arXiv subjects

M. Benisty

Publications and source records attributed to M. Benisty.

At least 91 records · Page 5Linked to original sources

arXiv2020

The GRAVITY Young Stellar Object survey IV. The CO overtone emission in 51 Oph at sub-au scales

51 Oph is a Herbig Ae/Be star that exhibits strong near-infrared CO ro-vibrational emission at 2.3 micron, most likely originating in the innermost regions of a circumstellar disc. We aim to obtain the physical and geometrical properties of the system by spatially resolving the circumstellar environment of the inner gaseous disc. We used the second-generation VLTI/GRAVITY to spatially resolve the continuum and the CO overtone emission. We obtained data over 12 baselines with the auxiliary telescopes and derive visibilities, and the differential and closure phases as a function of wavelength. We used a simple LTE ring model of the CO emission to reproduce the spectrum and CO line displacements. Our interferometric data show that the star is marginally resolved at our spatial resolution, with a radius of 10.58+-2.65 Rsun.The K-band continuum emission from the disc is inclined by 63+-1 deg, with a position angle of 116+-1 deg, and 4+-0.8 mas (0.5+-0.1 au) across. The visibilities increase within the CO line emission, indicating that the CO is emitted within the dust-sublimation radius.By modelling the CO bandhead spectrum, we derive that the CO is emitted from a hot (T=1900-2800 K) and dense (NCO=(0.9-9)x10^21 cm^-2) gas. The analysis of the CO line displacement with respect to the continuum allows us to infer that the CO is emitted from a region 0.10+-0.02 au across, well within the dust-sublimation radius. The inclination and position angle of the CO line emitting region is consistent with that of the dusty disc. Our spatially resolved interferometric observations confirm the CO ro-vibrational emission within the dust-free region of the inner disc. Conventional disc models exclude the presence of CO in the dust-depleted regions of Herbig AeBe stars. Ad hoc models of the innermost disc regions, that can compute the properties of the dust-free inner disc, are therefore required.

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arXiv2020

A single-armed spiral in the protoplanetary disk around HD34282 ?

During the evolution of protoplanetary disks into planetary systems we expect to detect signatures that trace mechanisms such as planet-disk interaction. Protoplanetary disks display a large variety of structures in recently published high-spatial resolution images. However, the three-dimensional morphology of these disks is often difficult to infer from the two-dimensional projected images we observe. We spatially resolve the disk around HD 34282 using VLT/SPHERE in polarimetric imaging mode. We retrieve a profile for the height of the scattering surface to create a height-corrected deprojection, which simulates a face-on orientation. The disk displays a complex scattering surface. An inner clearing or cavity extending up to r<0.28" (88 au) is surrounded by a bright inclined (i = 56 deg) ring with a position angle of 119 deg. The center of this ring is offset from the star along the minor axis with 0.07", which can be explained with a disk-height of 26 au above the mid-plane. Outside this ring, beyond its south-eastern ansa we detect an azimuthal asymmetry or blob at r ~ 0.4". At larger separation, we detect an outer disk structure that can be fitted with an ellipse, compatible with a circular ring seen at r = 0.62" (190 au) and height of 77 au. After applying a height-corrected deprojection we see a circular ring centered on the star at 88 au, while what seemed to be a separate blob and outer ring, now both could be part of a single-armed spiral. Based on the current data it is not possible to conclude decisively whether $H_{\rm scat} / r$ remains constant or whether the surface is flared with at most $H_{\rm scat} \propto r^{1.35}$ , although we favor the constant ratio based on our deprojections. The height-corrected deprojection allows a more detailed interpretation of the observed structures, after which we discern the detection of a single-armed spiral.

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arXiv2020

Direct confirmation of the radial-velocity planet $β$ Pic c

Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas direct detection is more sensitive to planets orbiting at a large distance from their host star. %, and thus on long orbital period. This dichotomy makes it difficult to combine the two techniques on a single target at once. Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way. We observed the recently-discovered giant planet $β$ Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer (VLTI). This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of $T = 1250\pm50$\,K and a dynamical mass of $M = 8.2\pm0.8\,M_{\rm Jup}$. At $18.5\pm2.5$\,Myr, this puts $β$ Pic c close to a 'hot start' track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7\,au, which is too close for disk instability to occur. The low apparent magnitude ($M_{\rm K} = 14.3 \pm 0.1$) favours a core accretion scenario. We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.

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arXiv2020

Investigating the magnetospheric accretion process in the young pre-transitional disk system DoAr 44 (V2062~Oph). A multiwavelength interferometric, spectropolarimetric, and photometric observing campaign

Young stars interact with their accretion disk through their strong magnetosphere. We investigate the magnetospheric accretion process in the young stellar system DoAr 44. We monitored the system over several rotational cycles, combining high-resolution optical and near-IR spectropolarimetry with long-baseline near-IR interferometry and multicolor photometry. DoAr 44 is a young 1.2 solar mass star, moderately accreting from its disk, and seen at a low inclination. We derive a rotational period of 2.96 d from the system's light curve. Several optical and near-IR line profiles probing the accretion funnel flows and the accretion shock are modulated at the stellar rotation period. The most variable line profile, HeI 1083 nm, exhibits modulated redshifted wings a signature of accretion funnel flows, as well as deep blueshifted absorptions indicative of transient outflows. The Zeeman-Doppler analysis suggests the star hosts a mainly dipolar magnetic field, inclined by about 20 deg. onto the spin axis, with an intensity reaching about 800 G at the photosphere, and up to 2 +/- 0.8 kG close to the accretion shock. The magnetic field appears strong enough to disrupt the inner disk close to the corotation radius, at a distance of about 4.6 stellar radii (0.043 au). This supports the upper limit of 5 stellar radii (0.047 au) we derived for the size of the magnetosphere from long baseline interferometry. DoAr 44 is a pre-transitional disk system, exhibiting a 25-30 au gap in its circumstellar disk, with the inner and outer disks being misaligned. On a scale of 0.1 au or less, our results indicate that the system steadily accretes from its inner disk through its tilted dipolar magnetosphere. We conclude that in spite of a highly structured outer disk, perhaps the signature of ongoing planetary formation, the magnetospheric accretion process proceeds unimpeded at the star-disk interaction level.

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arXiv2020

Observations of edge-on protoplanetary disks with ALMA I. Results from continuum data

We analyze a sample of 12 HST-selected edge-on protoplanetary disks for which the vertical extent of the emission layers can be constrained directly. We present ALMA high angular resolution continuum images (0.1arcsec) of these disks at two wavelengths, 0.89mm and 2.06mm (respectively ALMA bands 7 and 4), supplemented with archival band 6 data (1.33mm) where available. For most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. Six sources are resolved along their minor axis in at least one millimeter band, providing direct information on the vertical distribution of the millimeter grains. For the second largest disk of the sample, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. Furthermore, the only Class I object in our sample shows evidence of flaring in the millimeter. Along the major axis, all disks are well resolved. Four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. For all disks, we also derive the millimeter brightness temperature and spectral index maps. We find that the disks are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (<10K). The integrated spectral indices are similar to those of disks at lower inclination. The comparison of a generic radiative transfer disk model with our data shows that at least 3 disks are consistent with a small millimeter dust scale height, of a few au (measured at r=100au). This is in contrast with the more classical value of h_g\sim10au derived from scattered light images and from gas line measurements. These results confirm, by direct observations, that large (millimeter) grains are subject to significant vertical settling in protoplanetary disks.

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arXiv2020

The GRAVITY young stellar object survey III. The dusty disk of RY Lup

We use PIONIER data from the ESO archive and GRAVITY data that were obtained in June 2017 with the four 8m telescopes. We use a parametric disk model and the 3D radiative transfer code MCFOST to reproduce the Spectral Energy Distribution and match the interferometric observations. To match the SED , our model requires a stellar luminosity of 2.5 Lsun, higher than any previously determined values. Such a high value is needed to accommodate the circumstellar extinction caused by the highly inclined disk, which has been neglected in previous studies. While using an effective temperature of 4800 K determined through high-resolution spectroscopy, we derive a stellar radius of 2.29 Rsun. These revised fundamental parameters, when combined with the mass estimates available , lead to an age of 0.5-2.0 Ma for RY Lup, in better agreement with the age of the Lupus association than previous determinations. Our disk model nicely reproduces the interferometric GRAVITY data and is in good agreement with the PIONIER ones. We derive an inner rim location at 0.12~au from the central star. This model corresponds to an inclination of the inner disk of 50deg, which is in mild tension with previous determinations of a more inclined outer disk from SPHERE (70 deg in NIR) and ALMA(67 $\pm$5 deg) images, but consistent with the inclination determination from the ALMA CO spectra (55$\pm$5deg). Increasing the inclination of the inner disk to 70 deg leads to a higher line-of-sight extinction and therefore requires a higher stellar luminosity of 4.65 Lsun to match the observed flux levels. This luminosity would translate to a stellar radius of 3.13~Rsun, leading to an age of 2-3~Ma, and a stellar mass of about 2 Msun, in disagreement with the observed dynamical mass estimate of 1.3-1.5 Msun. Critically, this high-inclination inner disk model also fails to reproduce the visibilities observed with GRAVITY.

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arXiv2020

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): A close low mass companion to ET Cha

To understand the formation of planetary systems, one needs to understand the initial conditions of planet formation, i.e. the young gas-rich planet forming disks. Spatially resolved high-contrast observations are of particular interest, since substructures in disks, linked to planet formation, can be detected and close companions or even planets in formation embedded in the disk can be revealed. In this study we present the first result of the DESTINYS survey (Disk Evolution Study Through Imaging of Nearby Young Stars). DESTINYS is an ESO/SPHERE large program that aims at studying disk evolution in scattered light, mainly focusing on a sample of low-mass stars (<1$M_\odot$) in nearby (~200 pc) star-forming regions. In this particular study we present the observations of the ET Cha (RECX 15) system, a nearby 'old' classical T Tauri star (5-8 Myr, ~100 pc), which is still strongly accreting. We use SPHERE/IRDIS in H-band polarimetric imaging mode to obtain high contrast images of the ET Cha system to search for scattered light from the circumstellar disk as well as thermal emission from close companions. We additionally employ VLT/NACO total intensity archival data taken in 2003. We report here the discovery of a low-mass (sub)stellar companion with SPHERE/IRDIS to ET Cha. We are estimating the mass of this new companion based on photometry. Depending on the system age it is a 5 Myr, 50 $M_{Jup}$ brown dwarf or an 8 Myr, 0.10 $M_\odot$ M-type pre-main-sequence star. We explore possible orbital solutions and discuss the recent dynamic history of the system. Independent of the precise companion mass we find that the presence of the companion likely explains the small size of the disk around ET Cha. The small separation of the binary pair indicates that the disk around the primary component is likely clearing from the outside in, explaining the high accretion rate of the system.

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arXiv2020

Gap, shadows, spirals, streamers: SPHERE observations of binary-disk interactions in GG Tau A

A large fraction of stars is found to be part of binary or higher-order multiple systems. The ubiquity of planets found around single stars raises the question if and how planets in binary systems may form. Protoplanetary disks are the birthplaces of planets, and their characterization is crucial in order to understand the planet formation process. Our aim is to characterize the morphology of the GG Tau A disk, one of the largest and most massive circumbinary disks, and trace evidence for binary-disk interactions. We obtained observations in polarized scattered light of GG Tau A using the SPHERE/IRDIS instrument in the H-band filter. We analyze the observed disk morphology and substructures. We run 2D hydrodynamical models simulating the evolution of the circumbinary ring over the lifetime of the disk. The disk, as well as the cavity and the inner region are highly structured with several shadowed regions, spiral structures, and streamer-like filaments, some of them detected for the first time. The streamer-like filaments appear to connect the outer ring with the northern arc. Their azimuthal spacing suggests that they may be generated by periodic perturbations by the binary, tearing off material from the inner edge of the outer disk once during each orbit. By comparing observations to hydrodynamical simulations we find that the main features, in particular the gap size, as well as the spiral and streamer filaments, can be qualitatively explained by the gravitational interactions of a binary with semi-major axis of $\sim$35 au on an orbit coplanar with the circumbinary ring.

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arXiv2020

Ongoing flyby in the young multiple system UX Tauri

We present observations of the young multiple system UX Tauri to look for circumstellar disks and for signs of dynamical interactions. We obtained SPHERE/IRDIS deep differential polarization images in the J and H bands. We also used ALMA archival CO data. Large extended spirals are well detected in scattered light coming out of the disk of UX Tau A. The southern spiral forms a bridge between UX Tau A and C. These spirals, including the bridge connecting the two stars, all have a CO (3-2) counterpart seen by ALMA. The disk of UX Tau C is detected in scattered light. It is much smaller than the disk of UX Tau A and has a major axis along a different position angle, suggesting a misalignment. We performed PHANTOM SPH hydrodynamical models to interpret the data. The scattered light spirals, CO emission spirals and velocity patterns of the rotating disks, and the compactness of the disk of UX Tau C all point to a scenario in which UX Tau A has been perturbed very recently (about 1000 years) by the close passage of UX Tau C.

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arXiv2020

Annular substructures in the transition disks around LkCa 15 and J1610

We present high resolution millimeter continuum ALMA observations of the disks around the T Tauri stars LkCa 15 and J1610. These disks host dust-depleted inner regions, possibly carved by massive planets, and are of prime interest to study the imprints of planet-disk interactions. While at moderate angular resolution they appear as a broad ring surrounding a cavity, the continuum emission resolves into multiple rings at a resolution of ~60$\times$40 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~$7\,μ$Jy beam$^{-1}$ rms at 1.3 mm. In addition to a broad extended component, LkCa 15 and J1610 host 3 and 2 narrow rings, respectively, with two bright rings in LkCa 15 being radially resolved. The rings look marginally optically thick, with peak optical depths of ~0.5 (neglecting scattering), in agreement with high angular resolution observations of full disks. We perform hydrodynamical simulations with an embedded, sub-Jovian-mass planet and show that the observed multi-ringed substructure can be qualitatively explained as the outcome of the planet-disk interaction. We note however that the choice of the disk cooling timescale alone can significantly impact the resulting gas and dust distributions around the planet, leading to different numbers of rings and gaps and different spacings between them. We propose that the massive outer disk regions of transition disks are favorable places for planetesimals and possibly second generation planet formation of objects with a lower mass than the planets carving the inner cavity (typically few $M_{\rm Jup}$), and that the annular substructures observed in LkCa 15 and J1610 may be indicative of planetary core formation within dust-rich pressure traps. Current observations are compatible with other mechanisms being at the origin of the observed substructures, in particular with narrow rings generated at the edge of the CO and N$_2$ snowlines.

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arXiv2020

A family portrait of disk inner rims around Herbig Ae/Be stars: Hunting for warps, rings, self shadowing, and misalignments in the inner astronomical units

The innermost astronomical unit in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets that are located within the first au around their host star. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by infrared interferometry. We provide reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with PIONIER at the VLTI, using SPARCO. We find that 40% of the systems are centrosymmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for 30% of the objects and noncentrosymmetric morphology due to a nonaxisymmetric and possibly variable environment (30%). Among the systems with a disk-like structure, 20% show a resolved dust-free cavity. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies. At the angular resolution reached by near-infrared interferometric observations, most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models. Moreover, the nonaxisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission sensitive to temporal evolution with a time-scale down to a few weeks. The evidence of nonaxisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires alternative explanations, such as a warping of the inner disks. Interferometric observations can, therefore, be used to follow the evolution of the asymmetry of those disks at a sub-au scale.

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arXiv2020

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the BrG line in order to constrain the extent and geometry of the emitting regions. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that BrG emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (5 Rstar). Differential phase measurements between the BrG line and the continuum allow us to measure the astrometric displacement of the BrG line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Our results can be accounted for by a simple geometric model where the BrG line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

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arXiv2020

Spirals inside the millimeter cavity of transition disk SR 21

Hydrodynamical simulations of planet-disk interactions suggest that planets may be responsible for a number of the sub-structures frequently observed in disks in both scattered light and dust thermal emission. Despite the ubiquity of these features, direct evidence of planets embedded in disks and of the specific interaction features like spiral arms within planetary gaps still remain rare. In this study we discuss recent observational results in the context of hydrodynamical simulations in order to infer the properties of a putative embedded planet in the cavity of a transition disk. We imaged the transition disk SR 21 in H-band in scattered light with SPHERE/IRDIS and in thermal dust emission with ALMA band 3 (3mm) observations at a spatial resolution of 0.1". We combine these datasets with existing band 9 (430um) and band 7 (870um) ALMA continuum data. The Band 3 continuum data reveals a large cavity and a bright ring peaking at 53 au strongly suggestive of dust trapping.The ring shows a pronounced azimuthal asymmetry, with a bright region in the north-west that we interpret as a dust over-density. A similarly-asymmetric ring is revealed at the same location in polarized scattered light, in addition to a set of bright spirals inside the mm cavity and a fainter spiral bridging the gap to the outer ring. These features are consistent with a number of previous hydrodynamical models of planet-disk interactions, and suggest the presence of a ~1 MJup planet at 44 au and PA=11°. This makes SR21 the first disk showing spiral arms inside the mm cavity, as well as one for which the location of a putative planet can be precisely inferred. With the location of a possible planet being well-constrained by observations, it is an ideal candidate for follow-up observations to search for direct evidence of a planetary companion still embedded in its disk.

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arXiv2020

SPHERE+: Imaging young Jupiters down to the snowline

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei.

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arXiv2020

The GRAVITY young stellar object survey. II. First spatially resolved observations of the CO bandhead emission in a high-mass YSO

The inner regions of the discs of high-mass young stellar objects (HMYSOs) are still poorly known due to the small angular scales and the high visual extinction involved. We deploy near-infrared (NIR) spectro-interferometry to probe the inner gaseous disc in HMYSOs and investigate the origin and physical characteristics of the CO bandhead emission (2.3-2.4 $μ$m). We present the first GRAVITY/VLTI observations at high spectral (R=4000) and spatial (mas) resolution of the CO overtone transitions in NGC 2024 IRS2. The continuum emission is resolved in all baselines and is slightly asymmetric, displaying small closure phases ($\leq$8$^{\circ}$). Our best ellipsoid model provides a disc inclination of 34$^{\circ}$$\pm$1$^{\circ}$, a disc major axis position angle of 166$^{\circ}$$\pm$1$^{\circ}$, and a disc diameter of 3.99$\pm$0.09 mas (or 1.69$\pm$0.04 au, at a distance of 423 pc). The small closure phase signals in the continuum are modelled with a skewed rim, originating from a pure inclination effect. For the first time, our observations spatially and spectrally resolve the first four CO bandheads. Changes in visibility, as well as differential and closure phases across the bandheads are detected. Both the size and geometry of the CO-emitting region are determined by fitting a bidimensional Gaussian to the continuum-compensated CO bandhead visibilities. The CO-emitting region has a diameter of 2.74$\pm^{0.08}_{0.07}$ mas (1.16$\pm$0.03 au), and is located in the inner gaseous disc, well within the dusty rim, with inclination and $PA$ matching the dusty disc geometry, which indicates that both dusty and gaseous discs are coplanar. Physical and dynamical gas conditions are inferred by modelling the CO spectrum. Finally, we derive a direct measurement of the stellar mass of $M_*\sim$14.7$^{+2}_{-3.6}$ M$_{\odot}$ by combining our interferometric and spectral modelling results.

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arXiv2019

Discovery of a directly imaged disk in scattered light around the Sco-Cen member Wray 15-788

As part of our on-going survey we have carried out high-contrast imaging with VLT/SPHERE/IRDIS to obtain polarized and total intensity images of the young ($11^{+16}_{-7}$Myr old) K3IV star Wray 15-788 within the Lower Centaurus Crux subgroup of Sco-Cen. For the total intensity images, we remove the stellar halo by an approach based on reference star differential imaging in combination with principal component analysis. Both total intensity and polarimetric data resolve a disk around Wray 15-788. Modeling of the stellar spectral energy distribution suggests that this is a protoplanetary disk at a transition stage. We detect a bright, outer ring at a projected separation of $\sim$370mas ($\approx$56au), hints for inner substructures at $\sim$170mas ($\approx$28au) and a gap in between. Only within a position angle range of $60^\circ<φ<240^\circ$, we are confident at 5$σ$ level to detect actual scattered light flux from the outer ring of the disk; the remaining part is indistinguishable from background noise. For the detected part of the outer ring we determine a disk inclination of $i$=21$^\circ\pm$6$^\circ$ and a position angle of $φ$=76$^\circ\pm$16$^\circ$. Furthermore, we find that Wray 15-788 is part of a binary system with the A2V star HD 98363 at a separation of $\sim$50'' ($\approx$6900au). The detection of only half of the outer ring might be due to shadowing by a misaligned inner disk. A potential substellar companion can cause the misalignment of the inner structures and can be responsible for clearing the detected gap from scattering material. We can not, however, rule out the possibility of a non-detection due to our limited signal to noise ratio, combined with brightness azimuthal asymmetry. From our data, we can exclude companions more massive than 10$M_\mathrm{jup}$ within the gap at a separation of $\sim$230mas ($\approx$35au).

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arXiv2019

Shadowing and multiple rings in the protoplanetary disk of HD 139614

Shadows in scattered light images of protoplanetary disks are a common feature and support the presence of warps or misalignments between disk regions. These warps are possibly due to an inclined (sub-)stellar companion embedded in the disk. We study the morphology of the protoplanetary disk around the Herbig Ae star HD 139614 based on the first scattered light observations of this disk, which we model with the radiative transfer code MCMax3D. We obtained J- and H-band observations in polarized scattered light with VLT/SPHERE that show strong azimuthal asymmetries. In the outer disk, beyond ~30 au, a broad shadow spans a range of ~240° in position angle, in the East. A bright ring at ~16 au also shows an azimuthally asymmetric brightness, with the faintest side roughly coincidental with the brightest region of the outer disk. Additionally, two arcs are detected at ~34 au and ~50 au. We created a simple 4-zone approximation to a warped disk model of HD 139614 in order to qualitatively reproduce these features. The location and misalignment of the disk components were constrained from the shape and location of the shadows they cast. We find that the shadow on the outer disk covers a range of position angle too wide to be explained by a single inner misaligned component. Our model requires a minimum of two separate misaligned zones -- or a continuously warped region -- to cast this broad shadow on the outer disk. A small misalignment of ~4° between adjacent components can reproduce most of the observed shadow features. Multiple misaligned disk zones, potentially mimicing a warp, can explain the observed broad shadows in the HD 139614 disk. A planetary mass companion in the disk, located on an inclined orbit, could be responsible for such a feature and for the dust depleted gap responsible for a dip in the SED.

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arXiv2019

Time-resolved photometry of the young dipper RX J1604.3-2130A: Unveiling the structure and mass transport through the innermost disk

RX~J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk with respect to its face-on outer disk. We study the eclipses to constrain the inner disk properties.We use time-resolved photometry from the Rapid Eye Mount telescope and Kepler2 data to study the multi-wavelength variability, and archival optical and IR data to track accretion, rotation, and changes in disk structure. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius ($\sim$0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE variability reveal variations in the dust content in the innermost disk on a few years timescale, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v$sini$=16km/s confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.

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