scholarly journals Radio Observations of Mira Variables, OH/IR Stars and M-Supergiants

1995 ◽  
Vol 155 ◽  
pp. 113-126
Author(s):  
Jessica M. Chapman ◽  
H. J. Habing ◽  
N. E. B. Killeen
Keyword(s):  
Circumstellar Envelopes ◽  
Radio Observations ◽  
Mira Variables ◽  
Ir Stars

AbstractWe review radio maser observations of the circumstellar envelopes of oxygen-rich Mira variables, OH/IR stars and M-type supergiants.

scholarly journals De-projection of radio observations of axisymmetric expanding circumstellar envelopes

2018 ◽  
Vol 480 (3) ◽  
pp. 3324-3337 ◽  
Author(s):  
P T Nhung ◽  
D T Hoai ◽  
P Tuan-Anh ◽  
P Darriulat ◽  
T Le Bertre ◽  
...  
Keyword(s):  
Circumstellar Envelopes ◽  
Radio Observations

scholarly journals A Southern Survey of OH Masers at 1612 MHz

1981 ◽  
Vol 34 (3) ◽  
pp. 333 ◽  
Author(s):  
JL Caswell ◽  
RF Haynes ◽  
WM Goss ◽  
U Mebold
Keyword(s):  
Galactic Plane ◽  
Galactic Centre ◽  
Emission Sources ◽  
Classification Schemes ◽  
Mira Variables ◽  
Population Type ◽  
Ir Stars ◽  
Kinematic Properties ◽  
Line Type

A search for OH at 1612 MHz has been made along the galactic plane from longitude 3400 to the galactic centre, yielding 78 emission sources (mostly new discoveries); a further 5 sources have been found in a less sensitive survey between longitudes 2700 and 3260 Of these 83 sources 55 are masers of the variety showing two intensity peaks spaced in velocity-a characteristic of OH/IR stars. The velocity and spatial distributions of these new OHjIR stars (which are not as yet identified in the optical or infrared) are discussed, with special reference to their kinematic properties and population type; it is still not clear whether they are predominantly late-type giants (Mira variables) or supergiants. The other 28 OH sources detected include 11 of the type lIe variety (extended OH clouds exhibiting 1612 MHz emission with accompanying 1720 MHz absorption) and 4 with accompanying main-line (type 1)OH masers; the remaining 13 sources do not readily fit within existing classification schemes and are discussed individually

Mid-IR spectra of the M-type Mira variable R Tri observed with the Spitzer IRS

2020 ◽  
Vol 493 (1) ◽  
pp. 807-814
Author(s):  
Dana K Baylis-Aguirre ◽  
M J Creech-Eakman ◽  
Tina Güth
Keyword(s):  
Ir Spectra ◽  
Emission Feature ◽  
Absorption Feature ◽  
Cool Temperature ◽  
Circumstellar Envelopes ◽  
Mira Variables ◽  
Mira Variable ◽  
Molecular Lines ◽  
Infrared Spectrometer ◽  
Vibrational Bands

ABSTRACT We present analysis of mid-infrared (IR) spectra of the oxygen-rich Mira variable R Tri. The data were taken with the Spitzer Infrared Spectrometer (IRS) as part of a study tracking how Mira variables’ regular pulsations affect circumstellar envelopes. We detected strong emission lines at 13.87, 16.18, and 17.6 $\hbox{$\mu $m}$, and one strong absorption feature at 14.98 $\hbox{$\mu $m}$. The emission features at 13.87 and 16.18 $\hbox{$\mu $m}$ are excited vibrational bands of CO2, while the absorption feature is the fundamental ν2 band. The 17.6 $\hbox{$\mu $m}$ emission feature has a completely different character than the molecular lines and we report its identification as Fe i fluorescence. We used a two-slab model with the radiative transfer code radex to model the CO2 Q-branch bandheads. Our results indicate a slab of gas with T∼600 K located at ∼3–4 R*. The cool temperature discrepancy with the radius provides observational evidence for the previously theoretical ‘refrigeration zone’.

Variability of water masers in evolved stars on timescales of decades

2017 ◽  
Vol 13 (S336) ◽  
pp. 393-394 ◽  
Author(s):  
Jan Brand ◽  
Dieter Engels ◽  
Anders Winnberg
Keyword(s):  
Structural Changes ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Mira Variables ◽  
Velocity Gradients ◽  
Systemic Velocity ◽  
Secular Variations ◽  
Red Supergiants ◽  
Water Masers

AbstractFor several decades (1987-2015) we have been carrying out observations of water masers in the circumstellar envelopes (CSE’s) of Mira variables, Red Supergiants (RSG’s) and Semi-Regular Variables (SRV’s) with the Medicina 32-m and Effelsberg 100-m antennas. The single-dish monitoring observations provide evidence for strong H2O maser profile variations, which likely are connected to structural changes in the maser shells. Such variations include strong flares in intensity lasting several (tens of) months and systemic velocity gradients of maser components developing over years, as well as other secular variations which are superimposed on periodic variations following the stellar light variations.When complemented with interferometric observations, it is possible to derive the 3-D distribution of the maser spots, and their lifetime, as we have done for RX Boo (Winnberget al.2008) and U Her (Winnberget al.2011; Brandet al. in prep.).

The Galactic Distribution and Kinematics of OH Stars (A Preliminary Discussion)

1975 ◽  
Vol 2 (6) ◽  
pp. 362-363
Author(s):  
P.F. Bowers
Keyword(s):  
Large Scale ◽  
Velocity Dispersion ◽  
Neutral Hydrogen ◽  
Late Type ◽  
Velocity Range ◽  
Hydrogen Distribution ◽  
Mira Variables ◽  
Sky Survey ◽  
Ir Stars ◽  
Galactic Distribution

The majority of OH/IR stars have been identified as M-type Mira variables, but there are a few cases where the stars have been identified as M supergiants or late-type semi-regular variables. A large number of OH sources have also been discovered with the 1612 MHz OH characteristics of OH/IR stars but no apparent optical or infrared counterparts. In several cases the velocities of these unidentified sources (OH stars) have been outside the velocity range of the neutral hydrogen distribution, suggesting that some of these sources may represent a population with a higher velocity dispersion than Population I objects (Kerr and Bowers 1974a, b). The lack of infrared and optical counterparts may indicate that the sources are quite distant, since identified OH/IR stars are often bright infrared objects. A large-scale 1612 MHz sky survey has therefore been initiated to study the galactic distribution and kinematics of the OH stars and to investigate the possibility that they may represent an older population of stars (Bowers et al. 1974).

scholarly journals Submillimetre water masers at 437, 439, 471, and 474 GHz towards evolved stars

2020 ◽  
Vol 638 ◽  
pp. A19
Author(s):  
P. Bergman ◽  
E. M. L. Humphreys
Keyword(s):  
Radiative Transfer ◽  
Kinetic Temperature ◽  
Circumstellar Envelopes ◽  
Maser Emission ◽  
Evolved Stars ◽  
Mira Variables ◽  
Dust Temperature ◽  
Stellar Velocity ◽  
Maser Line ◽  
Water Masers

Aims. Here we aim to characterise submillimetre water masers at 437, 439, 471, and 474 GHz towards a sample of evolved stars. Methods. We used the Atacama Pathfinder Experiment (APEX1) to observe submillimetre water transitions and the CO (4–3) line towards 11 evolved stars. The sample included semi-regular and Mira variables, plus a red supergiant star. We performed radiative transfer modelling for the water masers. We also used the CO observations to determine mass loss rates for the stars. Results. From the sample of 11 evolved stars, 7 display one or more of the masers at 437, 439, 471, and 474 GHz. We therefore find that these masers are common in evolved star circumstellar envelopes. The fact that the maser lines are detected near the stellar velocity indicates that they are likely to originate from the inner circumstellar envelopes of our targets. We tentatively link the presence of masers to the degree of variability of the target star, that is, masers are more likely to be present in Mira variables than in semi-regular variables. We suggest that this indicates the importance of strong shocks in creating the necessary conditions for the masers. Typically, the 437 GHz line is the strongest maser line observed among those studied here. We cannot reproduce the above finding in our radiative transfer models. In general, we find that maser emission is very sensitive to dust temperature in the lines studied here. To produce strong maser emission, the dust temperature must be significantly lower than the gas kinetic temperature. In addition to running grids of models in order to determine the optimum physical conditions for strong masers in these lines, we performed smooth wind modelling for which we cannot reproduce the observed line shapes. This also suggests that the masers must originate predominantly from the inner envelopes.

scholarly journals Circumstellar envelopes of OH-IR sources

1987 ◽  
Vol 122 ◽  
pp. 229-239 ◽  
Author(s):  
R. J. Cohen
Keyword(s):  
Radio Interferometer ◽  
Circumstellar Envelope ◽  
Radio Lines ◽  
Circumstellar Envelopes ◽  
Radio Observations ◽  
Maser Emission ◽  
Ir Sources ◽  
Consistent Picture

This article reviews recent radio observations of maser emission from OH, H2O and SiO molecules in the circumstellar envelopes of OH-IR sources. The different radio lines require different conditions for their excitation, and each therefore probes different regions in the circumstellar envelope. For some stars radio interferometer maps of several maser lines are now available, and a consistent picture of the envelope structure is beginning to emerge.

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