E. K. Hege

Images From Astronomical Speckle Data: Weighted Shift-And-Add Analysis

We have applied a variant of the shift-and-add algorithm originally developed by Lynds, Worden, and Harvey [Astrophys. J. 207, 174 (1976)] to astronomical speckle interferometric data. A set of impulses corresponding in locations and magnitudes to the local maxima in each specklegram is generated and used to obtain an average speckle by means of a Wiener-type filter deconvolution procedure. This technique yields diffraction-limited images that appear to be self-calibrating for seeing effects. Realistic point spread functions have been obtained for a number of telescopes at different wavelengths, and results are also presented for the resolved red supergiant Alpha Orionis. The limiting signal-to-noise ratio of the technique as indicated by the results presented here suggests a dynamic range of =6 stellar magnitudes, with no evidence of residual seeing effects. A matched filter technique is demonstrated for use in locating the speckles of complicated objects or for objects dominated by photon noise.

Differential Speckle Imaging With The Cophased Multiple Mirror Telescope

Differential speckle interferometry has been applied to data obtained using the fully phased six-mirror aperture of the Multiple Mirror Telescope. Wavelength-dependent differences in the appearance of a stellar object are derived from simultaneous observations at two distinct wavebands. The supergiant star Alpha Orionis was observed this way to investigate its appearance in hydrogen-alpha emission. Data reduction consists of a frame-by-frame weighted deconvolution. An inherent Wiener-type filtering must be removed in order to preserve high spatial frequency information. Results for Alpha Orionis are compared to similar results for the unresolved source Gamma Orionis.

Use Of The Coherent MMT For Diffraction Limited Imaging

All six MMT telescopes can now be optically cophased simultaneously over a wide field of view yielding coherent coverage of the complete Fourier transform plane corresponding to that of a pupilmasked telescope of 6.86m aperture. Open-loop phasing control compensates for flexure-induced path-length changes due to variable gravitational loading as a function of elevation. The system has been used to produce diffraction limited images and differential images of Alpha Orionis using narrow-band (1.2A) filters centered both on Hydrogen-alpha and on a similar bandpass out of the absorption line. Corresponding wide (100A) and narrow-band images of Gamma and Epsilon Orionis show the expected result for unresolved sources at the diffraction limited resolution of the fully-phased MMT.