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 26Q
To determine
The magnitude of star through a
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12.
A star with spectral type MO has a surface temperature of 3750 K and a radius of 0.63 Rsun: How many
times more luminous is this star than the Sun? (if it is less luminous enter a number less than one)
Answer:
Submit All Answers Last Answer: 0.0923
Incorrect, tries 1/5.
Hint: Use the Luminosity equation, which says that L is proportional to R^2 T^4. If you keep these as
ratios compared to the sun, your L will also come out as a ratio compared to the Sun.
This star has a mass of 0.4 Msun- Using the simple approximation that we made in class, what is the
main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr.
Answer:
Submit All Answers
Compare this to the lifetime of a MO star listed in Table 22.1 (computed using a more sophisticated
approach). Is the value you calculated in the previous problem longer or shorter than what is reported
in the table? (L for longer, S for shorter) (You only get one try at this problem.)
Answer:
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3. By how many magnitudes is a K5 I star more luminous than a K5 V star? How many times more
luminous is this?
(Hint: you may wish to review magnitude scale information given in Labs NO3 and N04.)
O 1, 2.5 times as luminous
O 3, 16 times as luminous
O 6. 250 times as luminous
O 12. 63.000 times as luminous
14 Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude?
(Neglect any effects that might be caused by interstellar dust and gas.)
A
B
C
D
Star 1 is 10 times more distant than Star 2.
The luminosity of Star 1 is a factor of 100 less than the luminosity of Star 2.
Star 1 is 100 times nearer than Star 2.
Star 1 is 100 times more distant than Star 2.
E Without first knowing the distances to these stars, you cannot draw any conclusions about how their true luminosities compare to each other.
Chapter 17 Solutions
Universe: Stars And Galaxies
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- The apparent magnitude of a star on earth was measured to be +2. The zenith angle was 45° and the optical depth TO = 0.14. What is the apparent magnitude of the star above the earth's atmosphere? Round your answer to three significant figures. %3Darrow_forwardQ9. If the luminosity of star B is 25 times the luminosity of star A, then find the distance of star A if you know that the two stars have the same brightness, and that star B is 10 astronomical leagues away from us. Use the relationship: BB V BA da dg Q10: If you know that the difference of the apparent magnitude between two stars is equal to 5 magnitudes. What is their brightness? Use this equation Am т 3D ть — т, — —2.5 logio Q11. If the apparent magnitude of the first star in a binary star system is equal 1m and the apparent magnitude of the second star is equal 2m. Calculate the apparent magnitude of the system. Q12. Calculate the distance of a star if you know that its absolute magnitude is equal to (2m) and its apparent magnitude (-2m).arrow_forwardQ10: If you know that the difference of the apparent magnitude between two stars is equal to 5 magnitudes. What is their brightness? Use this equation Am BB -2.5 log10 () = mb - ma = BA Q11. If the apparent magnitude of the first star in a binary star system is equal 1m and the apparent magnitude of the second star is equal 2m. Calculate the apparent magnitude of the system. Q12. Calculate the distance of a star if you know that its absolute magnitude is equal to (2m) and its apparent magnitude (-2m).arrow_forward
- . The spectrum of Star A peaks at 700 nm. The spectrum of Star B peaks at 470 nm. We know nothing about what stage of stellar evolution either of these stars are in. Which of the following are true? A. Star A has a higher luminosity than Star B. B. Star B has a higher luminosity than Star A. C. Star A is cooler than Star B. D. Not enough information to comment on their luminosities. E. B and C F. C and Darrow_forwardProblem 4. Stellar Temperature, Color, and Size a) (Palen, et. al., 2nd, Problem 45) Rigel has a Hipparcos parallax of 0.00412 arcsec. Given Rigel and Betelgeuse appear almost equally bright in the sky, i) which star is actually more luminous? ii) Betelgeuse appears reddish while Rigel appears bluish white. Which star is larger and why? b) (Palen, et. al., 2nd, Problem 46) Sirius is actually a binary pair of two A-type stars. The brighter and fainter of the pair is called the Dog Star and Pup Star, respectively (they are in the constellation Canis Major). The Dog Star is 6,000 times brighter than the Pup Star even though both stars are the same distance from us. Compare the i) temperature ii) luminosities iii) sizes (radii) of these two stars. (CALCULATE using the principles of brightness and the Stefan-Boltzmann law, do not look up the answers! HINT: Star letter type is a measure of temperature)arrow_forwardThe spectrum of a typical star shows absorption lines at different wavelengths than their laboratory values. If the observed wavelength is greater than its laboratory value of 656.3 nm, one can conclude that ... A. The separation between Earth and the star is decreasing. B. The separation between Earth and the star is increasing. O C. The separation between Earth and the star is unchanging D. No conclusion is possible.arrow_forward
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