Download - Jan 7, 2009
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1 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Jan 7, 2009
The Interstellar Interaction Observed
N. A. Schwadron, J. Richardson, P. Wu, and C. Prested, D. McComas, and the IBEX-Hi and IBEX-Lo
Teams
The Interstellar Interaction Observed
N. A. Schwadron, J. Richardson, P. Wu, and C. Prested, D. McComas, and the IBEX-Hi and IBEX-Lo
Teams
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2 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Outline
• What we have learned about heliospheric asymmetries and energy distributions
• Implications for Models of ENAs
• Some Necessary Complications━ 100 AU to 1 AU━ Response Functions of the Sensors
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3 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Interstellar Interaction Components
• Outflowing solar wind contributes vast majority of Ram Pressure━ Time-dependence through Merged Interaction
Regions and Solar Cycle and longer term variations
━ Heliospheric Magnetic Field (Heliospheric Falts?)
• The Local Interstellar Cloud━ Inflowing neutral atoms give rise to a hydrogen
wall━ Pickup Ions Carried Out By the Solar Wind
(leading to ACRs)━ Interstellar Magnetic Field
• Energetic Particles━ Galactic Cosmic Rays ━ Anomalous Cosmic Rays━ Suprathermal Tails
• Dust, Grains━ From interstellar medium━ Kuiper Belt grains ━ Outer Source for Pickup Ions (heavy
composition)Courtesy Muller et a, 2006l
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4 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Where is the Nose?
• Predominantly a mix of H, He, O (neutral and singly ionized particles, GCRs and dust
• High FIP neutrals penetrate deeply into the heliosphere (observed as neutrals and Pickup ions)
• Gravitational focusing (radiation press. Negligible)• He neutral atoms measureed directly (Ulysses) and from Pickup Ions provide
our best mesaurement of interstellar flow direction (Witte et al., 1992, 2004; Moebius 2004, Gloeckler et al, 1996)━ Velocity = 26.3 0.4 km/s━ T = 6300 340 K━ Ec. Long.(J2000) = 75.4 0.5━ Ec. Lat. = 5.1 0.2━ n = 0.015 0.002
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5 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Evidence of N/S Asymmetry from H
• Interstellar H observed ━ Ly-━ Pickup ions━ Inferences from Mass Loading
• H experiences significant interaction (charge-exchange) in the heliosheath ━ inflow speed ~20 km/s, 6 km/s less
than He, and higher 1600 K temp (Lallement et al., 1993)
━ SOHO/SWAN indicates flow deflection by ~4 (Lallement et al., 2005)
━ Filtration in the heliosheath lowers the density relative to the interstellar medium
• LISM H - Nint~0.20.03 cm-3
• Filtered H - Nfilt~0.1 cm-3
Latitude
Longitude
Lallement et al., 2005
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6 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Asymmetry due to the Interstellar Magnetic Field(?)
• Field strength thought to be ~1 G; upper limit 2-4 G
• Deflection of H observed by SOH/SWAN suggests effect of asymmetric interstellar magnetic
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7 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Voyager 1 Unveils the Heliosheath
• The Source of Anomalous Cosmic Rays Missing from near the nose of the termination shock
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8 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Effects of a Blunt Termination Shock
• Acceleration of ACRs requires ~ 1 year (Mewaldt et al., 1996)
• This timescale is similar to that of the motions of field lines from the nose back to the flanks and tail of the termination shock
• But recent simulations (e.g., Pogorelov et al., 2006,8) show a more symmetric TS due to neutral interactions
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9 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
• Speed decrease starts 82 days, 0.7 AU before TS (but TS is likely moving outward).
• Crossing clear in plasma data
• Flow deflected as expected
• Crossing was at 84 AU, 10 AU closer than at V1
V2 crosses the TS In Aug. 2007 at 84 AU V
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10 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
• Purpose of shock is to make flow subsonic
• BUT, flow remains supersonic wrt thermal plasma in heliosheath.
• Energy must reside in pickup ions. Pickup ion energy must be 6-10 keV
TS
Pickup Ions Carry Substantial Energy
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11 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Decreasing Solar Wind Ram Pressure
Time
• Solar wind Ram Pressure decreasing with time • At least part of the reason for the differences in TS location observed
by V1/V2• Solar wind Ram Pressure, Energy, Density Correlated with Magnetic
Flux (Schwadron and McComas, 2003, 2006, 2008)
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12 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
How Big a Change in Ram Pressure between V1/V2 Crossings
• V1 Crosses Dec, 2004 at 94
• V2 Crosses Aug, 2007 at 84 AU
• Dynamic Pressure Changes in Fast Wind ~30%
• Dynamic Pressure Changes in Slow Wind much smaller
McComas et al., 2008
Note ~1 year lag
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13 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
N/S Asymmetry Reflected by V1-V2 Differences
• Models of TS (e.g., Pogorelov et al, 2006, Opher et al., 2006, 2007) generally show V2 closer than V1 by ~ 10 AU at a given time
• The distance observed by V1-V2 difference reflects, in part, a real N/S asymmetry Richardson et al., 2006
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14 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Summary of Observational Evidence
• Where’s the nose?━ He neutral observations (Ulysses) give us our main sense of direction
• Nose/Tail Asymmetry━ Predicted from Models━ Possible Evidence for Blunt Termination Shock from Absence of ACRs near
Nose━ Overall bluntness debated -- new models including neutral interactions
show more spherical shock
• North/South Asymmetry ━ Ly- observations suggest N/S asymmetry, possibly due to asymmetry in
interstellar B━ V1-V2 difference in TS location also suggests this asymmetry━ Heliosheatht thicker in the North
• Voyager 2 seems to show dominance of the pickup ion energy ━ More consistent with the Gruntman et al (2001) weak shock limit
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15 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
How does it Look in ENAs?
Maxwellian,
Opher Model
Kappa Dist.
Opher Model
Kappa Dist.
Pogorelov Model
0.45
keV
1.1
keV
2.6
keV
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16 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Possible N/S Asymmetry Near the Nose
• ENA flux at 6.8 keV from Opher et. al’s (2006,2007) MHD model of the heliosheath plasma
• Kappa distribution is used with kappa = 2.67
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17 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Forward Modeling
• Acounts for:━ Loss by ionization━ Deflection by rad
pressure━ Energy change
through heliospheric transmission
━ Sensor response functions
• Geometric Factors
• Angular Response
• Energy Response
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18 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Global Forward Mapping
• Above 0.1 keV, the global symmetries of the heliosphere are preserved in ENA maps
• Reduction in magnitude due to ENA ionization-loss
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19 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Predicted ENA distributions near HSp nose for strong (black) and weak (green) TS [Gruntman et al., 2001]. ENAs >1 keV are accelerated inner heliosheath protons based on projecting observed distributions beyond TS.
Energy Spectra in Strong and Weak limits
• ENA energy spectra provide direct measures of ions beyond TS: ━ Solar wind━ Pickup Protons━ Energetic protons
• Spectra as a function of direction show 3D configuration of the shock and energy partition of the ions at the shock
• Spectra also provide information about how EP pressure modifies the TS and what types of injection processes may be at work there
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20 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Energy Distribution Mapping
• Energy dependent ..━ ENA ionization loss━ ENA deflection━ These effects are all stronger at low energies
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21 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
More dramatic Effects at Low Energies
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22 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Incident Flux at 1 AU
• We have 14 channels: {hide-1 .. hide-6, lode-1 .. lode-8}
• We have one (H) differential energy flux j(E) (O is later)
• The channels are coupled through the sensor response:
_hide-1hide-2hide-3hide-4hide-5hide-6_= R_
flux-1flux-2flux-3flux-4flux-5flux-6_
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23 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Orbit-Spin Frame
• The natural frame to work in for all of the above is a frame built around IBEX's mean spin for the orbit.
• For Direct Events the sky is well sampled in the spinward direction (α)
• No information in the transverse direction (β)
• Our collimators are narrow enough that the effects are negligible for the moment. (A 1D FFT can be used if desired.)
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24 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Follow Trajectory out to 100 AU
• Trajectory can be traced backwards
• This can be as simple or as complicated as you chose to make it
• Simplest central-force, constant-μ used here
• Can be easily made more sophisticated
• Survivability is important
• Deflection angle changes with energy
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25 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Collecting Multiple Orbits
• Combining orbits can be done in any frame--- used an ecliptic one here
• Exaggerated the deflection (δ) for two orbits that are weeks apart
• The flux from pixels at 1 AU will contribute to one or more pixels at 100 AU.
• Different part of the band refer to different HS energies (E)
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26 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
IBEX-Hi at 1.11 keV
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27 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Summary
• We are about to discover a new global view of the heliosphere from ENAs!
• We expect to see asymmetries━ Nose/Tail asymmetry (which one should be brighter, we don’t yet know)━ North/South asymmetry (perhaps). Brighter emissions from the North?
• The energy distribution━ Voyager 2 results suggest prominence of pickup ions━ Will we see a knee in the pickup ions━ Relative contribution of kappa function & pickup-like distribution?
• Model interface at the IBEX Science Operations Center━ A first version up and running
• Forward modeling interfaces to models (to be expanded as much as possible/desired)
• Reverse modeling account for heliospheric transmission effects
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28 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
View time per Pixel for 2 year Mission
Reduction in view time due to magnetosphere obscuration
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29 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
Gravitational Focusing and the H shadow
• Backscattered Ly- (Bertaux and Blamont,1971; Thomas and Krassa, 1971) and He 58.4 nm radiation (Weller and Meier, 1979) reveal radiation pressure at work
• Radiation pressure weak for He, gravitational focusing cone
• Radiation pressure comparable to gravity for H, interstellar H shadow
Secondary
component from
interaction
Primary
component from
itnerstellar flow
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30 N. A. Schwadron - Hawaii -2009 Interstellar Interaction Observed
The Effects of Dust
• Grains serve as a secondary source of pickup ions━ Inner &
outer source
• Pickup Ions accelerated into Low-FIP ACRs