Group 4 :

Sweety Deswal -

Vaibhav Savant

Seljin Mathew

Poruri Sai Rahul

Sundar M.N

An efficient tool in the study of Dust Properties and Magnetic Fields

Project Guide – C. Eswaraiah (Post Doc)

Outline of the Presentation

Introduction

Aim of the project

Observations and data reduction

Results

Conclusions

Aim of the Project

Dust properties using multiband polarimetry

Finding the probable cluster members using Stoke’s plane

Magnetic field mapping

• The space between stars is not perfect vacuum: filled with gas (ions, atoms and molecules) and dust termed as ISM, which makes 10% of the visible mass in the Milky-Way.

• ISM components : Gas 99% of ISM [90%H, 10%He,

0.1% Metals], Dust ~1%.

• The presence of ISM Dust can be studied by

observing the Extinction, Polarizations and dust

emission.

Inter Stellar Medium (ISM)

Inter Stellar Medium (ISM)

• Morphology-highly complex: Diffuse clouds, hot and warm clouds, molecular cloud etc,

• Temperatures: 10-10^4 K;

• Densities: 10^2-8 H/cm^3).

• Molecular clouds have molecular H at low

temperature (~ 10K) and high densities (~10^4-9

cm^3) .

•Dust particles usually have sizes of 0.01 - 1 μm. •Chemical compositions :carbonaceous and silicates (based on extinction curve) •Dust in the space can be seen in silhouette as it blocks out the light from the background.

RGB mosaic image of entire sky (Mellinger 2009)

Properties Of Dust

Because of the small size of the dust particles, the blue light will scatter more than red light and, as a result the images from a dusty environment appear more red than they were without dust. This effect is known as interstellar reddening. When star light (or light from other astrophysical objects) passes through the ISM, some of the light will be absorbed and some of it will be scattered. These effective losses are known collectively as extinction.

Extinction?

Nd is the total column density of dust, a is the size of the dust grain and Qext is the extinction efficiency factor

Wavelength dependent of Extinction: Dust properties

Comparison between extinction and polarization

ISM dust polarization

Object of Interest: Stock 8

Emission Nebula in Auriga Constellation

RA: 05h 27m 36.00s

Dec: +34° 25‘ 00.0“

Distance: 2.05 ± 0.10 kpc(Jose et al 2008 )

Reddening varies from 0.40 to 0.60 mag (Jose et al., 2008 )

This cluster is located towards anti-center Galaxy.

Polarimetric Observations 104 cm Sampurnand Telescope

Johnsons UBV and Cousins RI U: 364 nm

B: 442 nm

V: 540 nm

R: 647 nm

I: 786.5 nm

Polarimetric observations – 17/12/2012

Polarized standard: HD236633 – to correct for the polarization angles

1.04 m Sampurnanad Telescope

AIMPOL attached to the telescope

FOV of ~8’ diameter. Linear Polarization BVRI bands CCD – 1k*1k (1024 X 1024) pixels(370 X 370 pixel^2) Gain: 7.0 e, R/N: 11.98 e/ADU FWHM: 2-3 pixels Plate scale: 1.73 arcsec/pixel Seeing: 3.5-5.0 arcsec (FHWM * Plate sclae)

Data Reduction & Analysis

Observation Pre-Processing Aperture

Photometry Polarimetry

Data Reduction & Analysis

pmi2fits conversion

.pmi2fits & .mt files

Master bias

zerocombine

Bias Subtraction

ccdproc

Alignment & Stacking

imalign

imcombine

Photometry

Phot

Stokes parameters, P, θ, Pmax, λmax

IDL

Data Reduction & Analysis

Polarization, Stokes parameters: I, Q, U and V

I : Total intensity Q, U : linear polarization V : circularly polarization

Total incoming light can be represente as a combination of following stokes parameters:

q=Q/I, u=U/I Polarization (%) P = sqrt(q^2 +u^2) Polarization Angle (radians) PA= 0.5 arctan(u/q)

To find P (polarization) and position angle:

R() {q, u, q1, u1} at => 0, 22.5, 45, 67.5 degree

FLAT FIELDING:

(Ramaprakash et al. 1998 & Medhi et al 2007, 2010, Eswaraiah et al. 2011, 2012)‏

σ R(α) {σ q , σ u , σq1 and σu1} σR(α) = [(Ne + No + 2Nb )/(Ne + No )]^(1/2), (Ramaprakash et al. 1998)

Data Reduction & Analysis

Fit using Serkowski law:- P/Pmax = exp[-K * ln2 (λmax/ λ)]

K = 1.66 λmax ( Whittet, 1992)‏

Standard stars were observed to correct for the instrumental polarization and zero-point polarization angles (ZPA)

Instrumental polarization < 0.1 %

The ZPA corrections in

B : 6 deg

V : 9 deg

R : 12 deg

I : 7 deg

Data Reduction & Analysis

The polarization vectors (yellow) of 20 stars that are distributed towards Stock 8 are over-plotted on the colour composite image made using WISE 3.4 micron(Red), 2MASS K-Band(Green) and DSS R-Band image.

Res

ult

s Polarization Vector Map

The Plots show the distribution of Pmax and λmax.

1. The Gaussian fitted mean values of the Pmax and λmax are found to be 2.33 ± 0.49 % and 0.584 ± 0.10 μm, respectively

2. The estimated λmax is approximately equal to the value corresponding to the general ISM (0.545 μm; Serkowski et al. 1975).

3. Using the relation RV = (5.6 ± 0.3) λmax, it was found that the value of total-to-selective extinction Rv =3.27 ± 0.58, which close to the average value for the Milky Way Galaxy (Rv = 3.1), indicating that the size of the dust grains within the cluster Stock 8 is normal.

Results

Stokes Plane:

Distribution of the Dust

Majority of the stars located within the 1σ box could be probable cluster members

Qv versus Uv of 20 stars. The square covered by Qv =0 and Uv =0 is the dust less Solar neighborhood. 1σ box is drawn with dashed line using the mean and standard deviation of Pv ± σPv = 1.74 ± 0.26 per cent and θv ± σθv =.163.41 ± 7.01

Pv ± 1σPv

θv ± σθv

Conclusions

Multiband Polarimetric data has been used to derive Serkowski Parameters Pmax ,λmax.

Mean λmax suggests that the dust size distribution is similar to the general diffused ISM. And thus suggesting normal extinction law.

Stokes Plane has been used to find the probable cluster members. And to study the dust distribution.

Majority of the polarization vectors are closely aligned with the Galactic parallel.

Thank You!!!