A SEARCH FOR RADIAL GRADIENTS OF THE MAGNETIC FIELDS IN THE ATMOSPHERES OF ALPHA ²CANUM VENATICORUM, 78 VIRGINIS, AND BETA CORONAE BOREALIS.

Zeeman spectrograms centered at N3500 and N4200 have been obtained for three Ap stars-a2 CVn, 78 Vir, and p CrB. For a star with Te = 10,000 K and log g = 4, optical depth 0.3 at 3647- occurs where the optical depth at A4200 = 0.02, and so the lines in these two spectral regions are formed in quite different layers of the atmosphere. The observations show that any variation in magnetic field strength over the optical depths probed by these observations cannot exceed 25%. Key words: magnetic stars-Zeeman effect-Ap stars