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04/Dec/2014 IAUS 305
Circumstellar Polarimetry
IAG Universidade de São Paulo
Antonio Mário Magalhães
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Polarimetry• Polarimetry Group at IAG-USP:
– Antonio Mário Magalhães ! Edgar Ramirez (Postdoc)
! Nadili Ribeiro (PhD)
! Daiane Seriacopi (MSc) Marcelo Rubinho (MSc) Tibério Ferrari (MSc)
– Collaborators: ! Alex Carciofi (IAG) ! Cláudia Rodrigues (INPE/DAS) ! Antonio Pereyra (IG, Peru) ! Elisabete M. G. Dal Pino (IAG) ! Diego Falceta-Gonçalves (USP)
! Marcelo Borges (ON-RJ) ! Armando Domiciano (Obs. Nice)
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Other collaborators:– Karen & Jon Bjorkman, U. Toledo
John Wisniewski, U. Washington ! Magellanic Cloud ISM, circumstellar disks
– Jean-Philippe Bernard & CESR teamFrederick Poidevin
! ISM/PILOT, PLANCK
– Aiara Gomes (MPIA, Heidelberg)Caroline Bot, U. Strasbourg
! SMC
– Pris Frisch, U. Chicago B-G Andersson, SOFIA/USRA V. Piirola, M. Juvela Finland
! Local ISM
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Summary• Introduction • Measuring Polarization • Observations & modeling
– Be Stars ✴ Disks ✴ Short- & medium-term variability ✴ Long-term variability
– WR Stars ✴ Binaries ✴ Single stars: blobs
– B[e] supergiants in the Magellanic Clouds – Polars – Herbig Ae/Be stars
• SOUTH POL • Conclusions
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Introduction• Dust Interstellar Polarization Arises from – Dust grainsaligned by
– ISM’s Magnetic Field
• ISM Polarization provides info on – Dust properties
! size, composition – Bsky
! B component projected on the sky
– It has to be taken into account5
adapted from Ponthieu, Lagache; www.planck.fr
B field
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Introduction• Polarization can also arise from
dust scattering
UY Aur (T Tauri) Potter et al. 00
– Polarimetry at 1.2µm
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Introduction• Polarization from dust
scattering
UY Aur (T Tauri) Potter et al. 00
– Dust model
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Introduction• Polarization from Rayleigh or e- scattering
www.giangrandi.ch/optics/polarizer/polarizer.shtml
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Introduction - e- scattering– The scattered intensity is
! per e- per unit incident flux
9
d�/d⌦ =
1
2
r2o
(1 + cos
2 ✓) =3
16⇡�e
(1 + cos
2 ✓)
www.giangrandi.ch/optics/polarizer/polarizer.shtml
θ
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Introduction - e- scattering– The scattered intensity is, in reality, wavelength dependent
– for a bound e-
10
www.giangrandi.ch/optics/polarizer/polarizer.shtml
Incoming Poynting flux ⟨S ⟩ (erg/s/cm2) is:
⟨S ⟩ =c
4π
2π/ω!
0
E20 cos
2 ωtdt
2π/ω=
c
8πE20. (4.67)
We can define the cross-section as the ratio of the scattered energy per unit time dW/dt (erg/s)to the incoming Poynting flux (erg/s/cm2).
σscat(ω) =⟨dW/dt⟩⟨S ⟩
=8πe4
3m2ec4
ω4
(ω2 − ω20)2 + ω2γ2
=
=8πr2
e
3
ω4
(ω2 − ω20)2 + ω2γ2
= σTω4
(ω2 − ω20)2 + ω2γ2
. (4.68)
The cross-section σ(ω)
..
radio−IR−optical X−ray
ω
classical radiationnot valid
σ (ω )= 6π ( )ω
γ
Lorentz profile
σ(ω)
σ ( )
ωω
0
c
0
T
red blue
0
peak
peak
2
σ
σ T
ωω
max= = 10 Hz 23c
re
ω ω0
<<
almost static E−field
ω ω0>>
ep
incoming radiation oscillatesvery fast. Can neglect the slowelectron motion around the nucleous (if the e is bound)=> scattering on "free" electronsm x = F
ext
..
e
E
mx= −m x+eE cos( t)
x=eE cos( t)/m
"static" displacementmedium is polarized
ω ω
ω ω
2
0
20
0
4
10 Hz 23
the last term is slowly varying
2
0
0
Thomson scattering Rayleigh scattering
yellow Sunred sunset blue sky
Resonance scatteringof line radiation (absorption and
emission)
Typicaltens of eV (UV) for line transitions
55
Poutanen
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Introduction - e- scattering– Polarization of the e- scattered light
11
www.giangrandi.ch/optics/polarizer/polarizer.shtml
p(✓) =(1� cos
2 ✓)
(1 + cos
2 ✓)
θ
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Introduction - dust scattering– x = size/wavelength
= 2π a / λ for spherical particles
– For small particles, x << 1 (Rayleigh domain):
– For arbitrary sizes, Mie’s theory provides:
12
m = complex index of refraction
http://www.ita.uni-heidelberg.de/~dullemond/
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Introduction - dust scattering– Índices of refraction
13
http://www.astro.uni-jena.de/Laboratory/Database/databases.html
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Introduction– Intensities in electron/Rayleigh & Mie scatterings
giangrandi.ch/optics/polarizer/polarizer.shtml
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Introduction• Polarization by e- scattering in Stellar Envelopes
– Direct, unpolarized stellar flux: In
– Polarized, scattered light in the envelope: Ip
– Resulting polarization fraction, p:
Be star disk
McDavid 2001
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IntroductionPolarization from an Exoplanet occultation
SpaceRef
Text
Polarization as a function of time & inclination
Carciofi & Magalhães 2005
84°
87°90°
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Summary• Introduction • Measuring Polarization • Observations & modeling
– Be Stars ✴ Disks ✴ Short- & medium-term variability ✴ Long-term variability
– WR Stars ✴ Binaries ✴ Single stars: blobs
– B[e] supergiants in the Magellanic Clouds – Polars – Herbig Ae/Be stars
• SOUTH POL • Conclusions
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Measuring Polarization• Optical/NIR Technique
– IAGPOL – Magalhães et al. 1996
– Rotatable waveplate+calcite prism+detector (CCD or NIR array)
• Counts @ waveplate angles ψi:
zi =
⇒ Q = z1 - z3 + z5 - z7 U = z2 - z4 + z6 - z8
κ Crucis
Magalhães et al. 2005
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Measuring Polarization
⇒
8x 5min images Vector map
Magalhaes et al. 2005
• Polarimeter – Rotating waveplate
+Calcite prism ! Savart plate
– Very accurate ! σP=0.002% (or better) possible
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Measuring Polarization• Observational uncertainties
– Hiltner 1951, ApJ 114, 241: ! p.e. = 0.0022 mag ⇔ σ = 0.15% (!) (photoelectric)
– Tinbergen 1982, A&A 105, 53: ! σ = .007% (photoelectric, combining data)
– Carciofi, Magalhães 2007, ApJ 671, L49: ! σ = 0.002% (CCD imaging, single obs)(σθ = 28.6 σ/P deg)
• High accuracy now possible opens up interesting possibilities!
20
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Measuring Polarization• For your star, you get:
Magalhães & Nordsieck 2000 ! Magalhães & Nordsieck 2000
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Measuring Polarization• VLT/SPHERE
! Spectro-Polarimetric High-Contrast Exoplanet REsearch
– Game changer for: ! study of circumstellar envelopes & extended atmospheres
! E.g., AGB stars - we know they’re non-spherically symmetrical – Landstreet & Angel 1977; Coyne & Magalhaes 1977, 1979;
McLean & Clarke 1977; McLean 1979; Harrington 1969
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http://www.eso.org/public/news/eso1417/
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AGB environment - Alpha Ori
WUPPE Astro-2 result Nordsieck et al. 94
Nordsieck et al. 1994; Magalhaes & Nordsieck 2000
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AGB environment - Alpha OriθWUPPE = (159±8)o
θHST = 235o
⇒ θWUPPE ≈ θHST - 90o! Magalhães & Nordsieck 00
24
Gilliland & Dupree 96
17/03/05
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Summary• Introduction • Measuring Polarization • Observations & modeling
– Be Stars ✴ Disks ✴ Short- & medium-term variability ✴ Long-term variability
– WR Stars ✴ Binaries ✴ Single stars: blobs
– B[e] supergiants in the Magellanic Clouds – Polars – Herbig Ae/Be stars
• SOUTH POL • Conclusions
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Be stars - Disks– We can estimate the continuum polarization
– Capps et al (1973), McLean (1979), Cassineli et al (1987)
– It can be approximated by ( )with = Stellar flux w/o the disk = Disk emission = = fraction of scattered flux = polarized flux = polarization @
26
P� =fpfsS�
S�(e�⌧ + fs) +D�
D�
S�
fsfp =
3
16⇡⌧
Z 2⇡
0p(✓)(1 + cos
2 ✓)d✓ =
3
16
⌧
www.asu.cas.cz
p(✓) =(1� cos
2 ✓)
(1 + cos
2 ✓)
P� =3⌧
16(1 +D�/S�)� 7⌧ ⌧ = ne
�e
(Ro
�Ri
)(optically thin disk)
fp =
3
16⇡⌧
Z 2⇡
0(1 + cos
2 ✓)d✓ =
9
16
⌧
fs /3
16⇡(1� e�⌧
)(1 + cos
2 ✓)
V j�
✓
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Be stars - Disks– Schematic behaviour of σbf:
! for all bound states with energy < hν
27
Seaquist
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Be stars - Disks• Model polarization
! normalized to 1 @ 450 nm Mc Lean (1978)
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www.asu.cas.cz
P� =3⌧
16(1 +D�/S�)� 7⌧
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Be stars - Disks• Model polarization
! normalized to 1 @ 450 nm Mc Lean (1978) www.asu.cas.cz
P� =3⌧
16(1 +D�/S�)� 7⌧
We know that:
so f-f is important in the NIR!
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Be stars - Disks– With some actual disk parameters:
! ne = 5 ⨉ 1011 cm-3
! τ = ne σe (Ro-Ri) ≤ 1(Ro-Ri) ≲ 5 R*
→ Polarization is produced within a few stellar radii
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Be stars - Disks• Example:
WUPPE UV spectropolarimetry of the Be star ζ Tau
– Absorption by FeII/III in the envelope
– Decrease in P across optical Fe lines
Bjorkman et al. 91
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Be stars - Disks– Monte Carlo disk models for arbitrary τ
– Wood et al 1997; Carciofi 2012
! %P levels higher %P Balmer jump higher
! Still geometrically thin disks
! Optical %P produced within a few (≲ 5) stellar radii
! For comparison:Hα is produced mostly from 5 - 20 R*
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Be stars - Disks• Disk Variability:
! Achernar (α Eri)
– Short term P variability ! ~hour ! Frequency ~ rotation
– 0.57 vs 0.49 cycles/day
– Short & long term var.in PA
33
Carciofi et al. (2007)
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Be star - variability• Disk Variability:
! Achernar (α Eri)
– Blob is formed &dissipates into a ring
– Ring model ! R* < r < Rr ! nr = ndisk x γ ! Time scale:
weeks
Carciofi et al. (2007)
Results: - 1.1 < Rr < 1.3 R* - 0 < γ < 3
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Be star - variability• Disk Variability:
! Achernar (α Eri)
– Blob model ! radii: 0.1R* < Rblob < 0.3 R* ! density: 1.5 n0 < nblob < 4.5 n0
– Results: ! blobs can account for
short time scale variations(~0.05%, ~6° )
Carciofi et al. (2007)
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Be star - variability• V/R variability
– Model using ! polarization ! photometry ! spectroscopy ! interferometryfor ζ Tau
36
Carciofi et al. 2009
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Be star - Long term variability• Monitoring of 60 Cyg
– 1992 to 2004 – spectropolarimetry &
spectroscopy ! Pine Bluff & Ritter Obs.
– For 60 Cyg: ! Be-phase to normal B:
~1,000 days(viscos.par. α ~0.14)
! Time lag between P and Hα max & min
– disk clearing from inside-out
37
Wisniewski et al. 2010
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Be star - Long term variability• 60 Cyg
– Well defined disk plane:PA=107.7° ± 0.4°⇒ θdisk = 17.7° on the sky
– Allows determination of Intestellar Polarization (= ISPol)
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Wisniewski et al. 2010
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WR stars in binaries• V444 Cyg
– O + WR binary
39
spacefellowship.com/news/art14845
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WR stars in binaries• V444 Cyg
– O + WR binary
– Monte Carlo model
– From fits to Flux, Polarization vs. phase: ! RWR =4 R☉ , RO = 10R☉ ! a = 40 R☉ ! LWR/LO = 0.18 ! ne(RWR) = 1.02x1012 cm-3 ! dM/dt = 0.9x10-5 M☉ yr-1
40
Rodrigues & Magalhães (1995)
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WR stars - variability• Isolated WRs present random variability in
– Flux (up to ~10%) ! Marchenko et al. (1998)
– Polarization (up to 0.5%) ! Moffat & Robert (1992)
– Spectral line profiles ! moving bumps; Robert (1994) ! discrete absorption components (DACs; Prinja & Smith 1992)
• Characteristics – Often correlated
! Robert (1994) – Same time scales
! hours to days – Sizes of ~1 R*
! Lepine & Moffat (1999)41
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WR stars - variability• Blobs in WR winds
– Monte Carlo model ! Rodrigues & Magalhães (2000)
– Regions of enhanced density – Multiple scattering – Finite source size
• Other work – Oudmaijer & Harris (2008)
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WR stars - variability• Blobs in WR winds
– Monte Carlo model ! Rodrigues & Magalhães (2000)
– Regions of enhanced density – Multiple scattering – Finite source size
• Dependence of ΔI & ΔP on – blob distance (in stellar radii)
43
Rodrigues & Magalhães 2000
dbl = 3.0
dbl = 5.0
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WR stars - variability• Blobs in WR winds
– Monte Carlo model ! Rodrigues & Magalhães (2000)
– Regions of enhanced density – Multiple scattering – Finite source size
• Dependence of ΔI & ΔP on – blob size (in stellar radii)
44
Rodrigues & Magalhães 2000
Rbl = 1.0
Rbl = 0.5
Rbl = 0.25
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WR stars - variability• Blobs in WR winds
– Monte Carlo model ! Rodrigues & Magalhães (2000)
– Regions of enhanced density – Multiple scattering – Finite source size
• Dependence of ΔI & ΔP on – blob number
! τbl=5.0, Rbl=0.5, dbl=3.0
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Rodrigues & Magalhães 2000
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B[e] SGs in the Magellanic Clouds
• Hot, Luminous Stars
• Relationship with WRs e LBVs?
Lamers et al. 1998
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B[e] SGs in the Magellanic Clouds• Spectroscopic evidence:
– two–component wind model ! Zickgraf et al 85, 86, 89, 96
hot, fast wind
cool, slow windZickgraf et al. 85
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B[e] SGs in the Magellanic Clouds• Are they polarized?
Yes!
⇒ non–spherically symmetric envelopes! (Magalhães 92)
• Polarigenic mechanism? – Thompson scattering
Melgarejo et al. 2001
R 82
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B[e] SGs in the Magellanic Clouds
• R82 : Continuum – P(λ) non-‘white’
• Polarizing mechanism – e– scattering + H–absorption? – Dust?
• Quantifying the role of the dust: – Models w/ e– + dust: HDUST ! Carciofi & Bjorkman (2006)
Magalhães et al. 2012; Seriacopi 2014
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B[e] SGs in the Magellanic Clouds
• R82 : detail around Hβ
– P Cyg profile appears in the polarized (i.e., scattered) flux
– Line produced byscattering in an expanding disk
Magalhães et al. 2012; Seriacopi 2014
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Model Best Fit Parameters– Using HDUST
! (Carciofi & Bjorkman 2006)
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Seriacopi (2014)
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Polars - going for the small...• Polarimetry of magnetic binaries
– (AM Her systems)
53
Red Dwarf
White Dwarf
acretion column(s), with B~107-8G field along it
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Polars - going for the small...• CYCLOPS - Cyclotron Emission of Polars
! Costa & Rodrigues (2009)
– Cyclotron radiation ! emission & absorption
– Bremstrahlung ! absorption in X-rays (mostly)
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Polars - going for the small...• Cyclops - Cyclotron Emission of Polars
! Costa & Rodrigues (2009) – Cyclotron radiation
! emission & absorption – Bremstrahlung
! absorption in X-rays (mostly)
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Polars - going for the small...• Cyclops - Cyclotron Emission of Polars
! Rodrigues et al. (2011)
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CP Tuc
Emitting region: small fraction of the Earth’s surface!
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Orientation of Stellar Envelopes• Polarimetry of Herbig Ae/Be objects
! Pre-MS, intermediate mass stars
! Comparison ofEnvelope Orientation vs. ISM B-field
! Statistics of Δθ = Intrinsic PA - ISM Pol PA can be done.
57
McDavid 2001
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Impact - Stellar Astrophysics• Polarimetry of Herbig Ae/Be objects
! Statistics of Δθ = Intrinsic PA - ISM Pol PA
58
– 9 –
Fig. 1.— Cumulative frequency distribution of the di⇥erence between the intrinsic and
interstellar polarization angle, ��, for our HAeBe sample.
Rodrigues et al. 2009
Text
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Impact - Stellar Astrophysics• Polarimetry of Herbig Ae/Be objects
! Statistics of Δθ = Intrinsic PA - ISM Pol PA
– For the more highlypolarized stars:Δθ → parallel to ambient B-Field
59
– 9 –
Fig. 1.— Cumulative frequency distribution of the di⇥erence between the intrinsic and
interstellar polarization angle, ��, for our HAeBe sample.
Rodrigues et al. 2009
{
Envelopes have memory of ISM B-field !
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Orientation of Stellar Envelopes• Polarimetry of Herbig Ae/Be objects
! Example: PDS 144
60
Pereyra et al. 2012
Red arrows: H-band polarization
PDS144 N: Keck AO, (Perrin et al. 2006)
Black arrows: detected jets (Grady et al. 2009)
NIR
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Orientation of Stellar Envelopes• Polarimetry of Herbig Ae/Be objects
! Example: PDS 144
61
Pereyra et al. 2012
Red arrows: H-band polarization
PDS144 N: Keck AO, (Perrin et al. 2006)
Black arrows: detected jets (Grady et al. 2009)
NIR
Polarization is indeed ⊥ to disk
PDS 144 N
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Impact - Stellar Astrophysics• Origin of Earth’s Magnetic
Field? – Dynamo from Earth’s rotation
– Earth’s rotation derived from Protosolar Nebula
– Nebula probably had memory of ISM B field Connection betweenEarth’s Magnetic Field &Interstellar Field !
62
Glatzmaier & Olson 2005
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Summary• Introduction • Measuring Polarization • Observations & modeling
– Be Stars ✴ Disks ✴ Short- & medium-term variability ✴ Long-term variability
– WR Stars ✴ Binaries ✴ Single stars: blobs
– B[e] supergiants in the Magellanic Clouds – Polars – Herbig Ae/Be stars
• SOUTH POL • Conclusions
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SOUTH POL Survey• SOUTH POL:
– Optical survey of the polarized Southern sky ! FAPESP, PI: A. M. Magalhães
• Goal: – Polarimetric accuracy of 0.1% at V~15-16
• Survey’s first epoch: – Sky South of Dec -15° – Complete in ~ 2 years
• It will gradually progress towards North
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Co-I’s - SOUTH POL– Cláudia M. de Oliveira (PI, TR-80)
– Dra. Elisabete M. G. Dal Pino (IAG-USP)
– Roberto Costa (IAG-USP)
– Marcos Diaz (IAG-USP)
– Alex Carciofi (IAG-USP)
– Claudia V. Rodrigues (INPE/DAS)
– Antonio Pereyra (IG, Peru)
• Project – Eng. Lucas Marrara (São Carlos, SP)
– Eng. Carlos Eduardo Firmino (Solunia, Araraquara, SP)
– Keith Taylor
Funding:
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SOUTH POL - How?...• 80cm Robotic Telescope
! FAPESP, PI: C. M. de Oliveira w/ A. Kanaan, W. Schönel, R. Calado & T. Ribeiro
– Currently being installed ! CTIO, Chile
–
– CCD: ! EEV, 9k x 9k, 92mm ! 2.0 sq degrees (!) 66
J-PAS T80 South
Doc.: Issue: Date: Page:
D2510/Tech Prop 2 04-02-2012 9
This document is the property of AMOS. It can be neither disclosed nor duplicated without prior authorization.
The image quality of the telescope is further detailed in Figure 4, Figure 5 and Figure 6. Figure 4 shows the uniformity of the polychromatic image quality in the FOV of 0.85° in radius. The monochromatic encircled energy is reproduced at center mid and edge FOV in Figure 5. The image quality is sensitive to the manufacturing quality of the optics, to element alignments and to environmental contributors. Given the individual tolerances on all the contributors (T°, gravity and wind), the image quality is evaluated through a Monte-Carlo analysis. All the parameters defining the nominal optical design are arbitrarily modified such that they remain within the defined tolerance limits and the encircled energy is calculated on these modified configurations. The result is shown in Figure 6. 80% of the random modified configurations are such that EE80 radius is smaller than 7µm.
Figure 5: Monochromatic diffractive encircled energy
Figure 6:Polychromatic encircled energy in 100 random configurations incorporating tolerances of the optical parameters
Table 1: Summary of the performance of the T80 design
Performances of design Aperture 0.840 m diameter
Plate scale 55.56 arcsec/mm Focal length 3712 mm
Field of view 110 mm (1.7°) with optimized image quality 155 nm (2.4°) with limited performances
Image Quality 50% EE = 5 µm / 0.28 arcsec (diameter) 80% EE = 13 µm / 0.72 arcsec (diameter)
Distortion 0.6%
4.4 M1 MIRROR
The primary M1 mirror will be manufactured from ZERODUR and will be F/1.5. The blank will be procured from SCHOTT and the mirror will be produced in AMOS workshop. The manufacturing sequence includes a first step of spherical lapping and polishing for controlling the mirror radius of curvature.
26/May/14
SOUTH POL
ASTROPOL 2014
How?...• T80S Robotic Telescope
! FAPESP, PI: C. M. de Oliveira ! Being installed @ CTIO
67
Cassegrain Module
Electronics/Control Module
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How?...• Polarimeter optics & mechanics
68
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Achromatic Half-wave plate116.0
58.0
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• Polarimeter status
– Optical components ! delivered to CTIO✓
– Mechanics & Electronics ! delivered to CTIO ✓
– Reduction pipeline ! Edgar Ramirez (IAG) &
James Davidson Jr. (UT) ! done ✓
69
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• Robotic Telescope site
70S. Heathcote, CTIO
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• Robotic Telescope site
71
S. Heathcote, CTIO
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• Robotic Telescope site
72
Gale Brehmer, CTIO
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL
73
T80-S @ CTIO October 2014
Courtesy: C. M. de Oliveira, IAG-USP
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
How?...• High Galactic Latitude
Clouds – From
models of stellar population synthesisof the Galaxy:
! V ≲ 15: covers 3 kpctowards b=90°
– In other words, ! Galactic dust layer will be
well sampled!
74
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - How?...• Combination of
– Southern 80cm Robotic Telescope in Chile ! funded by FAPESP
– Large field Imaging Polarimeter ! 2.0 sq.deg.
75
IAGPOL footprint
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - How?...• Combination of
– Southern 80cm Robotic Telescope in Chile ! funded by FAPESP
– Large field Imaging Polarimeter ! 2.0 sq.deg.
76
SOUTH POL footprint
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - Overall impact • Origin of CMB Polarization
– Thomson scattering ! Sound waves produce anisotropy → net polarization
77Dowell et al. 2014; BICEP2 Collaboration
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - Overall impact
78Dowell et al. 2014; BICEP2 Collaboration
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - Overall impact
79Dowell et al. 2014; BICEP2 Collaboration
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL - Overall impact • Galactic Dust Emission Polarization in the sub-mm
• Contribution by Galactic Dust to BICEP2?80
Bernard et al., Planck Collaboration (2014), arXiv
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• SOUTH POL:
– Optical survey of the polarized Southern sky
• Goal: – Polarimetric accuracy of 0.1% at V=15-16
• First epoch: – Sky South of Dec -15° – Completed in ~ 2 years
• Observations should help settle the foreground dust contribution 81
BICEP2 field
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
SOUTH POL• SOUTH POL
– unprecedented undertaking in the optical – accuracy of 0.1% down to V=15-16 – will cover -15° < dec < 90° in first 2 yrs
– will impact several areas ! Cosmology ! Extragalactic Astronomy (AGN) ! Stellar Astrophysics (GRBs, SNe, Star Formation, Circumstellar
environments) ! Galactic ISM ! Solar System (asteroids)
– Sinergy with Planck, ALMA, GAIA ! e.g., Galactic 3D magnetic field structure
82
04/Dec/2014
Circumstellar Polarimetry
IAUS 305
Conclusions• Circumstellar polarimetry: important tool for studying
– asymetries around stars ! young and evolved ! often unresolved
– time evolution of mass loss
• Future avenues: – more high cadence observations – model treating line formation & scattering fully – study disk alignment with local B-field – study winds with eclipse spectropolarimetry – aligned grains in disks from mid-IR/sub-mm polarimetry
83