arXiv subjects

Benjamin C. Bromley

Publications and source records attributed to Benjamin C. Bromley.

At least 19 recordsLinked to original sources

arXiv2026

An astrometric search for planets in debris disk systems

Debris disks are likely created and sculpted by planetary bodies in the orbital space they share. The properties of these disks, including mass, orbital extent, and morphology, can be indicators of their planetary shepherds. Recently, T. D. Pearce and collaborators placed limits on the masses and orbits of hypothetical planets around 178 stars with debris disks. Here, we consider 176 of these stars, all objects that have astrometric data in the Gaia Data Release 3 archive, to assess planet detection from astrometry. Our analysis begins with a set of stellar hosts of known exoplanets, selected to have parallax, apparent magnitude, and color similar to the 176 debris disk systems. We confirm that Gaia's ruwe parameter, a measure of the quality of astrometric fitting to a linear drift model, is sensitive to the presence of massive companions, even planetary ones. We also train a machine-learning model with a range of planet host properties from Gaia, considering more detailed astrometric data beyond ruwe that might indicate orbital motion. In addition, the model incorporates Gaia photometry to inform how brightness and stellar type affect detectability, with the risk that selection bias in the training set may affect reliability. Guided by ruwe and predictions of the machine-learning model, we identify stars with debris disks that may host as-yet-undiscovered planets. Overall, the model predictions, ruwe, and the mass limits from debris disk morphology do not show strong trends. Nonetheless, our top candidates with high ruwe and high planethood probability from the machine learning model will be compelling subjects for time-series analyses with Gaia Data Release 4.

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arXiv2026

The Cold Debris Disk Surveys I. Host Star Properties

We describe the dynamical, photometric, and spectroscopic data available for stars targeted by Spitzer and Herschel to search for cold circumstellar dust emission from debris disks, a collection that we name the Cold Debris Disk Surveys (CDDS). These data include Hipparcos and Gaia parallaxes, 0.4-1250 micron photometry, spectral types, effective temperatures, gravities, bolometric luminosities, visual extinctions, metallicities, lithium abundances, rotational periods, projected rotational velocities, the Ca~II HK and IR triplet activity indicators, and X-ray luminosities for 3675 stars. Within this sample, we investigate the frequency of stellar and planetary companions (including potential new proper motion companions); use the data to assign CDDS stars to the field or one of many moving groups, open clusters, or stellar associations; and investigate correlations between stellar activity indicators. In future papers, we plan to explore the magnitude and frequency of infrared excess emission as a function of host star properties; to search for new companions with Gaia; and to examine the evolution of infrared excesses with the ages of stars in clusters and the field.

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arXiv2026

Supermassive black hole growth from stellar binary encounters

The growth of supermassive black holes (SMBHs) remains a central problem in astrophysics, with current observations providing only limited constraints on the underlying mechanisms. One possible growth channel is stellar accretion via the Hills mechanism, wherein a SMBH tidally breaks up a passing binary star, capturing and eventually accreting a member of the binary. We adopt a framework based on kinematics to predict capture rates from parameters that include the central number density of stars, the stellar velocity dispersion, the binary fraction, and black hole mass. We then estimate the growth of SMBHs across a range of galactic environments. In a data set of 91 galaxies of various types and masses, we identify two candidates with SMBHs for which stellar accretion may be a driver of growth. Closer to home, a recent analysis of observed hypervelocity stars from the Large Magellanic Cloud (LMC) implicates binary star interactions with a massive black hole. Every hypervelocity star produced in this way leaves a bound partner that may be accreted, providing an active growth channel for the LMC's black hole.

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arXiv2025

Symbiotic star candidates in Gaia Data Release 3

Symbiotic stars, binary pairs with a cool giant fueling accretion onto a hot compact companion, offer unique insights to our understanding of stellar evolution. Yet, only a few hundred symbiotic stars are confirmed. Here, we report on a new search for symbiotic star candidates in Gaia Data Release 3 (GDR3), based entirely on the archive's astrometric, photometric, and spectroscopic information. To begin our search, we identified known symbiotic stars in GDR3 and assessed their absolute magnitude and colors, which are dominated by the cool giant. We also considered measures of astrometric quality that might be affected by binary motion in these systems. Finally, from those sources with Gaia spectroscopic data, we built a low-resolution spectral template that characterizes the unique features of these systems, including H$α$ emission from interaction with the giant's wind and radiation from the hot star. We then queried the full GDR3 archive for sources with spectroscopic data that are bright (< 17 mag in G-band), have modest relative parallax uncertainties (< 20%), and fall within a region of color-magnitude space characteristic of red giants, keeping only sources with spectra that quantitatively match our template. A machine-learning algorithm, trained on known symbiotic stars, produced a new catalog of 1,674 sources. From cross-matches with infrared and X-ray surveys, we present 25 of these sources as particularly compelling candidates for new symbiotic stars.

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arXiv2025

Light Echoes of Time-resolved Flares and Application to Kepler Data

Light echoes of stellar flares provide an intriguing option for exploring protoplanetary disks in young stellar systems. Previous work on light echoes of circumstellar disks made use of delta-function flares for modeling. We present a new model that incorporates echoes produced by extended, time-resolved flares. We then test this model on known disk-bearing stars with Kepler K2 data by estimating disk parameters from possible echo signals. We focus on two stars; the first appears to be a good candidate for use of this echo model, which predicts disk parameters that are consistent with known values. The second star turns out to be more problematic as a result of high brightness variability in its post-peak lightcurve. These two cases show both the promise and limitations of light echoes as a tool for exploring protoplanetary disks in the time domain

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arXiv2025

Cosmology with voids

Voids are dominant features of the cosmic web. We revisit the cosmological information content of voids and connect void properties with the parameters of the background universe. We combine analytical results with a suite of large n-body realizations of large-scale structure in the quasilinear regime to measure the central density and radial outflow of voids. These properties, estimated from multiple voids that span a range of redshifts, provide estimates of the Hubble parameter, $Ω_M$ and $Ω_Λ$. The analysis assumes access to the full phase-space distribution of mass within voids, a dataset that is not currently observable. The observable properties of the largest void in the universe may also test models. The suite of large n-body realizations enables construction of lightcones reaching ~3,000 $h^{-1}$Mpc. Based on these lightcones, we show that large voids similar to those observed are expected in the standard $Λ$CDM model.

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arXiv2025

A Pluto-Charon Sonata V. Long-term Stability of the HST State Vector

We analyze a new set of 275 n-body calculations designed to place limits on the masses of the small circumbinary satellites in the Pluto-Charon system. Together with calculations reported in previous papers, we repeat that a robust upper limit on the total mass of the four satellites is roughly $9.5 \times 10^{19}$ g. For satellite volumes derived from New Horizons, this mass limit implies a robust upper limit on the bulk densities of Nix and Hydra, $\lesssim 1.7$ g cm$^{-3}$, that are comparable to the bulk density of Charon. Additional calculations demonstrate that satellite systems with mass $\lesssim 8.25 \times 10^{19}$ g are robustly stable over the current age of the Sun. The bulk densities of Nix and Hydra in these lower mass systems are clearly smaller than the bulk density of Charon. These new n-body results enable accurate measurements of eccentricity and inclination for Nix, Kerberos, and Hydra that agree well with orbital elements derived from numerical calculations with new HST and New Horizons state vectors. With these new state vectors, Styx has a 37% larger eccentricity and an 85% smaller inclination, which makes it more prone to gravitational perturbations from Nix.

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arXiv2024

Light Echoes of Protoplanetary Disks

Light echoes offer a means of studying protoplanetary disks, including their geometry and composition, even when they are not spatially resolved. We present a test of this approach applied specifically to optically thick, geometrically flared disks around active stars. Here we adopt stellar parameters of an active M dwarf to calculate light echoes for disks and rings with radii that would produce time delays consistent with TESS short cadence (about 2 minutes) time bins. Our results show successful fits to disk parameters, highlighting the potential effectiveness of this method in the search for protoplanetary disks.

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arXiv2024

Polarization of circumstellar debris disk light echoes

Light echoes of debris disks around active stars can reveal disk structure and composition even when disks are not spatially resolved. Unfortunately, distinguishing reflected light from quiescent starlight and unexpected post-peak flare structure is challenging, especially for edge-on geometries where the time delay between observed flare photons and light scattered from the near side of the disk is short. Here, we take advantage of the fact that scattered light from a dusty disk is polarized, depending on the location of the scattering site and the orientation of the disk relative to a distant observer. Filtering reflected light into its polarized components allows echoes to stand out in predictable ways. We test this idea with a simple model for a disk around an active M dwarf. Our results demonstrate that the use of polarimetric data of flaring stars can significantly enhance echo signals relative to starlight and yield more robust and accurate fits to disk parameters compared to analyses based on the total intensity alone.

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arXiv2023

Supermassive Black Hole Binaries in Ultralight Dark Matter

We investigate the evolution of supermassive black hole (SMBH) binaries and the possibility that their merger is facilitated by ultralight dark matter (ULDM). When ULDM is the main dark matter (DM) constituent of a galaxy, its wave nature enables the formation of massive quasiparticles throughout the galactic halo. Here we show that individual encounters between quasiparticles and a SMBH binary can lead to the efficient extraction of energy and angular momentum from the binary. The relatively short coherence time of ULDM provides a steady-state population of massive quasiparticles, and consequently a potential solution to the final parsec problem. Furthermore, we demonstrate that, in the presence of stars, ULDM quasiparticles can also act as massive perturbers to enhance the stellar relaxation rate locally, replenish the stellar loss cone efficiently, and consequently resolve the final parsec problem.

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arXiv2023

Planetesimals drifting through dusty and gaseous white dwarf debris discs: Types I, II and III-like migration

The suite of over 60 known planetary debris discs which orbit white dwarfs, along with detections of multiple minor planets in these systems, motivate investigations about the migration properties of planetesimals embedded within the discs. Here, we determine whether any of the migration regimes which are common in (pre-)main-sequence protoplanetary discs, debris discs and ring systems could be active and important in white dwarf discs. We investigate both dust-dominated and gas-dominated regions, and quantitatively demonstrate that Type I and Type II migration, as well as their particulate disc analogues, are too slow to be relevant in white dwarf discs. However, we find that the analogue of Type III migration for particulate discs may be rapid in the dusty regions of asteroid- or moon-generated ($>10^{18}$ kg) white dwarf discs, where a planetesimal exterior to its Roche radius may migrate across the entire disc within its lifetime. This result holds over a wide range of disc boundaries, both within and exterior to $1R_{\odot}$, and such that the probability of migration occurring increases with higher disc masses.

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arXiv2023

A catalog of nearby accelerating star candidates in Gaia DR3

We describe a new catalog of accelerating star candidates with Gaia $G\le 17.5$ mag and distances $d\le 100$ pc. Designated as Gaia Nearby Accelerating Star Catalog (GNASC), it contains 29,684 members identified using a supervised machine-learning algorithm trained on the Hipparcos-Gaia Catalog of Accelerations (HGCA), Gaia Data Release 2, and Gaia Early Data Release 3. We take advantage of the difference in observation timelines of the two Gaia catalogs and information about the quality of the astrometric modeling based on the premise that acceleration will correlate with astrometric uncertainties. Catalog membership is based on whether constant proper motion over three decades can be ruled out at high confidence (greater than 99.9%). Test data suggest that catalog members each have a 68% likelihood of true astrometric acceleration; subsets of the catalog perform even better, with the likelihood exceeding 85%. We compare the GNASC with Gaia Data Release 3 and its table of stars for which acceleration is detected at high confidence based on precise astrometric fits. Our catalog, derived without this information, captured over 96% of sources in the table that meet our selection criteria. In addition, the GNASC contains bright, nearby candidates that were not in the original Hipparcos survey, including members of known binary systems as well as stars with companions yet to be identified. It thus extends the HGCA and demonstrates the potential of the machine-learning approach to discover hidden partners of nearby stars in future astrometric surveys.

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arXiv2022

Magnetic interactions in orbital dynamics

The magnetic field of a host star can impact the orbit of a stellar partner, planet, or asteroid if the orbiting body is itself magnetic or electrically conducting. Here, we focus on the instantaneous magnetic forces on an orbiting body in the limit where the dipole approximation describes its magnetic properties as well as those of its stellar host. A permanent magnet in orbit about a star will be inexorably drawn toward the stellar host if the magnetic force is comparable to gravity due to the steep radial dependence of the dipole-dipole interaction. While magnetic fields in observed systems are much too weak to drive a merger event, we confirm that they may be high enough in some close compact binaries to cause measurable orbital precession. When the orbiting body is a conductor, the stellar field induces a time-varying magnetic dipole moment that leads to the possibility of eccentricity pumping and resonance trapping. The challenge is that the orbiter must be close to the stellar host, so that magnetic interactions must compete with tidal forces and the effects of intense stellar radiation.

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arXiv2022

A Pluto--Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

We discuss a new set of $\sim$ 500 numerical n-body calculations designed to constrain the masses and bulk densities of Styx, Nix, Kerberos, and Hydra. Comparisons of different techniques for deriving the semimajor axis and eccentricity of the four satellites favor methods relying on the theory of Lee & Peale (2006), where satellite orbits are derived in the context of the restricted three body problem (Pluto, Charon, and one massless satellite). In each simulation, we adopt the nominal satellite masses derived in Kenyon & Bromley (2019a), multiply the mass of at least one satellite by a numerical factor $f \ge 1$, and establish whether the system ejects at least one satellite on a time scale $\le$ 4.5 Gyr. When the total system mass is large ($f \gg 1$), ejections of Kerberos are more common. Systems with lower satellite masses ($ f \approx$ 1) usually eject Styx. In these calculations, Styx often `signals' an ejection by moving to higher orbital inclination long before ejection; Kerberos rarely signals in a useful way. The n-body results suggest that Styx and Kerberos are more likely to have bulk densities comparable with water ice, $ρ_{SK} \lesssim$ 2 g cm$^{-3}$, than with rock. A strong upper limit on the total system mass, $M_{SNKH} \lesssim 9.5 \times 10^{19}$ g, also places robust constraints on the average bulk density of the four satellites, $ρ_{SNKH} \lesssim$ 1.4 g cm$^{-3}$. These limits support models where the satellites grow out of icy material ejected during a major impact on Pluto or Charon.

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arXiv2021

From Pebbles and Planetesimals to Planets and Dust: the Protoplanetary Disk--Debris Disk Connection

The similar orbital distances and detection rates of debris disks and the prominent rings observed in protoplanetary disks suggest a potential connection between these structures. We explore this connection with new calculations that follow the evolution of rings of pebbles and planetesimals as they grow into planets and generate dusty debris. Depending on the initial solid mass and planetesimal formation efficiency, the calculations predict diverse outcomes for the resulting planet masses and accompanying debris signature. When compared with debris disk incidence rates as a function of luminosity and time, the model results indicate that the known population of bright cold debris disks can be explained by rings of solids with the (high) initial masses inferred for protoplanetary disk rings and modest planetesimal formation efficiencies that are consistent with current theories of planetesimal formation. These results support the possibility that large protoplanetary disk rings evolve into the known cold debris disks. The inferred strong evolutionary connection between protoplanetary disks with large rings and mature stars with cold debris disks implies that the remaining majority population of low-mass stars with compact protoplanetary disks leave behind only modest masses of residual solids at large radii and evolve primarily into mature stars without detectable debris beyond 30 au. The approach outlined here illustrates how combining observations with detailed evolutionary models of solids strongly constrains the global evolution of disk solids and underlying physical parameters such as the efficiency of planetesimal formation and the possible existence of invisible reservoirs of solids in protoplanetary disks.

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arXiv2021

Seeking echoes of circumstellar disks in Kepler light curves

Light echoes of flares on active stars offer the opportunity for direct detection of circumstellar dust. We revisit the problem of identifying faint echoes in post-flare light curves, focusing on debris disks from on-going planet formation. Starting with simulations, we develop an algorithm for estimating the radial extent and total mass from disk echo profiles. We apply this algorithm to light curves from over 2,100 stars observed by NASA's Kepler mission, selected for multiple, short-lived flares in either the long-cadence or short-cadence data sets. While flux uncertainties in light curves from individual stars preclude useful mass limits on circumstellar disks, catalog-averaged light curves yield constraints on disk mass that are comparable to estimates from known debris disks. The average mass in micron- to millimeter-sized dust around the Kepler stars cannot exceed 10% of an Earth mass in exo-Kuiper belts or 10% of a Lunar mass in the terrestrial zone. We group stars according to IR excess, based on WISE W1-W3 color, as an indicator for the presence of circumstellar dust. The mass limits are greater for stars with strong IR excess, a hint that echoes are lurking not far beneath the noise in post-flare light curves. With increased sensitivity, echo detection will let time-domain astronomy complement spectroscopic and direct-imaging studies in mapping how, when, and where planets form.

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arXiv2021

A Pluto--Charon Concerto II. Formation of a Circumbinary Disk of Debris After the Giant Impact

Using a suite of numerical calculations, we consider the long-term evolution of circumbinary debris from the Pluto-Charon giant impact. Initially, these solids have large eccentricity and pericenters near Charon's orbit. On time scales of 100-1000 yr, dynamical interactions with Pluto and Charon lead to the ejection of most solids from the system. As the dynamics moves particles away from the barycenter, collisional damping reduces the orbital eccentricity of many particles. These solids populate a circumbinary disk in the Pluto-Charon orbital plane; a large fraction of this material lies within a `satellite zone' that encompasses the orbits of Styx, Nix, Kerberos, and Hydra. Compared to the narrow rings generated from the debris of a collision between a trans-Neptunian object (TNO) and Charon, disks produced after the giant impact are much more extended and may be a less promising option for producing small circumbinary satellites.

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arXiv2020

On the Estimation of Circumbinary Orbital Properties

We describe a fast, approximate method to characterize the orbits of satellites around a central binary in numerical simulations. A goal is to distinguish the free eccentricity -- random motion of a satellite relative to a dynamically cool orbit -- from oscillatory modes driven by the central binary's time-varying gravitational potential. We assess the performance of the method using the Kepler-16, Kepler-47, and Pluto-Charon systems. We then apply the method to a simulation of orbital damping in a circumbinary environment, resolving relative speeds between small bodies that are slow enough to promote mergers and growth. These results illustrate how dynamical cooling can set the stage for the formation of Tatooine-like planets around stellar binaries and the small moons around the Pluto-Charon binary planet.

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