VLBI observations of 12 GHz methanol masers

Very long baseline interferometric observations of 20 → 3-1E line of interstellar methanol (CH3OH) at 12.1 GHz toward three star-forming regions are reported. Toward the ultracompact H II region W3(OH), the methanol maser emission is found to emanate from multiple compact regions that are projected against the continuum emission. Individual maser spots have sizes of less than 0arcsec.002 (7×1013cm) and brightness temperatures greater than 2×1010K. For NGC 7538 and Cepheus A, the authors have determined absolute positions for one emission feature.