Hot cluster Horizontal Branch (HB) stars and field subdwarf B (sdB) stars are
core helium burning stars that exhibit abundance anomalies that are believed to
be due to atomic diffusion. Diffusion can be effective in these stars because
they are slowly rotating. In particular, the slow rotation of the hot HB stars
(T_eff > 11000K), which show abundance anomalies, contrasts with the fast
rotation of the cool HB stars, where the observed abundances are consistent
with those of red giants belonging to the same cluster. The reason why sdB
stars and hot HB stars are rotating slowly is unknown. In order to assess the
possible role of magnetic fields on abundances and rotation, we investigated
the occurrence of such fields in sdB stars with T_eff < 30000K, whose
temperatures overlap with those of the hot HB stars. We conclude that
large-scale organised magnetic fields of kG order are not generally present in
these stars but at the achieved accuracy, the possibility that they have fields
of a few hundred Gauss remains open. We report the marginal detection of such a
field in SB 290; further observations are needed to confirm it.Comment: 4 pages, 2 figures, 1 table, to appear in Astronomische Nachrichten,
Proceedings of the 7th Potsdam Thinkshop on "Magnetic Fields in Stars and
Exoplanets