Combining Fourier plane observables for high-contrast imaging of young giant exoplanets

The vast majority of the ~4000 exoplanets known of today have only been detected through indirect techniques, providing a limited amount of information on their physical properties and dynamical environment. On the other hand, direct techniques can provide astrometric, photometric, and spectroscopic information required to study the formation and evolution of exoplanets. However, such direct observations are challenging due to the high contrast between an exoplanet and its parent star, as well as their small apparent separation. Interferometric techniques at infrared wavelengths are able to overcome the limitation in terms of angular resolution, but are still limited in contrast at small angular separations. A further increase in contrast is necessary to make the bulk of young giant exoplanets, orbiting their parent star at Solar System scales, accessible to interferometry in general. Here, we focus on improving our understanding of and mitigating the systematic errors which limit the sensitivity of interferometric observations. With the kernel phase technique, we survey nearby and young stars for sub-stellar companions. We develop a data reduction pipeline capable of reconstructing saturated PSFs, centering them with sub-pixel accuracy and extracting their Fourier plane observables including correlations. These correlations are then used, together with a calibration strategy based on principal component analysis, to improve the sensitivity to faint companions. In archival VLT/NACO data, we detect eight low-mass stellar companions, five of which were previously unknown, and two have angular separations of ~0.8-1.2 lambda/D (i.e., ~80-110 mas). Furthermore, we achieve typical 5-sigma contrast limits of ~6 mag at separations of 0.2 arcsec and ~8 mag at separations of 0.5 arcsec for a Keck/NIRC2 survey of 55 single class I and class II stars in Taurus. These results clearly demonstrate that the kernel phase technique is now capable of detecting young giant exoplanets in the nearest star-forming regions. We further utilize this technique to obtain mid-infrared photometry of the famous T Tauri triple system, including its southern binary T Tau Sa/Sb at an apparent separation of only ~0.2 lambda/D. Our observations reveal a recent decrease in the mid-infrared brightness of T Tau Sb of ~2 mag. We suspect that it has moved along its orbit behind the southern circumbinary disk and now suffers from increased dust extinction. With the demonstration of the improved contrast and the unprecedented angular resolution in the mid-infrared, the kernel phase technique is a promising method for exoplanet imaging with the James Webb Space Telescope and the Extremely Large Telescopes. We finally extend our study to long-baseline interferometry by extracting the correlations present in VLTI/GRAVITY data. The GRAVITY instrument has recently been used to spectroscopically characterize exoplanets in the near-infrared. We develop an analytical model to describe the correlations and show that the faint source detection limits of GRAVITY improve by a factor of ~2 when accounting for them in the model fitting process. Exoplanet science with GRAVITY is still in its infancy and our technical improvements will help to increase its scientific return. Moreover, future instruments such as GRAVITY+, SCIFY, or LIFE will greatly benefit from a complete treatment of the systematic errors

PQL - A Descriptive Language for Querying, Abstracting and Changing Process Models

The increasing adoption of process-aware information systems (PAISs) has resulted in large process repositories comprising large and complex process models. To enable context-specific perspectives on these process models and related data, a PAIS should provide techniques for the flexible creation and change of process model abstractions. However, existing approaches focus on the formal model transformations required in this context rather than on techniques for querying, abstracting and changing the process models in process repositories. This paper presents a domain-specific language for querying process models, describing abstractions on them, and defining process model changes in a generic way. Due to the generic approach taken, the definition of process model abstractions and changes on any graph-based process notation becomes possible. Overall, the presented language provides a key component for process model repositories

Updatable Process Views for User-centered Adaption of Large Process Models

The increasing adoption of process-aware information systems (PAISs) has resulted in large process model collections. To support users having different perspectives on these processes and related data, a PAIS should provide personalized views on process models. Existing PAISs, however, do not provide mechanisms for creating or even changing such process views. Especially, changing process models is a frequent use case in PAISs due to changing needs or unplanned situations. While process views have been used as abstractions for visualizing large process models, no work exists on how to change process models based on respective views. This paper presents an approach for changing large process models through updates of corresponding process views, while ensuring up-to-dateness and consistency of all other process views on the process model changed. Respective update operations can be applied to a process view and corresponding changes be correctly propagated to the underlying process model. Furthermore, all other views related to this process model are then migrated to the new version of the process model as well. Overall, our view framework enables domain experts to evolve large process models over time based on appropriate model abstractions

Collaborative Process Modeling with Tablets and Touch Tables — A Controlled Experiment

Collaborative process modeling involves business analysts and subject matter experts in order to properly capture and document process knowledge. In this context, appropriate tool support is required to motivate these user groups to actively participate in collaborative process modeling. This paper presents a collaborative process modeling tool that enables the experts to create, visualize and evolve process models based on multi-touch devices (e.g., tablets and touch tables). In particular, users may edit process models on their tablets and share the created or changed process models with other team members on a common touch table. For this purpose, a sophisticated and intuitive interaction concept is provided. Furthermore, results of a controlled experiment, evaluating the influence the use of tablets has on collaborative process modeling based on touch tables, are presented. Altogether the experimental results emphasize the high potential of multi-touch tools for collaborative process modeling

User-centric Process Modeling and Enactment: The Clavii BPM Platform

The increasing adoption of process-aware information sys- tems (PAISs) has resulted in large process model collections involving different process participants. We present the Clavii BPM platform, which enables end users to participate not only in process model execution, but model creation as well. Clavii offers a modern user interface with a strong focus on ease of use, unifying different aspects of the BPM lifecycle in one tool, i.e., process model editor and process engine. As a result, end users are supported in managing and executing process models

Simulating reflected light coronagraphy of Earth-like exoplanets with a large IR/O/UV space telescope: impact and calibration of smooth exozodiacal dust

Observing Earth-like exoplanets orbiting within the habitable zone of Sun-like stars and studying their atmospheres in reflected starlight requires contrasts of $\sim1\mathrm{e}{-10}$ in the visible. At such high contrast, starlight reflected by exozodiacal dust is expected to be a significant source of contamination. Here, we present high-fidelity simulations of coronagraphic observations of a synthetic Solar System located at a distance of 10 pc and observed with a 12 m and an 8 m circumscribed aperture diameter space telescope operating at 500 nm wavelength. We explore different techniques to subtract the exozodi and stellar speckles from the simulated images in the face-on, the 30 deg inclined, and the 60 deg inclined case and quantify the remaining systematic noise as a function of the exozodiacal dust level of the system. We find that in the face-on case, the exozodi can be subtracted down to the photon noise limit for exozodi levels up to $\sim1000$ zodi using a simple toy model for the exozodiacal disk, whereas in the 60 deg inclined case this only works up to $\sim50$ zodi. We also investigate the impact of larger wavefront errors and larger system distance, finding that while the former have no significant impact, the latter has a strong (negative) impact. Ultimately, we derive a penalty factor as a function of the exozodi level and system inclination that should be considered in exoplanet yield studies as a realistic estimate for the excess systematic noise from the exozodi.Comment: 20 pages, 9 figures, accepted for publication in A

Mitigating Worst-Case Exozodiacal Dust Structure in High-contrast Images of Earth-like Exoplanets

Detecting Earth-like exoplanets in direct images of nearby Sun-like systems brings a unique set of challenges that must be addressed in the early phases of designing a space-based direct imaging mission. In particular, these systems may contain exozodiacal dust, which is expected to be the dominant source of astrophysical noise. Previous work has shown that it may be feasible to subtract smooth, symmetric dust from observations; however, we do not expect exozodiacal dust to be perfectly smooth. Exozodiacal dust can be trapped into mean motion resonances with planetary bodies, producing large-scale structures that orbit in lock with the planet. This dust can obscure the planet, complicate noise estimation, or be mistaken for a planetary body. Our ability to subtract these structures from high-contrast images of Earth-like exoplanets is not well understood. In this work, we investigate exozodi mitigation for Earth--Sun-like systems with significant mean motion resonant disk structures. We find that applying a simple high-pass filter allows us to remove structured exozodi to the Poisson noise limit for systems with inclinations $< 60^\circ$ and up to 100 zodis. However, subtracting exozodiacal disk structures from edge-on systems may be challenging, except for cases with densities $<5$ zodis. For systems with three times the dust of the Solar System, which is the median of the best fit to survey data in the habitable zones of nearby Sun-like stars, this method shows promising results for mitigating exozodiacal dust in future HWO observations, even if the dust exhibits significant mean-motion resonance structure.Comment: Accepted to AJ. 18 pages, 10 figure

Performance study of interferometric small-sats to detect exoplanets:Updated exoplanet yield and application to nearby exoplanets

Nulling interferometry is considered as one of the most promising solutions to spectrally characterize rocky exoplanets in the habitable zone of nearby stars. It provides both high angular resolution and starlight mitigation. It requires however several technologies that need to be demonstrated before a large interferometry space-based mission flies. A small-sat mission is a good technological precursor. Based on a Bracewell architecture, this unique satellite can demonstrate some key components (null capability, fiber injection, achromatic phase shifter). Scientific capabilities of such a mission are presented. An exoplanet detection yield is derived, and we show that the detection of exoplanets around nearby stars is feasible

GRAVITY K-band spectroscopy of HD 206893 B

Context. Near-infrared interferometry has become a powerful tool for studying the orbital and atmospheric parameters of substellar companions. Aims. We aim to reveal the nature of the reddest known substellar companion HD 206893 B by studying its near-infrared colors and spectral morphology and by investigating its orbital motion. Methods. We fit atmospheric models for giant planets and brown dwarfs and perform spectral retrievals with petitRADTRANS and ATMO on the observed GRAVITY, SPHERE, and GPI spectra of HD 206893 B. To recover its unusual spectral features, first and foremost its extremely red near-infrared color, we include additional extinction by high-altitude dust clouds made of enstatite grains in the atmospheric model fits. However, forsterite, corundum, and iron grains predict similar extinction curves for the grain sizes considered here.We also infer the orbital parameters of HD 206893 B by combining the  100 μas precision astrometry from GRAVITY with data from the literature and constrain the mass and position of HD 206893 C based on the Gaia proper motion anomaly of the system. Results. The extremely red color and the very shallow 1:4 μm water absorption feature of HD 206893 B can be fit well with the adapted atmospheric models and spectral retrievals. By comparison with AMES-Cond evolutionary tracks, we find that only some atmospheric models predict physically plausible objects. Altogether, our analysis suggests an age of  3–300 Myr and a mass of  5–30 MJup for HD 206893 B, which is consistent with previous estimates but extends the parameter space to younger and lower-mass objects. The GRAVITY astrometry points to an eccentric orbit (e = 0:29+0:06 0:11) with a mutual inclination of \u3c34:4 deg with respect to the debris disk of the system. Conclusions. While HD 206893 B could in principle be a planetary-mass companion, this possibility hinges on the unknown influence of the inner companion on the mass estimate of 10+5 4 MJup from radial velocity and Gaia as well as a relatively small but significant Argus moving group membership probability of  61%. However, we find that if the mass of HD 206893 B is \u3c30 MJup, then the inner companion HD 206893 C should have a mass between  8–15 MJup. Finally, further spectroscopic or photometric observations at higher signal-to-noise and longer wavelengths are required to learn more about the composition and dust cloud properties of HD 206893 B