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Imaging circumstellar environments with a nulling interferometer

Abstract

Extrasolar planets must be imaged directly if their nature is to be better understood. But this will be difficult, as the bright light from the parent star (or rather its diffracted halo in the imaging apparatus) can easily overwhelm nearby faint sources. Bracewell has proposed1 a way of selectively removing starlight before detection, by superposing the light from two telescopes so that the stellar wavefronts interfere destructively. Such a ‘nulling’ interferometer could be used in space to search for extrasolar Earth-like planets through their thermal emission and to determine through spectroscopic analysis if they possess the atmospheric signatures of life2,3,4. Here we report mid-infrared observations using two co-mounted telescopes of the Multiple Mirror Telescope that demonstrate the viability of this technique. Images of unresolved stars are seen to disappear almost completely, while light from a nearby source as close as 0.2 arcsec remains, as shown by images of Betelgeuse. With this star cancelled, there remains the thermal image of its surrounding, small dust nebula. In the future, larger ground-based interferometers that correct for atmospheric distortions (using adaptive optics) should achieve better cancellation, allowing direct detection of warm, Jupiter-size planets and faint zodiacal dust around other nearby stars5.

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Figure 1: Schematic of our nulling interferometer at the MMT.
Figure 2: Single short-exposure frames at 10.3-μm wavelength, showing constructive and destructive interference.
Figure 3: Averages of nulled images for α Ori and R Leo (also observed on 17–18 January 1998) showing the 10-μm dust nebulae with improved signal-to-noise ratio.
Figure 4: Stellar diffraction patterns obtained by subtracting the nulled images of Fig. 3 from the corresponding constructive images.

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Acknowledgements

We thank C. Foltz and the MMT staff for their essential support of the project. This work was supported by AFOSR, NASA and the US NSF.

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Correspondence to Philip M. Hinz.

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Hinz, P., Angel, J., Hoffmann, W. et al. Imaging circumstellar environments with a nulling interferometer. Nature 395, 251–253 (1998). https://doi.org/10.1038/26172

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