Zeeman Paschen-Back effects

Transcription

1 Zeeman Paschen-Back effects ZE: Weak Bfield Magnetic splitting level separation Splitting linear with B Equal total strength of σ b, π, σ r components (Anti-)symmetric Zero net polarization (Incomplete) PBE Strong Bfield Magnetic splitting level separation Splitting non-linear with B Relative strength of σ b, π, σ r components changed Asymmetric Stokes profiles Net polarization of profiles Mixing of levels (same m, different J) Forbidden lines

2 Outline 1. Description of polarized radiation 2. Zeeman and Paschen-Back effects 3. Solar activity Activity phenomena and role of magnetic field Solar activity cycle 4. Stellar magnetic fields 5. Scattering polarization

3 Coronal Mass Ejections (CME) (LASCO C3, SOHO)

4 Coronal Mass Ejections (CME)

5 Aurorae Saturn Earth Jupiter

6 Corona: X-ray (YOHKOH)

7 Magnetic loops and flares (TRACE Satellit)

8 Active Region Chromosphere, Hα Photosphere, G-band Dutch Open Telescope (DOT)

9 Photosphere Quiet Sun Convective motions Photosphere, G-band

10 Height dependence of the temperature

11 Magnetic fields Extremely high electrical conductivity of solar plasma magnetic field frozen to gas Upper atmosphere: Magnetically controlled Magnetic pressure dominates over gas pressure B field force-free Lower atmosphere: Hydrodynamicallycontrolled Gas pressure dominates Transition or regimes in chromosphere (TRACE Satellit)

12 Magnetic phenomena

13 Magnetic fields in sunspots Visible light Magnetogram(Stokes V) (Hinode satellite)

14 Why molecules? Solar photosphere = G stars Sunspot umbra = M stars McMath / NSO

15 Why molecules? Sunspot umbra: TiO Stokes V/I Sunspot penumbra: only atomic lines Stokes V/I IRSOL / ZIMPOL Wavelength [Å]

16 Sunspots: Imaging in molecular bands TiO band filter high contrast in umbra SST, Berger & Berdyugina (2003) Zakharov et al. (2005)

17 Sunspots: 3D structure Simultaneous inversion of Fe I and OH lines in the IR Bottom of photosphere log τ 0.5 = 0 Middle photosphere log τ 0.5 = 2 Wilson depression at τ 1.6 = Mag. Field, G Tempe erature, K Mathew et al. (2003) Mathew et al. (2004)

18 Small-scale magnetic fields 3D MHD models vs. observations in CH band Radiativelyheated magnetic flux concentrations Schüssler et al.(2003) Shelyag et al. (2004) SST

19 Small-scale magnetic fields CN band filter Excellent quantitative agreement with predictions CN contrast CH cont Zakharov et al.(2005)

20 Quiet Sun: fractal magnetic fields Fractal magnetic field structure Field strength probability distribution (1% by volume has 1 4 kg) Stenflo (2004) km km

21 Activity cycle: sunspot number Average monthly sunspot numbers 11-year cycle

22 Activity cycle: total solar irradiance (TSI) variations In phase with 11-year activity cycle Amplitude: 0.1% Maximum TSI during activity maximum

23 Surface magnetism Spots Faculae Network

24 Influence of spots on TSI

25 Influence of faculae on TSI

26 Influence of network on TSI

27 Activity cycle: wavelength variability of TSI Variability of the TSI: Total: 0.1% (dominated by visible) UV: factor of 2 X-ray: factor of 100 X-ray images (Yohkoh satellite) EUV images (Fe XII 195 Å, EIT, SOHO)

28 Activity cycle: Prediction of cycle 24

29 Activity cycle: dynamo theory Dynamo generating the solar activity cycle Oscillation between poloidal (dipole-like) and toroidal B field Polarity reversal every 11-years 22-year period of magnetic cycle Requirements: Turbulence Rotation Seed magnetic field

30 Activity cycle: dynamo theory Ω-effect: Poloidal toroidal (differential rotation) Location: tachocline Amplification to G Buoyant flux tubes rise to surface bipolar active regions α-effect: Toroidal poloidal Cyclonic convection (Coriolis force)

31 Outline 1. Description of polarized radiation 2. Zeeman and Paschen-Back effects 3. Solar activity 4. Stellar magnetic fields Overview Diagnostics Stellar activity Application: Gravity Probe B 5. Scattering polarization

32 Magnetic fields across the H-R diagram (L ) Luminosity ,000 20,000 10, (K) WR? G O-B 10 2 G <30% Ae-Be 10 2 (10 3 ) G 1 10%? BpAp G 5% WD G: 10% NS G:?% G 100%? AGB G RGB G T Tau %? Solar G?% red dwarfs G 5 40% O B A F G K M Spectral class Post-MS Pre-MS MS

33 Magnetic fields across the H-R diagram Idealized picture: Hot stars (outer radiation zone): Fossil fields Static Simple topology: dipole or low order multipole Cool stars (outer convection zone): Dynamo generated fields Stellar activity: starspots, plages, chromospheric emission, enhanced UV, X-ray, and radio emission, CMEs

34 Spectral class dependence: cool dwarfs Solar analogs: Convection envelope Deepens towards cooler dwarfs Red dwarfs: Become fully convective near M4 (expectation) Transition in dynamo: from solar type (in tachocline) to distributed, turbulent dynamo Sun, etc G?% red dwarfs G 5-40%

35 Magnetic fields in red dwarfs Drop near M7 (expected at M4) Consider spots and impact of B fields on internal structure

36 Magnetic field on White Dwarf G99-37 B = 7.5 ± 0.5 MG, molecules, Paschen-Back regime (net polarization!)

37 Magnetic field on White Dwarf G99-37 Paschen-Back effect

38 Magnetic field diagnostics Line splitting (broadening) Stokes I magnetic field strength B Polarization Stokes V B z Stokes Q, U, V Magnetic field vector B Atomic diagnostics: Hot stars Zeeman effect (except Ap stars and White Dwarfs) Molecular diagnostics: Cool stars Zeeman and Paschen-Back effects

39 Rotation Activity Faster rotation more active Single stars: slowing down with age

40 Evidence of cool spots Periodic brightness and color variations Brightness variations up to 0.6 mag When darker redder (i.e. cooler)

41 Doppler Imaging: atoms Unresolved star Spot on rotating star Bump in line profile Doppler shift bump moves across profile from blue to red side Doppler Imaging technique: Time-series of line profiles (Stokes I) surface image (temperature)

42 Doppler Imaging: molecules Molecules: Only in cool spots Lines visible simultaneously with spot Doppler shifts High temperature sensitivity Doppler Imaging with molecular spectra: Internal structure of spots

43 Doppler Imaging: starspots Properties of starspots (high activity stars): Area: 5 20% of surface Temperature difference to photosphere: K Latitude: >30 Lifetime: months IM Peg (RS CVnbinary; primary K2 III; P =24.6 d)

44 Doppler Imaging: starspots Time evolution activity cycle II Peg (RS CVn; K2 IV; rotation period 6.7 d)

45 Zeeman-Doppler Imaging Extension of Doppler Imaging: Inversion of all 4 Stokes parameters temperature map Bfield map (vector!) In practice: often only Stokes Iand V

46 Zeeman-Doppler Imaging Molecular bands additional constraints TiO band

47 Starspots: molecular bands in Stokes V EV Lac (M3.5e V; P = 4.38 d), TiOA 3 Φ X 3 system, telescope: CFHT

48 3D structure of starspots AU Mic(M1 V; P = 4.85 d) Observations: Stokes Iand V 4 phases Initial guess: Circular spots Background mixed field Radial component Inversions: ZDI TiO, CaH, Ti I, Fe I, FeH separately Results: T, B(ϕ,λ,h) 3D structure TiO: 210 km CaH: 190 km Coordinate grid Ti I: 160 km FeI: 120 km FeH: 60 km

49 3D structure of starspots: temperature 210 km AU Mic 130 km 60 km T 3650 K 3400 K 3150 K 2900 K 2650 K 2400 K

50 3D structure of starspots: magnetic field 210 km AU Mic 130 km 60 km B r G G G 4000 G

51 Stellar activity cycles: brightness variation (RS CVn) (Young solar analog)

52 Comparison solar stellar activity Outer convection zone required cool stars The faster rotation the more active Highly active stars: Darker at activity maximum Spot dominated (huge spots, high latitude) Low activity stars (including Sun): Brighter at activity maximum Faculae dominated With increasing age (single stars): high low activity

53 Gravity Probe B Satellite mission to test general relativity theory Polar Earth orbit Science data collection: August 2004 August 2005

54 Gravity Probe B Test of geodetic effect and frame-dragging effect, both acting on a orbiting gyroscope

55 Gravity Probe B Geodetic effect: Caused by parallel transport of vector in curved space Precession of orbiting vector (gyroscope): axis of gyroscope slowly drifting within orbital plane Frame-dragging effect (Lense-Thirringeffect): Caused by spinning Earth: drags local spacetime along Precession of vector: gyroscope axis drifting parallel to equator plane Much smaller effect Perpendicular drifts of the two effects

56 Gravity Probe B Measure drift of the four gyroscopes relative to a distant star with onboard telescope Selected guide star IM Peg Planned accuracy: Geodetic effect: 10 4 Frame-dragging : mas (Note: 0.7 mas 1 R = 13 R ) 300 light years IM Pegasi

57 Gravity Probe B How much is 0.5 mas? Width of human hair seen from 40 km Diameter 5 Rappen coin seen from 6000 km (Zurich-New York) Astronaut on moon seen from Earth

58 Gravity Probe B IM Peg: RS CVnbinary Optical centroid shifts Due to binary orbit (detection of secondary as side result) Due to large spots possible errors! daily monitoring; Doppler Imaging Result: Offset due to spots: 0.07 mas( 0.1 R )

59 Outline 1. Description of polarized radiation 2. Zeeman and Paschen-Back effects 3. Solar activity 4. Stellar magnetic fields 5. Scattering polarization Sun Extrasolar planets

60 Scattering Polarization Classical description: damped harmonic oscillators as antennas Scattered radiation linearly polarized perpendicular to scattering plane Requires spatial symmetry breaking anisotropy of incident radiation

61 Second solar spectrum Linearly polarized spectrum arising from coherent scattering Looks completely different than intensity spectrum second solar spectrum Complementary information Different physical mechanisms Continuum (Thomson & Rayleigh scattering, Lyα wings) Resonant line scattering Source of anisotropy: Temperature gradient ( limb darkening)

62 Second solar spectrum: examples Na ID 2 Na ID 1 Triplet peak Quantum interference

63 Second solar spectrum: examples Conspicuous molecular lines onlyin Q/I

64 Hanle effect Modification of scattering polarization due to magnetic field Signatures: Rotation of plane of polarization signature cancels in turbulent fields Depolarization (few exceptions: forward scattering) visible in turbulent fields

65 Hanle effect: examples Second solar spectrum: Ca II K Turbulent magnetic field depolarization 0 G 6 G 8 G 10 G 100 G

66 Hanle effect: examples C 2 lines with different Hanle sensitivities (different effective Landé factor) B= 0 G B= 15 G g eff = 0.01 g eff =

67 Hanle effect Zeeman effect Hanle effect: Weak fields G Directed and turbulent fields Turbulent fields: 99% of photospheric volume Zeeman effect: > 100 G Net magnetic flux Strong flux tubes: 1% of photospheric volume

68 Extrasolar planets Scattered light linearly polarized, perpendicular to scattering plane Periodically varying polarization Idea: Unresolved planet Planets light diluted by star Q/(I star + I planet ) Q/I star Periodic polarization signal (expected signal at most 10 4 ) Diagnostic potential: Orbital parameters Composition of planet s atmosphere Surface structure

69 Extrasolar planets First polarimetric detection of an extrasolar planet: HD b: Hot Jupiter Period 2.2 d Semi-major axis: AU Needs confirmation!