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Sun Table 1 Center Gal. long. Vr (km/s) parallax(") (degs) Disc 5.9 12 0.000556 The galactic coordinates use the 2 10 179 0.000125 Sun as the origin. Galactic longitude (l) is measured with primary direction from 15 20 0.000455 the Sun to the center of the galaxy in the galactic plane, while the galactic 17 24.2 0.000455 latitude (b) measures the angle of the object above the galactic plane. 20 138 0.000116 3) (10 points) High spatial and spectral resolution 29 52.4 0.000286 observations of Galactic HII regions at a variety of 39.9 48.1 0.000417 different Galactic Longitudes have provided 53.6 24 0.000909 measurements of their parallax and radial velocity (with respect to the Sun). These kinds of observations are used 63.1 22.2 0.000250 to construct a rotation curve for the Galaxy. In the 84.6 0.001250 calculations below, use Ro = 8.5 kpc and Vo = 220 km/s. a) (6 pts) Using the data in Table 1, calculate the 90.2 -60 0.000208 Galactocentric radius (R in kpc) and angular 102.9 -48.5 0.000238 orbital velocity (w in km s-1 kpc-1) of each HII 110.1 -51 0.000156 region. You may assume that b = 0° for each object. Make sure you show how the calculations 174 -7.2 0.000313 192.1 22.8 0.000120 are done (i.e. provide the equations and any needed diagrams to explain your calculations), show a sample calculation for the first object in the table, and then provide the rest of your results by adding 2 columns to Table 1. b) (4 pts) Plot w VS R and find the best power-law fit to the data i.e. in the form w = a R-° (km S providing you with a rotation curve for the Galaxy. 4) (10 points) The following spectrum is of the J = 7 - 6 transition of CS (carbon monosulfide; Vrest = 345.796 GHz) taken from the Caltech Submillimeter Observatory and indicates the presence of warm, very dense gas (making it an ideal spot for a star to form). Using the Galactic Rotation curve you defined in question 3, calculate the possible kinematic distances to this molecular cloud (i.e. distance from Earth) if its Galactic longitude (1) is 14.17° and its Galactic latitude (b) is 0° 1 0.5 TT 0.5 20 30 40 50 60 Velocity (km/s)

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