SiO ( v = 0 ) and 28 SiO ( v = 1 ) J = 2 − 1 maser emission from Orion IRc 2

We have observed with the IRAM interferom-eter at two different epochs and simultaneously the two transitions v = 0, J = 2 → 1 and v = 1, J = 2 → 1 of 29 SiO and 28 SiO in Orion IRc2. We have made the first maps of 29 SiO v = 0, J = 2 → 1 emission from Orion. These maps and properties of the 29 SiO spectra attest to maser emission. Our 28 SiO maps show the stable ring of maser spots observed in previous works. Combining our own data with published works we derive that the relative motion between the two ridges of the 28 SiO 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 features observed around 30 km s −1 seem to move with respect to the stable ring of 28 SiO main emission. Our relative 29 SiO (v = 0) and 28 SiO (v = 1) spot maps show that most 29 SiO and 28 SiO 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 various v state masers peak in different spatial regions. In addition, our maps of v = 0 and v = 1 emission suggest that local line overlaps due to turbulence and high gas temperature do not play a dominant role in the excitation of 28 SiO and 29 SiO , although excitation effects resulting from the overlap of Doppler-shifted ro-vibrational lines may still be significant.