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Announcements. Exam Grades Wednesday March 31 Angel Grade update Friday April 2 Star Assignment 6, due Wednesday March 31 Do Angel quiz,. Objectives. Plot an Hertzsprung-Russell Diagram Locate the regions of giant, main sequence and white dwarf stars. - PowerPoint PPT Presentation
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Announcements• Exam Grades Wednesday March 31• Angel Grade update Friday April 2• Star Assignment 6,
due Wednesday March 31Do Angel quiz,
Objectives
• Plot an Hertzsprung-Russell Diagram• Locate the regions of giant, main
sequence and white dwarf stars. • Describe the relations between
surface temperature, luminosity, mass and size for these types of stars.
• Describe the evolutionary state of the 16 brightest northern-hemisphere stars.
What should we do with our information?
• Luminosities
• Surface Temperatures
• Masses
Number of Stars vs Luminosity
LOWHIGH Luminosity1100 0.01 0.0001
Stellar Masses
What should we do with our information?
• Luminosities
• Surface Temperatures
• Masses
Look for Relationships
No Relationship
Luminosity - Mass Relation
L~M3.5
HRDiagram:Luminosity
vs.Surface
Temperature
Luminosity - Temperature
Relation: Hertzsprung-
Russell DiagramL
umin
osit
y ->
Temperature
Lu
min
osi
tyRecall:
Hotter -> BrighterHotter ->
BluerBigger -> Brighter
Then cool+
Luminous-> Large
Temperature
Lu
min
osi
tyRecall:
Hotter -> BrighterHotter ->
BluerBigger -> Brighter
Then small Luminosity
+ Hot -> small
Stellar Size, Mass
& HR
Diagram
Stars with low temperature and high luminosity must have large radius
Large radius
Small radius
Stars with low temperature and high luminosity must have large radius
GIANTS
SUPERGIANTS
WHITEDWARFS
Low-Mass Stars
High-Mass Stars Most Low Mass stars have
SmallLuminosity
Most Large Massstars have
LargeLuminosity
Regions of the H-R Diagram
Activity
• Answer the questions on your scantron sheet
Temperature
Lu
min
osi
ty
1. Which star is the hottest?
A
BC
D
Temperature
Lu
min
osi
ty
1. Which star is the hottest?
A
BC
AD
Temperature
Lu
min
osi
ty
2. Which star is the most luminous?
A
BC
D
Temperature
Lu
min
osi
ty
2. Which star is the most luminous?
A
BC
D C
Temperature
Lu
min
osi
ty
3. Which star is a main-sequence star?
A
BC
D
Temperature
Lu
min
osi
ty
3. Which star is a main-sequence star?
A
BC
D
D
Temperature
Lu
min
osi
ty
4. Which star has the largest radius?
A
BC
D
Temperature
Lu
min
osi
ty
4. Which star has the largest radius?
A
BC
DC
Temperature
Lu
min
osi
ty
5. Which star is most like our Sun?
A
B
C
D
Temperature
Lu
min
osi
ty
5. Which star is most like our Sun?
A
B
C
D
B
HOT COOL
BRIGHT
FAINT
HRDiagram
Astronomy Place Questions
6. Spica is a Main Sequence star, having a surface temperature of 26,000K. In order for a star with a surface temperature of only 6,000K to have the same Luminosity as Spica, its radius must be?
Luminosity = 4R2T4
If T ~ 4 x smaller, then R ~ 42 x larger = 16x
7. The rate of fusion (number of He nuclei produced per second) in the core of the star Vega (a main-sequence star with a temperature of about 10,000K is roughly?
Lvega = 60 Lsun, so rate of energy generation
= rate of energy loss is 60 x larger than Sun’s
8. A star having the same radius as the Sun, but a surface temperature 5 times higher than the Sun, would have a luminosity?
L ~ T4
54 = 625
9. A main-sequence star that is twice as massive as the Sun will have a Luminosity?
L ~ M3. 5
23 = 8, 24 = 16, so 23.5 in between
Lifetime on the Main Sequence
How long will it be before MS stars run out of fuel? i.e. Hydrogen?
How much fuel is there? M
How fast is it consumed? L M3.5
How long before it is used up?
M/L = M/M3.5 = M-2.5
Main SequenceLifetimes
Lifetime on the Main Sequence
• O & B Dwarfs burn fuel like a bus!
• M Dwarfs burn fuel like a compact car!
• Our Sun will last 1010 years on the Main Sequence
• MS Lifetime = 1010 yrs / M2.5
Stars occur alone
or in clusters
another type of cluster
Star Clusters
• Stars approximately the SAME AGE
• Stars approximately the SAME DISTANCE
Cluster HR
Diagrams
Same DistanceSame Age
Pleiades now has no stars with life expectancy less than around 100 million years
Main-sequenceturnoff
Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old
ClusterAges
Activity
• Answer the questions on your scantron sheet
Temperature
Lu
min
osi
ty
6. Which of these stars will have changed the least 10 billion years from now?
A
B
C
D
Temperature
Lu
min
osi
ty
6. Which of these stars will have changed the least 10 billion years from now?
A
B
C
D
C
Temperature
Lu
min
osi
ty
7. Which of these stars can be no more than 10 million years old?
A
B
C
D
Temperature
Lu
min
osi
ty
7. Which of these stars can be no more than 10 million years old?
A
B
C
D
A
A stars properties depend mostly on
1. Mass2. Age
NEXT TIME
• Evolution of Stars
• READ chapter 17
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