BOÖTIS STARS
The Boötis stars are
population I A-type stars which show marked
deficiencies in the iron-peak elements. Spectral analysis indicates that
the most
extreme of these stars can have metal deficiencies of nearly 2 dex below the
sun. Interestingly, they show nearly solar abundances of C, N, O, and S.
These stars are recognized spectroscopically by their weak Mg II 4481 lines.
However, since many peculiar types near A0 have weak
4481 lines, to
confirm a star as a
Boötis star, it is also necessary to show that it is
metal-weak. This can be done by first ascertaining the hydrogen-line
type of the star,
as the hydrogen lines are probably the best indicators of the effective
temperature. Notice that the hydrogen lines of HD 142703 are best matched by
the F0 V standard, HD 23585, whereas the metallic-line spectrum is only
slightly stronger than A0. This clearly indicates that the star is metal-weak.
The very broad hydrogen lines of the type star,
Boo itself, indicate that it is
an early A-type star, near to the ZAMS. Many
Boötis stars are young; a few
have been discovered in the Orion Association, including HD 37411, which is
an Ae star. Many Boötis
stars show evidence of circumstellar material, either
in the form of dust, or shell absorption.
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