Jeffrey L. Linsky JILA and the Department of Astrophysical and Planetary Sciences

1. When Space Plasmas Collide: Understanding the Interactions between the Solar Wind and the Interstellar Medium Jeffrey L. Linsky JILA and the Department of Astrophysical and Planetary Sciences University of Colorado Boulder CO USA 7-8 June 2007 In collaboration with: Seth Redfield (University of Texas) Brian Wood (University of Colorado)

2. Seminar Outlinehttp://www.astro.uu.se/forskarutb/long_term_V06.html • Structure of the heliosphere and local interstellar medium • Plasma and kinetic models of the outer heliosphere • What has Voyager I told us about the termination shock? • Observations of neutral hydrogen in the heliosphere from Lyman-αbackscattering • The ISM: theory and reality • Measuring the properties of interstellar clouds • Constituents of the Local Bubble (gas, dust, magnetic fields) • Astrospheres and winds of dwarf stars as a function of activity and age

3. The Dynamical Structure of the Local Interstellar Medium Seth Redfield (University of Texas at Austin) Adapted from Mewaldt & Liewer (2001)

4. The Dynamical Structure of the Local Interstellar Medium Seth Redfield (University of Texas at Austin) Adapted from Mewaldt & Liewer (2001)

5. Plasma and Kinetic Models of the Outer Heliosphere: Two Important Reviews • B. Wood (2004) “Astrosphere and Solar-like Stellar Winds” Living Reviews in Solar Physics, Vol 1, No.2. • G. P. Zank (1999) “Interaction of the Solar Wind with the Local Interstellar Medium: A Theoretical Perspective”, Space Science Reviews Vol. 89, 413.

6. Solar Wind Properties • Mass flux ~2x10^-14 solar masses/yr with little variation. • Fast speed wind in open field regions (~800 km/s). • Slow speed wind in magnetically complex regions (~400 km/s).

7. Heliosphere/ISM Interaction Terminology • Termination shock: where the supersonic solar wind (400-800 km/s) becomes subsonic and heated (94 AU for Voyager 1) • Heliopause: Interface around the Sun between the subsonic solar wind and ISM plasma (~150 AU) • Bow shock: where the incoming ISM (26 km/s) becomes subsonic (~250 AU). May not shock depends on magnetic field. • Hydrogen wall: Pileup of neutral H gas mostly in upwind direction with charge exchange (150-250 AU) • Plasma models: include electromagnetic and gravity forces on all ionized particles (either as one or multifluid models) • Kinetic models: treat neutral particles (e.g. H) with long path lengths by Boltzmann equation or Monte Carlo techniques. • Pickup ions: interstellar neutrals that are ionized (photoionization or charge exchange) and captured by the solar wind magnetic field and accelerated at the termination shock.

8. Heliosphere/ISM interaction: Examples of Code Types • Monte Carlo codes beginning with Baranov & Malama (1993, 1995). • Hydrodynamic four-fluid codes beginning with Zank et al. (1996) (one fluid for protons, 3 fluids for hydrogen:primary, secondary, tertiary atoms) • Hybrid codes beginning with Muller et al. (2000). • MHD codes (cf. Opher 2004).

9. Interaction of Stars with their LISM Heliosphere is the structure caused by the momentum balance (v2) between the outward moving solar wind and the surrounding interstellar medium. Magnetized solar wind extends out to heliopause, diverts plasma around Solar System, and modulates the cosmic ray flux into Solar System. Most neutrals stream in unperturbed, except neutral hydrogen, which due to charge exchange reactions, is heated and decelerated forming “Hydrogen Wall” (log NH (cm-2) ~ 14.5). Reviews of heliospheric modeling: Wood (2004), Zank (1999), and Baranov (1990). Reviews of interaction of LISM with heliosphere: “Solar Journey” Frisch (2006), and Redfield (2006) Müller (2004)

10. Zank & Frisch (1999) How large of a density increase is needed to significantly alter the structure of the heliosphere? NH(LISM) = 10 cm-3 Increase the density of the surrounding LISM by only a factor of 50 (nH from 0.2 to 10 cm-3) and the termination shock shrinks from 100 AU to 10 AU. Consequences of a compressed heliosphere: • (1) Cosmic rays flux modulated by magnetized solar wind: • Cloud nucleation, increase in planetary albedo (Marsh & Svensmark 2000, Carslaw et al. 2002) • Lightning production increase (Gurevich & Zybin 2005) • CR alters ozone layer chemistry (Randall et al. 2005) • CR source DNA mutation (Reedy et al. 1983) • (2) Direct deposition of ISM material onto planetary atmosphere: • Dust deposition could trigger “snowball” Earth episode (Pavlov et al. 2005) • Create mesospheric ice clouds, increase in planetary albedo (McKay & Thomas 1978) NH(LISM) = 0.2 cm-3 Müller (2004)

11. What has Voyager 1 told us about the Termination Shock? • Voyager 1 was launched 5 Sept 1977, passed Jupiter and Saturn and crossed the termination shock (TS) on 16 Dec 2004 at 94 AU from the Sun. • Onboard detectors measured the magnetic field and energies and directions of energetic electrons, protons, and He nuclei. • Weak shock: velocity jump (r=2.6). • TS not spherical due to magnetic field. • TS moves in and out with the solar cycle. • Solar wind in heliosheath slower, hotter, and denser than inside the TS. • The TS was expected to be the location where anomalous cosmic rays (ACRs) are accelerated, but peak in ACR flux not at the TS.

12. Stone et al. (2005) Science 309, 2017 • A: Energetic proton intensity streaming from the Sun. • B: Termination Shock Particle (TSP) streaming anisotropy decreases when cross the TS due to scattering by magnetic turbulence. • C: Intensities of high-energy protons and electrons. • D: Intensities of Galactic cosmic rays and He ions (anomalous cosmic rays).

13. Change in Magnetic Field Strength and Direction (heliographic) at the TS: Burlaga (2005) Science 309, 2027

14. Change in Magnetic Field at the TS: Burlaga et al. (2005) • Magnetic compression ratio across TS: 3+/-1. • Complete change in average field strength perhaps due to thermalization of the plasma by the TS. • Inward moving TS (>90 km/s) may have crossed Voyager 1: Jokipii (2005) ApJ 631, L163.

15. Effect of the Interstellar Magnetic Field on the Heliosphere (Opher et al. 2006, 2007) • 3-D MHD adaptive grid models with interstellar magnetic field (B~1.8μG)α=30-60 degrees from inflow direction. (60-90 degrees from Galactic plane). • vSW=450 km/s, vism=25.5 km/s Parker spiral B=2μG at equator • Produces a N-S asymmetry in the TS and heliosheath and a deflection in the current sheet. • TS moved in 2.0 AU for Voyager 1 with TSP streaming outward from Sun along a spiral field line that does not first go through the TS. • Moves TS inward more in S (Voyager 2) than N (Voyager 1). • Where Voyager 2 crosses the TS will be the critical test of value of α.

16. Observations of Neutral Hydrogen in the Heliosphere from Lyman-α Backscattering Measurements: References • Bertaux et al. (1995) Solar Phys. 162, 403 describes the SWAN (Solar Wind Anisotropies) experiment on SOHO (Solar and Heliospheric Observatory) satellite. • Lallement et al. (2005) Science 307, 1447. • Quémerais et al. (2006) A+A 455, 1135

17. SWAN maps Backscattered Lyman-αRadiation from Neutral Hydrogen Flowing into the Heliosphere using a Hydrogen Gas Absorption Cell Spectrometer • Maximum in the Lyman-αsky glow when inflowing H has maximum Doppler shift relative to SOHO. • Maps show Lyman-αglow at different times of year when SOHO has different velocities relative to the H inflow vector.

18. Deflection of Neutral H vs. He due to charge-exchanged Solar Wind Protons becoming H Secondaries • Incoming He atoms retain the ISM inflow direction. • H secondaries will be deviated if the interstellar magnetic field is inclined relative to the gas flow direction. • Measured deviation is 4+/-1 degrees.

19. Inferring the Direction of the Local Interstellar Magnetic Field • MHD models consistent with the deviation of H relative to He predict the magnetic field direction in Galactic coordinates (30-60 degrees from Galactic plane). • Magnetic field is parallel to the edges of the LIC and G clouds and likely compressed by the relative motion of the two clouds.

20. Measuring the Properties of Interstellar Clouds: References • Linsky et al. (2000) ApJ 528, 756 • Redfield & Linsky (2000) ApJ 534, 825 • Redfield & Linsky (2002) ApJS 139, 439 • Redfield & Linsky (2004) ApJ 602, 776 • Redfield & Linsky (2004) ApJ 613, 1004 • Redfield & Linsky (2007) ApJ, in press

21. Observational Diagnostics 1 ion, 1 sightline Velocity, Column Density Redfield & Linsky (2004a)

22. Observational Diagnostics 1 ion, 1 sightline Velocity, Column Density Temperature, Turbulence, Volume Density, Abundances, Depletion, Ionization Fraction multiple ions, 1 sightline

23. Redfield & Linsky (2004b)

24. Observational Diagnostics 1 ion, 1 sightline Velocity, Column Density Temperature, Turbulence, Volume Density, Abundances, Depletion, Ionization Fraction multiple ions, 1 sightline Global Morphology, Global Kinematics, Intercloud Variation multiple ions, multiple sightlines Origin and Evolution, Interaction of LISM Phases

25. Global Kinematics Our “observables”: Centroid velocity (vR) of LISM absorption, i.e., the radial component of the projected velocity in direction (l, b) Assume the simplest dynamical structure: a single vector bulk flow. vR = v0 (cos b cos b0 cos (l0 - l) + sin b0 sin b) Questions: Can the observed LISM velocities be characterized by a rigid bulk flow, or are they chaotic? How significant are any departures from a rigid flow vector? Is there a correlation between direction and departure from the bulk flow? Can multiple velocity vectors successfully characterize the majority of LISM observations?

26. LISM Sample 160 targets within 100 pc observed at high and moderate resolution that contain 270 LISM absorption components (~60% of UV observations taken for other purposes).

27. LISM Sample

28. Dynamical Modeling Procedure Iterative process: Fit dataset Remove outliers (in velocity and space) Repeat until satisfactory fit (use F-test to determine stopping point) Remove successful dynamical cloud sightlines from dataset Start over. Assumptions: All motions are rigid velocity vectors (i.e., a tensor dynamical characterization may result in two separate dynamical clouds, close in space, and with similar velocity vectors). The projected morphology of all clouds are contiguous (i.e., no “swiss cheese” clouds) Results: Fits largest surface area structures first (e.g., LIC and G vectors derived immediately). 15 velocity vectors satisfy 80% of LISM database. All velocity vectors are similar, and approximately opposite to the motion of the Sun. About 1/3rd of the dynamical clouds are filamentary. Search for unique cloud properties.

32. Heliocentric Vector Solutions

33. Upwind Velocity Distribution Relative to Sun: Upwind Velocity Distribution Relative to LSR: Vector Distribution: All LISM vectors are coming from a narrow range of directions A relatively wide range of velocity magnitudes, with mean around 20 km/s relative to LSR The solar trajectory (upstream: l ~ 208, b ~ -32, v ~ -13 km/s) is in almost the exact opposite direction (Dehnen & Binney 1998) Spatial correlation of velocity vectors are clear (e.g., Aql Cloud) Many dynamical clouds have filamentary structures possibly due to collisional interfaces

38. Do individual dynamical clouds have unique physical properties?

39. Is the Heliosphere located inside of the LIC or the G Cloud?

40. Macroscopic Velocity Differences All V magnitudes for clouds that share the same line of sight. Without distance information, it is unclear how many velocity differences are realized. Indicate that macroscopic motions can induce compression and shear flows. Transonic turbulent compression by warm interstellar clouds can successfully create cold neutral clouds (Vazquez-Semadeni et al. 2006). LIC/G

41. Radio Scintillation: IntraDay Variables (IDVs) 1% of all radio quasars show short timescale variability (hours). Diffraction of intervening screen can cause time delays in signal - use to get transverse motion of scintillating screen. As Earth moves through projection of diffraction pattern, the characteristic timescale of scintillation varies - which is repeatable over several years. Set characteristic scale length (~104 km) to Fresnel scale to put limits on screen distance: L < 10 pc! Dennett-Thorpe & de Bruyn (2002) Bignall et al. (2006)

42. Annual Scintillation Signature Annual variation of scintillation timescale is fit with 5 free parameters: diffraction scale length, axial ratio, orientation, and transverse velocity. For B1257-326, our derived transverse velocity of the Aur Cloud, which lies along the line of sight toward the quasar B1257-326, is consistent with the radio scintillation observations.! Bignall et al. (2006)

43. Radio Scintillation Sources Leo Cold Cloud (Meyer et al. 2006) Future Past

44. Astrospheres: References • Wood et al. (2001) ApJ 547, L49 (αCen and Prox Cen). • Wood et al. (2002) ApJ 574, 412 (4 new stars • Wood et al. (2005) ApJ 628, L143 (14 stars). • Frisch (1993) ApJ 407, 198 (first estimate of astropause radii for stars).

45. Journey of a Lyman-α Photon Detailed central profile of late-type star has little influence since at the core of absorption. log NH(LISM) < 18.7, otherwise obliterates any helio- or astrospheric signature. Nearby DI line critical to constraining fit of LISM absorption (and constancy of D/H in Local Bubble). Since HI is decelerated at heliosphere, the heliospheric absorption is always redshifted and the astrospheric absorption is always blueshifted. Wood et al. (2002)

46. Comparison of Lyman-α Profiles with hydrodynamic models assuming wind speed of 400 km/s and LISM parameters

47. Maps of Neutral Hydrogen Density with Sightline to Sun

50. Mass Loss rates vs. X-ray Surface Flux and Age of the Sun