Chapter 13Measuring the Distance to a StarMeasuring Properties via LightBrightness and LuminosityRadius and TemperatureMeasuring Radius DirectlyThe Magnitude SystemWhich of the following stars is the hottest?Slide 9Slide 10Slide 11Spectra of StarsThe effect of temperatureAttempting to classify starsSlide 15Measuring a star’s motionThe primary classification of stars is by which property?Slide 18Slide 19Binary StarsVisual and Spectroscopic BinariesEclipsing Binary StarsSlide 23The H-R DiagramConstructing the H-R DiagramH-R Diagram and SizeThe Mass-Luminosity RelationLuminosity ClassesSummary Table for determining stellar propertiesWhich star is brightest?Which star is the hottest?Which star is the biggest?Bullet PointsChapter 13Measuring the Properties of StarsMeasuring the Distance to a Star•Triangulation for nearby stars.•Parallax for far away stars.•dparsecs = 1/parallaxarc seconds (1 parsec = 3.26 light years)Measuring Properties via Light•Recall Wein’s Law: the higher the temperature, the lower the wavelength.•Blue stars are hotter than red stars.Brightness and Luminosity•Luminosity: How much energy a star puts out per second.•Sun: 4*1026 watts.•Brightness: How bright a star appears to us.•B = L/(4πd2)Radius and Temperature•If two stars have the same temperature, the one with the larger radius has the larger luminosity.•If two stars have the same radius, the one with the larger temperature has the larger luminosity.•Stefan-Boltzmann Law (L = σT4 * 4πR2)Measuring Radius Directly• Hubble Speckle Imaging Interferometer•Stephan-Boltzmann/interferometer observations: Most stars similar in radius to the sun Some 100s of times larger (giants) Smaller stars are called dwarfsThe Magnitude System•Smaller number = brighter star (negative numbers too)•Difference in magnitude is a ratio of brightness•Apparent magnitude vs absolute magnitude (10 parsecs)Which of the following stars is the hottest?A. Betelgeuse (red)B. The Sun (yellow)C. Rigel (blue)If we moved substantially closer to a star, which of the following would be true?A. Both the brightness and luminosity would increaseB. The brightness would increase but the luminosity would remain the sameC. The brightness would remain the same but the luminosity would increaseD. Both the brightness and the luminosity would remain the sameThe Stefan-Boltzmann Law describes the effect of which two variables on luminosity?A. Brightness and radiusB. Radius and temperatureC. Temperature and brightnessStar A has a magnitude of 5.0. Star B has a magnitude of 0.5.Star C has a magnitude of -3.0.Which star is the brightest? Which is the dimmest?A. Brightest: ADimmest: CB. Brightest: ADimmest: BC. Brightest: CDimmest: BD. Brightest: CDimmest: ASpectra of Stars•Absorption lines can tell you the star’s composition•Sun is in the center in the figure to the right.The effect of temperature•Lines will not always appear if the temperature is too hot or too cold, even if the element is present.Attempting to classify stars•1866: white, yellow, red, deep red•1872: Henry Draper found a way to record spectra on photographs —> Henry Draper Catalog•E.C. Pickering: A-D (white), E-L (yellow), M&N (red), new types•1901: Annie Jump Cannon: Reorders things by temperature•O B A F G K M (from hot to cold)•1920s: Cecilia Payne (USA): Showed that Cannon’s order was based on physical properties, not just spectrum.Measuring a star’s motion•Doppler shift•Red shifted = moving apart. Blue shifted = moving together.The primary classification of stars is by which property?A. SizeB. Temperature (color)C. Luminosity (energy output)D. Distance from usWhich of the following is the correct order of classifications from hot to cold?A. A B C D E F GB. M K G F A B OC. O B A F G K MD. O B A M A P L ZThe top spectrum is from a certain element as measured in a lab on Earth. The bottom spectrum is the same element from a star. What is that star’s direction relative to us?A. Toward usB. Away from usC. Sideways relative to usD. No motion at allBinary Stars•Systems with >2 stars exist.•Can determine mass.•Hotter stars more likely to have a companion.•Most only a few AU apart, some even “touch”•Singles dominate, brighter ones usually have companions.Visual and Spectroscopic Binaries•Visual Binaries: Can actually see the stars orbit each other•Spectroscopic Binaries: Can tell from red/blue-shifted spectrum•Measuring mass from modified Kepler’s 3rd Law (m+M)P2 = a3•Stellar masses: 0.1 - 30 M⊙Eclipsing Binary Stars•Can only happen for a specific orientation•Can determine radius of each star.For which type of binary star systems can we ALWAYS determine the radius of the stars?A. Visual binariesB. Spectroscopic binariesC. Eclipsing binariesD. All of the aboveE. None of the aboveThe H-R Diagram•Named for Enjar Hertzspring (Danish) and Henry Norris Russel (American)•Luminosity (rate of energy use) vs surface temperature (color)Constructing the H-R DiagramH-R Diagram and Size•At the same temperature (color) any difference in luminosity comes from a difference in size.•“Giant Branch” and Red Giants•White dwarfs•Age and size of stars are relatedThe Mass-Luminosity Relation•More mass = More luminous = ℒ ℳ3 (in solar units)Luminosity Classes•More luminous stars have narrower dark lines•Sun: G2VSummary Table for determining stellar propertiesWhich star is brightest?A. Enter answer text...B. Enter answer text...C. Enter answer text...D. Enter answer text...ABDCWhich star is the hottest?A. Enter answer text...B. Enter answer text...C. Enter answer text...D. Enter answer text...A. Enter answer text...B. Enter answer text...C. Enter answer text...D. Enter answer text...ABDCWhich star is the biggest?A. Enter answer text...B. Enter answer text...C. Enter answer text...D. Enter answer text...ABDCBullet Points•All stars have basically the same composition: 71% H, 27% He, 2% other•Most have surface temps between 3,000 & 30,000K.•Most have masses between 0.1 and 30 M⊙.BrightestMost MassBiggestSmallestDimmestLeast