Download A note on: Group Behavior Open Clusters

A note on: Group Behavior
• Open Clusters: contain a few hundred to a few
thousands of stars. Lie in the plane of the Milky Way
Galaxy. A few parsecs in diameter. Generally young
type stars
• Globular Clusters: Lie outside the plane of our galaxy.
Very far away, thousands of parsec. Contain no main
Sequence stars with masses > 0.8 Sun’s mass. Generally
Older stars.
Central Bulge
Open Clusters
Open vs. Globular
Page 507 Fig.19.8 A & B
More on Group Behavior
Associations:
T Type: Contain pre-main sequence stars.
O-B Type: Contain O,B stars
Cluster evolution.
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page 532 Figure 20.17
(a). Initially stars in main seq. burning steadily while stars
in lower end of the sequence are still forming.
 (b).O-Type stars left the main seq., some red giants visible.
 ©.Type B stars have evolved off the main seq. Stars in
lower end of seq. catching up.
 (d).Main Seq. comprised of stars up to Type A. Sub and
Red giants becoming apparent. Lower end completed.
 (e) Stars with < Sun’s mass remain on the sequence. White
dwarfs have now formed.
Blue Stragglers
Observed in many clusters.
 Main-Sequence beasts.
 Don’t make a whole lot of sense why they are what
they are but believed to be the result of Mergers
which are collisions between stars or the result of
binary evolutions.
 Explains why such young stars amongst a cluster
that may be at least 10 billion old.
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Binary Stars
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2 stars with a distance of
1000 star radii between
them have evolved
independently.
Closer than that then gravity
mates them.
Algol
Other class media
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Slides: H-R diagrams for open cluster, cluster
evolution.
Video: Stellar Formation part 1.
Tomorrow video: Stellar formation, part 2.
The life of a Star
The life cycle of a star.
4.
Collapsing cloud (done that)
Proto-star (done that)
Star (main sequence)
Dying star (main sequence turn-off)
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Lets review and look at some pretty pictures ..
1.
2.
3.
Stages in the life of a star
1. A gas cloud in
the Orion nebula
2. A collapsing cloud, proto-star
Region.
3. A genuine star
1. -> 2. -> 3.
Stages, continued.
4. Red Giant phase, turned off of
the main sequence.
4 -> 5a
5a. A planetary nebula, from a
smaller mass star like our sun.
Stages again
5b. Larger mass stars will supernova….
4
5a
5b
6
6. Leaving behind filamentary clouds
rich in heavy elements.
3. Main Sequence Star
a.
b.
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c.
Stars enter main sequence through the Hayashi
Track, a proto-star evolutionary path.
Once on the main sequence track, a stable star
spends most of its life here. What does it do
there?
p-p fusion (e.g. 4 H1 => He4 + energy)
Stays in Hydrostatic equilibrium
Energy produced in core through p-p chain
accounts for most of energy production
Dying Star
When H is depleted, inner core
(now mostly He) contracts &
heats up.
 The high temperature ignites
the shell of H around the
core.
 Increased pressure drives the
envelope of the star outward.
 Creating a giant or Supergiant.
c. Dying Star
Figure 20.2c, page 517
Figure 20.3, page516
He fusion
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2 He -> Be + energy
He + Be -> C + energy
Much higher temperatures (108 K) needed for He
fusion.
The Helium Flash:
•When Tcore ~ 108 K, He begins to burn.
1. He4 + He4 => Be8 , He + Be => C
2. He fusion in the core and H shell burning
3. Eventually He in core is exhausted
4. Contraction of the core raises the temperature
further
5. Both He and H shells now burning.
Our Sun and others
like it..
 Temp. never high
enough to attain
carbon fusion in
core.
 Some conversion
at He shell: C + He
=> O + energy.
 Through
subsequent
temperature and
density
fluctuations, He
shell flashes
occur.
 Surface layers
(envelope) become
unstable => blow
off-> planetary
nebula
Giants and Super Giants
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Red giant
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High mass stars > 12
solar masses..
High temperatures
insure creation of
heavier elements at a
rapid pace.
No He flash occurs.
Die explosively.
Lets look at the big picture =>
A.
B.
C.
D.
E.
Main sequence star
Sub Giant branch
He Flash
Horizontal branch
C core/planetary nebula
H-R diagrams
D
C
E
B
A
Some terms
White dwarf: remainder of low mass star evolution
 Shines only by the light of it’s stored energy.
Eventually becomes a black dwarf. A black dwarf
is a cold burned out star.
 Table 20.3 , page 531.
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Some low mass endings; planetary nebula
½ ly
Eskimo nebula, constellation Gemini
1500 pc away
NGC 3132 nebula, 2 stars, both unrelated,
Material receding from small star
High mass endings