Rob_K
30-06-2014, 09:55 PM
Been looking at some of Christian Buil's amazing hi-res comet spectroscopy, particularly spectra of comae etc.
http://www.astrosurf.com/buil/us/spe8/comet.htm
And I wondered what might be further gained by going over some of my low-res SA100 stuff.
A spectrum of C/2011 L4 (PANSTARRS) taken 1 March last year looked the most promising because it was a very bright comet and the tail registered fairly well. The tail wasn't positioned perfectly but I took three slices: one through the comet 'head', one a short distance along the tail and the third a short distance further along the tail. The first limitation of course is that there is no slit to get a neat slice and you're effectively dealing with an extended object. But perhaps not too extended at this scale.
The last slice was pretty useless (pinkish-purple graph in the attached). Very poor signal-to-noise ratio and about all you can say is that there is a rough hump probably representing mostly continuum (sunlight reflection). The first slice (dark blue graph) shows the hump of the continuum (exaggerated to fit the other two spectra underneath!), as well as two 'horns' representing diatomic carbon emissions. There is also a very strong sodium emission spike. The second slice (aqua graph) is the interesting one I think. The signal-to-noise ratio isn't that bad and it shows the continuum and the strong sodium emission, but no sign of diatomic carbon emissions.
How much you can read into spectra like these is very much open to debate but I'd like to think that these characterise the comet at this stage of its orbit as follows:
(i) Coma and bright central condensation are dusty with minor Swan band gas emissions and a strong sodium emission;
(ii) Tail is dusty with no strong Swan band emissions; strong sodium emissions continue along tail.
Comments welcome - I can see how framing the comet better next time (if I get a similarly bright comet again!) to get the tail at right-angles to the spear of the spectrum would help.
Cheers -
http://www.astrosurf.com/buil/us/spe8/comet.htm
And I wondered what might be further gained by going over some of my low-res SA100 stuff.
A spectrum of C/2011 L4 (PANSTARRS) taken 1 March last year looked the most promising because it was a very bright comet and the tail registered fairly well. The tail wasn't positioned perfectly but I took three slices: one through the comet 'head', one a short distance along the tail and the third a short distance further along the tail. The first limitation of course is that there is no slit to get a neat slice and you're effectively dealing with an extended object. But perhaps not too extended at this scale.
The last slice was pretty useless (pinkish-purple graph in the attached). Very poor signal-to-noise ratio and about all you can say is that there is a rough hump probably representing mostly continuum (sunlight reflection). The first slice (dark blue graph) shows the hump of the continuum (exaggerated to fit the other two spectra underneath!), as well as two 'horns' representing diatomic carbon emissions. There is also a very strong sodium emission spike. The second slice (aqua graph) is the interesting one I think. The signal-to-noise ratio isn't that bad and it shows the continuum and the strong sodium emission, but no sign of diatomic carbon emissions.
How much you can read into spectra like these is very much open to debate but I'd like to think that these characterise the comet at this stage of its orbit as follows:
(i) Coma and bright central condensation are dusty with minor Swan band gas emissions and a strong sodium emission;
(ii) Tail is dusty with no strong Swan band emissions; strong sodium emissions continue along tail.
Comments welcome - I can see how framing the comet better next time (if I get a similarly bright comet again!) to get the tail at right-angles to the spear of the spectrum would help.
Cheers -