arXiv subjects

M. R. Meyer

Publications and source records attributed to M. R. Meyer.

At least 19 recordsLinked to original sources

arXiv2024

Giant planets population around B stars from the first part of the BEAST survey

Exoplanets form from circumstellar protoplanetary discs whose fundamental properties (notably their extent, composition, mass, temperature and lifetime) depend on the host star properties, such as their mass and luminosity. B-stars are among the most massive stars and their protoplanetary discs test extreme conditions for exoplanet formation. This paper investigates the frequency of giant planet companions around young B-stars (median age of 16 Myr) in the Scorpius-Centaurus association, the closest association containing a large population of B-stars. We systematically search for massive exoplanets with the high-contrast direct imaging instrument SPHERE using the data from the BEAST survey, that targets an homogeneous sample of young B-stars from the wide Sco-Cen association. We derive accurate detection limits in case of non-detections. We found evidence in previous papers for two substellar companions around 42 stars. The masses of these companions are straddling the ~13 Jupiter mass deuterium burning limit but their mass ratio with respect to their host star is close to that of Jupiter. We derive a frequency of such massive planetary mass companions around B stars of 11-5+7%, accounting for the survey sensitivity. The discoveries of substellar companions bcen b and mu2sco B happened after only few stars in the survey had been observed, raising the possibility that massive Jovian planets might be common around B-stars. However our statistical analysis show that the occurrence rate of such planets is similar around B-stars and around solar-type stars of similar age, while B-star companions exhibit low mass ratios and larger semi-major axis.

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arXiv2024

Large Interferometer For Exoplanets (LIFE): XIII. The Value of Combining Thermal Emission and Reflected Light for the Characterization of Earth Twins

Following the recommendations to NASA and ESA, the search for life on exoplanets will be a priority in the next decades. Two direct imaging space mission concepts are being developed: the Habitable Worlds Observatory (HWO) and the Large Interferometer for Exoplanets (LIFE). HWO focuses on reflected light spectra in the ultraviolet/visible/near-infrared (UV/VIS/NIR), while LIFE captures the mid-infrared (MIR) emission of temperate exoplanets. We assess the potential of HWO and LIFE in characterizing a cloud-free Earth twin orbiting a Sun-like star at 10 pc, both separately and synergistically, aiming to quantify the increase in information from joint atmospheric retrievals on a habitable planet. We perform Bayesian retrievals on simulated data from an HWO-like and a LIFE-like mission separately, then jointly, considering the baseline spectral resolutions currently assumed for these concepts and using two increasingly complex noise simulations. HWO would constrain H$_2$O, O$_2$, and O$_3$, in the atmosphere, with ~ 100 K uncertainty on the temperature profile. LIFE would constrain CO$_2$, H$_2$O, O$_3$ and provide constraints on the thermal atmospheric structure and surface temperature (~ 10 K uncertainty). Both missions would provide an upper limit on CH$_4$. Joint retrievals on HWO and LIFE data would accurately define the atmospheric thermal profile and planetary parameters, decisively constrain CO$_2$, H$_2$O, O$_2$, and O$_3$, and weakly constrain CO and CH$_4$. The detection significance is greater or equal to single-instrument retrievals. Both missions provide specific information to characterize a terrestrial habitable exoplanet, but the scientific yield is maximized with synergistic UV/VIS/NIR+MIR observations. Using HWO and LIFE together will provide stronger constraints on biosignatures and life indicators, potentially transforming the search for life in the universe.

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arXiv2024

SPHERE RefPlanets: Search for epsilon Eridani b and warm dust

We carried out very deep VLT/SPHERE imaging polarimetry of the nearby system Eps Eri based on 38.5 hours of integration time with a 600 - 900 nm broadband filter to search for polarized scattered light from a planet or from circumstellar dust using AO, coronagraphy, high precision differential polarimetry, and angular differential imaging. We have improved several data reduction and post-processing techniques and also developed new ones to further increase the sensitivity of SPHERE/ZIMPOL. The data provide unprecedented contrast limits, but no significant detection of a point source or an extended signal from circumstellar dust. For each observing epoch, we obtained a point source contrast for the polarized intensity between $2\cdot 10^{-8}$ and $4\cdot 10^{-8}$ at the expected separation of the planet Eps Eri b of 1'' near quadrature phase. The polarimetric contrast limits are about six to 50 times better than the intensity limits because polarimetric imaging is much more efficient in speckle suppression. Combining the entire 14-month data set to the search for a planet moving on a Keplerian orbit with the K-Stacker software further improves the contrast limits by a factor of about two, to about $8 \cdot 10^{-9}$ at 1''. This would allow the detection of a planet with a radius of about 2.5 Jupiter radii. The surface brightness contrast limits achieved for the polarized intensity from an extended scattering region are about 15 mag arcsec$^{-2}$ at 1'', or up to 3 mag arcsec$^{-2}$ deeper than previous limits. For Eps Eri, these limits exclude the presence of a narrow dust ring and they constrain the dust properties. This study shows that the polarimetric contrast limits for reflecting planets with SPHERE/ZIMPOL can be improved to a level $<10^{-8}$ simply by collecting more data over many nights and using the K-Stacker software.

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arXiv2024

The SPHERE view of the Taurus star-forming region

The sample of planet-forming disks observed by high-contrast imaging campaigns over the last decade is mature enough to enable the demographical analysis of individual star-forming regions. We present the full census of Taurus sources with VLT/SPHERE polarimetric images available. The whole sample sums up to 43 targets (of which 31 have not been previously published) corresponding to one-fifth of the Class II population in Taurus and about half of such objects that are observable. A large fraction of the sample is apparently made up of isolated faint disks (equally divided between small and large self-shadowed disks). Ambient signal is visible in about one-third of the sample. This probes the interaction with the environment and with companions or the outflow activity of the system. The central portion of the Taurus region almost exclusively hosts faint disks, while the periphery also hosts bright disks interacting with their surroundings. The few bright disks are found around apparently older stars. The overall picture is that the Taurus region is in an early evolutionary stage of planet formation. Yet, some objects are discussed individually, as in an intermediate or exceptional stage of the disk evolution. This census provides a first benchmark for the comparison of the disk populations in different star forming regions.

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arXiv2023

An imaged 15Mjup companion within a hierarchical quadruple system

Since 2019, the direct imaging B-star Exoplanet Abundance Study (BEAST) at SPHERE@VLT has been scanning the surroundings of young B-type stars in order to ascertain the ultimate frontiers of giant planet formation. Recently, the $17^{+3}_{-4}$ Myr HIP 81208 was found to host a close-in (~50 au) brown dwarf and a wider (~230 au) late M star around the central 2.6Msun primary. Alongside the continuation of the survey, we are undertaking a complete reanalysis of archival data aimed at improving detection performances so as to uncover additional low-mass companions. We present here a new reduction of the observations of HIP 81208 using PACO ASDI, a recent and powerful algorithm dedicated to processing high-contrast imaging datasets, as well as more classical algorithms and a dedicated PSF-subtraction approach. The combination of different techniques allowed for a reliable extraction of astrometric and photometric parameters. A previously undetected source was recovered at a short separation from the C component of the system. Proper motion analysis provided robust evidence for the gravitational bond of the object to HIP 81208 C. Orbiting C at a distance of ~20 au, this 15Mjup brown dwarf becomes the fourth object of the hierarchical HIP 81208 system. Among the several BEAST stars which are being found to host substellar companions, HIP 81208 stands out as a particularly striking system. As the first stellar binary system with substellar companions around each component ever found by direct imaging, it yields exquisite opportunities for thorough formation and dynamical follow-up studies.

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arXiv2023

The high-albedo, low polarization disk around HD 114082 harbouring a Jupiter-sized transiting planet

We present new optical and near-IR images of debris disk around the F-type star HD 114082. We obtained direct imaging observations and analysed the TESS photometric time series data of this target with a goal to search for planetary companions and to characterise the morphology of the debris disk and the scattering properties of dust particles. HD 114082 was observed with the VLT/SPHERE instrument: the IRDIS camera in the K band together with the IFS in the Y, J and H band using the ADI technique as well as IRDIS in the H band and ZIMPOL in the I_PRIME band using the PDI technique. The scattered light images were fitted with a 3D model for single scattering in an optically thin dust disk. We performed aperture photometry in order to derive the scattering and polarized phase functions, polarization fraction and spectral scattering albedo for the dust particles in the disk. This method was also used to obtain the reflectance spectrum of the disk to retrieve the disk color and study the dust reflectivity in comparison to the debris disk HD 117214. We also performed the modeling of the HD 114082 light curve measured by TESS using the models for planet transit and stellar activity to put constraints on radius of the detected planet and its orbit. The debris disk appears as an axisymmetric debris belt with a radius of ~0.37$"$ (35 au), inclination of ~83$^\circ$ and a wide inner cavity. Dust particles in HD 114082 have a maximum polarization fraction of ~17% and a high reflectivity which results in a spectral scattering albedo of 0.65. The analysis of TESS photometric data reveals a transiting planetary companion to HD 114082 with a radius of $\sim$1~$\rm R_{J}$ on an orbit with a semi-major axis of $0.7 \pm 0.4$ au. Combining different data, we reach deep sensitivity limits in terms of companion masses down to ~5$M_{\rm Jup}$ at 50 au, and ~10 $M_{\rm Jup}$ at 30 au from the central star.

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arXiv2022

MIRAC-5: A ground-based mid-IR instrumentwith the potential to detect ammonia in gas giants

We present the fifth incarnation of the Mid-Infrared Array Camera (MIRAC-5) instrument which will use a new GeoSnap (3 - 13 microns) detector. Advances in adaptive optics (AO) systems and detectors are enabling ground-based mid-infrared systems capable of high spatial resolution and deep contrast. As one of the only 3 - 13 micron cameras used in tandem with AO, MIRAC-5 will be complementary to the James Webb Space Telescope (JWST) and capable of characterizing gas giant exoplanets and imaging forming protoplanets (helping to characterize their circumplanetary disks). We describe key features of the MIRAC-5 GeoSnap detector, a long-wave Mercury-Cadmium-Telluride (MCT) array produced by Teledyne Imaging Sensors (TIS), including its high quantum efficiency (> 65%), large well-depth, and low noise. We summarize MIRAC-5's important capabilities, including prospects for obtaining the first continuum mid-infrared measurements for several gas giants and the first 10.2-10.8 micron NH3 detection in the atmosphere of the warm companion GJ 504b (Teff ~550 K) within 8 hours of observing time. Finally, we describe plans for future upgrades to MIRAC-5 such as adding a coronagraph. MIRAC-5 will be commissioned on the MMT utilizing the new MAPS AO system in late 2022 with plans to move to Magellan with the MagAO system in the future.

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arXiv2022

A scaled-up planetary system around a supernova progenitor

Virtually all known exoplanets reside around stars with $M<2.3~M_\odot$; to clarify if the dearth of planets around more massive stars is real, we launched the direct-imaging B-star Exoplanet Abundance STudy (BEAST) survey targeting B stars ($M>2.4~M_\odot$) in the young (5-20 Myr) Scorpius-Centaurus association (Sco-Cen). Here we present the case of a massive ($M \sim 9~M_\odot$) BEAST target, $μ^2$ Sco. Based on kinematic information, we found that $μ^2$ Sco is a member of a small group which we label Eastern Lower Scorpius, refining in turn the precision on stellar parameters. Around this star we identified a robustly detected substellar companion ($14.4\pm 0.8 M_J$) at a projected separation of $290\pm 10$ au, and a probable second object ($18.5\pm 1.5 M_J$) at $21\pm 1$ au. The planet-to-star mass ratios of these objects are similar to that of Jupiter to the Sun, and their irradiation is similar to those of Jupiter and Mercury, respectively. The two companions of $μ^2$ Sco are naturally added to the giant planet b Cen b recently discovered by BEAST; although slightly more massive than the deuterium burning limit, their properties resemble those of giant planets around less massive stars and they are better reproduced by a formation under a planet-like, rather than a star-like scenario. Irrespective of the (needed) confirmation of the inner companion, $μ^2$ Sco is the first star that would end its life as a supernova that hosts such a system. The tentative high frequency of BEAST discoveries shows that giant planets or small-mass brown dwarfs can form around B stars. When putting this finding in the context of core accretion and gravitational instability, we conclude that the current modeling of both mechanisms is not able to produce this kind of companion. BEAST will pave the way for the first time to an extension of these models to intermediate and massive stars. (abridged)

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arXiv2022

Large Interferometer For Exoplanets (LIFE): I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission

One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale. We seek to quantify the exoplanet detection performance of a space-based mid-infrared nulling interferometer that measures the thermal emission of exoplanets. For this, we have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect over a certain time period. Two different scenarios to distribute the observing time among the stellar targets are discussed and different apertures sizes and wavelength ranges are considered. Within a 2.5-year initial search phase, an interferometer consisting of four 2 m apertures with a total instrument throughput of 5% covering a wavelength range between 4 and 18.5 $μ$m could detect up to ~550 exoplanets with radii between 0.5 and 6 R$_\oplus$ with an integrated SNR$\ge$7. At least ~160 of the detected exoplanets have radii $\le$1.5 R$_\oplus$. Depending on the observing scenario, ~25-45 rocky exoplanets (objects with radii between 0.5 and 1.5 $_{\oplus}$) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With an aperture size of 3.5 m, the total number of detections can increase to up to ~770, including ~60-80 rocky, eHZ planets. With 1 m aperture size, the maximum detection yield is ~315 exoplanets, including $\le$20 rocky, eHZ planets. In terms of predicted detection yield, such a mission can compete with large single-aperture reflected light missions. (abridged)

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arXiv2021

High-precision astrometric studies in direct imaging with SPHERE

Orbital monitoring of exoplanetary and stellar systems is fundamental for analysing their architecture, dynamical stability and evolution, and mechanisms of formation. Current high-contrast extreme-adaptive optics imagers like SPHERE, GPI, and SCExAO+CHARIS explore the population of giant exoplanets and brown dwarf and stellar companions beyond typically 10 au, covering generally a small fraction of the orbit (<20%) leading to degeneracies and biases in the orbital parameters. Precise and robust measurements over time of the position of the companions are critical, which require good knowledge of the instrumental limitations and dedicated observing strategies. The homogeneous dedicated calibration strategy for astrometry implemented for SPHERE has facilitated high-precision studies by its users since its start of operation in 2014. As the precision of exoplanet imaging instruments is now reaching milliarcseconds and is expected to improve with the upcoming facilities, we initiated a community effort, triggered by the SPHERE experience, to share lessons learned for high-precision astrometry in direct imaging. A homogeneous strategy would strongly benefit the VLT community, in synergy with VLTI instruments like GRAVITY/GRAVITY+, future instruments like ERIS and MAVIS, and in preparation for the exploitation of the ELT's first instruments MICADO, HARMONI, and METIS.

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arXiv2021

First light of the VLT planet finder SPHERE. III. New spectrophotometry and astrometry of the HR8799 exoplanetary system

The planetary system discovered around the young A-type HR8799 provides a unique laboratory to: a) test planet formation theories, b) probe the diversity of system architectures at these separations, and c) perform comparative (exo)planetology. We present and exploit new near-infrared images and integral-field spectra of the four gas giants surrounding HR8799 obtained with SPHERE, the new planet finder instrument at the Very Large Telescope, during the commissioning and science verification phase of the instrument (July-December 2014). With these new data, we contribute to completing the spectral energy distribution of these bodies in the 1.0-2.5 $μ$m range. We also provide new astrometric data, in particular for planet e, to further constrain the orbits. We used the infrared dual-band imager and spectrograph (IRDIS) subsystem to obtain pupil-stabilized, dual-band $H2H3$ (1.593 $μ$m, 1.667 $μ$m), $K1K2$ (2.110 $μ$m, 2.251 $μ$m), and broadband $J$ (1.245 $μ$m) images of the four planets. IRDIS was operated in parallel with the integral field spectrograph (IFS) of SPHERE to collect low-resolution ($R\sim30$), near-infrared (0.94-1.64 $μ$m) spectra of the two innermost planets HR8799d and e. The data were reduced with dedicated algorithms, such as the Karhunen-Loève image projection (KLIP), to reveal the planets. We used the so-called negative planets injection technique to extract their photometry, spectra, and measure their positions. We illustrate the astrometric performance of SPHERE through sample orbital fits compatible with SPHERE and literature data.

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arXiv2020

The Michigan Infrared Test Thermal ELT N-band (MITTEN) Cryostat

We introduce the Michigan Infrared Test Thermal ELT N-band (MITTEN) Cryostat, a new facility for testing infrared detectors with a focus on mid-infrared (MIR) wavelengths (8-13 microns). New generations of large format, deep well, fast readout MIR detectors are now becoming available to the astronomical community. As one example, Teledyne Imaging Sensors (TIS) has introduced a long-wave Mercury-Cadmium-Telluride (MCT) array, GeoSnap, with high quantum efficiency (> 65 %) and improved noise properties compared to previous generation Si:As blocked impurity band (BIB) detectors. GeoSnap promises improved sensitivities, and efficiencies, for future background-limited MIR instruments, in particular with future extremely large telescopes (ELTs). We describe our new test facility suitable for measuring characteristics of these detectors, such as read noise, dark current, linearity, gain, pixel operability, quantum efficiency, and point source imaging performance relative to a background scene, as well as multiple point sources of differing contrast. MITTEN has an internal light source, and soon an accompanying filter wheel and aperture plate, reimaged onto the detector using an Offner relay. The baseline temperature of the cryostat interior is maintained < 40 K and the optical bench maintains a temperature of 16 K using a two-stage pulse-tube cryocooler package from Cryomech. No measurable background radiation from the cryostat interior has yet been detected.

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arXiv2020

Orbital and spectral characterization of the benchmark T-type brown dwarf HD 19467B

Context. Detecting and characterizing substellar companions for which the luminosity, mass, and age can be determined independently is of utter importance to test and calibrate the evolutionary models due to uncertainties in their formation mechanisms. HD 19467 is a bright and nearby star hosting a cool brown dwarf companion detected with RV and imaging, making it a valuable object for such studies. Aims. We aim to further characterize the orbital, spectral, and physical properties of the HD 19467 system. Methods. We present new high-contrast imaging data with the SPHERE and NaCo instruments. We also analyze archival data from HARPS, NaCo, HIRES, UVES, and ASAS. We also use proper motion data of the star from Hipparcos and Gaia. Results. We refine the properties of the host star and derive an age of 8.0$^{+2.0}_{-1.0}$ Gyr based on isochrones, gyrochronology, and chemical and kinematic arguments. This estimate is slightly younger than previous estimates of ~9-11 Gyr. No orbital curvature is seen in the current imaging, RV, and astrometric data. From a joint fit of the data, we refine the orbital parameters for HD 19467B: period 398$^{+95}_{-93}$ yr, inclination 129.8$^{+8.1}_{-5.1}$ deg, eccentricity 0.56$\pm$0.09, longitude of the ascending node 134.8$\pm$4.5 deg, and argument of the periastron 64.2$^{+5.5}_{-6.3}$ deg. We assess a dynamical mass of 74$^{+12}_{-9}$ MJ. The fit with atmospheric models of the spectrophotometric data of HD 19467B indicates an atmosphere without clouds or with very thin clouds, an effective temperature of 1042$^{+77}_{-71}$ K, and a large surface gravity of 5.34$^{+0.08}_{-0.09}$ dex. The comparison to model predictions of the bolometric luminosity and dynamical mass of HD 19467B, assuming our system age estimate, indicates a better agreement with the Burrows et al. models; whereas the other evolutionary models used tend to underestimate its cooling rate.

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arXiv2020

HD 117214 debris disk: scattered-light images and constraints on the presence of planets

We performed observations of the Sco-Cen F star HD 117214 aiming at a search for planetary companions and the characterization of the debris disk structure. HD 117214 was observed with the SPHERE subsystems IRDIS, IFS and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with a spatial resolution reaching 25 mas and an inner working angle $< 0.1''$. With the observations with IRDIS and IFS we derive detection limits for substellar companions. The geometrical parameters of the detected disk are constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet-disk and planet-planet dynamical interactions. The obtained planetary architectures are compared with the detection limit curves. The debris disk has an axisymmetric ring structure with a radius of $0.42(\pm 0.01)''$ or $\sim45$ au and an inclination of $71(\pm 2.5)^\circ$ and exhibits a $0.4''$ ($\sim40$ au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of $(F_{\rm pol})_{\rm disk}/F_{\rm \ast}> (3.1 \pm 1.2)\cdot 10^{-4}$ in the RI band. The fractional scattered polarized flux of the disk is eight times smaller than the fractional infrared flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977 indicating that dust radiation properties are not very different between these two disks. Inside the disk cavity we achieve the high sensitivity limits on planetary companions with a mass down to $\sim 4 M_{\rm J}$ at projected radial separations between $0.2''$ and $0.4''$. We can exclude the stellar companions at a radial separation larger than 75 mas from the star.

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arXiv2019

RefPlanets: Search for reflected light from extra-solar planets with SPHERE/ZIMPOL

RefPlanets is a guaranteed time observation (GTO) programme that uses the Zurich IMaging POLarimeter (ZIMPOL) of SPHERE/VLT for a blind search for exoplanets in wavelengths from 600-900 nm. The goals of this study are the characterization of the unprecedented high polarimetic contrast and polarimetric precision capabilities of ZIMPOL for bright targets, the search for polarized reflected light around some of the closest bright stars to the Sun and potentially the direct detection of an evolved cold exoplanet for the first time. For our observations of Alpha Cen A and B, Sirius A, Altair, Eps Eri and Tau Ceti we used the polarimetric differential imaging (PDI) mode of ZIMPOL which removes the speckle noise down to the photon noise limit for angular separations >0.6". We describe some of the instrumental effects that dominate the noise for smaller separations and explain how to remove these additional noise effects in post-processing. We then combine PDI with angular differential imaging (ADI) as a final layer of post-processing to further improve the contrast limits of our data at these separations. For good observing conditions we achieve polarimetric contrast limits of 15.0-16.3 mag at the effective inner working angle of about 0.13", 16.3-18.3 mag at 0.5" and 18.8-20.4 mag at 1.5". The contrast limits closer in (<0.6") depend significantly on the observing conditions, while in the photon noise dominated regime (>0.6"), the limits mainly depend on the brightness of the star and the total integration time. We compare our results with contrast limits from other surveys and review the exoplanet detection limits obtained with different detection methods. For all our targets we achieve unprecedented contrast limits. Despite the high polarimetric contrasts we are not able to find any additional companions or extended polarized light sources in the data that has been taken so far.

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arXiv2019

Hint of curvature in the orbital motion of the exoplanet 51 Eridani b using 3 years of VLT/SPHERE monitoring

Context. The 51 Eridani system harbors a complex architecture with its primary star forming a hierarchical system with the binary GJ 3305AB at a projected separation of 2000 au, a giant planet orbiting the primary star at 13 au, and a low-mass debris disk around the primary star with possibly a cold component and a warm component inferred from the spectral energy distribution. Aims. We aim to better constrain the orbital parameters of the known giant planet. Methods. We monitored the system over three years from 2015 to 2018 with the VLT/SPHERE exoplanet imaging instrument. Results. We measure an orbital motion for the planet of ~130 mas with a slightly decreasing separation (~10 mas) and find a hint of curvature. This potential curvature is further supported at 3$σ$ significance when including literature GPI astrometry corrected for calibration systematics. Fits of the SPHERE and GPI data using three complementary approaches provide broadly similar results. The data suggest an orbital period of 32$^{+17}_{-9}$ yr (i.e. 12$^{+4}_{-2}$ au in semi-major axis), an inclination of 133$^{+14}_{-7}$ deg, an eccentricity of 0.45$^{+0.10}_{-0.15}$, and an argument of periastron passage of 87$^{+34}_{-30}$ deg [mod 180 deg]. The time at periastron passage and the longitude of node exhibit bimodal distributions because we do not detect yet if the planet is accelerating or decelerating along its orbit. Given the inclinations of the planet's orbit and of the stellar rotation axis (134-144 deg), we infer alignment or misalignment within 18 deg for the star-planet spin-orbit. Further astrometric monitoring in the next 3-4 years is required to confirm at a higher significance the curvature in the planet's motion, determine if the planet is accelerating or decelerating on its orbit, and further constrain its orbital parameters and the star-planet spin-orbit.

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arXiv2018

High-Resolution ALMA Observations of HD100546: Asymmetric Circumstellar Ring, and Circumplanetary Disk Upper Limits

We present long baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 870$\,μ$m dust continuum emission and CO (3-2) from the protoplanetary disk around the Herbig Ae/Be star HD 100546, which is one of the few systems claimed to have two young embedded planets. These observations achieve a resolution of 4 au (3.8 mas), an rms noise of 66$μ$Jy/beam, and reveal an asymmetric ring between $\sim$20-40 au with largely optically thin dust continuum emission. This ring is well fit by two concentric and overlapping Gaussian rings of different widths and a Vortex. In addition, an unresolved component is detected at a position consistent with the central star, which may trace the central inner disk ($<$2au in radius). We report a lack of compact continuum emission at the positions of both claimed protoplanets. We use this result to constrain the circumplanetary disk (CPD) mass and size of 1.44M$_{\rm Earth}$ and 0.44au in the optically thin and thick regime, respectively, for the case of the previously directly imaged protoplanet candidate at $\sim$55 au (HD100546 b). We compare these empirical CPD constraints to previous numerical simulations. This suggests that HD100546 b is inconsistent with several planet accretion models, while gas-starved models are also still compatible. We estimate the planetary mass as 1.65 M$_J$ by using the relation between planet, circumstellar, and circumplanetary masses derived from numerical simulations. Finally, the CO integrated intensity map shows a possible spiral arm feature that would match the spiral features identified in Near-Infrared scattered light polarized emission, which suggests a real spiral feature in the disk surface that needs to be confirmed with further observations.

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arXiv2018

High-Contrast study of the candidate planets and protoplanetary disk around HD~100546

The nearby Herbig Be star HD100546 is known to be a laboratory for the study of protoplanets and their relation with the circumstellar disk that is carved by at least 2 gaps. We observed the HD100546 environment with high contrast imaging exploiting several different observing modes of SPHERE, including datasets with/without coronagraphs, dual band imaging, integral field spectroscopy and polarimetry. The picture emerging from these different data sets is complex. Flux-conservative algorithms images clearly show the disk up to 200au. More aggressive algorithms reveal several rings and warped arms overlapping the main disk. The bright parts of this ring lie at considerable height over the disk mid-plane at about 30au. Our images demonstrate that the brightest wings close to the star in the near side of the disk are a unique structure, corresponding to the outer edge of the intermediate disk at ~40au. Modeling of the scattered light from the disk with a geometrical algorithm reveals that a moderately thin structure can well reproduce the light distribution in the flux-conservative images. We suggest that the gap between 44 and 113 au span between the 1:2 and 3:2 resonance orbits of a massive body located at ~70au that might coincide with the candidate planet HD100546b detected with previous thermal IR observations. In this picture, the two wings can be the near side of a ring formed by disk material brought out of the disk at the 1:2 resonance with the same massive object. While we find no clear evidence confirming detection of the planet candidate HD100546c in our data, we find a diffuse emission close to the expected position of HD100546b. This source can be described as an extremely reddened substellar object surrounded by a dust cloud or its circumplanetary disk. Its astrometry is broadly consistent with a circular orbital motion on the disk plane.

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