First VLBI mapping of a rare SiO isotopic substitution

We report the first VLBI map of the 7 mm v=0 J=1–0 maser line of the 29 SiO isotopic substitution in the long period variable star IRC +10011. We have found that this maser emission is composed of multiple features distributed in an incomplete ring, suggesting that this maser is also amplified tangentially as already proposed in other SiO circumstellar masers. We present also the results for some 28 SiO 7 mm and 3 mm maser lines. We confirm in this epoch that the 86 GHz maser v=1 J=2–1 in IRC +10011 is formed in an outer region of the circumstellar envelope compared to the other SiO masers studied. The 29 SiO masing region appears to be located in a layer in between the 28 SiO v=1 J=1–0 and 28 SiO v=1 J=2–1 lines. Finally, we discuss the possible implications of the observational results in the SiO maser pumping theory.