The Initial Magnetic Field Distribution in AB Stars

Stars are born with magnetic fields, but the distribution of their initial field strengths remains uncertain. We combine observations with theoretical models of magnetic field evolution to infer the initial distribution of magnetic fields for AB stars in the mass range of 1.6-3.4 M (circle dot). We tested a variety of distributions with different shapes and found that a distribution with a mean of similar to 800 G and a full width of similar to 600 G is most consistent with the observed fraction of strongly magnetized stars as a function of mass. Our most-favored distribution is a Gaussian with a mean of mu = 770 G and standard deviation of sigma = 146 G. Independent approaches to measure the typical field strength suggest values closer to 2-3 kG, a discrepancy that could suggest a mass-dependent and bimodal initial field distribution, or an alternative theoretical picture for the origin of these magnetic fields.