First On-sky Test of an Optical Vortex Coronagraph (OVC) Mary Anne Peters Undergraduate research advisor : Laird M. Close Matt Rademacher, Tom Stalcup Steward Observatory, University of Arizona Grover A. Swartzlander, Erin Ford, Rukiah S. Abdul-Malik Optical Sciences, University of Arizona Optical 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 next to their host star (~ contrast at 1AU in the optical)  Solution: Null out the host star light with an advanced phase mask (coronagraph)  Problem: Phase masks optimally work on ~100% Strehl images, and this is hard to achieve with telescopes on the ground  Solution: BESSEL

What Is Bessel?

Ray White Telescope (21”) at Steward Observatory (BESSEL and the Coronagraph mounted) Ray White Telescope (21”) Coronagraph BESSEL 8” refractor

Bessel’s Performance: How well does the tip/tilt system work? Target: Arcturus at λ=800nm (K2III super giant) loop closed loop open loop open 14 th airy 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 D≈r 0 region (target: Arcturus at λ=800nm) Strehl: 99.6% Strehl:91.7% Aperture: 2inch D/r 0 : 1.0 λ/D=3.248 arcsecs Strehl:71.1% Aperture: 3inch D/r 0 : 1.5 λ/D=2.166 arcsecs Strehl: 98.4% Aperture: 1inch D/r 0 : 0.5 λ/D= arcsecs

D/r 0 Peters, M.A. et al., New Astron. (2007)

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

Focal Plane images with an OVC on-sky ADS 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-sky OVC out OVC in OVC out OVC in

OVC out OVC in Radius (λ/D’) Normalized Pixel Value Peak of 1 st airy ring suppressed by ~10 Radial Plot for Betelgeuse

Conclusions  BESSEL provides the ~100% Strehls in the visible and the micron stability that are both needed for coronagraphs to be tested on the sky  The Optical Vortex Coronagraph (OVC) can achieve a factor of 10 suppression of the first airy ring of Betelgeuse (this result is limited mainly by fabrication errors in the mask)  This is the first on-sky test of an OVC  The OVC looks like a promising candidate for a TPF 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 OVC

Focal Plane images with an OVC in the Lab Pupil 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 in OVC out OVC in