atoms and atmospheres in strong magnetic fields · atoms and atmospheres in strong magnetic fields...
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![Page 1: Atoms and Atmospheres in Strong Magnetic Fields · Atoms and Atmospheres in Strong Magnetic Fields Wynn C.G. Ho School of Mathematics, Southampton MICRA2009 – 2428 August 2009 Gilles](https://reader035.vdocuments.mx/reader035/viewer/2022070905/5f73832b3c3f6a37de3c475e/html5/thumbnails/1.jpg)
Atoms and Atmospheres inStrong Magnetic Fields
Wynn C.G. HoSchool of Mathematics, Southampton
MICRA2009 – 2428 August 2009
Gilles Chabrier Ecole Normale Superieure de Lyon, CRAL, FrancePhilip Chang University of California, Berkeley, USADavid L. Kaplan – University of California, Santa Barbara, USADong Lai Cornell University, USAKaya Mori – Columbia University, USAAlexander Y. Potekhin Ioffe PhysicoTechnical Institute, RussiaMatthew van Adelsberg – University of California, Santa Barbara, USA
Collaborators
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Neutron StarSurface Emission
• Atmosphere scale heightH∼ 1 cm << R
• Chemically homogeneous
• Emission is anisotropic and polarized in magnetic field
• Vacuum polarizationimportant at B > BQ = me
2c3/eℏ = 4.4 × 1013 G
• Atomic structure altered by magnetic field⇒ bound atoms must betaken into account
Weber (2005)
Weber (2005)
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Atoms inStrong Magnetic Fields
• Atomic structure altered by magnetic field when
B > B0 = e3me2c/ℏ3
= 2.35 × 109 G
• Binding energy ~ (ln b)2
• L⊥ ~ b1/2
• Lz ~ (ln b)1
where b = (B/B0)
B = 1012 GEbind = 160 eV
B = 1013 GEbind = 310 eV
B = 1014 GEbind = 540 eV
B = 0Ebind = 13.6 eV
B
INSs (and some pulsars) have B > 1012 G and kT ∼ 100 eV!
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Model Atmosphere Spectra
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NSMAX (in XSPEC): Magnetic Atmosphere Modelshydrogen
silicon
carbon oxygen
neon
helium1012 G 1013 G1012 G1013 G
5 other magnetic fields
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nonmagnetic or magnetic but fullyionized hydrogen
magnetic partiallyionized hydrogen?
Spectral Models forRX J1856.53754 •Dim isolated NSs, aka,
“Magnificent Seven”•Thermal emission
•No spectral features•One BB underpredicts optical by 7•Two blackbodies
•kTX∞ = 63 eV, RX
∞ = 5.1 km
•kTopt∞ = 26 eV, Ropt
∞ = 21 km•Atmosphere overpredicts » 1 •Xray pulsations
•spin period = 7 s•pulse fraction ≈ 1%
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Magnetic Hydrogen Atmosphere Model for RX J1856.53754 •One BB underpredicts optical by 7
•Two blackbodies•kTX
∞ = 63 eV, RX∞ = 5.1 km
•kTopt∞ = 26 eV, Ropt
∞ = 21 km•Single atmosphere spectrum
•thin hydrogen atmosphere•Bp ≈ (67)×1012 G•kT∞ = 43 eV, R∞ ≈ 17 km•zg≈ 0.22⇒ R ≈ 14 km
•Xray pulsations•spin period = 7 s•pulse fraction ≈ 1%
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to observer
Constructing Model of Neutron Star Surface Emission
• Stitch together local patches of atmosphere with different Teff and B• Integrate total surface emission, including effect of gravitational
lightbending [redshift = (1 2GM/c2R)1/2]• Resulting emission depends on two angles (, ):
– = angle between rotation axis and observer– = angle between rotation and magnetic axes
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Neutron Star Geometry fromPulse Profiles and Phaseresolved Spectra
•realistic neutron star surface•magnetic fields•temperatures•light bending
•rotating star⇒ modulation of brightness and spectrum
to observer
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•Emission model with (Teff , Bp)surface distribution and relativistic effects
•Bp ≈ (67)×1012 G•kT∞ = 43 eV•R∞ ≈ 17 km•zg≈ 0.22• or < 6°• or ≈ 2045°
Surface Model for RX J1856.53754 and Phaseresolved Spectra
to observer
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(Yakovlev & Pethick 2004)
Physics fromRX J1856.53754
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Cassiopeia A Supernova Remnant
•Atoms altered when B > 2.35 × 109Z2 G with Ebind > 160 eV
•Observed neutron stars have B > 1012 G and kT ∼ 100 eV