INTRODUCTION

We are currently experiencing a grand revolution in ground based astronomy.

1. 1) Until now astronomers have been limited by the atmosphere "blurring" their images so that even the largest telescopes could not make images significantly better than backyard small 10 inch amateur telescopes.
2. 2) To solve this problem NASA launched the Hubble Space Telescope above the atmosphere to make sharp images.
3. 3) However, Hubble is now quite small compared to the twelve 6.5-10m class telescopes operating on the ground. Each theoretically is able to make images ~3-4 times sharper than the best Hubble can achieve.
4. 4) Hence a new technology has emerged over the last 10 years (20 years including military research) to give ground-based giant telescopes the ability to observe the universe in unparalleled sharpness.
5. 5) This new technology is called Adaptive Optics (AO) and it allows a telescope to correct (in real-time) the blurring due to the atmosphere.

THE ATMOSPHERE

The reason stars "twinkle" is the mixing of hot and cold air in the atmosphere. A good example of this is the "puddle mirage" that we see along a road in the summer time where the hot air just above the road "warps" light as it passes along the road. Here is a movie which shows how layers in the atmosphere bend light here on the surface of the earth.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

ADAPTIVE OPTICS

The principal of AO is simply:

1. 1) to sense very fast the way an image is being "warped" or distorted by the atmosphere (typically 1000 times each second!).
2. 2) based on the direction and strength of those measured distortions apply an equal but OPPOSITE distortion to a flexible "rubber" mirror.
3. 3) continue this "closed loop" feedback to give the science camera a distortion free image.

Here is a movie showing the real Hokupa'a AO system working. Hokupa'a was the first (and is still) the highest order curvature AO system in the world. It was built by the Honolulu based Institute for Astronomy AO group.  It is now the AO system for the 8m Gemini telescope in Hawaii shown in the previous movie. Hokupa'a means "immovable star" in Hawaiian (the name the Hawaiians gave to the pole star).
 

EXAMPLES OF ASTRONOMY WITH ADAPTIVE OPTICS

1) Young stars, binary stars: A very rich area of research in adaptive optics is that of binary stars and young stars.

Here is movie which shows how much better one can image a young binary (in fact a triple) star with adaptive optics at the 4th 8m VLT Telescope run by the European Southern Observatory.

Such images are in the infrared but sharper than the images Hubble can make from outside the atmosphere. Typically images made by large AO equipped telescopes will be 0.050" (20x sharper than a 1" image - which is the best one can hope for usually without AO).
 
 
 
 
 
 
 
 
 
 
 
 
 
 

2) The surface of the Sun: Another fascinating use of AO is to image the surface of the Sun. These images from the National Solar Observatory in New Mexico are a big improvement over non-AO images (as this movie proves). However, solar astronomers can combine AO and some image processing to pull up the sharpest features (see movie) to make even more impressive insights into the Sun's surface.

Also sun spot movies from the Swedish Solar telescope AO system are also amazing.
 
 
 
 
 
 
 
 
 
 
 
 

3) Planetary Astronomy: Studies of other planets in our solar system is also a ripe field of study for AO.

For example the planet Neptune has complex methane clouds that can be seen revolving as the planet turns (movie  from the University of Hawaii AO group Hokupa'a images).

Also recent images of Saturn's moon Titan which has a dense methane atmosphere show how this atmosphere can act like a lens as 2 background stars pass behind it (movie from the Mt Palomar PALAO system).
 

Also AO has been the only way to detect moons around asteroids --see Merline et al. Close et al.

However, adaptive optics are not just for the professionals on the largest telescopes. Even backyard telescopes can gain a lot from simple AO systems that cost only a few thousand dollars. Stellar Products builds a simple AO system that stabilizes and corrects the most common wavefront errors. Here is a movie of Jupiter taken in a backyard with a 9 inch telescope using such an AO system.
 
 
 
 
 
 
 
 
 
 
 

4) Planets Around Other Stars: The search for planets outside of our solar system is one of the great new fields in astronomy. In 1995 the first planet around another star (51 Peg) was inferred from radial velocity measurements of the primary. Today there are over 80 such stars that appear to have Jupiter like mass planets in orbit. However, there has not been a single direct detection of light from these planets.

Above we have an image of a brown dwarf around a nearby star (Mike Liu, IfA, Hokupa'a/Gemini image of 15 Sge)

It would be incredibly exciting to actually image a planet around another star. My prediction is that AO will do just this in the next year.

Already we can detect brown dwarfs around stars (see image above).
Brown Dwarfs are somewhere between 75-13 Jupiter masses. They are not massive enough to considered hydrogen burning stars, but they are likely too massive to be considered planets.

Above we show some of the first binary brown dwarfs and brown dwarf companions found with Hokupa'a/Gemini AO (see Close et al. 2002a, Close et al. 2002b). We have now found that of 40 low mass stars observed 9 have low mass companions. All of these companions could never have been found without AO. Hence it appears that brown dwarfs form into binaries as often as more massive stars but they tend to have smaller separations (typically ~4AU).

There is even hints of lower mass (planetary mass objects) in some of these images.
 
 
 
 
 
 
 
 
 
 
 
 

THE FUTURE

ADAPTIVE SECONDARIES AT THE UNIVERSITY OF ARIZONA

The second generation of AO systems is now under way. Here at Arizona we are developing the world's first (and only) adaptive secondary mirror. Having the "rubber" mirror placed at the location of the secondary will dramatically increase the throughput of the system and lower the amount of "heat" seen by the infrared detector.

Here is image produced by the secondary mirror closed loop in the lab:

The secondary mirror AO system should go on the 6.5m MMT telescope on Mt Hopkins in April/May 2002.
 
 
 
 
 
 
 
 
 

THE FAR FUTURE

Soon astronomers will desire to have even bigger fields of view corrected by AO. To do this will require several guide stars (maybe made by lasers) and several rubber mirrors all working together.

Here we show what a 2 arc minute field of View looks like without AO (movie).
Here we show what this field looks like with AO and one "rubber mirror" (movie).
Here we show what it could look like if you had 3 rubber mirrors (movie).

(These simulations are from Francois Rigaut and the Gemini Telescope.)
 

So the future for ground-based astronomy has never looked brighter (or sharper) thanks to AO.
 
 

AO is already indispensible to large telescopes today. It will play an even bigger role in the development of the 30m class telescopes of tomorrow.