chapter 10 the nature of stars. what do you think? what color are stars? are most stars isolated...
TRANSCRIPT
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Chapter 10 The Nature of Stars
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What do you think?
• What color are stars?
• Are most stars isolated from other stars, like the Sun?
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A star’s color reveals its surface temperature
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Photometry• Technique used to accurately measure the color
of stars using UBV filters– U - ultraviolet wavelengths– B - blue wavelengths– V - visible wavelength
• astronomers compare combinations of U minus B (U-B) and B minus V (B-V)
• these combinations are called color indices
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Stars are classified by their spectra as O, B, A, G, K, and M spectral types
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Stars are classified by their spectra as O, B, A, G, K, and M spectral types
• O B A F G K M
• hottest to coolest
• bluish to reddish
• An important sequence to remember:– Our Best Astronomers Feel Good Knowing
More– Oh Boy, An F Grade Kills Me– Oh Be a Fine Guy (or Girl), Kiss Me
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The Hertzsprung-Russell diagram
identifies a definite relationship between
temperature and absolute magnitude
HR DIAGRAM
Absolute magnitude vs temperature
or
luminosity vs spectral type
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Determining the Sizes of Stars from an HR Diagram
• Main sequence stars are found in a band from the upper left to the lower right
• Giant and supergiant stars are found in the upper right corner
• Tiny white dwarf stars are found in the lower left corner of the HR diagram
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Luminosity classes
• Class I includes all the supergiants
• Class V includes the main sequence stars
• e.g., the Sun is a G2 V
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Monitoring how binary stars move provide information about stellar masses
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Monitoring how binary stars move provide information about stellar masses
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There is a relationship
between mass and luminosity
for main-sequence stars
Bigger is brighter!
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There is a relationship
between mass and luminosity
for main-sequence stars
Bigger is brighter!
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The orbital motion of binary stars affects the wavelengths of their
spectral lines
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Radial-Velocity Curve showing the positions of the stars and their spectra at four instants in an orbital period.
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Some binary stars eclipse each other
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Mass transfer in close binary systems can produce unusual double stars
• Close binary systems are where only a few stellar diameters, or less, separate the stars
• Mass can be dramatically transferred between the stars– detached binary (no mass transfer)– semidetached binary(material can flow across
along a path called the Roche lobe)– contact binary (the two stars share a common
envelope of material)
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What did you think?
• What color are stars?Stars are found in a wide range of colors, from
red through violet as well as white.
• Are most stars isolated from other stars, like the Sun?In the vicinity of the Sun, two-thirds of the stars
are found in pairs or larger groups.
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Self-Check1: Describe the observations necessary for the determination of basic physical properties
of stars such as mass, temperature, luminosity, chemical composition, sizes, and motions.
2: Explain the classification of stars according to their spectra and their luminosity.
3: Draw and describe the H-R diagram and its value for displaying physical properties of stars and in expanding our knowledge about stellar sizes and distances.
4: List the classes of binary stars and state the criteria for determining membership in each.
5: Draw, label, and describe a graph of the mass-luminosity relation and specify limitations on its applicability.
6: Explain the characteristics of the radial-velocity curves for binary stars.
7: Describe the differences between the light curves for total and partial eclipsing binary stars.