NCP

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Galactic coordinates
in celestial equator plane
NCP
in galactic plane
galactic equator tilted 63 1/2 deg to
CE galactic center is toward Sagitarrius RA18h,
Dec -29deg
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Makeup of Milky Way Galaxy
Stars - Disk (O, B stars, SG, young to old open
clusters) Halo Bulge (RR Lyr,
globular clusters, MACHOs)
Gas - some in disk, hot gas in halo
Dust - in disk results in reddening E(B-V), Av
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DUST
m-M -5 5 log d A E(B-V) (B-V)observed -
(B-V)normal Av 3 E(B-V) 1 mag/kpc roughly

• Find E(B-V) from
• spectral type of star and observed B-V
• H? / H? ratio normal 3
• HI maps NH/E(B-V) 5x1021 atoms/cm2/mag
• 2200Å bump

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0
Extinction A(?)/E(B-V)
10
4
0
0
0
0
0
0
Wavelength (Å)
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Stellar Populations
z(pc) Age (109yrs) Z Distr
Examples
Extreme Pop I 120 0.04 patchy O,B,SG, open clusters Older
Pop I 160 0.1-10 0.03
patchy sun, A stars

Disk Pop II 400
3-10 0.02 smooth planetaries, RR
Lyr Intermed Pop II 700 10
0.01 smooth long P var Halo Pop II
2000 10 0.003 smooth
globular clusters
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Interstellar Gas

• optical absorption lines CaI, CaII, NaI
• HII regions (recombination around hot star)
  T10,000K, density 5000 ions/m3
• HI gas (21 cm) T100K, density 106 atoms/m3
• molecular clouds (radio) H2, OH, NH3 T10K,
  density 109 mol/m3
• X-rays (hot coronal gas) T 106K, density particles/m3

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Counting Stars D stars/unit volume Local
luminosity function stars/unit V with given Mv
total sky 4? steradians 41,253 sq deg for
solid angle ?, area ? r2 dV ? r2 dr N(r)
D(r)dV ? Dr2dr 1/3 Dr3 ? log r (m-M5)/5
0.2 m const (for given M) r 10(0.2mc) and
N(r) 10(0.6mc) since 100.6 4, expect
4xmore at m1 than m
dr
?r2
r
not observed
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Finding the mass of the Milky Way
Keplers law using suns orbit (P250 million
yrs, v250 km/s, a8kpc) mMW msun 4?2a3/GP2
1011M? Halo mass MACHOs, high vel stars Rotation
curve M rv2/G
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The Galactic Center (Sgr A)

• Evidence for a Supermassive BH at the center
• stationary (located at dynamic center of MW)
• energetic X-ray source
• small size (radio shows smaller than solar
  system)
• no visible object at opt nor IR from Keck images
• motions of nearby stars (1000s of km/s) imply 3
  million M?

• How does Supermassive BH form?
• stars in center are near sun)
• SN chain reaction could produce many stellar BHs
• collisions between BHs cause monster
  supermassive BH

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Galaxy Evolution

• Top Down large concentration of matter (1015M?)
  fragment into galaxies of 1012M?
• Bottom up small structures merge into galaxies,
  then clusters

• globulars formed 13 billion yrs ago
• collapse to disk
• star formation continued in disk
• collisions with dwarf galaxies add to halo
• in 5 billion yrs, collision with Andromeda
  could cause burst of star formation, uses up gas
  dust and turns MW into an elliptical galaxy

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Review of Astr 322- the Contents of the Milky Way
Content
Structure
Disk Bulge Halo Pop I Pop II Pop II
Stars Gas Dust Dark Matter
Hot, cold Av, E(B-V) MACHOs ?
Motion
Disk - LSR Halo - high v, elliptical
Viewing geometry
Single (sun), binary, clusters (open, globular)
Horizon (alt, azimuth) Celestial (RA,
Dec) Galactice (b, l)
Properties (d, T, L, Mv, spectra, mass,
radius) Evolution - low mass (T Tauri, MS, giant,
planetary, WD) - high mass (MS,
SG, SN, pulsar or BH) Variables - geometric,
eruptive, pulsating
Instrumentation
Telescopes (refractors, reflectors) CCDs,
spectrographs, Space