October JBAA

[stewartw]

Just received my October JBAA this morning - very nice article by Bill on meteor spectra - well done!

[arp]

I agree!

Congratulations Bill, on a well written article, clearly explaining meteor spectra and how they can be recorded using video techniques.

Would an integrating video camera help (such as a Mintron) by recording a longer exposure, e.g. from 0.02s up to 2.56s?

Well done,

Alex.

[BillW]

Thanks gents,
But when John asked for a couple of hundred words I didn't know it would be printed effectively as a stand alone item.
I would have worded some of it a bit differently as it was commentary rather than text.

The modern technology makes it so much easier now. The only limitation is resolution. That's when large format photography excelled but the photographic quantum efficiency is so low it's almost impossible to record anything except REALLY bright fireballs. The best resolved meteor spectra were taken in the 70's and 80's. These were huge fireballs and nothing like them has been caught since. Mine were only around -2 to -6.

Anyway, I've got my hands on a 600lpm transmission grating to try and improve the resolution issue. We'll see how that pans out over the winter meteor showers.

Regarding the integrating camera, it works fine, just like using a still camera in effect. The longer integrations don't have any influence on the meteor "detectivity" since the meteor is a fast moving target and the relative time over any particular pixel is very short. But the wide fov and much better QE gives more of a chance of catching a spectrum.

If the weather cooperates I'm planning on trying the CCD camera again with the 600lpm. The only problem is looking through thousands of images the next day. A distinct advantage of the automatic detections of UFO
capture!

cheers,
Bill.
Bill

[stewartw]

Hi Bill,

What are your thoughts on the HD video mode of modern DSLRs for gaining higher resolution spectra (and larger FOVs)?

William

[robinastro]

Hi Bill,

Hope you don't mind me dropping in but I saw someone from here visited my website so came to have a look.

Your article reminded me that John also asked me to do something for JBAA on meteor spectroscopy after I showed one I recorded a while back in a general presentation on spectroscopy at the 2012 Winchester weekend.
www.threehillsobservatory.co.uk/astro/spectra_20.htm
I was rather reluctant though having only manged to capture one very low resolution example and never having tried again. I was pleased to see in JBAA this month someone doing rather better at it !

I am no expert on the meteor observing side but might be of some use on the spectroscopy side if anyone is planning to take this further.

Cheers
Robin Leadbeater
www.threehillsobervatory.co.uk

[BillW]

Hi,
I've had a look at your site (and that particular page) a few times myself. I've used a star analyser a couple of times also.

The current video camera systems make meteor observing much easier now and capable of producing good results. I remember selotaping plastic grating to the front of a lubitel, happy days and years of absolutley nothing!!!

Catching a good spectrum is just luck, but it really is the only way to get at the physical properties of the meteroid. The dual spectrum is, as far as I can tell, completely unique. The sudden and extremely rapid change of spectral charactersitics can only be observed with video techniques and opens up some fairly serious avenues for those so inclined. Hopefully it might encourage others to have a go.

I'm developing my CCD meteor spectoscopy rig. This is to try and push the resolution further but we'll see how it pans out.

Cheers,
Bill.

[BillW]

William,

Yes, I tried to use a Canon dslr just on normal video but the results were not good. I see that sonotaco has a HD revision of UFO capture. Might be worth exploring if a more broad base of kit is available.

I think a middle ground would be if someone would make a "watec" style camera using one of the new sony chips that are now being used in other amateur CCD cameras. The problem is the same though, just how to hande the huge data stream.

One of the French professional groups built a really big camera for high resolution. www.imcce.fr/langues/en/ephemerides/phenomenes/meteor/CABERNET/index.php
Not video but an interesting project.

Cheers,
Bill.

[robinastro]

Hi Bill,

Do you have an idea of what resolution is needed to produce scientifically useful data? I had on line discussions with Ed Majden last year about this and he seemed to think we need to get down to a couple of Angstrom or so.
The discussions were on the astronomical_spectroscopy yahoo group around this thread
groups.yahoo.com/neo/groups/astronomical_spectroscopy/conversations/messages/5440
though you need to join to read them unfortunately

Based on this I did some back of envelope calculations and came up with a system based on an SBig ST8300 (any larger and the prices get silly) and a 300 or perhaps a 600l/mm grating. (transmission grating efficiency is dropping off by the time you get to 600l/mm). Is there anyone already doing this? Not video of course (so it would not for example pick up the differentiation due to fragmentation you saw) but with a nice big CCD and a fast (for an astro camera)1 sec download time. With a 5 sec exposure say the duty cycle would be 80%, sky background should not be excessive at this exposure given a reasonably dark site and the large dynamic range of 16 bit capture would reduce the risk of losing spectra compared with video). Software would throw the frames away with nothing new in them. All I need is someone to provide the funding ;-)



Cheers
Robin

[BillW]

Hi,
It really depends on how you define "scientifically useful". For example the best resolved spectra were enormously bright fireballs. One in 1968 by Borovika and another by Henry Soper from the Isle of Man. These produced very detailed spectra on very large format films. Completely un-repeatable (at the moment) with ccd's and not necessarily representative of meteoroid populations.

Getting to 1A is easy optically. However on a practical meteor spectrum is difficult due to all the compromises with detector size, focal length, fov and grating spec.
Returning to the useful point, since really high resolution is not practical what is probably more realistic is determining relative intensities of the main lines.
(I don't know if you're a member of IMO but the latest edition of the journal has a paper by a friend of mine looking at Geminid spectra. )
This is what the pro's do. After speaking with several researchers at the IMC and Meteoroids conferences in Poland it was interesting to hear about their work as they use the same kit as I and most other amateurs have. The key is good image reduction. There were some American observers who were setting up a system with multiple 12mm lens systems with 1200lpm gratings and some ESA scientists doing similar things.

Anyway given current devices, working at 1-2nm/pix can reveal variations in mineral content that would be very useful to possibly describe meteoroid populations related to parent bodies. So anyone who wants to get into the science can do so with not that much expenditure.

Cheers,
Bill.

[robinastro]

Oct 1, 2013 19:22:35 GMT BillW said:

what is probably more realistic is determining relative intensities of the main lines.
(I don't know if you're a member of IMO but the latest edition of the journal has a paper by a friend of mine looking at Geminid spectra. )
This is what the pro's do. After speaking with several researchers at the IMC and Meteoroids conferences in Poland it was interesting to hear about their work as they use the same kit as I and most other amateurs have. The key is good image reduction. There were some American observers who were setting up a system with multiple 12mm lens systems with 1200lpm gratings and some ESA scientists doing similar things.

Anyway given current devices, working at 1-2nm/pix can reveal variations in mineral content that would be very useful to possibly describe meteoroid populations related to parent bodies. So anyone who wants to get into the science can do so with not that much expenditure.

Thanks Bill,

That is the sort of information I was after. I am not an IMO member as meteor work has not been a major area for me (so far!) Amateur spectroscopy has progressed significantly in the past few years and I and other advanced amateurs (mainly in Europe) now are routinely producing research quality stellar spectroscopic data across the resolution range down to mag 15 up to R ~20k. (though not at the same time of course!) Other objects are less well covered however so this area could be an interesting new challenge. Data reduction techniques are now well established among amateurs for stellar spectra using long slit and fibre fed echelle spectrographs but for example flat fielding slitless systems to allow relative line intensity measurements, where you cannot guarantee where the target is going to turn up is tough. I would be interested in finding out more about what is being done in this area concerning data reduction as it has spin offs into other potential areas of amateur research using slitless systems such as wide field survey work and asteroid spectroscopy.

Cheers
Robin