POLICAN: A near infrared

imaging Polarimeter

Devaraj Rangaswamydev@inaoep.mx

Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), MÉXICO

Team members:Luis CarasscoAbraham LunaDevaraj RangaswamyDevaraj RangaswamyDivakara Mayya

OAGH: Observatorio Astrofsico Guillermo Haro, Cananea,

Sonora, Mexico

2.1m Ritchey Chretien design, F/12, Seeing 1.3 arcseconds

CANICA:Cananea near infrared camera

POLICAN:POLarmetro Infrarrojo para CANICA

Support: CONACYT – 182841, 2012

Key Science Drivers Galactic Magnetic fields

The role of the magnetic field

in helping to form molecular

clouds and in star formation

processes.

How are molecular clouds

influenced by magnetic fields?

STRONG FIELD MODELS

M < Mφ Sub Critical

Magnetic field is strong to prevent

gravitational collapse

WEAK FIELD MODELS

M > Mφ Super Critical

Gravity dominates

MODELS WITH SIGNIFICANT MAGNETIC

FIELDS AND TURBULENCE

Ambipolar diffusion – Magnetic field is

frozen in only ionized gas, hence

neutral gas contracts gravitationally Do magnetic fields affect cloud

collapse and morphology?

Stellar magnetic fields, PlanetaryNebulas

neutral gas contracts gravitationally

along the field to form cores.

Grain Alignment

Davis & Greenstien 1951

Lazarian 2003

Background Star Polarization and use of

Chandrasekhar Fermi method

Polarization is parallel to Bpos

4

5

Retarder plate

Polarizer

Detector

� Polarizing holographic wire network made of Calcium fluoride to a range of 1 to 10 microns

� The substrate is coated with a photo resistance material and exposed to a fringe pattern interferometrically from monochromatic light.

� It has a regular sinusoidal profile covered with a conductive material.a conductive material.

� Fine lines parallel to a given spatial period. 960:1 extinction ratio

� Made with a regular grid of 4000 lines / mm

� Aperture diameter 71 mm

7

Properties2.5

μm5 μm

10

μm

Transmission

efficiency (K1) %84 86 48

Transmission of

unwanted radiation

(K1) %

0.25 0.13 0.05

Degree of

polarization (K1-

K2)/(K1+K2) %

99.4 99.6 99.8

Extinction ratio

expressed as K1/K2336:1

662:

1960:1

� Retarding plate λ / 2 is made of quartz and

magnesium fluoride (MgF2)

� It operates in a spectral range of 600 - 2700 nm.

� Calculated optical path difference of λ / 2 ±

0.04%.

� The orientation of the optical axis (Ψ) changes

about 1 ± 0.2 ° in the entire spectral range.

� Aperture diameter of 50 mm.

� Three pairs of quartz and MgF2 plates cemented

together.

� Prismatic deviation <2 '

� Wavefront distortion <= 1 λ to λ = 550 nm.

� Exterior surfaces coated with anti-reflective

coating

CANICAPOLICAN

Detector format 1024 x 1024

Detector material HgCdTe

Spectral range 0.85 - 2.40 µm

Plate scale 0.32 ''/pixel

Pixel size 18.5 µm / pixel

Total field of view 5.5' x 5.5'

CANICA characteristics

Operating temperature 77 K

Readout noise ~ 15 e-/pixel

Gain 2.35e-/ADU

Dark current 0.02 e-/sec

Full well capacity 45 000 ADU/110.000 e-

Linearity (4%) 20 000 ADU/50.000 e-

Mean quantum efficiency 76 % (for 99.5% of pixels)

Minimum integration time0.1 sec (with shutter); 1 sec (in staring

mode)

Maximum integration time 1 hour (not recommanded)

Readout time (full frame) 1 second

Performance: Limiting magnitudes J=17.5, H=17.2,

K=16.0 for SNR = 10

CANICA Linearity performance

AS12-0 Northern NIR standard

H-band observation

AS12-0 Magnitude Mag Error

Published values 10.931 0.018

CANICA values 10.934 0.003

Zero Point = 20.5

Aperture size =14

FWHM = 5.0

Filter Zero Point Sky/sec Sky [mag/arcsec2]

J 20.20 30 14.5

H 20.50 100 13.0

K 20.60 320 11.6

Observe at four polarimetric angles (00, 45, 22 and 67 deg)

4images4images

Hex Dither pattern4images

4images4images

4images

Obtain the median combined sky from these 24 images

Image = (RAW - Dark) – median sky

Flat field using Polarimetric flats obtained with corresponding angle

Resultant image is Science ready

Final Astrometry correction and Photometric analysis

Resultant image is Science ready

Calculate Stokes Q and U to get 6 sets from the 24 images

Calculate P and PA for 6 sets and find mean P and PA with errors

Observation of polarimetric standards to convert positionangles to equatorial coordinatesystem and to estimate thelinear polarimetric efficiency

Instrumental Polarization~ 2% and PA correction 41deg

HD36583C resultsP% P.A

POLICAN 3.71 71MIMIR 3.71 71Whittet et. al 3.68 70

Observation of polarimetric standards to convert positionangles to equatorial coordinatesystem and to estimate thelinear polarimetric efficiency

Instrumental Polarization~ 2% and PA correction 41deg

HD36583C resultsP% P.A

POLICAN 3.71 71MIMIR 3.71 71Whittet et. al 3.68 70

IRAS 18236-1205 is an ultra compact HII region with a size of

around 15pc

IRAS 18236-1205 - GRS 13CO integrated velocity dispersion map overlaid with contours. Over plotted are

H-band polarization vectors (P/sp > 3, sPA < 10). ATLASGAL (870microns) dust clumps are marked in

yellow squares

Polarimetric efficiency 96.3 % at H-band

Saturation limit 5 magnitude

Photon noise Limiting magnitude J=17.5, H=17.2, K=16.0 for SNR = 10

Polarization Sensitivity δP < 0.5%:

Position Angle Sensitivity δθ < 3 degree

POLICAN's near infrared polarimetric studies will complement photometric, spectroscopic and

imaging analyses from wide number of surveys like

2MASS (J,H,K)

IRAS (12,25,60 and 100microns)

Spitzer GLIMPSE (3.6, 4.5, 5.8, and 8microns), MIPSGAL (24 and 70microns)

WISE (3.4, 4.6, 12 and 22 microns)

Herschel (110, 170, 250, 350 and 500microns)

Various observations are being carried out towards molecular clouds in the galactic plane in order to

study their magnetic properties and understand the star formation process.

Correction Angle 41 deg

The magnetic field of our Milky Way galaxy as seen by the Planck satellite. This image was

compiled from the first all-sky observations of polarized light emitted by interstellar dust

in the Milky Way.