Population III

1
Population III

• Common name for the first generation of stars
• Implies zero metallicity, where zero is the big
  bang abundance of elements ? 12C of 10-12
• May include extremely massive objects gt 150 M?
• Low z physics issues must be handled carefully

2
Consequences of low z

• Ionizing radiation
• low z ? low opacity, so ZAMS Pop III stars will
  be compact with high Teff
• Mass loss
• winds driven by line or continuum opacity, so
  PopIII stars should have weak winds BUT
• Very massive objects may be subject to
  eruptions/instabilities driven by H and He
  opacity bumps
• Self-enrichment by mixing of nucleosynthesis
  products due to rotation and waves - no Fe peak,
  but CNONe contribute to ?

3
Consequences of low z

• nuclear burning - stars have to run on PP chain -
  not enough energy generation to support star
• continues to contract until Tcore 108K - 3?
  starts producing CNO catalysts
• Once XCNO gt10-9 CNO cycle can produce enough
  energy to support star
• depending on degree of rotational and wave
  mixing, RGB (core He burning) may take place at
  Teff of main sequence

4
Very Massive Stars
5
Humphreys-Davidson Limit

• Luminous stars observed to have a lower limit on
  Teff dependent on L
• No stable stars observed in cool, high L portion
  of HR diagram
• Stars in outburst excurse into forbidden region

6
Luminous Blue Variables

• S Doradus type eruptions
• Highly irregular lightcurves
• Eruptions last for hundreds of days
• Photosphere is a massive, optically thick wind
  during eruption at 7000-9000 K - resembles an A
  hypergiant
• Wind velocities of a few hundred kms-1
• Between eruptions star has Teff gt 15,000K and
  lower mass loss rate, faster wind
• Bolometric luminosity of star roughly constant

7
Luminous Blue Variables

• ? Car type eruptions
• Highly irregular lightcurves
• Eruptions last for tens of years
• Bolometric luminosity of star increases
  considerably
• ? Cars Great Eruption released 1049 erg luminous
  energy 1050 erg kinetic energy
• Great eruption ejected 10 M? of material
• Material is partially CNO processed
• followed by 2nd smaller massive eruption 50 yrs
  later, many small outbursts

8
Luminous Blue Variables

• Car type eruptions
• No star observed to have multiple great eruptions
  - duty cycle gt centuries, but multiple shells
  around ? Car
• Massive dust production - visual magnitude
  declines precipitously after eruption
• Very high 10-2 - 10-1 and velocities of
  few 100 kms-1 with 10-3-10-4 currently
  with 1000 kms-1
• Zwickys Type V supernovae

9
Luminous Blue Variables

• Mechanism
• Uncertain but probably opacity driven

10
Luminous Blue Variables

• Mechanism
• Uncertain but probably opacity driven

11
Luminous Blue Variables

• Mechanism
• Uncertain but probably opacity driven

12
Luminous Blue Variables

• Mechanism
• Uncertain but probably opacity driven