announcements exam grades wednesday march 31 angel grade update friday april 2 star assignment 6,...
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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
Look for Relationships
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
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
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
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
Pleiades now has no stars with life expectancy less than around 100 million years
Main-sequenceturnoff
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
A