Circumstellar SiO masers in long period variable stars

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Circumstellar SiO masers in long period variable
stars

• Rebeca Soria Ruiz
• F. Colomer, J. Alcolea, V. Bujarrabal J.-F.
  Desmurs

OAN
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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
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Radiative or collisional?
Bujarrabal (1994)
Humphreys et al (2000 2002)
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Observations
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AGB sample
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R Leo
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TX Cam ( I )
28SiO v2 J1?0
28SiO v1 J1?0
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TX Cam ( II )
28SiO v2 J2?1
28SiO v1 J2?1
28SiO v2 J1?0
28SiO v1 J1?0
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Summary of results
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 IRC10011, R Leo y TX Cam, the spatial
distribution of the v 1 J1?0 and J2?1 is
completely different, the latter being produced
in an outer region BUT in chi Cyg, an S-type
star, the sizes are comparable
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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
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Line overlaps results
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Summary
28SiO masers In O-rich envelopes
Similar spatial distribution of the 7mm emissions
with the v2 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 dont 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.
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Work in progress

• 28SiO v1 and v2 J1?0 (_at_ 43 GHz) with the
  High Sensitivity Array
• in the OH/IR variable IRC10011
• Global VLBI observations of the 28SiO v1 and
  v2 J2?1 in O-rich
• envelopes
• Monitoring of the HCN (0, 20, 0) J1?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