2004A&A...416.1149B

During a survey of field strengths in upper main sequence stars in open clusters, we observed the star NGC 2244-334 in the Rosette Nebula cluster and discovered an extraordinarily large mean longitudinal field of about -9kG, the second largest longitudinal field known in a non-degenerate star. This star appears to be a typical Ap He-wk (Si) star of about 4M_☉. Spectrum synthesis using a line synthesis code incorporating the effects of the strong magnetic field indicates that He is underabundant by about 1.5dex, and C, O and Mg by about 0.1-0.4dex, while Si, Mn and Fe are overabundant by about 1dex, and Cr and Ti are nearly 2dex overabundant. Cluster membership for this star is secure, so its age is about 2x10⁶yr, which is less than 3% of its main sequence lifetime. This star is one of the very youngest magnetic upper main sequence stars with a well-determined age, and confirms that both magnetic fields and strong chemical peculiarity can appear in stars which are both extremely young and very close to the ZAMS.