Paper Session II-B - Four Years of Science with the WFPC2

As distant in time and space as the horizon of the visible Universe, and as near and contemporary as a string of comets colliding with Jupiter, the Wide Field and Planetary Camera 2 on the Hubble Space Telescope has brought us unprecedented views of our cosmic surroundings. Here we present highlights of the last four years of WFPC2 photometric imaging with the first large optical telescope in space, including new insights into the workings of our solar system, the life cycles of nebulae and stars in our galaxy, and the evolution of galaxies themselves over cosmic time

Complex apodization Lyot coronagraphy for the direct imaging of exoplanet systems: design, fabrication, and laboratory demonstration

We review the design, fabrication, performance, and future prospects for a complex apodized Lyot coronagraph for highcontrast exoplanet imaging and spectroscopy. We present a newly designed circular focal plane mask with an inner working angle of 2.5 λ/D. Thickness-profiled metallic and dielectric films superimposed on a glass substrate provide control over both the real and imaginary parts of the coronagraph wavefront. Together with a deformable mirror for control of wavefront phase, the complex Lyot coronagraph potentially exceeds billion-to-one contrast over dark fields extending to within angular separations of 2.5 λ/D from the central star, over spectral bandwidths of 20% or more, and with throughput efficiencies better than 50%. Our approach is demonstrated with a linear occulting mask, for which we report our best laboratory imaging contrast achieved to date. Raw image contrasts of 3×10^(-10) over 2% bandwidths, 6×10^(-10) over 10% bandwidths, and 2×10^(-9) over 20% bandwidths are consistently achieved across high contrast fields extending from an inner working angle of 3 λ/D to a radius of 15 λ/D. Occulter performance is analyzed in light of experiments and optical models, and prospects for further progress are summarized. The science capability of the hybrid Lyot coronagraph is compared with requirements for ACCESS, a representative space coronagraph concept for the direct imaging and spectroscopy of exoplanet systems. This work has been supported by NASA’s Strategic Astrophysics Technology / Technology Demonstrations for Exoplanet Missions (SAT/TDEM) program

Zodiac II: Debris Disk Imaging Potential

Zodiac II is a proposed coronagraph on a balloon-borne platform, for the purpose of observing debris disks around nearby stars. Zodiac II will have a 1.2-m diameter telescope mounted in a balloon-borne gondola capable of arcsecond quality pointing, and with the capability to make long-duration (several week) flights. Zodiac II will have a coronagraph able to make images of debris disks, meaning that its scattered light speckles will be at or below an average contrast level of about 10(exp -7) in three narrow (7 percent) bands centered on the V band, and one broad (20%) one at I band. We will discuss the potential science to be done with Zodiac II

Inhibition of RNA polymerase II transcription in human cells by synthetic DNA-binding ligands

Sequence-specific DNA-binding small molecules that can permeate human cells potentially could regulate transcription of specific genes. Multiple cellular DNA-binding transcription factors are required by HIV type 1 for RNA synthesis. Two pyrrole-imidazole polyamides were designed to bind DNA sequences immediately adjacent to binding sites for the transcription factors Ets-l, lymphoid-enhancer binding factor 1, and TATA-box binding protein. These synthetic ligands specifically inhibit DNA-binding of each transcription factor and HIV type 1 transcription in cell-free assays. When used in combination, the polyamides inhibit virus replication by >99% in isolated human peripheral blood lymphocytes, with no detectable cell toxicity, The ability of small molecules to target predetermined DNA sequences located within RNA polymerase II promoters suggests a general approach for regulation of gene expression, as well as a mechanism for the inhibition of viral replication

Fine Guidance Sensing for Coronagraphic Observatories

Three options have been developed for Fine Guidance Sensing (FGS) for coronagraphic observatories using a Fine Guidance Camera within a coronagraphic instrument. Coronagraphic observatories require very fine precision pointing in order to image faint objects at very small distances from a target star. The Fine Guidance Camera measures the direction to the target star. The first option, referred to as Spot, was to collect all of the light reflected from a coronagraph occulter onto a focal plane, producing an Airy-type point spread function (PSF). This would allow almost all of the starlight from the central star to be used for centroiding. The second approach, referred to as Punctured Disk, collects the light that bypasses a central obscuration, producing a PSF with a punctured central disk. The final approach, referred to as Lyot, collects light after passing through the occulter at the Lyot stop. The study includes generation of representative images for each option by the science team, followed by an engineering evaluation of a centroiding or a photometric algorithm for each option. After the alignment of the coronagraph to the fine guidance system, a "nulling" point on the FGS focal point is determined by calibration. This alignment is implemented by a fine alignment mechanism that is part of the fine guidance camera selection mirror. If the star images meet the modeling assumptions, and the star "centroid" can be driven to that nulling point, the contrast for the coronagraph will be maximized

Pressure Line Broadening and Feasibility of CO_2 Profile Retrieval using Near Infrared Observations of an Absorption Line

Analytic expressions are derived for the transmittance and reflectance of sunlight and their Jacobians for an absorption line with Lorentz line broadening. Rodgers information analysis is applied to calculate the information content, the degrees of freedom and the averaging kernel for a simple atmospheric model to investigate the feasibility of retrieving the profile of CO_2 using near-infrared (NIR) measurements over a single absorption line. The results have implications for the design of future space instruments with high spectral resolution and high signal to noise ratios to obtain global scale information on the CO_2 vertical distribution which is important for inferring the sources, sinks, and transport of CO_2

Assessing the performance limits of internal coronagraphs through end-to-end modeling: a NASA TDEM study

As part of the NASA ROSES Technology Development for Exoplanet Missions (TDEM) program, we are conducting a study of three internal coronagraphs (PIAA, vector vortex, hybrid bandlimited) to understand their behaviors in realistically-aberrated systems with wavefront control (deformable mirrors). This study consists of two milestones: (1) develop wavefront propagation codes appropriate for each coronagraph that are accurate to 1% or better (compared to a reference algorithm) but are also time and memory efficient, and (2) use these codes to determine the wavefront control limits of each architecture. We discuss the results from the study so far, with emphasis on representing the PIAA coronagraph and its wavefront control behavior

Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri

Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 μm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2". The arc shows an approximate symmetry along an axis toward the west-northwest, the direction of Hind's Nebula and the blueshifted molecular outflow. The morphology of the reflected light is similar to models of scattered light within an illuminated, axisymmetric outflow cavity in a circumbinary envelope, viewed ≈ 45° from the outflow axis. However, our model images do not successfully account for the amount of limb brightening that is seen. No optical counterpart to the infrared companion is seen to a limiting magnitude of V = 19.6, which suggests A_V > 7 mag toward this source. There is no evidence for an optical tertiary, to a limiting ΔV = 5.1 mag fainter than the primary, at the position where such an object has been previously reported