HW 10 - Entering the Universe

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University of Massachusetts, Lowell *

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1210

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Astronomy

Date

Oct 30, 2023

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pdf

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Tyler Opila Homework 10 Due: 11/6 11:59 pm Reading Chapters 17, 18, 20 Questions 1. (17.9) The star Antares has an apparent magnitude of 1.0, whereas the star Procyon has an apparent magnitude of 0.4. Which star appears brighter in the sky? The star Procyon is brighter because of its apparent magnitude is smaller. 2. (17.11) Order the seven basic spectral types from hottest to coldest. O, B, A, F, G, K, M 3. (18.31) Figure 18.7 shows the velocity of two stars in a spectroscopic binary system. Which star is the most massive? Explain your reasoning. 4. (20.18) Describe the spectrum of each of the following: a)starlight reflected by dust, b)a star behind invisible interstellar gas, and c) an emission nebula. A. The overall shape of the spectrum is like that of the star. The spectrum is slightly altered in that it will contain more blue and less red light than the original spectrum; due to the preferential scattering of blue light. B. The spectrum will look the same as for an unobscured star, except that it will be narrow absorption lines at certain wavelengths. C. The spectrum of an emission nebula is dominated by emission lines, mainly the Balmer line of hydrogen. Problems 5. (18.36) If two stars are in a binary system with a combined mass of 5.5 solar masses and an orbital period of 12 years, what is the average distance between the two stars? The average distance between the two stars is 792 light years 6. (20.36) H II regions can exist only if there is a nearby star hot enough to ionize hydrogen. Hydrogen is ionized only by radiation with wavelengths shorter than 91.2 nm. What is the temperature of a star that emits its maximum energy at 91.2 nm? (Use Wien’s law from Radiation and Spectra.) Based on this result, what are the spectral types of those stars likely to provide enough energy to produce H II regions?

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