arXiv subjects

Pablo Rivière-Marichalar

Publications and source records attributed to Pablo Rivière-Marichalar.

11 recordsLinked to original sources

arXiv2026

Azimuthal molecular variations in the AB Aur planet-forming disk

Late infall episodes are emerging as an important driver of disk evolution. Observed as filamentary streamers in molecular lines and scattered light, such accretion perturbs disk structures, yet its chemical consequences remain unconstrained. We present NOEMA 1.2 mm observations of AB Aur, a structured young Herbig disk showing evidence for ongoing infall and planet formation. We detect azimuthal chemical diversity: SO emission is enhanced in the northern disk near the inferred streamer-disk interaction region, while C$_2$H peaks on the opposite southern side; CS forms a nearly axisymmetric ring. HCN and HCO$^+$ peak near the dust continuum overdensity in the dust ring. Rotational diagram analyses show higher SO rotational temperatures and column densities in the north, whereas CS remains axisymmetric with lower rotational temperatures, suggesting that the species probe different disk layers. For C$_2$H, temperature variations may contribute to but cannot fully explain the asymmetries. The HCO$^+$/H$^{13}$CO$^+$ line ratio indicates that HCO$^+$ is optically thick across the molecular ring, while the elevated ratio inside the cavity suggests enhanced gas-phase $^{12}$C/$^{13}$C, consistent with isotope-selective photodissociation. Comparison with chemical models favors gas-phase C/O ratios near or above unity, with higher effective C/O in the C$_2$H-bright sector. We discuss two origins for the chemical asymmetries: (i) infall-induced heating and desorption of O-bearing ices enhance SO and lower gas-phase C/O near the streamer's impact site, and (ii) planet-driven substructures and localized heating or enhanced UV irradiation promote hydrocarbon-rich chemistry in the southern disk. These results highlight that environmental accretion and planet formation can jointly imprint azimuthal variations in disk chemistry, with potential impacts on forming planets' compositions.

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arXiv2026

Unveiling Complex Chemistry in Planet-forming Disks with the SKAO

The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. In recent years, we have made huge progress in characterizing disk chemistry. (Sub-)millimeter interferometers, such as ALMA, allowed us to detect emission lines from simple to complex organic molecules and to probe their radial and vertical distribution in disks. On the other hand, JWST has started to unveil the composition of disk ices, and line emission from the innermost disk regions. The advent of SKA will open new domains in the field, by observing emission lines from heavier molecules including heavy carbon chains and rings, and prebiotic molecules with peak emission in the cm range. Moreover, SKA will probe molecular emission from regions which are obscured by dust opacity at mm wavelengths, hence from the disk midplane, and often from the inner 30 au region. These observations will constrain the initial conditions for disk evolution and planet formation, allowing us to predict the chemical composition of the forming planets and their atmospheres. Comparison with forthcoming results on exoplanet atmospheres and on the chemistry of pristine bodies in the Solar System will provide new hints on the origin and evolution of planetary systems including our own.

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arXiv2026

AB Aur, a Rosetta stone for studies of planet formation (IV): C/O estimates from CS and SO interferometric observations

Context. Protoplanetary disks are the birthplace of planets. As such, they set the initial chemical abundances available for planetary atmosphere formation. Thus, studying elemental abundances, molecular compositions, and abundance ratios in protoplanetary disks is key to linking planetary atmospheres to their formation sites. Aims. We aim to derive the sulfur abundance and the C/O ratio in the AB Aur disk using interferometric observations of CS and SO. Methods. New NOEMA observations of CS 3-2 towards AB Aur are presented. We used velocity-integrated intensity maps to determine the inclination and position angles. Keplerian masks were constructed for all observed species to assess the presence of non-Keplerian motions. We use the CS/SO ratio to study the C/O ratio. We compare our present and previous interferometric observations of AB Aur with a NAUTILUS disk model to gain insight into the S elemental abundance and C/O ratio. Results. We derive an observational CS/SO ratio ranging from 1.8 to 2.6. Only NAUTILUS models with C/O > 1 can reproduce such ratios. The comparison with models points to strong sulfur depletion, with [S/H]=8e-8, but we note that no single model can simultaneously fit all observed species.

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arXiv2025

The sulfur plume in the Horsehead nebula: New detections of S$_2$H, SH$^+$, and CO$^+$

Sulfur is essential for life, but its abundance and distribution in the interstellar medium remain uncertain, with over 90% of sulfur undetected in cold molecular clouds. Sulfur allotropes (S$_{\rm n}$) have been proposed as possible reservoirs, but the only detected interstellar molecule with a disulfide bond is S$_2$H in the Horsehead Nebula, making the estimation of sulfur chains abundances difficult. Here we present total-power ALMA images of H$_2$S, S$_2$H, SO$_2$, CO$^+$, and SH$^+$ towards the Horsehead nebula. These observations, with unprecedented sensitivity (rms $\sim$ 1.5 mK), provide the first detections of SH$^+$ and CO$^+$ in this region, together with the identification of a new S$_2$H line. The comparison of the spectroscopic images of H$_2$S, S$_2$H, SO$_2$, CO$^+$ and SH$^+$ shows that the S$_2$H emission originates from a warm gas layer adjacent to the photodissociation front. The emission peak of S$_2$H is offset from those of reactive ions such as SH$^+$, CO$^+$, and SO$^+$, suggesting that gas-phase reactions involving SH$^+$ and H$_2$S are not the dominant formation pathway of S$_2$H. Instead, we propose that S$_2$H is desorbed from irradiated grain surfaces by non-thermal processes. The SH$^+$ detection indicates that sulfur is not significantly depleted at the UV-irradiated edge of the molecular cloud, arguing against a major refractory sulfur reservoir in the interior of molecular clouds.

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arXiv2025

Hints of Disk Substructure in the First Brown Dwarf with a Dynamical Mass Constraint

We present high-resolution ALMA observations at 0.89 mm of the Class II brown dwarf 2MASS J04442713+2512164 (2M0444), achieving a spatial resolution of 0$.\!\!^{\prime\prime}$046 ($\sim$6.4 au at the distance to the source). These observations targeted continuum emission together with $^{12}$CO (3-2) molecular line. The line emission traces a Keplerian disk, allowing us to derive a dynamical mass between 0.043-0.092 M${_{\odot}}$ for the central object. We constrain the gas-to-dust disk size ratio to be $\sim$7, consistent with efficient radial drift. However, the observed dust emission suggest that a dust trap is present, enough to retain some dust particles. We perform visibility fitting of the continuum emission, and under the assumption of annular substructure, our best fit shows a gap and a ring at 98.1$^{+4.2}_{-8.4}$ mas ($\sim$14 au) and 116.0$^{+4.2}_{-4.8}$ mas ($\sim$16 au), respectively, with a gap width of 20 mas ($\sim$3 au). To ensure robustness, the data were analyzed through a variety of methods in both the image and uv plane, employing multiple codes and approaches. This tentative disk structure could be linked to a possible planetary companion in the process of formation. These results provide the first dynamical mass of the lowest mass object to date, together with the possible direct detection of a substructure, offering new insights into disk dynamics and planet formation in the very low-mass regime. Future higher spatial resolution ALMA observations will be essential to confirm these findings and further investigate the link between substructures and planet formation in brown dwarf disks.

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arXiv2023

AB Aur, a Rosetta stone for studies of planet formation (III): continuum observations at 2 and 7 mm

Observational constraints on dust properties in protoplanetary disks are key to better understanding disks' evolution. We continue our exploration of the protoplanetary disk around AB Aur by characterizing its dust properties. We present ALMA observations at 2.2 mm and VLA observations at 6.8 mm. Together with previous ALMA and NOEMA observations at 0.87 and 1.1 mm, these observations are used to compute global spectral index profiles as well as spectral index maps. On the interpretation side, we present the results of a simple isothermal slab model to help constrain dust properties along the ring of continuum emission. We also present results of dust radiative transfer calculations based on a disc-planet hydrodynamical simulation to explain how the azimuthal contrast ratio of the ring emission varies with millimeter wavelength. The spectral energy distribution and the radial profiles of the spectral index indicate that the radiation from the compact source towards the center is not dominated by dust thermal emission, but most likely by free-free emission originating in the radio jet: it constitutes 93% of the emission at 6.8 mm, and 37% at 0.87 mm. The protoplanetary disk has a typical spectral index of 2.3. We estimate a dust disk mass of 8$\rm \times 10^{-5}$ M$\rm _{\odot}$ which, assuming a mean gas-to-dust ratio of 40, gives a total disk mass of 3.2$\rm \times 10^{-3}$ M$\rm _{\odot}$. The azimuthal contrast ratio of the ring outside the millimeter cavity is smaller at 2.2 mm than at 1.1 mm, in agreement with previous findings. The VLA image shows several knots of $5σ$ emission all along the ring, which are consistent with the ring emission being nearly axisymmetric at that wavelength. The decrease in the azimuthal contrast ratio of the ring emission from 0.87 to 6.8 mm can be explained by a dust-losing decaying vortex at the outer edge of a planet gap.

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arXiv2022

AB Aur, a Rosetta stone for studies of planet formation (II): H$_2$S detection and sulfur budget

The sulfur abundance is poorly known in most environments. Yet, deriving the sulfur abundance is key to understanding the evolution of the chemistry from molecular clouds to planetary atmospheres. We present observations of H$_2$S 110-101 at 168.763 GHz toward the Herbig Ae star AB Aur. We aim to study the abundance of sulfuretted species toward AB Aur and to constrain how different species and phases contribute to the sulfur budget. We present new NOrthern Extended Millimeter Array (NOEMA) interferometric observations of the continuum and H$_2$S 110-101 line at 168.763 GHz toward AB Aur. We derived radial and azimuthal profiles and used them to compare the geometrical distribution of different species in the disk. Assuming local thermodynamical equilibrium (LTE), we derived column density and abundance maps for H$_2$S, and we further used Nautilus to produce a more detailed model of the chemical abundances at different heights over the mid-plane at a distance of r=200 au. We have resolved H$_2$S emission in the AB Aur protoplanetary disk. The emission comes from a ring extending from 0.67 (109 au) to 1.69 (275 au). Under simple assumptions, we derived an abundance of (3.1$\pm$0.8)$\times$10$\rm ^{-10}$ with respect to H nuclei, which we compare with Nautilus models to deepen our understanding of the sulfur chemistry in protoplanetary disks. Chemical models indicate that H$-2$S is an important sulfur carrier in the solid and gas phase. We also find an important transition at a height of 12 au, where the sulfur budget moves from being dominated by ice species to being dominated by gas species. Studying sulfuretted species in detail in the different phases of the interstellar medium is key to solving the issue.

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arXiv2021

The search for gas in debris discs: ALMA detection of CO gas in HD 36546

Debris discs represent the last stages of planet formation and as such are expected to be depleted of primordial gas. Nonetheless, in the last few years the presence of cold gas has been reported in $\sim$ 20 debris discs from far-IR to (sub-)mm observations and hot gas has been observed in the optical spectra of debris discs for decades. While the origin of this gas is still uncertain, most evidences point towards a secondary origin, as a result of collisions and evaporation of small bodies in the disc. In this paper, we present ALMA observations aimed at the detection of CO gas in a sample of 8 debris discs with optical gas detections. We report the detection of CO ($^{12}$CO and $^{13}$CO) gas in HD 36546, the brightest and youngest disc in our sample, and provide upper limits to the presence of gas in the remaining seven discs.

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arXiv2021

Observational signatures of eccentric Jupiters inside gas cavities in protoplanetary discs

Predicting how a young planet shapes the gas and dust emission of its parent disc is key to constraining the presence of unseen planets in protoplanetary disc observations. We investigate the case of a 2 Jupiter mass planet that becomes eccentric after migrating into a low-density gas cavity in its parent disc. Two-dimensional hydrodynamical simulations are performed and post-processed by three-dimensional radiative transfer calculations. In our disc model, the planet eccentricity reaches ~0.25, which induces strong asymmetries in the gas density inside the cavity. These asymmetries are enhanced by photodissociation and form large-scale asymmetries in 12CO J=3-2 integrated intensity maps. They are shown to be detectable for an angular resolution and a noise level similar to those achieved in ALMA observations. Furthermore, the planet eccentricity renders the gas inside the cavity eccentric, which manifests as a narrowing, stretching and twisting of iso-velocity contours in velocity maps of 12CO J=3-2. The planet eccentricity does not, however, give rise to detectable signatures in 13CO and C18O J=3-2 inside the cavity because of low column densities. Outside the cavity, the gas maintains near-circular orbits, and the vertically extended optically thick CO emission displays a four-lobed pattern in integrated intensity maps for disc inclinations > 30 degrees. The lack of large and small dust inside the cavity in our model further implies that synthetic images of the continuum emission in the sub-millimetre, and of polarized scattered light in the near-infrared, do not show significant differences when the planet is eccentric or still circular inside the cavity.

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arXiv2019

Gas accretion within the dust cavity in AB Aur

AB Aur is a Herbig Ae star hosting a well-known transitional disk. Because of its proximity and low inclination angle, it is an excellent object to study planet formation. Our goal is to investigate the chemistry and dynamics of the molecular gas component in the AB Aur disk, and its relation with the prominent horseshoe shape observed in continuum mm emission. We used the NOEMA interferometer to map with high angular resolution the J = 3-2 lines of HCO+ and HCN. By combining both, we can gain insight into the AB Aur disk structure. Chemical segregation is observed in the AB Aur disk: HCO+ shows intense emission toward the star position, at least one bright molecular bridge within the dust cavity, and ring-like emission at larger radii, while HCN is only detected in an annular ring that is coincident with the dust ring and presents an intense peak close to the dust trap. We use HCO+ to investigate the gas dynamics inside the cavity. The observed bright HCO+ bridge connects the compact central source with the outer dusty ring. This bridge can be interpreted as an accretion flow from the outer ring to the inner disk/jet system proving gas accretion through the cavity.

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arXiv2014

The Herschel/PACS view of the Cep OB2 region: Global protoplanetary disk evolution and clumpy star formation

(Abridged) We use Herschel PACS observations at 70 and 160$μ$m to probe the protoplanetary disks around young stars in the CepOB2 clusters Tr37 and NGC7160 and to trace the small-scale cloud structure. We detect 95 protoplanetary disks at 70$μ$m, 41 at 160$μ$m, and obtain upper limits for over 130 objects. The detection fraction at 70$μ$m depends on the spectral type (88% for K4 or earlier, 17% for M3 or later stars) and on the disk type ($\sim$50% for full and pre-transitional disks, $\sim$35% for transitional disks, no low-excess/depleted disks detected). Non-accreting disks are consistent with significantly lower masses. Accreting transition and pre-transition disks have higher 70$μ$m excesses than full disks, suggestive of more massive, flared and/or thicker disks. Herschel data also reveal several mini-clusters in Tr37, small, compact structures containing a few young stars surrounded by nebulosity. Far-IR data are an excellent probe of the evolution of disks that are too faint for submillimetre observations. We find a strong link between far-IR emission and accretion, and between the inner and outer disk structure. Herschel confirms the dichotomy between accreting and non-accreting transition disks. Substantial mass depletion and global evolution need to occur to shut down accretion in a protoplanetary disk, even if the disk has inner holes. Disks likely follow different evolutionary paths: Low disk masses do not imply opening inner holes, and having inner holes does not require low disk masses. The mini-clusters reveal multi-episodic star formation in Tr37. The long survival of mini-clusters suggest that they formed from the fragmentation of the same core. Their various morphologies favour different formation/triggering mechanisms acting within the same cluster. Herschel also unveils what could be the first heavy mass loss episode of the O6.5 star HD206267.

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