Multi-transition VLBA observations of circumstellar SiO masers Rebeca Soria-Ruiz (Observatorio Astronómico Nacional, Spain) r.soria@oan.es Francisco Colomer (OAN) Javier Alcolea (OAN) Valentín Bujarrabal (OAN) Jean-Francois Desmurs (OAN) K. B. Marvel (AAS) D. Boboltz (USNO) P. J. Diamond (JBO) A. J. Kemball (NRAO)

SiO observational data (1) Mass loss values taken from Loup et al. , 1993, A&AS 99, 291 (2) Phase with respect to the NIR/SiO maximum extrapolated from Pardo J.R., Alcolea J. & Bujarrabal V. (in prep.) (3) Phases with respect to the optical maximum derived from the light curves available at http://www.aavso.org/lightcurves

IRC +10011: 28SiO v =1 J = 1 0 (43 GHz)

IRC +10011: 28SiO v =2 J =1 0

IRC +10011: v =1 vs. v =2 (J =1 0)  Similar spatial distribution  Ring-like structure sizes: v = 1: d  20 m.a.s. v = 2: d  18 m.a.s.  Consistent with Desmurs et al. (2000)

IRC +10011: 28SiO v =1 J = 2 1 (86 GHz)

 Spatial distribution quite different in both transitions IRC +10011: 7 mm vs. 3 mm (v = 1)  Spatial distribution quite different in both transitions and non-coincident.  Ring-like structure sizes: 7 mm: d  20 m.a.s. 3 mm: d  25-30 m.a.s. Contradiction with the current SiO masers pumping mechamisms  c f. similar study of R Cas by Phillips et al. (2003)

chi Cyg: 28SiO v =1 J =1 0 ( 43 GHz)

chi Cyg: 28SiO v =1 J = 2 1 (86 GHz)

 Ring-like structure sizes: chi Cyg: 7 mm vs. 3 mm (v = 1)  Spatial distribution different in both transitions: only one possible “coincident” spot ? Different flux-velocity distribution The emission arises in nearby (but not the same) projected regions.  Ring-like structure sizes: 7 mm: d  45 - 47 m.a.s. 3 mm: d  45 m.a.s.

TX Cam: 28SiO v =1 J = 1 0 (43 GHz)

TX Cam: 28SiO v =2 J = 1 0

TX Cam: v =1 vs. v = 2 (J =1 0)  Similar spatial distribution in both transitions.  Ring-like structure sizes: v = 1: d  28 m.a.s. v = 2: d  26 m.a.s.

* Results consistent with Desmurs J.F., et al. A&A, 360 , 189 (2000) Conclusions Source Comparison * Results consistent with Desmurs J.F., et al. A&A, 360 , 189 (2000)  Observational results clearly contradict the theoretical models, where the spatial distributions and “ring” structure sizes of the J =1-0 and J = 2-1 (v = 1) transitions should be similar.

Work in progress  We are investigating the prevalence of these results, on a second epoch already observed (both at 7mm and 3mm) on these sources and R Leo, as well as the detailed study of the possible effects on the pumping mechanism as a function of: Phase of the stellar pulsation Mass loss rate Chemical properties (in particular, line overlaps between ro-vibrational SiO and H2O transitions )