We demonstrate the use of existing observations from the CASSINI spacecraft to be used for studies of stellar targets. The stellar lightcurve produced as hard edges within the rings pass across the field of view produces a stellar occultation not unlike lunar occultations. These events are observed with an on-board spectrograph, providing coverage of the near infrared from 1 to 5 microns. Here we demonstrate how the technique can be used to make spatially resolved measurements of stellar structure and test these measurements against independently published angular sizes. We also show how this technique can be extended into mapping of complex circum stellar structure and identify molecular layers in the atmosphere of Omicron Ceti, an evolved star. Finally we demonstrate how several events can be combined tomographically to reconstruct high resolution images of stellar targets.
VAMPIRES is a high-angular resolution imager developed to directly image planet-forming circumstellar disks, and the signatures of forming planets that lie within. The instrument leverages aperture masking interferometry - providing diffraction-limited imaging despite seeing - in combination with fast-switching differential polarimetry to directly image structure in the inner-most regions of protoplanetary systems. VAMPIRES will use starlight scattered by dust in such systems to precisely map the disk, gaps, knots and waves that are key to understanding disk evolution and planet formation. It also promises to image the dusty circumstellar environments of AGB stars. This instrument perfectly compliments coronagraphic observations in the near-IR, and can operate simultaneously with a coronagraph, as part of the SCExAO extreme-AO system at the Subaru telescope. In this paper the design of the instrument will be presented, along with an explanation of the unique data analysis process and the results of the first on-sky tests.
Here we demonstrate a new generation of photonic pupil-remapping devices which build upon the interferometric framework developed for the <i>Dragonfly</i> instrument: a high contrast waveguide-based device which recovers robust complex visibility observables. New generation Dragonfly devices overcome problems caused by interference from unguided light and low throughput, promising unprecedented on-sky performance. Closure phase measurement scatter of only ~0.2° has been achieved, with waveguide throughputs of > 70%. This translates to a maximum contrast-ratio sensitivity (between the host star and its orbiting planet) at 1λ /D (1σ detection) of 5.3×10<sup>−4</sup> (when a conventional adaptive-optics (AO) system is used) or 1.8×10<sup>−4</sup> (for typical ‘extreme-AO’ performance), improving even further when random error is minimised by averaging over multiple exposures. This is an order of magnitude beyond conventional pupil-segmenting interferometry techniques (such as aperture masking), allowing a previously inaccessible part of the star to planet contrast-separation parameter space to be explored.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is one of a handful of extreme adaptive
optics systems set to come online in 2014. The extreme adaptive optics correction is realized by a combination of precise
wavefront sensing via a non-modulated pyramid wavefront sensor and a 2000 element deformable mirror. This system
has recently begun on-sky commissioning and was operated in closed loop for several minutes at a time with a loop
speed of 800 Hz, on ~150 modes. Further suppression of quasi-static speckles is possible via a process called "speckle
nulling" which can create a dark hole in a portion of the frame allowing for an enhancement in contrast, and has been
successfully tested on-sky.
In addition to the wavefront correction there are a suite of coronagraphs on board to null out the host star which include
the phase induced amplitude apodization (PIAA), the vector vortex, 8 octant phase mask, 4 quadrant phase mask and
shaped pupil versions which operate in the NIR (y-K bands). The PIAA and vector vortex will allow for high contrast
imaging down to an angular separation of 1 λ/D to be reached; a factor of 3 closer in than other extreme AO systems.
Making use of the left over visible light not used by the wavefront sensor is VAMPIRES and FIRST. These modules are
based on aperture masking interferometry and allow for sub-diffraction limited imaging with moderate contrasts of
~100-1000:1. Both modules have undergone initial testing on-sky and are set to be fully commissioned by the end of
High contrast imaging techniques such as aperture masking interferometry allow for the detection of faint companions
such as substellar companions by utilizing light from the planet itself. This allows access to study a larger population of
planetary companions as compared to the transit technique where only systems viewed edge on can be studied, for
example. However, aperture masking has several shortcomings including, low throughputs, limited Fourier coverage,
and leakage of residual atmospheric noise due to phase corrugations across each sub-apertures. These limitations can be
overcome by remapping the pupil with single-mode waveguides. We present an integrated pupil remapping
interferometer, known as Dragonfly, that aims to do just that. We discuss the progress we have made over the past year
in developing a stable and robust instrument and elucidate challenges and the innovative solutions that were applied.
Finally we discuss improvements to the instrument that will enable future scientific endeavors and outline the expected
Aperture-masking interferometry allows diffraction-limited images to be recovered despite the turbulent atmo sphere. Here, this approach has been combined with polarimetry to form a novel technique allowing the dusty environments of mass-losing stars (so-called AGB stars) and proto-planetary and debris disks to be imaged, the characterisation of which is key to understanding the recycling of matter and the formation of new planetary systems. Polarimetric aperture-masking interferometry produces images by exploiting the fact that starlight scattered by circumstellar dust becomes strongly polarised. Essentially, aperture-masking allows access to the small spatial scales (rv1Omas) necessary while polarimetry allows light from the dust and star to be differentiated. Furthermore, measurements at multiple wavelengths allow dust grain sizes to be calculated using Mie scattering theory. Excellent results have already been obtained at near-IR wavelengths using the NACO instrument at the VLT. The next step is to leverage the higher spatial resolution and polarisation signal found in the visible, rather than near-IR. To this end, a new instrument allowing precision polarimetric aperture masking interferometry at
600-800nm is being developed for an 8m class telescope, details of which will also be presented.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is an instrument designed to be inserted
between the Subaru AO188 system and the infrared HiCIAO camera in order to greatly improve the contrast in
the very close (less than 0.5") neighbourhood of stars.Next to the infrared coronagraphic path, a visible scientific
path, based on a EMCCD camera, has been implemented. Benefiting from both AO correction and new data
processing techniques, it is a powerful tool for high angular resolution imaging and opens numerous new science
opportunities. A factor 2 to 3 in Strehl ratio is obtained compared to the AO long exposure time: up to 25% Strehl
in the 650nm wavelength, depending on the image processing algorithm used and the seeing conditions. The
system is able to deliver diffraction limited images at 650 nm (17 mas FWHM). Our baseline image processing
algorithm is based on the selection of the best signal for each spatial frequency. We demonstrate that this
approach offers significantly better results than the classical select, shift and add approach (lucky imaging).
In 2009 our group started the integration of the SCExAO project, a highly flexible, open platform for high
contrast imaging at the highest angular resolution, inserted between the coronagraphic imaging camera HiCIAO
and the 188-actuator AO system of Subaru. In its first version, SCExAO combines a MEMS-based wavefront
control system feeding a high performance PIAA-based coronagraph. It also includes a coronagraphic low-order
wavefront sensor, a non-redundant aperture mask and a visible imaging mode, all of them designed to take full
advantage of the angular resolution that an 8-meter telescope has to offer. SCExAO is currently undergoing
commissioning, and this paper presents the first on-sky results acquired in August 2011, using together Subaru's
AO system, SCExAO and HiCIAO.
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.
The new operational mode of aperture masking interferometry has been added to the CONICA camera which
lies downstream of the Adaptive Optics (AO) corrected focus provided by NAOS on the VLT-UT4 telescope.
Masking has been shown to deliver superior PSF calibration, rejection of atmospheric noise and robust recovery
of phase information through the use of closure phases. Over the resolution range from about half to several
resolution elements, masking interferometry is presently unsurpassed in delivering high fidelity imaging and
direct detection of faint companions. Here we present results from commissioning data using this powerful new
operational mode, and discuss the utility for masking in a variety of scientific contexts. Of particular interest is
the combination of the CONICA polarimetry capabilities together with SAM mode operation, which has revealed
structures never seen before in the immediate circumstellar environments of dusty evolved stars.