What Are Population I and Population II Stars?

[randa177]

Can anybody explain to me what a Pop. I object is?

 

[randa177]

The youngest stars, including the Sun, that have the highest metal content, are known as Population I stars.

 

[SpaceTiger]

I guess you answered your own question...

Anyway, the Population I/II distinction is fairly arbitrary, but is based on an apparent bimodality in the metallicity distribution of the Milky Way. Pop I objects probably formed later than Pop II objects and were therefore made from gas that had already been polluted with a lot of heavy metals (mainly by supernovae). This type of star dominates the thin disk of the Milky Way, while the halo is dominated by Pop II objects.

 

[Astronuc]

Some discussions on Pop I and Pop II objects/stars, what they are and where they are:

http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/pop12.html

http://www.astro.umd.edu/educationalresources/astro/mw/pop.html

http://www.aoc.nrao.edu/~smyers/courses/astro12/L21.html#pop

http://www.astronomy.ohio-state.edu/~dhw/Intro/lec17.html

17.4 POPULATION I
The two stellar populations differ from each other in spatial distribution, age, and composition.

Features of Population I:
• occurs in disk
• old and young stars
• open clusters (and isolated/binary stars)
• roughly solar metallicity
[typical composition 70% hydrogen, 28% helium, 2% metals]

Associated with Population I:
• interstellar gas and dust
• star-forming gas clouds
• Type II supernovae

17.5 POPULATION II

Features of Population II:
• occurs in spheroid, especially the stellar halo
• old stars only (no blue main sequence stars)
• globular clusters (and isolated/binary stars)
• low metallicity, 1/1000 to 1/100 solar
[typical composition 75% hydrogen, 24.99% helium, 0.01% metals]

Associated with Population II:
• very little interstellar gas or dust
• no star formation
• only Type I supernovae

So where is the cutoff between Pop I and Pop II in terms of metallicity? 0.1% or 1% metals?

Interesting how Pop I stars are associated with Type II SN and Pop II stars are associated with Type I SN.

How Population I and II relate to Galaxies - http://www.astro.psu.edu/users/kluhman/a1/lec25.html

Milky Way Spiral Structure - http://www.seds.org/messier/more/mw_arms.html

http://articles.adsabs.harvard.edu/cgi-bin/nph-build_image?bg=%23FFFFFF&/seri/AJ.../0062/600/0000146.000&db_key=AST&bits=4&res=100&filetype=.gif