A Third Star in the T Tauri System

New speckle-holographic images of the T Tauri Infrared Companion (T Tauri IRC; T Tauri S) reveal it to be a double system with a sky-projected separation of 0".05, corresponding to a linear distance of 7 AU. The presence of this third star may account for the relative paucity of dust surrounding the IRC.Comment: 5 pages in AASTeX preprint form, including one grayscale figur

Imaging the Haro 6-10 Infrared Companion

We present an infrared imaging study of the low-mass pre-main-sequence binary system Haro 6-10. This system is one of a handful in which the optically visible primary has the characteristics of a normal T Tauri star, while the secondary is a so-called "infrared companion" (IRC), a strongly extincted object that emits most of its luminosity in the infrared. A speckle holographic technique was used to produce nearly diffraction-limited images on three nights over a 1 yr period starting in late 1997. The images show that the IRC is obscured and surrounded by a compact, irregular, and variable nebula. This structure is in striking contrast to the well-ordered edge-on disk associated with HK Tauri B, the extincted companion to another T Tauri star of similar age. A new, resolved intensity peak was found 0".4 southwest of the IRC. We suggest that it may represent light scattered by a clump of dusty material illuminated by starlight escaping along an outflow-carved cavity in the IRC envelope. The primary star became fainter and the companion became more extended during the observing period

Longitudinal dispersion control for the Keck interferometer nuller

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase)

An 11.6 Micron Keck Search For Exozodiacal Dust

We have begun an observational program to search nearby stars for dust disks that are analogous to the disk of zodiacal dust that fills the interior of our solar system. We imaged six nearby main-sequence stars with the Keck telescope at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and deconvolving the point spread function via classical speckle analysis. We compare our data to a simple model of the zodiacal dust in our own system based on COBE/DIRBE observations and place upper limits on the density of exozodiacal dust in these systems.Comment: 10 pages, figure1, figure2, figure3, and figures 4a-

Tabletop mid-infrared nulling testbed for the Keck interferometer and the Terrestrial Planet Finder

A tabletop rotational-shearing interferometer experiment has been constructed and operated at JPL to serve as a testbed for the mid-infrared (~10 μm) nulling beam combiners on the Keck Interferometer and the Terrestrial Planet Finder. The testbed is a pupil-plane combiner in which destructive combination of the incoming wavefronts is achieved using a rooftop mirror system in which the polarization vector is flipped along the vertical axis on one arm and the horizontal axis on the other. The optical pathlength along one arm is adjustable using a linear stage driven by picomotor and piezoelectric actuators. The combined light is focussed onto a single-pixel LN_2-cooled HgCdTe detector. In order to provide adequate sensitivity in the presence of the very bright thermal emission from the room-temperature optics, the light source is modulated and the output is demodulated using a lock-in amplifier. The optical pathlength difference (OPD) is stabilized under computer control by slowly dithering the actuated arm and balancing the leakage signal on either side of the null. The system has produced a stabilized null depth of < 10^(-4) using a diode laser source emitting at a wavelength of 9.2 μm, and transient nulls of 10^(-2) with a broadband thermal IR source in a 6.4% optical bandpass

Recent progress at the Keck Interferometer

In this paper we report on progress at the Keck Interferometer since the 2004 SPIE meeting with an emphasis on the operations improvements for visibility science

Longitudinal dispersion control for the Keck interferometer nuller

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase)

Tabletop mid-infrared nulling testbed for the Keck interferometer and the Terrestrial Planet Finder

A tabletop rotational-shearing interferometer experiment has been constructed and operated at JPL to serve as a testbed for the mid-infrared (~10 μm) nulling beam combiners on the Keck Interferometer and the Terrestrial Planet Finder. The testbed is a pupil-plane combiner in which destructive combination of the incoming wavefronts is achieved using a rooftop mirror system in which the polarization vector is flipped along the vertical axis on one arm and the horizontal axis on the other. The optical pathlength along one arm is adjustable using a linear stage driven by picomotor and piezoelectric actuators. The combined light is focussed onto a single-pixel LN_2-cooled HgCdTe detector. In order to provide adequate sensitivity in the presence of the very bright thermal emission from the room-temperature optics, the light source is modulated and the output is demodulated using a lock-in amplifier. The optical pathlength difference (OPD) is stabilized under computer control by slowly dithering the actuated arm and balancing the leakage signal on either side of the null. The system has produced a stabilized null depth of < 10^(-4) using a diode laser source emitting at a wavelength of 9.2 μm, and transient nulls of 10^(-2) with a broadband thermal IR source in a 6.4% optical bandpass