First On-sky Test of an Optical First On-sky Test of an Optical Vortex Coronagraph (OVC)Vortex Coronagraph (OVC)

Mary Anne PetersMary Anne PetersUndergraduate research advisorUndergraduate research advisor: Laird M. Close: Laird M. Close

MattMatt RademacherRademacher, Tom Stalcup, Tom StalcupSteward Observatory, University of ArizonaSteward Observatory, University of Arizona

Grover A. Swartzlander, Erin Ford, Rukiah S. Grover A. Swartzlander, Erin Ford, Rukiah S. Abdul-MalikAbdul-Malik Optical Sciences, University of ArizonaOptical Sciences, University of Arizona

The waterline in the atmospheres of extrasolar planets will indicate the possibility of life. Only the direct imaging of extrasolar planets will allow us to image the lines in the atmosphere (using spectroscopy), and hence determine if the planet is habitable.

Problem: It’s hard to see earth like planets Problem: It’s hard to see earth like planets next to their host star (~10next to their host star (~10-10-10 contrast at contrast at 1AU in the optical)1AU in the optical)

Solution: Null out the host star light with an Solution: Null out the host star light with an advanced phase mask (coronagraph)advanced phase mask (coronagraph)

Problem: Phase masks optimally work on Problem: Phase masks optimally work on ~100% Strehl images, and this is hard to ~100% Strehl images, and this is hard to achieve with telescopes on the groundachieve with telescopes on the ground

Solution: BESSELSolution: BESSEL

What Is Bessel?What Is Bessel?

Ray White Telescope (21”) at Steward Observatory Ray White Telescope (21”) at Steward Observatory (BESSEL and the Coronagraph mounted)(BESSEL and the Coronagraph mounted)

Ray White Telescope

(21”)Coronagraph

BESSEL

8” refractor

Bessel’s Performance:Bessel’s Performance:How well does the tip/tilt system work?How well does the tip/tilt system work?

Target: Arcturus at Target: Arcturus at λλ==800nm800nm(K2III super giant)(K2III super giant)

loop closedloop closed loop openloop open1414thth airy airy ring!ring!

Diffraction off the CCD

Ghosts from 8 inch refractor

Peters, M.A. et al., New Astron. (2007)

Radial Plot of Arcturus

Behavior of Strehls in the DBehavior of Strehls in the D≈≈rr00 region region

(target: Arcturus at (target: Arcturus at λλ=800nm)=800nm)

• Strehl: 99.6% • Strehl:91.7%

• Aperture: 2inch

• D/r0: 1.0

• λ/D=3.248 arcsecs

• Strehl:71.1%

• Aperture: 3inch

• D/r0: 1.5

• λ/D=2.166 arcsecs

• Strehl: 98.4%

• Aperture: 1inch

• D/r0: 0.5

• λ/D= 6.497 arcsecs

D/r0

Peters, M.A. et al., New Astron. (2007)

Optical Vortex Coronagraph (OVC)Optical Vortex Coronagraph (OVC)

Pupil plane 1

Focal plane 1

Pupil plane 2

Focal plane 1

Left image: This image shows the surface profile of an optical vortex coronagraph (OVC). Opposite stair steps have a phase difference of pi. The OVC is a type of Nulling coronagraph. High throughput and small inner working angle (~λ/D).

Right image: This image illustrates the difference between a Lyot and Nulling coronagraph. The Nulling coronagraph puts the light from the star outside the pupil

http://www.u.arizona.edu/~grovers/ovc.html

Guyon, O. et al., PASP (1999)

Focal Plane images with an OVC on-skyFocal Plane images with an OVC on-skyADS 8706AB

Left image: ADS 8706AB without the vortex in

Right image: ADS 8706AB with the vortex in (A small tip/tilt errors will give you a donut shape in the focal plane)

19.0”

Betelgeuse

Left image: Betelgeuse without the vortex in

Right image: Betelgeuse with the vortex in (Almost all the light is thrown outside the pupil)

Pupil Plane Images with an OVC on-skyPupil Plane Images with an OVC on-sky

OVC out

OVC inOVC out

OVC in

• OVC out

• OVC in

Radius (λ/D’)

No

rmal

ized

Pix

el V

alu

e

Peak of 1st airy ring

suppressed by ~10

Radial Plot for Betelgeuse

ConclusionsConclusions

BESSEL provides the ~100% Strehls in the BESSEL provides the ~100% Strehls in the visible and the micron stability that are both visible and the micron stability that are both needed for coronagraphs to be tested on the skyneeded for coronagraphs to be tested on the sky

The Optical Vortex Coronagraph (OVC) can The Optical Vortex Coronagraph (OVC) can achieve a factor of 10 suppression of the first achieve a factor of 10 suppression of the first airy ring of Betelgeuse (this result is limited airy ring of Betelgeuse (this result is limited mainly by fabrication errors in the mask)mainly by fabrication errors in the mask)

This is the first on-sky test of an OVCThis is the first on-sky test of an OVC The OVC looks like a promising candidate for a The OVC looks like a promising candidate for a

TPF coronagraphTPF coronagraph

This project is supported in part by NASA Space Grant, Dr. Close’s NASA Origins Grant, and Dr. Swartzlander’s DoD Grant

Performance of the OVCPerformance of the OVC

Focal Plane images with an OVC in the LabFocal Plane images with an OVC in the Lab

Pupil Plane Images with an OVC in the LabPupil Plane Images with an OVC in the Lab

Left image: 785nm laser diode without the vortex in

Right image: 785nm laser diode with the vortex in

Left image: 785nm laser diode without the vortex in

Right image: 785nm laser diode with the vortex in (Almost all the light is thrown outside the pupil)

OVC out

OVC inOVC out

OVC in