NIGHT TIME POLARIMETRY. Stefano Bagnulo (Armagh Observatory)

Transcription

1 NIGHT TIME POLARIMETRY Stefano Bagnulo (Armagh Observatory)

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5 (Position) Intensity Intensity vs. time Intensity vs. wavelength Intensity vs. time AND vs. wavelength HOW MUCH?

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8 POLARIZATION BY ABSORPTION

9 polarization.html

10 REFLECTED LIGHT IS POLARIZED! du/~whu/intermediate/polari zation/polar1.html

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16 THE STOKES PARAMETERS I ( natural light, or intensity ) Q & U ( linear polarization ) V ( circular polarization ) Georges Gabriel Stokes (1852)

17 STOKES PARAMETERS: THE CHOICE OF A REFERENCE SYSTEM Right handed coordinate system (x,y,z), where: z-axis is directed along the direction of propagation x-axis is directed along an arbitrary direction x-axis: celestial meridian passing through the object

18 OPERATIONAL DEFINITIONS OF STOKES PARAMETERS Q = - U = - V = - Positive, right handed Negative, left handed

19 ANGLE θ P = (Q 2 + U 2 ) 1/2 Q = P cos2θ U = P sin2θ

20 USING RELATIVE UNITS P Q = Q/I P U = U/I P V = V/I

21 AN IDEAL POLARIMETER Landi Degl Innocenti & Landolfi (2004)

22 BASIC FORMULAS FOR AN IDEAL POLARIMETER

23 BASIC FORMULAS FOR AN IDEAL POLARIMETER

24 BASIC FORMULAS FOR AN IDEAL POLARIMETER

25 What happens if things change between the two measurements (i.e. k is not constant)? Use a beam splitter!

26 POLARIMETRIC OPTICS α = position angle of the fast axis γ = phase retardation β = position angle of the acceptance axis Retarder waveplate + Wollaston prism V/I: γ = 90 o ; α = -45 o, +45 o, Q/I, U/I: γ = 180 o ; α = 0 o, 22.5 o, 45 o, β = 0 o and β = 90 o

27 IMAGING POLARIMETRY (STOKES Q) α=0 o I+Q I-Q Parallel beam Perpendicular beam Nucleus of 133P/Elst-Pizarro

28 IMAGING POLARIMETRY (STOKES U) α=22.5 o I+U I-U Parallel beam Perpendicular beam Nucleus of 133P/Elst-Pizarro

29 IMAGING POLARIMETRY (STOKES Q) α=0 o I+Q I-Q Parallel beam Perpendicular beam Nucleus of 133P/Elst-Pizarro

30 IMAGING POLARIMETRY (STOKES U) α=22.5 o I+U I-U Parallel beam Perpendicular beam Nucleus of 133P/Elst-Pizarro

31 STOKES V SPECTRA FROM RCP AND LCP I+V (RCP) I-V (LCP)

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33 IMAGING LOW-MID RESOLUTION SPECTROPOLARIMETRY (R<10000) (slitfed) HIGH RESOLUTION SPECTROPOLARIMETRY (R= ) (fiber fed)

34 VLT (IMAGING + LOW RESOLUTION SPECTROPOLARIMETRY)

35 WHT (LOW - MID RESOLUTION SPECTROPOLARIMETRY)

36 & CHFT (HIGH RESOLUTION SPECTROPOLARIMETRY)

37 ZEEMAN EFFECT ν 0 + ν L ν 0 σ ν 0 ν L ν 0 + ν L σ π σ ν 0 ν L

38 Zeeman Effect

39 Zeeman Effect: Local case Transverse Field Circular polarization B = 10 kg Stokes I Linear polarization Stokes V Linear polarization Stokes Q Stokes U

40 ZEEMAN EFFECT: LOCAL CASE Longitudinal Field Circular Polarization B = 10 kg Stokes I Linear Polarization Stokes V Linear Polarization Stokes Q Stokes U

41 Zeeman Effect Circular polarization σ π Stokes I σ Stokes V Linear polarization Linear polarization B = 10 kg Stokes Q Stokes U

42 THE UNPOLARIZED SPECTRUM OF HD 96441

43 94600 Hε Hδ Hγ Hβ

44 FIELD? V/I = (1/λ 2 ) (1/I) (di/dλ) <Bz> <Bz> = ± 110 G Stokes I σv/i V/I

45 THE OBLIQUE ROTATOR MODEL B d = 10 kg, β=45 o ; i = 90 o, v sini = 10 kms -1

46 SOLAR AND STELLAR MAGNETISM Session I on Monday: Solar and Stellar Magnetic fields I Session VII on Wednesday: Solar and Stellar Magnetic fields II Session V on Tuesday: Data analysis techniques for polarimetric observations

47 SURFACES, DUST, ATMOSPHERES This afternoon: Tutorial by Michael Mischenko Session VIII on Thursday: Polarization diagnostic of Atmospheres and Circumstellar Environments (including star forming regions, Herbig Ae/Be stars, M dwarfs, Earthshine, SNe )

48 POLARIZATION OF REFLECTED LIGHT du/~whu/intermediate/polari zation/polar1.html

49 POLARIZATION FROM REFLECTION Incident light (unpolarized) PHASE ANGLE Reflected light (polarized)

50 Cellino et al. (2015)

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53 POLARIZATION OF REFLECTED LIGHT du/~whu/intermediate/polari zation/polar1.html

54 POLARIMETRY OF SOLAR SYSTEM OBJECTS Session IX on Thursday afternoon: Polarimetry as a tool for discovery science I.

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56 I + Q spectrum I - Q spectrum Polarised spectrum

57 REFLECTANCE AND POLARIZATION FROM EARTH-LIKE PLANETS Stam (2008)

58 EXO-PLANETS Session X on Friday morning: Polarimetry as a tool for discovery science II.

59 THANK YOU!