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We suggest that high-order g modes can be used as a probe of the internalmagnetic field of SPB (slowly pulsating B) stars. The idea is based on earlierwork by the authors which analytically investigated the effect of a verticalmagnetic field on p and g modes in a plane-parallel isothermal stratifiedatmosphere. It was found that even a weak field can significantly shift theg-mode frequencies -- the effect increases with mode order. In the presentstudy we adopt the classical perturbative approach to estimate the internalfield of a 4 solar mass SPB star by looking at its effect on a low-degree($l=1$) and high-order ($n=20$) g mode with a period of about 1.5 d. We findthat a polar field strength of about 110 kG on the edge of the convective coreis required to produce a frequency shift of 1%. Frequency splittings of thatorder have been observed in several SPB variables, in some cases clearly toosmall to be ascribed to rotation. We suggest that they may be due to a poloidalfield with a strength of order 100 kG, buried in the deep interior of the star.Comment: 4 pages, 2 figures (to appear in Astronomy & Astrophysics

Probing the internal magnetic field of slowly pulsating B-stars through g modes