arXiv subjects

Sacha Gavino

Publications and source records attributed to Sacha Gavino.

15 recordsLinked to original sources

arXiv2026

Orbital stability of compact three-planet systems III. The role of three-body resonances

Observational surveys show that at least ~ 30% of short-period multiplanetary systems host tightly packed planets, some of which are locked in stable chains of mean-motion resonances. Despite recent progress, the dynamical stability of these systems remains only partially understood. Numerical simulations have established a general exponential increase in system lifetime with orbital separation, with mean-motion resonances playing a key role in regulating stability. Tightly packed three-planet systems exhibit a distinctive behavior not seen in higher-multiplicity systems: a small yet significant region of phase space is anomalously stable. This study investigates the dynamics of extremely compact three-planet systems, focusing on anomalously long-lived configurations and their connection to resonant chains observed in exoplanetary systems. We perform numerical integrations of coplanar, initially circular, equal-mass three-planet systems over stellar-lifetime timescales and at high resolution in orbital separation, and interpret the results in the context of recent analytical work. We identify regions of phase space hosting anomalously stable orbits, including systems surviving multiple orders of magnitude longer than predicted by the exponential trend. We demonstrate a clear link between stability and isolated three-body mean-motion resonances, showing that extremely compact systems can remain stable when captured into a small subset of isolated zeroth-order resonances. Stability further depends on the initial orbital longitudes and on the interplay between the three-body and two-body resonance networks.

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arXiv2025

Early Planet Formation in Embedded Disks (eDisk). XX. Constraining the Chemical Tracers of Young Protostellar Sources

Recent studies indicate that the formation of planets in protoplanetary disks begins early in the embedded Class 0/I phases of protostellar evolution. The physical and chemical makeup of the embedded phase can provide valuable insights into the process of star and planet formation. This study aims to provide a thorough overview of the various morphologies for molecular emissions observed on disk scales toward nearby embedded sources. We present high angular resolution (0.1", 15 au) molecular line emissions for $^{12}$CO, $^{13}$CO, C$^{18}$O, SO, SiO, DCN, CH$_3$OH, H$_2$CO, and c-C$_3$H$_2$ towards 19 nearby protostellar sources in the context of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program "Early Planet Formation in Embedded Disks (eDisk)". Emissions in $^{12}$CO are seen towards all sources and primarily trace outflowing materials. A few sources also show high-velocity jets in SiO emission and high-velocity channel maps of $^{12}$CO. The $^{13}$CO and C$^{18}$O emissions are well-known tracers of high-density regions and trace the inner envelope and disk regions with clear signs of rotation seen at continuum scales. The large-scale emissions of $^{13}$CO also delineate the outflow cavity walls where the outflowing and infalling materials interact with each other, and exposure to UV radiation leads to the formation of hydrocarbons such as c-C$_3$H$_2$. Both DCN and CH$_3$OH, when detected, show compact emissions from the inner envelope and disk regions that peak at the position of the protostar. The CH$_3$OH emissions are contained within the region of DCN emissions, which suggests that CH$_3$OH traces the hot core regions. Likewise, a few sources also display emissions in CH$_3$OH towards the outflow. Both SO and H$_2$CO show complex morphology among the sources, suggesting that they are formed through multiple processes in protostellar systems.

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arXiv2025

Early Planet Formation in Embedded Disks (eDisk) XXII: Keplerian disk, disk structures and jets/outflows in the Class 0 protostar IRAS 04166+2706

We present ALMA observations of the Class 0 protostar IRAS 04166+2706, obtained as part of the ALMA large program Early Planet Formation in Embedded Disks (eDisk). These observations were made in the 1.3 mm dust continuum and molecular lines at angular resolutions of $\sim 0.05''$ ($\sim 8$ au) and $\sim 0.16''$ ($\sim25$ au), respectively. The continuum emission shows a disk-like structure with a radius of $\sim22$ au. Kinematical analysis of $^{13}$CO(2-1), C$^{18}$O(2-1), H$_2$CO (3$_{0,3}$-2$_{0,2}$), CH$_3$OH (4$_2$-3$_1$) emission demonstrates that these molecular lines trace the infalling-rotating envelope and possibly a Keplerian disk, enabling us to estimate the protostar mass to be $0.15 \rm{M_\odot} < \rm{M_\star} < 0.39 M_\odot$. The dusty disk is found to exhibit a brightness asymmetry along its minor axis in the continuum emission, probably caused by a flared distribution of the dust and the high optical depth of the dust emission. In addition, the CO(2-1) and SiO(5-4) emissions show knotty and wiggling motions in the jets. Our high angular resolution observations revealed the most recent mass ejection events, which have occurred within the last $\sim 25$ years.

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arXiv2025

Early Planet Formation in Embedded Disks (eDisk) XVII: A Compact but Structured Keplerian Disk and Large-scale Streamers Revealed in the Class I Protostellar System IRAS 04169+2702

We present high-resolution ($\sim$0.05"; 8 au) dust continuum and molecular line observations toward the Class I protostellar system IRAS 04169+2702 in the Taurus B213 region, as part of the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk). The 1.3-mm dust continuum emission traces a circumstellar disk with a central depression toward the protostar. Our VLA observations of the same target reveal a single central peak dominated by the free-free emission, which coincides with the depression of the thermal dust emission. The mean spectral index of the thermal dust emission from 1.3 mm to 1.4 cm is approximately 2.8, suggestive of the presence of grains grown to millimeter or centimeter sizes in the disk. Velocity gradients along the disk major axis are seen in emission from $^{12}$CO (2-1), $^{13}$CO (2-1), and C$^{18}$O (2-1) molecular lines. The position-velocity diagrams of these lines unveil a Keplerian-rotating disk with a radius of $\sim$21 au around a 1.3 $M_{\odot}$ protostar, as well as an infalling and rotating envelope with the angular momentum conserved. In addition to the compact disk, large-scale infalling spiral structures extending up to approximately 1400 au, streamers, are discovered in C$^{18}$O (2-1), SO (6$_5$-5$_4$), and H$_2$CO (3$_{0, 3}$-2$_{0, 2}$) as well as in the 1.3-mm continuum emission. Notably, in the region closer to the protostar, the spatial coincidence of C$^{18}$O and SO may indicate the presence of a shock related to accretion through the spiral arms.

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arXiv2024

UV-processing of icy pebbles in the outer parts of VSI-turbulent disks

Icy dust particles emerge in star-forming clouds and are subsequently incorporated in protoplanetary disks, where they coagulate into larger pebbles up to mm in size. In the disk midplane, ices are shielded from UV radiation, but moderate levels of disk turbulence can lift small particles to the disk surface, where they can be altered, or destroyed. Nevertheless, studies of comets and meteorites generally find that ices at least partly retained their interstellar medium (ISM) composition before being accreted onto these minor bodies. Here we model this process through hydrodynamical simulations with VSI-driven turbulence in the outer protoplanetary disk. We use the PLUTO code in a 2.5 D global accretion setup and include Lagrangian dust particles of 0.1 and 1 mm sizes. In a post-processing step, we use the RADMC3D code to generate the local UV radiation field to assess the level of ice processing of pebbles. We find that a small fraction ($\sim$17$\%$) of 100 $μ$m size particles are frequently lifted up to $Z/R=0.2$ which can result in the loss of their pristine composition as their residence time in this layer allows for effective CO and water photodissociation. The larger 1 mm size particles remain UV-shielded in the disk midplane throughout the dynamical evolution of the disk. Our results indicate that the assembly of icy bodies via the accretion of drifting mm-size icy pebbles can explain the presence of pristine ice from the ISM, even in VSI-turbulent disks. Nevertheless, particles $\leq$ 100 $μ$m experience efficient UV processing and may mix with unaltered icy pebbles, resulting in a less ISM-like composition in the midplane.

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arXiv2024

Early Planet Formation in Embedded Disks (eDisk). XI. A high-resolution view toward the BHR 71 Class 0 protostellar wide binary

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the binary Class 0 protostellar system BHR 71 IRS1 and IRS2 as part of the Early Planet Formation in Embedded Disks (eDisk) ALMA Large Program. We describe the $^{12}$CO ($J$=2--1), $^{13}$CO ($J$=2--1), C$^{18}$O ($J$=2--1), H$_2$CO ($J=3_{2,1}$--$2_{2,0}$), and SiO ($J$=5--4) molecular lines along with the 1.3 mm continuum at high spatial resolution ($\sim$0.08" or $\sim$5 au). Dust continuum emission is detected toward BHR 71 IRS1 and IRS2, with a central compact component and extended continuum emission. The compact components are smooth and show no sign of substructures such as spirals, rings or gaps. However, there is a brightness asymmetry along the minor axis of the presumed disk in IRS1, possibly indicative of an inclined geometrically and optically thick disk-like component. Using a position-velocity diagram analysis of the C$^{18}$O line, clear Keplerian motions were not detected toward either source. If Keplerian rotationally-supported disks are present, they are likely deeply embedded in their envelope. However, we can set upper limits of the central protostellar mass of 0.46 M$_\odot$ and 0.26 M$_\odot$ for BHR 71 IRS1 and BHR 71 IRS2, respectively. Outflows traced by $^{12}$CO and SiO are detected in both sources. The outflows can be divided into two components, a wide-angle outflow and a jet. In IRS1, the jet exhibits a double helical structure, reflecting the removal of angular momentum from the system. In IRS2, the jet is very collimated and shows a chain of knots, suggesting episodic accretion events.

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arXiv2024

Early Planet Formation in Embedded Disks (eDisk) XIV: Flared Dust Distribution and Viscous Accretion Heating of the Disk around R CrA IRS 7B-a

We performed radiative transfer calculations and observing simulations to reproduce the 1.3-mm dust-continuum and C$^{18}$O (2-1) images in the Class I protostar R CrA IRS7B-a, observed with the ALMA Large Program ``Early Planet Formation in Embedded Disks (eDisk)". We found that the dust disk model passively heated by the central protostar cannot reproduce the observed peak brightness temperature of the 1.3-mm continuum emission ($\sim$195 K), regardless of the assumptions about the dust opacity. Our calculation suggests that viscous accretion heating in the disk is required to reproduce the observed high brightness temperature. The observed intensity profile of the 1.3-mm dust-continuum emission along the disk minor axis is skewed toward the disk far side. Our modeling reveals that such an asymmetric intensity distribution requires flaring of the dust along the disk's vertical direction with the scale-height following $h/r \sim r^{0.3}$ as function of radius. These results are in sharp contrast to those of Class II disks, which show geometrically flat dust distributions and lower dust temperatures. From our modeling of the C$^{18}$O (2-1) emission, the outermost radius of the gas disk is estimated to be $\sim$80 au, larger than that of the dust disk ($\sim$62 au), to reproduce the observed distribution of the C$^{18}$O (2-1) emission in IRS 7B-a. Our modeling unveils a hot and thick dust disk plus a larger gas disk around one of the eDisk targets, which could be applicable to other protostellar sources in contrast to more evolved sources.

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arXiv2023

Early Planet Formation in Embedded Disks (eDisk) IX: High-resolution ALMA Observations of the Class 0 Protostar R CrA IRS5N and its surrounding

We present high-resolution, high-sensitivity observations of the Class 0 protostar RCrA IRS5N as part of the Atacama Large Milimeter/submilimeter Array (ALMA) large program Early Planet Formation in Embedded Disks (eDisk). The 1.3 mm continuum emission reveals a flattened continuum structure around IRS5N, consistent with a protostellar disk in the early phases of evolution. The continuum emission appears smooth and shows no substructures. However, a brightness asymmetry is observed along the minor axis of the disk, suggesting the disk is optically and geometrically thick. We estimate the disk mass to be between 0.007 and 0.02 M$_{\odot}$. Furthermore, molecular emission has been detected from various species, including C$^{18}$O (2$-$1), $^{12}$CO (2$-$1), $^{13}$CO (2$-$1), and H$_2$CO (3$_{0,3}-2_{0,2}$, 3$_{2,1}-2_{2,0}$, and 3$_{2,2}-2_{2,1}$). By conducting a position-velocity analysis of the C$^{18}$O (2$-$1) emission, we find that the disk of IRS5N exhibits characteristics consistent with Keplerian rotation around a central protostar with a mass of approximately 0.3 M$_{\odot}$. Additionally, we observe dust continuum emission from the nearby binary source, IRS5a/b. The emission in $^{12}$CO toward IRS5a/b seems to emanate from IRS5b and flow into IRS5a, suggesting material transport between their mutual orbits. The lack of a detected outflow and large-scale negatives in \tlvco~observed toward IRS5N suggests that much of the flux from IRS5N is being resolved out. Due to this substantial surrounding envelope, the central IRS5N protostar is expected to be significantly more massive in the future.

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arXiv2023

Early Planet Formation in Embedded Disks (eDisk). VII. Keplerian Disk, Disk Substructure, and Accretion Streamers in the Class 0 Protostar IRAS 16544-1604 in CB 68

We present observations of the Class 0 protostar IRAS 16544-1604 in CB 68 from the ''Early Planet Formation in Embedded Disks (eDisk)'' ALMA Large program. The ALMA observations target continuum and lines at 1.3-mm with an angular resolution of $\sim$5 au. The continuum image reveals a dusty protostellar disk with a radius of $\sim$30 au seen close to edge-on, and asymmetric structures both along the major and minor axes. While the asymmetry along the minor axis can be interpreted as the effect of the dust flaring, the asymmetry along the major axis comes from a real non-axisymmetric structure. The C$^{18}$O image cubes clearly show the gas in the disk that follows a Keplerian rotation pattern around a $\sim$0.14 $M_{\odot}$ central protostar. Furthermore, there are $\sim$1500 au-scale streamer-like features of gas connecting from North-East, North-North-West, and North-West to the disk, as well as the bending outflow as seen in the $^{12}$CO (2-1) emission. At the apparent landing point of NE streamer, there are SO (6$_5$-5$_4$) and SiO (5-4) emission detected. The spatial and velocity structure of NE streamer can be interpreted as a free-falling gas with a conserved specific angular momentum, and the detection of the SO and SiO emission at the tip of the streamer implies presence of accretion shocks. Our eDisk observations have unveiled that the Class 0 protostar in CB 68 has a Keplerian rotating disk with flaring and non-axisymmetric structure associated with accretion streamers and outflows.

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arXiv2023

Early Planet Formation in Embedded Disks (eDisk) III: A first high-resolution view of sub-mm continuum and molecular line emission toward the Class 0 protostar L1527 IRS

Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here, we present Atacama Large Millimeter/submillimeter Array (ALMA) observations of dust continuum at $\sim$0.06" (8 au) resolution and molecular line emission at $\sim$0.17" (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures, but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of $^{12}$CO, $^{13}$CO, C$^{18}$O, H$_2$CO, c-C$_3$H$_2$, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in $^{12}$CO. The $^{13}$CO brightness temperature and the H$_2$CO line ratio confirm that the disk is too warm for CO freeze out, with the snowline located at $\sim$350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk-envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk-envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100" or 14,000 au) outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

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arXiv2023

Early Planet Formation in Embedded Disks (eDisk). I. Overview of the Program and First Results

We present an overview of the Large Program, ``Early Planet Formation in Embedded Disks (eDisk)'', conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The ubiquitous detections of substructures, particularly rings and gaps, in protoplanetary disks around T Tauri stars raise the possibility that at least some planet formation may have already started during the embedded stages of star formation. In order to address exactly how and when planet formation is initiated, the program focuses on searching for substructures in disks around 12 Class 0 and 7 Class I protostars in nearby ($< $200 pc) star-forming regions through 1.3 mm continuum observations at a resolution of $\sim7$ au (0.04"). The initial results show that the continuum emission, mostly arising from dust disks around the sample protostars, has relatively few distinctive substructures, such as rings and spirals, in marked contrast to Class II disks. The dramatic difference may suggest that substructures quickly develop in disks when the systems evolve from protostars to Class II sources or alternatively that high optical depth of the continuum emission could obscure internal structures. Kinematic information obtained through CO isotopologue lines and other lines reveals the presence of Keplerian disks around protostars, providing us with crucial physical parameters, in particular, the dynamical mass of the central protostars. We describe the background of the eDisk program, the sample selection and their ALMA observations, the data reduction, and also highlight representative first-look results.

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arXiv2023

Early Planet Formation in Embedded Disks (eDisk). II. Limited Dust Settling and Prominent Snow Surfaces in the Edge-on Class I Disk IRAS 04302+2247

While dust disks around optically visible, Class II protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. As part of the Atacama Large Millimeter/submillimeter Array (ALMA) large program, Early Planet Formation in Embedded Disks, we analyze the edge-on, embedded, Class I protostar IRAS 04302+2247, also nicknamed the ``Butterfly Star." With a resolution of 0.05" (8~au), the 1.3 mm continuum shows an asymmetry along the minor axis which is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. There is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. With 0.1" (16~au) resolution, we resolve the 2D snow surfaces, i.e., the boundary region between freeze-out and sublimation, for $^{12}$CO $J$=2--1, $^{13}$CO $J$=2--1, C$^{18}$O $J$=2--1, $H_{2}$CO $J$=$3_{0,3}$--$2_{0,2}$, and SO $J$=$6_{5}$--$5_{4}$, and constrain the CO midplane snow line to $\sim 130$ au. We find Keplerian rotation around a protostar of $1.6 \pm 0.4 M_{\odot}$ using C$^{18}$O. Through forward ray-tracing using RADMC-3D, we find that the dust scale height is $\sim 6$ au at a radius of 100~au from the central star and is comparable to the gas pressure scale height. The results suggest that the dust of this Class~I source has yet to vertically settle significantly.

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arXiv2022

A VLA View of the Flared, Asymmetric Disk Around the Class 0 Protostar L1527 IRS

We present high resolution Karl G. Jansky Very Large Array (VLA) observations of the protostar L1527 IRS at 7 mm, 1.3 cm, and 2 cm wavelengths. We detect the edge-on dust disk at all three wavelengths and find that it is asymmetric, with the southern side of the disk brighter than the northern side. We confirm this asymmetry through analytic modeling and also find that the disk is flared at 7 mm. We test the data against models including gap features in the intensity profile, and though we cannot rule such models out, they do not provide a statistically significant improvement in the quality of fit to the data. From these fits, we can however place constraints on allowed properties of any gaps that could be present in the true, underlying intensity profile. The physical nature of the asymmetry is difficult to associate with physical features due to the edge-on nature of the disk, but could be related to spiral arms or asymmetries seen in other imaging of more face-on disks.

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arXiv2021

Orbital stability of compact three-planet systems, I: Dependence of system lifetimes on initial orbital separations and longitudes

We explore the orbital dynamics of systems consisting of three planets, each as massive as the Earth, on coplanar, initially circular, orbits about a star of one solar mass. The initial semimajor axes of the planets are equally spaced in terms of their mutual Hill radius, which is equivalent to a geometric progression of orbital periods for small planets of equal mass. Our simulations explore a wide range of spacings of the planets, and were integrated for virtual times of up to 10 billion years or until the orbits of any pair of planets crossed. We find the same general trend of system lifetimes increasing exponentially with separation between orbits seen by previous studies of systems of three or more planets. One focus of this paper is to go beyond the rough trends found by previous numerical studies and quantitatively explore the nature of the scatter in lifetimes and the destabilizing effects of mean motion resonances. In contrast to previous results for five-planet systems, a nontrivial fraction of three-planet systems survive at least several orders of magnitude longer than most other systems with similar initial separation between orbits, with some surviving $10^{10}$ years at much smaller orbital separations than any found for five-planet systems. Substantial shifts in the initial planetary longitudes cause a scatter of roughly a factor of two in system lifetime, whereas the shift of one planet's initial position by 100 meters along its orbit results in smaller changes in the logarithm of the time to orbit crossing, especially for systems with short lifetimes.

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arXiv2021

Orbital stability of compact three-planet systems, II: Post-instability impact behaviour

Recent observational missions have uncovered a significant number of compact multi-exoplanet systems. The tight orbital spacing of these systems has led to much effort being applied to the understanding of their stability; however, a key limitation of the majority of these studies is the termination of simulations as soon as the orbits of two planets cross. In this work we explore the stability of compact, three-planet systems and continue our simulations all the way to the first collision of planets to yield a better understanding of the lifetime of these systems. We perform over $25,000$ integrations of a Sun-like star orbited by three Earth-like secondaries for up to a billion orbits to explore a wide parameter space of initial conditions in both the co-planar and inclined cases, with a focus on the initial orbital spacing. We calculate the probability of collision over time and determine the probability of collision between specific pairs of planets. We find systems that persist for over $10^8$ orbits after an orbital crossing and show how the post-instability survival time of systems depends upon the initial orbital separation, mutual inclination, planetary radius, and the closest encounter experienced. Additionally, we examine the effects of very small changes in the initial positions of the planets upon the time to collision and show the effect that the choice of integrator can have upon simulation results. We generalise our results throughout to show both the behaviour of systems with an inner planet initially located at $1$ AU and $0.25$ AU.

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