The Sun as a Star

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The Sun as a Star
The Surface of the Sun and Its Structure
Outer Layers 3 distinct region Photosphere Chrom
osphere Corona
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Photosphere -- light sphere
The surface in visible light T 6500 - 4000
K Depth 100s kms
Granulation cellular pattern due to convection
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Chromosphere color sphere, seen at solar
eclipse
T 6000 - 100,000 K, 2000 km thick Hot, low
density gas, also granular appearance
supergranulation
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The Corona or Halo
T 1-2 x 106 K , extends millions kms Very
hot, low density gas
Source of energy to heat chromosphere and corona
??
Coronal holes -- in X ray images
Flux of charged particles solar wind - from the
holes, governed by magnetic fields Heating via
magnetic waves and mechanical flux from
convective layers deep in interior
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Sunspots and the Solar Activity Cycle
Appear dark lower temp. 4500 K vs 6000 K
Strong magnetic fields several thousand Gauss
normal Sun few Gauss Opposite polarity between
sides of a large spot group
Magnetic disturbance or storm
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The 11 yr sunspot cycle -- magnetic cycle every
22 yrs.
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Maunder Minimum and the little ice
age
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Solar Activity Prominences associated with
large spot groups
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Solar Flares -- most violent form of solar
activity
A sudden brightening, above large spot group,
between regions of opposite polarity
Outburst of charged particles (cosmic rays),
increase in high energy radiation
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Sunspots, prominences, flares all associated with
magnetic fields All increase and reach maximum
with 11 yr solar activity cycle
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The Solar Interior and the energy source of the
Sun and Stars
Gravitational (contraction/collapse)
Nuclear Fission --- radioactive elements
Nuclear Fusion --- ???
p p -gt ? How?
the Coulomb barrier
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Nuclear Fusion and Nucleosynthesis in the Stars
The proton-proton chain or hydrogen fusion,
requires 107o K
1. p p ? np e neutrino np
deuteron (deuterium)
2. d p ? n2p gamma ray
n2p 3He
3. 3He 3He ? 4He 2 p
Net Result -- 4H ? 1He
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Alternative -- CNO cycle in more massive stars
gt 2 Msun
The CNO cycle converts hydrogen to helium The
mass-12 isotope of C captures a proton and emits
a gamma-ray producing the mass-13 isotope of N.
N-13 is unstable and beta decays to the mass-13
isotope of C with a half-life of approximately 10
minutes. The mass-13 isotope of C captures a
proton and emits a gamma-ray to become the
mass-14 isotope of N. The mass-14 isotope of N
captures another proton and emits a gamma-ray to
become the mass-15 isotope of O. The mass-15
isotope of O undergoes a beta decay to become the
mass-15 isotope of N. The mass-15 isotope of N
captures a proton and emits an alpha-particle
(that is, a nucleus of helium) to close the cycle
and return to C-12.
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Beyond Hydrogen Fusion
He Fusion to Carbon, Oxygen 3He4 ? C12
C12
He4 ? O16 requires 108o K
C, O fusion to heavier elements up to Fe (iron)
requires 5 x 108o K C12 C12 ? Mg24 ,
O16 He4 ? Ca20
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The Solar Interior
Hydrostatic Equilibrium (Pressure) gas pressure
out gravity in
Thermal Equilibrium (Temperature) Energy (heat)
in Energy out gt Energy production rate
luminosity of the star
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Transfer of energy Radiative (inner) and
convection (outer) Random walk of photons