Mid-infrared source multiplicity within hot molecular cores traced by methanol masers

Abstract

We present high resolution, mid-infrared (MIR) images towards three hot molecular cores signposted by methanol maser emission: G173.49+2.42 (S231, S233IR), G188.95+0.89 (S252, AFGL-5180) and G192.60-0.05 (S255IR). Each of the cores was targeted with Michelle on Gemini North using five filters from 7.9 to 18.5 mu m. We find each contains both large regions of extended emission and multiple, luminous point sources which, from their extremely red colours (F-18.5/F-7.9 >= 3), appear to be embedded young stellar objects. The closest angular separations of the point sources in the three regions are 0.79, 1.00 and 3.33 arcsec corresponding to linear separations of 1700, 1800 and 6000 au, respectively. The methanol maser emission is found closest to the brightest MIR point source (within the assumed 1-arcsec pointing accuracy). Mass and luminosity estimates for the sources range from 3 to 22 M circle dot and from 50 to 40 000 L circle dot, respectively. Assuming the MIR sources are embedded objects and the observed gas mass provides the bulk of the reservoir from which the stars formed, it is difficult to generate the observed distributions for the most massive cluster members from the gas in the cores using a standard form of the initial mass function.