Keck telescopes
Encyclopedia
The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of 4145 metre near the summit of Mauna Kea
in Hawai'i
. The primary mirrors of each of the two telescopes are 10 metres (32.8 ft) in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio Canarias
. The telescopes can operate together to form a single astronomical interferometer
.
gave $70 million to fund the design and construction of the Keck I Telescope. The key advance that allowed the construction of the Keck's large telescopes was the ability to operate smaller mirror segments as a single, contiguous mirror. In the case of the Keck each of the primary mirrors is composed of 36 hexagonal segments that work together as a single unit. The mirrors were made from Zerodur
glass-ceramic
by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics
, which uses extremely rigid support structures in combination with adjustable warping harnesses. During observation, a computer-controlled system of sensors and actuators adjusts the position of each segment, relative to its neighbors, to an accuracy of four nanometers. This twice-per-second adjustment counters the effect of gravity as the telescope moves, in addition to other environmental effects that can affect the mirror shape.
Each Keck telescope sits on an altazimuth mount. During the design stage, computer analysis determined that this mounting style provides the greatest strength and stiffness for the least amount of steel, which totals about 270 tons per telescope. The weight of each telescope is about 300 tons.
The telescopes are equipped with a suite of instruments, both camera
s and spectrometers that allow observations across much of the visible and near infrared spectrum.
is capable of gathering spectra from 130 galaxies or more in a single exposure. In “Mega Mask” mode, DEIMOS can take spectra of more than 1,200 objects at once, using a special narrow-band filter.
HIRES : The largest and most mechanically complex of the Keck’s main instruments, the High Resolution Echelle Spectrometer breaks up incoming starlight into its component colors to measure the precise intensity of each of thousands of color channels. Its spectral capabilities have resulted in many breakthrough discoveries, such as the detection of planets outside our solar system and direct evidence for a model of the Big Bang
theory. This instrument has detected more extrasolar planets than any other in the world. The radial velocity precision is up to one meter per second (1.0 m/s) The instrument detection limit at 1 AU
is 0.2 MJ
LRIS : The Low Resolution Imaging Spectrograph
is a faint-light instrument capable of taking spectra and images of the most distant known objects in the universe. The instrument is equipped with a red arm and a blue arm to explore stellar populations of distant galaxies, active galactic nuclei, galactic clusters, and quasar
s.
NIRC : The Near Infrared Camera for the Keck I telescope is so sensitive it could detect the equivalent of a single candle flame on the Moon
. This sensitivity makes it ideal for ultra-deep studies of galactic formation and evolution, the search for proto-galaxies
and images of quasar environments. It has provided ground-breaking studies of the Galactic center, and is also used to study protoplanetary disk
s, and high-mass star-forming regions
.
NIRC-2 : The second generation Near Infrared Camera works with the Keck Adaptive Optics system to produce the highest-resolution ground-based images and spectroscopy in the 1–5 micrometres (µm) range. Typical programs include mapping surface features on Solar System
bodies, searching for planets around other stars, and analyzing the morphology of remote galaxies.
NIRSPEC : The Near Infrared Spectrometer studies very high redshift radio galaxies
, the motions and types of stars located near the Galactic Center
, the nature of brown dwarf
s, the nuclear regions of dusty starburst galaxies, active galactic nuclei, interstellar
chemistry, stellar
physics, and Solar System science.
OSIRIS
: The OH-Suppressing Infrared Imaging Spectrograph is a near-infrared spectrograph for use with the Keck II adaptive optics system. OSIRIS takes spectra in a small field of view to provide a series of images at different wavelengths. The instrument allows astronomers to ignore wavelengths where the Earth’s atmosphere shines brightly due to emission from OH (hydroxyl
) molecules, thus allowing the detection of objects 10 times fainter than previously available.
Both Keck telescopes are equipped with adaptive optics
, which compensates for the blurring due to atmospheric turbulence
. The first AO system operational on a large telescope, the equipment has been constantly upgraded to expand the capability. Only the Keck II Telescope currently has a laser reference star
available for use with the AO system. However, a 40 watt laser was installed on Keck I, which had first light in March 2011. Commissioning should be completed by the end of 2011, when it will join Keck II to perform Laser Guide Star Adaptive Optics.
In addition, the Keck I and Keck II telescopes can work together as the Keck Interferometer. The 85 metres (278.9 ft) separation between the two telescopes gives them the effective angular resolution in one direction of an 85 metres (278.9 ft) mirror. Along this axis, the Keck Interferometer has a spatial resolution
of 5 milliarcseconds (mas) at 2.2 µm, and 24 mas at 10 µm. In its most sensitive configuration, the interferometer would reach K=21 and N=10 mag in 1000 seconds of integration per baseline). The interferometer has several back-end instruments, allowing for a variety of observation types. The lack of additional outrigger telescopes makes the Keck Interferometer unsuitable for interferometric imaging
, so work has concentrated on nulling interferometry and angular diameter measurements instead. In September 2005, the Keck Interferometer demonstrated nulling interferometry for the first time, with a modest null depth of 100 times.
The Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501(c)(3) organization whose board of directors includes representatives from Caltech and the University of California
. Construction of the telescopes was made possible through private grants totaling more than $140 million provided by the W. M. Keck Foundation. The National Aeronautics and Space Administration (NASA) joined the partnership in October 1996, at the time Keck II commenced observations. The Keck I telescope began observations in May 1993.
Telescope time is allocated by the partner institutions. Caltech, the University of Hawai'i System, and the University of California accept proposals from their own researchers. NASA accepts proposals from researchers based in the United States, while the National Optical Astronomy Observatory (NOAO)
accept proposals from researchers around the world.
Mauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
in Hawai'i
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. The primary mirrors of each of the two telescopes are 10 metres (32.8 ft) in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio Canarias
Gran Telescopio Canarias
The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
. The telescopes can operate together to form a single astronomical interferometer
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....
.
Overview
In 1985, Howard B. Keck of the W. M. Keck FoundationW. M. Keck Foundation
The W. M. Keck Foundation is an American charitable foundation supporting scientific, engineering, and medical research in the United States. It was founded in 1954 by William Myron Keck, founder and president of Superior Oil Company . The Foundation's trust fund currently has assets in excess of 1...
gave $70 million to fund the design and construction of the Keck I Telescope. The key advance that allowed the construction of the Keck's large telescopes was the ability to operate smaller mirror segments as a single, contiguous mirror. In the case of the Keck each of the primary mirrors is composed of 36 hexagonal segments that work together as a single unit. The mirrors were made from Zerodur
Zerodur
Zerodur®, a registered trademark of Schott Glass Technologies, is a lithium aluminosilicate glass-ceramic produced by Schott AG since 1968. It has been used for a number of very large telescope mirrors including Keck I and Keck II. With its very low coefficient of expansion it can be used to...
glass-ceramic
Glass-ceramic
Glass-ceramics are polycrystalline material produced through controlled crystallization of base glass. Glass-ceramic materials share many properties with both glasses and ceramics...
by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics
Active optics
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, mechanical stress...
, which uses extremely rigid support structures in combination with adjustable warping harnesses. During observation, a computer-controlled system of sensors and actuators adjusts the position of each segment, relative to its neighbors, to an accuracy of four nanometers. This twice-per-second adjustment counters the effect of gravity as the telescope moves, in addition to other environmental effects that can affect the mirror shape.
Each Keck telescope sits on an altazimuth mount. During the design stage, computer analysis determined that this mounting style provides the greatest strength and stiffness for the least amount of steel, which totals about 270 tons per telescope. The weight of each telescope is about 300 tons.
The telescopes are equipped with a suite of instruments, both camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s and spectrometers that allow observations across much of the visible and near infrared spectrum.
Instruments
DEIMOS : The Deep Extragalactic Imaging Multi-Object SpectrographSpectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
is capable of gathering spectra from 130 galaxies or more in a single exposure. In “Mega Mask” mode, DEIMOS can take spectra of more than 1,200 objects at once, using a special narrow-band filter.
HIRES : The largest and most mechanically complex of the Keck’s main instruments, the High Resolution Echelle Spectrometer breaks up incoming starlight into its component colors to measure the precise intensity of each of thousands of color channels. Its spectral capabilities have resulted in many breakthrough discoveries, such as the detection of planets outside our solar system and direct evidence for a model of the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
theory. This instrument has detected more extrasolar planets than any other in the world. The radial velocity precision is up to one meter per second (1.0 m/s) The instrument detection limit at 1 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
is 0.2 MJ
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
LRIS : The Low Resolution Imaging Spectrograph
Spectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
is a faint-light instrument capable of taking spectra and images of the most distant known objects in the universe. The instrument is equipped with a red arm and a blue arm to explore stellar populations of distant galaxies, active galactic nuclei, galactic clusters, and quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
s.
NIRC : The Near Infrared Camera for the Keck I telescope is so sensitive it could detect the equivalent of a single candle flame on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. This sensitivity makes it ideal for ultra-deep studies of galactic formation and evolution, the search for proto-galaxies
Galaxy formation and evolution
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...
and images of quasar environments. It has provided ground-breaking studies of the Galactic center, and is also used to study protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
s, and high-mass star-forming regions
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
.
NIRC-2 : The second generation Near Infrared Camera works with the Keck Adaptive Optics system to produce the highest-resolution ground-based images and spectroscopy in the 1–5 micrometres (µm) range. Typical programs include mapping surface features on Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
bodies, searching for planets around other stars, and analyzing the morphology of remote galaxies.
NIRSPEC : The Near Infrared Spectrometer studies very high redshift radio galaxies
Radio galaxy
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...
, the motions and types of stars located near the Galactic Center
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
, the nature of brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s, the nuclear regions of dusty starburst galaxies, active galactic nuclei, interstellar
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
chemistry, stellar
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
physics, and Solar System science.
OSIRIS
OSIRIS
OSIRIS is the name of three entirely separate astronomical instruments. The duplication of names is coincidental, partly driven by two scientific teams trying to make acronyms using similar words.-OH-Suppressing Infrared Integral Field Spectrograph:...
: The OH-Suppressing Infrared Imaging Spectrograph is a near-infrared spectrograph for use with the Keck II adaptive optics system. OSIRIS takes spectra in a small field of view to provide a series of images at different wavelengths. The instrument allows astronomers to ignore wavelengths where the Earth’s atmosphere shines brightly due to emission from OH (hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
) molecules, thus allowing the detection of objects 10 times fainter than previously available.
Both Keck telescopes are equipped with adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
, which compensates for the blurring due to atmospheric turbulence
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
. The first AO system operational on a large telescope, the equipment has been constantly upgraded to expand the capability. Only the Keck II Telescope currently has a laser reference star
Laser guide star
Laser guide stars are a form of artificial star created for use in astronomical adaptive optics imaging.Adaptive optics systems require a wavefront reference source in order to correct atmospheric distortion of light...
available for use with the AO system. However, a 40 watt laser was installed on Keck I, which had first light in March 2011. Commissioning should be completed by the end of 2011, when it will join Keck II to perform Laser Guide Star Adaptive Optics.
In addition, the Keck I and Keck II telescopes can work together as the Keck Interferometer. The 85 metres (278.9 ft) separation between the two telescopes gives them the effective angular resolution in one direction of an 85 metres (278.9 ft) mirror. Along this axis, the Keck Interferometer has a spatial resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
of 5 milliarcseconds (mas) at 2.2 µm, and 24 mas at 10 µm. In its most sensitive configuration, the interferometer would reach K=21 and N=10 mag in 1000 seconds of integration per baseline). The interferometer has several back-end instruments, allowing for a variety of observation types. The lack of additional outrigger telescopes makes the Keck Interferometer unsuitable for interferometric imaging
Aperture synthesis
Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection...
, so work has concentrated on nulling interferometry and angular diameter measurements instead. In September 2005, the Keck Interferometer demonstrated nulling interferometry for the first time, with a modest null depth of 100 times.
The Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501(c)(3) organization whose board of directors includes representatives from Caltech and the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
. Construction of the telescopes was made possible through private grants totaling more than $140 million provided by the W. M. Keck Foundation. The National Aeronautics and Space Administration (NASA) joined the partnership in October 1996, at the time Keck II commenced observations. The Keck I telescope began observations in May 1993.
Telescope time is allocated by the partner institutions. Caltech, the University of Hawai'i System, and the University of California accept proposals from their own researchers. NASA accepts proposals from researchers based in the United States, while the National Optical Astronomy Observatory (NOAO)
National Optical Astronomy Observatory
The National Optical Astronomy Observatory is the United States national observatory for ground based nighttime ultraviolet-optical-infrared astronomy. The National Science Foundation funds NOAO to provide forefront astronomical research facilities for US astronomers...
accept proposals from researchers around the world.
See also
- Mauna Kea ObservatoryMauna Kea ObservatoryThe Observatories at Mauna Kea, , are an independent collection of astronomical research facilities located on the summit of Mauna Kea on the Big Island of Hawai'i, USA. The facilities are located in a special land use zone known as the "Astronomy Precinct," which is located in the Mauna Kea...
- List of largest optical reflecting telescopes
- List of largest optical telescopes historically
- List of astronomical interferometers at visible and infrared wavelengths
External links
- W. M. Keck Observatory (official site)
- The Mauna Kea Observatory (official site)
- Keck Observatory Archive (KOA)
- Lawrence Berkeley Lab, Revolution in telescope design
- Indigenous Controversy
- Photos of Keck telescopes and other Mauna Kea observatories from "A Gentle Rain of Starlight: The Story of Astronomy on Mauna Kea" by Michael J. West. ISBN 0-93154-899-3.