Download Ch 15 Mar 12

Most luminous
stars:
106 LSun
Least luminous
stars:
10–4LSun
(LSun is luminosity
of Sun)
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How do we measure stellar
temperatures?
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Hottest stars:
50,000 K
Coolest stars:
3000 K
(Sun’s
surface is
5800 K.)
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Absorption lines in star’s spectrum tell us its ionization level.
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Lines in a star’s spectrum correspond to a spectral type that
reveals its temperature.
(Hottest)
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O B A F G K M
(Coolest)
Remembering Spectral Types
(Hottest)
O B A F G K M
(Coolest)
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Clicker Question
Which kind of star is hottest?
A.
B.
C.
D.
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M star
F star
A star
K star
Clicker Question
Which kind of star is hottest?
A.
B.
C.
D.
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M star
F star
A star
K star
Pioneers of Stellar Classification
• Annie Jump
Cannon and the
“calculators” at
Harvard laid the
foundation of
modern stellar
classification.
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Most massive
stars:
100MSun
Least massive
stars:
0.08MSun
(MSun is the
mass of the Sun.)
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Largest star known is VY Canis Majoris. It is a red
hypergiant, ~ 2,000 solar radii or ~ 1.9 billion miles
in diameter. If it were in our solar system, its size
would extend past Uranus. It is ~ 4,900 light years
away.
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What is a Hertzsprung-Russell
diagram?
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Luminosity
An H-R
diagram plots
the luminosity
and temperature
of stars.
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Temperature
Most stars fall
somewhere
on the main
sequence of
the H-R
diagram.
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Stars with lower
T and higher L
than mainsequence stars
are larger and
are called giants
and supergiants.
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Stars with higher
T and lower L
than mainsequence stars
are smaller and
are called white
dwarfs.
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A stars full classification includes spectral type
and luminosity class. Every spectral type is
subdivided into 10 subtypes. For example: A0,
A1, A2 ….A9, F0, F1, …..F9, etc.
I - supergiant
II - bright giant
III - giant
IV - subgiant
V - main sequence
Examples: Sun - G2 V
Sirius - A1 V
Proxima Centauri - M5.5 V
Betelgeuse - M2 I
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H-R diagram
depicts:
Luminosity
Temperature
Color
Spectral type
Luminosity
Radius
Temperature
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Luminosity
Which
star is the
hottest?
Temperature
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Luminosity
Which
star is the
hottest?
A
Temperature
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Luminosity
Which star
is the most
luminous?
Temperature
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Which star
is the most
luminous?
Lumiosity
C
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Temperature
Luminosity
Which star
is a mainsequence
star?
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Temperature
Luminosity
Which star
is a mainsequence
star?
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D
Temperature
Luminosity
Which star
has the
largest
radius?
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Temperature
Luminosity
Which star
has the
largest
radius?
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C
Temperature