ground-based telescope coronagraphsdmawet/meetings/... · 2018. 10. 17. · carlomagno, vortex...

BrunellaCarlomagnoCaltech,PasadenaPhDStudentVORTEXWorkshopThesissupervisor:OlivierAbsil17/08/2016

Ground-based telescope coronagraphs

Content

•  E-ELT/METIS instrument

•  AO phase screens

•  Coronagraphic solutions

•  ADI contrast

•  Conclusions & Perspectives

2Carlomagno,VORTEXWorkshop,17/08/2016

E-ELT

Circular Cold Stop

•  798 hexagonal segments (1.45 side to side) •  39.3m à 37m •  11m central obstruction (30%) •  six 50cm-wide spider arms


METIS instruments

Science cases:

•  Exoplanet detection and characterization

•  Formation and evolution of protoplanetary disks

Design concept

•  Diffraction limited imaging at L, M and N band

•  IFU-fed high-resolution spectrograph in L and M band


PROPER simulation tool

•  Library of optical propagation in near-field and far-field conditions, in IDL environment, created by John Krist (JPL).

•  It uses Fourier transform algorithm (angular spectrum, Fresnel approximation).

•  Propagation wavefront described by amplitude and phase.

Simulation parameters: •  2048 grid •  Beam ratio: 0.25 à 5.25 mas/pix •  λ = 3.77µm


AO residual phase screens

6

•  3992 actuators, 72 sub-apertures across the pupil, sampled with 6x6 pixels each, 0.5m sub-aperture size

•  0.44” Zenith seeing at 3µm, K-star of 4.45mag, 30° away from Zenith

•  Shack-Hartmann WFS, operating at K band •  Tip-tilt jitter included, telescope vibration not

included

CourtesyofMarkusFeldt

Carlomagno,VORTEXWorkshop,17/08/2016

VC2 vs VC4

-30λ/D +30λ/D -30λ/D +30λ/D

1e-17 1e-41e-17 1e-4

7

VC2 VC4


VC2 vs VC4


Optimized Lyot Stop

9

Isodata: it divides the image into “background” and “foreground”, computes mean, uses it as new threshold, repeat until threshold stop changing (Ridler & Calvard 1978).

Otsu: histogram shape-based method. It finds threshold, by minimizing the weighted within-class variance (Otsu1979).

Moments: Moment-based method. The greyscale image as a blurred version of an ideal binary image (Tsai 1985).

Max Entropy: entropy-based method. The image as 2 classes events with a proper PDF, threshold from maximizing the entropy of the 2 PDFs (Kapur, Sahoo & Wong 1985).


Optimized Lyot Stop: PSFs

10

Isodata Otsu

Moments Max Entropy

EE(0l/D) TE(0l/D)

Isodata 0.794 0.916

Otsu 0.5049 0.7504

Moments 0.652 0.84

MaxEntropy

0.4946 0.7391

1e-17

1e-4

1e-17

1e-4


Optimized Lyot Stop: Radial Profile


Ring Apodized Vortex Coronagraph

12

RingApodizedVortexCoronagraph(RAVC)•  combinesthevortexcoronagraphwithanamplitude

ringapodizerinordertocompensateforthecentralobstrucWon

•  entrancepupilisapodizedbyaringwithatransmissionlowerthan1(analyWcallycalculated)

VC LSRA

-30λ/D +30λ/D

Mawet2013

1e-17

1e-4

•  r1=0.6326•  t1=0.7498


Lyot Phase Mask

13

LyotPhaseMask(LPM)•  phaseopWcalelement,placedattheLyot

planetoimproveperformanceoftheVC•  Halfandfullannulusbetween3and20λ/D

Ruane2015

-π π 1e-17 1e-4

-30λ/D +30λ/D

-30λ/D +30λ/D


Apodized Phase Plate

14

ApodizedPhasePlate(APP)•  Pupil-planeonestageopWcaldevice•  Halfannulusbetween2and10λ/D•  NextgeneraWon:vAPP

Kenworthy2007

1e-17 1e-4

-30λ/D +30λ/D

CourtesyofChristophU.Keller


Radial Profile


Throughput

16

Imagingconcept

EE(10λ/D) TE(10λ/D) EE(0λ/D) TE(0λ/D)

Nocoro 1 1 / /

VC2 0.81 0.88 0.95 0.97

VC2+LSopWm

0.4396 0.6619 0.5049 0.7504

VC2+LPM 0.18 0.87 0.20 0.97

RAVC2 0.18 0.33 0.20 0.36

APP 0.35 0.99 / /


Pointing Jitter


ADI contrast

18

•  2000 screens as 1h observing sequence (1.8sec/screen) •  Star at dec=-4.6° (transit at 20° from Zenith) •  40° parallactic angle rotation •  No NCPA

•  Background added assuming target with L=5 (Metis simulator input, courtesy of Jeff Meisner)

•  Flux scaling: aperture photometry on off-axis PSF •  Algorithm: vip.pca.pca with ncomp =10 •  Noise radial profile: as standard deviation of the aperture fluxes

measured in as many independent resolution elements as possible at a given angular separation from the star


ADI contrast


Missing Segments

20

VC2

VC2+LPM

RAVC2

1e-17

1e-6


Conclusions & Perspectives

21

§  Compromise(contrast,throughput,IWA,opWcalcomplexity,sciencecases,etc)

§  Metrics(contrast,throughput,EE,TE,etc)

§  Errors(NCPA,lensimperfecWon,masktransmission,etc)

§  LongerADIsequence§  Exozodiacaldust,debrisdisk…


Thank you

Additional slides

23

-0.30µm

+0.30µm

-0.055µm

-0.045µm


EE: IWA


ground-based telescope coronagraphsdmawet/meetings/... · 2018. 10. 17. · carlomagno, vortex...

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