The LBT Interferometer

Overview Science Goals Partners People Instrument Library Wiki

With the advent of large telescopes and progress with associated technology, planets around other stars are now detectable, both in principle and in reality. In order to further this search, Steward Observatory is undertaking the construction of the LBT Inteferometer (LBTI). The NASA-funded project will use the Large Binocular Telescope as a testbed to develop nulling and Fizeau interferometry for this purpose. Nulling interferometry is a technique which cancels the overwhelming glare from a star by interference of light. This allows the detection of nearby planets or dust disks which would otherwise be obscured by the much brighter star. The technique is being studied in preparation for NASA's Terrestrial Planet Finder Misson. The project is currently completing its design phase. In addition to searching for extrasolar planets the instrument will provide for high resolution, wide-field imaging, allowing the LBT to create images with ten times the resolving power of the Hubble Space Telescope.

Overview

The large Binocular Telescope (LBT), currenlty being built on Mt. Graham in Arizona, will be the world's largest telescope. The observatory consists of two 8.4 m primary mirrors mounted in a single structure, 14.4 m apart. The telescopes can be used separately or, by sending the light to a single camera between the telescopes, be used as a single telescope with a maximum baseline of 22.8 m. Since the baseline is a measure of how sharp an image can be created, the LBT, when used in this fashion, will be able to create extraordinarily sharp pictures, able to discern detail roughly ten times smaller than images using the Hubble Space Telescope.

Forming sharp images will be a powerful feature of the LBTI, but the binocular configuration of the LBT lends itself to a powerful technique in the search for extrasolar planets called nulling interferometry. Perhaps the primary problem for detecting a planet around a star is the fact that the parent star is orders-of-magnitude brighter than the planet and, as seen by us, the planet is extremely close to the star. This makes it imperative to get rid of the glare from the star in order to be able to detect any planets right next to it. This is exactly what nulling interferometry does. The technique takes advantage of the wave-nature light to create destructive interference of the starlight coming from two telescopes loooking at the star. The light is manipulated so that the crest of a lightwave from one telescope lines up with the trough of the lightwave from the other telescope. In the final image, this technqiue makes the star effectively disappear.

Science Goals

The specific science goals of the LBTI are to perform a survey of nearby stars to look for evidence of planetary systems. The survey will be able to directly image faint zodiacal dust disks (indicative of planetesimals) as well as gas giant, Jupiter-like planets around nearby stars. A survey of a large sample of stars close to our sun will reveal how common the makeup of our own solar system is and identify which stars have planetary systems potentially suitable for life-bearing, terrestrial planets.

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Roger Angel
Tom Connors
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Bill Hoffmann
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Chien Peng

Instrument

The LBTI instrument is located between the two primary mirrors on the central instrument platform of the LBT. The instrument is composed of a Universal Beamcombiner (UBC) which reimages the two telescope beams to a common focal plane, the Nulling Interferometer for the LBT (NIL) which interferes the light from the telescopes out of phase to suppress the light from a star, and the Nulling Optimized Mid-Infrared Camera (NOMIC), which forms an image of the field about the star and is capable of detecting infrared emission from surrounding dust disks and planets.