  The biaxial smectic-A* (Sm-A_B*) phase, appearing in the phase sequence
Sm-A*--Sm-A*_B--Sm-C*, is analyzed using Landau theory. It is found to possess
a helical superstructure with a pitch that is significantly shorter than the
pitch of the Sm-C* helical superstructure. The Sm-A_B*--Sm-C* transition can be
either 1st or 2nd order, and correspondingly there will be either a jump or
continuous variation in the pitch. The behaviors of the birefringence and
electroclinic effect are analyzed and found to be similar to those of a
Sm-C*_alpha phase. As such, it is possible that the Sm-A_B* phase could be
misidentified as a Sm-C*alpha phase. Ways to distinguish the two phases are
discussed.

Soft Condensed Matter