Refining Nulling Interferometry with the Old and New Multiple Mirror Telescope

Details Refining Nulling Interferometry with the Old and New Multiple Mirror Telescope Refining Nulling Interferometry with the Old and New Multiple Mirror Telescope

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...193.9712h&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #97.12; Bulletin of the American Astronomical Society, Vol. 30, p.1393

Astronomy and Astrophysics

Astronomy

2

Scientific paper

Nulling interferometry is a technique which requires a high degree of precision if it is to achieve the cancellation necessary to study dim extrasolar zodiacal dust and planets. We made the first demonstration of this technique using two mirrors of the now historic Multiple Mirror Telescope(MMT). The 5 m baseline allowed us to detect material as close as 0.2 arcsec from the star at 10 microns. Using MIRAC2, an arsenic-doped silicon BIB array detector to record short-exposure images at 8.8, 9.6, 10.3, and 12.5 microns we obtained direct images of Betelgeuse's circumstellar dust cloud, relatively free of any starlight contamination. The images show significant asymmetry and demonstrate the ability of a nulling interferometer to reveal dim circumstellar structure. Atmospheric turbulence limited the level of cancellation with this instrument to 5%. We are currently designing a nulling instrument which will mask off two large sections of the 6.5 m MMT for nulling in a similar manner. When operated with the adaptive secondary of the MMT, this instrument will be capable of achieving cancellation to 0.01% given precise control of phase and amplitude balance between the beams over a usably wide passband. A key element in our design is a symmetric 50% transmission beamsplitter which creates a half-wave achromatic phase shift in the 8-13 micron region and a three-quarter wave phase shift at 2.2 microns. Interference measured at 2.2 micron will be used as a direct, sensitive indicator of phase differences between the beams, allowing correction of phase errors arising from the atmosphere or flexure. This level of nulling will achieve sensitivity to milliJansky-level fluxes around nearby stars in the 8-13 micron region, allowing us to detect zodiacal emission a factor of 1000 fainter than the dust cloud surrounding Beta Pictoris.

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