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European Extremely
Large Telescope (E-ELT)
Natali Kuzkova
13th January 2015, Ph.D. seminar
Introduction
 The E-ELT will be the largest optical/infrared telescope in the world is the world's biggest
eye on the sky and will gather 13 times more light than the largest optical telescopes
existing today. The E-ELT will be able to correct for the atmospheric distortions from the
start, providing images 16 times sharper than those from the Hubble Space Telescope.
 Currently being built by the European Southern Observatory (ESO) on top of Cerro
Armazones in the Atacama Desert of northern Chile.
 The design comprises a reflecting telescope with a 39.3-metre-diameter segmented
primary mirror, a 4.2-metre-diameter secondary mirror, and will be supported by adaptive
optics and multiple instruments.
 It is expected to allow astronomers to probe the earliest stages of the formation of
planetary systems and to detect water and organic molecules in proto-planetary discs
around stars in the making.
Bild
Construction start: July 2014
Planned completion: 2022
First light: 2024
Four Centuries of the Telescope —
Four Centuries of Discovery
• In 1669, a few decades after the invention of the refracting
telescope, a design based on lenses, Isaac Newton
introduced the first practical reflecting telescope, using
mirrors. Over the following 300 years, these two telescope
design concepts competed and evolved into ever more
powerful research facilities. Refractor technology peaked
towards the end of the 19th century with the big Lick and
Yerkes Refractors, which used lenses of 90 centimetres and 1
metre in diameter, respectively. However, these lenses and
their supports proved to be the largest that could practically
be constructed, and thus reflecting telescopes finally won the
day.
• Reflecting telescopes in the 19th century suffered from the
poor reflectivity and thermal properties of their mirrors.
Despite this limitation, William Herschel and William Parsons,
the third Earl of Rosse, were able to build reflectors with
diameters ranging from 1.25 to 1.80 metres, with which they
discovered more planets and moons in the Solar System,
expanding the boundaries of the then known Universe further.
 Over the last 60 years, astronomers have developed telescopes that are able to observe right across the
electromagnetic spectrum. Space observatories have allowed observations to be pushed to shorter wavelengths,
into the ultraviolet, X-ray and gamma-ray regimes. This opening up of the high energy frontier generated a further
flood of discoveries such as X-ray stars, gamma-ray bursts, black hole accretion discs, and other exotic
phenomena. Previously unknown physical processes were taking place in the Universe around us. These
discoveries led to a number of Nobel Prizes in Physics (in 1974, 1978, 1993, 2002 and 2006) and to giant leaps in
our understanding of the cosmos. The first exoplanets were detected, and the current generation of 8–10-metre
class telescopes even allowed us to take the first pictures of a few of these objects.
E-ELT compared to other ELTs
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Diameter: 24 m
Collecting Area: 400 m2
Diffraction limit at 1μm: 9 mas
Planned in 2020
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Diameter: 30 m
Collecting Area: 600 m2
Diffraction limit at 1μm: 7 mas
Planned in 2020
Diameter: 4 x 8.2-metre Unit
Telescopes, plus 4 x 1.8-metre
moveable Auxiliary Telescopes
Operating since 2012
Diameter: 40 m
Collecting Area: 1000 m2
Diffraction limit at 1μm: 5 mas
Planned in 2020
Existing Very Large Telescope (VLT) is a complex of four separate 8.2-meter optical
telescopes. Discoveries with ground-based telescopes such as ESO’s VLT and its
VLTI, and other 8–10-metre class telescopes will have prepared the scene for further
fascinating discoveries with the E-ELT.
Evolution of the telescopes
• Comparison of nominal sizes of primary mirrors of some notable
optical telescopes:
http://www.eso.org/sci/facilities/eelt
The star symbols mark refracting telescopes, asterisks
stand for speculum reflectors, circles for glass reflectors.
European Extremely Large Telescope
Name:
Site:
Altitude:
Enclosure:
Type:
Optical design:
Diameter. Primary
M1:
European Extremely Large Telescope
(E-ELT)
Cerro Armazones
3060 m
Hemispherical dome
Optical/near-infrared Giant Segmented
Mirror Telescope
Five-mirror design: three-mirror on-axis
anastigmat + two fold mirrors used for
adaptive optics
39 m (798 hexagonal 1.4 m mirror
segments)
Diameter. Secondary 4 m
M2:
Diameter. Tertiary
M3:
3.75 m
First Light date:
Early 2020s
Active Optics:
Yes
Adaptive Optics:
2.60 m adaptive M4 using 6 Laser
Guide Stars
Open questions for E-ELT
Extra-solar planets
Discovering and characterizing planets and protoplanetary systems around other stars will be one of
the most important and exciting aspects of the EELT science programme.
This will include not only the discovery of planets
down to Earth-like masses using the radial velocity
technique but also the direct imaging of larger
planets and possibly even the characterization of
their atmospheres.
The E-ELT will be capable of detecting reflected light
from mature giant planets (Jupiter to Neptune-like)
and may be able to probe their atmospheres through
low resolution spectroscopy.
More than 400 exoplanets have been found so far. With the E-ELT,
the sensitivity of the radial velocity method will be improved by a
factor of 1000.
The radial velocity technique, which measures the induced Doppler
shift of features in the spectrum of the parent star, can only find certain
kinds of planets. With the current generation of telescopes, this
technique is limited both by the precision and the stability of the
velocity measurements: current measurements have pushed the limit
down to an already impressive ~1 m/s precision retained over several
years. The radial velocity technique — reaching 1 cm/s accuracy.
Open questions for E-ELT
Cosmology and fundamental physics
A simulation of the accuracy of the redshift drift
experiment, which will be achieved by the E-ELT. The
results strongly depend on the number of known bright
quasars at a given redshift.
The discovery that the expansion of the Universe
has recently begun to accelerate, presumably driven
by some form of dark energy, was arguably one of
the most important as well as mysterious scientific
breakthroughs of the past decade.
The E-ELT will help us to elucidate the nature of dark
energy by helping to discover and identify distant
type Ia supernovae. These are excellent distance
indicators and can be used to map out space and its
expansion history.
In addition to this geometric method the E-ELT will
also attempt, for the first time, to constrain dark
energy by directly observing the global dynamics of
the Universe: the evolution of the expansion rate
causes a tiny time-drift in the redshifts of distant
objects and the E-ELT will be able to detect this
effect
in
the
intergalactic
medium.
This
measurement will offer a truly independent and
unique approach to the exploration of the expansion
history of the Universe.
The ultra-stable high resolution spectrograph proposed for the E-ELT will essentially remove the systematic uncertainties due to the wavelength calibration which plague current measurements. It will improve the constraints on the stability
of fundamental constants by two orders of magnitude. These fundamental quantities include the fine structure constant,
α, and the strong interaction coupling constant, μ.
Open questions for E-ELT
Resolved stellar populations in a representative
sample of the Universe
The E-ELT offers the exciting prospect of reconstructing the
formation and evolution histories of a representative sample of
galaxies in the nearby Universe by studying their resolved stellar
populations.
A galaxy's stellar populations carry a memory of its entire star
formation history, and decoding this information offers detailed
insights into the galaxy's past. However, studying stellar
populations requires the capability of resolving and measuring
individual stars and so up until now such studies have been
limited to our own Galaxy and its nearest neighbours. In
particular, no examples of large elliptical galaxies are within
reach of current telescopes for this type of study.
With its superior resolution and photon collecting power the EELT will allow us to perform precise photometry and
spectroscopy on the stellar populations of a much more
representative sample of galaxies, reaching out to the nearest
giant ellipticals at the distance of the Virgo cluster.
Thus, the E-ELT will provide detailed information on the star
formation, metal enrichment and kinematic histories of nearby
galaxies, showing us how they were formed and built-up over
time.