Schedule and Talk Abstracts

To understand how image form, for both classical imaging and interferometry, I created a few jupyter notebooks to get acquainted to the notions of image formation. It includes a tool to analyze any type of pupils and another to create an object and see how it translates in terms of image, interferogram, squared visibility and closure phase. A last step is to add different types of noise (atmospheric turbulence, adaptive optics residuals or any other instrumental aberration) and see how it affects the observables.

This talk will give a brief overview for sparse aperture interferometry: where it came from, what is happening today, and where it is going.

In gather town!

The main hindrance to directly imaging exoplanets comes from optical aberrations that produce speckles that can be difficult to distinguish from real planets. Kernel phase, a generalization of closure phase, uses a linear approximation to diffraction to separate out a linear subspace that is immune to these aberrations (kernel phases). The technology underlying deep learning - automatic differentiation or 'autodiff' - allows us to take derivatives by the chain rule of arbitrary numerical simulations, for example finding the kernel phase transfer matrix as the Jacobian of Fourier visibilities with respect to the phase of incoming light. We demonstrate how this can be used for kernel phase, as well as for phase retrieval and optical design in highly nonlinear regimes. By rewriting the popular optical simulation package 'poppy' using the autodiff library Jax, we present 'morphine', a powerful new open source tool for optics and data analysis.

In gather town!

AMICAL is developed to provide an easy-to-use solution to process Aperture Masking Interferometry (AMI) data from major existing facilities: NIRISS on the JWST, SPHERE and VISIR from the European Very Large Telescope (VLT) and VAMPIRES from SUBARU telescope. We focused our efforts to propose a user-friendly interface, though different sub-classes allowing to (1) Clean the reduced datacube from the standard instrument pipelines, (2) Extract the interferometrical quantities using a Fourier sampling approach and (3) Calibrate those quantities to remove the instrumental biases. In addition (4), we include two external packages called CANDID and Pymask to analyse the final outputs obtained from a binary-like sources. In this talk, I propose to go through these different features and retrieve a good overview of its possibilities.

In gather town!

Planets form around young stars within extended disks of gas and dust called protoplanetary disks, some of which are revealed to contain large gaps in their dust distribution through mm continuum and scattered light imaging. These gaps are believed to be caused by the action of embedded planets sculpting the disk material, however, only within the PDS 70 disk have planets been robustly confirmed through direct imaging. This lack of detection is due in part to the difficulty of separating a faint planet from the surrounding disk emission, which has led to several spurious detection claims (e.g. LkCa 15). Aperture Masking Interferometry (AMI) is an extremely successful technique for detecting faint binary companions with clear applicability to planet detection studies. Forthcoming GTO JWST observations of three disks using the AMI mode of NIRISS will provide a high sensitivity to embedded protoplanets, provided possibly contaminating disk emission can be adequately modelled. We will discuss our recent progress in robustly distinguishing between disk emission and young planets using machine learning and geometrical modelling based methods. These methods were applied to VLT/SPHERE AMI data of LkCa 15 to observe the inner disk and search for point sources in the field of view. By subtracting the best fit multi-ring model from the data, the brightest point-like residual observed in the field of view was at a separation of 98 milliarcseconds and had a contrast of 1500, a factor of 6 fainter than what was found when naively performing binary fitting, ignoring the bright disk. Though this is not a robust detection, it demonstrates that this technique can be used to significantly improve the contrast limit for observing point-like objects when a bright disk is present.

In Fourier plane imaging, faint companions are most commonly identified using model fitting techniques. Due to the sparse uv-coverage and model redundancies, detection maps often show periodic signals and ghosts from higher-order phase noise. In this talk, I will present a companion search tool which can account for correlated errors and fit data from all aperture masking, kernel-phase, and long-baseline interferometry observations. Moreover, I will show our efforts to extract correlations from NACO/NIRC2 kernel-phase and GRAVITY long-baseline interferometry observations as well as a principal-component based calibration approach for larger libraries of kernel-phase data.

In gather town!

Holographic aperture masking (HAM) aims at (i) increasing the throughput of SAM by selectively combining all subapertures across a telescope pupil in multiple interferograms using a phase mask, and (ii) adding low-resolution spectroscopic capabilities. In this talk I present the design, construction, and commissioning of a prototype holographic aperture mask at the Keck OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS) Imager. This diffractive liquid-crystal phase mask consists of an 11-hole SAM design as the central component and a holographic component comprising 19 different subapertures that creates additional off-axis interferograms. The holographic component yields 26 closure phases with spectral resolutions between R ~ 6.5 and R ~ 15, depending on the interferogram positions. I will summarize the observations of the binary star HDS 1507 in the Hbb filter (λ0 = 1638 nm and ∆λ = 330 nm), where we retrieved a constant separation of 120.9±0.5 mas for the independent wavelength bins. Lastly, I will discuss current the limitations of HAM and future upgrades.

In gather town!

After its scheduled launch in October later this year, the James Webb Space Telescope (JWST) will transform our ability to characterise directly imaged exoplanets. As a part of our Director’s Discretionary-Early Release Science program (JWST DD-ERS Program 1386), we will obtain coronagraphic images for the exoplanet HIP 65426 b into the mid infrared. In addition to imaging and spectroscopy, the program will also test JWST’s Near Infrared Imager and Slitless Spectrograph’s (NIRISS) Aperture Masking Interferometry (AMI) mode with the HIP 65426 b observations. This mode will enable imaging of any additional planetary mass companions in nearby systems within the instrument’s diffraction limit for the first time with a space telescope. Initial results from simulations relying on Beta Pictoris and TW Hydrae moving groups indicate that for some targets in young moving groups, companions at close in separations (less than 10 AU from the star) with masses less than 10 times that of Jupiter can be imaged using AMI with a confidence of >80%. A series of such successful detections of companions in this parameter space with potential future surveys using JWST NIRISS would be a testament to the abundance of exoplanets being formed with core accretion, the same method with which the planets of our Solar system were formed. These potential discoveries will hence convey that Solar System analogues are not uncommon and inform our understanding of the conditions that may be suitable for habitability on exoplanets.

A time slot that will hopefully be reasonable for folks on US/Eastern, US/Pacific, and CET time for general discussion!

In gather town!

Direct detection of close-in companions is notoriously difficult: coronagraphs and point spread function (PSF) subtraction techniques are significantly limited in separation and contrast. Non-redundant aperture masking interferometry (NRM or AMI) can be used to detect companions well inside the PSF of a diffraction limited image, though the technique is severely flux-limited since the mask discards ~95% of the gathered light. Kernel-phase analysis applies similar interferometric techniques to an unobscured diffraction limited image, allowing archival studies of high resolution imaging surveys. I have developed a new faint companion detection pipeline which analyzes kernel-phases, and demonstrate the use of this pipeline on a large sample of archival HST/NICMOS images of nearby brown dwarfs. I refine astrometry of previously known companions and search for new companions, in order to constrain formation models at au scales. I will present contrast curves to demonstrate the strength of this technique at separations inaccessible to classical imaging techniques. Using this method, it will be possible to detect companions down to flux ratios of ~10^2—reaching the planetary-mass regime for young targets—at half the classical lambda/D diffraction limit while using a fraction of the telescope time as NRM.

In gather town!

Polarimetric differential imaging (PDI) is an amazing tool to image scattered-light structures such as protoplanetary disks and stellar mass-loss nebula, but in its conventional form it is limited to wide spatial scales. Aperture masking is great at ultra-high resolution imaging, but good calibration is key. Combine the two and you have differential polarimetric aperture masking, which tackles both these challenges! Here I’ll explain how, in this technique, you calibrate the visibilities of one polarisation against another for the same star, rather than between two stars. By using a set of fast polarisation modulation techniques this means these observations are self-calibrated, with no need for a PSF calibrator star. I’ll show some nice results where mass-loss shells 10s of milliarcseconds in diameter are clearly resolved around AGB stars. Finally I’ll talk about the current instruments available to you all that can do this mode, including our team’s VAMPIRES instrument, installed at the Subaru telescope, which is specially designed for this technique.

A time slot that will hopefully be reasonable for folks on US/Pacific and AEST time for general discussion!

In gather town!

During this talk, I will briefly describe a python data reduction software which I have been developing during the last year to analyze Sparse Aperture Masking (SAM) data. The general idea of developing this tool is to provide a flexible code to the community for the data reduction of SAM, which can be adapted to different instruments such as the JWST, SPHERE, VISIR. etc. I will describe the principles of fringe fitting directly to the interferograms in the image plane and how can we obtain the interferometric observables from this. I will also show a few examples of the use of this code on real and simulated data.

Abstract coming soon