Astro 1050 Wed. Oct. 22, 2003
|
|
|
Today: Finish Chapter 9,
Stellar Structure |
|
HW discussion |
|
Review with time remaining |
Mass-Luminosity
relationship
|
|
|
L µ M3.5 Why? |
|
|
|
Higher mass means higher internal
pressure |
|
Higher pressure goes with higher
temperature |
|
Higher temperature means heat leaks out
faster |
|
Star shrinks until T inside is high
enough for
fusion rate (which is very sensitive to temperature)
to balance heat leak rate |
|
|
|
|
|
|
Lifetime on Main Sequence
|
|
|
L µ M3.5 T
µ
fuel / L = M/M3.5 = M-2.5 |
|
Example: M=2 MSun L = 11.3 LSun T =1/5.7 TSun |
|
|
|
|
How about a 0.5 solar
mass star?
|
|
|
M = 0.5 Msun |
|
Time = |
|
Luminosity = |
|
|
How about a 0.5 solar
mass star?
|
|
|
M = 0.5 Msun |
|
Time = 5.7 times solar lifetime |
|
Luminosity = 0.09 solar luminosity |
|
|
Width of Main Sequence –
and Stellar Aging
|
|
|
|
|
As star converts H to He you have more
massive nuclei |
|
Pressure related to number of nuclei |
|
Gravity related to mass of nuclei |
|
Pressure would tend to drop unless
something else happens |
|
Temperature must rise (slightly) to
compensate |
|
Luminosity must
rise (slightly) as heat leaks out faster |
|
|
|
|
|
|
Orion Nebula: A
Star-Forming Region
|
|
|
Red light = Hydrogen emission |
|
Blue light = reflection nebula |
|
Dark lanes = dust |
|
|
|
Astronomy Picture of the Day:
http://antwrp.gsfc.nasa.gov/apod |
Protoplanetary Disks in
the Orion Nebula
|
|
|
|
|
Dusty disk seen in silhouette |
|
|
|
Central star visible at long
wavelengths |
Herbig-Haro objects: The
angular momentum problem
|
|
|
|
|
As clouds try to collapse angular
momentum makes them spin faster |
|
A disk forms around the protostar |
|
Material is ejected along the rotation
axis |
|
|
Herbig-Haro 34 in Orion
|
|
|
|
|
Jet along the axis visible as red |
|
|
|
Lobes at each end where jets run into
surrounding gas clouds |
Motion of Herbig-Haro 34
in Orion
|
|
|
|
|
Can actually see the knots in the jet
move with time |
|
|
|
In time jets, UV photons, supernova,
will disrupt the stellar nursery |
Homework #6
|
|
|
Won’t go through solutions here, but we
can visit WebCT for specific problems and discuss their solution. Particularly issues so far seem to involve
spectroscopic parallax and density. |
For Exam #2:
|
|
|
|
“Essay Questions” (2) will involve at
least some of the topics below: |
|
Temperature of Stars |
|
Binary Stars |
|
HR Diagram |
|
Ages/Lifetimes of Stars |
|
Stellar Fusion |
|
|
Review Chapters 5-9
|
|
|
|
Chapter 5: Astronomical Tools |
|
Electromagnetic Spectrum |
|
Optical Telescopes |
|
Resolving Power of Telescopes |
|
Space Astronomy |
|
(No Questions about Pink Floyd or the
Dark Side of the Moon!) |
Review Chapters 5-9
|
|
|
|
|
Chapter 6: Starlight and Atoms |
|
Model Atom, Energy Levels |
|
Absorption Lines |
|
Blackbody Spectrum |
|
Wien’s Law |
|
Steffan-Boltzmann Law |
|
Temperature of Stars |
|
Wien’s Law, the Balmer “Thermometer” |
|
Stellar Classification (OBAFGKM) |
|
Doppler Effect |
Review Chapters 5-9
|
|
|
|
Chapter 7: The Sun |
|
Atmospheric Structure |
|
Sunspots/Magnetic Phenomena |
|
Nuclear Fusion – proton-proton chain |
|
Solar Neutrino “Problem” |
Review Chapters 5-9
|
|
|
|
|
Chapter 8: The Properties of Stars |
|
Distances to Stars |
|
Parallax and Parsecs |
|
Spectroscopic Parallax |
|
Intrinsic Brightness: Luminosity |
|
Absolute Magnitude |
|
Luminosity, Radius, and Temperature |
|
Hertzsprung-Russell (H-R) Diagram |
|
Luminosity Classes (e.g., Main
Sequence, giant) |
|
Masses of Stars |
|
Binary Stars and Kepler’s Law |
|
Mass-Luminosity Relationship |
|
|
Review Chapters 5-9
|
|
|
|
|
Ch. 9: The Formation & Structure of
Stars |
|
Interstellar Medium |
|
Types of Nebulae (emission, reflection,
dark) |
|
Interstellar Reddening from dust |
|
Star formation |
|
Protostar Evolution on H-R Diagram |
|
Fusion (CNO cycle, etc.) |
|
Pressure-Temperature “Thermostat” |
|
Stellar Structure (hydrostatic
equilibrium, etc.) |
|
Convection, radiation, and opacity |
|
Stellar Lifetimes |
|
|
|
|