Metal production at M_i < M_up

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Metal production at M_i lt M_up Supernovae

• Dong-hyun Lee

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Metal production at M_i lt M_up

• M_i initial mass, M_up 8M_?
• Form white dwarfs, contain most of the C, O,
  alpha elements
• In a naïve picture enrich the ISM only with He
• More realistic dredge products up from their
  interiors into their envelopes
• Need to know the diff. b/w abundances of the
  ejecta those characteristic of the ISM nearby
• These diff. is largest to measure in sys.s with a
  metal-poor ISM, such as the SMC N/H is larger
  in planetaries than in HII regions by 1dex cf)
  In LMC Galactic planetaries .8, .4 dex
• Enhanced production of N when C nuclei absorb
  the neutrons
• Planetary nebulae important source of s-process
  elements
• M_i lt M_up plays an important role in the
  chemical evol. of galaxies, especially early on
  when the ISM is rel. metal-poor
• Unfortunately, difficult to determine the rate at
  which these stars pump freshly made metals into
  the ISM
• Models of stellar evol. Cannot predict the mass
  of heavy elements

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Supernovae

• Supernovae the prime sources of both iron-peak
  r-process nuclei
• Classified according to spectra near max.
  brightness
• Type? contain H lines , Type? do not
• Type?a absorption due to Si , Type?b all
  others
• Type?b He lines, physically more closely rel.
  to Type?
• Type?a quite tightly bunched peak around 9.6e9
  L_? , Type? span a broader range peaks (0.4e9,
  4e9) L_?
• Type? do not occur in early-type galaxies,
  Type?a occur in all types
• In spiral galaxies, Type? tend to occur in spiral
  arms. Cf) Type?a do not
• Spiral arms short-lived massive stars
• In the Milky Way, supernovae rate one per 40yrs
  ( 15 Type?a)
• Core-collapse supernovae both Type?b Type?
  when a high-mass star, Type?b lost their H
  envelopes, either to a stellar wind or a binary
  companion, before suffering core collapse. At the
  moment of core collapse, these have He rather
  than H envelopes -gt fail to display H lines
• Type?a thermonuclear explosion of a C/O white
  dwarf lt- triggered by the accretion of material
  from a binary companion

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Supernovae

• Metal production by core-collapse supernovae
• How much of the star will be blown away by the
  imploding core
• What changes will occur in its chemical
  composition as it is blown away
• 99 of the E released emerges in a vast blast of
  neutrinos
• Extremely hard to determine tiny (1) fraction
  of the E of implosion is transferred to the
  stellar envelope to determine whether the
  envelope is ejected a supernova produced.
• Some implosions may not produce readily
  detectable EM radiation
• Rough-and-ready treatment mass-cut
• define a radius within the pre-collapse star
  such that everything outside this radius is
  ejected everything interior falls in to form
  the remnant
• Shock wave induces a violent burst of nuclear
  reactions in the departing material substantial
  mass of Si is burnt to iron-peak nuclides
• During this nuclear flash, iron-peak elements are
  subject to intense neutron bombardment , many are
  converted to r-process elements
• Layers of material, C, O, alpha nuclides
  s-process nuclides are ejected by the shock

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Supernovae

• Metal production by core-collapse supernovae
  (continued)

• Obtained by calculating the composition of each
  star immediately prior to core collapse
  choosing a mass-cut
• 1st col. the mass of the He core at the onset
  of He burning what determines the subsequent
  evol. of the star
• 2nd col. initial mass that would lead to such a
  He core in the absence of mass loss

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Supernovae

• Study of the type? 1987A (McCray, 1993, ARA, 31 ,
  175)
• Spectacular burst of neutrinos carries away most
  of the E (only 10s)
• Its progenitor star He ignited when the He core
  contained 6 M_? it was a blue rather than a red
  giant from table1, its initial mass exceeded 20
  M_?
• Supernovas light emission was largely powered by
  the radioactive decay of 0.069M_? of 56 Ni to 1st
  56Co then 56Fe (after 100d explosion)
• Interval 100-300d, shape of the light curve
  declining exponential with a time-const.
  perfectly fits the 111.3d mean-life 56Co
  0.069M_? of 56Ni
• After 300d, the light curve declined faster than
  exponentially the ejecta had become too
  rarefied to degrade into optical photons all the
  gamma rays carry much of the E released by the
  decaying Co
• Total kinetic E 1.5e44J in the ejecta.
• Outermost layers of the stars envelope were
  ejected at gt 20000km/s
• Structure of the envelope was made highly complex
  by the development of hydrodynamical
  instabilities soon after the passage of the blast
  wave

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Supernovae

• Metal production by Type?a supernovae
• Progenitors C/O white dwarfs by accretion from
  a binary companion achieve a mass 1.38 M_?, just
  smaller than Chandrasekhars liminting mass
• Electrons near the center are highly degenerate
  stars nuclear fuel is liable to ignite
  explosively (Box 5.1 5.2 in GA)
• A wave of burning sweeps through the star in
  which about half of the stars C O are
  converted to iron-group elements in about a
  second
• Predicted light-curve mix of nuclides produced
  by this event depend on the speed with which the
  wave sweeps through the star
• Deflagration wave propagates nearly as fast as
  the sound speed but not as fast or faster for a
  discussion of the dynamics of Type?a
• Explosion of a C/O white dwarf releases only 1
  of E that of type?, but a large fraction of it is
  channeled into the kinetic E of the ejecta
• Mechanical E of Type?a is identical with the
  mechanical E of a core-collapse supernova 1e44J
  this E is concentrated in 1.4 M_? rather than
  over 10 M_? of ejecta, the characteristic
  ejection vel. Is larger
• The star leaves no remnant roughly 5-10times as
  much as 56Fe as SN1987A did ? significant sources
  of r-process elements