PowerPoint Presentation

Probing Coronal Magnetismwith Multi-wavelength PolarimetrySilvano FineschiINAF-Torino Astrophysical Observatory, Italy25 May, 2013, Bern (CH)

Coronal Magnetism

B & resonance scattering from anisotropic sourceUV (permitted) lines: Blos ;losVIR (forbidden) lines: posScattering and Superradial Doppler-dimming effectUV lines: Effect of B on ions v (i.e., kinetic T& T//)Beta

1.05 Ro10 Ro2 RoTemp. minimum(photospheric field range: 100-2500 G)Photospheric VIR lines CIV 150 nmMgII h & k 280 nm HI Lyman series, OVI 103.2 nm& Fe IR lines G.A.Gary. 2001HI Ly- 122 nm4 Yohkoh coronal X-ray images have shown that CME explosions are more likely to occur in regions having sigmoidal coronal magnetic fields than in regions with less contorted field configurations. The degree to which the contorted fields depart from a potential configuration, representing the free magnetic energy content of the region, is evidently a good indicator of whether a region will produce CMEs. This qualitative lead should be pursued. The free magnetic energy content of a region can be calculated from integrals over vector magnetograms, but accuracy depends on the fields being measured at a sufficient height in the atmosphere for them to be very nearly force free.Also, the force-free fields in the transition region and corona may undergo large changes in direction without measurablechange in the photospheric roots. So, to follow the evolution of the 3D force-free field (both for CME studies and for moregeneral purposes), the vector magnetograms from which the field is extrapolated must be obtained from a force-free layer.Therefore, a goal of SEC and LWS should be to measure the vector magnetic field in the middle to upper chromosphereand/or lower transition region (See Figure 1).

The profiles of the MgII h and k lines at 2795 and 2803 formed ~2900 km and at a temperature of ~2e4 K.The CIV (2s-2p) lines, at 1548.2 and 1550.8 , are observed to have simple emission profiles that are formed ~200 km higher than the MgII lines and at a temperature of ~1e5 K.

Hanle Effect (tutorial)

Larmour AP is // or BIf Larmour >> A (VIR forbidden lines)

incident lightWhat is the Hanle effect sensitivity of coronal UV lines to magnetic fields?

How many photons are needed to detect the Hanle effect in UV coronal lines? A [107 s-1] ~ 0.88 gJ B [G]

Hanle effect SensitivityA FeXIII = 14 Hz BHanle 0.2-2 G

A FeXIII 200 million K !

The fastest solar wind flow is expected to come from dim coronal holes.In June 1996, the first measurements of heavy ion (e.g., O+5) line emission in the extended corona revealed surprisingly wide line profiles . . .The impact of UVCS Discoveries

UVCS has led to new views of the collisionless nature of solar wind acceleration.Key results include:The fast solar wind becomes supersonic much closer to the Sun (~2 Rs) than previously believed.In coronal holes, heavy ions (e.g., O+5) both flow faster and are heated hundreds of times (250 MK) more strongly than protons (3 MK) and electrons (1 MK), and have anisotropic temperatures. (e.g., Kohl et al. 1997,1998)

Ion cyclotron waves (10 to 10,000 Hz) suggested as a natural energy source that can be tapped to preferentially heat & accelerate heavy ions.

16Anisotropic temperatures from Ion-cyclotron resonancebetween Alfven waves and Larmor gyrations of ions+

This mechanism is the resonance between left-hand polarized Alfven waves and the Larmor gyrations of positive ions. Ion cyclotron waves (10 to 10,000 Hz) suggested as a natural energy source that can be tapped to preferentially heat & accelerate heavy ions.

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Super-radial Anisotropic Resonance PolarizationFineschi (2001)Raouafi & Solanki (2002)

Anisotropic Super-radial Doppler-dimming effectFineschi (2001)Raouafi & Solanki (2002)20Source of the Solar Wind

Habbal, Fineschi, et al. ApJ (1997)20

Anisotropic Super-radial Doppler-dimming effect (OVI 103.2 nm line)

Kahn (2012)

B & wind speed 0Solar wind effects on UV PolarizationB & wind speed = 0Khan, Fineschi et al., 2011

HI Ly-Khan (2012)

Anisotropic Super-rad Doppler-dimming effect Integration along LOS2 different electron density models (Cranmer ApJ 2008)

HI Ly-HI Ly-HI Ly-Khan, DeglInnocenti, Fineschi et al. (2011)Effects on Polarization of B, Anisotropic Distributions, Active Regions, (Min. Detectable Rot. Angle) ~ P/P SNR ~ (P ) -1 What does it take to measure it? ~ 5 ~ 10-1 rad P ~ 10-1 SNR ~ 102

UV Spectro-polarimetryPolarimetry UV coronal linesSpectroscopyUV coronal lines+Coronal B effects on plasma(coronal heating mechanisms, solar wind acceleration)Coronal B(Blos ;los)Hanle effectCoronal plasma parms(Nion, w, T//, T)Doppler-dimming-shift, -width Super-radial Doppler-dimmingeffect

SUMER Measurement of Hanle and ASD effects?P=(92)%; = 96

Helioctr. Dist. = 1.3 RWind speed w 40 km/s

(Raouafi,1999)Hanle effect: B > 10 G; B < 10; w > 50 km/sSR Doppler-dim.: B < 3 G; B > 30; w > 50 km/sAnisotr. SR Doppler-dim.: B