Polarization in astronomy and its registration. EDIPO project.

Sergey Guziyon behalf of a large collaboration

(NNU, Nikolaev, Ukraine)

(IAA-CSIC Granada, Spain)

Tarusa, 2015

Alberto J. Castro-Tirado (IAA-CSIC, Spain)Javier Gorosabel (IAA-CSIC)

Sergiy Guziy (AO NNU, Ukraine,IAA-CSIC)Dolores Pérez-Ramírez (Univ. de Jaén)Antonio de Ugarte Postigo (IAA,CSIC)

Petr Kubánek (UV, IAA-CSIC)Martin Jelínek (IAA-CSIC)

Miguel Andrés Sánchez (IAA-CSIC)Ovidio Rabaza (IAA-CSIC)

Ronan Cunniffe (IAA-CSIC)Concepción Cárdenas (IAA-CSIC)

Yuriy Ivanov (MAO, Ukraine)Ivan Syniavskiy (MAO, Ukraine)

Basic definitions (1)

Polarimetry refers to the art or process of measuring the polarization of the light. A more scientific definition: the science of measuring the polarization state of a light beam and the diattenuating, retarding and depolarizing properties of materials.

Considering a plane wave, the Electric field vector :

The shape traced out in a fixed plane by the electric field vector as such a plane wave passes over it (a Lissajous figure) is description of the polarization state

Basic definitions (2)

The polarization state of a light beam can be represented by four parameters which are called the Stokes parameters, which are defined as follows:

I ≡ total intensity

Q ≡ I(0) – I(90) = difference in intensities between horizontal and vertical linearly polarized components

U ≡ I(+45) – I(-45) = difference in intensities between linearly polarized components oriented at +45 deg and -45 degV ≡ I(rcp) – I(lcp) = difference in intensities between right and left circularly polarized components

The Stokes parameters are often combined into a vector, known as the Stokes vector:

Basic definitions (3)Polarization ellipse. The electric vector traces out an ellipse in the

plane

The Poincaré sphere is the parametrisation of the last three Stokes' parameters in spherical coordinates

Basic definitions (4)Polarimeter: an optical instrument for determining the polarization state of a light beam or the polarization-altering properties of a sample.

Simple polarimeter

If we will have Ie,o (φ) with four position of analyser φ = 0o, 45o, 90o и 135o,

can calculate:

Q/I = [Io(0o) – Io(90o)] / [Ie(0

o) + Ie(90o)]U/I = [Io(45o) – Io(135o)] / [Ie(45o) + I e(135o)]

Basic definitions (5)

Two classes of polarimeters

Light-measuring polarimeters (Stokes polarimeters), which measures the polarization states of a light-beam in terms of the Stokes parameters. It is typically used to measure the polarization paramaters of a light source.

Sample-measuring polarimeters (Mueller polarimeters), to measure the properties of a sample in terms of diattenuation, retardation and depolarization.

Two subclasses

Complete (or full) Stokes polarimeter, a Stokes polarimeter measures all the four Stockes parameters.Special (or incomplete) Stokes polarimeter, a Stokes polarimeter which cannot measure all the four Stokes parameters.

Polarimeters became common user instruments in the 1980’s but has rarely been included in the baseline design of either telescopes and instruments. Very few telescopes can obtain polarimetric observations on a regular basis

Basic definitions (6)Analyzers

Calcite plate

Beamsplitter polarizing cubes

Wollastone prism

Polaroid film

AstronomyPolarimetry has played a very important role in the development of optical and infrared astronomy ever since the 1920s when Lyot observed the scattered and hece polarized sunlight from planetary atmospheres.

The polarization state of radiation contains a wealth of information:

-on the nature of radiation sources,

-on the geometrical and velocity relationship between a radiation source, scatterer and observer,

-on the chemical and physical properties of the dust grains,

-on the direction of the magnetic field as projected on the plane of the sky (for the case where these are aligned).

Astronomy

Map of interstellar polarization in our Galaxy

Astronomy

Variability of polarizationSX Cas star in B band

Magnetic field on the star. Zeeman effect in spectrum of peculiar star HD66318

Astronomy

Variability of circle polarization for polar V405 Aur and geometry reconstruction filed on surface of white dwarf

EDIPO project

Efficient & Dedicated wide-field Imaging POlarimeter

MotivationI. SCIENCE

1. Very early polarimetric observations of GRBs (prompt/afterglow) (10%)

2. Regular polarimetric observations of interesting sources (20% of time)

3. A pathfinder for an all-sky polarimetric survey complete to 17th mag (50% of the time) Never done so far !

Note: Calibrations will take another 20% of the time.

II. TECHNOLOGY

a. A state-of-the-art WIDE-FIELD Stokes polarimeter (coupled to a 1.4m robotic telescope), with the instrument available 100% of the time

b. Other capabilities:-circular polarization-multicolour photometry -low-res spectroscopy

Motivation: Science (1)1. Very early polarimetric observations of GRBs (prompt/afterglow) [10% of obs time]

The 2.0m LT (+RINGO) already responded to two GRBs: GRB 060418 in ~200s imposing a 2-σ limit of P < 8% and detecting significant polarization(10%) for GRB 090102 in a 60s exposure taken 150s after the event (Steele et al. 2009, Nat 462, 767). Support is given to a higher polarization which may be highly variable (as might have seen in γ-rays for GRB 041219A; see also Götz et al. 2009, ApJ 695, L208). We should do much better, responding in 60s with time resolved polarimetry.

Motivation: Science (2)2. Regular polarimetric observations of highly polarized sources: Cataclismic variables (e.g. polars), Galactic compact objects (e.g. microquasars), Active Galaxies (eg. Blazars) [20% of obs time]

Motivation: Science (3)3. A pathfinder for monitoring 10% of the sky to better define and optimize the procedure for obtaining an all-sky polarimetric survey complete to 18th mag down to 1% level. Never done so far! [50% of time] Previous works: 1) 560 sqr deg of the sky were surveyed in 1993 with large format Schmidt plates and polarizing plates searching for blazars downto5% level. 2) 48 sq deg towards the Pipe Nebule (= Barnard 59, 65–67 & 78). (Alves et al. 2008, A&A 486, L13)

We plan to select fields in the Galactic Plane, Ecliptic Plane and North Galactic Pole covering 4000 sqr deg in order to derive some statistics about the expected number of interesting objects to be detected. 20 million of objects will be detected.

The Stockes polarimeter-photometer optical design

1. Introduction

There are many known schemes for Stocks polarimeters. For simultaneous recording of the Stocks parameters the separating the input light flux in the amplitude or the pupil is necessary. However, none of the methods of separation of the amplitude can not provide a wide FOV and a wide spectral range simultaneously. Therefore, we propose a scheme with the division of the pupil. Feature of this scheme is the need for the three optical properties simultaneously: - Entrance optics must collimated beams after the main focus of the telescope. - The collimator should create quality image of the entrance pupil. - Camera lens must correct the telescope's aberrations for wide FOV.

2. Requirements

2.1. Optics requirements Focal Station RC 1.4 m FOV 30’ x 30’ Polarimeter effective focal length 4480 mm Polarimeter F ratio 3.2 Pixel size 10 x 10 or 20 x 20 μm Pixel scales 0.56 or 1.08 arcsec/pixel Direct Imaging Over the whole FOV Wavelength range 0.5 – 1.0 μm Filters V, R, I or r, i, z System focusing mechanism Telescope M2

Layout of Stocks Polarimeter

Exploded view of the Polarimeter.

The exploded view of the polarimeter is presented. The detector be mount to a back part of the unit of wheels with using of stiffening truss.

Exploded view of the Wheel mechanism.

The Detector

Four detectors, one per channel

U16 (Kodak KAF-16801)

Alta® U16 Specifications

- 4096 x 4096 array, 9 x 9 micron pixels - 5 MHz 12-bit and 1 MHz 16-bit digitization - 32Mbyte camera memory - USB 2.0 interface: no plug in cards or external controllers

Lenses

Testing on telescope (1)

Carol Alto Astronomical observatory, 1.23 м telescope.

Testing on telescope (2)

EDIPO with telescope Filter wheel

First light(1)

Cluster М3

First light (2)

Cluster М56

First light (3)

Galaxy М101

Thank you !