Chemical Composition

[neoterryjoe]

Spectroscopy allows us to see the composition of and the temperature of the stars but one twist is that the temperature determines which kind of atoms can produce visible absorption lines; it does not mean that the absence of the line would mean the absence of the element.

So in view of this situation, how do we find out the elements which the star compose of and yet not being able to show in spectroscopy? Or is this question of importance in the first place(knowing ALL the elements/ions which compose of the star)?

[ykchia]

Hi :

Never mind about a/c ALL the elements but 'quantitative' analysis of the spectra ( peak integration) shows the predom. important elements - H, He ... couple with the fusion theory ... you probably can arrive at what fuel the star and the higher order elements producted..

http://imagine.gsfc.nasa.gov/docs/ask_a ... 1112a.html

rgds
ykchia

[chrisyeo]

I'm not a physics person but I'll try my best to answer..

Spectroscopy is not just about emission lines but also absorption lines. Note Gustav Kirchhoff's observation (Kirchhoff's laws) that:

-A hot solid, liquid or gas, under high pressure, gives off a continuous spectrum.

-A hot gas under low pressure produces a bright-line or emission line spectrum.

-A dark line or absorption line spectrum is seen when a source of a continuous spectrum is viewed behind a cool gas under pressure.

Stars are so hot that they produce a continous spectrum, so stellar compositions can still be found by looking at their absorption lines.

Also, our knowledge of what stars are made of is also informed by our knowledge of nuclear processes in star birth. By observing spectra and then theorising about stellar evolution, we can be fairly certain about the chemical composition of most stars.

Hope this helps.
Chris

[neoterryjoe]

Hi all!
Thanks a lot!!