CEPHEIDS AS TRACERS OF STAR-FORMATION IN M-31 .2. NGC-206 - EVIDENCE FOR SPIRAL ARM INTERACTIONS

NGC 206 in the Andromeda Galaxy (M 31) is the largest and perhaps the most massive region in the Local Group with coherent star formation ta king place on a timescale of similar to 30 Myr. We have incorporated o bservations of the H I emission and blue stars with our new identifica tions of Cepheid variables and those from observations by Baade and co llaborators to study the star formation history in this region in comp arison with the rest of M 31. We find that NGC 206 represents the late st phase of an enhanced level of star formation in the southern region of M 31. NGC 206 is located at the intersection of two spiral arms, s uggesting that the interaction between the spiral arms is responsible for the enhanced levels of star formation. The locations of the Cephei d variables demonstrate the motion of the interaction point. We find a relative velocity of 32 km sec(-1) between the velocity of the stars in M 31 and the velocity of the spiral arm pattern.