The first stars: a classification of CEMP-no stars

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Table 1

Attempt at a classification of the CEMP-no stars based on the effects of successive mixing phases between the H- and He-burning zones and then mass loss from the source stars.

Physics	Class	[Ba/Fe]	[Sr/Fe]	[Na/Fe]	[Mg/Fe]	[Al/Fe]	¹²C/¹³C	[C/N]	[O/N]	[]

	EMP stars with none or very few heavy elements
Initial abund.	0	Very low abundances of all heavy elements
Prod. of H-burn.	0+	He-, light ¹³C-, and ¹⁴N-enrichments possible if metallicity Z> 10^-9

	CEMP stars with products of He-burning, without H (objects like WC and WO stars) ^a
He-burn.(WC star)	1	low	low	low	low	low	∞	∞	∞	very high
He-burn.(WO star)	1+	Same, with less ¹²C, more ¹⁶O, ^20,22Ne present, maybe some ²⁴Mg

	CEMP-no stars with no s-elements and generally no Mg and Al ^b
Mild 2nd H-burn.	2	~0	~0	low	low	~0	low-mid	≥ 0	≥ 0	low-mid
Strong 2nd H-burn.	2+	low	low	low	low	low	low	≤ 0.2	≤ 0.3	low-mid

	CEMP stars with s-elements possible, (CEMP-no, low-s, CEMP-s) ^c
Mild 2ndHe-burn.	3	low-mid	low-mid	low	low-mid	low	high	mid-high	mid-high	mid-high
Strong 2ndHe-burn.	3+	mid	high	any	mid-high	any	high	> 0.3	> 0.4	mid-high
More n-emission	3++	high	high	any	high	any	high	> 0.3	> 0.4	high

	CEMP stars with s-elements possible, (CEMP-no, low-s, CEMP-s) ^d
H-burn. of Class 3	4	mid	mid	high	mid	any	low-mid	mid	mid	mid-high
H-burn. of Class 3+	4+	mid	high	high	mid-high	mid	low	≤ 0.3	≤ 0.4	mid-high
H-burn. of Class 3++	4++	high	high	high	high	high	low	low	low	high

Notes. Enhancements in helium should also be present in CEMP stars.

^(a)

the existence of such stars is uncertain at extremely low Z, but products of 1 and 1+ intervene in mixing.

^(b)

Ne-Na cycle may produce Na from Ne, especially for 2+, thus leading to Class 2+Na. Mg-Al cycle unlikely.

^(c)

If Na produced in stages 2, Stages 3Na, 3+Na, 3++Na may result. Mg present, but Al unlikely.

^(d)

Third passage in the H-burning zone. Na always high. Burning intensity is increasing from 4 to 4++. Further mild mixing also leads to 4++, see text.

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