Other
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apn....39.....a&link_type=abstract
A Peculiar Newsletter, vol. 39
Other
Polarisation, Stars: Magnetic Fields, Stars: Peculiar
Scientific paper
We describe an ongoing observational programme, using the MuSiCoS spectropolarimeter at Pic du Midi Observatory, aimed at detecting the weakest magnetic fields of Ap/Bp stars. For the 21 stars observed up to now, we have obtained 19 detections of Stokes V Zeeman signatures. This remarkable detection rate strongly suggests that all Ap stars having "magnetic" behaviour (Preston 1974; i.e. essentially all stars classified spectroscopically as Ap/Bp) actually harbour magnetic fields. In other words, all Ap stars appear to be observably magnetic.
For some of our stars with sufficient measurements and suitable phase sampling, dipolar oblique rotator models have been determined. Although results are preliminary, we find that magnetic geometry or rotational phase variations can explain the apparent faintness of the measured fields, and that the dipole strength for this small sample is at least several hundred G. In other words, at present we find no evidence for inferred dipolar surface fields weaker than a few hundred G in any Ap star. As suggested by Glagolevskij & Chountonov (2002), this result may indicate that there is a minimum field strength for which Ap-type characteristics are produced. This minimum strength appears to be of order the photospheric equipartition field (around 230 G for a main sequence A0 star).
Auriere Michel
Bagnulo Stefano
Donati Jean-Francois
Johnson Nan
Landstreet John Darlington
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