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lec31 - Lecture 31 The Milky Way Kinematics Lecture 31...

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Lecture 31 The Milky Way: Kinematics Purdue University, Astronomy 364 1 Lecture 31

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Reminder HW07 is due NOW! HW08 has been posted. Lecture 31 Purdue University, Astronomy 364 2
Motion of Disk Stars Lecture 31 Purdue University, Astronomy 364 3 The Sun and other disk stars are not on perfectly circular orbits. They tend to undergo epicyclic motion around a mean circular orbit. Local Standard of Rest (LSR) A reference frame that has its origin at the Sun’s location (8 kpc from the Galactic center) and moves in a circular orbit with a velocity of 220 km/s. With respect to the LSR, the Sun moves at a speed of roughly 20 km/s.

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Peculiar Motion Lecture 31 Purdue University, Astronomy 364 4 The motion of a star with respect to the LSR is referred to as peculiar motion. Choose a cylindrical coordinate system with its origin at the Galactic center ( R=0, z=0 ). The azimuthal coordinate is =0 at the Sun’s location and increases in the direction of the LSR’s motion. The coordinates of the Sun are (R 0 , 0, z 0 )=(8 kpc,0,0 kpc). The velocity of the LSR is ( 0 , 0, Z 0 )=(0,220,0) km/s. The peculiar velocity of a star is: (u * ,v *, w * )=( *  0 , *  0 , *  0 ).
Example: the Sun Lecture 31 Purdue University, Astronomy 364 5

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