Microwave OH maser emission in the circumstellar envelopes of late-type stars

Nature ◽  
1981 ◽  
Vol 291 (5814) ◽  
pp. 382-385 ◽  
Author(s):  
P. F. Bowers ◽  
K. J. Johnston ◽  
J. H. Spencer
Keyword(s):  
Late Type ◽  
Circumstellar Envelopes ◽  
Maser Emission

scholarly journals A VLBI polarization study of SiO masers towards VY CMa

2007 ◽  
Vol 3 (S242) ◽  
pp. 328-329
Author(s):  
L. L. Richter ◽  
A. J. Kemball ◽  
J. L. Jonas
Keyword(s):  
Magnetic Field ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Maser Emission ◽  
Evolved Stars ◽  
Polarization Study ◽  
Wide Range ◽  
Supergiant Star

AbstractMaser emission from the SiO molecule has been widely observed in the near-circumstellar envelopes of late-type, evolved stars. VLBI images can resolve individual SiO maser spots, providing information about the kinematics and magnetic field in the extended atmospheres of these stars. This poster presents full polarization images of several SiO maser lines towards the supergiant star VY CMa. VY CMa is a particularly strong SiO maser source and allows observations of a wide range of maser transitions. We discuss implications of these observations for VY CMa morphology, polarization, and pumping models.

scholarly journals Water vapour masers in long-period variable stars

2020 ◽  
Vol 644 ◽  
pp. A45
Author(s):  
J. Brand ◽  
D. Engels ◽  
A. Winnberg
Keyword(s):  
Stellar Wind ◽  
Constant Velocity ◽  
Variable Stars ◽  
Circumstellar Envelopes ◽  
Maser Emission ◽  
Evolved Stars ◽  
Outflow Velocity ◽  
Regular Variable ◽  
Individual Features

Context. Water masers emitting at a radiofrequency of 22 GHz are often found in the circumstellar envelopes of evolved stars. We monitored the H2O maser emission of a larger sample of evolved stars of different types to study the maser properties as a function of stellar type. Aims. We wish to understand the origin and evolution of the H2O masers in circumstellar envelopes. In this paper, we take a closer look at R Crt and RT Vir, two nearby (<250 pc) semi-regular variable stars. The findings complement our monitoring results for RX Boo and SV Peg, two other semi-regular variable stars that we have discussed in a previous paper. Methods. Within the framework of the Medicina/Effelsberg H2O maser monitoring programme, we observed the maser emission of R Crt and RT Vir for more than two decades with single-dish telescopes. To get insights into the distribution of maser spots in the circumstellar envelopes at different times, to get an idea of their longevity, and, where possible, to be able to link the phenomena seen in our observations to maser locations within the envelopes, we collected interferometric data for these stars, taken within the same period, from the literature. Results. The H2O masers in R Crt and RT Vir exhibit brightness variations on a variety of timescales. We confirm short-time variations of individual features on timescales of months to up to 1.5 yr, as seen by previous monitoring programmes. Also decade-long variations of the general brightness level, independent from individual features, were seen in both stars. These long-term variations are attributed to brightness variations occurring independently from each other in selected velocity ranges and they are independent of the optical light curve of the stars. Expected drifts in velocity of individual features are usually masked by the blending of other features with similar velocities. However, in RT Vir, we found the exceptional case of a single feature with a constant velocity over 7.5 yr (<0.06 km s−1 yr−1). Conclusions. We attribute the long-term brightness variations to the presence of regions with higher-than-average density in the stellar wind and hosting several clouds which emit maser radiation on short timescales. These regions typically need ~20 yr to cross the H2O maser shell, where the right conditions for exciting H2O masers are present. Different clouds contained in such a region all move within a narrow range of velocities, and so does their maser emission. This sometimes gives the impression of longer-living features in single-dish spectra, in spite of the short lifetimes of the individual components that lie at their origin, thus, naturally explaining the longer timescales observed. The constant velocity feature (11 km s−1) is likely to come from a single maser cloud, which moved through about half of RT Vir’s H2O maser shell without changing its velocity. From this, we infer that its path was located in the outer part of the H2O maser shell, where RT Vir’s stellar wind has, apparently, already reached its terminal outflow velocity. This conclusion is independently corroborated by the observation that the highest H2O maser outflow velocity in RT Vir approaches the terminal outflow velocity, as given by OH and CO observations. This is generally not observed in other semi-regular variable stars. All four stars in our study are of optical variability type SRb, indicating the absence of periodic large-amplitude variations. Therefore, any likely responses of the maser brightness to variations of the optical emission are masked by the strong short-term maser fluctuations.

scholarly journals OH masers in envelopes of late type stars

1987 ◽  
Vol 122 ◽  
pp. 243-244
Author(s):  
A.M. Le Squeren ◽  
P. Sivagnanam ◽  
F. Tran Minh ◽  
M. Dennefeld ◽  
F. Foy
Keyword(s):  
Radio Telescope ◽  
Detection Rate ◽  
Point Sources ◽  
Spectral Classification ◽  
Late Type ◽  
Maser Emission ◽  
Galactic Longitude

Two studies of OH maser emission in envelopes of late type stars -miras (3) and OH/IR objects- have been performed with the Nancay radio-telescope. Mainly, the OH miras are found with thicker dust envelopes than the non OH ones. A sample of unidentified IRAS point sources selected on their colors has been observed. We have detected 46 new OH sources. The OH detection rate is a function of the galactic longitude and of the IRAS spectral classification.

scholarly journals The Galactic Distribution of OH/IR Stars

1977 ◽  
Vol 42 ◽  
pp. 399-433
Author(s):  
H.J. Habing
Keyword(s):  
Present Status ◽  
Line Emission ◽  
Microwave Line ◽  
Late Type ◽  
Maser Emission ◽  
Long Period ◽  
Ir Stars ◽  
Long Period Variables ◽  
Recent Compilation ◽  
Galactic Distribution

In 1967 Wilson and Barrett (1968, 1970) discovered that some long period variables, very red and apparently very late type stars, emit OH microwave line emission that is especially strong in the 1612 MHz line at 18 cm. At present some 65 such OH-emitting stars have been identified - for a recent compilation see Bowers and Kerr (1977, M giants) and Baudry et al. (1977, M supergiants). Several stars show maser emission in H2O and SiO as well. At this colloquium Winnberg will review the present status of our knowledge of these stars.

Observation of a ring structure in SiO maser emission from late-type stars

1994 ◽  
Vol 430 ◽  
pp. L61 ◽  
Author(s):  
P. J. Diamond ◽  
A. J. Kemball ◽  
W. Junor ◽  
A. Zensus ◽  
J. Benson ◽  
...  
Keyword(s):  
Ring Structure ◽  
Late Type ◽  
Maser Emission

scholarly journals Maser emission during post-AGB evolution

2012 ◽  
Vol 8 (S287) ◽  
pp. 217-224 ◽  
Author(s):  
J.-F. Desmurs
Keyword(s):  
Planetary Nebulae ◽  
Transition Phase ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Circumstellar Envelopes ◽  
Maser Emission ◽  
Giant Branch Stars ◽  
Short Transition

AbstractThis contribution reviews recent observational results concerning astronomical masers toward post-AGB objects with a special attention to water fountain sources and the prototypical source OH 231.8+4.2. These sources represent a short transition phase in the evolution between circumstellar envelopes around asymptotic giant branch stars and planetary nebulae. The main masing species are considered and key results are summarized.

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