Stellar Initial Mass Function

1
Stellar Initial Mass Function

• What do you mean you can predict the future?

2
What We Saw Last Week

• We found that the distribution of stars looked
  like it followed a few different patterns.

• What patterns/trends do you see for this chart?

3
The H-R Diagram

• You learned about the H-R Diagram in lecture this
  past week. Do our charts resemble the H-R Diagram?

4
List findings on the board
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Conclusions?

• Lets make a list of our findings
• (space reserved for students ideas about what
  they are seeing)

6
Where are the stars we saw in the night sky on
the H-R Diagram?
3. Cooler, Red Giant Stars
2. Large, Sun-Like Temperature Stars
1. Large, Hot, Luminous Stars
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What is the IMF?

• The Initial Mass Function was developed by Edwin
  Salpeter in 1955.
• This function predicts the types of stars (in
  terms of mass) astronomers can expect to form
  from condensing gas clouds.
• The math and physics behind it are far beyond our
  grasp, but the findings are not so we will
  focus on those!

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Lets analyze the IMF as a sample of stellar mass
distribution at the time of their formation
Mass (solar) Number Relative to Solar
Mass (solar) Number Relative to
Solar
We see here that for low mass stars, our sample
found there was over 40 formed with masses less
than 1 Solar Mass There were less than 5 formed
with masses greater than 1 Solar Mass
Right away we can see that it is very uncommon
for high mass stars to form, compared to lower
mass stars
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Mass Contribution
This graph shows the contributions of different
stars to the mass of a galaxy
We see stars with a mass of ½ Solar Masses are
the most common stars in the galaxy
10
Light Contribution
This graph shows the contributions of different
stars to the luminosity of a galaxy
We see that the rarer, larger stars contribute
most of the light we see in the galaxy
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Where are ½ Solar Mass Stars on the H-R Diagram?
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What Did We Find Last Week?

• So we have observed that the majority of stars we
  are seeing are much bigger and much brighter than
  our sun
• (are they all hotter? Does this make sense?)
• The IMF States that stars with masses less than
  the Sun are most likely to form.
• Either Edwin Salpeter is wrong or we are seeing a
  bias sample.

We will assume the IMF is correct ? Where are
the missing stars from the night sky?