arXiv subjects

Marija R. Jankovic

Publications and source records attributed to Marija R. Jankovic.

16 recordsLinked to original sources

arXiv2026

The ALMA View of the Edge-on Gomez's Hamburger System: A Highly-Dynamic, Asymmetric Protoplanetary Disk Reveals the Earliest Phases of Giant Planet Formation

Chemical tracers provide some of the strongest observational signatures of ongoing planet formation and localized dynamical perturbations in protoplanetary disks. In particular, sulfur-bearing molecules are predicted to be enhanced in regions of shock heating, ice sublimation, and gravitational instability. Here, we present high-angular-resolution ($\approx$0.$^{\prime\prime}$2) Atacama Large Millimeter/submillimeter Array observations of $^{12}$CO J=3-2, $^{13}$CO J=3-2, CS J=7-6, and SO J$_{\rm N}$=8$_8$-7$_7$ toward the large, edge-on Gomez's Hamburger ('GoHam'; IRAS 18059-3211) disk. We detect a narrow, one-sided arc of SO emission that peaks near a previously-identified gas over-density, suggesting localized heating around an early-stage giant protoplanet or disk fragment. The edge-on geometry of GoHam enables us to place this chemical signature in the broader context of the disk gas and dust structure. To do so, we map the vertical distribution of molecular gas relative to millimeter- and (sub)-micron-sized dust, identify a pronounced north-south continuum asymmetry, and detect non-Keplerian $^{12}$CO and $^{13}$CO emission indicative of a disk wind. We also derive a dynamical stellar mass of 2.2 $\pm$ 0.5 M$_{\odot}$ and a revised dust-extinction-map-based distance of 139 $\pm$ 24 pc, which places GoHam in the outskirts of the Scorpius-Centaurus association. Together, these observations reveal a highly dynamic disk in which localized sulfur chemistry may trace one of the earliest observable stages of wide-separation giant planet formation.

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arXiv2026

Viscously Stirring Particle Disks into Lorentzians and Gaussians to Infer Dynamical and Collisional Masses (ARKS XIII)

Disks (Keplerian or otherwise, particulate or fluid) are often assumed to have densities that drop off vertically as Gaussians. Recent mm-wave imaging of circumstellar debris disks contradicts this assumption, revealing vertical profiles in dust that resemble Lorentzians. As part of the ARKS ALMA Large Program, we show how Lorentzians and Gaussians define an evolutionary sequence for disks of gravitationally scattering (viscously stirring) particles. When orbits are crossing and eccentricities $e \gg$ inclinations $i$, each scattering can change a particle's inclination by $\pm \,Δi \propto i$. A random walk with fixed steps in $Δi/i = Δ\ln i$ produces a thick, log normal tail at large $i$ that leads to Lorentzian tails in density. This result holds independent of the origin of the large eccentricities, which may characterize either the stirrers or the objects being stirred; what matters is that relative motions parallel to the disk midplane are faster than perpendicular motions, and that vertical displacements during encounters are smaller than horizontal displacements. After enough scatterings, $i$ comes into equipartition with $e$, $Δi$ stops exponentiating, and the vertical density relaxes to a Gaussian. We identify four regimes of dispersion-dominated viscous stirring, three of which are out-of-equipartition and where $i$ is stirred faster than $e$. The stirrers for ARKS debris disks may range from Pluto to a few times Mars in size, and be sufficiently few as to be collisionless. Or the stirrers may be even smaller, and be so numerous and collide so frequently that they source the collisional cascades that produce observable dust.

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arXiv2026

An SMA Molecular Inventory of the Edge-on Protoplanetary Disk Gomez's Hamburger

Gomez's Hamburger (IRAS 18059-3211, GoHam) is a massive, edge-on protoplanetary disk that is potentially gravitationally unstable and hosts an overdensity that may be the site of a forming giant planet, making it a particularly interesting source for the study of planet formation in the direct collapse scenario. In this study, we present a molecular inventory of GoHam's disk combining several Submillimeter Array observations for a wideband survey at an angular resolution on the order of ~1 arcsecond. We detect 11 different molecules, including 15 individual lines, and measure their disk-integrated fluxes. We also infer column densities for several species over a range of fixed excitation temperatures. We find that the molecular inventory of GoHam and the inferred column densities for select molecules are broadly consistent with the general population of large protoplanetary disks. We explore the putative gravitational instability (GI) in GoHam's disk via possible enhancements in the gas-phase H$_2$CO abundance, but find no definitive evidence of GI. The results of this study can guide future, higher-resolution studies of GoHam, as well as efforts to characterize the giant protoplanet candidate GoHam b.

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arXiv2026

The multi-wavelength vertical structure of the archetypal $β$ Pictoris debris disk

Thermal imaging of debris disks is resolving the vertical height in an increasing number of systems, enabling the use of the vertical structure to decode the dynamical state of the planetary system. In this study, we examine the multi-wavelength structure of the archetypical edge-on debris disk of $β$ Pic, extensive imaging of which across mid-infrared to millimeter wavelengths makes it the prime system to study the vertical height across different grain size populations. We non-parametrically modelled the radial profiles and constrained the vertical height at each wavelength while taking into account the vertical warping, finding the disk to be on average 1.5 times thicker vertically in the mid-infrared compared to the millimeter and the scale height to be relatively constant across radius. The decreasing scale height with wavelength is in contrast to predictions from collisional damping, and could be a result of the combined effect of radiation pressure and random collisions. We also show that the disk is warped at millimeter wavelengths and find tentative evidence for clumps in ALMA images which will require follow-up observations to confirm. The millimeter vertical warping is consistent with findings in scattered light and the secular perturbation interpretation due to the inner giant planets, which could also explain the relatively constant apparent scale height across radius, and potentially earlier findings of a non-Gaussian vertical profile which this study confirms.

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arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) II. The radial structure of debris discs

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) was recently completed to cover the lack of high-resolution observations of debris discs and to investigate the prevalence of substructures such as radial gaps and rings in a sample of 24 discs. This study characterises the radial structure of debris discs in the ARKS programme. To identify and quantify the disc substructures, we modelled all discs with a range of non-parametric and parametric approaches. We find that of the 24 discs in the sample, 5 host multiple rings, 7 are single rings that display halos or additional low-amplitude rings, and 12 are single rings with at most tentative evidence of additional substructures. The fractional ring widths that we measured are significantly narrower than previously derived values, and they follow a distribution similar to the fractional widths of individual rings resolved in protoplanetary discs. However, there exists a population of rings in debris discs that are significantly wider than those in protoplanetary discs. We also find that discs with steep inner edges consistent with planet sculpting tend to be found at smaller (<100 au) radii, while more radially extended discs tend to have shallower edges more consistent with collisional evolution. An overwhelming majority of discs have radial profiles well-described by either a double power law or double-Gaussian parametrisation. While our findings suggest that it may be possible for some debris discs to inherit their structures directly from protoplanetary discs, there exists a sizeable population of broad debris discs that cannot be explained in this way. Assuming that the distribution of millimetre dust reflects the distribution of planetesimals, mechanisms that cause rings in protoplanetary discs to migrate or debris discs to broaden soon after formation may be at play, possibly mediated by planetary migration or scattering.

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arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) III: The vertical structure of debris disks

Debris disks -- collisionally sustained belts of dust and sometimes gas around main sequence stars -- are remnants of planet formation processes and are found in systems ${\gtrsim}10$ Myr old. Millimeter-wavelength observations are particularly important, as the grains probed by these observations are not strongly affected by radiation pressure and stellar winds, allowing them to probe the dynamics of large bodies producing dust. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is analyzing high-resolution observations of 24 debris disks to enable the characterization of debris disk substructures across a large sample for the first time. For the most highly inclined disks, it is possible to recover the vertical structure of the disk. We aim to model and analyze the most highly inclined systems in the ARKS sample in order to uniformly extract the vertical dust distributions for a sample of well-resolved debris disks. We employed both parametric and nonparametric methods to constrain the vertical dust distributions for the most highly inclined ARKS targets. We find a broad range of aspect ratios, revealing a wide diversity in vertical structure, with a range of best-fit parametric values of $0.0026 \leq h_{\rm HWHM} \leq 0.193$ and a median best-fit value of $h_{\rm HWHM}=0.021$. The results obtained by nonparametric modeling are generally consistent with the parametric modeling results. We find that five of the 13 disks are consistent with having total disk masses less than that of Neptune (17 $M_{\oplus}$), assuming stirring by internal processes (self-stirring and collisional and frictional damping). Furthermore, most systems show a significant preference for a Lorentzian vertical profile rather than a Gaussian.

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arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) IX: Gas-driven origin for the continuum arc in the debris disc of HD 121617

Debris discs were long considered to be largely gas-free environments governed by collisional fragmentation, gravitational stirring, and radiative forces. Recent CO detections show that gas is present, but its abundance and origin remain uncertain. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) revealed a narrow gas and dust ring in the disc HD 121617 with an asymmetric arc 40% brighter than the rest of the ring. We aim to constrain the total gas mass in HD 121617 assuming the dust arc is produced by hydrodynamical gas-dust interactions. We used the Dusty FARGO-ADSG code, modelling dust as Lagrangian particles, including radiation pressure and dust feedback, and varying the total gas mass. Simulations were compared to observations using radiative transfer. An unstable gas ring creates a size-dependent radial and azimuthal dust trap whose efficiency depends on gas mass. Two models, with 50 and 5 Earth masses of gas, reproduce both the ALMA band 7 arc and the outward offset of the VLT/SPHERE scattered-light ring via gas drag and radiation pressure. We infer a conservative gas-mass range of 2.5 to 250 Earth masses. If the ALMA asymmetry is caused by gas drag, the required gas mass compared with the observed CO implies substantial H2, consistent with primordial gas. HD 121617 would then be a hybrid disc between protoplanetary and debris stages. Since a planet could also create an arc, future observations are needed to distinguish these scenarios.

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arXiv2024

Collisional damping in debris discs: Only significant if collision velocities are low

Context. Dusty debris discs around main sequence stars are observed to vary widely in terms of their vertical thickness. Their vertical structure may be affected by damping in inelastic collisions. Although kinetic models have often been used to study the collisional evolution of debris discs, these models have not yet been used to study the evolution of their vertical structure. Aims. We extend an existing implementation of a kinetic model of collisional evolution to include the evolution of orbital inclinations and we use this model to study the effects of collisional damping in pre-stirred discs. Methods. We evolved the number of particles of different masses, eccentricities, and inclinations using the kinetic model and used Monte Carlo simulations to calculate collision rates between particles in the disc. We considered all relevant collisional outcomes including fragmentation, cratering, and growth. Results. Collisional damping is inefficient if particles can be destroyed by projectiles that are of much lower mass. If that is the case, catastrophic disruptions shape the distributions of eccentricities and inclinations, and their average values evolve slowly and at the same rate for all particle sizes. Conclusions. The critical projectile-to-target mass ratio (Yc) and the collisional timescale jointly determine the level of collisional damping in debris discs. If Yc is much smaller than unity, a debris disc retains the inclination distribution that it is born with for much longer than the collisional timescale of the largest bodies in the disc. Such a disc should exhibit a vertical thickness that is independent of wavelength even in the absence of other physical processes. Collisional damping is efficient if Yc is of order unity or larger. For millimetre-sized dust grains and common material strength assumptions, this requires collision velocities of lower than ~40 m/s. Abridged

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arXiv2024

On the likely magnesium-iron silicate dusty tails of catastrophically evaporating rocky planets

Catastrophically evaporating rocky planets provide a unique opportunity to study the composition of small planets. The surface composition of these planets can be constrained via modelling their comet-like tails of dust. In this work, we present a new self-consistent model of the dusty tails: we physically model the trajectory of the dust grains after they have left the gaseous outflow, including an on-the-fly calculation of the dust cloud's optical depth. We model two catastrophically evaporating planets: KIC 1255b and K2-22b. For both planets, we find the dust is likely composed of magnesium-iron silicates (olivine and pyroxene), consistent with an Earth-like composition. We constrain the initial dust grain sizes to be $\sim$ 1.25-1.75 $μ$m and the average (dusty) planetary mass-loss rate to be $\sim$ 3$M_\oplus \mathrm{Gyr^{-1}}$. Our model shows the origin of the leading tail of dust of K2-22b is likely a combination of the geometry of the outflow and a low radiation pressure force to stellar gravitational force ratio. We find the optical depth of the dust cloud to be a factor of a few in the vicinity of the planet. Our composition constraint supports the recently suggested idea that the dusty outflows of these planets go through a greenhouse effect-nuclear winter cycle, which gives origin to the observed transit depth time variability. Magnesium-iron silicates have the necessary visible-to-infrared opacity ratio to give origin to this cycle in the high mass-loss state.

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arXiv2023

The effect of sculpting planets on the steepness of debris-disc inner edges

Debris discs are our best means to probe the outer regions of planetary systems. Many studies assume that planets lie at the inner edges of debris discs, akin to Neptune and the Kuiper Belt, and use the disc morphologies to constrain those otherwise-undetectable planets. However, this produces a degeneracy in planet mass and semimajor axis. We investigate the effect of a sculpting planet on the radial surface-density profile at the disc inner edge, and show that this degeneracy can be broken by considering the steepness of the edge profile. Like previous studies, we show that a planet on a circular orbit ejects unstable debris and excites surviving material through mean-motion resonances. For a non-migrating, circular-orbit planet, in the case where collisions are negligible, the steepness of the disc inner edge depends on the planet-to-star mass ratio and the initial-disc excitation level. We provide a simple analytic model to infer planet properties from the steepness of ALMA-resolved disc edges. We also perform a collisional analysis, showing that a purely planet-sculpted disc would be distinguishable from a purely collisional disc and that, whilst collisions flatten planet-sculpted edges, they are unlikely to fully erase a planet's signature. Finally, we apply our results to ALMA-resolved debris discs and show that, whilst many inner edges are too steep to be explained by collisions alone, they are too flat to arise through completed sculpting by non-migrating, circular-orbit planets. We discuss implications of this for the architectures, histories and dynamics in the outer regions of planetary systems.

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arXiv2021

MRI-active inner regions of protoplanetary discs. II. Dependence on dust, disc and stellar parameters

Close-in super-Earths are the most abundant exoplanets known. It has been hypothesized that they form in the inner regions of protoplanetary discs, out of the dust that may accumulate at the boundary between the inner region susceptible to the magneto-rotational instability (MRI) and an MRI-dead zone further out. In Paper I we presented a model for the viscous inner disc which includes heating due to both irradiation and MRI-driven accretion; thermal and non-thermal ionization; dust opacities; and dust effects on ionization. Here we examine how the inner disc structure varies with stellar, disc and dust parameters. For high accretion rates and small dust grains, we find that: (1) the main sources of ionization are thermal ionization and thermionic and ion emission; (2) the disc features a hot, high-viscosity inner region, and a local gas pressure maximum at the outer edge of this region (in line with previous studies); and (3) an increase in the dust-to-gas ratio pushes the pressure maximum outwards. Consequently, dust can accumulate in such inner discs without suppressing the MRI, with the amount of accumulation depending on the viscosity in the MRI-dead regions. Conversely, for low accretion rates and large dust grains, there appears to be an additional steady-state solution in which: (1) stellar X-rays become the main source of ionization; (2) MRI-viscosity is high throughout the disc; and (3) the pressure maximum ceases to exist. Hence, if planets form in the inner disc, larger accretion rates (and thus younger disks) are favoured.

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arXiv2021

MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure

Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magneto-rotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($\dot{M}$$\sim$$10^{-8}$M$_\odot$yr$^{-1}$) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the midplane. As a result, both the disc midplane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges onto grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.

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arXiv2020

A Three Dimensional View of Gomez's Hamburger

Unraveling the 3D physical structure, the temperature and density distribution, of protoplanetary discs is an essential step if we are to confront simulations of embedded planets or dynamical instabilities. In this paper we focus on Submillimeter Array observations of the edge-on source, Gomez's Hamburger, believed to host an over-density hypothesised to be a product of gravitational instability in the disc, GoHam b. We demonstrate that, by leveraging the well characterised rotation of a Keplerian disc to deproject observations of molecular lines in position-position-velocity space into disc-centric coordinates, we are able to map out the emission distribution in the (r, z) plane and (x, y, z) space. We show that 12CO traces an elevated layer of $z\,/\,r \sim 0.3$, while 13CO traces deeper in the disc at $z\,/\,r \lesssim 0.2$. We localize emission associated with GoHam b, finding it at deprojected radius of approximately 500 au and at polar angle of +\- 30 degrees from the disc major axis. At the spatial resolution of $\sim 1.5^{\prime\prime}$, GoHam b is spatially unresolved, with an upper limit to its radius of $<190$~au.

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arXiv2019

Close-in Super-Earths: The first and the last stages of planet formation in an MRI-accreting disc

We explore in situ formation and subsequent evolution of close-in super-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetary gas disc structure that arises from viscous accretion due to the magneto-rotational instability (MRI). We consider the evolution of dust in the inner disc, including growth, radial drift and fragmentation, and find that dust particles that radially drift into the inner disc fragment severely due to the MRI-induced turbulence. This result has two consequences: (1) radial drift of grains within the inner disc is quenched, leading to an enhancement of dust in the inner regions which scales as dust-to-gas-mass-flux-ratio at ~1 AU; (2) however, despite this enhancement, planetesimal formation is impeded by the small grain size. Nevertheless, assuming that planetary cores are present in the inner disc, we then investigate the accretion of atmospheres onto cores and their subsequent photoevaporation. We then compare our results to the observed exoplanet mass-radius relationship. We find that: (1) the low gas surface densities and high temperatures in the inner disc reduce gas accretion onto cores compared to the minimum mass solar nebula, preventing the cores from growing into hot Jupiters, in agreement with the data; (2) however, our predicted envelope masses are still typically larger than observed ones. Finally, we sketch a qualitative picture of how grains may grow and planetesimals form in the inner disc if grain effects on the ionization levels and the MRI and the back-reaction of the dust on the gas (both neglected in our calculations) are accounted for.

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arXiv2018

Observing substructure in circumstellar discs around massive young stellar objects

Simulations of massive star formation predict the formation of discs with significant substructure, such as spiral arms and clumps due to fragmentation. Here we present a semi-analytic framework for producing synthetic observations of discs with substructure, in order to determine their observability in interferometric observations. Unlike post-processing of hydrodynamical models, the speed inherent to our approach permits us to explore a large parameter space of star and disc parameters, and thus constrain properties for real observations. We compute synthetic dust continuum and molecular line observations probing different disc masses, distances, inclinations, thermal structures, dust distributions, and number and orientation of spirals and fragments. With appropriate spatial and kinematic filtering applied, our models predict that ALMA observations of massive YSOs at <5 kpc distances should detect spirals in both gas and dust in strongly self-gravitating discs (i.e. discs with up to two spiral arms and strong kinematic perturbations). Detecting spirals will be possible in discs of arbitrary inclination, either by directly spatially resolving them for more face-on discs (inclinations up to ~50 degrees), or through a kinematic signature otherwise. Clumps resulting from disc fragmentation should be detectable in the continuum, if the clump is sufficiently hotter than the surrounding disc material.

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arXiv2018

Inside-Out Planet Formation. V. Structure of the Inner Disk as Implied by the MRI

The large population of Earth to super-Earth sized planets found very close to their host stars has motivated consideration of $in$ $situ$ formation models. In particular, Inside-Out Planet Formation is a scenario in which planets coalesce sequentially in the disk, at the local gas pressure maximum near the inner boundary of the dead zone. The pressure maximum arises from a decline in viscosity, going from the active innermost disk (where thermal ionization of alkalis yields high viscosities via the magneto-rotational instability (MRI)) to the adjacent dead zone (where the MRI is quenched). Previous studies of the pressure maximum, based on $α$-disk models, have assumed ad hoc values for the viscosity parameter $α$ in the active zone, ignoring the detailed physics of the MRI. Here we explicitly couple the MRI criteria to the $α$-disk equations, to find steady-state (constant accretion rate) solutions for the disk structure. We consider the effects of both Ohmic and ambipolar resistivities, and find solutions for a range of disk accretion rates ($\dot{M}$ = $10^{-10}$ - $10^{-8}$ ${\rm M}_{\odot}$/yr), stellar masses ($M_{\ast}$ = 0.1 - 1 ${\rm M}_{\odot}$), and fiducial values of the $non$-MRI $α$-viscosity in the dead zone ($α_{\rm {DZ}} = 10^{-5}$ - $10^{-3}$). We find that: (1) A midplane pressure maximum forms radially $outside$ the inner boundary of the dead zone; (2) Hall resistivity dominates near the midplane in the inner disk, which may explain why close-in planets do $not$ form in $\sim$50% of systems; (3) X-ray ionization can be competitive with thermal ionization in the inner disk, because of the low surface density there in steady-state; and (4) our inner disk solutions are viscously unstable to surface density perturbations.

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