arXiv subjects

Jonathan P. Williams

Publications and source records attributed to Jonathan P. Williams.

At least 37 records · Page 2Linked to original sources

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.

astro-ph.SR↗

arXiv2025

Generalized Universal Inference on Risk Minimizers

A common goal in statistics and machine learning is estimation of unknowns. Point estimates alone are of little value without an accompanying measure of uncertainty, but traditional uncertainty quantification methods, such as confidence sets and p-values, often require distributional or structural assumptions that may not be justified in modern applications. The present paper considers a very common case in machine learning, where the quantity of interest is the minimizer of a given risk (expected loss) function. We propose a generalization of universal inference specifically designed for inference on risk minimizers. Notably, our generalized universal inference attains finite-sample frequentist validity guarantees under a condition common in the statistical learning literature. One version of our procedure is also anytime-valid, i.e., it maintains the finite-sample validity properties regardless of the stopping rule used for the data collection process. Practical use of our proposal requires tuning, and we offer a data-driven procedure with strong empirical performance across a broad range of challenging statistical and machine learning examples.

stat.ME↗

arXiv2025

Asymptotic efficiency of inferential models and a possibilistic Bernstein--von Mises theorem

The inferential model (IM) framework offers an alternative to the classical probabilistic (e.g., Bayesian and fiducial) uncertainty quantification in statistical inference. A key distinction is that classical uncertainty quantification takes the form of precise probabilities and offers only limited large-sample validity guarantees, whereas the IM's uncertainty quantification is imprecise in such a way that exact, finite-sample valid inference is possible. But is the IM's imprecision and finite-sample validity compatible with statistical efficiency? That is, can IMs be both finite-sample valid and asymptotically efficient? This paper gives an affirmative answer to this question via a new possibilistic Bernstein--von Mises theorem that parallels a fundamental Bayesian result. Among other things, our result shows that the IM solution is efficient in the sense that, asymptotically, its credal set is the smallest that contains the Gaussian distribution with variance equal to the Cramer--Rao lower bound. Moreover, a corresponding version of this new Bernstein--von Mises theorem is presented for problems that involve the elimination of nuisance parameters, which settles an open question concerning the relative efficiency of profiling-based versus extension-based marginalization strategies.

math.ST↗

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.

astro-ph.EP↗

arXiv2025

The Ophiuchus DIsk Survey Employing ALMA (ODISEA): A Unified Evolutionary Sequence of Planet-Driven Substructures Explaining the Diversity of Disk Morphologies

Understanding the origin of substructures in protoplanetary disks and their connection to planet formation is currently one of the main challenges in astrophysics. While some disks appear smooth, most exhibit diverse substructures such as gaps, rings, or inner cavities, with varying brightness and depth. As part of the Ophiuchus Disk Survey Employing ALMA (ODISEA), we previously proposed an evolutionary sequence to unify this diversity, driven by the formation of giant planets through core accretion and subsequent planet-disk interactions. By combining the disk evolution and planet formation code PLANETALP with the radiative transfer code RADMC-3D, we have now reproduced the key aspects of the proposed evolutionary sequence. Starting with a smooth disk (like e.g., WLY 2-63), we modeled the evolution of a fiducial disk with a 1 Jupiter-mass planet at 57 au. Within a few hundreds of orbits, a narrow gap forms, resembling ISO-Oph 17. By $\sim$0.1 Myr, the gap widens, and dust accumulates at the cavity edge, producing a structure similar to Elias 2-24. At $\sim$0.4 Myr, the disk evolves further into a morphology akin to DoAr 44, characterized by a smaller inner disk and a brighter inner rim. By $\sim$1 Myr, the system transitions to a single narrow ring, resembling RXJ1633.9-2442. This line of work strongly supports the planetary origin of substructures and enables the possibility of identifying a population of planets that is currently beyond the reach of more direct detection techniques.

astro-ph.EP↗

arXiv2025

Early Planet Formation in Embedded Disks (eDisk) XXI: Limited role of streamers in mass supply to the disk in the Class 0 protostar IRAS 16544-1604

Asymmetric and narrow infalling structures, often called streamers, have been observed in several Class 0/I protostars, which is not expected in the classical star formation picture. Their origin and impact on the disk formation remain observationally unclear. By combining data from the James Cleark Maxwell Telescope (JCMT) and Atacama Large Millimeter/submillimeter Array (ALMA), we investigate the physical properties of the streamers and parental dense core in the Class 0 protostar, IRAS 16544$-$1604. Three prominent streamers associated to the disk with lengths between 2800 to 5800 au, are identified on the northern side of the protostar in the C$^{18}$O emission. Their mass and mass infalling rates are estimated to be in the range of (1-4)$\times$10$^{-3}$ $M_\odot$ and (1-5)$\times$10$^{-8}$ $M_\odot$ yr$^{-1}$, respectively. Infall signatures are also observed in the more diffuse extended protostellar envelope observed with the ALMA from the comparison to the infalling and rotating envelope model. The parental dense core detected by the JCMT observation has a mass of $\sim$0.5 $M_\odot$, sub to transonic turbulence of $\mathcal{M}$ $=$ 0.8-1.1, and a mass-to-flux ratio of 2-6. Our results show that the streamers in IRAS 16544-1604 only possess 2% of the entire dense core mass and contribute less than 10% of the mass infalling rate of the protostellar envelope. Therefore, the streamers in IRAS 16544-1604 play a minor role in the mass accretion process onto the disk, in contrast to those streamers observed in other sources and those formed in numerical simulations of collapsing dense cores with similar turbulence and magnetic field strengths.

astro-ph.SR↗

arXiv2025

A high-resolution survey of protoplanetary disks in Lupus and the nature of compact disks

Most of the exoplanets discovered in our galaxy to date orbit low-mass stars, which tend to host small disks in their early stages. To better elucidate the link between planet formation and disk substructures, observational biases should be reduced through observations of these small, faint disks at the highest resolution using the Atacama Large Millimeter Array (ALMA). In this work, we present new high-resolution (0.03-0.04") ALMA observations at 1.3 mm of 33 disks located in the Lupus star-forming region. Combining archival data and previously published work, we provide a near-complete high resolution image library of 73 protoplanetary (Class II) disks in Lupus. This enable us to measure dust disk radii down to a limit of 0.6 au and analyze intensity profiles using visibility modeling. We show that 67% of Lupus protoplanetary disks have dust radii smaller than 30 au, with new substructures detected in 11, showing some of the shortest separation gaps. The size-luminosity relation in Lupus aligns well with a drift-dominated dust evolution scenario and, for the most compact disks (< 30 au), we found dust masses ranging from 0.3 to 26.3 Earth masses. Assuming that the detected substructures were dynamical effects of planets, we estimated the planet masses to range from 20 to 2000 Earth masses with separations between 2 to 74 au. Our results indicate that two-thirds of the protoplanetary disks in Lupus are smooth, and compact, with substructures being more prominent in the few larger disks. These compact disks are consistent with drift-dominated evolution, with their masses and optical depths suggesting that they may have already experienced some planet formation, with most of the small solids converted into planetesimals and planets. This makes them prime candidates, for explaining the formation and origin of super-Earths. [Abridged]

astro-ph.EP↗

arXiv2025

Bin-Conditional Conformal Prediction of Fatalities from Armed Conflict

Forecasting armed conflicts is a critical area of research with the potential to save lives and mitigate suffering. While existing forecasting models offer valuable point predictions, they often lack individual-level uncertainty estimates, limiting their usefulness for decision-making. Several approaches exist to estimate uncertainty, such as parametric and Bayesian prediction intervals, bootstrapping, quantile regression, but these methods often rely on restrictive assumptions, struggle to provide well-calibrated intervals across the full range of outcomes, or are computationally intensive. Conformal prediction offers a model-agnostic alternative that guarantees a user-specified level of coverage but typically provides only marginal coverage, potentially resulting in non-uniform coverage across different regions of the outcome space. In this paper, we introduce a novel extension called bin-conditional conformal prediction (BCCP), which enhances standard conformal prediction by ensuring consistent coverage rates across user-defined subsets (bins) of the outcome variable. We apply BCCP to simulated data as well as the forecasting of fatalities from armed conflicts, and demonstrate that it provides well-calibrated uncertainty estimates across various ranges of the outcome. Compared to standard conformal prediction, BCCP offers improved local coverage, though this comes at the cost of slightly wider prediction intervals.

stat.ME↗

arXiv2025

Uncertainty quantification in automated valuation models with spatially weighted conformal prediction

Non-parametric machine learning models, such as random forests and gradient boosted trees, are frequently used to estimate house prices due to their predictive accuracy, but a main drawback of such methods is their limited ability to quantify prediction uncertainty. Conformal prediction (CP) is a model-agnostic framework for constructing confidence sets around predictions of machine learning models with minimal assumptions. However, due to the spatial dependencies observed in house prices, direct application of CP leads to confidence sets that are not calibrated everywhere, i.e., the confidence sets will be too large in certain geographical regions and too small in others. We survey various approaches to adjust the CP confidence set to account for this and demonstrate their performance on a data set from the housing market in Oslo, Norway. Our findings indicate that calibrating the confidence sets on a spatially weighted version of the non-conformity scores makes the coverage more consistently calibrated across geographical regions. We also perform a simulation study on synthetically generated sale prices to empirically explore the performance of CP on housing market data under idealized conditions with known data-generating mechanisms.

stat.ML↗

arXiv2025

The Ophiuchus DIsk Survey Employing ALMA (ODISEA): Complete Size Distributions for the 100 Brightest Disks Across Multiplicity and SED Classes

The size of a protoplanetary disk is a fundamental property, yet most remain unresolved, even in nearby star-forming regions (d $\sim$ 140-200 pc). We present the complete continuum size distribution for the $105$ brightest protoplanetary disks (M$_{\text{dust}}$ $\gtrsim$ 2 M$_{\oplus}$) in the Ophiuchus cloud, obtained from ALMA Band 8 (410 GHz) observations at 0.05$^{\prime\prime}$ (7 au) to 0.15$^{\prime\prime}$ (21 au) resolution. This sample includes 54 Class II and 51 Class I and Flat Spectrum sources, providing a comprehensive distribution across evolutionary stages. We measure the Half Width at Half Maximum (HWHM) and the radius encircling $68\%$ of the flux ($R_{68\%}$) for most non-binary disks, yielding the largest flux-limited sample of resolved disks in any star-forming region. The distribution is log-normal with a median value of $\sim$14 au and a logarithmic standard deviation $σ_{\log} = 0.46$ (factor of 2.9 in linear scale). Disks in close binary systems ($<$ 200 au separation) have smaller radii, with median value of $\sim$5 au, indicating efficient radial drift as predicted by dust evolution models. The size distribution for young embedded objects (SED Class I and Flat Spectrum, age $\lesssim$ 1 Myr) is similar to that of Class II objects (age $\sim$ a few Myr), implying that pressure bumps must be common at early disk stages to prevent mm-sized particle migration at au scales.

astro-ph.EP↗

arXiv2024

Multiple Testing in Generalized Universal Inference

Compared to p-values, e-values provably guarantee safe, valid inference. If the goal is to test multiple hypotheses simultaneously, one can construct e-values for each individual test and then use the recently developed e-BH procedure to properly correct for multiplicity. Standard e-value constructions, however, require distributional assumptions that may not be justifiable. This paper demonstrates that the generalized universal inference framework can be used along with the e-BH procedure to control frequentist error rates in multiple testing when the quantities of interest are minimizers of risk functions, thereby avoiding the need for distributional assumptions. We demonstrate the validity and power of this approach via a simulation study, testing the significance of a predictor in quantile regression.

stat.ME↗

arXiv2024

Multivariate and Online Transfer Learning with Uncertainty Quantification

Untreated periodontitis causes inflammation within the supporting tissue of the teeth and can ultimately lead to tooth loss. Modeling periodontal outcomes is beneficial as they are difficult and time consuming to measure, but disparities in representation between demographic groups must be considered. There may not be enough participants to build group specific models and it can be ineffective, and even dangerous, to apply a model to participants in an underrepresented group if demographic differences were not considered during training. We propose an extension to RECaST Bayesian transfer learning framework. Our method jointly models multivariate outcomes, exhibiting significant improvement over the previous univariate RECaST method. Further, we introduce an online approach to model sequential data sets. Negative transfer is mitigated to ensure that the information shared from the other demographic groups does not negatively impact the modeling of the underrepresented participants. The Bayesian framework naturally provides uncertainty quantification on predictions. Especially important in medical applications, our method does not share data between domains. We demonstrate the effectiveness of our method in both predictive performance and uncertainty quantification on simulated data and on a database of dental records from the HealthPartners Institute.

stat.ME↗

arXiv2024

Dust Drift Timescales in Protoplanetary Disks at the Cusp of Gravitational Instability

Millimeter emitting dust grains have sizes that make them susceptible to drift in protoplanetary disks due to a difference between their orbital speed and that of the gas. The characteristic drift timescale depends on the surface density of the gas. By comparing disk radii measurements from ALMA CO and continuum observations at millimeter wavelengths, the gas surface density profile and dust drift time can be self-consistently determined. We find that profiles which match the measured dust mass have very short drift timescales, an order of magnitude or more shorter than the stellar age, whereas profiles for disks that are on the cusp of gravitational instability, defined via the minimum value of the Toomre parameter, Qmin ~ 1-2, have drift timescales comparable to the stellar lifetime. This holds for disks with masses of dust > 5 MEarth across a range of absolute ages from less than 1 Myr to over 10 Myr. The inferred disk masses scale with stellar mass as Mdisk ~ Mstar / 5Qmin. This interpretation of the gas and dust disk sizes simultaneously solves two long standing issues regarding the dust lifetime and exoplanet mass budget and suggests that we consider millimeter wavelength observations as a window into an underlying population of particles with a wide size distribution in secular evolution with a massive planetesimal disk.

astro-ph.EP↗

arXiv2024

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from $-$30 to 275 days relative to peak UV/optical emission using high-cadence, multi-wavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite (TESS) data, we determine that the ANT began to brighten on 2020 June 22.8 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 30 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of $L = (3.15 \pm 0.04) \times 10^{43}$ erg s$^{-1}$. The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to $L_{x} \sim 1.5 \times 10^{42}$ erg s$^{-1}$ and then slowly declined over time. The X-ray emission is well-fit by a power law with a photon index of $Γ\sim 2.3 - 2.6$. Both the optical and near infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events (TDEs) and active galactic nuclei (AGNs), it cannot be definitively classified with current data.

astro-ph.HE↗

arXiv2024

A Survey of Protoplanetary Disks Using the Keck/NIRC2 Vortex Coronagraph

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of protoplanetary disks in the millimeter continuum have shown a variety of radial gaps, cavities, and spiral features. These substructures may be signposts for ongoing planet formation, and therefore these systems are promising targets for direct imaging planet searches in the near-infrared. To this end, we present results from a deep imaging survey in the $L'$-band (3.8 $μ$m) with the Keck/NIRC2 vortex coronagraph to search for young planets in 43 disks with resolved features in the millimeter continuum or evidence for gaps/central cavities from their spectral energy distributions. Although we do not detect any new point sources, using the vortex coronagraph allows for high sensitivity to faint sources at small angular separations (down to ${\sim}$0$^{\prime\prime}$.1), allowing us to place strong upper limits on the masses of potential gas giant planets. We compare our mass sensitivities to the masses of planets derived using ALMA observations, and while we are sensitive to $\sim$1 M$_{Jup}$ planets in the gaps in some of our systems, we are generally not sensitive to planets of the masses expected from the ALMA observations. In addition to placing upper limits on the masses of gas giant planets that could be interacting with the dust in the disks to form the observed millimeter substructures, we are also able to map the micron-sized dust as seen in scattered light for 8 of these systems. Our large sample of systems also allows us to investigate limits on planetary accretion rates and disk viscosities.

astro-ph.EP↗

arXiv2024

Early Planet Formation in Embedded Disks (eDisk) XVI: An asymmetric dust disk driving a multi-component molecular outflow in the young Class 0 protostar GSS30 IRS3

We present the results of the ALMA Large Program Early Planet Formation in Embedded disks observations of the Class 0 protostar GSS30 IRS3. Our observations included 1.3 mm continuum with a resolution of 0.''05 (7.8 au) and several molecular species including $^{12}$CO, $^{13}$CO, C$^{18}$O, H$_{2}$CO and c-C$_{3}$H$_{2}$. The dust continuum analysis unveiled a disk-shaped structure with a major axis size of $\sim$200 au. We observed an asymmetry in the minor axis of the continuum emission suggesting that the emission is optically thick and the disk is flared. On the other hand, we identified two prominent bumps along the major axis located at distances of 26 and 50 au from the central protostar. The origin of the bumps remains uncertain and might be due to an embedded substructure within the disk or the result of the temperature distribution instead of surface density due to optically thick continuum emission. The $^{12}$CO emission reveals a molecular outflow consisting of three distinct components: a collimated one, an intermediate velocity component exhibiting an hourglass shape, and a wider angle low-velocity component. We associate these components with the coexistence of a jet and a disk-wind. The C$^{18}$O emission traces both a Keplerian rotating circumstellar disk and the infall of the rotating envelope. We measured a stellar dynamical mass of 0.35$\pm$0.09 M$_{\odot}$.

astro-ph.SR↗

arXiv2024

Beyond time-homogeneity for continuous-time multistate Markov models

Multistate Markov models are a canonical parametric approach for data modeling of observed or latent stochastic processes supported on a finite state space. Continuous-time Markov processes describe data that are observed irregularly over time, as is often the case in longitudinal medical data, for example. Assuming that a continuous-time Markov process is time-homogeneous, a closed-form likelihood function can be derived from the Kolmogorov forward equations -- a system of differential equations with a well-known matrix-exponential solution. Unfortunately, however, the forward equations do not admit an analytical solution for continuous-time, time-inhomogeneous Markov processes, and so researchers and practitioners often make the simplifying assumption that the process is piecewise time-homogeneous. In this paper, we provide intuitions and illustrations of the potential biases for parameter estimation that may ensue in the more realistic scenario that the piecewise-homogeneous assumption is violated, and we advocate for a solution for likelihood computation in a truly time-inhomogeneous fashion. Particular focus is afforded to the context of multistate Markov models that allow for state label misclassifications, which applies more broadly to hidden Markov models (HMMs), and Bayesian computations bypass the necessity for computationally demanding numerical gradient approximations for obtaining maximum likelihood estimates (MLEs). Supplemental materials are available online.

stat.CO↗

arXiv2024

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): PDS 111, an old T Tauri star with a young-looking disk

The interplay between T Tauri stars and their circumstellar disks, and how this impacts the onset of planet formation has yet to be established. We studied a seemingly old T Tauri star, PDS 111, and its disk. We analyzed optical, infrared, and sub-millimeter observations obtained with VLT/X-shooter, Mercator/HERMES, TESS, VLT/SPHERE, and ALMA, providing a new view on PDS 111 and its protoplanetary disk. The multi-epoch spectroscopy yields photospheric lines to classify the star, and emission lines to study variability in the hot inner disk and to determine the mass-accretion rate. The SPHERE and ALMA observations are used to characterize the dust distribution of the small and large grains, respectively. PDS 111 is a weak-line T Tauri star with spectral type G2, exhibits strong H$α$ variability and with a low mass-accretion rate of $1-5\times10^{-10}$\,M$_{\odot}$\,yr$^{-1}$. We measured an age of the system of 15.9$^{+1.7}_{-3.7}$ Myr using pre-main sequence tracks. The SPHERE observations show a strongly flaring disk with an asymmetric substructure. The ALMA observations reveal a 30 au cavity in the dust continuum emission with a low contrast asymmetry in the South-West of the disk and a dust disk mass of 45.8\,$M_\oplus$. The $^{12}$CO radial extension is at least three times larger than that of the dust emission. Although the measured age is younger than suggested in literature, PDS 111 still seems relatively old; this provides insight into disk properties at an advanced stage of pre-main sequence evolution. The characteristics of this disk are very similar to its younger counterparts: strongly flaring, an average disk mass, a typical radial extent of the disk gas and dust, and the presence of common substructures. This suggests that disk evolution has not significantly changed the disk properties. These results show similarities with the "Peter Pan disks" around M-dwarfs.

astro-ph.EP↗