OSIUM Os Z = 76

This element was discovered by S. Tennant in London in 1803. The name comes from the Greek osme (smell).

Ionization energies
OsI 8.7 eV, OsII 16.6 eV, OsIII 24.9 eV.

Absorption lines of OsI
The equivalent width of OsI 3232(3) in the sun is 0.018. OsI is present in M2III stars (Davis 1947).

Behavior in non-normal stars
OsI and OsII lines were identified by Guthrie (1969) in one Ap star of the Cr-Eu-Sr subgroup W(4608, OsII) = 0.038 and W(4421, OsI) = 0.040. Brandi and Jaschek (1970) and Cowley (1987) later identified this element in other Ap stars.

Os has seven stable isotopes, Os 184, 186, 187, 188, 189, 190 and 192. These occur in the solar system with frequencies 0.02%, 2%, 2%, 13%, 16%, 26% and 41% respectively. There also exist 12 unstable isotopes and isomers.

Os 189, 190 and 192 are pure r process products. Os188 can be produced by both the r process and the s process. Os186 and Os187 are pure s process products and Os184 is produced only by the p process.

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