High resolution observations of SiO masers: comparing the spatial distribution at 43 and 86 GHz

Abstract

We present sub-milliarcsecond observations of SiO masers in the late-type stars IRC +10011 and Chi Cyg. We have used the NRAO Very Long Baseline Array (VLBA) to map the 43 GHz (v=1, 2 J=1-0) and the 86 GHz (v=1, 2 J=2-1) SiO masers. All the transitions have been imaged except the v=2 J=2-1 in IRC +10011. We report the first VLBI map of the v=1 J=2-1 28SiO maser in IRC +10011 as well as the first VLBA images of SiO masers in an S-type Mira variable, Chi Cyg. In this paper we have focused on the study of the relative spatial distribution of the different observed lines. We have found that in some cases the observational results are not reproduced by the current theoretical pumping models, either radiative or collisional. In particular, for IRC +10011, the v=1 J=1-0 and J=2-1 28SiO lines have different spatial distributions and emitting region sizes, the J=2-1 emission being located in an outer region of the envelope. For Chi Cyg, the distributions also differ, but the sizes of the masing regions are comparable. We suggest that the line overlaps between ro-vibrational transitions of two abundant molecular species, H2O and 28SiO, is a possible explanation for the discrepancies found between the observations and the theoretical predictions. We have introduced this overlapping process in the calculations of the excitation of the SiO molecule. We conclude that the line overlaps can strongly affect the excitation of SiO and may reproduce the unexpected observational results for the two sources studied.

16 pages, 12 figures

References in corpus (2)

• A movie of a star: multi-epoch VLBA imaging of the SiO masers towards the Mira variable TX Cam
• Numerical simulations of stellar SiO maser variability. Investigation of the effect of shocks

Cited by in corpus (32)

• A Feature Movie of SiO Emission 20-100 AU from the Massive Young Stellar Object Orion Source I
• An Improved Model of SiO Maser Emission in Miras
• First Surface-resolved Results with the IOTA Imaging Interferometer: Detection of Asymmetries in AGB stars
• Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-Frequency SiO Masers
• First Images of R Aquarii and its Asymmetric H${}_2$O Shell
• Correlation between Infrared Colors and Intensity Ratios of SiO Maser Lines
• SiO masers from AGB stars in the vibrationally excited v=1,v=2, and v=3 states
• Mapping the circumstellar SiO maser emission in R Leo
• Astrometrically Registered Simultaneous Observations of the 22 GHz H${}_2$O and the 43GHz SiO masers towards R Leonis Minoris using KVN and Source/Frequency Phase Referencing
• Inward Motions of the Compact SiO Masers Around VX Sagittarii
• Astrometrically registered maps of H2O and SiO masers toward VX Sagittarii
• VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I
• First VLBI mapping of circumstellar 29SiO maser emission
• Carbon- and Oxygen-rich Asymptotic Giant Branch (AGB) stars in the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey
• Water vapor and silicon monoxide maser observations in the protoplanetary nebula OH 231.8+4
• Simultaneous VLBA polarimetric observations of the v={1,2} J=1-0 and v=1, J=2-1 SiO maser emission toward VY CMa: maser morphology and pumping
• The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216
• Simultaneous VLBI Astrometry of H2O and SiO Masers toward the Semiregular Variable R Crateris
• Asymmetric distributions of H2O and SiO masers towards V627 Cas
• Relative astrometry of the J=1-0, v=1 and v=2 SiO masers towards R Leonis Minoris using VERA
• The Science Case for Simultaneous mm-Wavelength Receivers in Radio Astronomy
• Ground Vibrational State SiO Emission in the VLA BAaDE Survey
• Very fast variations of SiO maser emission in evolved stars
• Pilot VLBI Survey of SiO v=3 J=1--0 Maser Emission around Evolved Stars
• Stellar masers, circumstellar envelopes, and supernova remnants
• A Comparison of the Velocity Parameters of SiO v=1, J=1-0 and J=2-1 Maser Emission in Long Period Variables
• First detection of 22 GHz H2O masers in TX Camelopardalis
• A Phase Dependent Comparison of the Velocity Parameters of SiO v=1, J=1-0 and J=2-1 Maser Emission in Long Period Variables
• Probing the fast outflow in IRAS 15452-5459 with ATCA observations of OH, H2O, and SiO masers
• Long-term Simultaneous Monitoring Observations of SiO and H2O Masers toward the Mira Variable WX Serpentis
• Ammonia in the hot core W51-IRS2: Maser line profiles, variability, and saturation
• Maser Studies in Evolved Stars