SULFUR S Z = 16

This element was known to the ancients. The Latin word is sulphurum.

Ionization energies
SI 10.4 eV, SII 23.3 eV, SIII 34.8 eV, SIV 47.3 eV, SV 72.7 eV, SVI 88.0 eV, SVII 281 eV, SVIII 328 eV.

Note that the resonance line of S I is at 8695(6). In the sun W(8695) = 0.034.

SI is present in A- to M-type stars without noticeable change in intensity. A positive luminosity effect exists for supergiants. The ultraviolet resonance line at 1807(2) seems not to have been studied.

Emission lines of SI
The lines of (UV M.9) excited by pumping of O I are present in the spectra of cool giant and supergiant stars Joras 1986).

Absorption lines of SII

SII (for instance 4162) appears weakly in early B-type stars, decreasing its intensity toward A-type stars.

Forbidden lines of SII
Forbidden S II lines appear in emission in a typical B[e] star (Swings 1973).

Many T Tau stars show the forbidden lines 4068 and 4076 (FM 1) in emission (Sun et al. 1985).

One typical VV Cep star shows [S II] in emission (Rossi et al. 1992).

[S II] lines appear in long-period variables around minimum light (Querci 1986). Forbidden lines of S II and S III are often seen in symbiotic objects (Swings and Struve 1941a, Freitas Pacheco and Costa 1992). These lines are also visible in novae (Joy and Swings 1945).

Absorption lines of SIII

S III (see the line at 4284) is present in early B-type stars, with a maximum around B 1 to B 2. A positive luminosity effect exists.

Emission lines of SIII
The ultraviolet lines 1012-1021 of M.2 are seen in emission in the solar spectrum (Feldman and Doschek 1991).

Forbidden SIII lines
The lines 9069 and 9532 are seen in B[e] stars in faint emission (Andrillat and Swings 1976, Ciatti et al. 1974) and in compact infrared sources associated with H II regions (McGregor et al. 1984).

Lines of [SIII] were also seen in at least one nova (Joy and Swings 1945).

Emission lines of SIV
The ultraviolet lines at 1062(1) and 1073(1) are visible in emission in the solar spectrum (Feldman and Doschek 1991).

Behavior in non-normal stars
SII lines are very strong in the spectrum of the extreme He star upsilon Sgr (Morgan 1935).

S behaves erratically in Bp stars of the Hg-Mn subgroup (Takada-Hidai 1991).

S is underabundant in two Ap stars of the Cr-Eu-Sr subgroup (Sadakane and Okyudo 1989).

In lambda Boo stars S is normal with respect to C, N and O, but overabundant with respect to Fe (Venn and Lambert 1990).

S seems to behave in a manner parallel to that of Mg (Spite 1992) in metal-weak stars.

S seems to behave in a manner parallel to that of Fe in stars of the Magellanic Clouds (Barbuy et al. 1981, Spite and Spite 1990), whereas other studies resulted in a slight overabundance with respect to Fe (Wheeler et al. 1989).

Bond and Luck (1988) detected one F-type halo supergiant in which S I is very strong, implying an overabundance by one order of magnitude. This object also has considerable overabundances of C, N and O by factors of ten or more with respect to iron. More objects of this type have been discussed by Waelkens et al. (1991, 1992). Some typical values for SI are W(8694) = 0.110 and W(4694) = 0.052. S is also overabundant in one F-type globular cluster supergiant(Gonzalez and Wallerstein 1992). The S overabundance is considered by Bond (1991) as a common feature of post-asymptotic branch stars, a name given to a group of objects that are evolving toward planetary nebulae. Similar ideas were put forward by Parthasarathy (1989).

In the nebular stage of novae [SVIII] lines sometimes appear (like that at 9911)in emission (Warner 1989).

Strong S II lines are present in the spectra of supernovae of type Ia (Branch 1990).

Isotopes
S has four stable isotopes, namely S 32, 33, 34 and 36, which occur in the solar system with frequencies 95 %,1 %,4% and 0.02 % respectively. There also exist six short-lived isotopes.

Origin
All four stable isotopes can be produced by explosive nucleosynthesis, but S³² and S³⁴ can also be produced by oxygen burning and S³⁶ either by Ne burning or by the s process.

Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.