Aperture masking interferometry 1532134 187785259 2008-01-29T22:00:40Z BenFrantzDale 41799 hyphen [[Image:Speckle_aperture_masking.svg|thumb|400px|a) shows a simple experiment using an aperture mask in a re-imaged aperture plane. b) and c) show diagrams of aperture masks which were placed in front of the [[secondary mirror]] of the [[Keck telescope]] by [[Peter George Tuthill|Peter Tuthill]] and collaborators. The solid black shapes represent the subapertures (holes in the mask). A projection of the layout of the [[Keck Telescope|Keck]] primary mirror segments is overlaid.]] '''Aperture Masking Interferometry''' is a form of [[speckle interferometry]], allowing [[diffraction limited]] imaging from ground-based [[telescopes]]. This technique allows ground based telescopes to reach the maximum possible resolution, allowing ground-based telescopes with large diameters to produce far sharper images than the [[Hubble Space Telescope]]. The principal limitation of the technique is that it is limited to relatively bright astronomical objects. A mask is placed over the telescope which only allows light through a small number of holes. This array of holes acts as a miniature [[astronomical interferometer]]. The method was developed by [[John E. Baldwin]] and collaborators in the [[Cavendish Astrophysics Group]]. In the aperture masking technique, the [[speckle masking|bispectral analysis]] (speckle masking) method is typically applied to data taken through masked apertures, where most of the aperture is blocked off and light can only pass through a series of small holes (subapertures). The aperture mask removes atmospheric noise from these measurements, allowing the bispectrum to be measured more quickly than for an un-masked aperture. For simplicity the aperture masks are usually either placed in front of the [[secondary mirror]] (e.g. Tuthill et al. (2000)) or placed in a re-imaged aperture plane as shown in Figure 1.a) (e.g. Haniff et al. (1987); Young et al. (2000); Baldwin et al. (1986)). The masks are usually categorised either as non-redundant or partially redundant. Non-redundant masks consist of arrays of small holes where no two pairs of holes have the same separation vector (the same '''baseline''' - see [[aperture synthesis]]). Each pair of holes provides a set of fringes at a unique spatial frequency in the image plane. Partially redundant masks are usually designed to provide a compromise between minimising the redundancy of spacings and maximising both the throughput and the range of spatial frequencies investigated (Haniff & Buscher, 1992; Haniff et al. , 1989). Figures 1.b) and 1.c) show examples of aperture masks used in front of the secondary at the Keck telescope by Peter Tuthill and collaborators; Figure 1.b) is a non-redundant mask while Figure 1.c) is partially redundant. Although the signal-to-noise of [[speckle masking]] observations at high light level can be improved with aperture masks, the faintest limiting magnitude cannot be significantly improved for photon-noise limited detectors (see Buscher & Haniff (1993)). ===See also=== [[List of astronomical interferometers at visible and infrared wavelengths]] ===External links=== *[http://www.abc.net.au/science/news/stories/s1404731.htm Old method brings life to new stars] - ABC Science Online *[http://www.physics.usyd.edu.au/~gekko/wr104.html Examples of high-resolution time-lapse movies produced with aperture masking] *[http://www.amonline.net.au/eureka/scientific_research/2005_winner.htm#tuthill Peter Tuthill awarded Eureka award for aperture masking work] === References === * [http://www.physics.usyd.edu.au/~gekko/papers/thesis.ps Peter Tuthill's PhD thesis on aperture masking] as a [[PostScript]] file which can be viewed in [http://www.cs.wisc.edu/~ghost/gsview/ GSView] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1986Natur.320..595B&db_key=AST Baldwin et al. (1986)] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1993OSAJ...10.1882B&db_key=INST Buscher & Haniff (1993)] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1987Natur.328..694H&db_key=AST Haniff et al. (1987)] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1989MNRAS.241P..51H&db_key=AST Haniff et al., 1989] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1992OSAJ....9..203H&db_key=INST Haniff & Buscher, 1992] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=2000PASP..112..555T&db_key=AST Tuthill et al. (2000)] * [http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=2000MNRAS.315..635Y&db_key=AST Young et al. (2000)] [[Category:Interferometry]] [[Category:Astronomical imaging]] [[Category:Speckle imaging]]