Download Stellar Properties 2

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.
• 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
100
HIGH
1
0.01
Luminosity
0.0001
LOW
Stellar
Masses
What should we do with our
information?
• Luminosities
• Surface Temperatures
• Masses
Look for Relationships
No Relationship
Luminosity - Mass Relation
HR
Diagram:
Luminosity
vs.
Surface
Temperature
Luminosity Temperature
Relation:
HertzsprungRussell
Diagram
Luminosity
Recall:
Hotter ->
Brighter
Hotter ->
Bluer
Bigger ->
Brighter
Temperature
Then cool
+
Luminous
-> Large
Luminosity
Recall:
Hotter ->
Brighter
Hotter ->
Bluer
Bigger ->
Brighter
Temperature
Then small
Luminosity
+ Hot
-> small
Stellar
Size,
Mass
&
HR
Diagram
Large radius
Small radius
Stars with low
temperature and
high luminosity
must have large
radius
SUPERGIANTS
GIANTS
WHITE
DWARFS
Stars with low
temperature and
high luminosity
must have large
radius
High-Mass Stars
Low-Mass Stars
Most
Low Mass
stars have
Small
Luminosity
Most
Large Mass
stars have
Large
Luminosity
Regions of
the H-R
Diagram
Activity
• Answer the questions on your scantron
sheet
C
Luminosity
B
1. Which
star is the
hottest?
D
A
Temperature
C
Luminosity
B
1. Which
star is the
hottest?
D
A
Temperature
A
C
Luminosity
B
2. Which star
is the most
luminous?
D
A
Temperature
C
Luminosity
B
2. Which star
is the most
luminous?
D
A
Temperature
C
C
Luminosity
B
D
A
Temperature
3. Which
star is a
mainsequence
star?
C
Luminosity
B
D
A
3. Which
star is a
mainsequence
star?
D
Temperature
C
Luminosity
B
4. Which star
has the
largest
radius?
D
A
Temperature
C
Luminosity
B
4. Which star
has the
largest
radius?
D
C
A
Temperature
A
Luminosity
D
B
C
Temperature
5. Which star
is most like
our Sun?
A
Luminosity
D
5. Which star
is most like
our Sun?
B
B
C
Temperature
BRIGHT
HOT
COOL
FAINT
HR
Diagram
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 = 4pR2sT4
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M
3.5
How long before it is used up?
M/L = M/M
3.5
-2.5
=M
Main
Sequence
Lifetimes
Lifetime on the Main Sequence
• O & B Dwarfs burn fuel like a bus!
• M Dwarfs burn fuel like a compact car!
10
• Our Sun will last 10 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 Distance
Same Age
Pleiades now has
no stars with life
expectancy less
than around 100
million years
Main-sequence
turnoff
Detailed
modeling of the
oldest globular
clusters reveals
that they are
about 13 billion
years old
Cluster
Ages
Activity
• Answer the questions on your scantron
sheet
A
Luminosity
D
B
C
Temperature
6. Which of
these stars
will have
changed the
least 10
billion years
from now?
A
Luminosity
D
B
C
Temperature
6. Which of
these stars
will have
changed the
least 10
billion years
from now?
C
A
Luminosity
D
B
C
Temperature
7. Which of
these stars
can be no
more than
10 million
years old?
Luminosity
A
D
7. Which of
these stars
can be no
more than
10 million
years old?
C
A
B
Temperature
A stars properties depend mostly on
1. Mass
2. Age
NEXT TIME
• Evolution of Stars
• READ chapter 17