Off the Main Sequence

1
Off the Main Sequence Stages 7 - 9
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Off the Main Sequence Stages 7 - 9
While on the main sequence, the star is burning
hydrogen. Its luminosity is determined by the
stars mass. The most intense fusion is occurring
at the center regions of the core (highest
pressure and temperature).
3
Off the Main Sequence Stage 8
Initial depletion of hydrogen occurs in the
interior of the hydrogen burning core
4
Off the Main Sequence Stage 8
Once the hydrogen in the central core is
depleted, hydrostatic equilibrium is lost and the
central core begins to collapse as a result of
strong gravity
5
Off the Main Sequence Stage 8
Turn Off the location on the H-R diagram where
the star first leaves the main sequence as a
result of hydrogen deletion in the core.
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Off the Main Sequence Stage 8
Heating of the gaseous envelope causes it to
expand. Burning hydrogen in the expanding shell
increases the luminosity
Gravitational collapse of the core increases the
temperature of the core. Hydrogen continues to
burn outside of the central core.
7
Off the Main Sequence Stage 8
Hydrogen Shell Burning the fusion of hydrogen
in shells of a star outside of the hydrogen
depleted core.
8
Off the Main Sequence Stage 8
Heating of the gaseous envelope causes it to
expand. Burning hydrogen in the expanding shell
increases the luminosity
Gravitational collapse of the core increases the
temperature of the core. Hydrogen continues to
burn outside of the central core.
9
Off the Main Sequence Stage 8
Stage 8 Red Subgiant Stage
Gravitational collapse of the core increases the
temperature of the core. Hydrogen continues to
burn outside of the central core.
10
Off the Main Sequence Stage 8
Red Subgiant Branch the portion of the H-R
Diagram that corresponds to the hydrogen shell
burning portion of the life of a star related to
the expansion of the radius and increase in
luminosity of the star before helium burning is
triggered in the core of the expanding star.
There is a decrease in the surface temperature of
the star as it expands.
11
Off the Main Sequence Stage 9
Outer envelop cools. Hydrogen burning still
occurs in the shells at a rapid rate producing
very high luminosity
12
Off the Main Sequence Stage 9
Radius and luminosity will continue to grow as
the hydrogen continues to burn in the shells.
What happens next is determined by the mass of
the star