The intermediate stellar mass population in the M31 OB association NGC 206

As part of our effort to determine what affects the star formation process by looking at the products of that process, we have obtained broadband Hubble Space Telescope images of the large OB association NGC 206 in the nearby spiral galaxy M31. Our images cover approximately the southern half of the association. We have detected stars down to an F555W magnitude of 25.5 and measure stars on the main sequence in NGC 206 to an M(F555W,0) of -1 or a mass of similar to 6 M(circle dot). From a comparison with isochrones, ages up to about 8 Myr are plausible, and we adopt an age of 6 Myr. For stellar masses 6-15 M(circle dot), we determine an initial mass function slope of -1.4 +/- 0.5. This is close to the value for a Salpeter mass function, although the uncertainty is large. The uncertainty in the slope represents disagreement among the individual mass bins. In terms of intermediate-mass stars (6-15 M(circle dot)) the NGC 206 star formation event appears to be typical of star formation processes in other nearby galaxies, and it is part of a growing number of studies that are finding similarities in the products of the star formation processes in a wide variety of star formation events and galactic environments. Nevertheless, the density of stars formed in NGC 206 is much lower than that in giant H II regions such as NGC 604 in M33 or 30 Doradus in the LMC and in typical OB associations.