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UF - AST 1002 - Class Notes - Week 3

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UF - AST 1002 - Class Notes - Week 3

School: University of Florida
Department: Astronomy
Course: Discovering the Universe
Term: Fall 2015
Tags:
Name: AST 1002, Week 3
Description: These notes cover the content in class.
Uploaded: 03/16/2018
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background image 1. Luminosity a. So, by measuring brightness and distance, we get a star’s luminosity.
b. We find:
i. Most luminous stars: 10^6 L(sun) ii. Least Luminous Stars: 10^4 L (sun) 2. How hot are stars? a. Blue stars are hot
b. Red stars are cool stars
c. Every object emits  thermal radiation  with a spectrum that depends
on its temperature d. Recall Blackbody -> Laws of Thermal Radiation i. Hotter objects emit more light at all wavelengths  ii. Hotter objects tend to emit more light at shorter wavelengths e. Lines in a star’s spectrum correspond to a  spectral  type  that also reveals its temperature: i. (Hottest)  O B A F G K M  (Coolest) 1. Oh, Be A Florida Gator, Kiss Me!
2. Sun is a G star
f. Level of ionization also revels a star’s temperature  3. High Temperature Stars a. O-B T> 15000 K
b. No spectral lines from metals
i. Metals have lower ionization levels -> ionized c. Weak Hydrogen lines 4. Medium Temperature Stars a. A-F-G T= 5000-12000 K
b. Some metal lines
c. Strong Hydrogen Lines
5. Low Temperature Stars a. K & M < 5000 K
b. Complex spectra
c. No spectral lines from Hydrogen or Helium, but most other elements
present d. Spectral lines from metals
e. Molecular Lines
i. Cooler temperatures -> slower particle speeds allow atoms to combine to form molecules 6. Questions a. Which kind of star is hottest?
background image AST 1002 Week 3 Notes  March 12-16 i. A Star 7. Stellar Spectra a. Wien’s law = (0.29 cm) / T
b. Hottest stars: 50,000 K
c. Coolest Stars: 3000 L
d. (Sun’s surface is 5800 K)
8. The Hertzsprung-Russell Diagram (The “H-R” Diagram) a. Correlations i. A correlation exists if: 1. Two properties are related
2. When   one   changes,   the   other   also   changes   in   a
predictable way b. Stars   with   low   temperature   and   high   luminosity   must   have   a   large radius c. Stars with high temperature and low luminosity must have small radius
d. H-R Diagram depicts:
i. Temperature ii. Color iii. Spectral Type iv. Luminosity v. Radius vi. Mas ** vii. Lifespan ** 9. “Arrival” on the Main Sequence a. The mass of the protostar determines: i. How long the protostar phase will last ii. Where the new-born star will land on the MS iii. i.e.,   what   spectral   type   the   star   will   have   while   on   the   main sequence  10.Star’s ifetime on the Main Sequence a. How long will it be before MS stars run out of fuel?  i. i.e Hydrogen? b. How much fuel is there? i. E=mc^2 ii. Mass c. How fast is it consumed?  1. Luminosity 11.We use binary stars to measure directly the masses of stars every type. This leads to the: a. Mass-Luminosity Relation i. For main sequence stars only 12.Star’s Lifetime on the Main Sequence
13.Lifetime Estimates for Different Masses
a. Lifetime= Amount of fuel/ Rate that fuel is used
background image AST 1002 Week 3 Notes  March 12-16 b. Sun’s life expectancy: 10 billion years i. Until core hydrogen (10% of total) is used up c. Life expectancy of 10 M(sun) star: i. 10 billion years x 10^-2.5= 30 million years d. Life expectancy of 0.1M(sun) star: i. 10 billion years x (0.1^-2.5) = 14.Lifetime on the Main Sequence a. B2 dwarf (10 M) lasts 3.2 x 10^7 yr
b. F0 (2M) lasts 1.8 x 10^9 yr
c. M0 dwarf (0.5 M) lasts 5.6 x 10^10 yr
d. But the Universe is 1.37 x 10^10 yr old
e. Every M dwarf that was ever created is still on the main sequence
15.Main Sequence Star Summary a. High Mass: i. High Luminosity ii. Short-Lived  iii. Large Radius iv. Blue b. Low Mass: i. Low Luminosity ii. Long-Lived iii. Small Radius Red 16.Main Sequence Stars a. Massive Star i. 40 X Sun’s Mass ii. 40,000 degrees iii. Emits 500,000 times Sun’s Power b. Sun i. 6,000 degrees c. Low-Mass Star i. 1/10 Sun’s Mass ii. 2400 degrees iii. Emits 0.0008 times Sun’s Power

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School: University of Florida
Department: Astronomy
Course: Discovering the Universe
Term: Fall 2015
Tags:
Name: AST 1002, Week 3
Description: These notes cover the content in class.
Uploaded: 03/16/2018
8 Pages 32 Views 25 Unlocks
  • Better Grades Guarantee
  • 24/7 Homework help
  • Notes, Study Guides, Flashcards + More!
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