This element was discovered in 1817 by J. Arfvedson in Stockholm. The name comes from the Greek lithos (stone).
LiI 5.3 eV, LiII 75.6 eV.
Absorption lines of LiI
Li I (for instance 6707) appears in A-type stars and decreases toward K-type. No LiII line has been observed in stars.
Behavior in the stars
Li is normal or weak in late Am stars (Burkhart and Coupry 1991) and behaves erratically in Ap stars (Faraggiana et al. 1986).
In F-type stars in open clusters a curious gap appears around F 7. Before and after the gap (or dip), Li is abundant, whereas in the gap it almost disappears (Boesgaard and Tripicco 1986, Balachandran 1990). A detailed investigation by Lambert et al. (1991) of F-type stars shows that the gap may also depend upon the stellar population.
In G-, K- and M-type stars large scatter usually exists in Li line strengths, which is attributed to the evolutionary status of these stars, but other factors may also play a role. In one star Cayrel de Strobel and Cayrel (1989) find W(6707) = 0.2 Å.
In old stars Li is still present, although rather weak (Rebolo 1991, Hobbs and Thorburn 1991). Spite (1992) finds no correlation between Li and Fe for metal-weak stars in the range -3 < Fe/H < - 1.2 dex. Thorburn (1992) has recently found some metal-weak stars with apparently no Li at all.
In giant stars Li lines are generally weak, except for a few stars in which Li is very strong, for instance the S-type stars and the so-called weak G-band stars (Vauclair 1991). Brown etal. (1989) analyzed over 600 G- and K-t,vpe giants and found strong Li lines (up to W(6707) = 0.45) in about 1% of these stars. It is possible that such overabundances might be connected with anomalies in the C12 / C13 ratio. This was confirmed by Pilachowski et al. (1990).
G and K supergiants show a large scatter in Li strengths (Luck 1977).
In chromospherically active RS CVn stars Li is very strong, whereas in inactive stars it is weak or absent (Pallavicini et al. 1992). An investigation of T Tau stars showed that a large variety of Li strengths exists (0.25 < W < 1.17 Å) (Basri et al.1991).
The `Li stars' of type SC or CS were analyzed by Catchpole and Feast (1976). In a sample of 380 S and C stars they found five Li stars. These Li-rich (also called 'super-lithium-rich') stars have W(6707) between 3 and 8 Å. The latter value was measured in WZ Cas, which has been called the `lithium star'. Keenan (1957) even found an object with W = 10 Å. Such high values imply large overabundances and probably mean that Li is created in situ (Abia et al. 1991). It should, however, be mentioned that there exist also late C and SC stars in which Li is highly deficient (Kilston 1975, Wallerstein 1989, Kipper and Wallerstein 1990). Denn et al. (1991) measured LiI in many cool carbon stars and found no relation with the C12 / C13 ratio. They remarked that the Li abundance seems to be lower in these stars than in M-type giants.
Li-strong stars are also present in the Magellanic Clouds (Smith and Lambert l990a, l990b).
Li has three stable isotopes, Li 5, 6 and 7. In the sun, one observes only Li6 and Li7 and their ratio is about 0.08. This ratio can be ascertained through the isotopic shift of the Li(6707) line, which is of the order of 0.2Å. According to the discussion of Boesgaard (1976a), apparently Li6 is not present in large quantities in stars. More recent data suggest a Li6/Li7 ratio of less than 0.1 (Ryan 1992).
Li6 is produced by cosmic ray spallation. Li7 arises from cosmological nucleo-synthesis, cosmic ray spallation or hydrogen burning.
Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.