The Planetary Imaging Concept Testbed Using a Rocket Experiment (PICTURE 36.225 UG) was designed
to directly image the exozodiacal dust disk of ǫ Eridani (K2V, 3.22 pc) down to an inner radius of 1.5 AU.
PICTURE carried four key enabling technologies on board a NASA sounding rocket at 4:25 MDT on October
8th, 2011: a 0.5 m light-weight primary mirror (4.5 kg), a visible nulling coronagraph (VNC) (600-750 nm), a
32x32 element MEMS deformable mirror and a milliarcsecond-class fine pointing system.
Unfortunately, due to a telemetry failure, the PICTURE mission did not achieve scientific success. Nonetheless,
this flight validated the flight-worthiness of the lightweight primary and the VNC. The fine pointing system,
a key requirement for future planet-imaging missions, demonstrated 5.1 mas RMS in-flight pointing stability.
We describe the experiment, its subsystems and flight results. We outline the challenges we faced in developing
this complex payload and our technical approaches.
The Joint Milliarcsecond Pathfinder Survey (JMAPS) is a small, space-based, all-sky, visible wavelength astrometric
and photometric survey mission for 0th through 14th I-band magnitude stars with a planned 2013
launch. The primary objective of the JMAPS mission is the generation of an astrometric star catalog with 1
milliarcsecond (mas) positional accuracy or better, and photometry to the 1% accuracy level or better at 1st
to 12th mag. Achieving this level of accuracy in the final catalog requires a demanding attention to reducing
We present our findings on distortion, signal to noise, and the astrometric bandpass necessary to obtain the
desired accuracy for JMAPS.
We present progress in the development of the monolithic achromatic nulling interference coronagraph (MANIC),
an optic designed for enabling direct detection and characterization of exoplanetary systems around nearby stars.
MANIC is a fully symmetric implementation of a rotational shearing interferometer consisting of fused quartz
prisms and a symmetric beamsplitter optically contacted in an arrangement that geometrically flips the fields
in the TR and RT arms about orthogonal axes such that upon recombination, a centro-symmetric, theoretically
achromatic null is produced. In addition to a small inner working angle (⪅ 1λ/D), built-in alignment and
stability are inherent benefits of the compact monolithic design, which make MANIC a competitive alternative
to conventional discrete element nullers proposed for imaging exoplanetary environments. Following MANIC's
initial fabrication, the path error between its TR and RT arms was measured. This measurement was used to
fabricate compensator plates of varying thicknesses that were bonded to the optic to reduce dispersion imbalance,
thereby improving broadband nulling performance. In performing this correction, initial OPD was reduced from
949 ± 44 nm to 63 ± 10 nm, which in the absence of any other asymmetries, corresponds to an increase in a
107 R-band (λc = 648 nm) nulling bandpass from monochromatic to 25%, or at the 106 level, from 5% to 50%.
Current benchtop laser and polychromatic nulling strategies are described. The potential science return from
using MANIC on a sub-orbital platform is discussed.
We present progress in the development of the monolithic achromatic nulling interference coronagraph (MANIC),
a nulling optic designed to enable direct imaging of nearby Jupiter-like exoplanets. The experimental testbed
for measuring the optical path difference (OPD) between the two arms of the nuller and characterizing the
nuller's performance is described. The OPD measurement will be used to determine the relative thicknesses of
compensator plates needed to complete MANIC's fabrication. Demonstrating the performance of the monolith
will include sub-aperture nulling of laser and white-light sources using a single PZT-controlled delay line on one
half of a bisected input beam.
DAVINCI is a dilute aperture nulling coronagraph that has the potential of directly detecting an Earth in the habitable zone around ~100 nearby stars. The novel feature of this mission concept is to replace a filled aperture 5-6 meter telescope with 4 by 1.1 meter
telescopes in a phased array, dramatically reducing the cost by
potentially by a factor of 5-10.
We report progress on a nulling coronagraph intended for direct imaging of extrasolar planets. White light is suppressed
in an interferometer, and phase errors are measured by a second interferometer. A 1020-pixel MEMS deformable mirror
in the first interferometer adjusts the path length across the pupil. A feedback control system reduces deflections of the
deformable mirror to order of 1 nm rms.
During the last two years we have used the Palomar Testbed Interferometer to observe several explosive variable stars, including V838 Monocerotis, V1663 Aquilae and recently RS Ophiuchi. We observed V838 Monocerotis approximately 34 months after its eruption, and were able to resolve the ejecta. Observations of V1663 Aql were obtained starting 9 days after peak brightness and continued for 10 days. We were able to resolve the milliarcsecond-scale emission and follow the expansion of the nova photosphere. When combined with radial-velocity information, these observations can be used to infer the distance to the nova. Finally we have resolved the recurrent nova RS Oph and can draw some preliminary conclusions regarding the emission morphology.
A new observing mode for the Palomar Testbed Interferometer was developed in 2002-2003 which enables differential astrometry at the level of 20 micro-arcseconds (μas) for binary systems with separations of several hundred milli-arcseconds (mas). This phase-referenced mode is the basis of the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES), a search for giant planets orbiting either the primary or secondary star in fifty binary systems. We present the first science results from the PHASES search. The properties of the stars comprising binary systems are determined to high precision. The mutual inclinations of several hierarchical triple star systems have been determined. We will present upper limits constraining the the existence of giant planets
in a few of the target systems.
We describe the advantages of a nulling coronagraph instrument behind a single aperture space telescope for detection and spectroscopy of Earth-like extrasolar planets in visible light. Our concept synthesizes a nulling interferometer by shearing the telescope pupil into multiple beams. They are recombined with a pseudo-achromatic pi-phase shift in one arm to produce a deep null on-axis, attenuating the starlight, while simultaneously transmitting the off-axis planet light. Our nulling configuration includes methods to mitigate stellar leakage, such as spatial filtering by a coherent array of single mode fibers, balancing amplitude and phase with a segmented deformable mirror, and post-starlight suppression wavefront sensing and control. With diffraction limited telescope optics and similar quality components in the optical train (λ/20), suppression of the starlight to 10-10 is readily achievable. We describe key features of the architecture and analysis, present the status of key experiments to demonstrate wide bandwidth null depth, and present the status of component technology development.
The nulling coronagraph is one of 5 instrument concepts selected by NASA for study for potential use in the TPF-C
mission. This concept for extreme starlight suppression has two major components, a nulling interferometer to suppress
the starlight to ~10-10 per airy spot within 2 λ/D of the star, and a calibration interferometer to measure the residual
scattered starlight. The ability to work at 2 λ/D dramatically improves the science throughput of a space based
coronagraph like TPF-C. The calibration interferometer is an equally important part of the starlight suppression system.
It measures the measures the wavefront of the scattered starlight with very high SNR, to 0.05nm in less than 5 minutes
on a 5mag star. In addition, the post coronagraph wavefront sensor will be used to measure the residual scattered light
after the coronagraph and subtract it in post processing to 1~2x10-11 to enable detection of an Earthlike planet with a
SNR of 5~10.
It has recently been suggested that up to half of the wavefront variance can be removed from the total atmospheric distortion by correcting only the lowest seeing layer (Rigaut 2000, 2001). This Ground-Layer AO (GLAO) correction could provide improved image quality over a very wide field of view; however, no development work has been done on existing telescopes. The implications are profound for optical designs of future AO optimized telescopes (e.g. the ELTs) as accurately compensating for this ground-layer strongly favors an adaptive element conjugated to the median height of the ground-layer. The gains of GLAO are tantalizing but substantially unproven, and thus, the Giant Magellan Telescope (GMT) project has developed a multi-phased study with the goal of providing an on-sky demonstration of GLAO technology at the Magellan Telescopes.
The first phase of this experiment is to measure the the height and
boundary of the ground-layer through multiple, fixed wavefront sensors
on very bright cluster fields over the full 24 arcminute Magellan
field of view. With a typical wind speed of 9 m/s and a presumed secondary ground-layer conjugation error of 100 m, the equivalent decoherence time is approximately 0.04 seconds. Therefore, we have designed and constructed high resolution Shack-Hartmann sensors running at 100 frames per second with coarse, 0.6m sub-apertures.
We present a technical description of the wavefront sensors and image
analyzer, as well as current results from the first deployment of
this instrument at Magellan. In addition, we discuss the implications
for ground-layer modeling and describe the next phases of the GMT's
The Antarctic Planet Interferometer is a concept for an instrument designed to detect and characterize extrasolar planets by exploiting the unique potential of the best accessible site on earth for thermal infrared interferometry. High-precision interferometric techniques under development for extrasolar planet detection and characterization (differential phase, nulling and astrometry) all benefit substantially from the slow, low-altitude turbulence, low water vapor content, and low temperature found on the Antarctic plateau. At the best of these locations, such as the Concordia base being developed at Dome C, an interferometer with two-meter diameter class apertures has the potential to deliver unique science for a variety of topics, including extrasolar planets, active galactic nuclei, young stellar objects, and protoplanetary disks.
The Palomar Testbed Interferometer has observed several binary star
systems whose separations fall between the interferometric coherence
length (a few hundredths of an arcsecond) and the typical atmospheric
seeing limit of one arcsecond. Using phase-referencing techniques we
measure the relative separations of the systems to precisions of a few
tens of micro-arcseconds. We present the first scientific results of
these observations, including the astrometric detection of the faint third stellar component of the kappa Pegasi system.
Atmospheric turbulence is a serious problem for ground-based
interferometers. It places tight limits on both sensitivity and
measurement precision. Phase referencing is a method to overcome these
limitations via the use of a bright reference star. The Palomar
Testbed Interferometer was designed to use phase referencing and so
can provide a pair of phase-stabilized starlight beams to a second
(science) beam combiner. We have used this capability for several
interesting studies, including very narrow angle astrometry. For close
(1-arcsecond) pairs of stars we are able to achieve a differential
astrometric precision in the range 20--30 micro-arcseconds.
This paper describes the latest progress for visible direct detection of Earth like extrasolar planets using a nulling coronagraph instrument behind a 4m class telescope. Such a system is capable of satisfying the scientific objectives of the Terrestrial Planet Finder mission In our design, a 4 beam nulling interferometer is synthesized from the telescope pupil, producing a very deep null proportional to θ4 which is then filtered by a coherent array of single mode fibers to suppress the residual scattered light. With diffraction limited telescope optics and similar quality components in the optical train (λ/20), suppression of the starlight to 10-10 is achievable. Such a telescope with this nulling interferometer as back-end instrument can image and detect planets, or provide the input to a low resolution spectrometer. Shown are key features of this system in a space mission, latest results of laboratory measurements demonstrating achievable null depth, and progress toward fabrication of coherent single mode fiber arrays.
Researches have suggested several techniques (ie.: pupil masking, coronography, nulling interferometry) for high contrast imaging that permit the direct detection and characterization of extrasolar planets. Our team at JPL, in previous papers, has described an instrument that will combine the best of several of these techniques: a single aperture visible nulling corograph. The elegant simplicity of this design enables a powerful planet-imaging instrument at modest cost. The heart of this instrument is the visible light nulling interferometer for producing deep, achromatic nulls over a wide optical band pass, and a coherent array of single mode optical fibers 2 that is key to suppressing the level of scattered light. Both of these key components are currently being developed and have
produced intial results. This paper will review, in detail, the design of the nulling interferometer experiment and review the latest experimental results. These results illustrate that we are well on our way to developing the fundamental components necessary for planned mission. Likewise, our results demonstrate that the current nulling levels are already consistent with final requirements.
The primary limitation to ground based astronomy is the Earth's atmosphere. The atmosphere above the Antarctic plateau is different in many regards compared to the atmosphere at temperate sites. The extreme altitude, cold and low humidity offer a uniquely transparent atmosphere at many wavelengths. Studies at the South Pole have shown additionally that the turbulence properties of the night time polar atmosphere are fundamentally different to mid latitudes. Despite relatively strong ground layer turbulence, the lack of high altitude turbulence combined with low wind speeds presents favorable conditions for interferometry. The unique properties of the polar atmosphere can be exploited for Extrasolar Planet studies with differential astrometry, differential phase and nulling intereferometers. This paper combines the available data on the properties of the atmosphere at the South Pole and other Antarctic plateau sites for Extrasolar Planet science with interferometry.
Direct diameter measurements of Cepheid variables are used to calibrate the Barnes-Evans Cepheid surface brightness relation.
More than 50 separate Cepheid diameter measurements from four different optical interferometers are used to calculate surface brightnesses as a function of magnitude and color. For two Cepheids, η Aquilae and ζ Geminorum, high precision diameter measurements as a function of pulsation phase are available from the Palomar Testbed Interferometer (PTI). Relations using only these diameters are found for each individual Cepheid in order to search for differences between Cepheids of different pulsation period. In all cases the best-fit relations are simple linear relations between surface brightness and color with the constraint that for a spectral type A0 star (where all colors equal zero) all relations must yield the same surface brightness (i.e., there must be a common zero-point). The derived relations found using interferometric Cepheid diameters are consistent with functions in the literature found using
interferometric observations of non-variable giant and supergiant stars. In addition, while the separate relations for η Aquilae and ζ Geminorum are marginally consistent within the errors they do differ in the direction predicted for Cepheids of differing pulsation period. Using these new surface brightness relations the
distance is calculated to the nearby Cepheid δ Cephei for which
a new distance has been found using trigonometric parallax with
the Hubble Space Telescope. These distances are well within the
errors of the distance derived from trigonometric parallax.
We discuss recent work from the Palomar Testbed Interferometer (PTI), including science results and system improvements. In the past two years PTI has been used to observe a wide range of scientifically interesting sources, including binaries, Cepheids and Miras. In addition PTI has been used to observe departures from spherical symmetry in several stars. Recent system improvements incude a new low read-noise camera based on a HAWAII infrared array, routine opteration in two baselines, and operation in the J band. Future developments include an upgrade to three-aperture combination and closure phase measurements, and double-Fourier interferometry.
The Palomar Testbed Interferometer is a long-baseline near- infrared interferometer operating at Palomar Observatory, CA. The interferometer has a maximum baseline of 110 m, 40- cm collecting apertures, and active fringe tracking. It also incorporates a dual-star architecture to enable cophasing and narrow-angle astrometry. We will discuss recent system improvements and engineering results. These include upgrades to allow for longer coherent integration times, H band operation, and cophasing using delay line feedforward. Recent engineering tests of astrometry in dual-star mode have shown a night-to-night repeatability of 100 (mu) as on a bright test target. Several new observation planning tools have been developed, and data reduction tools have been automated to allow fully pipelined nightly reductions and archiving.
The Palomar Testbed Interferometer is a long-baseline interferometer that uses both phase and group-delay measurements for narrow-angle astrometry. The group-delay measurements are performed using 5 spectral channels across the band from 2.0 to 2.4 micrometers . Group delay is estimated from phasors (sine and cosine of fringe phase) calculated for each spectral channel using pathlength modulation of one wavelength. Normally the group delay is estimated to be the delay corresponding to the peak of the power spectrum of these complex phasors. The Fourier transform does not however yield a least-squares estimate of the delay. Nevertheless, the precision of phase estimation can be achieved in a group-delay estimate using a least-squares approach. We describe the least-squares group-delay estimator that has been implemented at PTI and illustrate its performance as applied to narrow-angle astrometry.
The Palomar Testbed Interferometer (PTI) is an infrared, phase-tracking interferometer in operation at Palomar Mountain since July 1995. It was funded by NASA for the purpose of developing techniques and methodologies for doing narrowangle astrometry for the purpose of detecting extrasolar planets. The instrument employs active fringe trackingin the infrared (2.0-2.4 μm) to monitor fringe phase. It is a dual-star interferometer; it is able to measure fringes on two separate stars simultaneously. An end-to-end heterodyne laser metrology system is used to monitor the optical path length of the starlight. Recently completed engineering upgrades have improved the initial instrument performance. These upgrades are:extended wavelength coverage, a single mode fiber for spatial filtering, vacuum pipes to relay the beams, accelerometers on the siderostat mirrors and a new baseline. Results of recent astrometry data indicate the instrument is approaching the astrometric limit as set by the atmosphere.