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C.J. Lonsdale, S.S. Doeleman (MIT Haystack Obs.), S. Liechti (Centro Astr. de Yebes, Spain), V.I. Slysh (Astro. Space Ctr., Russia), J. Alcolea, V. Bujarrabal, F. Colomer (Centro Astr. de Yebes, Spain), V.V. Goluber (Moscow State U.), S.V. Kalenski (Astro. Space Ctr., Russia), R.B. Phillips, P. Pratap (MIT Haystack Obs.), C.R. Predmore (FCRAO), I.E. Val'tts (Astro. Space Ctr., Russia), P. deVicente (Centro Astr. de Yebes, Spain)
Several strong class-I methanol maser sources have been observed using a short VLBI baseline, from Haystack Observatory in Westford MA to the FCRAO 15m telescope in Quabbin MA, in the 80 - 71A+ 95.2 GHz transition. Despite total maser flux densities of order 100 Jy, the masers were not detected on this baseline, indicating maser spot sizes in excess of several milliarcseconds. This result is consistent with previous studies, which suggest spot sizes of several tens of milliarcseconds for class-I masers, and at least rough cospatiality between the many transitions associated with class-I methanol masers. This is in contrast with the milliarcsecond scale sizes of class-II methanol masers, of which the 6GHz and 12GHz masers are members.