat field correction does not work with slitless spectrographs. The usual workround is to place  the reference star at the same position in the field thus cancelling gross flat field errors but again this is tricky here, particularly if the spectrum is generated by integrating along the track.  Measurements of reference stars at the apropriate locations in the field the night after the meteor observations could perhaps be used though. Measuring standard star spectra with the star positioned at different points in the field and comparing them would give an idea of the severity of the flat field problem.

Cheers

Robin

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Background subtraction errors

Background subtraction errors are also a common souce of  instrument response problems in slitless spectroscopy and are worth looking out for. These tend to be most pronounced at the blue end where the instrument response drops off sharply so small zero errors have a large effect.   

Robin

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Hi Bill,

Hi Bill,

You wrote..

> In the basic library with Visual Spec the spectrum of Vega, for example has a sharp cut off then some oscillating components. 

There may be something wrong here.  The 5A/pixel Pickles A0v spectrum in the Vspec library (file a0v.dat) shows a smooth decline in the continuum at the blue end as the Balmer lines merge towards the Balmer jump and a relatively flat continuum beyond that.

 You can see it here for example where I use it to calculate the instrument response of my star analyser setup

http://www.threehillsobservatory.co.uk/astro/Spectroscopy_BAA_VSS_worksh...

in slide 38

Are you using a different spectrum at very high resolution perhaps ?

Note that correcting just using the CCD (or photdiode) response will not give a good result as the response of the grating (and the atmosphere) is also significant here

Robin

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This document showing how a

This document showing how a range of slitless (Star Analyser) spectra were corrected for instrument response using a MILES standard A0v star might also be of interest

http://www.threehillsobservatory.co.uk/astro/SA100_miles_instrument_resp...

from this page

http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm

The results are pretty good, though some small errors can be seen at the blue end due to atmospheric extinction which was only partially corrected for. Using matched reference stars at the same elevation as each target star rather than a common reference would have improved this. 

Robin

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Hi Gents,

Hi Gents,

Thanks for the comments. It's great to hear alternative perspectives and different experiences!

Robin, do you mean this....

Perhaps not worded too cleverly on my part. The "oscillations" being the converging H lines. However using this method on meteors is not quite the same as using it on stars. For example when you divide a meteor spectrum through by a stellar spectrum there is still the issue of where exactly to select points to derive a continuum to act as the response.

I tended to end up with curves that were rather wavy. Below is an a quick plot I've made using an actual repsonse from an early test. Maybe its the methodology (as you describe in the examples on your web site) but for meteor spectrum correction I just don't think it's quite right.

If one uses ones imagination it approximates the nominal silicon photodiode curve as it surely must. (Unless there is evidence that a silicon based detector was not used in the visible of course). Thats what put it into my mind to invesitgate further.

Here is a nominal silicon photodiode response curve I produced from date taken from a large photodiode manufacturers website.

Dividing thorugh by this will give a form to the meteor spectrum then the other calibrations and corrections can be done as you discuss. However the problem with this approach is that although the form of the curve remains the same the peak moves slightly depending on how each photodiode site is biased by the electronics. THAT is a dark secret known only to the manufacturer!

From my experience at work I'd say the peak was closer to 820-850nm in real photodoides but I think that can be corrected itself by  the appropriate normalisation point before division.

But then again maybe we're right back to where we started.... It's great fun!

There are a couple of papers by the various experts such as Borovicka and Jenniskens deriving absolute fluxes which is what we'd like. They seem to rely on various measurements made on the ratio of particular groups of lines (such iron lines in the blue) to derive an effective temperature. I'm not sure I understand the maths behind it but in some cases,  but as promoted by Borovicka, there are different temperature regimes that complicate the matter further. These temperatures are generated by the particular properties of the meteoroid and its encounter with Earth, size, composition, velocity angle of entry etc. So getting what would be in effect an inverse black body curve for the appropriate physical temperature to do further calibration with is very difficult because we don't know this in advance!

It is rather ironic that the very atmosphere that generates the meteor itself scatters efficiently in the blue. Right where the interesting lines are that we need to measure in the first place. Who's say Pacha Mama doesn't have a sense of humour....

I'm beginning to think "tricky" just doesn't cover it ;-).

cheers,

Bill.

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Hi,

Hi,

Sorry Andy, I forgot to add the response to your question, which is I'm not sure. This is at the hub of the "temperature problem".

The curve should be the emission spectrum superimposed on a black body curve dependant on the physical temperature in the atmosphere. However in physics speak it is a "far from equlibrium process" This I believe is what leads to the catch 22 with the analysis based of line ratios. The get the correct line intensities you need to know the temperaure but to get the temperature you need to use the corrected line ratios. Somewhere an assumption has to be used to break the log jam. That's how I read it anyhow. I can't put my hand on the copy I have right now but there is a good book from the 60's that give a good outline of whats going on in reasonably understandable terms. I'll put the details on here shortly in case you want to get into it a bit more.

cheers,

Bill.

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Response Correction

Hi Bill,

Reading your post I notice that you say:

"when you divide a meteor spectrum through by a stellar spectrum"

I'm not sure if this is what you really meant, as this is not how corrections are applied.

When creating a response correction you divide a stellar spectrum by a professional corrected spectrum for the same star, or at least by a standard spectrum for the spectral class of the star. This gives you your instrument and atmospheric correction. This is an imperfect process since the resolutions will be different resulting different line widths, the alignment may not be perfect, and you have atmospheric telluric lines in your spectrum. However, a smooth curve can usually be obtained by tweaking parameters and applying some smoothing to get rid of sharp bumps due to anomalies near absorption lines.

This is then your response correction. Robin's links show this process with illustrations of actual spectra. You can the apply this response correction curve to a meteor spectrum.

The problem is this is best done with the star at the same altitude as the target. Otherwise the effect of increasing airmass has a big impact on the spectrum with decreasing altitude and the response correction will be wrong. So ideally you'd have an image with the same setup, but perhaps a longer exposure, that would include an A type star at the same altitude as the meteor. Of course the meteor is not at a single altitude so even this is not straight forward. A star at around the mid-altitude of the meteor might suffice as an approximation.

I also find it difficult to get a good correction at the extreme blue or red. When producing a corrected spectrum I just accept that I may have to crop off the extreme wavelengths.

Apologies if this is just going over what you already know.

Best wishes,

Andy

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Hi Andy,

Hi Andy,

No worries, an assumption on my part that the meaning was understood. This is the start if the process, Then the supressing lines etc etc etc.

It is interesting you say you crop the dodgy stuff, that's part of the problem with meteors. If you want to get a real feel for what's going on you can't! I suppose thats the premise of much of the discussion here.

Maybe I missed it but what software do you use?  One of my fellow meteor spectroscopists from Switzerland has been doing some really interetsing stuff with the ISIS package, also by Christian Buil, and orthographic corrections to properly linearise (is that a word?) meteor spectra. I am hoping, if nothing else, that a few people will set up a camera with a grating and stick it out for a year.

If half a dozen people do that then at one fell swoop we'll have more spectra that at any time in the past. I got 105 meteor spectra in 714 hours of observing and I live in probably the cloudiest and wettest part of the UK. That was two cameras and occasionally a third during showers.

The EDMOND database which I believe both Nemetode and UKMON contribute to, now has 3 MILLION light curves (not orbits as I intially thought). The number of spectra from all the amatuers (Basically me so far in the uk on an ongoing basis as far as I can tell!) and several professional projects across Europe might have produced a few hundred or a thousand spectra. To do any decent statistical work, of course, more would be nice!

I hope you'll maybe have a go. Any prior experience with spectroscopy makes it even easier and there are programs like RSpec which are quite user friendly. Some of the basic geometric transformations needed are available as little slider bars.

Its easy(ish) ;-) all one needs is a little patience.

Cheers,

Bill.

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Meteor Spectroscopy

Hi Bill,

I might give meteor spectroscopy a go sometime, but probably not just yet. I'm in the final stages of getting a new telescope and observatory setup for spectroscopy, so that is taking up all my astronomy time at the moment. I'm guessing you use a grating in front of the camera lens? Apologies if you posted above in the thread. I'd be interested to see a picture of your meteor setup.

I've been using a mix of BASS and ISIS. I'm gradually moving more to ISIS now as it is highly automated but a steeper learning curve.

If I'm trying to get an accurate corrected spectrum then I'll crop off the areas I can't properly correct. However, if I'm just looking and measuring the lines which are in the spectrum then I'll usually keep the whole spectrum.

Cheers,

Andy

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Hi Andy,

Hi Andy,

I hope you have a go sometime. The arrangement for meteor spectroscopy couldn't really be any simpler. I use an empty filter holder of the appropriate size (so the square transmission gratings fits into the circular aperture) secure it with the mounting ring (sometimes a piece of black card and some tape are needed to make up a holder to ensure a secure fit) then screw the the thing onto the lens.

There are some schools of thought about tilting the grating, since we're using transmission gratings, to optimise performance in a given order. I don't think its really worth the extra mechanical akwardness. Mind you I've yet to see any spectra from a tilted grating system to do a comparison with, so maybe it is.... Achieving good focus across as wide a range of wavelengths as possible is difficult (this is where tilting the grating might make a difference as well) It's definitely a trade off between utility and absolute performance. Optical aberations, quality of lens design and the way it's been corrected come into play as well. Is it worth tilting the grating and all that entails to do it only to have the quality dimished by lens limitations? Defocus in the near UV/Blue is rapid and dramatic in most CCTV lenses as they're not really designed for astronomical spectroscopy! If they were they'd be made of fused silica/quartz and cost a LOT! (however such lenses are available if you REALLY want to get into it....)

Yes, I've been looking at ISIS as well. Some of the results Christian gets are simply remarkable. I had a look at his page recently and theres stuff about detecting startspots. Who'd have thought that amateurs would ever have the tools to do that!

You're right about the learning curve but I think that's a consequence of whats he's trying to do, process a lot of stellar spectra in as automated and efficient a manner as possible. Like most things once you figure it out, it all seems quite straighforward ;-)

Personally I think it's rather wonderful he makes his software available for free!

Anyway, I'm preparing to set off to the International Meteor Conference in Austria and looking forward to it immensely....

cheers,

Bill.

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Hi Bill,

Hi Bill,

Yes, it is wonderful that Christian makes his software available for free. Spectroscopy is particularly well catered for in having a number of free good software packages out there. I'm also just learning to use PHD2 for guiding. Another free software package, really easy to use and even allows you to place a rectangle on the screen for spectroscopy so you know where the slit is.

I hope you enjoy the International Meteor Conference.

Andy

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Step by step we progress...

Step by step we progress...

I caught a nice bright meteor on the morning of the 8th Jan 2016. However this time it was on one of the medium resolution set ups with  the 830g/mm grating.  Whilst this gives sub nm/pix dispersion it's not quite down to my target of 1nm resolution but I'm getting closer and closer! Below is the graph and a colourised version.

The lines are nicely resovled, with the usual suspects present.

The spectrum did extend up to the near IR but due to it passing through the text at the bottom of the video fov I had to split it to eliminate the artifacts caused by the text. Here's the IR part. This graphs looks a little more "chunky" than the visible due to the focus. The spectrum is focussed on the visible part and the IR is a little defocused as a consequence.

At first it was a bit confusing as to what the "extra" lines were. (The lines have been colourised deep red as they would of course be invisible other wise!) These turned out to be bright lines from the 2nd order overlapping the 1st order. This is a problem with gratings and it only gets worse as ones goes to higher line counts and higher orders. (One benefit from the 2nd order is that the dispersion is twice that of the 1st though.)

By measuring the wavelengths and comparing the differences in these wavelengths its possible to approximate the first order value and hence what the lines are. From the graph it can be seen what I've tentatively identified these to be. If one could actually "see" both the near IR and the near UV lines it might look something like this instead...

Cheers,

Bill.

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Meteor 8th Jan

Hi Bill,

That is an excellent presentation of your results. You certainly had to do some detective work to find out where the lines came from, but I find that is part of the fun.

I'm not sure if you have any opinion on my post about the possibility of creating a BAA database of spectroscopic observations? Would you be interested in submitting meteor spectra to such a database? I should also run it by John Mason, and other section directors.

Best wishes,

Andy

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Hi Andy,

Hi Andy,

Thanks for the comments and yes I read your spectroscopy thoughts. From my persepctive the answer is yes! In fact I've already had some communication with William Stewart of the nemetode group about this. Although this was specifically about meteors.

I'm really pleased that several other observers have now set up meteor spectroscopy systems.

In 7+ years I'm getting close to my target of ~1nm resolution but this has taken continuous upgrades of lenses and gratings as they have become available.

The issue of resolution is important as it dictates what can be done with spectrum. With our low/med resolutions we can look at statistical methods of extracting info but that needs quite a large sample. Hence many more spectrum are needed. This is where a database would be useful but this is also where the various standards of data and reduction processes needs to be addressed. As you say it is also a BIG undertaking and getting the right people might not be easy. It's quite a commitment to do this sort of thing.

As what I've christened "Survey Video Meteor Spectroscopy" is a brand new field it will take a bit more time for the various observers (and I still include myself here as there is lots to do) to find their feet then determine what and where is best to go. I've no doubt it's do-able though!

Cheers,

Bill.

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Database and Spectra Resolution

Hi Bill,

Thanks for your feedback, which is useful to know. This does sound like it would be a worthwhile endeavour to create a database that covers as wide a range of objects as possible.

It is very interesting to see the improvement in resolution you have made over the years. The detail in your latest spectra are astounding when compared to the early ones.

Cheers,

Andy

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Hi,

Hi,

The sky has a never ending supply of surprises! Got two spectra over the night of 14/15 Feb. The first didn't produce anything useful but the second was quite intriguing...

Took quite a bit of time to get the lines to fit what I think is the correct configuration but part of the problem was that it just didn't look right. Not very scientific but it is surprising how quickly the brain starts to recognise patterns and this one looked odd.

After doing further geometric corrections to flatten the spectrum as best I could (it had rather a poor dispersion angle at the edge of the fov, never a good combination ;-) ) it twigged what I was seeing.

This particular meteor is VERY sodium deficient. There is much in the literature about sodium deficient meteors but this is only the second time I's seen no sodium. Unlike the first, further back up the postings, this has other rocky minerals like Si and Mg though. There is a weak line at the Na emission, ~589nm, but this may not be sodium. Many of the small little peaks over the spectrum are processing artifacts from the re-orientation and de-slanting of the spectrum image prior to binning. This is what I term a "noisy spectrum". However there is definitely no prominent Na line like most of the other spectra I've posted here.

Another interesting result from the meteor spectroscopy survey world...

Thanks to the Nemetode guys there are other observations of this meteor so I'm hoping I'll be able to get an orbit. William S. did get a Q1 orbit for the other spectrum as there were a couple of other stations that picked it up sadly nothing viable from my end. However if an orbit can be derived for the sodium deficient meteor then that will be an even better result. :-)
 

Cheers,

Bill.

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.

...and the orbit is equally interesting...

A high inclination making the orbit retrograde. So, the meteoroid hit the Earth in a head on direction resulting in a speedy sporadic.

Thanks to Alex Pratt (of Nemetode) for checking my initial plot and giving it a tweak.

cheers,

Bill.

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Another increment in

Another increment in dispersion ~.4nm/pix BUT this is a purely speculative version. That is, I've just assumed a couple  of lines and knocked up this colourised version for illustration purposes only. I can't get any lines to fit this no matter what I do!

I've circulated the original image to the Nemetode group to see if fresh eyes can help however this is a beautifully dispersed spectrum and at the moment it's completely unknown.

The wavelengths could also be running in the opposite direction. I've tried that too and still no joy. It is VERY frustrating. If any one wants a challenge contact me and I'll be happy supply the orginal .bmp image produced by UFO capture. It'll save me tearing any more hair out ;-) !

cheers,

Bill.

PS. Just for the record. I've edited this post and reversed the colourisation. IF the meteor ran as thought the wavelengths would run as the new graphic shows. Short wavelength on the left to longer wavelength on the right.

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Hi,

Hi,

To try and increase the number of spectra captured I've been doing some tests with a zoom lens (3.5mm - 8mm f1) set at around 7mm. The lenses of this type I have are designed for 1/3 inch chips. When operated towards the longer focal length setting, offer full coverage of the Watec 1/2 inch chips. By viewing the screen whilst adjusting the focal length and focus I checked when the image looked just about fully illuminated.

The weather has been lousy of late but I did catch one good spectrum to at least check the system and make some comparisons. This was using a 830g/mm fused silica uv grating. The other longer lines are the spectrum of the compact fluorescent tube light in my kitchen ;-)

This is the spectrum image with a few stars id'd for magnitude comparisons with a 12mm image.

Looks not too bad. The dispersion is ~1.45nm/pix. Here'e the spectrum...

...and the a synthetic colourised version...

Examining the graph, it can be seen that the blue focus is quite poor, that might be tweakable but I'll need to experiment. However there are a couple of distinct (if broadened) features in the blue.  Probably ionised calcium and a sequence of strong Fe lines.

By coincidence I caught the very same meteor with a 12mm f0.8 system. It is strongly foreshortened and there are definite optical disortions right at the edge of the fov but I've marked Arcturus for another magnitude reference. My 12mm systems give about 1.2nm/pix dispersion by comparison.

Roughly speaking the wider fov "see's" about three times the area of sky but still has sufficient aperture to allow a good limiting magnitude for astrometry. I'm quite pleased with this. However the 7mm system is definitley missing the longer IR lines. The cameras are very sensitive to these wavelengths so there might be some vignetting going on. Need some more results to verify this.

I wasn't sure how a low cost zoom lens would stack up but on the whole I think it's pretty good. Time will tell...

cheers,

Bill.

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Hi,

Hi,

The weather's been pretty poor here but there were a few breaks over the Lyrid period. I caught a nice spectrum that had, once again, some unusal characteritics. (It's beginning to look like they're ALL unusual ... ;-) )

This is an instrument corrected spectrum so the blue end is raised to address the loss of sensitivity  at the blue of the silicon sensors. It's not particularly detailed but it shows relatively "weaker" Fe lines than many of the other spectra captured over the past year. However the Mg line(s) at 517nm is seen to be very strong.

Again, luck was on our side and several of the Nemetoders caputured the same meteor. Alex Pratt ran the observations thorugh the UFO Anaylser and UFO Orbit and this yielded a most unusual orbit. This is by far the most "cometary" sporadic meteor I've caught that there's also an orbit for.

Another outstanding result!.

Cheers,

Bill.

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That's a great investigation

That's a great investigation Bill. Fascinating to see the orbit of the meteor to go with the spectrum.

The instrument response correction cannot be easy over a wide field. At high resolution on a star, it is surprisingly straight forward once you've done it a few times as it is for a narrow part of the spectrum on a tiny field of view. (Though somehow I've managed to get a dodgy response curve tonight, but it is still clear so I can redo it.) It must be quite a challenge for meteor spectroscopy through a wide angle lens across a wide spectral range,

Cheers,

Andy

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Hi,

Hi,

Normally I don't do the correction as theres not that much to be gained data wise at these resolutuions. However this time the size of the Mg line was immense.

I wanted to see if it would still be "higher" than the other metal lines in the blue after correction. Mostly this isn't the case as a lot of the emissions from the meteors are in the blue but look faint due to the sensitivty issues discussed further back. I just divided the whole spectrum by a Vega spectrum and lo and behold the big Mg line was still the highest peaking line. This meteor may have looked pretty green if it had been seen visually.

cheers,

Bill.

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Hi,

Hi,

The remarkable spectrum of post #35 has become even more remarkable after attending a presentation by the meteor spectroscopy expert Jiri Borovicka at the International Meteor Conference in the Netherlands a few days ago. (A wonderful event I can recommend!)

The reason that I couldn't identify many of the lines is that they are not atomic lines. Atomic lines are the only ones I have in the software databases I use but the lines visible are actually compounds! They are probably mostly emissions from oxides such as aluminum oxide. This makes it an even more unusal meteor.

Good stuff!

cheers,

Bill.

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Hi,

Hi,

After the long twilights it was back to the spectro action last night!

Fortune gave me a very bright spectrum this morning. Both good dispersion and good resolution.

Many iron lines with a strong sodium line so very probably a stony iron meteoroid. However doing a instrument flux correction shows the "true" brightness of the blue iron lines.

The video was quite interesting because the sodium line was very prominent on it's own for a significant proportion of the meteors duration before the other lines lit up.

cheers,

Bill.

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Impressive spectrum, Bill.

Impressive spectrum, Bill. Well done! You should be able to dig out quite of lot of information from that.

Too much to hope that somone else also captured the meteor to allow a triangulation, I suppose?

Good to hear darkeness has returned - looking forward to seeing more meteor spectra in the weeks ahead.

Jeremy

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Hi,

Hi,

Thanks, Unfortunately the zero order fell outside my fov because David Anderson did catch it also. It was a really nice sporadic.

Here is Davids picture.

It would have been nice, I was very pleased with it for a first order spectrum. The dispersion was almost perfect at ~0.9nm/pix (a rare occurence with meteor spectroscopy!) and the effective resolution was ~1.9nm/pix fwhm on the blue/green irons lines. The multi station, multi technique data is slowly building up, we'll get plenty more with the additional spectro stations now,

cheers,

Bill.

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Hi,

Hi,

The Perseids have been a washout both metaphorically and literally. A ton of rain came down on Thursday night.

However ever the optimist I watched the skies closely and after 48 hours of cloud and rain there was a mysterious clearance for around 20 minutes last night. Rain stopped, wind dropped to near zero and the sky cleared. So I deployed my camera rigs as quickly as possible and I managed to capture a few meteors and one spectrum. Unfortunately the spectrum was contaminated by both scattered light and some in frame clouds. However if was well dispersed and showed some really nice detail at the red end.

The direction indicated it was a perseid fireball but the spectrum had the tell-tale emission at 557.7nm typical of high speed meteors. What was interesting about this one was the detail in the atmospheric bands. Perseids are high speed meteors and they carry a lot of energy. This energy is available for excitation as the meteors kinetic energy is transformed into heat.

Slight diversion... in 2002 astronomers at the VLT caught a spectrum by chance using the FORS1 spectrograph. After removing the redshifted lines of the supernova the remaining lines were of the atmospheric emissions of O, O2, N, N2.

As this was a highly accurate instrument the line measurements are invaluable for calibrating meteor spectrum. I thought it would be interesting to compare the results of a multi-million euro instrument against my 500 quid system...

VLT spectrum sections are in black. The modeling done by the astronomers indicates this is the profile of an emission of 4200K at a height of 95km.

As the devil is in the detail if you look closely at the model line (at around 755nm from O2) it is missing from the VLT observation but it is a distinct line in my spectrum. Another cool aspect is the "height" of the lines in the regions marked. Comparing the various scalings shows a very good ratio relation. So it would suggest that my real spectrum matches the modelling quite well. 4200K it is!

Not too terrible at all... ;-)

cheers,

Bill.

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Perseid compared to VLT spectrum

Hi Bill,

That is a very interesting comparison between your Perseid spectrum and the VLT meteor. Encouraging that they show a similar continuum and line profiles.

Cheers,

Andy

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Hi All,

Hi All,

Been getting some interesting results recently but the other night I got a spectrum on 3 cameras of the same meteor! Only two were useable and even these were quite noisy. Meteor was maybe mag 0 - -1. (This might be more properly placed on the "Fading meteor" thread but as its about spectra... ;-) )

HOWEVER, this (or these) are the first spectrum I've got from a "melting" meteor. This one, like to others just faded out.

The graphs are very similar (as one would expect) but a few differences creep in from different resolution and processing artifacts.

The first graph is from a system with a 830l/mm grating.

...and this from a 600l/mm grating.

Careful review of the video reveals many of the lines are real but it is interetsing to note a large fraction are artifacts. I don't know if the spectrum actually tell us anything new yet, but it's a step on the way.

Need to graph the light curve now for the other forum thread...

Cheers,

Bill.

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Hi,

Hi,

Another interesting capture. Very complex with dispersion ~.5nm/pix. With the efforts of Alex and William of the Nemetode group it's been tentatively identified as an October Camelopardalid.

The green magnesium line is very broad. Maybe seen as resolved if it hadn't bloated as the terminal flare saturated.

Some broad similarities between this spectrum and the one in Post #41. Many Fe lines!

cheers,

Bill.

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Had some really nice results

Had some really nice results recently. Got this nicely detailed spectrum a few nights ago. This one has strong O lines at 557.7nm and 615.6nm as well as several Si+ lines indicating a fairly speedy meteor!

It is worth remembering that the colouration is wavelength stretched and false, the spectrum actually spans from ~370nm to 780nm so, rather sadly, you'd never see it look so nice...

cheers,

Bill.

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Hi Bill,

Hi Bill,

I've been following this thread with a great deal of interest.  i is something I'd very much like to get involved with and I've been looking at setting up my own station using a Watec 910 HX /RC mono camera (that I could also use for asteroid/star occultation events as and when)

I'd like a little more guidance on camera lenses and  diffraction gratings and how to source them and mount them in relation to the camera lens.  Maybe you could drop me an email.

Eric

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Latest meteor spectrum

Hi Bill,

That is a fantastic looking spectrum with lots of features in it.

If you are able to convert your meteor spectra to 1D FITS format then you will be able to load them into the new BAA Spectroscopy Database. Let me know if you are interested and if I can be of any assistance.

Cheers,

Andy

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Hi Bill,

Hi Bill,

I've been following this thread with a great deal of interest.  i is something I'd very much like to get involved with and I've been looking at setting up my own station using a Watec 910 HX /RC mono camera (that I could also use for asteroid/star occultation events as and when)

I'd like a little more guidance on camera lenses and  diffraction gratings and how to source them and mount them in relation to the camera lens.  Maybe you could drop me an email.

Eric

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