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A Hundred Times Sharper Than Hubble: Stellar imaging with intensity interferometry

Jensen, Hannes LU (2010) In Lund Observatory Examensarbeten ASTM31 20101
Lund Observatory
Department of Astronomy and Theoretical Physics
Abstract
Imaging of stellar surfaces in visible wavelengths is one of the current frontiers in astronomy. With a few exceptions, stars can not be seen in visible light as anything but point objects with current technology. Being able to properly image stars would open up the door to a vast field of new discoveries, permitting direct studies of phenomena such
as rotationally deformed stars, circumstellar disks and clouds, stellar winds and wind collision zones, mass accretion structures, pulsating stars etc. Ground based phase interferometers have been able to produce images of a few large stars in infrared light by connecting several telescopes over distances of ∼100 m, but are limited by the need to keep the optical path constant down to a... (More)
Imaging of stellar surfaces in visible wavelengths is one of the current frontiers in astronomy. With a few exceptions, stars can not be seen in visible light as anything but point objects with current technology. Being able to properly image stars would open up the door to a vast field of new discoveries, permitting direct studies of phenomena such
as rotationally deformed stars, circumstellar disks and clouds, stellar winds and wind collision zones, mass accretion structures, pulsating stars etc. Ground based phase interferometers have been able to produce images of a few large stars in infrared light by connecting several telescopes over distances of ∼100 m, but are limited by the need to keep the optical path constant down to a fraction of the wavelength of the light over very large distances. Intensity interferometry works around these problems by measuring correlations in light intensity fluctuations, essentially removing the need for high-quality optics and making the system virtually immune to atmospheric disturbances, permitting the connection of a great number telescopes to form one giant kilometer-scale hypertelescope. This comes at the cost of higher light intensity requirements and the loss of the phase of the Fourier transform of the stellar surface brightness. Invented in the 1940’s by Robert Hanbury Brown, intensity interferometry has not been used in astronomy since the 1970’s (though the physical principle behind it has become very important in particle physics), due to the requirement for very large flux
collectors and fast photo-detectors. However, recent technological advances and new mathematical algorithms for image reconstruction have sparked a renewed interest in this technique. A “digital revival” of intensity interferometry would enable visible-light imaging of
stellar objects at resolutions that are orders of magnitude better than what is possible today or in the foreseeable future. An interesting possibility is to use air Cherenkov telescopes – which happen to share many requirements with intensity interferometry. In this thesis, the theory and history behind intensity interferometry are laid out and
a number of astrophysically interesting targets of study are identified. A new method for simulating intensity interferometry measurements, valid for modern photon-counting detectors, is derived and implemented as a simulation software package. It is also shown how this method can be extended to higher-order correlations. The simulation software is applied to a number of astronomical objects with extra attention given to the use of the upcoming European mega-project CTA (Cherenkov Telescope Array) as an intensity interferometer. Finally, the results from laboratory experiments at Lund Observatory are presented. (Less)
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author
Jensen, Hannes LU
supervisor
organization
course
ASTM31 20101
year
type
H2 - Master's Degree (Two Years)
subject
publication/series
Lund Observatory Examensarbeten
report number
2010-EXA41
language
English
id
2517944
date added to LUP
2012-04-25 14:01:21
date last changed
2012-04-25 14:01:21
@misc{2517944,
  abstract     = {Imaging of stellar surfaces in visible wavelengths is one of the current frontiers in astronomy. With a few exceptions, stars can not be seen in visible light as anything but point objects with current technology. Being able to properly image stars would open up the door to a vast field of new discoveries, permitting direct studies of phenomena such
as rotationally deformed stars, circumstellar disks and clouds, stellar winds and wind collision zones, mass accretion structures, pulsating stars etc. Ground based phase interferometers have been able to produce images of a few large stars in infrared light by connecting several telescopes over distances of ∼100 m, but are limited by the need to keep the optical path constant down to a fraction of the wavelength of the light over very large distances. Intensity interferometry works around these problems by measuring correlations in light intensity fluctuations, essentially removing the need for high-quality optics and making the system virtually immune to atmospheric disturbances, permitting the connection of a great number telescopes to form one giant kilometer-scale hypertelescope. This comes at the cost of higher light intensity requirements and the loss of the phase of the Fourier transform of the stellar surface brightness. Invented in the 1940’s by Robert Hanbury Brown, intensity interferometry has not been used in astronomy since the 1970’s (though the physical principle behind it has become very important in particle physics), due to the requirement for very large flux
collectors and fast photo-detectors. However, recent technological advances and new mathematical algorithms for image reconstruction have sparked a renewed interest in this technique. A “digital revival” of intensity interferometry would enable visible-light imaging of
stellar objects at resolutions that are orders of magnitude better than what is possible today or in the foreseeable future. An interesting possibility is to use air Cherenkov telescopes – which happen to share many requirements with intensity interferometry. In this thesis, the theory and history behind intensity interferometry are laid out and
a number of astrophysically interesting targets of study are identified. A new method for simulating intensity interferometry measurements, valid for modern photon-counting detectors, is derived and implemented as a simulation software package. It is also shown how this method can be extended to higher-order correlations. The simulation software is applied to a number of astronomical objects with extra attention given to the use of the upcoming European mega-project CTA (Cherenkov Telescope Array) as an intensity interferometer. Finally, the results from laboratory experiments at Lund Observatory are presented.},
  author       = {Jensen, Hannes},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lund Observatory Examensarbeten},
  title        = {A Hundred Times Sharper Than Hubble: Stellar imaging with intensity interferometry},
  year         = {2010},
}