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A new view of the Universe II Fred Watson, AAO April 2005 A new view of the Universe II Fred Watson, AAO April 2005
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 camera dd collimator ii detector 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
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… r 0 is Fried’s parameter for wavefront distortion C n 2 is the refractive index structure constant C n 2 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?
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
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?
The thinking goes like this…
VLT: Very Large Telescope 4×8 m (16 m equiv.) ELT: Extremely Large Telescope 25 m CELT: California Extremely Large Telescope 30 m GSMT: Giant Segmented-Mirror Telescope 30m TMT: 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?
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 …