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BETTII: Balloon Experimental Twin Telescope for Infrared Interferometry

Staff: Matt Griffin, Enzo Pascale, Peter A Ade.
Postdocs: Georgina Klemencic.
Collaborators: Giorgio Savini, Bruce Swinyard, Roser Juanola-Parramon (University College London); Stephen Rinehart, Dave Leisawitz and the BETTII team (NASA Goddard); Locke Spencer (University of Lethbridge).

Schematic of BETTII interferometer

Optical layout of the BETTI balloon-borne FIR interferometer (click to enlarge).

Cardiff University and University College London are collaborating with astronomers and engineers at NASA, the University of Maryland, and Johns Hopkins University to build BETTII: the Balloon Experimental Twin Telescope for Infrared Interferometry. BETTII will be an eight-meter baseline interferometer designed to fly on a balloon, high in the stratosphere at an altitude of 40 km, to get above most of the Earth’s atmosphere. It will observe in the far infrared (FIR) part of the spectrum, which is blocked by water vapour in the Earth’s atmosphere and so cannot be observed from the ground.

For a single telescope spatial resolution is limited by its diameter, but for an interferometer it is determined by the distance between the telescopes. BETTII’s pioneering feature will be that it will use a technique known as interferometry, combining the light from two telescopes separated by an 8-metre baseline, to provide a sharper, more detailed view of the sky.

Graph showing BETTII, Herschel, ALMA, HST and JWST angular resolution vs. wavelength.

BETTII will complement the high spatial resolution of other facilities, filling a critical need for higher angular resolution in the FIR (click to enlarge).

BETTII will observe in two FIR bands (30-50 µm and 60-90 µm), with a spatial resolution of 0.5″, which is unprecedented at these wavelengths. The most important advances to be made by BETTII will derive from this high spatial – twenty times better than the Spitzer space observatory at 30-50 µm (a range covered neither by JWST nor Herschel) and six times better than Herschel at 60-90 µm. BETTII’s main science goals are tailored to this unique ability to resolve spatial details in the far infrared. It will study clustered star formation using its ability to distinguish individual emitting objects within a cluster, and it will investigate the nature of active galactic nuclei (AGN), with its ability to distinguish between the emission of the central nucleus and that of the host galaxy in which it is located.

With its first flight planned for 2015, BETTII will carry out unique and pioneering science, and will also serve as a technological and scientific pathfinder for a future space-based interferometer. Cardiff/UCL contributions to BETTI include

Our participation in BETTII is supported by an STFC PRD award.
For more details of the BETTII projects, see the BETTII home page at NASA Goddard.