Astro 1050 Fri. Oct. 11, 2002
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Today: Chapter 8, Properties of
Stars |
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Please bring calculators to
class |
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Astronomy New Articles |
How to recognize patterns
in data
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What patterns matter for people – and
how do we recognize them? |
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Weight and Height are easy to measure |
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Knowing how they are related gives
insight into health |
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A given
weight tends to go with a given height |
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Weight either very high or very low
compared to trend ARE important |
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Plot weight vs. height and look for
deviations from simple line |
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Example of cars from the book |
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Note “main sequence” of cars |
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Weight plotted backwards |
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Just make main sequence a line
which goes down rather than up |
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Points off main sequence are
“unusual” cars |
Stars: Patterns of L, T, R
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The Hertzsprung-Russsell (H-R) diagram |
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Plot L vs. backwards T. (We can find R given L and T) |
How are L, T, and R
related?
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L = area ´sT4 = 4 p R2 sT4 |
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Stars can be intrinsically bright
because of either large R or large T |
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Use ratio equations to simplify above
equation |
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(Note book’s symbol for Sun is circle
with dot inside) |
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Example: Assume T is different but size is same |
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A star is ~ 2 ´ as hot as sun, expect L
is 24 = 16 times as bright |
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M star is ~1/2 as hot as sun, expect L
is 2-4 = 1/16 as bright |
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B star is ~ 4 ´ as hot as sun, expect L is 44 = 256 times as bright |
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Example: Assume T same but size is different |
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If you have a G star 4 ´ as large as
sun, expect L would be 42=16 times
as bright |
L, T, R, and the H-R
diagram
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L = 4 p R2 sT4 |
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The main sequence consists very roughly
of similar size stars |
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The giants, supergiants, and white
dwarfs are much larger or smaller |
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Lines of constant R in
the H-R diagram
Slide 7
Different “types” of H-R
diagrams
Luminosity Classes
Spectra of Different
Luminosity Classes
Spectroscopic “Parallax”
What fundamental property
of a star
varies along the main sequence?
Masses of Binary stars
Masses of Binary stars
Masses of Binary stars
Measuring a and P of
binaries
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Two types of binary stars |
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Visual binaries: See separate stars |
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a large, P long |
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Can’t directly measure component of a
along line of sight |
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Spectroscopic binaries: See Doppler shifts in spectra |
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a small, P short |
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Can’t directly measure component of a
in plane of sky |
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If star is visual and spectroscopic
binary get get full set of information and then get M |
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Masses and the HR Diagram
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Main Sequence position: |
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M:
0.5 MSun |
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G: 1 MSun |
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B:
40 Msun |
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Luminosity Class |
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Must be controlled by something else |
The Mass-Luminosity
Relationship
Eclipsing Binary Stars
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System seen “edge-on” |
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Stars pass in front of each other |
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Brightness drops when either is hidden |
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Used to measure: |
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size of stars (relative to orbit) |
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relative “surface brightness” |
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area hidden is same for both eclipses |
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drop bigger when hotter star hidden |
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tells us system is edge on |
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useful for spectroscopic binaries |