COSMIC PERSPECTIVE
COSMIC PERSPECTIVE
9th Edition
ISBN: 9780135729458
Author: Bennett
Publisher: PEARSON
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Chapter 15, Problem 58EAP
To determine

To Calculate: The stellar radii of the Sirius 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: Submit All Answers
Sirius A has a luminosity of 26 Lsun and a surface temperature of about 9400 K. Part A What is its radius? (Hint: See Cosmic Calculations 12.2: Radius of a Star.) Express your answer using two significant figures. m Submit Previous Answers Request Answer
Suppose 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.
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