Large Interstellar Polarisation Survey Stefano Bagnulo Nikolai Voshchinnikov Nick Cox PI Dust extinction emission amp polarisation in the diffuse ISM Simultaneously model ID: 935300
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Slide1
Extinction, emission and polarisation of dust Large Interstellar Polarisation Survey
Stefano
Bagnulo
, Nikolai
Voshchinnikov
, Nick Cox (PI)
Dust extinction, emission &
polarisation
in the diffuse ISM
Slide2Simultaneously
model :- Extinction - Emission - Polarisation
ISM dust
Fitzpatrick
(1999
)
Slide3PAH absorptioncross section
+ ‘’2200” bump
Malloci et al. (2007)
Verstraete
et al. 1992
Siebenmorgen et al. (2014)
Slide4Si
+ aC : 60Å < a < 0.2-0.3µm ~ a-3.5Graphite : 5Å < a < 80 Å ~ a-3.5
PAH : 30, 200 C
Abundances [X/H in
ppm
]:
31Si + 150
aC
+ 50gr + 30PAH
Siebenmorgen et al. (2014)
ISM dust Solar neighborhood
Slide5Di-
chroic polarisation Voshchinnikov(2012)
Siebenmorgen et al. (2014)
Slide6Linear ISM
polarisation empirical Serkowski formulae
Siebenmorgen et al. (2014)
Slide7Linear
polarisation Silicate feature
Siebenmorgen et al. (2014)
Slide8Siebenmorgen et al. (2014)
circular polarisationlinear polarisation
Slide9Siebenmorgen et al. (2014)
Influence of model parameters:Upper and lower particle radius
Slide10Siebenmorgen et al. (2014)
Influence of model parameters:Exponent of size distribution
Slide11FIR/
submm
extinction cross section:
Prolate
/Sphere
Siebenmorgen et al. (2014)
Slide12Observing
polarisation
spectra
FORS/VLT data = space based observations
Siebenmorgen et al. (2014)
Slide13Large Interstellar
Polarisation Survey (LIPS, PI:Cox) Target distribution (l,b):- Literature: 174 known stars- LIPS: 108 targets
Slide14LIPS: Calibration
Observing low (<0.3%)polarisation:individual readsre-binned
Slide15LIPS: Calibration
Slide16Serkowski
parameters:
Slide17LIPS: First Results
strong polarisationSerkowski fit
Slide18LIPS: First Results
low polarisationSerkowski fit
Slide19~108 stars
LIPS detection statistics ofpmax, λmax, K
Slide20Distribution of linear polarisation
pmax within LIPS
Slide21Distribution of Serkowski
parameter λmax within LIPS <λ max
> ~ 5500
Slide22Distribution of
Serkowski parameter K within LIPS K ~ 1.15
Slide23~174 known starsf
rom literatureVoshchinnikov &Hirashita (2014)K viz λmax
Slide24Magnetic filed and/or grain alignment(Voshchinnikov
& Hirashita 2014)rcutTΩδ0
P
max
viz
λmax
-> degenerated (Ω, δ0)
Slide25Simultaneous fit of
extinction & polarisationSiebenmorgen et al. (2014)
Slide26Extinction fit
Dust attenuation Dust extinction cross section..of particle of population
Siebenmorgen et al. (2014)
Υ
Slide27Extinction: 6 fit parameters
Particle sizeExponent of size distributionSiebenmorgen et al. (2014)
Relative dust abundances
(n-1) = 4 parameters
Dust attenuation
Slide28Caveats on extinction fit
Siebenmorgen et al. (2014)Scattering in or out-of-the beam
Slide29Caveats on extinction fit
Scattering in or out-of-the beamdust clumpScicluna & Siebenmorgen, 2015
Slide30Milky Way dust ✕
scattering medium -> SMC type extinction curve , , A&A, 2009Caveats on extinction fitsSMC type
MW
type
Slide31Caveats on extinction fit
Particle sizeSiebenmorgen et al. (2014)
Scattering (
Sicluna
&
Siebenmorgen 2015)
0.5nm ~ OK
Slide32SPHERE:
XAO diffraction limited optical polarimetry of supergiant
VYCMa
->
Mean grain size
50
times larger than in
ISM
Scicluna
et al (2015)
Slide33r+
(Silicates) = r+(amorph.Carbon)Particle sizeSiebenmorgen et al. (2014)
Is the growth of silicates and
aC
grains similar?
Holds: r+(ext
) = r
+(pol) ?
Slide34Extinction fit parameters
Siebenmorgen et al. (2014)Particle sizeExponent of size distribution-> simplified assumption
Scattering (
Scicluna
&
Siebenmorgen
2015)
Slide35Extinction fit parameters
Siebenmorgen et al. (2014)Particle sizeExponent of size distributionSimplified assumption
Relative dust abundances
->
(
n-1) = 4 parameters
Scattering (
Scicluna
&
Siebenmorgen
2015)
Slide36Caveats on polarisation
fitSiebenmorgen et al. (2014)For number of dust clouds along the line-of-sight of LIPS targets > 1->Adding-up of Stokes vectors results in de-
polarisation
Slide37Local dust distribution
(Lallement et al. 2015)
Slide38Local dust distribution
By high resolution spectroscopy (UVES@VLT)of IS lines: Ca II doublet (warm ISM)KI line (cold ISM)NaI, …
Slide39Local dust distribution
Jacek Krelowski, private comm.1 cloud1 cloud dominatedseveral velocity components
Slide4052 LIPS targets with UVES spectra
Slide41Extinction & polarisation
fitUV extinction (Valencic et al. 2014)Optical extinction RV (F&M2004)
Slide42Extinction & polarisation
:… more examples
Slide43LIPS: … fit first 7 stars
nvsg = no very small grainsp5 = 5 free parametersP7 = 7 free parameters
Slide44LIPS: … median best fit models
p7p5nvnv
= no very small grainsp
5 = 5 free parametersp7 = 7 free parameters
Slide45Summary
First results of the Large Interstellar Polarisation Survey includes 108 FORS spectra and 52 existing UVES high resolution spectra.Optical polarisation explained by aligned prolates, with silicates as major contributorneed 10
µ
m polarisation spectroscopy
Simultaneous fit of extinction +
polarisation - need VSG - q ~ 3.1 - r
-
pol ~ 100nm, r+ ~ 330nm
Slide46p7p5nv
Thank You
n
v
= no very small grains
p
5 = 5 free parameters
p7
= 7 free parameters