|
|
Post by BillW on Mar 19, 2012 15:10:38 GMT
Hi all, I use my camera about half the time with a 12mm lens and a 300 lpm blazed grating mounted on it. In two years I've caught quite a few spectra but all too faint to be really useful until this one.  Processed with IRIS and VSpec here's the spectrum:  Resolution is quite low but after a bit of research I found this spectrum from a paper in FIRST RESULTS OF HIGH-DEFINITION TV SPECTROSCOPIC OBSERVATIONS OF THE 1999 LEONID METEOR SHOWER  Apart from one atmospheric line in the IR it looks pretty close. The wavelength calibration is out a bit on mine I think due to the low res but I think I can conclude that my spectra was of an early leonid fireball. Well pleased with the result! Cheers, Bill. |
|
|
|
Post by stewartw on Mar 19, 2012 20:14:46 GMT
Hi Bill,
Very interesting ... have not looked into this aspect before.
What is it that is characteristic of Leonids - is it the Mg line or the ratio of O lines?
Where do you mount the grating? I've never been able to fit filters (eg BW Aberration filter) between the lens and camera body.
Best regards
William
|
|
|
|
Post by leolion on Mar 19, 2012 20:41:37 GMT
|
|
|
|
Post by BillW on Mar 19, 2012 20:56:26 GMT
Hi,
From all the stuff I've read it seems to be a remarkably complex subject.
My specturm is not radiometrically corrected, but it was the qualitative aggrement of the metals in the blue/green part of the spectrum that matched up well. From what I understand it is the metals and refractory components that are important. The emission form the O and N are dictated by the energy of the meteroid and how much the meteoroid heats up the atmosphere. (but don't quote me!)
By happy coincidence my grating fits inside the focussing ring of the lens perfectly, a little cardboard holder and some blu tak and that's it. The height of optical sophistication!
cheers,
Bill.
|
|
|
|
Post by BillW on Sept 5, 2012 7:49:36 GMT
Hi,
Back to spectroscopic mode for the rest of the year for me now.
I would encourage everyone to have a go. It takes patience even with modern kit but it's the only way to truly analyze the meteor itself.
cheers,
Bill.
|
|
|
|
Post by stewartw on Sept 6, 2012 12:22:01 GMT
Hi Bill,
How bright does the meteor have to be for you to obtain a useful spectrum?
Best regards
William
|
|
|
|
Post by BillW on Sept 6, 2012 13:47:19 GMT
Hi, From my other reply here is the only example of the meteor being in the frame too. This is a pretty typical frame. They are basically empty as most stars are too faint to see through the grating. With a bit of tweaking you can faintly see 1st mag stars on later attempts.  (This was my very first capture on video of a meteor spectrum and I can't believe it was four years ago!) |
|
|
|
Post by stewartw on Sept 7, 2012 11:12:17 GMT
Hmmm - with my system the minimum stellar magnitude is around 5.5 (on the best nights), somewhat less when there's thin clouds and / or the moon is out.
Minimum detection level is around 3-4 magnitude so for my system I'd conservatively estimate (based on Perseid data for early August - which may not be an appropriate representation) that around 8% would be bright enough ...
Probably halve that as the moon is out 50% of the time.
Does refraction by the optical elements (lens) have a significant detrimental impact on the light reaching the grating? In other words do you only get dood data if the meteor passes through the centre of the FOV?
Best regards
William
|
|
|
|
Post by BillW on Sept 12, 2012 8:04:23 GMT
Hi,
On all of the meteor spectroscopy systems I've used I've had the grating in front of the lens. So the light is diffracted before reaching the objective.
However any light entering the lens off axis will be subject to abberations. If you look at the spectrum I got last year the meteor was out of the frame and the spectrum was at the edge of the image. You can see some defocus towards the red end, the right hand side in this image. but it's not too bad.
So if you have decent focus the image should ok in most places but there are unavoidable image degradations to some degree in every system.
cheers,
Bill.
|
|
|
|
Post by BillW on Oct 26, 2012 7:52:09 GMT
Been using the grating to try and catch an orionid.
Caught one last night and it must have been a real fireball as the spectrum spans the full height of the image.
This means a higher order spectrum and to get it this bright in higher order it must have been very bright.
I'll get the image on later. The time was 01.57UT in case anyone else caught it.
Cheers,
Bill.
|
|
|
|
Post by stewartw on Oct 29, 2012 19:25:24 GMT
Hi Bill,
Congratulations on the capture - looking forward to seeing the image.
I don't have a capture for 20121026_0157__ so I suspect it may have been outside my FOV.
Best regards
William
|
|
|
|
Post by BillW on Oct 30, 2012 19:37:50 GMT
Hi,
For reasons that are not entirely clear it appears I cannot upload the files to the server.
Which is strange as I can open them on my PC ok. When I try to ftp them I get an odd error.
I have been trying for 3 days now. I'll get them here eventually!
cheers,
Bill.
|
|
|
|
Post by BillW on Oct 30, 2012 20:05:02 GMT
Hopefully a breakthrough! Meteor image 640x480 binned 2x2 to improve s/n  Spectrum  Y axis: Pixel value X axis: Pixel Hurrah it worked, now for the bad news. A perfect meteor orientation but I don't know if the meteor went above or below the camera field of view. This reverses the direction of dispersion on the image and as it's also a second order image, (really good spectral resolution) I don't know what the overlapping lines are either because I don't know the initial direction of dispersion! An almost perfect result that is near useless!!! The only line I'm confident about is the oxygen line which tends to leave a distinct train. That can be seen on the image. I'll definitely need to invest in a second camera to monitor the same part of the sky as normal video so that I can determine orientation in future. A minor technical difficulty... |
|
|
|
Post by stewartw on Oct 31, 2012 7:45:16 GMT
Hi Bill,
What was your location and FOV (alt / az)? I know a few people who operate meteor cameras but who are not on this forum - they may have caught it and are thus able to help out with the meteor's direction.
Best regards
William
|
|
|
|
Post by BillW on Oct 31, 2012 9:05:42 GMT
Not on the forum!, you'll need to have stern words with them then...
The camera was oriented az ~100 deg and alt ~45 deg.
The lens was a 12mm so the fov was rather narrow. I'l need to work it out. But basically I was pointing to the SE.
Although I was trying to catch Orionids, this might have been a Taurid given it's diretion of travel. The dispersed vertical line on the image is Juipter, so the meteor was travelling west to east.
Bill.
|
|
