Eugene Serabyn

Nulling interferometry: symmetry requirements and experimental results

This paper provides a derivation from first principles of the stringent symmetry and stability requirements which deep stellar nulling demands, and also includes a brief status report on recent nulling results obtained with the Jet Propulsion Laboratorys fiber-coupled rotational-shearing interferometer. To date, the deepest transient nulls obtained (at red wavelengths) are 2 X 10-6 with a laser diode source, and 1.4 X 10-5 with a single- polarization thermal white-light source filtered to provide an 18% passband. In addition, both the laser and white light nulls have been stabilized to the 10-4 level. This visible wavelength laboratory nuller thus meets essentially all of the performance goals for the planned nulling experiment on board NASAs Space Interferometer Mission, with the sole exception of dual-polarization operation.

Review of small-angle coronagraphic techniques in the wake of ground-based second-generation adaptive optics systems

Small-angle coronagraphy is technically and scientifically appealing because it enables the use of smaller telescopes, allows covering wider wavelength ranges, and potentially increases the yield and completeness of circumstellar environment – exoplanets and disks – detection and characterization campaigns. However, opening up this new parameter space is challenging. Here we will review the four posts of high contrast imaging and their intricate interactions at very small angles (within the first 4 resolution elements from the star). The four posts are: choice of coronagraph, optimized wavefront control, observing strategy, and post-processing methods. After detailing each of the four foundations, we will present the lessons learned from the 10+ years of operations of zeroth and first-generation adaptive optics systems. We will then tentatively show how informative the current integration of second-generation adaptive optics system is, and which lessons can already be drawn from this fresh experience. Then, we will review the current state of the art, by presenting world record contrasts obtained in the framework of technological demonstrations for space-based exoplanet imaging and characterization mission concepts. Finally, we will conclude by emphasizing the importance of the cross-breeding between techniques developed for both ground-based and space-based projects, which is relevant for future high contrast imaging instruments and facilities in space or on the ground.

Observations of DG Tauri with the Keck Interferometer

We present the first science results from the Keck Interferometer, a direct-detection infrared interferometer utilizing the two 10 m Keck telescopes. The instrument and system components are briefly described. We then present observations of the T Tauri object DG Tau, which is resolved by the interferometer. The resolved component has a radius of 0.12-0.24 AU, depending on the assumed stellar and extended component fluxes and the model geometry used. Possible origins and implications of the resolved emission are discussed.

The Vector Vortex Coronagraph: sensitivity to central obscuration, low-order aberrations, chromaticism, and polarization

The Vector Vortex Coronagraph is a phase-based coronagraph, one of the most efficient in terms of inner working angle, throughput, discovery space, contrast, and simplicity. Using liquid-crystal polymer technology, this new coronagraph has recently been the subject of lab demonstrations in the near-infrared, visible and was also used on sky at the Palomar observatory in the H and K bands (1.65 and 2.2 μm, respectively) to image the brown dwarf companion to HR 7672, and the three extra-solar planets around HR 8799. However, despite these recent successes, the Vector Vortex Coronagraph is, as are most coronagraphs, sensitive to the central obscuration and secondary support structures, low-order aberrations (tip-tilt, focus, etc), bandwidth (chromaticism), and polarization when image-plane wavefront sensing is performed. Here, we consider in detail these sensitivities as a function of the topological charge of the vortex and design features inherent to the manufacturing technology, and show that in practice all of them can be mitigated to meet specific needs.

Keck Interferometer Nuller Data Reduction and On-Sky Performance

We describe the Keck Interferometer nuller theory of operation, data reduction, and on-sky performance, particularly as it applies to the nuller exozodiacal dust key science program that was carried out between 2008 February and 2009 January. We review the nuller implementation, including the detailed phasor processing involved in implementing the null-peak mode used for science data and the sequencing used for science observing. We then describe the Level 1 reduction to convert the instrument telemetry streams to raw null leakages, and the Level 2 reduction to provide calibrated null leakages. The Level 1 reduction uses conservative, primarily linear processing, implemented consistently for science and calibrator stars. The Level 2 processing is more flexible, and uses diameters for the calibrator stars measured contemporaneously with the interferometer’s K-band cophasing system in order to provide the requisite accuracy. Using the key science data set of 462 total scans, we assess the instrument performance for sensitivity and systematic error. At 2.0 Jy we achieve a photometrically-limited null leakage uncertainty of 0.25% rms per 10 minutes of integration time in our broadband channel. From analysis of the Level 2 reductions, we estimate a systematic noise floor for bright stars of ~0.2% rms null leakage uncertainty per observing cluster in the broadband channel. A similar analysis is performed for the narrowband channels. We also provide additional information needed for science reduction, including details on the instrument beam pattern and the basic astrophysical response of the system, and references to the data reduction and modeling tools.

ACCESS – A Concept Study for the Direct Imaging and Spectroscopy of Exoplanetary Systems

ACCESS is one of four medium-class mission concepts selected for study in 2008-9 by NASAs Astrophysics Strategic Mission Concepts Study program. ACCESS evaluates a space observatory designed for extreme high-contrast imaging and spectroscopy of exoplanetary systems. An actively-corrected coronagraph is used to suppress the glare of diffracted and scattered starlight to contrast levels required for exoplanet imaging. The ACCESS study considered the relative merits and readiness of four major coronagraph types, and modeled their performance with a NASA medium-class space telescope. The ACCESS study asks: What is the most capable medium-class coronagraphic mission that is possible with telescope, instrument, and spacecraft technologies available today? Using demonstrated high-TRL technologies, the ACCESS science program surveys the nearest 120+ AFGK stars for exoplanet systems, and surveys the majority of those for exozodiacal dust to the level of 1 zodi at 3 AU. Coronagraph technology developments in the coming year are expected to further enhance the science reach of the ACCESS mission concept.

Nulling Interferometry Progress

The field of nulling interferometry has seen significant progress over the past several years, in both the conceptual and experimental arenas. Deep, broadband nulling has been demonstrated at optical wavelengths, the techniques have seen initial implementation on telescopes, and the introduction of a symmetric beam-combiner concept has eliminated many of the residual obstacles. Here an overview is provided of promising techniques for effecting the deep cancellation of starlight, and recent results obtained with laboratory and astronomical nulling interferometers are discussed. The next step is the exploitation of nulling techniques at 8-10 m class separated-aperture telescope facilities, and in this vein, a brief overview of the architecture of the Keck Interferometer Nuller is also provided.

Terrestrial Planet Finder Interferometer: 2007-2008 Progress and Plans

This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized.

Recent results of the second generation of vector vortex coronagraphs on the high-contrast imaging testbed at JPL

The Vector Vortex Coronagraph (VVC) is an attractive internal coronagraph solution to image and characterize exoplanets. It provides four key pillars on which efficient high contrast imaging instruments can be built for ground- and space-based telescopes: small inner working angle, high throughput, clear off-axis discovery space, and simple layout. We present the status of the VVC technology development supported by NASA. We will review recent results of the optical tests of the second-generation topological charge 4 VVC on the actively corrected High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL). New VVC contrast records have been established.

Taking the vector vortex coronagraph to the next level for ground- and space-based exoplanet imaging instruments: review of technology developments in the USA, Japan, and Europe

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris- Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive optics, extremely large ground-based telescopes, and space-based internal coronagraphs.