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A cloud of gas and dust surrounding a star or other astronomical object. Stellar envelopes are of many types. Hot young stars generate hot glowing envelopes, either by ionizing the surrounding gas or by ejecting hot material. Evolved stars shed their outer layers and generate cool circumstellar envelopes which are rich in dust and molecules. When the hot core of the old star is exposed, the envelope is ionized and may be detected as an emission nebula—as a planetary nebula, for example.

Subjects: Astronomy and Astrophysics.

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