Transcript Stellar Evolution - Fort Lewis College

Charles Hakes
Fort Lewis College
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Light Pollution
Stellar Evolution
Charles Hakes
Fort Lewis College
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Lab Notes
• Be sure you have started your “report” lab.
• Constellation presentations next week.
• Observatory field trips…
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Fort Lewis College
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Night Lights
• http://apod.nasa.gov/apod/ap101104.html
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Fort Lewis College
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Limiting Magnitude
and
Light Pollution
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Fort Lewis College
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Limiting Magnitude
• Limiting Magnitude is a measure of the dimmest
star visible from a given location.
•
•
•
•
Center of a big city: ~2.0
Suburbs: ~4.5
Downtown Durango: ~5.5
La Plata County (FLC observatory): ~6.5
• Depends on observer experience
• Depends on local glare
• Depend on how dark adapted your eyes are. You
should wait 20-30 minutes to measure this.
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Fort Lewis College
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Limiting Magnitude
• Use stars of known magnitude (e.g. Little Dipper)
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Fort Lewis College
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Limiting Magnitude
• Count the stars in a well-defined region
• Chose one of the predefined star regions that is
overhead
• Count the number of stars visible within the region
boundary
• Look up the number on the published tables to find
the corresponding limiting magnitude
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Fort Lewis College
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Limiting Magnitude
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Fort Lewis College
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Limiting Magnitude
Alpha-Epsilon-Beta Gem
stars LM
1
1.2
2
2.4
3
3.2
4
3.9
5
4.3
6
5.0
7
5.1
8
5.3
9
5.6
10 5.7
11 5.9
12 6.1
13 6.2
14 6.3
15 6.4
16 6.5
18 6.6
20 6.7
22 6.9
23 7.0
25 7.2
30 7.5
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Fort Lewis College
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How many Stars Can You See?
Magnitude
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Charles Hakes
Fort Lewis College
Range
Cumulative Stars
-1.50 to -0.51
-0.50 to +0.49
+0.50 to +1.49
+1.50 to +2.49
+2.50 to +3.49
+3.50 to +4.49
+4.50 to +5.49
+5.50 to +6.49
+6.50 to +7.49
+7.50 to +8.49
+8.50 to +9.49
+9.50 to +10.49
+10.50 to +11.49
+11.50 to +12.49
+12.50 to +13.49
+13.50 to +14.49
+14.50 to +15.49
+15.50 to +16.49
+16.50 to +17.49
+17.50 to +18.49
+18.50 to +19.49
+19.50 to +20.49
% Increase Seen
2
8
22
93
283
893
2,822
8,768
26,533
77,627
217,689
626,883
1,823,573
5,304,685
15,431,076
44,888,260
130,577,797
379,844,556
1,104,949,615
3,214,245,496
9,350,086,162
27,198,952,706
11
400%
275%
423%
304%
316%
316%
311%
303%
293%
280%
288%
291%
291%
291%
291%
291%
291%
291%
291%
291%
291%
How many Stars Can You See?
• Dark-adapted naked eye (1x7 binoculars)
• Can see to magnitude 6.5 -> ~104 stars
• Light gathering ability scales with area.
•
•
•
•
Magnitude Increase = log10(Area increase) / 0.4
10x50 binoculars ~50x area -> +4.25 magnitudes
16” SCT ~64x area -> +4.5 magnitudes
10m Keck telescope ~625x area -> +7 magnitudes
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Fort Lewis College
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How many Stars Can You See?
• So for naked eye observing
• 10x50 binoculars
• 50x area
• +4.25 magnitudes (to 10.75) > 106 stars
• 16” SCT
• 64x area
• +4.5 magnitudes (to 15.25) > 108 stars
• 10m Keck telescope
• 625x area
• +7 magnitudes (to 22.75) > 1011 stars
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Fort Lewis College
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Figure 10.6
Apparent Magnitude
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Fort Lewis College
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Light Pollution
• Generally not an issue in La Plata county.
• Durango has a dark sky ordinance, but
only for new construction.
• Fort Lewis is making progress with outside
light fixtures.
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Fort Lewis College
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Light Pollution
Earth at Night
Credit: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive
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Fort Lewis College
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Light Pollution
From IDA Website: http://www.darksky.org/images/sat.html
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Fort Lewis College
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Light Pollution
You Are Here
Observatory
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Fort Lewis College
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Figure 10.15
Hipparcos H–R Diagram
• Plot the
luminosity vs.
temperature.
• This is called a
HertzsprungRussell (H-R)
diagram
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Fort Lewis College
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What fraction of the stars on an H-R
diagram are on the main sequence
A.
B.
C.
D.
0-50%
50-70%
70-80%
>80%
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Fort Lewis College
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What fraction of the stars on an H-R
diagram are on the main sequence
A.
B.
C.
D.
0-50%
50-70%
70-80%
>80%
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Fort Lewis College
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Distance Scale
• If you know brightness and distance,
you can determine luminosity.
• Turn the problem around…
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Fort Lewis College
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Distance Scale
• If you know brightness and distance,
you can determine luminosity.
• Turn the problem around…
• If a star is on the main sequence,
then we know its luminosity. So
• If you know brightness and luminosity,
you can determine a star’s distance.
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Fort Lewis College
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Distance Scale
• Spectroscopic Parallax - the process
of using stellar spectra to determine
distances.
• Can use this distance scale out to
several thousand parsecs.
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Fort Lewis College
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Figure 10.16
Stellar Distances
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Fort Lewis College
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Stellar Evolution
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Fort Lewis College
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Figure 11.16
Atomic Motions
• Low density clouds are too sparse for gravity.
• A perturbation could cause one region to start
condensing.
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Fort Lewis College
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Figure 11.17
Cloud Fragmentation
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Fort Lewis College
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Figure 11.20
Interstellar Cloud Evolution
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Fort Lewis College
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

http://discovermagazine.com/2009/interact
ive/star-formation-game/
google “star formation game”
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Fort Lewis College
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H-R diagram review
• The H-R diagram shows luminosity vs.
temperature.
• It is also useful for describing how stars
change during their lifetime even though
“time” is not on either axis.
• How to do this may not be obvious.
• Exercise - Get in groups of ~four and get
out a blank piece of paper.
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Fort Lewis College
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Group Exercise
• As a group, create a diagram with
“financial income” on the vertical axis, and
“weight” on the horizontal axis.
• Use this graph to describe the past and
future of a fictitious person (or a group
member).
• Label significant events, for example
•
•
•
•
birth
college
retirement
death
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Fort Lewis College
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Stellar Evolution
1 - interstellar cloud - vast (10s of parsecs)
2(and 3) - a cloud fragment may contain 1-2
solar masses and has contracted to
about the size of the solar system
4 - a protostar
• center ~1,000,000 K
• Too cool for fusion, but hot enough to
see. (photosphere ~3000 K)
• radius ~100x Solar
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Fort Lewis College
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How would the luminosity of a one-solar-mass
protostar compare to the sun?
A) Less than .1x as bright
B) A little lower.
C) About the same.
D) A little brighter
E) More than 10x brighter
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Fort Lewis College
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How would the luminosity of a one-solar-mass
protostar compare to the sun?
A) Less than .1x as bright
B) A little lower.
C) About the same.
D) A little brighter
E) More than 10x brighter
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Fort Lewis College
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Figure 11.19
Protostar on the H–R
Diagram
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
5 - Gravity still dominates
the radiation pressure, so
the star continues to
shrink.
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Fort Lewis College
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Figure 11.18
Orion Nebula, Up Close
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Fort Lewis College
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Figure 11.23
Protostars
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
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Fort Lewis College
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Stars A and B formed at the same time. Star B has 3
times the mass of star A. Star A has an expected lifetime
of 3 billion years. What is the expected lifetime of star B?
A) more than 9 billion years
B) about 9 billion years
C) 3 billion years
D) about 1 billion years
E) less than 1 billion years
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Fort Lewis College
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Stars A and B formed at the same time. Star B has 3
times the mass of star A. Star A has an expected lifetime
of 3 billion years. What is the expected lifetime of star B?
A) more than 9 billion years
B) about 9 billion years
C) 3 billion years
D) about 1 billion years
E) less than 1 billion years
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Fort Lewis College
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Stellar Lifetimes
• Proportional to mass
• Inversely proportional to luminosity
• Big stars are MUCH more luminous,
so they use their fuel MUCH faster.
• The distribution of star types is
representative of how long stars
spend during that portion of their life.
• Example - snapshots of people.
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Fort Lewis College
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Figure 10.21
Stellar Masses
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Fort Lewis College
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Figure 11.24
Prestellar
Evolutionary Tracks
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Fort Lewis College
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Figure 11.25
Brown Dwarfs
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Fort Lewis College
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Figure 11.22
Protostellar Outflow
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Fort Lewis College
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Stellar Evolution
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
5 - Gravity still dominates
the radiation pressure, so
the star continues to
shrink.
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
5 - Gravity still dominates
the radiation pressure, so
the star continues to
shrink.
Can have violent “winds”
streaming outwards; often
bipolar flow from poles;
T-Tauri phase
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
5 - Gravity still dominates
the radiation pressure, so
the star continues to
shrink.
Can have violent “winds”
streaming outwards; often
bipolar flow from poles;
T-Tauri phase
6 - a newborn star
Core temperature high
enough to ignite nuclear
fusion.
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Fort Lewis College
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Figure 11.21
Newborn Star on
the H–R Diagram
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Fort Lewis College
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Stars A and B formed at the same time. Star B has 3
times the mass of star A. Star A has an expected lifetime
of 3 billion years. What is the expected lifetime of star B?
A) more than 9 billion years
B) about 9 billion years
C) 3 billion years
D) about 1 billion years
E) less than 1 billion years
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Fort Lewis College
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Stellar Lifetimes
• Proportional to mass
• Inversely proportional to luminosity
• Big stars are MUCH more luminous,
so they use their fuel MUCH faster.
• The distribution of star types is
representative of how long stars
spend during that portion of their life.
• Example - snapshots of people.
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Fort Lewis College
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Figure 10.21
Stellar Masses
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Fort Lewis College
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Figure 11.24
Prestellar
Evolutionary Tracks
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Fort Lewis College
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Figure 12.1
Hydrostatic Equilibrium
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Fort Lewis College
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Figure 11.24
Prestellar
Evolutionary Tracks
The final location on
the main sequence
depends entirely on
the size (mass) of
the condensing
cloud.
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Fort Lewis College
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Figure 11.25
Brown Dwarfs
Not big enough to start fusion.
Mass <~ 0.08 solar masses
~=80x mass of Jupiter.
These are likely very numerous
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Fort Lewis College
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Stellar Evolution
7 - the star stays on the main sequence
for most (~90%) of its lifetime.
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Fort Lewis College
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Figure 10.15
Hipparcos H–R Diagram
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Fort Lewis College
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Stars A and B formed at the same time. Star B has 3
times the mass of star A. Star A has an expected lifetime
of 3 billion years. What is the expected lifetime of star B?
A) more than 9 billion years
B) about 9 billion years
C) 3 billion years
D) about 1 billion years
E) less than 1 billion years
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Fort Lewis College
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Stars A and B formed at the same time. Star B has 3
times the mass of star A. Star A has an expected lifetime
of 3 billion years. What is the expected lifetime of star B?
A) more than 9 billion years
B) about 9 billion years
C) 3 billion years
D) about 1 billion years
E) less than 1 billion years
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Fort Lewis College
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Figure 10.21
Stellar Masses
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Fort Lewis College
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What forces a star like our Sun to
evolve off the main sequence?
A) It loses all its neutrinos, so fusion must cease.
B) It completely runs out of hydrogen.
C) It builds up a core of inert helium.
D) It explodes as a violent nova.
E) It expels a planetary nebula to cool off and release
radiation.
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Fort Lewis College
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What forces a star like our Sun to
evolve off the main sequence?
A) It loses all its neutrinos, so fusion must cease.
B) It completely runs out of hydrogen.
C) It builds up a core of inert helium.
D) It explodes as a violent nova.
E) It expels a planetary nebula to cool off and release
radiation.
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Fort Lewis College
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Figure 12.2
Solar Composition Change
7 - fusion of H to He
occurs in the core
until the H is used up.
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Fort Lewis College
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After hydrogen fusion stops in the core of
a star, the core…
A) expands and cools
B) expands and heats
C) contracts and cools
D) contracts and heats
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Fort Lewis College
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After hydrogen fusion stops in the core of
a star, the core…
A) expands and cools
B) expands and heats
C) contracts and cools
D) contracts and heats
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Fort Lewis College
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After hydrogen fusion stops in the core of
a star, the star as a whole…
A) expands
B) contracts
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Fort Lewis College
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After hydrogen fusion stops in the core of
a star, the star as a whole…
A) expands
B) contracts
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Fort Lewis College
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Figure 12.3
Hydrogen Shell Burning
Charles Hakes
Fort Lewis College
7 - fusion of H to He
occurs in the
core until the H
is used up.
8 - the He core
begins to shrink
(and heat!),
while the Hburning region
moves out into a
shell
72
Figure 12.4
Red Giant on the H–R
Diagram
9 - the He core
continues to
shrink (just a
few times bigger
than Earth) and
heat (to 108 K)
Heat  pressure
demo
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Fort Lewis College
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Figure 12.1
Hydrostatic Equilibrium
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Fort Lewis College
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Figure 12.5
Horizontal Branch
Charles Hakes
Fort Lewis College
9 - the Helium flash is
when the He in the
core begins to fuse
into carbon. This
happens when the
core is ~108K.

Core expands and
cools.

New equilibrium on
the “horizontal
branch.”
10 - New equilibrium on
the “horizontal
branch.”
75
Figure 11.27b
Globular Cluster

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Fort Lewis College
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Note the
“horizontal
branch”
Question

What happens when the He in the
core is used up?
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Fort Lewis College
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Figure 12.6
Helium Shell Burning
In the He shell
burning stage, the
star expands just
like in the H shell
burning stage
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Fort Lewis College
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Figure 12.7
Reascending the
Giant Branch
11 - Helium shell
burning begins.

Core shrinks and
heats.

Exterior expands
and cools.
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Fort Lewis College
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Figure 12.10
White Dwarf
on H–R Diagram
12 - For 1 solar mass
stars, that is all that
will fuse.

(need 600 million K
for the next reactions
to occur.)

The outer shell gets
“blown off” by the
hot, dense, core.

Result is a planetary
nebula around a
white dwarf (13).
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Fort Lewis College
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Figure 12.9
Planetary Nebulae
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Fort Lewis College
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White Dwarf stage




Just the core of the star remains
Very small - about the size of Earth
Very dense - about half as massive as the
sun.
Will eventually fade and become a black
dwarf (stage 14).
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Fort Lewis College
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Figure 12.8
G-Type Star Evolution
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Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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Earth Hour
• Saturday, March 27, 2010.
• 8:30 P.M.
• Turn off lights - save energy.
• http://www.myearthhour.org/
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Fort Lewis College
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How many Stars Can You See?
• But who uses naked eye observing any more?
• High quantum efficiency CCD cameras greatly
extend the depth of a telescope.
• Image stacking lets you go even deeper.
• Depth scales linearly until star brightness is about the
same as the background sky brightness.
• A dark sky on Earth is about magnitude 21/arcsec2.
• For film, this would be about as deep as you could go.
• 16” SCT should reach magnitude 21.5 with a 5
minute exposure using SBIG full frame CCDs
• For deeper images, the signal only scales as the
~sqrt(time)
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Fort Lewis College
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