In this paper we report 23 magnetic field measurements of the B3IV star HD 23478 : 12 obtained from high resolution Stokes V spectra using the ESPaDOnS ( CFHT ) and Narval ( TBL ) spectropolarimeters , and 11 from medium resolution Stokes V spectra obtained with the DimaPol spectropolarimeter ( DAO ) .
HD 23478 was one of two rapidly rotating stars identified as potential “ centrifugal magnetosphere ” hosts based on IR observations from the Apache Point Observatory Galactic Evolution Experiment survey .
We derive basic physical properties of this star including its mass ( M = 6.1 ^ { +0.8 } _ { -0.7 } M _ { \odot } ) , effective temperature ( T _ { eff } = 20 \pm 2 \text { kK } ) , radius ( R = 2.7 ^ { +1.6 } _ { -0.9 } R _ { \odot } ) , and age ( \tau _ { age } = 3 ^ { +37 } _ { -1 } \text { Myr } ) .
We repeatedly detect weakly-variable Zeeman signatures in metal , He and H lines in all our observations corresponding to a longitudinal magnetic field of \langle B _ { z } \rangle \approx - 2.0 \text { kG } .
The rotational period is inferred from Hipparcos photometry ( P _ { rot } = 1.0498 ( 4 ) \text { d } ) .
Under the assumption of the Oblique Rotator Model , our obsevations yield a surface dipole magnetic field of strength B _ { d } \geq 9.5 \text { kG } that is approximately aligned with the stellar rotation axis .
We confirm the presence of strong and broad H \alpha emission and gauge the volume of this star ’ s centrifugal magnetosphere to be consistent with those of other H \alpha emitting centrifugal magnetosphere stars based on the large inferred Alfvén to Kepler radius ratio .