Circumstellar SiO masers in long period variable stars Rebeca Soria Ruiz F. Colomer, J. Alcolea, V. Bujarrabal & J.-F. Desmurs OAN

Why SiO masers ? TX Cam R Leo Schematic view of an AGB star Pardo et al 1998 Schematic view of an AGB star Why SiO masers ? Produced in the innermost regions of the circumstellar envelopes around AGB stars Ring-like structures at 24 R* (Diamond et al 1994) composed of compact spots, with typical sizes of a few mas, and high brightness temperatures  perfect targets for VLBI Maser emission is shown in 28SiO, 29SiO and 30SiO in many rotational transitions, which have been extensively studied in single-dish Multi-line simultaneous observations help in constraining the current pumping mechanisms

Radiative or collisional? IR stellar radiation: RADIATIVE MODELS Collisions with gas particles (H2): COLLISIONAL MODELS Bujarrabal (1994) Humphreys et al (2000; 2002) Nph (1043 s-1) v =1 J =21 v =1 J =10 v =2 J =10 n (H2) (cm-3) v =3 J =10 v =1 J = 10 v =1 J = 21 v =2 J = 10

Observations 28SiO 29SiO SiO transition frequency (MHz) band (MHz) channels resolution (km s-1) 28SiO v=1 J=10 43122.080 8 256 0.22 28SiO v=2 J=10 42820.587 29SiO v=0 J=10 42879.916 28SiO v=2 J=21 85640.456 16 512 0.11 29SiO v=0 J=21 85759.132 28SiO v=1 J=21 86243.442 v =0 28SiO v =1 v =2 29SiO  1780 K

AGB sample IRC+10011 R Leo TX Cam chi Cyg 7.1 10–6 7.1 10–8 2.5 10–6 source IRC+10011 R Leo TX Cam chi Cyg variability OH/IR Mira spectral type M9 M8 M8.5 S7 (Msol /año) 7.1 10–6 7.1 10–8 2.5 10–6 3.9 10–7 period (days) 660 310 557 408 distance (pc) 470 101 330 106 VLSR (km/s) 9.2 -0.5 11.8 10.2 phase 0.10 0.50 1.00 0.45 0.35 0.25

R Leo 28SiO v =1 J =10 28SiO v =2 J =10 28SiO v =1 J =21

TX Cam ( I ) 28SiO v =1 J =10 28SiO v =2 J =10 5 UA 28SiO v=2 J=10

TX Cam ( II ) 28SiO v =1 J =10 28SiO v =2 J =10 28SiO v =1 J =21 5 UA 28SiO v =2 J =10 28SiO v =1 J =21 28SiO v=2 J=21 28SiO v =2 J =21 28SiO v=1 J=21 28SiO v=2 J=10 28SiO v=1 J=10

Summary of results 28SiO 29SiO Similar spatial distribution of the v =1 and v =2 J =10 28SiO maser emissions in the O-rich stars. The v =2 emission is located in an inner region, with a separation of  13 mas In IRC+10011, R Leo y TX Cam, the spatial distribution of the v =1 J=10 and J=21 is completely different, the latter being produced in an outer region BUT in chi Cyg, an S-type star, the sizes are comparable

H2O 2 = 0 127,5  2 = 1 116,6 + SiO v = 1 J = 0  v = 2 J = 1 Pumping models: line overlaps Proposed by Olofsson (1981; 1985) to explain the quenching of the 28SiO v =2 J = 21 maser in O-rich stars If Tex (H2O) > Tb and the H2O line is optically thick, the v =2 J =1 rotational level is overpopulated H2O 2 = 0 127,5  2 = 1 116,6 + SiO v = 1 J = 0  v = 2 J = 1 The model (based on Bujarrabal et al 1996) Excitation of both molecules under the Large Velocity Gradient approximation H2O not including the overlap SiO including the overlap

Line overlaps: results greys v = 1 J =10 v = 2 J =10 v = 1 J =21 v = 2 J =21 Soria-Ruiz et al 2004 overlap included overlap not included

Summary 28SiO masers In O-rich envelopes: Similar spatial distribution of the 7mm emissions with the v=2 located in an inner region. The 3mm is produced further away (not in S-type envelopes where the 7 & 3mm regions have comparable sizes). Current models don’t explain the observed results in O-rich stars. The line overlaps strongly affect the excitation of SiO and should be introduced in the pumping models. 29SiO masers First maps of the 29SiO v = 0 J = 1– 0 maser transition in a circumstellar envelope. When detected, the line profile is composed of narrow peaks near or at the stellar velocity, suggesting tangential amplification as in the 28SiO maser lines.

Work in progress in the OH/IR variable IRC+10011 28SiO v=1 and v=2 J=10 (@ 43 GHz) with the High Sensitivity Array in the OH/IR variable IRC+10011 Global VLBI observations of the 28SiO v=1 and v=2 J=21 in O-rich envelopes Monitoring of the HCN (0, 20, 0) J=10 maser in C-rich envelopes using the Pico de Veleta (IRAM, Spain) 30m telescope VLBA observations of HCN maser transitions in the variable CIT6