Stars and Nebulae
The Sirius System
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[3.1]
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Sirius B formed at the same time as Sirius A from the same cloud.
Sirius B was the larger star and burned more brightly than Sirius A.
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[3.2]
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When the hydrogen in Sirius B's core was exhausted, helium fusion began
and the star swelled to a red giant.
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[3.3]
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During the red giant phase, Sirius A captured some material from
its companion's swollen atmosphere.*
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[3.4]
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At the end of the red giant phase,
The star's outer layers were cast off as a planetary nebula.
A white hot compact core was all the remained of the former massive star.
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[3.5]
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During the planetary nebula phase, Sirius A captured further material
from its companion.*
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[3.6]
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Today, Sirius A's companion is Sirius B, the white dwarf.
There is no sign of nebulosity in the system.
Sirius B's red giant phase must have occurred well before historical times.
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*Sirius A has a higher than usual proportion of metals in its atmosphere.
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