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02/20/1962: John Glenn becomes 1 st American to orbit Earth “Evidence from the motions of old stars that the Galaxy collapsed” • Eggen, O.J., Lynden-Bell, D., & Sandage, A.R. 1962, ApJ, 136, 748 (ELS62) • • • 01/28/1962: Ranger 3 misses Moon by 22,000 miles
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“Evidence from the motions of old stars that the Galaxy collapsed”•Eggen, O.J., Lynden-Bell, D., & Sandage, A.R. 1962, ApJ, 136, 748 (ELS62)• • •
01/28/1962: Ranger 3 misses Moon by 22,000 miles
04/26/1962: Ranger 4 impacts Lunar surface without returning any scientific data
Olin J. Eggen (1919-1998): Renowned observer. In addition to ELS62, known for work on moving groups and pioneering work on discovering white dwarfs. 346 refereed publications on ADS, ~90% single author.
Donald Lynden-Bell (1935-): Famous for theoretical work on dynamics, black holes, accretion disks, and more. Two appearances on list of eligible papers for this seminar.
Allan R. Sandage (1926-): Famous observer. Known for galaxy atlases, work on quasars, and insistence that H0≈50 km/s/Mpc. 337 refereed publications on ADS, 220 first author.About the Authors• • •
Evaluate b using Oort constants A=15 km/s/kpc and B=–10 km/s/kpc, and assuming R0=10 kpc and vc0=250 km/s b=2.74 kpc.
For stars in the solar neighborhood, use observed space motions ( U´,V´ ) to calculate orbit. Define:
Calculated eccentricity becomes simply a measure of non-coplanarity
(1) Galactic potential was always axisymmetric
(2) Stars do not exchange angular momenta with each other or with gas
Stars conserve their angular momenta
(1) Slow: little change during one orbital period
(2) Rapid: large change during one orbital period
small change in eccentricity
On average, eccentricity increases
Dark circles: stars with accurate space motions
Light circles: stars with large space motions
Age correlates with eccentricity.
Age anti-correlates with angular momentum.
Dark circles: large (U-B)
X’s: intermediate (U-B)
Light circles: small (U-B)
Makes sense if stars form preferentially near apocenter
Stars form with low eccentricities
Large eccentricities never occur
CDM theory hierarchical structure formation
“Science may benefit very much (or only very little) from what we do, but since we do it for ourselves, for the satisfaction of our own curiosity, we should be thankful for the circumstances that permit a life in the dark.”
-Olin J. Eggen, “Notes from a Life in the Dark”, 1993, ARA&A, 31, 1