Aperture masking interferometry and Adaptive Optics (AO) are two of the competing technologies attempting
to recover diffraction-limited performance from ground-based telescopes. However, there are good arguments
that these techniques should be viewed as complementary, not competitive. Masking has been shown to deliver
superior PSF calibration, rejection of atmospheric noise and robust recovery of phase information through the use
of closure phases. However, this comes at the penalty of loss of flux at the mask, restricting the technique to bright
targets. Adaptive optics, on the other hand, can reach a fainter class of objects but suffers from the difficulty
of calibration of the PSF which can vary with observational parameters such as seeing, airmass and source
brightness. Here we present results from a fusion of these two techniques: placing an aperture mask downstream
of an AO system. The precision characterization of the PSF enabled by sparse-aperture interferometry can now
be applied to deconvolution of AO images, recovering structure from the traditionally-difficult regime within the
core of the AO-corrected transfer function. Results of this program from the Palomar and Keck adaptive optical
systems are presented.
We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats.
The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models. Using the derived Rosseland angular radii and the spectral energy distributions (SEDs) reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from T_eff=3192 +/- 200 K at phase 0.13 to 2918 +/- 183 K at phase 0.26. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from 28.9 +/- 0.3 mas
(corresponding to a Rosseland radius of 332 +/- 38 Rsun for a distance of D=107 +/- 12 pc) at phase 0.13 to 34.9 +/- 0.4 mas (402 +/- 46 Rsun) at phase 0.4. The observational error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1%.