Polarimetry of the Sun, stars and exoplanets

Polarimetry of the Sun, stars and exoplanets

Svetlana Berdyugina

Kiepenheuer Institute for Solar Physics, Freiburg, Germany

Outline

• Polarimetry Magnetic fields

Zeeman, Paschen-Back, Hanle effects in atomic and molecular lines

Atmosphere and surface inhomogeneities Scattering by gas, liquid and solid particles, surface reflection, indirect imaging

• Sun Sunspots, quiet photosphere, Corona

• Stars Starspots, imaging of unresolved magnetic structures

• Exoplanets Atmospheres, clouds, biosignatures, surface imaging

Magnetic fields across the HRD

Ae-Be102 (103)G 1-10%?

T Tau 103

100%?

BpAp103-104G 5%

Solar 1-103 G 100%

reddwarfs 10-103 G 100%

WD106-109 G: 10% 1-106 G: ?%

RGB 1-103 G

AGB 10-3-10 G

WR ? G

O-B 102 G <30%

O B A F G K M Spectral class

Lum

inos

ity (

L )

106

104

102

1

102

104

40,000 20,000 10,000 7500 5500 4500 3000 (K)

NS109-1015G 100%?

Pre

-MS

MS

Pos

t-M

S

(Berdyugina 2009+)

Magnetic phenomena on the Sun

• Sunspots• Network• Flares• Prominences• Coronal loops• CME

Zeeman Effect

• Sunspots (1908)• Line splitting (broadening)

Stokes I <|B|>• Polarization

Stokes V <Bz>

Stokes QUV B Muller matrix, Polarized RT

• Atomic & Molecular diagnostics ZE & PBE

I/Ic

Q/I

U/I

V/I

(ZIMPOL, J. Stenflo)

Molecular Polarization• Full theory for arbitrary molecular electronic states

Zeeman and Paschen-Back effects Scattering & Hanle effect

• Peculiarities due to the PBE New diagnostics and higher sensitivity! Stokes profile asymmetries Net polarization across line profiles Wavelength shifts and polarization sign changes depending on B Weakening of main branch and strengthening of satellite and forbidden lines

(Berdyugina et al. 2000-2013)

• Active Sun: sunspot B~3-4 kG

Sunspots: Zeeman effect

• Magnetic field from Stokes IQUV

Hinode

GREGOR (Franz et al. 2014)

8

Sunspots: 3D structure

• Simultaneous inversion of atomic and molecular lines Fe I & OH at 1.56 um

Tem

pera

ture

, K2

00

0

40

00

6

00

01

00

0

20

00

30

00

Mag

. Fie

ld, G

Bottom of photosphere log 0.5= 0

Middle photosphere log 0.5=2

Mathew et al. (2003) Mathew et al. (2004)

Wilson depressionat 1.6=1

Quiet Sun Magnetic Field: Hanle effect• Network: 1kG, Internetwork: 200G,

Quiet Sun: 1-10G

Zeeman effectStokes V: 0.2%Bl <<100 G

Hanle effectStokes Q: 0.1%Bt ~ 8 G

Berdyugina & Fluri 2004, Kleint et al. 2010, 2011)

Fractal-likedistribution

Solar Corona

• In optical and X-ray • Magnetic Field Measurements [Fe XIII] Zeeman Stokes V -> BLOS

(Lin et al. 2004)

[Fe XIII] saturated Hanle -> angles (Bommier 2012, Tomczyk et al.)

[Fe XIII], [SiX] saturated Hanle + He I unsaturated Hanle -> vector B (Dima, Kuhn, Berdyugina 2016)

Sun as a star• Dec 2002 • Stokes V: 510–4 (0.05%)

• Inferred Bl : 0.8 G

Stokes V

comes mainly from spots!

(Demidov, priv. comm.)

4

B* B

phot

40% 1% 0.2 0.5 0.04%

TV V f C

T

Indirect Imaging of stars• Spatial resolution

Espadons:

~0.1Å

Cool stars:

~ 0.1Å

Hot stars:

~ (0.5-1)Å

Lack of spatial resolutionAssumption on multi-pole distribution

(Piskunov & Kochukhov 2002; Donati et al. 2006)

(Semel 1989, Donati et al. 1997)

• Zeeman-Doppler Imaging (ZDI)

*bin

loc instr

2 sin

( ) /

v iN

c

instr

loc *bin

2 sin~

5km/s

v iN

loc *bin

2 sin~

(25 50)km/s

v iN

T Tau stars with disks (CTTS)Lower mass CTTS: Dipole topology (Donati et al. 2008, LSD, MPE)

Higher mass CTTS: Complex topology (Hussain et al. 2009, LSD, MPE)

BP Tau

vsini = 9 km/smax(B)~2.5 kG

vsini = 35 km/smax(B)=400G

Underestimated

complexity and flux?

T Tau stars with disks (CTTS)

(Johns-Krull 2007)

Fields are not dipolarAverage flux Bf=2.5kG

Solar-type stars

(Petit et al. 2008)

Poloidal (P~20d) Toroidal (P~10d)

vsini = 1.2 km/smax(B)=10G

vsini = 4.3 km/smax(B)=10G

Solar-type stars• Magnetic cycle with reversal?

(Fares et al. 2009)

Boo June 2007 January 2008 June 2008 July 2008

vsini = 16 km/smax(B)=10G

M dwarfs

M4: axisymmetric poloidal (EV Lac, Morin et al. 2008 )

M1: toroidal +NAS-poloidal (OT Ser, Donati et al. 2008)

vsini = 6 km/smax(B)=400G

vsini = 4 km/smax(B)=2kG

M dwarfsJohns-Krull & Valenti (2000)

Average Bf ~ (2–4) kG

Stellar Coronae

• Unresolved X-ray observations M dwarfs are brightest X-ray

sources on the night sky

• Reconstructions from ZDI Only Brad is used for potential

field extrapolations Invisible pole is a random choice

of visible pole ZDI Heavily biased by assumptions

Chandra (Currie et al. 2009)

(Jardin et al.+)

ZDI with molecular lines• Increase spatial resolution with molecular lines

Atomic lines Molecular lines

Starspots: Atomic lines

Fe I Fe I Ti I Ti I Ti I

Starspots: Molecular lines

3D structure of starspots: T

60 km

130 km

210 km

3650 K3400 K3150 K2900 K2650 K2400 K

T

AU Mic

(Berdyugina 2011)

3D structure of starspots: B

longitudelatit

ude

heig

ht, k

m

60 km

130 km

210 km

longitudelatit

ude

heig

ht, k

m

+4000 G

+2000 G

02000 G

4000 G

Br

AU Mic

(Berdyugina 2011)

Starspots vs Sunspots• Temperature • Magnetic field strength

sunspot

starspots

starspots

sunspot

sunspot

starspots

Penumbral edgeUmbral dotsDark core

Penumbral edgeUmbral dots

(Berdyugina 2011)

• Detection of reflected light direct probe of planetary environment• Physics: scattering polarization

• Polarization is perpendicular to the scattering plane• Max. polarization at 90 scattering angle• Stellar light is unpolarized (or modulated with a different period)• Polarization varies as planet orbits the star

Polarimetry of Exoplanets

pola

rimet

er

i=98, =270, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=98, =270, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=98, =225, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=98, =180, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=135, =270, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=180, =270, e=0

R = 1.2RJ

a = 0.03 AUP = 2.2 d

i=130, =270, e=0.5, =270

R = 1.2RJ

a = 0.03 AUP = 2.2 d

Effects of Atmosphere Composition• Particles of 1m

• Molecules (1), tropospheric clouds (2), stratospheric haze (3)

Seager et al. (2000)

Stam et al. (2004)

Incidentlight

First Detection: HD189733b

• Transiting hot Jupiter mass 1.15 MJ

period 2.2 d semimajor axis 0.03 AU

• B band (440nm, DiPol, KVA60) (Berdyugina et al. 2008)

93 nightly measurements (3h) Errors ~510–5

• UBV (360,440,550nm, TurPol)(Berdyugina et al. 2011a)

35 nightly meas. (3-4h) 29 standard stars for

calibration: ~(1-2)10–5

Errors ~110–5

• Monte Carlo error analysis• Amplitude (9 1)x10–5

(Berdyugina et al. 2011a)

(Berdyugina et al. 2008)

B

UB

HD189733b: Orbit

• Two solutions:(Berdyugina et al. 2008)

Model with Condensates: HD189733b

• Polarimetry and transit data fit with one model

• Semi-empirical model Rayleigh/Mie scattering: H, H2,

He, CO, H2O, CH4, e–, MgSiO3

Absorption: H, H–, H2–, H2+,He, He–, metals

Haze: High-altitude condensate layer with 20-30nm particles

R=1/RJ(U)~1.190.24 Scat

R=1/RJ(B)~1.180.10 Scat (in agreement with Sing et al. 2011)

R=1/RJ(V)<0.750.20 Abs

R=1/RJ(RI)<0.43 Abs

(Berdyugina 2011, SPW6,arXiv:1011.0751)

Lucas et al. (2009)

Wiktorovicz (2009)

Berdyugina et al. (2008, 2011)

++ Pont et al. (2007), 550 nm

HD189733b: Blue Planet

Geometrical Albedo, Ag:

• Strong function of 0.60.3 at 370 nm

0.610.12 at 450 nm,

0.280.15 at 550 nm,

<0.2 at 600 nm

<0.1 at >800 nm

• Similar to that of Neptune blue: Rayleigh and Raman

scattering on H2

red: absorption by molecules

• Blue Planet

(Berdyugina et al. 2011)

HD189733b: Blue Planet

• Primary transit spectroscopy, HST (Sing et al. 2011): Raleigh scattering – opacity increases to the blue Additional opacity (absorption?) at 300-400nm

R(~1)Observations areinconsistentwith cloudlessatmosphere

HD189733b: Blue Planet

• Secondary eclipse spectroscopy, HST (Evans et al. 2013): Geometrical albedo: 0.400.12 @300-450nm, <0.1 @450-590nm

Polarized Signatures of Bio-Molecules• Photosynthesis is the interaction of life with stellar light

produces conspicuous biosignatures in polarized light (broadly used in botanic and agriculture for remote sensing of crops)

source of energy for nearly all life on Earth (captures 130 TW) very likely to emerge early and last long on another planet

Common photosynthetic bio-molecules (pigments) in plants, algae, bacteria: Chlorophyl (green) Carotenoids (yellow/orange) Anthocyanins (red/purple) Phycobilin (blue)

Lab Experiment

• Lab measurements: reflection spectra 400-1000 nm R~100-200 different angles full Stokes vector

• Samples: vegetation bacteria sand/rocks paper

sample iris

/4 LP

fiber

(Berdyugina et al. 2015, IJA)

Chlorophyl(Berdyugina et al. 2015, IJA)

Carotenoids(Berdyugina et al. 2015, IJA)

Anthocyanins(Berdyugina et al. 2015, IJA)

Cyanobacterium

Microbacterium

Sands

Green Planets

• Green leaf vs green sand

Earths with 100% Vegetation

• Bio-molecules are distinguished best in polarized light!

(Berdyugina et al. 2015, IJA)

Earths with 100% Sand & Rocks

• Sandy and Vegi Earths differ in polarized light (exc red?)

80% Vegetation + 20% Clouds

• Clouds gradually wash out flux signal need clear days!

clouds100%

80% Vegetation + 20% Ocean

• Black ocean with specular reflection preserves bio-signals

clear ocean 100%

Chirality?

• Circular polarization of PS microbes: <0.001 in the lab

• Useful for in-situ studies• Unsuitable for remote sensing

• Lab Measurements of bacteria(Sparks et al. 2009)

Exoplanet Surface Imaging (EPSI)

• NASA Earth Observations (NEO) database: Albedo maps

Exo-Earth Light Curve

(Berdyugina & Kuhn 2017)

Rotational modulation of planet brightness

Exo-Earth Light Curve Simulation

Exo-Earth Light Curve Simulation

Orbital modulation of the planet brightness

Exo-Earth Light Curve Simulation

Orbital modulation of the planet brightness

6x6 North upirot=60, iorb=30, orb=60 (Npix=1800)

Porb = 60Prot (Mdata=3000)

S/N=200

IQ=89%, SD=10%

Exo-Earth Light Curve Inversion

(Berdyugina & Kuhn 2017)

Exo-Earth Light Curve Inversion

6x6 South upirot=60, iorb=30, orb=60 (Npix=1800)

Porb = 60Prot (Mdata=3000)

S/N=200

IQ=89%, SD=15%

(Berdyugina & Kuhn 2017)

• Surface imaging of Proxima b & exo-Earths:

Resolved Surface Biosignatures

(Berdyugina & Kuhn 2017)

• Interferometric Telescope-Coronagraph (Polarimeter) array of 16 off-axis telescopes (5m-8m M1, 30-50cm M2) low scattered light, segment phasing creates movable 10-8 “dark

hole”

Exo-Life Finder (ELF)

SPIE 9145, 91451, 2014

Berdyugina & Kuhn, 2017;Kuhn et al. 2014, 2018; Moretto et al. 2016

Conclusions

Solar Polarimetry: Towards smallest magnetic structures -> 30km (DKIST) Vector magnetic fields through the entire atmosphere

Stellar Polarimetry: Tremendous progress in observations (ESPADONS, NARVAL,

HARPSpol, LRISp, PEPSI, SPIROU) Advanced data modeling (full PRT, molecular lines, ZDI) provides

magnetic field topologies From 1D (mean field) to 2D (ZDI) to 3D (starspots)

• Exoplanet Polarimetry: Provides direct probes of atmospheres and surfaces Indirect surface imaging of exoplanets is possible with large

telescopes

Thank you!