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STRONTIUM Sr Z = 38

This element was first isolated by H. Davy in London in 1808. Its name alludes to the Latin word Strontian (Scotland).

Ionization energies
SrI 5.7 eV, SrII 11.0 eV, SrIII 43.6 eV.

Absorption lines of SrI

Table 1. Equivalent widths of SrI 4607(2) (resonance line)
Group V III Ib
F5 0.020   0.017
F8     0.042
G0 0.032    
G2 0.033   0.040
S 0.036    
G5     0.038
G8     0.075
K0   0.087  
K2   0.094 0.122
K5 0.161,0.170    

Table 2. Equivalent widths of SrI 6550(12)
Group V III Ib
S 0.005    
G2     0.021,0.040
G5     0.038,0.046
G6     0.111
G8     0.075
K0   0.018  
K2     0.076
K3   0.040 0.107
K5     0.083

SrI (see the line at 4067, which is a resonance line) appears in F-type stars and increases toward later types. No luminosity effect is perceptible.

Absorption lines of SrII

Table 3. Equivalent widths of SrII 4077 (one resonance line)
Group V I
B9 0.057  
A0 0.06  
A1 0.126  
A2 0.24 0.141(Ia)
A7 0.27  
FO 0.33 0.32(II) 0.630(Ia)
F4 0.38  
F5 0.39,0.34 0.72,0.68(Ib)
F6 0.41  
F8 0.41 0.71(Ib)
G0 0.35  
G1 0.56  
G2 0.33  
S 0.428  
G5 0.4  
K5 0.71,0.42  

Table 4. Equivalent widths of SrII 10914(2)
Group V III
G2 0.125  
S 0.098  
K2   0.200

SrII (see for instance the line at 4077) appears in late B-type stars and increases toward later spectral types. It has a strong positive luminosity effect, which has frequently been used as a luminosity criterion.

Figure 52

Emission lines of SrII
Lines of M.1 appear in emission in T Tau stars (Joy 1945) and in long-period variables after maximum light (Querci 1986).

Figure 53

Behavior in non-normal stars
SrII lines are strong in Bp stars of the Hg-Mn subgroup. The average W(4077) = 0.090 (Kodaira and Takada 1978). SrII lines are also strong in the Ap stars of the Cr-Eu-Sr subgroup (Adelman 1973b). According to Sadakane (1976), typically W(4077) = 0.34.

SrII lines are strong in Am stars; the W values are larger by a factor of about 1.5-2.0 than in normal stars of the same temperature (Smith 1973, 1974). In delta Del stars, SrII is strengthened, as in Am stars (Kurtz 1976).

SrII lines are weakened in lambda Boo stars: typically Wvalues are smaller by factors of the order of two than in normal stars of the same temperature (Venn and Lambert 1990).

Sr II lines are weakened in F-type HB stars with respect to normal stars of the same color, by factors up to ten in W (Adelman and Hill 1987). The same holds for HB stars in general (Adelman and Philip 1992a).

Sr seems to be underabundant with respect to iron in metal-weak stars (Luck and Bond 1985). The same is valid for the most metal-weak stars with Fe / H = 10-4 (Molaro and Bonifacio 1990).

Sr lines are prominent in Ba stars, which leads to an overabundance of an order of magnitude (Lambert 1985, Smith 1984). Typically W(4607) = 0.220 for a K 0III Ba star (Danziger 1965). Sr lines are strengthened in subgiant CH stars (Luck and Bond 1982, Krishnaswamy and Sneden 1985).

Sr lines are enhanced in S-type stars (Smith and Lambert 1986) and in C starscooler than C 3 (Dominy 1984).

Sr seems to be normal in the Magellanic Cloud stars (Luck and Lambert 1992).

Isotopes
Sr has four stable isotopes, namely Sr 84, 86, 87 and 88, which occur in the solar system with frequencies 0.6%,10%,7% and 83 % respectively. There also exist 14 short-lived isotopes and isomers.

Origin
Sr84 is only produced by the p process, Sr86 and Sr87 by the s process. Sr88 can be produced by either the s process or the r process.


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

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