rp-process nuclosynthesis in type i x-ray bursts
DESCRIPTION
Rp-process Nuclosynthesis in Type I X-ray Bursts. A.M. Amthor Church of Christ, Kingdom of Heaven National Superconducting Cyclotron Laboratory, Michigan State University Department of Physics and Astronomy, Michigan State University. Outline. Quick Review of X-ray bursts - PowerPoint PPT PresentationTRANSCRIPT
Phy 983 - Spring2005
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Rp-process Nuclosynthesis in Type I X-ray Bursts
A.M. AmthorChurch of Christ, Kingdom of HeavenNational Superconducting Cyclotron Laboratory, Michigan State UniversityDepartment of Physics and Astronomy, Michigan State University
Phy 983 - Spring2005
2AMA
Outline
• Quick Review of X-ray bursts
• Delineation of burst types by total accretion rate
• Method of breakout to start the rp-process in a mixed H/He burst
• Observations – compared to expectations
• Simulations
Phy 983 - Spring2005
3AMA
X-ray burst basics – mostly review
Accretion – of matter from companion star
Accumulation – of matter on the NS surface
Ignition – near the base of the accreted column
Explosion – runaway fusion chain reactions through the p and rp-process
Burst flux
Persistent flux
Interesting quantities are:
- the total mass accretion rate
- the specific accretion rate
- the ratio of persistent flux to burst flux
- the recurrence time
Also the burst duration and regularity
Bursts happen for :
M
m
rect
R
MGME
MeV
R
GMmp 200
dT
d
dT
coolingd reac.)(
18. 102 yrMMM sunEdd
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4AMA
Burst types(Assuming accreted material with )
For we have which allows unstable CNO H burning.
110102 yrMM sun KT 7108
For we have for which the HCNO cycle leads to stable H burning.
110102 yrMM sun KT 7108
BurstBurstdT
d
dT
coolingd CNO
)(
So for and the burst ignition will be by unstable 3
110102 yrMM sun KT 7108
BurstBurstdT
d
dT
coolingd 3)(
01.0CNOZ
110104.4 yrMM sun 110104.4 yrMM sun
Hrect
Pure He Burst
Hrect
Mixed H/He Burst
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5AMA
Breakout to Rp-process (H/He burst)
Significant boundaries in temperature vs. density for the development of the rp-process
3 4 5 6 7 8
9 10
11 12 13
14
C (6) N (7)
O (8) F (9)
N e (10)N a (11)
M g (12)
3 flow
Hot CNO cycle below curve a)
Beyond curve b) is dominantFpNe 2019 ),( Beyond curve a) is dominant
NeO 1915 ),(
By curve d) dominates the flow, then avoiding all decays up to that point
NapNe 2118 ),(
Beyond curve c) the rp-process rate is limited by decays not by
NeO 1915 ),(
Schatz, Phy 983 notes spring 2003.
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6AMA
Observations
Line for 1Mtrec
Extended study of GS1826-238
Measures total accretion rate
Increased total accretion rate for the same type of
burst
Reduced time to build to critical column depth
&
Increased temperature in accreted layer from gravitational energy
release
Reduced recurrence time
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7AMA
ms Oscillations
Strohmayer, T. E. and L. Bildsten, Compact Stellar X-ray sources, astro-ph/0301544 (2003).
From the neutron star binary 4U 1702-429
Oscillations likely caused by asymmetric burst ignition.
Frequencies closely related to the neutron star rotation frequencies.
Frequency drift possibly caused by expansion of the burning envelope during the burst.
Contraction recouples the envelope to the surface resulting in spin up approaching NS’s rotation frequency.
Spin up – Spin down ?
Burst rise – Burst tail ?
R
R
2
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8AMA
Unexplained observations
• LMXB with accretion rates consistent with steady bursting which show few or no bursts
• Transition between bursting regimes at total accretion rates not consistent with theory
• Large frequency drifts in oscillations
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9AMA
Simulations
van Wormer et al. ApJ. 432:326 (1994)
Truncated Network
1-Zone Model
Constant temperature
Constant density
Limited reaction network
Reaction Network Calculations
Given adequate hydrogen and slow cooling, burning would continue to a closed cycle in Sn, Sb, and Te.
Phy 983 - Spring2005
10AMA
Newer model calculations
Multi-Zone/1d-Model
Variable temperature
Variable density
1300 isotopes in adaptive network
Convective and semiconvective mixing and energy transport
Compositional inertia in burst trains
Still assumes spherical symmetry!
Phy 983 - Spring2005
11AMA
Thank you – any questions?
?