arXiv subjects

S. Ertel

Publications and source records attributed to S. Ertel.

At least 19 recordsLinked to original sources

arXiv2026

Asgard/NOTT: Status of laboratory nulling performance

Nulling interferometry enables the direct detection of faint companions and circumstellar structures at angular separations unresolvable by classical, diffraction-limited imagers, whilst dramatically improving the measurable contrast. The Asgard/NOTT nulling instrument aims to achieve a contrast performance of 10^-5 in the L' wavelength band (3.5 - 4.0 {\mu}m), enabling observation and characterization of young giant exoplanets near the snowline and hot exozodiacal dust. Previous studies have verified the nulling capabilities, of the chip in ambient conditions and of the test bench in cryogenic conditions. This work aims to add the first ambient performance assessment of the test bench with spectrally dispersed light. Necessary revisions are made to the data acquisition and calibration pipeline and fringe scans are carried out, modeled and fitted. The splitting ratios of the 4-telescope nulling beam combiner, a photonic Gallium Lanthanum Sulfide (GLS) chip, are moreover characterized on the bench, showing tentative agreement with previous chip characterization. The null performance has worsened, the achieved contrast of ~ 10^-1 being one order of magnitude higher than what earlier characterized performance showed. Multiple future changes to the test bed and to the approach taken promise an improved characterization of performance. In particular, the input beam intensities will be deliberately mismatched to account for the imbalanced splitting ratios of the directional couplers. With the installation of the final cryostat and camera, the developed tools will be leveraged to re-assess the performance in ambient and cryogenic conditions.

astro-ph.IM↗

arXiv2026

Performance Analysis of the Asgard/NOTT Nulling Interferometer: Optimizing Observing Modes for High-contrast Detection

We evaluate the performance of three beam-combination schemes, single-Bracewell, asymmetric dual-Bracewell, and symmetric dual-Bracewell, for the forthcoming Asgard/NOTT nulling interferometer at the Very Large Telescope Interferometer. Utilizing the SCIFYsim end-to-end simulator, we assess the instrument's performance by deriving the precision of calibrated null measurements as a function of stellar magnitude and simulating observations of varying hot exozodiacal dust (HEZD) distributions and a hot Jupiter. The study reveals distinct trade-offs for each observing mode. The single-Bracewell mode provides high throughput and preserves spatial information but suffers from poor error suppression. The asymmetric dual-Bracewell mode offers the strongest error suppression for detecting point-like sources, but it inherently suppresses symmetric astrophysical signals such as expected from HEZD. The symmetric dual-Bracewell mode provides a middle ground with modest error suppression while being sensitive to symmetric emission. We conclude that utilizing a combination of all three observing modes provides a robust strategy for detecting HEZD, constraining the structure of its distribution, and identifying false positives from stellar companions.

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arXiv2026

Spectrally dispersed non-redundant aperture-masking interferometry in the thermal infrared with LBTI/ALES

Non-redundant aperture-masking interferometry maximizes the angular resolution of a telescope by turning it into an interferometric array using pupil plane masks. If the interference pattern on the detector is spectrally dispersed, deeper contrasts of the astrophysical scenery and an improved coverage of its spatial Fourier modes is achieved. We combined a non-redundant aperture mask with the integral field spectrograph ALES of LMIRcam at the Large Binocular Telescope Interferometer (LBTI). With this setup, we recorded spectrally dispersed non-redundant aperture-masking observations in the $L$ band ($\sim$3-4$\,\mu$m). We present commissioning data with which we recovered a known binary star and derived contrast detection limits for further point-source components of ${\sim} 5 \times 10^{-3}$ for separations of ${\gtrsim} 80\,$mas. This is the first time that an integral field spectrograph was combined with a non-redundant aperture mask in the $L$ band. Opening up the thermal infrared for this technique, this new capability enables the LBTI to efficiently survey nearby, bright stars for faint companions, which is of great importance for studies on hot exozodiacal dust and target vetting for future exo-Earth imaging missions such as NASA's Habitable Worlds Observatory. A further application is aperture synthesis of extended sources such as active galactic nuclei or evolved stars.

astro-ph.IM↗

arXiv2026

Asgard/NOTT: Cryogenic characterization of the mid-infrared chip

NOTT is part of the new visitor instrument suite Asgard for the Very Large Telescope Interferometer (VLTI), and the first long-baseline nulling interferometer that will be operational in the southern hemisphere. It is an L'-band (3.5-4$\,\mu$m) instrument optimized for imaging hot exozodiacal dust and young giant planets orbiting around the snowline of nearby main-sequence stars. For planet imaging, the L' band has the advantage of relaxing the requirements on the star-planet contrast to $\sim 10^{-5}$ while limiting the level of background noise compared with longer wavelengths. Nulling interferometry in the L'-band was made possible by the development of mid-infrared integrated optics with high throughput. NOTT uses a photonic beam combiner made of Gallium Lanthanum Sulfide (GLS), manufactured at Macquarie University and characterized at ambient temperatures at Universit\"at zu K\"oln. This first characterization showed that the chip could achieve the broadband contrast requirement for exoplanet imaging. Using the test bench of the NOTT instrument assembled at KU Leuven, and its test cryostat, we successfully cooled the chip down to $\sim 138\,$K and performed its first characterization at cryogenic temperatures. The results show a raw broadband contrast of $\sim1\,\%$, similar to the previous measurements done at ambient temperatures. The splitting ratios of the different couplers are also shown to remain stable at cryogenic temperatures, with less than $\sim 2\,\%$ uncertainty compared to ambient measurements. These results thus show that the beam-combining properties and splitting ratios are behaving as expected at 138$\,$K. The current maximum throughput of the chip is estimated at $\sim37\,\%$. Future work will investigate an anti-reflection coating to reduce its Fresnel losses and increase its throughput to $\sim50\,\%$.

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arXiv2026

Follow-up of three exocomet-host candidates

Exocomets are small bodies that evaporate when they approach their host star. They are detected through variability of non-photospheric features with spectroscopy and/or asymmetric transits in time-series photometry. In the past four decades ~30 systems have shown such variations, and were therefore classified as exocomet host stars. However, some publications have pointed out mechanisms that might mimic exocometary features, and therefore, careful monitoring is needed to confirm the origin of the observed variability. With this paper we aim to investigate the exocomet nature of the non-photospheric variable features observed in the exocomet candidate stars HD 36546, HD 42111 and HD 85905. All of them have shown some degree of variability, particularly in their Ca II K line. We analysed the non-photospheric Ca II K line features from high-resolution spectra obtained using new NOT/FIES and Mercator/HERMES, and some additional archival spectra of the target stars. The variability was quantified through the changes in the equivalent widths of those features, which are assumed to be of circumstellar origin. Column densities were also estimated for each variable feature. Strong variability was found for HD 85905, consistent with a potential link to exocometary activity. However, the binarity of the system, which we confirmed through interferometric VLTI/PIONIER observations, complicates the interpretation of these signatures and prevents us from drawing definitive conclusions. The remaining two sources do not show any significant variability, but due to the sporadic nature of the exocometary events, we cannot discard the exocomet hypothesis. Further monitoring of the stars will be necessary to carry out a robust determination of the variability patterns and timescales that would completely rule out other scenarios.

astro-ph.SR↗

arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) V: Comparison between scattered light and thermal emission

Debris discs are analogues to our own Kuiper belt around main-sequence stars and are therefore referred to as exoKuiper belts. They have been resolved at high angular resolution at wavelengths spanning the optical to the submillimetre-millimetre regime. Short wavelengths probe the light scattered by such discs, which is dominated by micron-sized dust particles, while millimetre wavelengths probe the thermal emission of millimetre-sized particles. Determining differences in the dust distribution between millimetre- and micron-sized dust is fundamental to revealing the dynamical processes affecting the dust in debris discs. We aim to compare the scattered light from the discs of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS) with the thermal emission probed by ALMA. We focus on the radial distribution of the dust. We used high-contrast scattered light observations obtained with VLT/SPHERE, GPI, and the HST to uniformly study the dust distribution in those systems and compare it to the dust distribution extracted from the ALMA observations carried out in the course of the ARKS project. We also set constraints on the presence of planets by using these high-contrast images combined with exoplanet evolutionary models. 15 of the 24 discs comprising the ARKS sample are detected in scattered light, with TYC9340-437-1 being imaged for the first time at near-infrared wavelengths. For 6 of those 15 discs, the dust surface density seen in scattered light peaks farther out compared to that observed with ALMA. These 6 discs except one are known to also host cold CO gas. Conversely, the systems without significant offsets are not known to host gas, except one. This observational study suggests that the presence of gas in debris discs may affect the small and large grains differently, pushing the small dust to greater distances where the gas is less abundant.

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arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) I: Motivation, sample, data reduction, and results overview

The outer regions of planetary systems host dusty debris discs analogous to the Kuiper belt (exoKuiper belts), which provide crucial constraints on planet formation and evolution processes. ALMA dust observations have revealed a great diversity, and that some belts contain CO gas, whose origin and implications are uncertain. Most of this progress, however, has been limited by low-resolution observations. We conducted the first ALMA large programme dedicated to debris discs: the ALMA survey to Resolve exoKuiper belt Substructures (ARKS). We selected the 24 most promising belts to constrain their detailed radial and vertical structure, and to characterise the gas content. We constrained the radial and vertical distribution of dust, as well as the presence of asymmetries. For a subset of six belts with CO gas, we constrained the gas distribution and kinematics. To interpret these observations, we used a wide range of dynamical models. The first ARKS results are presented as a series of ten papers. We discovered that up to 33% of our sample exhibits multiple dusty rings. For highly inclined belts, we found that non-Gaussian vertical distributions are common and are indicative of multiple dynamical populations. We also found that 10 of the 24 belts present asymmetries. We find that the CO gas is radially broader than the dust, but this could be an effect of optical depth. At least one system shows non-Keplerian kinematics due to strong pressure gradients, which may have triggered a vortex that trapped dust in an arc. Finally, we find evidence that the micron-sized grains may be affected by gas drag in gas rich systems. ARKS has revealed a great diversity of structures in exoKuiper belts that may arise when they are formed in protoplanetary discs or subsequently via interactions with planets and/or gas. We encourage the community to explore the reduced data and data products.

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arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): VI. Asymmetries and offsets

Asymmetries in debris discs provide unique clues to understand the evolution and architecture of planetary systems.** The aim of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is to expand our understanding of radial and vertical dust structures, as well as gas distributions and kinematics, in debris discs.** Here, in ARKS~VI, we present a systematic analysis of the asymmetries and stellocentric offsets present in the ALMA continuum data for the ARKS survey. Our aims are to identify asymmetries in debris disc dust distributions, quantify debris disc asymmetry properties, and discuss the potential origins of debris disc asymmetries.** We utilised empirical methods to identify emission asymmetries** and the presence of offset emission between disc centres and the locations of the host stars, via an analysis of their calibration procedures and disc properties. We associated observational asymmetry types** and plausible physical classes** associated with each source. We show that there are ten systems, almost half of the ARKS sample, that host either a continuum emission asymmetry or offset emission. Three systems host offsets (HD15115, HD32297, and HD109573 (HR4796)), four host azimuthal asymmetries (HD9672 (49Ceti), HD92945, HD107146, and HD121617), two host an asymmetry in their major axis (HD10647 (q$^1$ Eri), and HD39060 ($\beta$ Pic)), and one hosts an asymmetry in their minor axis (HD61005). We attribute the offset asymmetries to non-zero eccentricities, and three of the azimuthal asymmetries to arcs. The presence of an asymmetry or offset in the ARKS sample appears to be correlated with the fractional luminosity of cold dust.** Conclusions: This study demonstrates that debris disc asymmetries in the ARKS sample are common, and plausibly so in the wider population of debris discs at (sub)-millimetre wavelengths.** ** = ABRIDGED FOR ARXIV: FULL ABSTRACT IN PAPER

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arXiv2025

Interferometric Detection and Orbit Modeling of the Subcomponent in the Hot-dust System $\kappa$ Tuc A: A Low-mass Star on an Eccentric Orbit in a Hierarchical-quintuple System

The system $\kappa$ Tuc A is part of a hierarchical-quintuple system and is a prime target for studies of hot-exozodiacal dust, because a time-variable near-infrared excess has been detected. We observed the system with the Multi Aperture mid-Infrared Spectroscopic Experiment (MATISSE) and GRAVITY at the Very Large Telescope Interferometer, and detected the stellar companion to the primary $\kappa$ Tuc Aa that was previously inferred by astrometry, $\kappa$ Tuc Ab. Its $L$-band flux ratio to the primary is 1.32% and its signature in the MATISSE closure phases is mostly smaller than +/- 2{\deg}, which makes $\kappa$ Tuc Ab the highest-contrast companion ever detected with MATISSE closure phases. We verified with GRAVITY that relative astrometry with milliarcsecond precision can be retrieved from MATISSE closure phases. Using multiple epochs of observations, we obtain a full orbital solution for $\kappa$ Tuc Ab. Its orbit has an eccentricity of 0.94 and a semi-major axis of 4.8au. The orbit of $\kappa$ Tuc Ab and the orbit of the wider separation companion $\kappa$ Tuc B are mutually inclined. Based on the measured flux ratio of $\kappa$ Tuc Ab to Aa and their dynamical mass, we estimate the spectral type of $\kappa$ Tuc Ab to be M3.5V to M4.5V. While the then unknown star $\kappa$ Tuc Ab might have caused the putative detection of hot-exozodiacal dust around $\kappa$ Tuc Aa in 2012 and 2014, this cannot be for the detection in 2019, giving rise to an intriguing system architecture. This motivates studies investigating the interplay of the low-mass star on an eccentric orbit, the hot-exozodiacal dust, and a possible planetesimal reservoir.

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arXiv2025

The HOSTS Survey: Suspected variable dust emission and constraints on companions around {\theta} Boo

During the HOSTS survey by the LBTI, an excess emission from the main sequence star {\theta} Boo (F7V spectral type, 14.5pc distance) was observed. This excess indicates the presence of exozodiacal dust near the habitable zone (HZ) of the star. Previous observations from Spitzer and Herschel showed no sign of outer cold dust within their respective detection limits. Additional nulling and high-contrast AO observations were taken to spatially constrain the dust distribution, search for variability, and directly image potential companions in the system. This study presents the results of these observations and provides an interpretation of the inner system's architecture. The star was observed using the LBTI's N'-band nulling mode during three epochs in 2017, 2018, and 2023. The dust distribution is modeled and constrained for each epoch using the standard LBTI nulling pipeline, assuming a vertically thin disk with a face-on inclination. In addition, high-contrast AO observations are performed in the L'-band and H-band to constrain the presence of substellar companions around the star. Several solutions are found for the dust distribution, and for each epoch. However, the LBTI nulling observations are not able to discriminate between them. Using the upper limits from previous observations, we constrain the representative size of the dust grains around 3-5$\mu$m. A tentative increase in dust brightness is also measured at the Earth-equivalent insolation distance between 2017 and 2023. Several options are considered to explain the origin of the observed dust and its variability, but no clear sources could be identified from the current observations. Partly because our high-contrast AO observations could only constrain the presence of companions down to $11M_\text{Jup}$ at 1.3" separation.

astro-ph.EP↗

arXiv2025

REsolved ALMA and SMA Observations of Nearby Stars (REASONS): A population of 74 resolved planetesimal belts at millimetre wavelengths

Planetesimal belts are ubiquitous around nearby stars, and their spatial properties hold crucial information for planetesimal and planet formation models. We present resolved dust observations of 74 planetary systems as part of the REsolved ALMA and SMA Observations of Nearby Stars (REASONS) survey and archival reanalysis. We uniformly modelled interferometric visibilities for the entire sample to obtain the basic spatial properties of each belt, and combined these with constraints from multi-wavelength photometry. We report key findings from a first exploration of this legacy dataset: (1) Belt dust masses are depleted over time in a radially dependent way, with dust being depleted faster in smaller belts, as predicted by collisional evolution. (2) Most belts are broad discs rather than narrow rings, with much broader fractional widths than rings in protoplanetary discs. We link broad belts to either unresolved substructure or broad planetesimal discs produced if protoplanetary rings migrate. (3) The vertical aspect ratios (h = H/R) of 24 belts indicate orbital inclinations of 1-20 degrees, implying relative particle velocities of 0.1-4 km/s, and no clear evolution of heights with system age. This could be explained by early stirring within the belt by large bodies (with sizes of at least 140 km to the size of the Moon), by inheritance of inclinations from the protoplanetary disc stage, or by a diversity in evolutionary pathways and gravitational stirring mechanisms. We release the REASONS legacy multidimensional sample of millimetre-resolved belts to the community as a valuable tool for follow-up multi-wavelength observations and population modelling studies.

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arXiv2024

A multi-technique detection of an eccentric giant planet around accelerating star HD 57625

The synergy between different detection methods is a key asset in exoplanetology, allowing for both precise characterization of detected exoplanets and robust constraints even in the case of non-detection. Recently, the interplay between imaging, radial velocities and astrometry has produced significant advancements in exoplanetary science. We report a first result of an ongoing survey performed with SHARK-NIR, the new high-contrast near-infrared imaging camera at the Large Binocular Telescope, in parallel with LBTI/LMIRCam in order to detect planetary companions around stars with significant proper motion anomaly. In this work we focus on HD 57625, a F8 star for which we determine a $4.8^{+3.7}_{-2.9}$Ga age, exhibiting significant astrometric acceleration and for which archival radial velocities hint at the presence of a previously undetected massive long-period companion. We analyse the imaging data we collected with SHARK-NIR and LMIRCam in synergy with the available public SOPHIE radial velocity time series and Hipparcos-Gaia proper motion anomaly. With this joint multi-technique analysis, we aim at characterizing the companion responsible for the astrometric and radial velocity signals. The imaging observations result in a non-detection, indicating the companion to be in the substellar regime. This is confirmed by the synergic analysis of archival radial velocity and astrometric measurements resulting in the detection of HD 57625 b, a ${8.43}_{-0.91}^{+1.10}$M$_{\rm Jup}$ planetary companion with an orbital separation of ${5.70}_{-0.13}^{+0.14}$au and ${0.52}_{-0.03}^{+0.04}$ eccentricity. HD 57625 b joins the small but growing population of giant planets in outer orbits with true mass determination provided by the synergic usage of multiple detection methods, proving once again the importance of multi-technique analysis in providing robust characterization of planetary companions.

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arXiv2024

Deep imaging of three accelerating stars using SHARK-NIR and LMIRCam at LBT

The combination of detection techniques enhances our ability to identify companions orbiting nearby stars. We employed high-contrast imaging to constrain mass and separation of possible companions responsible for the significant proper motion anomalies of the nearby stars HIP 11696, HIP 47110 and HIP 36277. These targets were observed using the LBT's high-contrast camera, SHARK-NIR, in H-band using a Gaussian coronagraph, and with the LMIRCam instrument in the L'-band and using a vAPP coronagraph. Both observations were conducted simultaneously. Additionally, constraints at short separations from the host star are derived analyzing the renormalized unit weight error (RUWE) values from the Gaia catalogue. We find that the companion responsible for the anomaly signal of HIP 11696 is likely positioned at a distance from 2.5 to 28 astronomical units from its host. Its mass is estimated to be between 4 and 16 Jupiter masses, with the greater mass possible only at the upper end of the separation range. Similar limits were obtained for HIP 47110 where the companion should reside between 3 and 30 au with a mass between 3 and 10 MJup. For HIP 36277, we identified a faint stellar companion at large separation, though it might be substellar depending on the assumed age for the star. Considering the older age, this object accounts for the absolute value of the PMa vector but not for its direction. Additionally, we found a substellar candidate companion at a closer separation that could explain the PMa signal, considering a younger age for the system.

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arXiv2023

How much large dust could be present in hot exozodiacal dust systems?

An infrared excess over the stellar photospheric emission of main-sequence stars has been found in interferometric surveys, commonly attributed to the presence of hot exozodiacal dust (HEZD). While submicrometer-sized grains in close vicinity to their host star have been inferred to be responsible for the found near-infrared excesses, the presence and amount of larger grains as part of the dust distributions are weakly constrained. We quantify how many larger grains (above-micrometer-sized) could be present in addition to submicrometer-sized grains, while being consistent with observational constraints. This is important in order to distinguish between various scenarios for the origin of HEZD and to better estimate its observational appearance when observed with future instruments. We extended a model suitable to reproduce current observations of HEZD to investigate a bimodal size distribution. By deriving the characteristics of dust distributions whose observables are consistent with observational limits from interferometric measurements in the $K$ and $N$ bands we constrained the radii of sub- and above-micrometer-sized grains as well as their mass, number, and flux density ratios. In the most extreme cases of some of the investigated systems, large grains $\gtrsim 10\,\mu$m might dominate the mass budget of HEZD while contributing up to 25$\,$% of the total flux density originating from the dust at a wavelength of 2.13$\,\mu$m and up to 50$\,$% at a wavelength of 4.1$\,\mu$m; at a wavelength of 11.1$\,\mu$m their emission might clearly dominate over the emission of small grains. While it is not possible to detect such hot-dust distributions using ALMA, the ngVLA might allow us to detect HEZD at millimeter wavelengths. Large dust grains might have a more important impact on the observational appearance of HEZD than previously assumed, especially at longer wavelengths.

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arXiv2022

The SHARDDS survey: limits on planet occurrence rates based on point sources analysis via the Auto-RSM framework

In the past decade, HCI surveys provided new insights about the frequency and properties of substellar companions at separation larger than 5 au. In this context, our study aims to detect and characterise potential exoplanets and brown dwarfs within debris disks, by considering the SHARDDS survey, which gathers 55 Main Sequence stars with known bright debris disk. We rely on the AutoRSM framework to perform an in-depth analysis of the targets, via the computation of detection maps and contrast curves. A clustering approach is used to divide the set of targets in multiple subsets, in order to reduce the computation time by estimating a single optimal parametrisation for each considered subset. The use of Auto-RSM allows to reach high contrast at short separations, with a median contrast of 10-5 at 300 mas, for a completeness level of 95%. Detection maps generated with different approaches are used along with contrast curves, to identify potential planetary companions. A new planetary characterisation algorithm, based on the RSM framework, is developed and tested successfully, showing a higher astrometric and photometric precision for faint sources compared to standard approaches. Apart from the already known companion of HD206893 and two point-like sources around HD114082 which are most likely background stars, we did not detect any new companion around other stars. A correlation study between achievable contrasts and parameters characterising HCI sequences highlights the importance of the strehl, wind speed and wind driven halo to define the quality of high contrast images. Finally, planet detection and occurrence frequency maps are generated and show, for the SHARDDS survey, a high detection rate between 10 and 100 au for substellar companions with mass >10MJ.

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arXiv2021

Signs of late infall and possible planet formation around DR Tau using VLT/SPHERE and LBTI/LMIRCam

Context. Protoplanetary disks around young stars often contain substructures like rings, gaps, and spirals that could be caused by interactions between the disk and forming planets. Aims. We aim to study the young (1-3 Myr) star DR Tau in the near-infrared and characterize its disk, which was previously resolved through sub-millimeter interferometry with ALMA, and to search for possible sub-stellar companions embedded into it. Methods. We observed DR Tau with VLT/SPHERE both in polarized light (H broad band) and total intensity (in Y, J, H, and K spectral bands). We also performed L' band observations with LBTI/LMIRCam on the Large Binocular Telescope (LBT). Results. We found two previously undetected spirals extending north-east and south of the star, respectively. We further detected an arc-like structure north of the star. Finally a bright, compact and elongated structure was detected at separation of 303 +/- 10 mas and position angle 21.2 +/- 3.7 degrees, just at the root of the north-east spiral arm. Since this feature is visible both in polarized light and in total intensity and has a flat spectrum it is likely caused by stellar light scattered by dust. Conclusions. The two spiral arms are at different separation from the star, have very different pitch angles, and are separated by an apparent discontinuity, suggesting they might have a different origin. The very open southern spiral arm might be caused by infalling material from late encounters with cloudlets into the formation environment of the star itself. The compact feature could be caused by interaction with a planet in formation still embedded in its dust envelope and it could be responsible for launching the north-east spiral. We estimate a mass of the putative embedded object of the order of few M_Jup .

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arXiv2021

A near-infrared interferometric survey of debris-disk stars. VII. The hot/warm dust connection

(abridged) Context. The origin of hot exozodiacal dust and its connection with outer dust reservoirs remains unclear. Aims. We aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (> 100 K) in asteroid belts. Methods. We use precision near-infrared interferometry with VLTI/PIONIER to search for resolved emission at H band around a selected sample of nearby stars. Results. Our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars, four of which are shown to be due to a previously unknown stellar companion. The 13 other H-band excesses are thought to originate from the thermal emission of hot dust grains. Taking into account earlier PIONIER observations, and after reevaluating the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17.1(+8.1)(-4.6)% for H-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14.6(+4.3)(-2.8)% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we however find tentative evidence at the 3{\sigma} level that H-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than H-band excesses around stars with no detectable outer dust. Conclusions. Our observations do not suggest a direct connection between warm and hot dust populations, at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of H-band excesses and the presence of outer dust reservoirs in general.

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arXiv2021

The HOSTS survey: evidence for an extended dust disk and constraints on the presence of giant planets in the Habitable Zone of $\beta$ Leo

The young (50-400 Myr) A3V star $\beta$ Leo is a primary target to study the formation history and evolution of extrasolar planetary systems as one of the few stars with known hot ($\sim$1600$^\circ$K), warm ($\sim$600$^\circ$K), and cold ($\sim$120$^\circ$K) dust belt components. In this paper, we present deep mid-infrared measurements of the warm dust brightness obtained with the Large Binocular Telescope Interferometer (LBTI) as part of its exozodiacal dust survey (HOSTS). The measured excess is 0.47\%$\pm$0.050\% within the central 1.5 au, rising to 0.81\%$\pm$0.026\% within 4.5 au, outside the habitable zone of $\beta$~Leo. This dust level is 50 $\pm$ 10 times greater than in the solar system's zodiacal cloud. Poynting-Robertson drag on the cold dust detected by Spitzer and Herschel under-predicts the dust present in the habitable zone of $\beta$~Leo, suggesting an additional delivery mechanism (e.g.,~comets) or an additional belt at $\sim$5.5 au. A model of these dust components is provided which implies the absence of planets more than a few Saturn masses between $\sim$5 au and the outer belt at $\sim$40 au. We also observationally constrain giant planets with the LBTI imaging channel at 3.8~$\mu$m wavelength. Assuming an age of 50 Myr, any planet in the system between approximately 5 au to 50 au must be less than a few Jupiter masses, consistent with our dust model. Taken together, these observations showcase the deep contrasts and detection capabilities attainable by the LBTI for both warm exozodiacal dust and giant exoplanets in or near the habitable zone of nearby stars.

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