Stellar populations

Stellar populations

Table
Stellar populations
Population I disk population Population II
extreme
Population I older
Population I intermediate
Population II halo
Population II
members gas A-type stars stars of galactic nucleus high-velocity stars with z-velocities >30 km/sec subdwarfs
young stars associated with the present spiral structure strong-line stars planetary nebulae (planetary nebula) long-period variables with periods <250 days and spectral types earlier than M5e globular clusters (globular cluster)
supergiants Me dwarfs novae (nova) RR Lyrae stars (RR Lyrae star) with periods
Cepheids (Cepheid variable) RR Lyrae stars with periods
<0.4 days
T Tauri stars (T Tauri star) weak-line stars
galactic clusters of Trumpler's class I
average height over galactic plane (parsecs) 120 160 400 700 2,000
average velocity perpendicular to galactic plane z(km/sec) 8 10 17 25 75
axial ratio of spheroidal distribution 100 ? 25? 5 2
concentration toward centre little little strong? strong strong
distribution extremely patchy; spiral arms patchy; spiral arms smooth? smooth smooth
age (109 years) 0.1 0.1–1.5 1.5–5.0 5.0–6.0 6
total mass
(109 suns) 2 5 47 (combined disk and intermediate Population II) 16
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Universalium. 2010.

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