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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!
