Results 191 to 200 of about 1,537 (221)

A survey of CN in circumstellar envelopes

Astronomy & Astrophysics, 1997
We have conducted a survey of CN N=2-1 and N=1-0 line emission in the envelopes of evolved stars. The sample consists of 42 objects, including C-rich and O-rich envelopes, S-stars, detached envelopes, and proto-planetary nebulae. Confident detections have been achieved in 30 objects.
Bachiller, R, Fuente, A, Bujarrabal, V, Colomer, F, Loup, C, Omont, A, de Jong, T   +6 more
core   +3 more sources

HACA's Heritage: A Free‐Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars [PDF]

Angewandte Chemie - International Edition, 2017
The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison ...
Tao Yang, Ralf I Kaiser, Tyler P Troy
exaly   +2 more sources

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The Circumstellar Envelope of S Persei

Astrophysics and Space Science, 1995
We present MERLIN observations of OH and H2O masers in the circumstellar envelope of S Per. The results are consistent with a model of a thick shell of H2O masers in a region which is still accelerating.
Richards, A M S, Cohen, R J, Yates, J A
openaire   +2 more sources

On the shaping of circumstellar envelopes

Publications of the Astronomical Society of the Pacific, 1992
In this paper, we examine the evolutionary process of expansion of a magnetized ring of cool matter ejected from a Red Giant. The subsequent formation of a circumstellar shell or preplanetary nebula is also analyzed. The velocity, density and magnetic field are calculated along a time-sequence, on a large two-dimensional grid of points close to and far
G. Pascoli, J. Leclercq, B. Poulain
openaire   +1 more source

Chemistry and distribution of daughter species in the circumstellar envelopes of O-rich AGB stars [PDF]

Astronomy and Astrophysics, 2016
Context. Thanks to the advent of Herschel and ALMA, new high-quality observations of molecules present in the circumstellar envelopes of asymptotic giant branch (AGB) stars are being reported that reveal large differences from the existing chemical ...
Xiaohu Li, T J Millar, A N Heays
exaly   +2 more sources

The structure of circumstellar envelopes

Astrophysics and Space Science, 1995
Copious mass loss on the Asymptotic Giant Branch dominates the late stages of stellar evolution. Maps of extended circumstellar envelopes provide a history of mass loss and trace out anisotropic mass loss. This review concentrates on observations of millimeter wavelength molecular line emission, on high resolution maps of maser emission and on ...
openaire   +1 more source

Observations in circumstellar envelopes

Journal of Physics G: Nuclear and Particle Physics, 1993
During the very late stages of the red giant phase (late 'asymptotic giant branch' or AGB), the mass-loss rate considerably increases and generates massive and thick circumstellar envelopes. AGB circumstellar envelopes are very luminous infrared sources and emit many millimeter molecular lines.
openaire   +1 more source

The Circumstellar Envelope of VX Sagittarii

1986
Radio maser emission from OH, H2O and SiO masers provides a means of studying the circumstellar envelopes of long period variable stars. The OH 1612 MHz maser emission arises in the cool outer layers of the envelopes at distances >101 6cm from the photosphere and is pumped by infrared photons (Elitzur 1982). The maser lines of the OH molecule at 1665/7
Jessica M. Chapman, R. J. Cohen
openaire   +1 more source

The Physical and Chemical Properties of Circumstellar Envelopes

Astrophysics and Space Science, 1995
An overview is given of recent results on some basic properties of the circumstellar envelopes of evolved stars. The focus is on well studied examples which illustrate envelopes of different types and at different stages of evolution. The close connection between the physical and chemical properties of the envelopes is emphasized.
openaire   +1 more source

Models for the Circumstellar Envelopes of Be Stars

1976
A survey is presented of the theoretical attempts to determine the structure of the circumstellar matter around Be stars. The general equations describing the structure and dynamics of Be star envelopes are given. The complications introduced by various physical phenomena are briefly discussed and initial attempts to solve restricted problems are ...
openaire   +1 more source