arXiv subjects

C. Bergez-Casalou

Publications and source records attributed to C. Bergez-Casalou.

5 recordsLinked to original sources

arXiv2026

Impact of accretion variability on the CO emission of a disk around a very-low-mass star with JWST

Studying the structure of very-low-mass stars ($M_\star<0.2M_\odot$) protoplanetary disk is crucial to understand the formation of Earth-like planets. In this paper, we characterize the innermost regions of the disk around a known very-low-mass star, 2MASS J16053215-1933159 (J1605 hereafter), by analyzing new JWST/NIRSpec observations taken in 2024, 2 years after a first observation with JWST/MIRI. We find that between the two epochs (2022 \& 2024), the CO flux is reduced by a factor $\sim 3$, the flux of the HI 10-6 line seen by both NIRSpec and MIRI is reduced by a factor $\sim13$, and the total continuum density flux is reduced by $\sim 15 \%$. The accretion rate derived from individual HI lines is consistent with a decrease of a factor $\sim13$ in 2 years. After correcting the spectrum from the CO absorption present in J1605 stellar photosphere, we find that the decrease of the disk's CO emission is consistent with a CO gas of same column density and temperature at each epoch, but originating from a smaller emitting area when the accretion rate is low. While warm hydrocarbons ($\simeq 500~$K) are detected with MIRI-MRS with extremely high column densities of $\rm C_2H_2$, no hydrocarbons features are seen with NIRSpec. We propose that non-LTE effects quench the near-IR emission of hydrocarbons in the warm reservoir. The variation of the accretion luminosity of J1605 correlates with the variation of its fundamental CO luminosity in a similar way as in T-Tauri stars, supporting the idea that very-low-mass stars could be seen as scaled-down versions of T-Tauri stars. The detection of the emission of the fundamental band of CO in disks around cold objects is challenging because of the presence of CO absorption in their photosphere. Future observations (e.g., with ELT/METIS) looking for such emission will require robust ways to constrain the photosphere emission.

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arXiv2024

Observing planetary gaps in the gas of debris disks

Recent ALMA observations discovered consequent amounts (i.e., up to a few $10^{-1}\; \rm M_\oplus$) of CO gas in debris disks that were expected to be gas-free. This gas is in general estimated to be mostly composed of CO, C, and O (i.e., $\rm H_2$-poor), unlike the gas present in protoplanetary disks ($\rm H_2$-rich). At this stage, the majority of planet formation already occurred, and giant planets might be evolving in these disks. While planets have been directly observed in debris disks (e.g., $β$ Pictoris), their direct observations are challenging due to the weak luminosity of the planets. In this paper, with the help of hydrodynamical simulations (with FARGO3D) coupled with a radiative transfer code (RADMC-3D) and an observing tool (CASA), we show that planet-gas interactions can produce observable substructures in this late debris disk stage. While it is tricky to observe gaps in the CO emission of protoplanetary disks, the unique properties of the gaseous debris disks allow us to observe planetary gaps in the gas. Depending on the total mass of the gaseous debris disk, kinks can also be observed. We derive a simple criterion to estimate in which conditions gaps would be observable and apply it to the known gaseous debris disk surrounding HD138813. In our framework, we find that planets as small as $0.5 \; \rm M_J$ can produce observable gaps and investigate under which conditions (i.e., gas and planets characteristics) the substructure become observable with ALMA. The first observations of planet-gas interactions in debris disks can lead to a new way to indirectly detect exoplanets, reaching a population that could not be probed before, such as giant planets that are too cold to be detected by direct imaging.

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arXiv2022

Constraining giant planet formation with synthetic ALMA images of the Solar System's natal protoplanetary disk

New ALMA observations of protoplanetary disks allow us to probe planet formation in other systems, giving us new constraints on planet formation processes. Meanwhile, studies of our own Solar System rely on constraints derived in a completely different way. However, it is still unclear what features the Solar System's disk could have produced during its gas phase. By running 2D isothermal hydro-simulations and a dust evolution model, we derive synthetic images at 1.3 mm wavelength using the radiative transfer code RADMC3D. We find that the embedded multiple giant planets strongly perturb the radial gas velocities of the disk, creating traffic jams in the dust. They produce over-densities different from the ones created by pressure traps and located away from the planets' positions in the disk. By deriving the images at 1.3mm from these dust distributions, we show that the traffic jams, observable with a high resolution, further blur the link between the number of gaps and rings in disks and the number of embedded planets. We additionally show that a system of 3 compact giant planets does not automatically produce bright outer rings at large radii in the disk. This means that high resolution observations of disks of various sizes are needed to distinguish between different giant planet formation scenarios during the disk phase, where the giants form either in the outer regions of the disks or in the inner regions. Finally, we find that, even when the dust temperature is determined self-consistently, the dust masses derived observationally might be off by up to a factor of ten compared to the dust contained in our simulations due to the creation of optically thick regions. Our study clearly shows that in addition to the constraints from exoplanets and the Solar System, ALMA has the power to constrain different stages of planet formation already during the first few million years.

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arXiv2021

Perturbers: SPHERE detection limits to planetary-mass companions in protoplanetary disks

The detection of a wide range of substructures such as rings, cavities and spirals has become a common outcome of high spatial resolution imaging of protoplanetary disks, both in the near-infrared scattered light and in the thermal millimetre continuum emission. The most frequent interpretation of their origin is the presence of planetary-mass companions perturbing the gas and dust distribution in the disk (perturbers), but so far the only bona-fide detection has been the two giant planets around PDS 70. Here, we collect a sample of 15 protoplanetary disks showing substructures in SPHERE scattered light images and present a homogeneous derivation of planet detection limits in these systems. We also estimate the mass of these perturbers through a Hill radius prescription and a comparison to ALMA data. Assuming that one single planet carves each substructure in scattered light, we find that more massive perturbers are needed to create gaps within cavities than rings, and that we might be close to a detection in the cavities of RX J1604, RX J1615, Sz Cha, HD 135344B and HD 34282. We reach typical mass limits in these cavities of 3-10 Mjup. For planets in the gaps between rings, we find that the detection limits of SPHERE are about an order of magnitude away in mass, and that the gaps of PDS 66 and HD 97048 seem to be the most promising structures for planet searches. The proposed presence of massive planets causing spiral features in HD 135344B and HD 36112 are also within SPHERE's reach assuming hot-start models.These results suggest that current detection limits are able to detect hot-start planets in cavities, under the assumption that they are formed by a single perturber located at the centre of the cavity. More realistic planet mass constraints would help to clarify whether this is actually the case, which might point to perturbers not being the only way of creating substructures.

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arXiv2020

Influence of planetary gas accretion on the shape and depth of gaps in protoplanetary discs

It is widely known that giant planets have the capacity to open deep gaps in their natal gaseous protoplanetary discs. It is unclear, however, how gas accretion onto growing planets influences the shape and depth of their growing gaps. We performed isothermal hydrodynamical simulations with the Fargo-2D1D code, which assumes planets accreting gas within full discs that range from 0.1 to 260 AU. The gas accretion routine uses a sink cell approach, in which different accretion rates are used to cope with the broad range of gas accretion rates cited in the literature. We find that the planetary gas accretion rate increases for larger disc aspect ratios and greater viscosities. Our main results show that gas accretion has an important impact on the gap-opening mass: we find that when the disc responds slowly to a change in planetary mass (i.e., at low viscosity), the gap-opening mass scales with the planetary accretion rate, with a higher gas accretion rate resulting in a larger gap-opening mass. On the other hand, if the disc response time is short (i.e., at high viscosity), then gas accretion helps the planet carve a deep gap. As a consequence, higher planetary gas accretion rates result in smaller gap-opening masses. Our results have important implications for the derivation of planet masses from disc observations: depending on the planetary gas accretion rate, the derived masses from ALMA observations might be off by up to a factor of two. We discuss the consequences of the change in the gap-opening mass on the evolution of planetary systems based on the example of the grand tack scenario. Planetary gas accretion also impacts stellar gas accretion, where the influence is minimal due to the presence of a gas-accreting planet.

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