* Astronomy

Title: Confirming HD 23478 as a new magnetic B star hosting an H alpha-bright centrifugal magnetosphere
Author: James Sikora, Gregg Wade, David Bohlender, Coralie Neiner, Mary Oksala, Matt Shultz, David Cohen, Asif ud-Doula, Jason Grunhut, Dmitry Monin, Stan Owocki, Véronique Petit, Thomas Rivinius, Richard Townsend

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} solar masses), effective temperature (T_eff=20±2kK), radius (R=2.7^{+1.6}_{-0.9} solar radii), and age (T_age==3^{+37}_{-1} 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 {B_z} approx -2.0kG. The rotational period is inferred from Hipparcos photometry (P_rot=1.0498(4)d). Under the assumption of the Oblique Rotator Model, our observations yield a surface dipole magnetic field of strength B_d \geq 9.5kG that is approximately aligned with the stellar rotation axis. We confirm the presence of strong and broad H 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 Alfven to Kepler radius ratio.

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