arXiv subjects

Jessica Speedie

Publications and source records attributed to Jessica Speedie.

16 recordsLinked to original sources

arXiv2026

Demographics of planet-forming disks with the SKAO

Understanding how solid material in planet-forming disks evolves from micron-sized dust to planetary cores is a central challenge in modern astrophysics. This study has advanced dramatically in the past decade, largely driven by ALMA and high-contrast imaging facilities. However, major uncertainties remain regarding the presence, evolution, and role of centimeter-sized grains (the pebbles) in planet formation. The SKAO will fill this gap by enabling the first large-scale, high-resolution survey of disk emission at centimeter wavelengths. This chapter presents the scientific rationale and observational strategies to detect and characterize pebbles in the planet-forming disks of nearby star-forming regions. By resolving their spatial distribution, spectral properties, and evolutionary trends, SKA will offer essential constraints on dust growth and disk dynamics. This work provides observational strategies, target selection, and predictions on the detectability of hundreds of nearby disks. The chapter also explores SKA's potential to uncover the actual dust mass in disks, protoplanets and their circumplanetary disks, and other aspects of the planet formation. Together, these capabilities will establish SKAO as a cornerstone facility for planet formation science in the coming decade.

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arXiv2026

Substructures in Planet-Forming Disks with the SKAO

Disks of gas and dust orbiting young stars are the arenas and material reservoirs for planet formation. Over the past decade, multiwavelength observations, from infrared to radio, have resolved the spatial distribution of hundreds of protoplanetary disks in nearby star-forming regions, revealing a diverse zoo of substructures. These substructures are morphological features such as rings, gaps, spirals, vortices, asymmetries, warps, or clumps that trace variations in density, temperature, or composition relative to an otherwise smooth distribution of gas and dust. Many unknowns persist as to the origin of these substructures, their role in planet assembly, and their true properties. SKA-Mid Band 5b continuum observations, offering angular resolutions of $\sim 0.05''$ ($\sim 0.15''$) with AA4 (AA*) at $12.5$ GHz / $2.4$ cm, will enable new progress at this frontier. In this chapter, we outline the open questions in the field of disk substructure that SKA-Mid is uniquely poised to address, with a lens on dust thermal emission.

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arXiv2026

Reading between the rings: observed dust ring properties as probes of planet masses

We hypothesise that dust rings in protoplanetary discs formed by an embedded planet should have properties that reflect the planet's mass. We use 2D hydrodynamical simulations of planet-disc interactions to investigate this, focusing on planets ranging 0.5-2.0x the pebble-isolation mass, for three different aspect ratios. We find the ring's dust mass, peak location, and width to correlate with planet mass. We confirm a positive linear relationship between a planet's Hill radius and the location of a ring's density peak and demonstrate how this relationship can be used to constrain planet masses in observed systems by applying it to PDS 70. The dust ring width and mass change with planet mass for planet masses up to the pebble-isolation mass, beyond which they become constant. The steepness of the gas pressure radial profile is asymmetric, with the direction of the asymmetry being determined by whether the planet mass is above or below the pebble-isolation mass. We therefore propose a new way to define the pebble-isolation mass: the minimum planet mass which perturbs the gas enough for the pressure gradient interior to the pressure maximum to exceed the pressure gradient exterior to it. We discuss how our findings could be used to constrain or estimate planet masses from gas or dust observations of discs with measurable substructures and apply our results to 5 discs in the exoALMA sample to estimate planet masses and constrain disc aspect ratios. We also discuss how the potential for planetesimal formation in a ring varies with planet mass.

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arXiv2026

Dynamical Mass Constraints on Transition Disk Perturbers with the G23H Catalog

We present dynamical mass constraints on perturbers in 11 transition disk systems using a novel combination of calibrated Hipparcos and Gaia absolute astrometry data. Out of the sample of 11, we find support for companions in four systems, with significant detections in two. These systems are: HD 142527, where we clearly detect the known low-mass stellar companion HD 142527 B and MWC 758, where we detect a likely sub-stellar companion. We also find moderate evidence of companions to AB Aur and UX Tau A. For the seven systems with non-detections, we find no evidence for companions more massive than $\sim$12 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 3 au for both HD 100546 and HD 100453, nor for companions more massive than $\sim$3 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 2 au for TW Hya. We also find no evidence for stellar mass companions with semi-major axes between $\sim$4 and $\sim$25 au for HD 34282, HD 97048, CQ Tau and RY Lup. In addition to our fiducial model, we perform cross validation between astrometry sources. By comparing results across models, we find tentative evidence of a short timescale excess astrometric noise that may impact some protoplanetary disk systems. We conclude with predictions for the prospects of making dynamical mass constraints on protoplanets in protoplanetary disk systems with Gaia data release 4 using detailed simulations of Gaia DR4 data of PDS 70 and WISPIT 2.

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arXiv2026

Detecting and Characterizing Companions with a Calibrated Gaia DR2, DR3, and Hipparcos Catalog (G23H)

Gaia DR4 epoch astrometry will enable the detection of thousands of exoplanets through astrometric motion. Here, we present a composite catalog and modeling framework that extracts the maximum information from existing Hipparcos and Gaia data releases. We calibrate Gaia DR2 proper motions and DR3-DR2 scaled position differences against the Gaia DR3 reference frame, and combine these with the Hipparcos-Gaia Catalog of Accelerations, the Hipparcos intermediate astrometric data, Gaia astrometric excess noise, and Gaia radial velocity variability constraints. We implement a joint likelihood model for these data in Octofitter that marginalizes over Gaia's unpublished observation epochs. This results in full orbit posteriors that can be computed uniformly for a large class of companions. We compare these posteriors to published orbital solutions for 25 stellar binaries from the Sixth Catalog of Orbits of Visual Binary Stars, recovering all companions at high significance and broadly consistent orbital separations. We then recover independent evidence to support 94 of 120 tested Jovian exoplanetary systems from the NASA Exoplanet Archive (plus 3 known stellar companions, and one previously detected planet we now rule out). We demonstrate that in cases like 14 Her b, the posteriors confirm the planetary nature of a signal using only Gaia and Hipparcos data. We find no false positives among 25 RV-quiet standard stars without significant Hipparcos-Gaia accelerations. Our method can break degeneracies inherent to proper motion anomaly or excess noise modeling alone by resolving orbital curvature within the Gaia baseline. The catalog and updated Octofitter are made publicly available to the community.

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arXiv2025

Picture an Astronomer: Best Practices for Retaining Talent in Astrophysics

Women are consistently underrepresented in astrophysics yet are simultaneously subject to disproportionate attrition at every career stage. This disparity between demonstrated efficacy in job performance and ultimate career outcome was the primary motivation for the Picture an Astronomer series, which included both targeted public outreach to increase representation of women in astrophysics and high-level, solution-oriented discussions among professional astronomers. In March 2025, more than 200 astronomers came together in a hybrid-format symposium focused on the state of the field for female scientists, combining scientific exchange with discussions of policies and practices to strengthen retention of talent in the field. This white paper is the result of those discussions, offering a wide range of recommendations developed in the context of gendered attrition in astrophysics but which ultimately support a healthier climate for all scientists alike.

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arXiv2025

Mapping the merging zone of late infall in the AB Aur planet-forming system

Late infall events challenge the traditional view that planet formation occurs without external influence. Here we present deep ALMA $^{12}$CO $J=2-1$ and SO $J_{N}=5_6-4_5$ observations toward AB Aurigae, a Class II disk system with strong signs of gravitational instability and ongoing planet formation. By applying Keplerian and anti-Keplerian masks, we separate disk-like and non-disk-like motions of $^{12}$CO, considering the two outputs as the 'disk' and 'exo-disk' (out of disk) emission components, respectively. The disk component of $^{12}$CO extends to $\sim 1600$ au in radius and exhibits a stunningly rich architecture of global spiral structure. The exo-disk emission consists predominantly of three spiral structures -- S1, S2 and S3 -- whose projections are co-spatial with the disk. We successfully reproduce their trajectories with a ballistic accretion flow model, finding that S1 and S2 (both redshifted) are infalling toward the disk from in front, and S3 (blueshifted) is infalling from behind. Where the terminal ends of S1 and S2 become indistinguishable from the disk, we observe a brightness peak in SO emission $2.5\times$ the azimuthal average of a background SO ring. This merging zone lies within a relatively confined region $15-100$ degrees east of north, and between $\sim150-300$ au from the star, at scales relevant to where planet candidates have been previously identified. The AB Aur system provides a unified picture of late infall inducing replenishment of the disk, triggering gravitational instability, and modifying the conditions of forming planets.

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arXiv2024

Anatomy of a Fall: Stationary and super-Keplerian spiral arms generated by accretion streamers in protostellar discs

Late-stage infall onto evolved protoplanetary discs is an important source of material and angular momentum replenishment, and disc substructures. In this paper we used 3D smoothed particle hydrodynamics simulations to model streamer-disc interactions for a prograde streamer. The initially parabolic streamer interacts with the disc material to excite disc eccentricity, which can last on the order of $10^5$ years. We found that the spiral arms the streamer excited in the disc can have a variety of pattern speeds, ranging from stationary to super-Keplerian. Spiral arms with various pattern speeds can exist simultaneously, providing a way to diagnose them in observations. Streamer induced spirals appear similar to those generated by a massive outer companion, where the pitch angle of the spiral increases towards the source of the perturbation. Additionally, the spirals arms can show large and sudden pitch angle changes. Streamer induced spirals are long-lived, lasting approximately $3-4\times$ longer than the initial streamer infall timescale ($\sim$$10^4$ years). After the initial interaction with the disc, a long lasting low $m$ azimuthal mode persists in the disc.

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arXiv2024

Gravitational instability in a planet-forming disk

The canonical theory for planet formation in circumstellar disks proposes that planets are grown from initially much smaller seeds. The long-considered alternative theory proposes that giant protoplanets can be formed directly from collapsing fragments of vast spiral arms induced by gravitational instability -- if the disk is gravitationally unstable. For this to be possible, the disk must be massive compared to the central star: a disk-to-star mass ratio of 1/10 is widely held as the rough threshold for triggering gravitational instability, inciting significant non-Keplerian dynamics and generating prominent spiral arms. While estimating disk masses has historically been challenging, the motion of the gas can reveal the presence of gravitational instability through its effect on the disk velocity structure. Here we present kinematic evidence of gravitational instability in the disk around AB Aurigae, using deep observations of 13CO and C18O line emission with the Atacama Large Millimeter/submillimeter Array (ALMA). The observed kinematic signals strongly resemble predictions from simulations and analytic modelling. From quantitative comparisons, we infer a disk mass of up to 1/3 the stellar mass enclosed within 1" to 5" on the sky.

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arXiv2024

Observational Signatures of Circumbinary Discs II: Kinematic Signatures in Velocity Residuals

Kinematic studies of protoplanetary discs are a valuable method for uncovering hidden companions. In the first paper of this series, we presented five morphological and kinematic criteria that aid in asserting the binary nature of a protoplanetary disc. In this work we study the kinematic signatures of circumbinary discs in the residuals of their velocity maps. We show that Doppler-flips, spiral arms, eccentric gas motion, fast flows inside of the cavity, and vortex-like kinematic signatures are commonly observed. Unlike in the planetary mass companion case, Doppler-flips in circumbinary discs are not necessarily centred on a companion, and can extend towards the cavity edge. We then compare the kinematic signatures in our simulations with observations and see similarities to the Doppler-flip signal in HD 100546 and the vortex-like kinematic signatures in HD 142527. Our analysis also reveals kinematic evidence for binarity in several protoplantary disks typically regarded as circumstellar rather than circumbinary, including AB Aurigae and HD 100546.

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arXiv2024

Angular momentum transport via gravitational instability in the Elias 2-27 disc

Gravitational instability is thought to be one of the main drivers of angular momentum transport in young protoplanetary discs. The disc around Elias 2-27 offers a unique example of gravitational instability at work. It is young and massive, displaying two prominent spiral arms in dust continuum emission and global non-axisymmetric kinematic signatures in molecular line data. In this work, we used archival ALMA observations of $^{13}$CO line emission to measure the efficiency of angular momentum transport in the Elias 2-27 system through the kinematic signatures generated by gravitational instability, known as 'GI wiggles'. Assuming the angular momentum is transported by the observed spiral structure and leveraging previously-derived dynamical disc mass measurements, the amount of angular momentum transport we found corresponds to an $\alpha-$viscosity of $\alpha=0.038\pm0.018$. This value implies an accretion rate onto the central star of $\log_{10}\dot{M}_\star=-6.99\pm0.17\text{M}_\odot/\text{yr, which}$ reproduces the one observed value of $\log_{10}\dot{M}_{\star,\text{obs}}=-7.2\pm0.5\text{M}_\odot/\text{yr }$ very well. The excellent agreement we have found serves as further proof that gravitational instability is the main driver of angular momentum transport acting in this system.

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arXiv2024

Searching for planet-driven dust spirals in ALMA visibilities

ALMA (Atacama Large Millimetre/submillimetre Array) observations of the thermal emission from protoplanetary disc dust have revealed a wealth of substructures that could evidence embedded planets, but planet-driven spirals, one of the more compelling lines of evidence, remain relatively rare. Existing works have focused on detecting these spirals using methods that operate in image space. Here, we explore the planet detection capabilities of fitting planet-driven spirals to disc observations directly in visibility space. We test our method on synthetic ALMA observations of planet-containing model discs for a range of disc/observational parameters, finding it significantly outperforms image residuals in identifying spirals in these observations and is able to identify spirals in regions of the parameter space in which no gaps are detected. These tests suggest that a visibility-space fitting approach warrants further investigation and may be able to find planet-driven spirals in observations that have not yet been found with existing approaches. We also test our method on six discs in the Taurus molecular cloud observed with ALMA at 1.33 mm, but find no evidence for planet-driven spirals. We find that the minimum planet masses necessary to drive detectable spirals range from $\approx$ 0.03 to 0.5 $M_{\text{Jup}}$ over orbital radii of 10 to 100 au, with planet masses below these thresholds potentially hiding in such disc observations. Conversely, we suggest that planets $\gtrsim$ 0.5 to 1 $M_{\text{Jup}}$ can likely be ruled out over orbital radii of $\approx$ 20 to 60 au on the grounds that we would have detected them if they were present.

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arXiv2022

Testing velocity kinks as a planet-detection method: Do velocity kinks in surface gas emission trace planetary spiral wakes in the midplane continuum?

Spiral density waves generated by an embedded planet are understood to cause ``kinks'' in observed velocity channel maps of CO surface emission, by perturbing the gas motion within the spiral arms. If velocity kinks are a reliable probe of embedded planets, we should expect to see the planet-driven spiral arms in other observational tracers. We test this prediction by searching the dust continuum for the midplane counterparts of the spirals responsible for all of the velocity kink planet candidates reported to date, whose orbits lie inside the dust continuum disk. We find no clear detection of any spiral structure in current continuum observations for 6 of the 10 velocity kink planet candidates in our sample (DoAr 25, GW Lup, Sz 129, HD 163296 #2, P94, and HD 143006), despite the high planet masses inferred from the kink amplitude. The remaining 4 cases include 3 clear detections of two-armed dust spirals (Elias 27, IM Lup and WaOph 6) wherein neither spiral arm aligns with a wake originating from reported planet location, suggesting that under the planetary-origin hypothesis, an accurate method for inferring the location of the planet in the midplane may need to encompass vertical effects. The 10th case, HD 97048, is inconclusive with current knowledge of the disk geometry.

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arXiv2022

Observing planet-driven dust spirals with ALMA

ALMA continuum observations of thermal emission from the dust component of protoplanetary disks have revealed an abundance of substructures that may be interpreted as evidence for embedded planets, but planet-driven spiral arms -- perhaps one of the most compelling lines of evidence -- have proven comparatively elusive. In this work, we test the capabilities of ALMA to detect the planet-driven spiral signal in continuum emission. Carrying out hydrodynamic simulations and radiative transfer calculations, we present synthetic Band 7 continuum images for a wide range of disk and observing conditions. We show that thermal mass planets at tens of au typically drive spirals detectable within a few hours of integration time, and the detectable planet mass may be as low as $\sim$Neptune mass ($0.3 \, M_{\rm th}$). The grains probed by ALMA form spirals morphologically identical to the underlying gas spiral. The temperature of the dust spiral is crucial in determining its contrast, and spirals are easier to detect in disks with an adiabatic equation of state and longer cooling times. Resolving the spiral is not necessary for its detection; with the help of residual maps, the optimal beam size is a few times the spiral width at a constant noise level. Finally, we show how the presence of gaps and rings can impair our ability to recognize co-located spirals. Our work demonstrates the planet-finding potential of the current design specification of ALMA, and suggests that observing capability is not the bottleneck in searching for spirals induced by thermal mass planets.

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arXiv2021

Turbulent Disk Viscosity and the Bifurcation of Planet Formation Histories

ALMA observations of dust ring/gap structures in a minority but growing sample of protoplanetary disks can be explained by the presence of planets at large disk radii - yet the origins of these planets remains debated. We perform planet formation simulations using a semi-analytic model of the HL Tau disk to follow the growth and migration of hundreds of planetary embryos initially distributed throughout the disk, assuming either a high or low turbulent $\alpha$ viscosity. We have discovered that there is a bifurcation in the migration history of forming planets as a consequence of varying the disk viscosity. In our high viscosity disks, inward migration prevails and yields compact planetary systems, tempered only by planet trapping at the water iceline around 5 au. In our lower viscosity models however, low mass planets can migrate outward to twice their initial orbital radii, driven by a radially extended region of strong outward-directed corotation torques located near the heat transition (where radiative heating of the disk by the star is comparable to viscous heating) - before eventually migrating inwards. We derive analytic expressions for the planet mass at which the corotation torque dominates, and find that this "corotation mass" scales as $M_{\rm p, corot} \sim \alpha^{2/3}$. If disk winds dominate the corotation torque, the corotation mass scales linearly with wind strength. We propose that the observed bifurcation in disk demographics into a majority of compact dust disks and a minority of extended ring/gap systems is a consequence of a distribution of viscosity across the disk population.

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arXiv2019

The Structure and Stability of Extended, Inclined Circumplanetary Disk or Ring Systems

Large dips in the brightness for a number of stars have been observed, for which the tentative explanation is occultation of the star by a transiting circumplanetary disk or ring system. In order for the circumplanetary disk/rings to block the host star's light, the disk must be tilted out of the planet's orbital plane, which poses stability problems due to the radial extent of the disk required to explain the brightness dip durations. This work uses N-body integrations to study the structure and stability of circumplanetary disk/ring systems tilted out of the planet's orbital plane by the spinning planet's mass quadrupole. Simulating the disk as a collection of test particles with orbits initialized near the Laplace surface (equilibrium between tidal force from host star and force from planet's mass quadrupole), we find that many extended, inclined circumplanetary disks remain stable over the duration of the integrations (~3-16 Myr). Two dynamical resonances/instabilities excite the particle eccentricities and inclinations: the Lidov-Kozai effect which occurs in the disk's outer regions, and ivection resonance which occurs in the disk's inner regions. Our work places constraints on the maximum radial extent of inclined circumplanetary disk/ring systems, and shows that gaps present in circumplanetary disks do not necessarily imply the presence of exomoons.

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