Heavy calcium in CP stars ★

Abstract

Large wavelength shifts of infrared triplet lines of Ca ii have been observed in the spectra of HgMn and magnetic Ap stars. They have been attributed to the heavy calcium isotopes, including 48 Ca. One member of the triplet, Λ8542, had been either unavailable, or of poor quality in earlier spectra. The present material shows conclusively that the stellar Λ8542 shifts are consistent with an interpretation in terms of 48 Ca. We find no relation between isotopic shifts of the Ca ii triplet lines, and those of Hg iiΛ3984. There is a marginal indication that the shifts are anticorrelated with the surface field strengths of the magnetic stars. We see sparse evidence for 48 Ca in other chemically peculiar stars, for example, Am stars, metal-poor stars or chemically peculiar red giants. However, the sample is still very small, and the wavelengths of all three triplet lines, including those in the Sun, show slight positive shifts with respect to terrestrial positions. Some profiles of the Ca ii infrared triplet in the magnetic stars show extensive wings beyond a well-defined core. We can obtain reasonable fits to these profiles using a stratified calcium abundance similar to that used by previous workers. There is no indication that either the stratification or the Zeeman effect significantly disturbs the measurement of isotope shifts.