(SIO)-SI-29 (UPSILON = 0) AND (SIO)-SI-28 (UPSILON = 1) J=2-1 MASER EMISSION FROM ORION-IRC2

We have observed with the IRAM interferometer at two different epochs and simultaneously the two transitions upsilon = 0, J = 2 --> 1 and up silon = 1,J = 2 --> 1 of (SiO)-Si-29 and (SiO)-Si-28 in Orion IRc2. We have made the first maps of (SiO)-Si-29 upsilon = 0, J = 2 --> 1 emis sion from Orion. These maps and properties of the (SiO)-Si-29 spectra attest to maser emission. Our (SiO)-Si-28 maps show the stable ring of maser spots observed in previous works. Combining our own data with p ublished works we derive that the relative motion between the two ridg es of the (SiO)-Si-28 emission ring is less than about 0.7 AU/yr over a period of 7 years. On the other hand, the weak high velocity maser f eatures observed around 30 km s(-1) seem to move with respect to the s table ring of 28SiO main emission. Our relative (SiO)-Si-29 (upsilon = 0) and (SiO)-Si-28 (upsilon = 1) spot maps show that most (SiO)-Si-29 and 28Si0 emission features are closely related but have not the same spatial extent. We conclude that these masers are not excited in the same gas layers in agreement with pumping models which predict that va rious upsilon state masers peak in different spatial regions. In addit ion, our maps of upsilon = 0 and upsilon = 1 emission suggest that loc al line overlaps due to turbulence and high gas temperature do not pla y a dominant role in the excitation of (SiO)-Si-28 and (SiO)-Si-29, al though excitation effects resulting from the overlap of Doppler-shifte d re-vibrational lines may still be significant.