This element was discovered by J. Gadolin in Abo, Finland in 1794. The name alludes to its origin, a mineral that came from Ytterby, a Swedish town.
YI 6.4 eV, YII 12.2 eV, YIII 20.5 eV.
Absorption lines of YI
YI (see for instance the line at 6435) appears in G-type stars and grows in intensity toward later types. There is a positive luminosity effect.
Absorption lines of YII
YII (see for instance the lines at 4177 and 5200) appears in late B-type, grows toward a maximum for F-type and decreases toward G-type stars. According to Smith and Lambert (1985), the YII 7450 line is still present in M5III stars. There is a strong positive luminosity effect.
YII also has two strong lines, at 6614(26) and 6795(26) in the red spectral region. These lines are easily visible in M, C and S stars (Keenan 1957).
Behavior in non-normal stars
YII lines are strong in the spectra of the Bp stars of the Hg-Mn subgroup. Typically, equivalent widths are about twice as large as for normal stars of the same spectral type (Kodaira and Takada 1978). Adelman (1974) found YIII in one star of this subgroup. The presence of this species has been confirmed by Redfors (1991) and studied in detail by Redfors and Cowley (1993).
YII lines are somewhat stronger than normal in the spectra of Ap stars of the Cr-Eu-Sr subgroup (Adelman 1973b). Typically W(4398) = 0.040 (Sadakane 1976).
YII lines are strengthened in the spectra of Am stars, the W values being typically twice as large as in normal stars of the same temperature (Smith 1973, 1974). The delta Del stars show a similar behavior (Kurtz 1976).
YII is weakened in HB stars (Adelman and Philip 1992a).
Magain (1989) and Zhao and Magain (1991) find that, in metal-weak stars, Y behaves in a manner parallel to that of Fe. The same is probably true for stars in globular clusters (Wheeler et al. 1989).
YI and YII lines are strengthened in Ba stars, which leads to an overabundance of one order of magnitude (Lambert 1985, Smith 1984). YII lines are strengthened in the spectra of subgiant CH stars, which are also called hot Ba stars (Luck and Bond 1982).
Y lines are very strong in S-type stars (when compared with M stars of the same temperature), which leads to overabundances of one order of magnitude (Smith and Lambert 1986). However, the Y overabundances are unexpectedly less than those of Nd and La, although all three elements are produced by the s process. In MS stars the overabundance of Y is less pronounced (Smith et al. 1987).
YI and YII lines are very strong in the spectra of C-type stars later than C 3, which implies a large overabundance of this element. Fujita et al. (1963) found that the line at 4900 (Y II) has W typically of the order of about one angström unit. Y is also overabundant in SC stars (Kipper and Wallerstein 1990).
Y seems to be normal in the Magellanic Cloud stars (Luck and Lambert 1992).
Y has one stable isotope, Y89, and 20 short-lived isotopes and isomers.
Y can only be produced by the s process.
Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.