Many high-contrast coronagraph designs have recently been proposed. In this paper, their suitability for direct imaging of extrasolar terrestrial planets is reviewed. We also develop a linear algebra based model of coronagraphy that can both explain the behavior of existing coronagraphs and quantify the coronagraphic performance limit imposed by fundamental physics. We find that the maximum theoretical throughput of a coronagraph is equal to 1 minus the nonaberrated noncoronagraphic PSF of the telescope. We describe how a coronagraph reaching this fundamental limit may be designed, and how much improvement over the best existing coronagraph design is still possible. Both the analytical model and numerical simulations of existing designs also show that this theoretical limit rapidly degrades as the source size is increased: the ''highest performance'' coronagraphs, those with the highest throughput and smallest inner working angle (IWA), are the most sensitive to stellar angular diameter. This unfortunately rules out the possibility of using a small IWA (

Using two aspheric mirrors, it is possible to apodize a telescope beam without losing light or angular resolution: the output beam is produced by ''remapping'' the entrance beam to produce the desired light intensity distribution in a new pupil. We present the phase-induced amplitude apodization coronagraph ( PIAAC) concept, which uses this technique, and show that it allows efficient direct imaging of extrasolar terrestrial planets with a small-sized telescope in space. The suitability of the PIAAC for exoplanet imaging is due to a unique combination of achromaticity, small inner working angle (about 1.5k/d ), high throughput, high angular resolution, and large field of view. Three-dimensional geometrical ray tracing is used to investigate the off-axis aberrations of PIAAC configurations and show that a field of view of more than 100k/d in radius is available thanks to the correcting optics of the PIAAC. Angular diameter of the star and tip-tilt errors can be compensated for by slightly increasing the size of the occulting mask in the focal plane, with minimal impact on the system performance. Earth-sized planets at 10 pc can be detected in less than 30 s with a 4 m telescope. Wave-front quality requirements are similar to classical techniques.

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Abstract. We present the results of diffraction-limited optical speckle interferometry and infrared bispectrum speckle interferometry of 111 double and 10 triple systems performed in 1998-1999 with the 6-m telescope of the Special Astrophysical Observatory in Zelenchuk. The observations concentrated on nearby close binaries discovered during the Hipparcos mission. Many nearby fast-orbiting low-mass binaries known before Hipparcos were also included in the program. New companions were first resolved in 4 systems: HIP 5245, ADS 3179, Kui 99, and ADS 16138. In addition to accurate relative positions, magnitude differences were measured for most of the pairs. We combined our results with the Hipparcos parallaxes to derive absolute magnitudes and spectral types for 63 binaries and 4 triples. Preliminary orbital elements and the mass-sum are derived for HIP 689, and improved orbits are presented for HIP 16602 (CHR 117) and HIP 21280 (CHR 17).

We report imaging observations of the symbotic long-period Mira variable R Aquarii (R Aqr) at near-infrared and radio wavelengths. The near-infrared observations were made with the IOTA imaging interferometer in three narrowband filters centered at 1.51, 1.64, and 1.78 µm, which sample mainly water, continuum, and water features, respectively. Our near-infrared fringe visibility and closure phase data are analyzed using three models. (a) A uniform disk model with wavelength-dependent sizes fails to fit the visibility data, and is inconsistent with the closure phase data. (b) A three-component model, comprising a Mira star, water shell, and an off-axis point source, provide a good fit to all data. (c) A model generated by a constrained image reconstruction analysis provides more insight, suggesting that the water shell is highly non-uniform, i.e., clumpy. The VLBA observations of SiO masers in the outer molecular envelope show evidence of turbulence, with jet-like features containing velocity gradients.

Properly apodized pupils can deliver point spread functions (PSFs) free of Airy rings, and are suitable for high dynamical range imaging of extrasolar terrestrial planets (ETPs). To reach this goal, classical pupil apodization (CPA) unfortunately requires most of the light gathered by the telescope to be absorbed, resulting in poor throughput and low angular resolution. Phaseinduced amplitude apodization (PIAA) of the telescope pupil (Guyon 2003) combines the advantages of classical pupil apodization (particularly low sensitivity to low order aberrations) with full throughput, no loss of angular resolution and little chromaticity, which makes it, theoretically, an extremely attractive coronagraph for direct imaging of ETPs. The two most challenging aspects of this technique are (1) the difficulty to polish the required optics shapes and (2) diffraction propagation effects which, because of their chromaticity, can decrease the spectral bandwidth of the coronagraph. We show that a properly designed hybrid system combining classical apodization with the PIAA technique can solve both problems simultaneously. For such a system, the optics shapes can be well within today's optics manufacturing capabilities, and the 10 −10 PSF contrast at ≈ 1.5λ/D required for efficient imaging of ETPs can be maintained over the whole visible spectrum. This updated design of the PIAA coronagraph maintains the high performance of the earlier design, since only a small part of the light is lost in the classical apodizer(s).

Abstract. We present first orbits for 6 new Hipparcos binaries. The orbits were determined from speckle interferometric measurements collected mainly at the 6 m BTA telescope of the Special Astrophysical Observatory in Zelenchuk. Three of the systems, HIP 11352, HIP 14075 and HIP 14230, have late G-or early K-type components, while HIP 14669 = GJ 125, HIP 106972 = GJ 4210 and HIP 111685 = GJ 4287 have M-type components. The periods of the orbits are in the range of 6−28 years. Mass sums and their errors are derived for the systems. The Hipparcos parallax error is the dominating error source of the mass determination.

Abstract. This paper is a continuation of diffraction-limited speckle interferometry of binary and multiple stars carried out at the 6-m telescope of the Special Astrophysical Observatory in Zelenchuk. The program has concentrated on nearby (π > 10 mas) close binaries discovered or measured during the Hipparcos mission. Here, we present 132 measurements of relative positions and magnitude differences for 99 pairs and 8 measurements for 6 triple systems. 54 entries in the paper are new Hipparcos binaries. New triple systems with late-type dwarf components, discovered in the course of observations, are HIP 8533 and HIP 25354.