POLICAN: A near infrared imaging Polarimeter

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1 POLICAN: A near infrared imaging Polarimeter Devaraj Rangaswamy dev@inaoep.mx Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), MÉXICO

2 Team members: Luis Carassco Abraham Luna Devaraj Rangaswamy Divakara 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 , 2012

3 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? Do magnetic fields affect cloud collapse and morphology? Stellar magnetic fields, Planetary Nebulas 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 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

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6 Retarder plate Polarizer Detector

7 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. 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 Properties Transmission efficiency (K1) % Transmission of unwanted radiation (K1) % Degree of polarization (K1- K2)/(K1+K2) % 2.5 μm 5 μm 10 μm Extinction ratio expressed as K1/K2 336:1 662: 1 960:1 7

8 Retarding plate λ / 2 is made of quartz and magnesium fluoride (MgF2) It operates in a spectral range of 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

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11 POLICAN CANICA

12 CANICA characteristics Detector format 1024 x 1024 Detector material HgCdTe Spectral range µm Plate scale Pixel size Total field of view Operating temperature Readout noise Gain Dark current 0.32 ''/pixel 18.5 µm / pixel 5.5' x 5.5' 77 K ~ 15 e-/pixel 2.35e-/ADU 0.02 e-/sec Full well capacity ADU/ e- Linearity (4%) ADU/ e- Mean quantum efficiency Minimum integration time Maximum integration time Readout time (full frame) 76 % (for 99.5% of pixels) 0.1 sec (with shutter); 1 sec (in staring mode) 1 hour (not recommanded) 1 second

13 Performance: Limiting magnitudes J=17.5, H=17.2, K=16.0 for SNR = 10

14 CANICA Linearity performance

15 AS12-0 Northern NIR standard H-band observation AS12-0 Magnitude Mag Error Published values CANICA values Zero Point = 20.5 Aperture size =14 FWHM = 5.0 Filter Zero Point Sky/sec Sky [mag/arcsec2] J H K

16 Observe at four polarimetric angles (00, 45, 22 and 67 deg) 4images 4images 4images Hex Dither pattern 4images 4images 4images Obtain the median combined sky from these 24 images

17 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 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

18 Observation of polarimetric standards to convert position angles to equatorial coordinate system and to estimate the linear polarimetric efficiency Instrumental Polarization ~ 2% and PA correction 41deg HD36583C results P% P.A POLICAN MIMIR Whittet et. al

19 Observation of polarimetric standards to convert position angles to equatorial coordinate system and to estimate the linear polarimetric efficiency Instrumental Polarization ~ 2% and PA correction 41deg HD36583C results P% P.A POLICAN MIMIR Whittet et. al

20 IRAS is an ultra compact HII region with a size of around 15pc

21 IRAS 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

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23 Polarimetric efficiency Saturation limit 96.3 % at H-band 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 Correction Angle δθ < 3 degree 41 deg 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.

24 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.