Interstellar dust grains localized around various types of stars, such as asymptotic giant branch stars. Circumstellar dust occurs in the form of a spherical shell or a disk and is at the origin of an
infrared excess for the central star.
A very extensive envelope of cold gaseous materials surrounding evolved cool stars, notably red giants, red supergiants (Mira variables), or asymptotic giant branch stars. The typical size of such env
elopes is several thousand times that of the stellar radius and their temperature ranges from 1000 to 10 K. Circumstellar envelopes result from mass loss from the central star (10-7 to 10-4 solar masses per year) and expand with moderate velocities (10 to 15 km sec^-1). The low temperature of the envelope is at the origin of the formation of molecules, which in certain conditions provide maser emission (H_{2}O, OH, SiO). Similarly, dust grains form in the envelope produce an infrared excess emission.
A shell of dust, molecules, and neutral gas around an evolved star resulting from an intensive mass loss phase, such as the asymptotic giant branch phase for low- and intermediate mass stars and LBVs
or supernovae for massive stars.
A shell of dust, molecules, and neutral gas around an evolved star resulting from an intensive mass loss phase, such as the asymptotic giant branch phase for low- and intermediate mass stars and LBVs
or supernovae for massive stars.
Located in an arm chair shaped bedrock hollow; No tongue developed, in contrast to simple basin; As wide or even wider as their length; Catchmant area is created through the process of glacial erosion
; Occupies a separate, rounded, steep-walled recess which it has formed on a mountain side
A bowl-shaped, amphitheater-like depression eroded into the head or the side of a glacier valley. Typically, a cirque has a lip at its lower end. The term is French and is derived from the Latin word
circus. Rounded recess on a mountain side formed by glacial action and usually occupied by a glacier.
(from the French) An armchair-shaped hollow with steep sides and back wall, formed as a result of glacial erosion high on a mountainside, and often containing a rock basin with a tarn (q.v.) (known as
corrie or cwm in Britain).