| About 5% of the main sequence A and B type stars display strong and organised magnetic fields. These stars are known as the peculiar A stars, or Ap/Bp stars. The magnetic field of these stars can be as weak as 300 gauss or as strong as 100 kilogauss, although the reason for such a large range of field strengths has yet to be discovered. This thesis investigates the possible presence of Ap-type magnetic fields in the Herbig Ae/Be (HAEBE) stars, pre-main sequence progenitors of the main sequence A and B type stars. Since those stars have not reached the main-sequence and yet are observable optically, they represent the perfect tool in attempting to trace the magnetic fields of Ap/Bp stars back to earlier evolutionary stages.; The results of the present thesis seem to indicate that magnetic fields appear in some intermediate mass stars before they reach the main sequence. The incidence, intensity, and structure of these fields are consistent with them being of a nature similar to those of the main sequence Ap/Bp stars. Therefore, detection of magnetic fields in HD 101412 and HD 72106 may well represent the first confident identification of the pre-main sequence progenitors of the magnetic Ap/Bp stars. Nevertheless, one should remain careful. The spectroscopic features of the HAEBE stars, caused by the material surrounding them, their unfinished contraction, their apparently weak fields, and the characteristics of the method of detection can potentially lead to misinterpretation. As an example of the potential for spurious detection, the recent claims of detection of a field in HD 139614 by Hubrig et al. (2004) are discussed. (Abstract shortened by UMI.)... |
