Transcript Talk, ppt

Polarization in astronomy and its registration.
EDIPO project.
Sergey Guziy
on 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 deg
V ≡ 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(0o) + Ie(90o)]
U/I = [Io(45o) – Io(135o)] / [Ie(45o) + I e(135o)]
Basic definitions (5)
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
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.
Basic definitions (6)
Analyzers
Calcite plate
Beamsplitter polarizing cubes
Wollastone prism
Polaroid film
Astronomy
Polarimetry 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 polarization
SX 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
Motivation
I. 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 polarimeterphotometer 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
FOV
Polarimeter effective focal length
Polarimeter F ratio
Pixel size
Pixel scales
Direct Imaging
Wavelength range
Filters
System focusing mechanism
RC 1.4 m
30’ x 30’
4480 mm
3.2
10 x 10 or 20 x 20 μm
0.56 or 1.08 arcsec/pixel
Over the whole FOV
0.5 – 1.0 μm
V, R, I or r, i, z
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 !