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Galactic Astronomy


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

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

5.3.3 The accreting-box model
  • Initially total mass of gas and dust is very
  • Chemical evolution proceed according to close-box
  • 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.

  • 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

3 of all dwarf stars should be more metal poor
than 0.25Z_sun.
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.
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.

  • 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?

? Luminosity of old population is expected to be
a decreasing function of time.
  • 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.

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