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# HW2_12 - r = 30 km/s Determine the galactic radius R of the...

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AST3019 Homework #2 Assigned: Feb. 2, 2012 Due: Feb. 16 1. Use Figure 16.6 in the textbook as a reference for the following problem. For material observed at a radial velocity v r along a line of sight at galactic longitude l, find an expression for the separation between the near and far points producing that v r . Leave your expression in terms of galactic radius R and longitude l. 2. Suppose the rotation curve of the Milky Way is flat out to 2R o . What mass does this imply out to that distance? How does this compare with the approximate number of stars in the Milky Way? 3. Calculate the Schwartzschild radius for a 5 million solar mass black hole. How does this compare with the sizes of structures measured near the center of the galaxy (e.g. the size of the radio source Sag A*)? 4. At a galactic longitude of 45 degrees, we observe v
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Unformatted text preview: r = +30 km/s. Determine the galactic radius R of the gas at this radial velocity and its distance from us, d. Use R o = 8.5 kpc and V o = 220 km/s. Refer to Figure 16.9 for the rotation curve of the Galaxy. 5. Determine the proper motion relative to the LSR for a star in circular orbit about the Galactic center at a distance d = 5 kpc from the Sun (LSR) and at a galactic longitude of 45 degrees. Assume a flat rotation curve for the Galaxy as in Figure 16.9. 6. Given the luminosity profile in eq. 17.1 used to describe elliptical galaxies, what would the luminosity be at a) r = r o , b) r = 2r o ? Use L(0) = 2 x 10 5 L sun /pc 2 . 7. Given the luminosity profile in eq. 17.2 used to describe the disks of spiral galaxies, what would the luminosity be at a) r = D, b) r = 2D? Express your answer in terms of L o ....
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