Polarization properties of silicate-like grains in circumstellar envelopes of late-type stars due to temperature variations

1975 ◽  
Vol 34 (1) ◽  
pp. 149-154
Author(s):  
J. Svatoš ◽  
M. Šolc ◽  
V. Vanýsek
Keyword(s):  
Late Type ◽  
Circumstellar Envelopes ◽  
Temperature Variations

scholarly journals Stellar masers, circumstellar envelopes and supernova remnants

2007 ◽  
Vol 3 (S242) ◽  
pp. 236-245
Author(s):  
Athol J. Kemball
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Supernova Remnants ◽  
Stellar Mass ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Open Future ◽  
Circumstellar Envelopes ◽  
Recent Advances

AbstractThis paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

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 Masers and Stellar Magnetic Fields

1990 ◽  
Vol 140 ◽  
pp. 21-25
Author(s):  
Mark J. Reid
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Average Surface ◽  
Stellar Photosphere ◽  
Type Giant ◽  
Stellar Magnetic Fields ◽  
The Magnetic Field ◽  
Field Strengths

Observations of circular polarization of molecular masers associated with late type giant and supergiant stars can be used to estimate the magnetic field strength in the masing region. Magnetic field strengths of ~ 5 mG are deduced for OH masers in circumstellar envelopes at distances of ~ 1016 cm from the star, and magnetic field strengths of ~ 50 G are deduced for SiO masers that reside above the photosphere. Extrapolation to the stellar photosphere suggests that average surface magnetic fields are on the order of 103 G.

scholarly journals Radio Molecular Line Observations of Late Type Stars

1977 ◽  
Vol 42 ◽  
pp. 495-520 ◽  
Author(s):  
A. Winnberg
Keyword(s):  
Near Infrared ◽  
Spectral Lines ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Long Baseline ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Opening Up ◽  
Excellent Tool ◽  
Geometry And Kinematics

Radio observations of spectral lines from OH, H2O, SiO and CO have put the spot-light on late-type stars and revived the interest in them. Especially they have helped the understanding of the outer envelopes of these stars and of their mass loss. They also have revealed late-type stars that are hidden from observation at optical and near-infrared wavelengths by their dense surrounding shells of gas and dust. The strong maser lines from OH, H2O and SiO have additionally given us an excellent tool in mapping the distribution of late-type variables throughout the Galaxy. On the other hand, the interpretation of the maser amplified lines in terms of a model is difficult. Very-long-baseline interferometry (VLBI) of these lines might be a way of studying the geometry and kinematics of the envelopes but there are a few problems connected with these observations which I will point out in this paper. However, recently “thermal” microwave lines of SiO and CO have been observed from late-type stars. These lines might be easier to interpret regarding physical processes in the outer circumstellar envelopes. As so often when a new field is opening up in astronomy the solutions to several old problems have been found but at the same time many more new problems have been brought up.

scholarly journals VLBI Observations of the V=1 and V=2 SiO Masers in W Hydra and VX Sagittarius

1980 ◽  
Vol 87 ◽  
pp. 535-536 ◽  
Author(s):  
A. P. Lane ◽  
P. T. P. Ho ◽  
C. R. Predmore ◽  
J. M. Moran ◽  
R. Genzel ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Angular Size ◽  
Energy Separation ◽  
Equivalent Temperature ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Vibrational States ◽  
High Brightness ◽  
Mira Variable ◽  
Vlbi Observations

Our previous observations established the small angular size and high brightness temperature of emission from the v=1, J=1-0 transition of SiO from the circumstellar envelopes of the supergiant VX Sgr and the Mira variable R Cas. We performed a second VLBI experiment on the SiO masers in several late type stars on 31 Oct.-2 Nov. 1978 to compare the physical characteristics of the SiO masers in the v=1 and v=2 states. With an energy separation of 1258 cm-1 (an equivalent temperature of 1753 K) between the two vibrational states, differences in excitation and pumping of the maser states may lead to different maser properties.

scholarly journals Theoretical Aspects of Mass Loss from Late-Type Stars

1977 ◽  
Vol 42 ◽  
pp. 577-590 ◽  
Author(s):  
Ray J. Weymann
Keyword(s):  
Mass Loss ◽  
Neutral Hydrogen ◽  
Radio Radiation ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Molecular Line ◽  
Infrared Excess ◽  
Line Radiation ◽  
Stellar Radiation ◽  
Expanding Shells

Since Deutsch’s (1956) discovery that in α Herculis the displaced circumstellar absorption lines common in the spectra of late-type giants and supergiants really represented a loss of matter, the evidence that this is a very extensive and common feature among all late giants and supergiants has become very persuasive. To the extensive optical spectroscopic evidence for mass loss from these stars originally obtained by Deutsch and subsequently by others, we may now add observations of infrared excess from dust in circumstellar envelopes (Merrill 1977), radio molecular line radiation from expanding shells (Winnburg 1971), thermal and possibly 21 cm radio radiation from ionized and neutral hydrogen respectively (Smolinski et al. 1977; Zuckerman 1977) and the direct photographs of the envelope of α Ori in the light of one of the potassium resonance lines from scattered stellar radiation (Bernat et al. 1977).

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