Discovery of the pre-main sequence progenitors of the magnetic Ap/Bp stars?

Abstract

We report the discovery, using FORS1 at the ESO-VLT and ESPaDOnS at the CFHT, of magnetic fields in the young A-type stars HD 101412, V380 Ori and HD 72106A. Two of these stars (HD 101412 and V380 Ori) are pre-main sequence Herbig Ae/Be (HAeBe) stars, while one (HD 72106A) is physically associated with a HAeBe star. Remarkably, evidence of surface abundance spots is detected in the spectra of HD 72106A. The magnetic fields of these objects display intensities of order 1 kG at the photospheric level, are ordered on global scales, and appear in approximately 10% of the stars studied. Based on these properties, the detected stars may well represent pre-main sequence progenitors of the magnetic Ap/Bp stars. The low masses inferred for these objects (2.6, 2.8 and 2.4 M ⊙) represent additional contradictions to the hypothesis of Hubrig et al. (2000, ApJ, 539, 352), who claim that magnetic fields appear in intermediate-mass stars only after 30% of their main sequence evolution is complete. Finally, we fail to confirm claims by Hubrig et al. (2004, A&A, 428, L1) of magnetic fields in the Herbig Ae star HD 139614. © ESO 2005.