arXiv subjects

C. Dougados

Publications and source records attributed to C. Dougados.

At least 19 recordsLinked to original sources

arXiv2026

The GRAVITY young stellar object survey -- XV. The star-disk interaction region of the T Tauri star DO Tau

Protoplanetary disks around young Sun-like stars are the cradles of the vast majority of detected exoplanets. Probing these disks at multiple spatial scales is key to uncovering how planets form. We aim to spatially and spectrally resolve the inner disk and star-disk interaction region of the M0.3 T Tauri star DO Tau by combining two complementary techniques. We used high-resolution near-infrared spectra from CFHT/SPIRou to constrain the magnetospheric star-disk interaction process and optical long-baseline interferometry with ESO VLTI/GRAVITY to determine the sizes of the K-band continuum and Br$\gamma$ line emitting regions. From the SPIRou spectra, we confirmed that this ~0.5 M$_\odot$ star is a strong accretor. The HI and HeI lines exhibit strong variability on a daily timescale, consistent with the burster classification of DO Tau derived from its K2 light curve. We derived an upper limit of 0.35 on the ratio between the magnetospheric truncation radius and the disk corotation radius, indicative of an ordered unstable accretion regime. The size of the Br$\gamma$ line emitting region obtained from GRAVITY is much smaller than the K-band continuum emitting region. This compact Br$\gamma$ emission region ($R_{Br\gamma} \sim$ 0.011 au) suggests that most of the line flux originates from the magnetospheric accretion region and/or from an inner wind close to the magnetosphere-disk interface. The inclination we derived for the inner disk (45-55{\deg}) differs from that of the outer disk inferred from the ALMA continuum (30{\deg}). This points toward a misalignment or warp of the outer disk that may originate from the suspected past encounter with the neighboring HV Tau system.

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arXiv2026

Magnetic field measurements in a sample of Class I and flat-spectrum protostars observed with SPIRou

Magnetic fields play a crucial role throughout stellar evolution, regulating angular momentum, channelling accretion, and launching jets and outflows. While the magnetic properties of Classical T Tauri Stars (CTTS) are well characterised, those of their progenitors, Class I and Flat-Spectrum (FS) protostars, remain poorly constrained due to observational challenges linked to their embedded nature. We aim to detect and characterise large-scale magnetic fields in a sample of Class I and FS protostars, which are expected to host strong dynamo-generated fields. Using SPIRou, a high-resolution near-infrared spectropolarimeter, we analysed polarised spectra and applied the Least Squares Deconvolution (LSD) technique to extract magnetic signatures and measure longitudinal fields from Stokes V profiles. We report new detections of large-scale magnetic fields in 5 FS protostars. Including the previously known magnetic FS protostar V347 Aur, 40% of our sample (15 objects) is confirmed to be magnetic. These stars exhibit clear Zeeman signatures, with longitudinal field strengths ranging from ~80 to ~200 G. The remaining targets show no detectable Stokes V signature, with upper limits on dipolar fields between 500 G and >5 kG. These results indicate that Class I and FS protostars can host large-scale magnetic fields, possibly weaker than in CTTS, supporting the idea that magnetic processes are already active during the main accretion phase and may influence star-disk interactions from the earliest stages.

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arXiv2025

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) VII: the layered molecular outflow from HL Tau and its relationship with the ringed disk

The ringed disk around HL Tau stands out as the iconic signature of planet formation, but the origin of the substructures is still debated. The HL Tau system also drives a powerful bipolar wind, and we analyze its outermost component traced by CO emission, to determine the relationship of the flow with the disk and its substructures. We use ALMA observations of the ${}^{12}$CO (2-1) line at 1.3 mm, with 0.2 km/s and ~ 0.28" resolution, conducted within the ALMA-DOT project. The channel maps and position-velocity diagrams show a rich structure of concatenated bubble- and arc-shaped features, whose size and distance from the source increase with velocity. The superposition of the features generates the apparent conical shape. The tomographic reconstruction of the morphology and kinematics of the red-shifted lobe suggests the presence of distinct nested shells having higher velocity and steeper velocity gradient for shells closer to the axis, rotating in the same sense of the disk. Such configuration can be justified by different classes of models. In this paper we compare the derived wind parameters with the predictions of magnetohydrodynamic (MHD) disk winds. Under this hypothesis, the launch radii of the three outermost shells are found to be at about the position of three adjacent dust rings in the disk at 58, 72 and 86 au. The wind may be capable of removing angular momentum from the outer disk, and we derive a magnetic lever arm of $\lambda \sim 4 - 5$, higher than that commonly adopted for MHD winds from these regions. Interpretations are discussed. The arrangement of the wind in nested shells with brighter emission rooted at the location of ring substructures could support the results of non-ideal MHD simulations according to which magnetic instabilities can generate the disk ring-gap system with a connected layered wind, alternatively to the action of yet undetected protoplanets.

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arXiv2024

Forbidden Emission Line spectro-imaging of the RU Lupi jet and Low Velocity Component

The first images of the jet and low velocity component (LVC) from the strongly accreting classical T Tauri star RU Lupi are presented. Adaptive optics assisted spectro-imaging of forbidden emission lines was used. The main aim of the observations was to test the conclusion from a recent spectro-astrometric study that the narrow component of the LVC is tracing an MHD disk wind, and to estimate the mass loss rate in the wind. The structure and morphology of the component supports a wind origin for the NC. An upper limit to the launch radius and semi-opening angle of the wind in [O I]{\lambda}6300 emission are estimated to be 2 au and 19{\deg} in agreement with MHD wind models for high accretors. The height of the [O I]{\lambda}6300 wind emitting region, a key parameter for the derivation of the mass loss rate, is estimated for the first time at approximately 35 au giving M_out = 2.6 x 10^-11 M_sun/yr. When compared to the derived mass accretion rate of M_acc = 1.6 x 10^-7 M_sun/yr, the efficiency in the wind is too low for the wind to be significantly contributing to angular momentum removal.

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arXiv2024

The interplay between disk wind and magnetospheric accretion mechanisms in the innermost environment of RU Lup

Aims: Our aim is to build upon the analysis presented in our previous work by attempting to match the observational data obtained with VLTI GRAVITY for RU Lup in 2021 with an expanded radiative transfer model of Br$\gamma$ emission. Specifically, we will determine if the inclusion of an additional disk wind as a Br$\gamma$ emitter in the inner disk will be able to reproduce the trend of increasing sizes at higher velocities, as well as the observed photocenter shifts. Methods: We make use of the MCFOST radiative transfer code to solve for Br$\gamma$ line formation in the innermost disk of an RU Lupl-like system. From the resulting images we compute synthetic interferometric observables. We first investigate how individual parameter variations in a pure magnetospheric accretion model and a pure parameteric disk wind model translate to changes in these derived quantities. Then we attempt to reproduce the RU Lup GRAVITY data with different parameter variants of magnetospheric accretion models, disk wind models, and combined hybrid models. Results: We demonstrate that magnetospheric accretion models and disk wind models on their own can emulate certain individual characteristics from the observational results, but individually fail to comprehensively reproduce the observational trends. Disk wind plus accretion hybrid models are in principle capable of explaining the variation in characteristic radii across the line and the corresponding flux ratios. While the model parameters of the hybrid models are mostly in good agreement with the known attributes of RU Lup, we find that our best-fitting models deviate in terms of rotational period and the size of the magnetosphere. The best-fitting hybrid model does not respect the co-rotation criterion, as the magnetospheric truncation radius is about 50% larger than the co-rotation radius.

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arXiv2024

The GRAVITY young stellar object survey XIV : Investigating the magnetospheric accretion-ejection processes in S CrA N

The dust- and gas-rich protoplanetary disks around young stellar systems play a key role in star and planet formation. While considerable progress has recently been made in probing these disks on large scales of a few tens of astronomical units (au), the central au needs to be more investigated. We aim at unveiling the physical processes at play in the innermost regions of the strongly accreting T Tauri Star S CrA N by means of near-infrared interferometric observations. The K-band continuum emission is well reproduced with an azimuthally-modulated dusty ring. As the star alone cannot explain the size of this sublimation front, we propose that magnetospheric accretion is an important dust-heating mechanism leading to this continuum emission. The differential analysis of the Hydrogen Br$\gamma$ line is in agreement with radiative transfer models combining magnetospheric accretion and disk winds. Our observations support an origin of the Br$\gamma$ line from a combination of (variable) accretion-ejection processes in the inner disk region.

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arXiv2024

Binary orbit and disks properties of the RW Aur system using ALMA observations

The dynamical interactions between young binaries can perturb the material distribution of their circumstellar disks, and modify the planet formation process. In order to constrain the impact and nature of the binary interaction in the RW Aur system (bound or unbound), we analyzed the circumstellar material at 1.3 mm wavelengths, as observed at multiple epochs by ALMA. We analyzed the disk properties through parametric visibility modeling, and we used this information to constrain the dust morphology and the binary orbital period. We imaged the dust continuum emission of RW Aur with a resolution of 3 au, and we find that the radius enclosing 90% of the flux (R90%) is 19 au and 14 au for RW Aur A and B, respectively. By modeling the relative distance of the disks at each epoch, we find a consistent trend of movement for the disk of RW Aur B moving away from the disk of RW Aur A at an approximate rate of 3 mas/yr (about 0.5 au/yr in sky-projected distance). By combining ALMA astrometry, historical astrometry, and the dynamical masses of each star, we constrain the RW Aur binary stars to be most likely in a high-eccentricity elliptical orbit with a clockwise prograde orientation relative to RW Aur A, although low-eccentricity hyperbolic orbits are not ruled out by the astrometry. Our analysis does not exclude the possibility of a disk collision during the last interaction, which occurred $295_{-74}^{+21}$ yr ago relative to beginning of 2024. Evidence for the close interaction is found in a tentative warp of 6 deg in the inner 3 au of the disk of RW Aur A, in the brightness temperature of both disks, and in the morphology of the gas emission. A narrow ring that peaks at 6 au around RW Aur B is suggestive of captured material from the disk around RW Aur A.

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arXiv2024

A kinematical study of the launching region of the blueshifted HH 46/47 outflow with SINFONI K-band observations

Studying outflows is important as they may significantly contribute to angular momentum removal from the star/disk system, affecting disk evolution and planet formation. To investigate the different outflow components; the collimated jet, wide-angled molecular outflow, and outflow cavity, of the Class I HH 46/47 outflow system. We focus on their kinematics. We present Near Infrared (NIR) K-band integral field observations of the blue-shifted HH 46/47 outflow base obtained using VLT/SINFONI with an angular resolution of 0".81. Our analysis focuses on [Fe II], H2 1-0 S(1), and, Br-gamma emission. We employ a wavelength recalibration technique based on OH telluric lines to probe the kinematics of the wide-angled flow with an accuracy of 1 km/s - 3 km/s. A velocity gradient of 10 km/s transverse to the outflow direction is confirmed in the wide-angled H2 outflow cavity. The H2 cavity peaks at radial velocities of -15 km/s to -30 km/s, and the atomic jet at v = -210 km/s. The outflow exhibits a layered structure; the high-velocity [Fe II] and Br-gamma jet is surrounded by a wide-angled H2 outflow cavity, which is in turn nested within the continuum emission and CO molecular outflow. The continuum emission and H2 outflow cavity are asymmetric with respect to the jet axis. We propose that the origin of the asymmetries and the velocity gradient detected in the wide-angled H2 cavity, is due to a wide-angled outflow or successive jet bowshocks expanding into an inhomogeneous ambient medium, or the presence of a secondary outflow. We eliminate outflow rotation as an exclusive origin of this velocity gradient due to large specific angular momenta values, J(r)= 3000 - 4000 km/s au calculated from 1" to 2" along the outflow. The observations reveal the complexities inherent in outflow systems, and the risk of attributing transverse velocity gradients solely to rotation.

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arXiv2024

The GRAVITY young stellar object survey XIII. Tracing the time-variable asymmetric disk structure in the inner AU of the Herbig star HD98922

Temporal variability in the photometric and spectroscopic properties of protoplanetary disks is common in YSO. However, evidence pointing toward changes in their morphology over short timescales has only been found for a few sources, mainly due to a lack of high cadence observations at mas resolution. We combine GRAVITY multi-epoch observations of HD98922 at mas resolution with PIONIER archival data covering a total time span of 11 years. We interpret the interferometric visibilities and spectral energy distribution with geometrical models and through radiative transfer techniques. We investigated high-spectral-resolution quantities to obtain information on the properties of the HI BrG-line-emitting region. The observations are best fitted by a model of a crescent-like asymmetric dust feature located at 1 au and accounting for 70% of the NIR emission. The feature has an almost constant magnitude and orbits the central star with a possible sub-Keplerian period of 12 months, although a 9 month period is another, albeit less probable, solution. The radiative transfer models show that the emission originates from a small amount of carbon-rich (25%) silicates, or quantum-heated particles located in a low-density region. Among different possible scenarios, we favor hydrodynamical instabilities in the inner disk that can create a large vortex. The high spectral resolution differential phases in the BrG-line show that the hot-gas component is offset from the star and in some cases is located between the star and the crescent feature. The scale of the emission does not favor magnetospheric accretion as a driving mechanism. The scenario of an asymmetric disk wind or a massive accreting substellar or planetary companion is discussed. With this unique observational data set for HD98922, we reveal morphological variability in the innermost 2 au of its disk region.

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arXiv2024

The GRAVITY young stellar object survey XII. The hot gas disk component in Herbig Ae/Be stars

The region of protoplanetary disks closest to a star (within 1-2\,au) is shaped by a number of different processes, from accretion of the disk material onto the central star to ejection in the form of winds and jets. Optical and near-IR emission lines are potentially good tracers of inner disk processes if very high spatial and/or spectral resolution are achieved. In this paper, we exploit the capabilities of the VLTI-GRAVITY near-IR interferometer to determine the location and kinematics of the hydrogen emission line Bracket gamma. We present VLTI-GRAVITY observations of the Bracket gamma line for a sample of 26 stars of intermediate mass (HAEBE), the largest sample so far analysed with near-IR interferometry. The Bracket gamma line was detected in 17 objects. The emission is very compact (in most cases only marginally resolved), with a size of 10-30R* (1-5 mas). About half of the total flux comes from even smaller regions, which are unresolved in our data. For eight objects, it was possible to determine the position angle (PA) of the line-emitting region, which is generally in agreement with that of the inner-dusty disk emitting the K-band continuum. The position-velocity pattern of the Bracket gamma line-emitting region of the sampled objects is roughly consistent with Keplerian rotation. The exception is HD~45677, which shows more extended emission and more complex kinematics. The most likely scenario for the Bracket gamma origin is that the emission comes from an MHD wind launched very close to the central star, in a region well within the dust sublimation radius. An origin in the bound gas layer at the disk surface cannot be ruled out, while accreting matter provides only a minor fraction of the total flux. These results show the potential of near-IR spectro-interferometry to study line emission in young stellar objects.

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arXiv2023

The GRAVITY young stellar object survey: XI. Imaging the hot gas emission around the Herbig Ae star HD 58647

We aim to investigate the origin of the HI Br$\gamma$ emission in young stars by using GRAVITY to image the innermost region of circumstellar disks, where important physical processes such as accretion and winds occur. With high spectral and angular resolution, we focus on studying the continuum and the HI Br$\gamma$-emitting area of the Herbig star HD58647. Using VLTI-GRAVITY, we conducted observations of HD58647 with both high spectral and high angular resolution. Thanks to the extensive $uv$ coverage, we were able to obtain detailed images of the circumstellar environment at a sub-au scale, specifically capturing the continuum and the Br$\gamma$-emitting region. Through the analysis of velocity-dispersed images and photocentre shifts, we were able to investigate the kinematics of the HI Br$\gamma$-emitting region. The recovered continuum images show extended emission where the disk major axis is oriented along a position angle of 14\degr. The size of the continuum emission at 5-sigma levels is $\sim$ 1.5 times more extended than the sizes reported from geometrical fitting (3.69 mas $\pm$ 0.02 mas). This result supports the existence of dust particles close to the stellar surface, screened from the stellar radiation by an optically thick gaseous disk. Moreover, for the first time with GRAVITY, the hot gas component of HD58647 traced by the Br$\gamma$ ,has been imaged. This allowed us to constrain the size of the Br$\gamma$-emitting region and study the kinematics of the hot gas; we find its velocity field to be roughly consistent with gas that obeys Keplerian motion. The velocity-dispersed images show that the size of the hot gas emission is from a more compact region than the continuum (2.3 mas $\pm$ 0.2 mas). Finally, the line phases show that the emission is not entirely consistent with Keplerian rotation, hinting at a more complex structure in the hot gaseous disk.

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arXiv2023

Star-disk interactions in the strongly accreting T Tauri Star S CrA N

Aims : We aimed at constraining the accretion-ejection phenomena around the strongly-accreting Northern component of the S CrA young binary system (S CrA N) by deriving its magnetic field topology and its magnetospheric properties, and by detecting ejection signatures, if any. Methods : We led a two-week observing campaign on S CrA N with the ESPaDOnS optical spectropolarimeter at the Canada-France-Hawaii Telescope. We recorded 12 Stokes I and V spectra over 14 nights. We computed the corresponding Least-Square Deconvolution (LSD) profiles of the photospheric lines and performed Zeeman-Doppler Imaging (ZDI). We analysed the kinematics of noticeable emission lines, namely He I $\lambda 5876$ and the four first lines of the Balmer series, known to trace the accretion process. Conclusions : The findings from spectropolarimetry are complementary to those provided by optical long-baseline interferometry, allowing us to construct a coherent view of the innermost regions of a young, strongly accreting star. Yet, the strong and complex magnetic field reconstructed for S CrA N is inconsistent with the observed magnetic signatures of the emission lines associated to the post-shock region. We recommend a multi-technique, synchronized campaign of several days to put more constrains on a system that varies on a $\sim$ 1 day timescale.

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arXiv2023

New insights on the near-infrared veiling of young stars using CFHT/SPIRou data

Veiling is ubiquitous at different wavelength ranges in accreting stars. However, the origin of the veiling in the IR domain is not well understood. The accretion spot alone is not enough to explain the shallow photospheric IR lines in accreting systems, suggesting that another source is contributing to the veiling in the NIR. The inner disk is often quoted as the additional emitting source meant to explain the IR veiling. In this work, we aim to measure and discuss the NIR veiling to understand its origins and variability timescale, using a sample of 14 accreting stars observed with the CFHT/SPIRou spectrograph, within the framework of the SPIRou Legacy Survey. We compared the veiling measurements with accretion and inner disk diagnostics. The measured veiling grows from the Y to the K band for most of the targets in our sample. The IR veiling agrees with NIR emission excess obtained using photometric data. However, we also find a linear correlation between the veiling and the accretion properties of the system, showing that accretion contributes to the inner disk heating and, consequently, to the inner disk emission excess. We also show a connection between the NIR veiling and the system's inclination with respect to our line of sight. This is probably due to the reduction of the visible part of the inner disk edge, where the NIR emission excess is expected to arise, as the inclination of the system increases. The NIR veiling appears variable on a timescale of a day, showing the night-by-night dynamics of the optical veiling variability. In the long term, the mean NIR veiling seems to be stable for most of the targets on timescales of a month to a few years. However, during occasional episodes of high accretion, which affect the system's dynamic, the veiling also seems to be much more prominent at such times, as we found in the case of the target RU Lup.

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arXiv2022

Modeling the CO outflow in DG Tau B: Swept-up shells versus perturbed MHD disk wind

The origin of outflows and their exact impact on disk evolution and planet formation remain crucial open questions. DG Tau B is a Class I protostar associated with a rotating conical CO outflow and a structured disk. Hence it is an ideal target to study these questions. We aim to characterize the morphology and kinematics of the DG Tau B outflow in order to elucidate its origin and potential impact on the disk. Our analysis is based on Atacama Large Millimeter Array (ALMA) 12CO(2-1) observations of DG Tau B at 20 au angular resolution. We characterize three different types of substructures in this outflow (arches, fingers, and cusps) with apparent acceleration. Wind-driven shell models with a Hubble law fail to explain these substructures. In contrast, both the morphology and kinematics of the conical flow can be explained by a steady conical magnetohydrodynamic (MHD) disk wind with foot-point radii r0= 0.7-3.4 au, a small magnetic level arm parameter lambda < 1.6), and quasi periodic brightness enhancements. These might be caused by the impact of jet bow shocks, source orbital motion caused by a 25 MJ companion at 50 au, or disk density perturbations accreting through the wind launching region. The large CO wind mass flux (four times the accretion rate onto the central star) can also be explained if the MHD disk wind removes most of the angular momentum required for steady disk accretion. Our results provide the strongest evidence so far for the presence of massive MHD disk winds in Class I sources with residual infall, and they suggest that the initial stages of planet formation take place in a highly dynamic environment.

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arXiv2022

The GRAVITY Young Stellar Object survey -- IX. Spatially resolved kinematics of hot hydrogen gas in the star/disk interaction region of T Tauri stars

Aims: We aim to spatially and spectrally resolve the Br-gamma hydrogen emission line with the methods of interferometry in order to examine the kinematics of the hydrogen gas emission region in the inner accretion disk of a sample of solar-like young stellar objects. The goal is to identify trends and categories among the sources of our sample and to discuss whether or not they can be tied to different origin mechanisms associated with Br-gamma emission in T Tauri stars, chiefly and most prominently magnetospheric accretion. Methods: We observed a sample of seven T Tauri stars for the first time with VLTI GRAVITY, recording spectra and spectrally dispersed interferometric quantities across the Br-gamma line in the NIR K-band. We use them to extract the size of the Br-gamma emission region and the photocenter shifts. To assist in the interpretation, we also make use of radiative transfer models of magnetospheric accretion to establish a baseline of expected interferometric signatures if accretion is the primary driver of Br-gamma emission. Results: From among our sample, we find that five of the seven T~Tauri stars show an emission region with a half-flux radius in the range broadly expected for magnetospheric truncation. Two of the five objects also show Br-gamma emission primarily originating from within the corotation radius, while two other objects exhibit extended emission on a scale beyond 10 R$_*$, one of them even beyond the K~band continuum half-flux radius of 11.3 R$_*$. Conclusions: We find strong evidence to suggest that for the two weakest accretors in the sample, magnetospheric accretion is the primary driver of Br-gamma radiation. The results for the remaining sources imply either partial or strong contributions coming from spatially extended emission components in the form of outflows, such as stellar or disk winds.

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arXiv2022

The Morphology of the HD 163296 jet as a window on its planetary system

HD163296 is a Herbig Ae star which drives a bipolar knotty jet with a total length of ~6000au. Strong evidence exists that the disk of HD163296 harbors planets. Studies have shown that the presence of companions around jet-driving stars could affect the morphology of the jets. This includes a `wiggling' of the jet axis and a periodicity in the positions of the jet knots. In this study we investigate the morphology (including the jet width and axis position) and proper motions of the HD163296 jets, and use our results to better understand the whole system.This study is based on optical integral-field spectroscopy observations obtained with VLT/MUSE in 2017. Using spectro-images and position velocity diagrams extracted from the MUSE data cube, we investigated the number and positions of the jet knots. A comparison was made to X-Shooter data collected in 2012 and the knot proper motions were estimated. The jet width and jet axis position with distance from the star were studied from the extracted spectro-images. We observe the merging of knots and identify two previously undetected knots. Measurements of the jet axis position reveal a similar pattern of deviation in all forbidden emission lines along the first 20 arc seconds of the jets. This result is interpreted as being due to asymmetric shocks and not due to a wiggling of the jet axis. The number of new knots detected and their positions challenge the 16-year knot ejection periodicity proposed in prior studies, arguing for a more complicated jet system than was previously assumed. We use the non-detection of a jet axis wiggling to rule out companions with a mass $>$0.1~\Msun\ and orbits between 1~au and 35~au. Any object inferred at these distances using other methods must be a brown dwarf or planet, otherwise it would have impacted the jet axis position. Both the precession and orbital motion scenarios are considered.

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arXiv2021

The GRAVITY Young Stellar Object survey. VII. The inner dusty disks of T Tauri stars

These protoplanetary disks in T Tauri stars play a central role in star and planet formation. We spatially resolve at sub-au scales the innermost regions of a sample of T Tauri's disks to better understand their morphology and composition. We extended our homogeneous data set of 27 Herbig stars and collected near-IR K-band observations of 17 T Tauri stars, spanning effective temperatures and luminosities in the ranges of ~4000-6000 K and ~0.4-10 Lsun. We focus on the continuum emission and develop semi-physical geometrical models to fit the interferometric data and search for trends between the properties of the disk and the central star. The best-fit models of the disk's inner rim correspond to wide rings. We extend the Radius-luminosity relation toward the smallest luminosities (0.4-10 Lsun) and find the R~L^(1/2) trend is no longer valid, since the K-band sizes measured with GRAVITY are larger than the predicted sizes from sublimation radius computation. No clear correlation between the K-band half-flux radius and the mass accretion rate is seen. Having magnetic truncation radii in agreement with the K-band GRAVITY sizes would require magnetic fields as strong as a few kG, which should have been detected, suggesting that accretion is not the main process governing the location of the half-flux radius of the inner dusty disk. Our measurements agree with models that take into account the scattered light. The N-to-K band size ratio may be a proxy for disentangling disks with silicate features in emission from disks with weak and/or in absorption silicate features. When comparing inclinations and PA of the inner disks to those of the outer disks (ALMA) in nine objects of our sample, we detect misalignments for four objects.

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arXiv2021

The GRAVITY Young Stellar Object survey VIII. Gas and dust faint inner rings in the hybrid disk of HD141569

The formation and evolution of planetary systems impact the primordial accretion disk. HD141569 is the only known pre-main sequence star characterized by a hybrid disk. Observations probed the outer-disk structure showing a complex system of rings and interferometric observations attempted to characterize its inner 5 au region, but derived limited constraints. The goal of this work was to explore with new high-resolution interferometric observations the properties of the dust and gas in the internal regions of HD141569. We observed HD141569 on mas scales with GRAVITY/VLTI in the near-infrared at low and high spectral resolution. We interpreted the visibilities and spectral energy distribution with geometrical models and radiative transfer techniques to constrain the dust emission. We analyzed the high spectral resolution quantities to investigate the properties of the Br-Gamma line emitting region. Thanks to the combination of three different epochs, GRAVITY resolves the inner dusty disk in the K band. Data modeling shows that an IR excess of about 6% is spatially resolved and that the origin of this emission is confined in a ring of material located at a radius of 1 au from the star with a width smaller than 0.3 au. The MCMax modeling suggests that this emission could originate from a small amount of QHPs, while large silicate grain models cannot reproduce at the same time the observational constraints on the properties of near-IR and mid-IR fluxes. The differential phases in the Br-Gamma line clearly show an S-shape that can be best reproduced witha gas disk in Keplerian rotation, confined within 0.09 au. This is also hinted at by the double-peaked Br-Gamma emission line shape. The modeling of the continuum and gas emission shows that the inclination and position angle of these two components are consistent with a system showing relatively coplanar rings on all scales.

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