Transcript Achromatic Interfero Coronagraph with Variable Rotational Shear for

Pavel Frolov
Space Research Institute (IKI) of RAS
Common-Path Achromatic Interfero
Coronagraph with Variable
Rotational Shear (CP-ARC)
for Direct Imaging of Extrasolar
Planets
2016
Introduction
• 1988 – the first report on possible (sub) stellar companion
of double star Gamma Cephei
• 1992 – discovery of a planetary system
around millisecond pulsar PSR B1257+12
• 1995 – the first definitive detection of a hot Jupiter
around a solar-type star 51 Pegasi
• Nearly 3500 extrasolar planets have been confirmed as of May 2016
(http://exoplanet.eu, http://exoplanets.org), …
• Plus about 3000 unconfirmed planet candidates discovered by Kepler Space
Observatory (http://exoplanetarchive.ipac.caltech.edu/docs/data.html)
• Main detection methods are indirect ones:
Method
Transit
Radial
velocity
Planets
~ 2600
~ 650
Direct
imaging
Gravitational
microlensing
Timings
69
46
30
Direct imaging of exoplanets
• Primary objective:
– direct imaging of earth-like planet within the habitable zone around mature
nearby stars AND obtaining its spectrum in a wide wavelength range
• Instruments:
– ground-based (limited performance due to
stratospheric or space telescope – to collect light
atmosphere
– adaptive optics – to correct wavefront
– stellar coronagraph – to suppress bright star light
Very bright
actually –
brightness
ratio is up to
10 orders of
magnitude
The first detection of
exoplanet by direct
imaging: a giant planet
orbiting a young brown
dwarf discovered in
2004 by VLT-UT4
influence),
Types of coronagraphs:
Stellar coronagraphs can be divided into several sets of groups. Many coronagraph approaches
known to date can achieve contrast on the order of 10-10 at IWA (inner working angle) of several
λ/D and therefore are able to image earth-like exoplanets around nearby stars with large
telescope (about 10 meters and more) in the visible and near infrared.
The place among other coronagraphs
1997
2010
AIC
Better star light
suppression
ARC
Mechanical
stability
CP-AIC
CP-ARC
2005
2011
Common-path achromatic Interfero
Coronagraph with Variable Rotational Shear –
principle and optical design
(a) principle
(b) optical scheme
Simulated
coronagraphic image:
Suppressed Sun AND
giant planets of the
Solar system (Jupiter,
Saturn, Uranus,
Neptune) at the dark
output of CP-ARC.
10 parsecs away, 2.4m telescope,
λ=0.35…0.85µm,
rotational shear 3.6°,
zero orbital
inclination.
Intensity is in
logarithmic scale,
dynamic range
(between black and
white) is six orders of
magnitude
Variable rotational shear – why?
Laboratory prototype
Laboratory testbed
CP-ARC. Experiment on the
suppression of simulated star
Green laser represents the star, red laser represents the planet (initially unseen over bright background)
Rotational shear 180°
Rotational shear 20°
CP-ARC. Experiment on the
suppression of white light
Rotational shear 10°, only star light (simulated), only pupil plane
CP-ARC advantages and drawbacks
Pluses of CP-ARC:
• Fully achromatic suppression of the star light. Achromatic performance in a wide wavelength range
(typically 0.5…2µm).
• Simple in engineering terms and mechanically stable common-path design.
• Meets the requirement of imaging exoJupiter around nearby stars.
• Works with a number of aperture shapes (circular, square, hexagon …), segmented and diluted
apertures with a large number of particular values of rotational shear since the aperture is invariant
under a rotation.
• Can be adapted to the experimental conditions over a wide range since variable angle of rotational
shear defines IWA (starting from the lowest possible) and star light suppression level.
• Sensitive to the polarization of the planet light.
Minuses of CP-ARC:
• Increased IWA.
• Still sensitive to the angular size of the star and pointing errors.
• Maximum transmission of the planet light is 28% (14% in every copy of the planet). However, half of
the light collected by telescope is not lost; it is linearly polarized and can be used by another
instrument (the same coronagraph with another angle of rotational shear, for example).
• Double image at the output complicates analysis of low-contrast or small-scale structures of the star
vicinity.
CP-ARC application in space experiments:
Russian space telescopes planned to be equipped with stellar
coronagraph to observe exoplanets around nearby stars
“Planetary Monitoring” (development stage)
60-cm space telescope (2018++)
Technological objective is to perform test observations of nearby stars with
stellar coronagraph. No adaptive optics
“Star Patrol” (research stage)
1.5…2-m space telescope (2022+++)
Meant for direct imaging and study of extrasolar planets through
photometry in the visible and low resolution spectroscopy and polarimetry in
the visible and near infrared
Direct imaging completed space missions
PICTURE 2011 (NASA)
(Planet Imaging Concept Test bed Using a Rocket Experiment)
50-cm telescope + adaptive optics + coronagraph VNC
Launched with the sounding rocket Black Brant 9
Scientific data transmitter failure
PICTURE 2015 (NASA)
Another attempt with the same instruments
Successfully completed – results are still not published
Direct imaging future space missions
PICTURE-C 2017 (NASA)
(Planet Imaging Concept Test bed Using a Recoverable Experiment Coronagraph)
50-cm telescope + adaptive optics + coronagraph /// stratospheric balloon
James Webb Space Telescope Oct.2018 (NASA)
Segmented 6.5-m primary mirror + NIRcam + MIRI + coronagraph
WFIRST-AFTA mid 2020 (NASA)
(Wide Field Infrared Survey Telescope - Astrophysics Focused Telescope
Assets)
2.4-m single dish telescope + adaptive optics + coronagraph
Thank you for attention!