A characterization of Buekenhout-Metz unitals in PG(2, q 2), q even

Abstract

The known examples of embedded unitals (i.e. Hermitian arcs) in PG(2, q2) are B-unitals, i.e. they can be obtained from ovoids of PG(3, q) by a method due to Buekenhout. B-unitals arising from elliptic quadrics are called BM-unitals. Recently, BM-unitals have been classified and their collineation groups have been investigated. A new characterization is given in this paper. We also compute the linear collineation group fixing the B-unital arising from the Segre-Tits ovoid of PG(3, 2 r ), r≥3 odd. It turns out that this group is an Abelian group of order q2.