Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 17, Problem 65Q
To determine
The difference between red and blue main-sequence stars.
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Using solar units, we find that a star has 4 times the luminosity of the Sun, a mass 1.25 times the mass of the Sun, and a surface temperature of 4090 K (take the Sun's surface temperature to be 5784 K for the sake of this problem). This means the star has a radius of.................... solar radii and is a .................... star (use the classification).
Assume that an O main-sequence star (40,000 K) and a G main-sequence star (5,500 K) have the same radius. How many times brighter is the O star?
LO
LG
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Star B is located 2.6 times farther from earth than Star A, but both have the same apparent visual magnitude of 1 mag. Which star is intrinsically brighter?How many times brighter is the star?
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Chapter 17 Solutions
Universe: Stars And Galaxies
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- Which of the following can you determine about a star without knowing its distance, and which can you not determine: radial velocity, temperature, apparent brightness, or luminosity? Explain.arrow_forwardAccording to the text, a star must be hotter than about 25,000 K to produce an H II region. Both the hottest white dwarfs and main-sequence O stars have temperatures hotter than 25,000 K. Which type of star can ionize more hydrogen? Why?arrow_forwardIf a star has a surface temperature of 3000 K but a luminosity 150 times greater than our Sun, what size is this star? Give your answer in units of the solar radius, R .arrow_forward
- The sketch below shows an H-R diagram for a star cluster. Consider the star to which the arrow points. How is it currently generating energy? Temperature A. by hydrogen shell burning around an inert helium core B. by gravitational contraction C. by core hydrogen fusion D.by core helium fusion combined with hydrogen shell burning E. by both hydrogen and helium shell burning around an inert carbon core Luminosity -→arrow_forwardThe mass-luminosity relation describes the mathematical relationship between luminosity and mass for main sequence stars. It describes how a star with a mass of 4 M⊙ would have a luminosity of ______ L⊙. If a star has a radius 1/2 that of the Sun and a temperature 4 that of the Sun, how many times higher is the star's luminosity than that of the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125) If a star has a radius 2 times larger than the Sun's and a luminosity 1/4th that of the Sun, how many times higher is the star's temperature than that of the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125) If a star has a surface temperature 2 times lower than the Sun's and a luminosity the same as the Sun, how many times larger is the star than the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125)arrow_forwardSuppose a star has a luminosity of 7.0x1026 watts and an apparent brightness of 4.0x10-12 watt/m?. How far away is it? Give your answer in both kilometers and light-years.arrow_forward
- 12: A star with spectral type A0 has a surface temperature of 9600 K and a radius of 2.2 RSun. How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) Answer: 36.854 13:This star has a mass of 3.3 MSun. what is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Please answer question 13 thank you.arrow_forwardZebulon is a binary star system composed of a 10 M sun main sequence star and a 1 M sun red giant. Is this strange? yes or no. explain the reasoning.arrow_forwardA star has a surface temperature of T = 10,000 K and a radius three times that of the Sun, R = 3R (recall that symbolizes the Sun). What is its luminosity, L, in units of solar luminosities, L ? Give your answer to three significant figures. answer, expressed in solar luminosities, tells how many times more luminous this star is than the Sun.arrow_forward
- "51 Pegasi" is the name of the first normal star (besides the Sun) around which a planet was discovered. It is in the constellation Pegasus the horse. Its parallax is measured to be 0.064 arcsec. a. What is its distance from us? b. The apparent brightness is 1.79 × 10-10 J/(s·m2 ). What is the luminosity? How does that compare with that of the Sun? Look up the temperature: how doarrow_forwardWhat is the life expectancy (in years) of a 10 M⊙ main-sequence star? What is the life expectancy (in years) of a 70 M⊙ main-sequence star?arrow_forwardStar A and Star B are both on the main sequence. Star A is 74 times more luminous than Star B. What is the ratio of their main-sequence lifetimes? Hint: Refer to the stellar life expectancies equation,arrow_forward
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