The Planet Formation Imager (PFI) is a near- and mid-infrared interferometer project with the driving science goal of imaging directly the key stages of planet formation, including the young proto-planets themselves. Here, we will present an update on the work of the Science Working Group (SWG), including new simulations of dust structures during the assembly phase of planet formation and quantitative detection efficiencies for accreting and non-accreting young exoplanets as a function of mass and age. We use these results to motivate two reference PFI designs consisting of a) twelve 3m telescopes with a maximum baseline of 1.2km focused on young exoplanet imaging and b) twelve 8m telescopes optimized for a wider range of young exoplanets and protoplanetary disk imaging out to the 150K H2O ice line. Armed with 4 x 8m telescopes, the ESO/VLTI can already detect young exoplanets in principle and projects such as MATISSE, Hi-5 and Heimdallr are important PFI pathfinders to make this possible. We also discuss the state of technology development needed to make PFI more affordable, including progress towards new designs for inexpensive, small field-of-view, large aperture telescopes and prospects for Cubesat-based space interferometry.
The TOLIMAN space telescope is a low-cost, agile mission concept dedicated to astrometric detection of exoplanets in the near-solar environment, and particularly targeting the Alpha Cen system. Although successful discovery technologies are now populating exoplanetary catalogs into the thousands, contemporary astronomy is still poorly equipped to answer the basic question of whether there are any rocky planets orbiting any particular star system. Toliman will make a first study of stars within 10 PC of the sun by deploying an innovative optical and signal encoding architecture that leverages the most promising technology to deliver data on this critical stellar sample: high precision astrometric monitoring. Here we present results from the Foundational Mission Study, jointly funded by the Breakthrough Prize Foundation and the University of Sydney which has translated innovative underlying design principles into error budgets and potential spacecraft systems designs.
The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to ~100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.
We present several engineering and algorithmic aspects of non-redundant masking (NRM) as they pertain to the James Webb Space Telescope (JWST). NRM's fundamental data structures have multiple uses in wavefront sensing as well in as high resolution imaging. Kernel phases are a full aperture generalization of NRM applicable to moderate and high Strehl ratio images. Eigenphases, the complement to kernel phases, provide wavefront sensing with single in-focus images. Thus this set of phases is relevant to wavefront sensing with routine science images on any Nyquist-sampled science camera on JWST. We attempt to organize these apparently diverse aspects of such Fizeau interferometry into an inter-related picture in order to facilitate their development and potential use on JWST and future space telescopes.
The limits for adaptive-optics-assisted and space-based astronomical imaging at high contrast and high resolution are typically determined by residual phase errors due to non-common-path aberrations not sensed by the wavefront sensor. These impose quasi-static speckles on the image, which are difficult to calibrate as they vary in time and with telescope orientation. Typical approaches require phase diversity of some sort,1 which requires many iterations and is accordingly time-consuming. This is especially true of integral field spectrographs, where use of standard phase diversity based techniques is additionally complicated by the presence of the image slicer/integral field unit. We present the first application of the kernel phase based ‘asymmetric pupil Fourier wavefront sensing’ scheme to ground-based AO-corrected integral field spectroscopy, whereby an asymmetric pupil mask and a single image are sufficient to map aberrations up to high order, including non-common-path error. This method is closely connected with kernel phase interferometry, already applied to space-based and AO-assisted imaging, in which a phase transfer matrix formalism partitions focal plane Fourier phases into a kernel space which is self- calibrating with respect to pupil aberrations, and a row space which can be used to determine those aberrations via a matrix pseudo-inverse. This requires two key conditions be satisfied: the first, that phase errors are < 1 radian in magnitude. These conditions are typically satisfied for space-based telescopes such as the HST, or AO-corrected ground-based telescopes in the near-infrared. The second requirement is that the telescope pupil is not centro-symmetric; this can be achieved simply by placing an asymmetric mask in the optical path. The row phase reconstruction then provides a phase map which can be applied directly to a deformable mirror as a static offset. While in our approach we have iteratively applied corrections, we have deliberately damped correction steps, and in principle this can be done in a single step. We push toward internally diffraction-limited performance with the Oxford-SWIFT integral field spectrograph coupled with the PALM-3000 extreme AO system on the Palomar 200-inch telescope. This represents the first observation in which the PALM3000 + SWIFT internal point-spread-function has closely approached the Airy pattern. While this can only be used on SWIFT with an internal stimulus source, as at short wavelengths the uncorrected atmospheric wavefront errors are still < 1 radian, this nevertheless demonstrates the feasibility of detecting non-common-path errors with this method as an active optics paradigm for near-infrared, AO-corrected instruments on Palomar such as PHARO or Project 1640 (P1640), or other instruments such as VLT-SPHERE or the Gemini Planet Imager (GPI). We note that this is a particularly promising approach for correcting integral field spectrographs, as the diversity of many narrowband images provides strong constraints on the wavefront error estimate, and the average of reconstructions from many narrow bands can be used to improve overall reconstruction quality.
Interest in pupil-remapping interferometry, in which a single telescope pupil is fragmented and recombined using
fiber optic technologies, has been growing among a number of groups. As a logical extrapolation from several
highly successful aperture masking programs underway worldwide, pupil remapping offers the advantage of spatial
filtering (with single-mode fibers) and in principle can avoid the penalty of low throughput inherent to an aperture
mask. However in practice, pupil remapping presents a number of difficult technological challenges including
injection into the fibers, pathlength matching of the device, and stability and reproducibility of the results.
Here we present new approaches based on recently-available photonic technologies in which coherent threedimensional
waveguide structures can be sculpted into bulk substrate. These advances allow us to miniaturize
the photonic processing into a single, robust, thermally stable element; ideal for demanding observatory or
spacecraft environments. Ultimately, a wide range of optical functionality could be routinely fabricated into
such structures, including beam combiners and dispersive or wavelength selective elements, bringing us closer to
the vision of an interferometer on a chip.
We present the first integrated multimode photonic spectrograph, a device we call PIMMS #1. The device comprises
a set of multimode fibres that convert to single-mode propagation using a matching set of photonic lanterns. These
feed to a stack of cyclic array waveguides (AWGs) that illuminate a common detector. Such a device greatly reduces
the size of an astronomical instrument at a fixed spectroscopic resolution. Remarkably, the PIMMS concept is
largely independent of the telescope diameter, input focal ratio and entrance aperture - i.e. one size fits all! The
instrument architecture can also exploit recent advances in astrophotonics (e.g. OH suppression fibres). We present a
movie of the instrument's operation and discuss the advantages and disadvantages of this approach.