Heavy calcium in CP stars

COWLEY, C. R.; HUBRIG, S.; CASTELLI, F.; GONZÁLEZ, J. F.; WOLFF, B.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Blackwell Publishing

Año: 2007 vol. 377 p. 1579 - 1587

0035-8711

Large wavelength shifts of infrared triplet lines of CaII have been observed in the spectra of HgMn and magnetic Ap stars. They have been attributed to the heavy calcium isotopes, including 48Ca. One member of the triplet, lambda 8542, had been either unavailable, or of poor quality in earlier spectra. The present material shows conclusively that the stellar lambda 8542 shifts are consistent with an interpretation in terms of 48Ca. We find no relation between isotopic shifts of the CaII triplet lines, and those of HgII 3984. There is a marginal indication that the shifts are anticorrelated with the surface field strengths of the magnetic stars. We see sparse evidence for 48Ca 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 CaII 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.