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Galactic Astronomy

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Galactic Astronomy. 5.3.3 ~ 5.4.1. Kim, Dae-Won_at_???. 2007/04/09. ??? ... Chemical evolution proceed according to close-box model. ... – PowerPoint PPT presentation

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Title: Galactic Astronomy


1
Galactic Astronomy 5.3.3 5.4.1
  • Kim, Dae-Won_at_???

2
5.3.3 The accreting-box model
  • Initially total mass of gas and dust is very
    small.
  • Chemical evolution proceed according to close-box
    model.
  • After 90 of gas converts into star, roughly half
    of all stars will be more metal-poor than a third
    of the current interstellar abundance.
  • Now feed metal-free gas into the box.

3
  • Small additional mass
  • In a steady state, an exactly equal mass becomes
    locked up in stellar remnants.
  • Freshly heavy elemental
  • Thus, metallicity of the ISM will eventually
    settle to the value Z p.
  • The fraction of low-metallicity stars will be
    negligible.

4
3 of all dwarf stars should be more metal poor
than 0.25Z_sun.
5
5.4 Evolution of stellar populations
  • Even HST can obtain colors spectra for individual
    stars only if they line in the nearest galaxies.
  • What can we learn from the colors or the spectrum
    of integrated light?
  • Presumably, we will not be ale to reconstruct the
    galaxys CM from single spectrum.
  • We might hope to estimate the mean metallicity of
    the system and perhaps constrain its age.

The simplest case is that where all stars
formed at the same time.
6
5.4.1 Analytical results
  • Table 5.2 at P.271 and Figure 5.2 at P.266
  • Massive stars live less than 5Gyr. ? after 5Gyr,
    there remains only light stars.
  • Low-mass stars emit most of their light during
    1Gyr, say on the RGB, HB and AGB.

7
  • Effective T of RGB, HB and AGB change only slowly
    with the masses of stars on them for M lt 2M_sun.
  • But, luminosity will still be evolving.
  • Evolution of luminosity?

8
? Luminosity of old population is expected to be
a decreasing function of time.
9
  • Relation between heavy elemental and luminosity ?
    Luminosity vs. IMF
  • Suppose the heavy elementals were all contributed
    by massive stars of M_Z gt M_GB.
  • Suppose these massive stars return a fraction of
    f of their original mass to the ISM in the form
    of heavy elements.

10
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