Nulling interferometry for studying other planetary systems: Techniques and observations

Abstract

Nulling interferometry is an important technique in the quest for direct detection of extrasolar planets. It is central to NASA's plans for a Terrestrial Planet Finder (TPF) mission to detect and characterize Earth-like planets. This thesis presents the first experiments to demonstrate that the technique is a useful tool for ground-based observations as well. It demonstrates the ability of the technique to study faint, circumstellar environments otherwise not easily observed. In addition the observations and experiments allow more confident estimation of expected sensitivity to planetary systems around nearby stars. The old MMT was used for the first telescope experiments of stellar suppression via nulling. The stellar suppression achieved was sufficient to observe thermal emission from cool dust in the outflows around late-type stars. Based on the original MMT prototype, which worked at ambient temperature, I have constructed a cryogenic nulling interferometer for use with the renovated 6.5 m MMT. Features include the capability of sensing and correcting the phase between the two arms of the interferometer, achromatic tuning of the null using a unique symmetric beam-splitter, and compatibility with the deformable secondary of the MMT. The instrument has been used in a laboratory setup with an artificial source to demonstrate a high level of suppression. Commissioning of the instrument took place at the MMT in June 2000 using the fixed f/9 secondary. The instrument was aligned, phased, and used for science observations of 17 stars over five nights. The future impact of nulling with the MMT and the Large Binocular Telescope is sketched out. These telescopes will be sensitive to very faint levels of zodiacal dust, indicative of planetary companions and giving us clues as to the make up of planetary systems. Substellar companions down to near Jupiter mass will be detectable around the nearest stars for the LBT, allowing direct imaging of long-period giant planets. The detection of such companions will be complementary to the Doppler velocity searches, currently so successful in verifying the existence of planets, thus giving a balanced view of the prevalence and range of separations possible for giant planets around nearby stars.