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A new view of the Universe IIFred Watson, AAOApril 2005

A new view of the Universe IIFred Watson, AAOApril 2005

The secret obsessions of astronomers

The secret obsessions of astronomers

Characteristics of astronomy today• Highly comprehensive range of instrumentation• Infinite computing power• Access to every part of the electromagnetic

spectrum:-rays, X-rays, UV, visible (optical), IR, mm-wave, radio

• Not to mention particles, gravitational waves… (So we won’t.)

The Universe through different eyes...

What’s so good about optical astronomy?

• Visible light is emitted by ‘ordinary matter’ in the Universe—i.e. stars

• The visible spectrum is rich in the ‘bar-code’ of atomic and molecular features

• Optical observations bridge long and short wavebands

• You can do it with your feet on the ground

The Schematic Ground-Based Optical Telescope

• Something large to collect and focus the radiation

• A complicated bit in the middle for analysis

• An optical detector

• A ground-based mounting

Detectors…

Astronomical cameras are

not small…

(This is IRIS2, a multi-purpose infrared

camera on the AAT)

Subtracting the sky…

Other complicated bits…

Spectrographs conventionally use a grating, prism or grism

Sends light of different wavelengths in different directions…Hence (via the spectrograph camera) to different positions on the detector (which is a CCD or an infrared array).(This slide and the next three courtesy Gordon Robertson)

Reflection grating spectrograph (schematic)

grating

camerad

collimator

idetector

cc

slit

b

• 3-d modulations of refractive index in gelatin layer• Peak efficiency up to ~90%• Wavelength of peak efficiency can be tuned• Transmission gratings• DCG layer (hologram) is protected on both sides• Each grating is an original, made to order• Large sizes possible

Volume phase holographic (VPH) gratings

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

400 500 600 700 800 900 1000

Wavelength (nm)

Effic

ienc

y

f/2.2

f/1.7

Ralcon 1516 l/mm grating - June 2000

Note: no antireflection coatings

Test of a prototype VPH grating

Why make telescopes ever bigger?

• To gather more light from faint sources because there are no further gains to be made in detector sensitivity

• To improve resolution:

R = 1.22 / D

As the mirror diameter D gets bigger, the resolution R gets finer.

Large Telescope Mirror, 1969

A 3.9-metre mirror can resolve 0.03 arcsec

BUT…

r0 is Fried’s parameter for wavefront distortion

Cn2 is the refractive index structure constant

Cn2 is integrated over the full height of the

atmosphere

The end-product is…

This is very depressing indeed

1 arcsecond

Can you do anything useful in such

conditions?

Can you do anything useful in such

conditions?

Detection of extra-solar planets

Multi-object spectroscopy with fibre optics

The answer to life, the Universe and everything...

Detector

Spectrograph

Slit

Galaxies…

Basic building-blocks of the Universe

If this was our Galaxy,we’d be here •Around 100,000,000,000 stars

•Lots of gas and dust (in spirals)•Around 100,000 light years across (or 1,000,000,000,000,000,000 km)

Antidotes to atmospheric turbulence

Antidotes to atmospheric turbulence

The Eagle Nebula—stellar birthplace

But – the Hubble project’s total cost

is

$US 6 billion.

That would buy 60 of today’s

ground-based 8-metre telescopes…

The world’s largest telescopes, 2005

The crowded summit of Mauna Kea

Antu, Kueyen, Melipal and Yepun

1 arcsecond

It’s all to do with atmosphere…

But at the VLT, on the same scale…

What do we do next?

What do we do next?

The thinking goes like this…

VLT: Very Large Telescope 4×8 m (16 m equiv.)ELT: Extremely Large Telescope 25 mCELT: California Extremely Large Telescope 30 mGSMT: Giant Segmented-Mirror Telescope 30mTMT: Thirty-metre Telescope (US + Canada + ?)Euro50: formerly SELT…

Future plans for large telescopes...

OWL—Sharp-eyed and OverWhelmingly Large

…And what can we do with such monsters?

…And what can we do with such monsters?

Earth-like planets out to about 75 l.y. by direct

imaging

What might we study with OWL?

Individual stars in moderately distant galaxies – galactic archaeology

Galaxies forming at look-back times up to 10 billion years

Exploding stars at look-back times up to 12.5 billion years

Not to mention the completely unexpected …