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A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
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A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
A1 16 Stars
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A1 16 Stars

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Miller's Astronomy 1 lecture notes on Stars

Miller's Astronomy 1 lecture notes on Stars

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  • 1. Hertzsprung–Russell diagram LACC §16.2 16.3, 17.4 • Spectral Classes • Luminosity Classes • distribution; masses & lifetimes An attempt to answer the “big questions”: What is out there? Thursday, April 22, 2010 1
  • 2. 30 Second People Study • Imagine you are from an alien race who live out their lives at an accelerated rate. • Imagine you have discovered the planet Earth with your advanced telescopes which allow you to make observations of Earth’s human population. • After collecting data for about 30 seconds, what would you be able to say about human physiology? Thursday, April 22, 2010 2
  • 3. The Solar Spectrum http://ess.geology.ufl.edu/ess/Notes/040-Sun/spectrum.GIF Thursday, April 22, 2010 3
  • 4. Stellar Spectra http://homepages.wmich.edu/~korista/phys325.html Thursday, April 22, 2010 4
  • 5. Stellar Spectra [Our Sun is type G2] http://www.maryspectra.org/classical/ classical.htm Thursday, April 22, 2010 5
  • 6. Stellar Spectra -- Composition http://faculty.fortlewis.edu/tyler_c/classes/206/notes4.htm Thursday, April 22, 2010 6
  • 7. Stellar Spectra-- Color and Brightness Wien’s Law Stefan-Bolzmann Law http://www.oswego.edu/~kanbur/a100/images/planck.jpg Thursday, April 22, 2010 7
  • 8. HR Diagram: Luminosity vs Temperature http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html Thursday, April 22, 2010 8
  • 9. HR Diagram and Mass Highest Mass: about 150 Msun Lowest Mass: about 0.072 Msun http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter17.html Thursday, April 22, 2010 9
  • 10. Low mass more common than High mass http://zebu.uoregon.edu/textbook/imf1.gif Thursday, April 22, 2010 10
  • 11. The stars we see -- m vs M Why aren’t they mostly M and K type stars? http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html Thursday, April 22, 2010 11
  • 12. Star Sizes http://commons.wikimedia.org/wiki/Category:Star_size_comparisons Thursday, April 22, 2010 12
  • 13. HR Diagram and Radius http://abyss.uoregon.edu/~js/ast122/lectures/lec11.html Thursday, April 22, 2010 13
  • 14. Stellar Mass and Lifetimes 0.07 Msun NOTE: This in not last about an HR Diagram. 10,000,000,000,000 On an HR Diagram, massive stars would be on years the top left, not the bottom right 150 Msun last about 1,000 years http://www.frostydrew.org/observatory/courses/astro/mass_life.gif Thursday, April 22, 2010 14
  • 15. Main Sequence Turn-Off Point H-R diagrams of two clusters, the open cluster M67 (a young cluster), and the globular cluster M4 (an old cluster). The main sequence is significantly shorter for the older cluster; the luminosity and temperature of stars at the 'turnoff point' can be used to date these clusters. http://astro.berkeley.edu/~dperley/univage/univage.html Thursday, April 22, 2010 15
  • 16. Hertzsprung–Russell diagram LACC §16.2 16.3, 17.4 • Spectral Classes: O B A F G K M; blue (hot) --> red (cool); Wien’s Law (λ ∝ 1/T); absorption features • Luminosity Classes: I II III IV V; supergiant (I) --> dwarf (V); Stefan-Bolzmann Law (Flux ∝ T4); size (increases as you move up and right) • distribution: (main sequence (90%), white dwarfs (10%), blue giants (rare), red dwarfs (common), red giants (dying), white dwarfs (dead)); masses & lifetimes: blue m.s. (high mass, short life) --> red m.s. (low mass, long life) What is out there? Thursday, April 22, 2010 16
  • 17. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 17, p. 392-393: 13 (expect test question(s) like this) • Ch 18: Image Analysis Quizzes accessible from: http://www.brookscole.com/cgi-brookscole/ course_products_bc.pl? fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due beginning of next class period. Thursday, April 22, 2010 17
  • 18. Stars LACC §16.2 16.3, 17.4 • Spectroscopy • Imaging • Photometry An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 18
  • 19. Proper Motion (Imaging) http://csep10.phys.utk.edu/astr162/lect/motion/proper.html Thursday, April 22, 2010 19
  • 20. Radial Velocity using Doppler Shift (Spectroscopy) http://spiff.rit.edu/classes/phys301/lectures/doppler/doppler.html Thursday, April 22, 2010 20
  • 21. Spectroscopic Binaries (Spectroscopy) http://csep10.phys.utk.edu/astr162/lect/binaries/spectroscopic.html Thursday, April 22, 2010 21
  • 22. Eclipsing Binaries (Photometry) http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap17/FG17_21.jpg Thursday, April 22, 2010 22
  • 23. Light curve of 2MASS J05352184–0546085 at 0.8  m http://www.nature.com/nature/journal/v440/n7082/fig_tab/ nature04570_F1.html Thursday, April 22, 2010 23
  • 24. Stellar Because of the size and proximity of this star it has the third largest angular diameter as Diameters: viewed from Earth, smaller only than the Sun and R Doradus. Betelgeuse [Betelgeuse] is one of only a dozen (Imaging) or so stars telescopes have imaged as a visible disk....The distance to Betelgeuse is not known with precision but if this is assumed to be 640 light years, the star's diameter would be about 950 to 1000 times that of the Sun. Betelgeuse ... is thought to have a mass of about 20 solar masses. Though only 20 times more massive than the Sun, this star could be hundreds of millions times greater in volume (as with a beach ball compared to a large stadium). Betelgeuse http://www.lesia.obspm.fr/ was the first star on which starspots were ~titania/results.html resolved in optical images by a telescope, Thursday, April 22, 2010 24
  • 25. Stellar Diameters (Photometry) The occulted star, a K0 giant, has an angular diameter of 0.55 mas (not 1.11 mas, as indicated erroneously on the figure, to be corrected), corresponding to 7.5 km projected at Titania. The star being at 170 parsecs from the Earth, this yields a stellar radius of 10 solar radii, a reasonable value for this kind of stars. http://www.lesia.obspm.fr/~titania/results.html Thursday, April 22, 2010 25
  • 26. Brown Dwarfs Astronomers have found many types of objects in orbit around stars. These range from other full- sized stars like our sun (binary star systems) to Jupiter sized planets (never directly imaged but inferred from radial-velocity spectroscopy). The relative sizes of these various types of bodies are shown above for comparison. Even though a brown dwarf can be similar in diameter to a Jupiter sized planet, brown dwarfs are 13-75 times more massive and they can appear on the order of 100-1,000,000 times brighter than a Jupiter sized planet at infrared wavelengths when they are studied with telescopes. Credit: Gemini Observatory/Artwork by Jon Lomberg http://www.spaceflightnow.com/news/n0205/22closest/ Thursday, April 22, 2010 26
  • 27. Radius-Mass Ratios http://www.astrophysicsspectator.com/topics/overview/SizeStarsPlanets.html Thursday, April 22, 2010 27
  • 28. Radius-Mass Ratios The material inside a degenerate object like Saturn is softer than in the smaller planets; unlike the solid rock of Earth, the material at the center of Saturn gives when it is squeezed.  This means that as the mass of a degenerate object increases, which increases the pressure required to counter the object's self-gravity, the density also increases. The consequence is that the radius can decrease as the mass increases.  For cold bodies of the same composition, the radius goes as the inverse of the cube root of the mass.  For bodies with some internal heat—and generally there is some internal heat left over from the creation of the body—the radius decreases more slowly than for the cold bodies as the mass rises.  This residual heat causes Jupiter to be slightly larger than Saturn, and it causes most of the known brown dwarfs to be about the size of, rather than much smaller than, Jupiter. http://www.astrophysicsspectator.com/topics/overview/SizeStarsPlanets.html Thursday, April 22, 2010 28
  • 29. Brown Dwarfs: Sizes http://homepages.wmich.edu/%7Ekorista/stargal-images/sunMLTJ_visseq.jpg Thursday, April 22, 2010 29
  • 30. Stars LACC §16.2 16.3, 17.4 • Spectroscopy: Temperature, Composition, Radial Velocity, Age of a Cluster, Binary Systems (Spectroscopic Binaries) • Imaging: Diameters, Proper Motion, Binary Systems (Visual Binaries) Clusters (Open vs Globular) • Photometry: Variable Stars, Diameters, Binary Systems (Eclipsing Binaries); light curves An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 30
  • 31. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 16, pp. 371-372: 6. • Ch 19: Image Analysis Quizzes accessible from: http://www.brookscole.com/cgi-brookscole/ course_products_bc.pl? fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due beginning of next class period. Thursday, April 22, 2010 31

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