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Table 2

Possible steps in the physical processes of partial mixing and nuclear H- and He-burning in massive very low Z stars.

Steps Acting physical processes Main nuclear products Stars and properties

0 Absence of mixing Initial composition Low Z stars without C excess
0+ Core H-burning 13C, 14N Very low CNO, but N > C, O
1 Core He-burning 12C, 16O, no N Visible only in WC stars
1+ Advanced He-burning 12C , 16O, low 20Ne Visible only in WO stars
2 Partial mixing 12C, 16O in H-burning shell 12C, 13C, 14N, 16O CEMP-no with [C/N] > 0, [O/N] > 0
2+ Idem with advanced H-burning Idem CEMP-no with [C/N] < 0, [O/N] < 0
2Na Idem from 1+ with the Ne-Na cycle Idem, 20,21,22Ne, 23Na CEMP-no, [C/N] > 0, [O/N] > 0, Na
2+Na Idem 2Na, advanced H-burning Idem, 20,21,22Ne, 23Na CEMP-no, [C/N] < 0, [O/N] < 0, Na
3 Partial mixing prod. (2, 2+) in He-burn. zone 18O, 22Ne CEMP-no, N , O-strong, 22Ne
3+ Idem with advanced α captures O, 20,22Ne, 25,26Mg, Sr, Y CEMP-no, idem, Mg, s-elem.(1st peak)
3++ Idem with more 22Ne (α,n)25Mg captures Idem, Ba weak Low s-star, Mg,s-el. (1st, 2nd peak)
The same above 3 cases from (2Na, 2Na+) Same properties as in above cases
−→ cases 3Na, 3+Na, 3++Na with Na present
4 Part. mix. 3 in H-burn., CNO, Ne-Na CNO, Ne, Na, CEMP-no, N, Ne, Na,
4+ Part. mix. 3+ in H-burn., CNO, Ne-Na, Mg-Al CNO, Ne, Na, Mg, Al CEMP-no, Na, Mg, Al, s-el.(1st peak)
4++ Partial mixing of 3++, idem Idem Low s, Na, Mg, Al, s-el.(1st, 2nd peak)

Notes. He should be enriched in all cases, except for step number 0. See text for more details.

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