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Originally Posted by Weltevreden SA
Hi again, Terry . . . Thanks for the ursusmajor.ch link and the info I found there. Now I'm wondering where the Ti comes from in an M star. I assume you mean an M red dwarf and not, as I occasionally see, a red giant whose color temp is the same as an M dwarf but is 5 - 6 mags brighter. A red dwarf core converts via the p-p chain and I'm wondering where the spare neutrons come from to generate Na, Si, all the way to Ti. I looked up Ti synthesis via CNO cycling and it comes to ~2.4 Myr and requires T on the order of ~40 million K. So far as I know, M dwarfs don't reach the CNO cycle temps. Does the Ti come from several prior generations of Type 2 SN that the M dwarf accreted in the pre-MS phase? Does your spectrum show significant SI2, Na, Al, or Mg lines? The last 3 would come via the Ne/Na and Mg/Al cycles, which occur via He burning in the horizontal branch, massive RG, or AGB stars. Your spectrum has prompted some fun head-scratching over here, but so far all that has fallen out is (yet more) grey hairs. Thanks . . . Dana in SA
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The Ti and all of the heavier elements came from prior supernova and are not made in the star that we are observing. Thre are lots of lines of "metals" in our sun as well but none have been made in the sun.
The spectra of a M dwarf vs an M giant is quite similar even thought they are completely different stars. The reason that TiO becomes significant even though it is quite an uncommon element is that it is a very good absorber of light- hence the reason we use it as sunscreen.
At high temperatures, TiO is ionised along with lots of other elements. This is why hot stars like A and B stars have very few absorption lines (except hydrogen).
Cooler stars allow molecules to form near the surface and these absorb the blackbody light continuum resulting in absorption lines. TiO is just very good at absorbing light so it is very promonent in the spectra.
Na lines are also visible but I haven't identified then specifically.
Cheers
Terry