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A most unusual meteor spectrum

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BillW's picture
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A most unusual meteor spectrum

Hi All,

With a little practice it becomes quite straightforward to cast ones eye over a meteor spectrum and get a feel for what's going on.

I've now captured many spectra and most have the same basic structure.

Most show some sodium and magnesium along with iron and calcium. There are the occasional Nickel irons with just those lines.

There are the subtle differences discussed elsewhere in the meteor forum but every now and again something unusual appears.

This morning I captured one that did catch my eye as it immediately looked "different". Took a few seconds to figure out what was missing.

The particular meteor shows absolutely no sodium whatsoever. A very weak signature could be buried in the noise as it wasn't a particularly bright spectrum but this is the first I've seen in a decade where I've picked up the other main lines without even a hint of sodium.

An unusual spectrum to be sure. Conventional thinking is that over time the sodium is depleted from the meteoroid. Thus, if true then this must have been an "old" meteoroid. How old is old?, I have no idea...!

cheers,

Bill.

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Hi Bill,

Hi Bill,

your observation just prompted me to wonder if any " orbiting space junk" has had it's spectra captured on a burn up re-entry?

Eric

A R Pratt's picture
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A most unusual meteor spectrum

Hi Bill,

My Leeds_N camera recorded a mag 1 Perseid matching the time of your spectrum. I've attached the composite image from the video capture and its ground plot. Does this alignment agree with your general azimuth?

This is a single station result, so if other cameras recorded it we should be able to confirm its shower membership and orbit, etc. I'll let you know.

Cheers,

     Alex.

BillW's picture
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Hi,

Hi,

I was hoping you'd catch something with your N facing camera. However even considering the diffration angles involved I don't think that was the one. I'm on a different machine at the moment but I will double check.

cheers,

Bill.

A R Pratt's picture
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A most unusual meteor spectrum

Hi Bill,

The meteor was also recorded by Andy McCrea (Bangor, NI). He and Michael O'Connell analysed his video clip. My single-station analysis was a good match for a Perseid, but our 2-station result suggests it was a sporadic of absolute mag -2.5 from a radiant in northern Cam with a Vg of 50.6 km/s.

Its short path length of 12 km and our non-optimal viewing geometry only give a Q1-quality solution, so there's some uncertainty in its computed orbit. I'll let you know if more data are forthcoming.

Clear skies,

     Alex.

BillW's picture
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Here's the frame I used to

Here's the frame I used to extract the spectrum. The star field can be identified by Dubhe, brightest star lower left. The actual meteor would be ~30/40mm off the edge of the frame on this scale. I hope someone else has it because I'd be surprised if this pans out to be a Perseid, it doesn't fit the profile.... but you never know!

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Satellite reentry spectra

Hi Eric,

Peter Jenniskens is a well known meteor expert, often funded via NASA, and a quick search shows that he has been a co-authored a number of papers related to the spectra of re-entering satellites.

The advantage of satellites is that their trajectory / timing can be defined well in advance which allows the observer to point their camera at the right part of the sky at the right time (and have the grating correctly orientated). Alas meteors are somewhat less predictable.

One of the papers is available here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160000307.pdf

Best regards

William 

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space junk

I wondered this too.  A piece of Mg alloy not large enough to have been tracked but enough to produce a trail ?

Robin

BillW's picture
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Hi,

Hi,

Regarding space junk, I'm not sure. The fact that the spectrum had a set of the near IR atmospheric lines suggests it was doing a fair clip. All of the re-entry video's and spectra I've seen have been relatively slow (and horrendously complex!)  Whilst the most prominent metal lines are certainly Mg and Ca there are weak Fe features which are in the background of most spectra. No guarantee but I'd put my money on it being a tiny bit of something natural.

Cheers,

Bill.

BillW's picture
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Hi,

Hi,

I am relieved, put it down as another success for my comparative meteor spectroscopy method...!

The power of the spectrum!

cheers,

Bill.

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Nice work lads, well done!

Nice work lads, well done!

Regards,

Michael