Transcript Common Stages 7 to 9

Off the Main Sequence
Stages 7 - 9
Off the Main Sequence
Stages 7 - 9
While on the main sequence, the star is burning hydrogen. It’s luminosity is
determined by the stars mass.
The most intense fusion is occurring at the center regions of the core
(highest pressure and temperature).
Off the Main Sequence
Stage 8
Initial depletion of
hydrogen occurs in
the interior of the
hydrogen burning
core
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
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.
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.
Off the Main Sequence
Stage 8
Hydrogen Shell Burning – the fusion of hydrogen in shells of a star
outside of the hydrogen depleted core.
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.
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.
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.
Off the Main Sequence Stage 9
Outer envelop cools.
Hydrogen burning
still occurs in the
shells at a rapid rate
producing very high
luminosity
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