However gravity focuses stars and enhances cross

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Unformatted text preview: ASTR 323, SP13, Eric Agol ©2013 12 Outline: The Milky Way II •  •  •  •  •  Kinema8cs of the Milky Way Stellar collisions Oort constants GM (< R) 2 Rota8on curve VC ( R) = R Evidence for halo € 4/4/13 UW, ASTR 323, SP13, Eric Agol ©2013 14 Galactocentric Coordinates 4/4/13 UW, ASTR 323, SP13, Eric Agol ©2013 15 Local Standard of Rest (LSR) •  A star on a hypothe8cal circular orbit at distance of Sun from GC is LSR •  Sun is not on precisely circular orbit – moving about 13 km/s w.r.t. LSR •  Radial velocity: __ =Π- ΠLSR •  Azimuthal velocity: __ =Θ- ΘLSR •  Ver8cal velocity: __ =Z- ZLSR 4/4/13 UW, ASTR 323, SP13, Eric Agol ©2013 16 Kinema8cs of the Milky Way •  The velocity dispersion of the disk scales as: σz≈zdisk(4πGρ)1/2=(23 km/s)(zdisk/100pc)[ρ(M¤༊ pc- 3)]1/2; _______ components have _____ velocity dispersions •  ρ≈0.076 M¤༊ pc- 3; zthin ≈ 300 pc, so σz≈ •  Disk stars: ______angular momentum vectors •  Halo stars (& dark mager) have randomly oriented orbits è༎ low ________ __________ 4/4/13 UW, ASTR 323, SP13, Eric Agol ©2013 17 D...
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