Astronomy & Astrophysics

Free access article

A&A 421, L1-L4 (2004)
DOI: 10.1051/0004-6361:20040164

Letter

The Ca II infrared triplet as indicator of anomalous Ca isotopic mixture in HgMn stars

F. Castelli^{1, 2} and S. Hubrig³

¹ Instituto di Astrofisica Spaziale e Fisica Cosmica, CNR, via del Fosso del Cavaliere, 00133 Roma, Italy
² Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, Trieste, Italy
³ European Southern Observatory, Casilla 19001, Santiago 19, Chile

(Received 13 April 2004 / Accepted 8 May 2004 )

Abstract
For the first time we present observational evidence for an anomalous isotopic structure of $\ion{ii}$ in mercury-manganese (HgMn) stars. The centroid wavelengths of $\ion{ii}$ infrared triplet lines in a number of stars have been found redshifted with respect to the centroids of the terrestrial $\ion{ii}$ lines. The record holder is the star HD 175640 for which the measured wavelength is consistent with $\ion{ii}$ being present in the atmosphere entirely in form of the heaviest stable isotope $\element[][48]$ . This is a very striking result as $\element[][48]$ makes up only 0.187% of the terrestrial Ca mixture.

Key words: stars: abundances -- stars: atmospheres -- stars: chemically peculiar -- stars: atomic data -- stars

Offprint request: F. Castelli, castelli@ts.astro.it

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