Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 Announcements: -Skipping section 12.4 Extra Credit opportunity!! Friday, April 17, 2007 Telescope Viewing at Evergreen Valley College for more information and directions: You will need to get handout from class (or on class website) and complete it at the event in order to get credit!!
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 Chapter 12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3 Measuring the Properties of Stars (Chp. 12) Distance from the Sun Temperature Luminosity (magnitudes) Mass Composition Rotation How we classify and categorize them
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 4 Astronomers can determine the composition of a star many light-years away by: a)sending probes to collect atmospheric material from the star and analyzing it with a mass spectrometer. b) Observing the spectrum of the star and applying Wien’s law. c) Observing the absorption line spectrum and matching up lines with the laboratory spectra of various elements.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 5 How would you design a mission that could exceed the performance of the Hipparcos satellite? a) Use a larger baseline: the orbital diameter of Mars, for example. b) Use a larger baseline: select more distant stars, for example. c) Use a smaller baseline for higher accuracy.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 Which unit of distance is larger, the light-year or the parsec? a)light-year b)parsec c)The parsec is a measure of angle, not distance d)They are the same.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Stars are classified according to the types of absorption lines they have. The classification nomenclature is a)Based upon a numeric scheme running backwards from 25 to 1 (and missing some numbers). b)Based upon roman numerals one through ten (I, II, III, IV, V, VI, VII, VIII, IX, and X) c)Based upon an alphabetic scheme that does not include all of the letters and is not necessarily in alphabetic order. READING QUIZ
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 8 Inverse-Square Law of Brightness
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9 The Luminosity of a Star
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 10 Stefan-Boltzmann law Figure 12.5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 11 Brightness: energy per unit area -intrinsic -apparent Luminosity: Total energy emitted -intrinsic -apparent
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 12 Star A has a radius R and a temperature T. Star B has the same temperature and is at the same distance from the Sun as star A. However, it is 4 times larger than star A. How many times more luminous is star B? a) 16 b) 4 c) both have the same luminosity d) not enough information to tell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13 Star A has a radius R and a temperature T. Star B is at the same distance from the Sun as star A. However, it is 4 times larger than star A and two times cooler. How many times more luminous is star B? a) 16 b) 4 c) both have the same luminosity d) not enough information to tell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 14 Classification of Stellar Spectra
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15 Stellar spectra are not all the same! A B C What causes these differences?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 16 Plotting a Spectrum Absorption lines
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 17 Annie Jump Cannon: Hired as an assistant in 1896 by Edward Pickering of Harvard College Obervatory. Classified stars by their spectra. Looked at hundreds of thousands of spectra. Published the Draper Catalogue.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 18 Letters ordered by decreasing temperature: hot cold
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19 What causes such large differences in spectra? 1920’s: Cecilia Payne PhD thesis, Harvard College (1925) Differences due to temperature, not composition! All stars made mostly of hydrogen (very controversial!)
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 25 O:Ionized helium B:Neutral helium, stronger hydrogen A:Very strong hydrogen lines F:Absorption lines from other elements (metals) begin to appear (like ionized Calcium) G:Weaker hydrogen, neutral metals K:Some lines from molecules begin to appear M:Lots of lines from molecules like TiO, water Sun is a G2!
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26 The HR Diagram
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27 The Hertzsprung-Russell Diagram
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 28 Constructing an H-R diagram requires that you know the absolute (intrinsic) luminosity. You can compute this quantity by measuring the apparent luminosity and determining the distance to the star.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 29 The H-R diagram Figure 12.16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 30 Stellar luminosity classes ISupergiants IIBright Giants (not widely used) IIIGiants IVSubgiants VDwarfs (Main Sequence Stars) White Dwarfs