Elemental abundance analyses with coadded Dominion Astrophysical Observatory spectrograms – II. The mercury–manganese stars 53 Tauri, Mu Leporis and Kappa Cancri

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Abstract
Elemental abundance analyses based on the coaddition of at least 10 2.4 Å mm−1 IIa-O Dominion Astrophysical Observatory spectrograms have been performed for three mercury–manganese stars, 53 Tauri, Mu Leporis, and Kappa Cancri. These fine analyses show a greater degree of internal consistency than previous studies based on lower signal-to-noise data. Lines as weak as of order 3 mÅ are employed in these studies, and lines of atomic species not previously identified have been discovered. The status of 53 Tau as an anomalous member of this class is confirmed in that it lacks a Hg IIλ3984 line even at the 2 mÅ level. Further, its surface gravity indicates it is less evolved than µ Lep and ϰ Cnc. Violations of the odd–even effect in the photospheric abundances of all three stars suggest that non-nuclear processes have operated in their atmospheres. Some of the values are substantially changed from their presumably initial solar values. How this happened before the helium completely diffused out of the atmospheres is a critical question for radiative diffusion theories.

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