adaptive optics in astronomy

Speaker: Laird Close University of Arizona

ADAPTIVE OPTICS IN ASTRONOMY

THE PROBLEM:

Since Newton’s time it was realized that the mixing of hot and cold air “blurs” starlight passing to the surface of the Earth.

Hence ground-based telescopes, regardless of size, are similarly limited in their ability to make sharp images.


THE SOLUTION: 1) Use expensive small space-based telescopes like

the Hubble space telescope.2) Use cutting-edge opto-mechanical

instrumentation to correct (in real time) distortions caused by the atmospheric blurring. Such “adaptive” correction is known as adaptive optics.

NOTE: Modern 8-10 meter class telescopes equipped with adaptive optics can make images up to 4 times sharper than the 2.4 meter Hubble Space Telescope.



Here is a movie

showing a

schematic of the Gemini North

Telescope

Adaptive Optics System

on Mauna

Kea Hawaii(Credit Gemini, NSF, & Aura)



Here is a movie (by

Buzz Graves, AOptix) of the University of Hawaii AO system,

Hokupa’a, going from AO “off” to correction “on”. The

mirror must change shape

1200 times each second to correct the atmosphere



Astronomical Adaptive Optics Science

With adaptive optics (AO) all large ground based telescopes can now reach their theoretical resolution limit. Hence 8 meter AO equipped telescopes (like Gemini) can read a license plate 20 miles away (this is 20 times farther than without AO).

For astronomical science adaptive optics has made the sharpest, clearest images of:

1) The Sun, Asteroids, planets, moons, comets

2) Nearby stars, disks around young stars, clusters of stars

3) The black hole at the center of the Galaxy

4) Nearby galaxies, active galactic nuclei, quasars and their host galaxies

Graves et al. 1998; Close et al. 1998



The Sun with the Swedish

1.0 meter AO

solar telescope(Scharme

ret al.)



Binary Asteroids

By following the orbit of two

asteroids we can solve for the

asteroid’s density and understand its composition(Merline et al.

1999;Close et al. 2000).



Here we see a movie of Jupiter’s moon Io with its

volcanoes (Keck AO; Marchis et al. 2002).

The gas giant

Neptune without

then with AO

correction(Keck AO; CfAO web

page).



AO can sharpen all the stars in a field. Here is a movie of “turning on”

AO at the Keck

telescope imaging the

massive black hole at the center of our galaxy.(Ghez et al.

2002)



Planets Around Other Stars

Here we see a Gemini AO image of a brown dwarf around a star (Liu et al.

2002)

And a planetary mass companion to a brown

dwarf, which is most likely a background source (Close

et al. 2003)



THE FUTURE: Direct Imaging of Planets Around

Other Stars

By building special AO cameras we can remove much of the “blinding glare” of a star and reveal any gas giant planets in orbit around that star. Here are typical images from an new “Simultaneous differential Imager” (SDI) on the 8 meter VLT in Chile (Close et al. 2003; Lenzen et al. 2003)

This new SDI AO camera can image a 2 Jupiter mass planet at 4, 6, 8 and 10 “earth-SUN” distances (AU) around the 10 Million year old star shown here. This is impossible with Classical AO alone.



THE FUTURE: Adaptive

Secondaries

The University of Arizona has pioneered the development of making the secondary mirror of a telescope the “rubber” or deformable mirror in the AO system. This open new science fields –like AO imaging in the thermal IR.(Wildi et al. 2003)

RV Boo’s disk (Biller et al. 2004)

adaptive optics in astronomy

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