the nature of stars exam #3 – will not be april 5th it has been re-scheduled for thursday april...
TRANSCRIPT
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The Nature of Stars
EXAM #3 – WILL NOT BE APRIL 5th it has been re-scheduled for THURSDAY APRIL 12th 4/12 (Wednesday)
Tailgate Party!! For Exam #3 Wed April 11th
Observing Logs Due IN CLASS May 1st
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red
A star’s color reveals its surface temperature
What color is this star?
bluegreen
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Spectra of Stars
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Diversity Leads to Revolution
• Annie Jump Cannon
• Antonia Maury
• Meghnad Saha
• Cecilia Payne-Gaposchkin
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Women Computers (1890)
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Annie Jump Cannon (1863-1941)
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Classification SchemeA
B
C
D
E
.
.
.
S
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Antonia Maury (1866-1952)
Spectral classes might make more sense if arranged by temperature
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O
B
A
F
G
K
M
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A Revolution
• Most astronomers believed that the differences in spectral lines were due to subtle differences in chemical abundance.
• Indian physicist Meghnad Saha offered another explanation, which was confirmed at Harvard by Cannon and Maury’s work.
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Meghnad Saha (1893-1956)Theory of thermal ionization of atoms
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Cecelia Payne-Gaposchkin (1900-1979)First PhD in Astronomy from Harvard/Radcliffe
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Together Saha and Payne-Gaposchkin
• Gave theoretical explanation for Cannon’s classification scheme.
• Showed that the differences in spectra (absorption lines) are due to temperature and thermal ionization of atoms not abundance of elements
• Provided a convincing argument that stars are mostly made of hydrogen.
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Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types
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What does this give us?
• a new way to classify stars
• color, peak wavelength of the black body curve, and spectral class all of which are indicators of a star’s temperature
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Summary of Spectral Classes
O hotter than 25,000 KB 11,000 - 25,000 KA 7500 - 11,000 KF 6000 - 7500 KG 5000 - 6000 KK 3500 - 5000 KM cooler than 3500 K
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Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types
• O B A F G K M• hottest to coolest• bluish to reddish• An important sequence to remember:
– Oh Be a Fine Guy (or Girl), Kiss Me
– Overseas Broadcast - A Flash: Godzilla Kills Mothra
– Over-Budget Adult Films Give Knights Merriment
– One Boring Afternoon, Frank Grew Killer Marijuana
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For thousands of nearby stars we can find:
• the total luminosity
• the temperature (color or spectral type)
• the size (radius)
• the distance
CAN WE FIND ANY RHYME, REASON, OR RELATIONSHIPS?
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Looking for correlations:
Height vs. IQ ?
Height vs. Weight ?
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QUESTIONS:• Are more luminous stars always
larger?
• What combinations of temperature and luminosity are possible?
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THE H-R DIAGRAM• done independently by Enjar
Hertzsprung and Henry Norris Russell
• graph of luminosity (or absolute magnitude) versus temperature (or spectral class)
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The Hertzsprung-Russell (H-R) diagram
identifies a definite relationship between
temperature and absolute magnitude
HR DIAGRAM
absolute magnitude vs temperature
or
luminosity vs spectral type
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The Hertzsprung-Russell (H-R)
diagram identifies a definite relationship between temperature
and absolute magnitude
HR DIAGRAM
absolute magnitude vs temperature
or
luminosity vs spectral type
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MAIN SEQUENCE• Goes from top left (hot and
bright) to bottom right (cool and dim).
• 90% of the stars are in the Main Sequence stage of their lives
• Includes our Sun.
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• Main Sequence stars are found in a band from the upper left to the lower right
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RED GIANTSRED GIANTS• Really Big, Not Very Hot but Really Big, Not Very Hot but
VERY BRIGHT!VERY BRIGHT!
• Betelgeuse: 3500 K , 100,000 Betelgeuse: 3500 K , 100,000 times more luminous than the suntimes more luminous than the sun
• radius must be 1000x that of Sun!radius must be 1000x that of Sun!
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• Red Giant and Supergiant stars are found above and to the right of the Main Sequence stars
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WHITE DWARFS• Very Small, Very Hot but Very Small, Very Hot but
Not Very BrightNot Very Bright• Sirius BSirius B: 27,000 K, but gives : 27,000 K, but gives
off 1000 times less light than off 1000 times less light than the Sunthe Sun
• 100 times smaller than the Sun100 times smaller than the Sun
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• Tiny White DwarfWhite Dwarf stars are found in the lower left corner of the HR diagram
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Determining the Sizes of Stars from an HR Diagram
• The Smallest stars are the tiny White Dwarf stars and are found in the lower left corner of the HR diagram
• Main sequence stars span a range of sizes from the small found in the lower right to the large found in the upper left
• The largest stars are the Giant and Supergiant stars which are found in the upper right corner
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Determining the Sizes of Stars from an HR Diagram
• The Smallest stars are the tiny White Dwarf stars and are found in the lower left corner of the HR diagram
• Main sequence stars span a range of sizes from the small found in the lower right to the large found in the upper left
• The largest stars are the Giant and Supergiant stars which are found in the upper right corner
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Tutorial: H-R Diagram (p.73)
• Work with a partner!• Read the instructions and questions carefully.• Discuss the concepts and your answers with one
another. Take time to understand it now!!!!• Come to a consensus answer you both agree on.• If you get stuck or are not sure of your answer, ask
another group.
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c
e
Temperature (K)
Lu
min
osit
y (s
olar
un
its)
Spectral Type
Ab
solute m
agnitu
de
20,000 10,000 5,000
O5 B5 A5 F5 G5 K5 M5
10,000
1,000
100
10
1
.1
.01
.001
.0001
a
b
d
f
-5
0
5
10
15
Main Sequence
Red Giants
White Dwarfs
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0/0
How does the size of a star near the top left of the H-R diagram compare with a star of the same
luminosity near the top right of the H-R diagram?
1. They are the same size.2. The star near the top left is
larger.3. The star near the top right
is larger.4. There is insufficient
information to determine this.
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0/0
The star Rigel is about 100,000 times brighter than the Sun and belongs to spectral type B8. The star Sirius B is about 3000 times dimmer than the Sun and also belongs to spectral type B8. Which star
has the greatest surface temperature?
1. Rigel2. Sirius B3. They have the same
temperature.4. There is insufficient
information to determine this.
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Which is hotter a B3 or an A7? Which is hotter a B0 or a B9?
c
e
Temperature (K)
Lu
min
osit
y (s
olar
un
its)
Spectral Type
Ab
solute m
agnitu
de
20,000 10,000 5,000
O5 B5 A5 F5 G5 K5 M5
10,000
1,000
100
10
1
.1
.01
.001
.0001
a
b
d
f
-5
0
5
10
15
Main Sequence
Red Giants
White Dwarfs
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Which is hotter a B3 or an A7? Which is hotter a B0 or a B9?
c
e
Temperature (K)
Lu
min
osit
y (s
olar
un
its)
Spectral Type
Ab
solute m
agnitu
de
20,000 10,000 5,000
O5 B5 A5 F5 G5 K5 M5
10,000
1,000
100
10
1
.1
.01
.001
.0001
a
b
d
f
-5
0
5
10
15
Main Sequence
Red Giants
White Dwarfs
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c
e
Temperature (K)
Lu
min
osit
y (s
olar
un
its)
Spectral Type
Ab
solute m
agnitu
de
20,000 10,000 5,000
O5 B5 A5 F5 G5 K5 M5
10,000
1,000
100
10
1
.1
.01
.001
.0001
a
b
d
f
-5
0
5
10
15
Main Sequence
Red Giants
White Dwarfs
B9B0
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What about the Masses of Stars on the H-R Diagram?
• Main Sequence stars range from 0.1M to
~100M
• The masses of Main Sequence stars increase
with increasing luminosity, size and temperature
• Main Sequence stars increase in mass from the
lower right to the upper left of the H-R Diagram
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There is a relationship
between mass and luminosity
for Main Sequence stars
Bigger (more massive) is brighter and hotter!
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There is a relationship
between mass and luminosity
for Main Sequence starsthe numbers shown are masses in terms of the Sun’s mass
Bigger (more massive) is brighter and hotter!
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There is not simple relationship for the Mass of Non-Main Sequence stars:
• Giants and Supergiants: range from M to about 20M
• White Dwarfs: approximately M or less
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Average Densities:• SUN: about density of water
• GIANTS: One thousand times less dense than AIR!
• DWARFS: about 1 million times the Sun’s density– one teaspoon: 5 tons!!!