No GdI lines are seen in the solar spectrum.

Absorption lines of GdII

GdII appears in late F-type stars and intensifies toward cooler types.

GdII is also seen in one F 0Ib star (Reynolds et al. 1988).

Emission lines of GdII
Some GdII lines, excited by fluoreseence from H epsilon, have been observed in emission in one Mira variable (Grudzinska 1984).

Behavior in non-normal stars
GdII is weakly present in some Bp stars of the Hg-Mn subgroup, with W(3850) = 0.005 (Adelman 1989).

GdII is strong in Ap stars of the Cr-Eu-Sr subgroup (Adelman 1973b).

Typical values are W(4251) = 0.04 (Sadakane 1976). There even exists a star in which, exceptionally of all rare earths, only GdII is strengthened (Cowley and Henry 1979). GdIII is seen in Ap stars of the Cr-Eu-Sr subgroup (Cohen et al. 1969).

GdII is also strong inAm stars. Typical values for W(4251) of early types are 0.020 and of late types, W = 0.100 (Smith 1973, 1974). Similar values are found in delta Del stars (Kurtz 1976).

GdI and GdII lines are enhanced in some Ba stars (Lambert 1985). In these stars the W values may be twice as large as in normal giants of the same temperature.

GdII lines are present in S-type stars (Merrill 1947).

Gilroy et al. (1988) observed GdII 4130(M.19,49) in a number of metal weak G- and K-type dwarfs. These authors find the element to be overabundant with respect to iron. See also Part Two, section 2.2.

Isotopes
Gd has seven isotopes - Gd 152, 154, 155, 156, 157, 158 and 160. In the solar system Gd 155,156, 157, 158 and 160 are present as 15%, 21%, 16%, 25% and 22% of all Gd. Furthermore, there exist ten other short-lived isotopes, among them Gd¹⁵⁰, with a half life of 2 × 10⁶ years.

Origin
Gd is made by several processes: Gd 155, 156, 157 and 158 by either the r or the s process, Gd¹⁵² by the p or the s process, Gd¹⁵⁴ only by the s process and Gd¹⁶⁰ only by the r process.

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