Three distinct types of peculiar early A-type stars are illustrated here.
The first star, 
Dra is a classical
"Ap" silicon star, in that it shows an
enhancement of the Si II 4128-32 doublet. Many of these stars are strongly
magnetic. Notice that in comparison with the A0 Va standard (previous page),
the metallic-line spectrum is quite peculiar, indicating that the star shows
enhancements of other elements besides silicon. The second star, HR 5597,
shows enhancements of not only Si II, but also Sr II (at 4077 Å)
and Cr II (at
4111 Å, in the wing of H
). The metallic-line spectrum is clearly very peculiar.
The bottom star, 
1 Boo is
an example of a mercury-manganese star, showing
enhancements of Hg II (at 3984 Å) and Mn II (most clearly seen at
4136 Å and
4206 Å). Mercury-manganese stars, in contrast to most other types
of Ap stars, do not appear to have strong magnetic fields.
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