Astro 322 Stars in our Galaxy Jan. 9, 2009 Carroll & Ostlie, Fig. 12.3

Initial mass functions

• Turnover at low mass • Variation in high mass end

Ivan Baldry, LJMU How faint?

• HST on NGC 6397, 2nd nearest globular cluster • Identify faint white dwarfs, faintest M stars

Richer+06, HST Faintest stars

• Identify cluster stars by proper motions • Predicted stellar limit marked--0.08 Msun

Richer+06 Galactic Structure Supernova 1987a

• Ring illuminated months after SN • Brightened years later; SN shell impact

HST

NGC 891, KPNO/Barentine • Age vs. vz, for local F, G stars. • Pleiades cluster

Credit Lanoue • Black: 100 Myr • Green: no reddening • Blue: 16 Myr • Binaries above MS • Spread in MS due to age, metallicity, binaries • Subdwarfs ~1 mag left of MS

Hipparcos CMD Orion Nebula HST (NASA/ESA) Orion Nebula: optical vs. infrared, HST (NASA/ESA) • Globular cluster M15 Faint globular cluster Palomar 5

Courtesy SDSS • Tidal tails of Palomar 5 • Cluster being shredded

SDSS • Galactic orbit of Palomar 5

SDSS • CMDs of globular clusters • 47 Tuc 10x metals of M92 • Globular cluster M3 over 1 night • Note RR Lyrae stars

Hartman & Stanek Milky Way in near-IR, COBE

NGC 891, KPNO/Barentine Map of Milky Way, Spitzer Space Telescope Hydrogen lines Gross structure

Carroll & Ostlie Fine-structure transitions

• Fine structure: coupling of electron spin, orbit • Hyperfine structure: coupling electron spin, nucleus spin • Smaller energy jumps H1 21-cm Radiation

• “Forbidden”--low density • 21 cm accessible in radio Forbidden transitions

• Violate quantum selection rules • Low probability, occur slowly • Observed in low-density gas

Ring Nebula, HST HI throughout Galaxy

• Atomic H fills majority of volume of Galaxy Galactic rotation

• Vr=Vcosα-V0sin(ℓ) • Vr=R0sin(ℓ)(V/R-V0/R0) • V/R drops with radius Carroll & Ostlie 21-cm velocities

• Tangent points: rotation curve • Uncertainties Milky Way rotation