arXiv subjects

M. Joyce

Publications and source records attributed to M. Joyce.

At least 19 recordsLinked to original sources

arXiv2026

Calibrating Mid-Infrared Emission Features As Diagnostics of Star Formation in Infrared-Luminous Galaxies via Radiative Transfer Modeling

Luminous infrared galaxies are key sites of obscured stellar mass assembly at z > 0.5. Their star formation rates (SFRs) are often estimated using the luminosities of the 6.2 micron and 11.2 micron polycyclic aromatic hydrocarbon (PAH) features, or those of the [Ne II] and [Ne III] fine-structure lines, as they are minimally affected by obscuration. It is uncertain whether the calibration of these features as SFR tracers depends on the starburst bolometric luminosity or the level of Active Galactic Nucleus (AGN) activity. We here investigate the relationship between the luminosities of PAH and Neon lines with star formation rate for highly luminous objects using radiative transfer modeling and archival observations of 42 local Ultraluminous (>= 10^12 L_sun) Infrared Galaxies (ULIRGs). We find that PAH and [Ne II] features arise mainly in star-forming regions, with small contributions from the AGN or host, but that the [Ne III] line has a mixed contribution from both star formation and AGN activity. We present relations between L_PAH and L_NeII, and both starburst luminosity and SFR. We find relations for lower luminosity (L_IR ~= 10^10-10^12 L_sun) systems underestimate the SFRs in local ULIRGs by up to ~1 dex. The 6.2 micron and 11.2 micron PAH features, and the [Ne II] line, are thus good tracers of SFR in ULIRGs. We do not find that a more luminous AGN affects the relationship between SFR and PAH or Neon luminosity, but that it can make PAH emission harder to discern. Our results and derived relations are relevant to studies of star-forming and composite galaxies at z < 3 with the James Webb Space Telescope.

astro-ph.GA↗

arXiv2025

Stranger Things: A Grid-based Survey of Strange Modes in Post-Main Sequence Models

We present a systematic survey of strange mode pulsations in Cepheids using MESA and for the linear stability analysis, MESA RSP. Our model grid spans $2-15\,M_\odot$ in mass and [Fe/H] $= -0.95$-$0.17$ ($Z = 0.0015$-$0.0200$) in metallicity, with four convective overshoot prescriptions. Strange modes were identified in a relatively small fraction ($5-12.5$ %) of models, occurring at $n_\mathrm{pg} = 5-9$, with $n_\mathrm{pg} = 6$-$7$ as the most frequent radial modes. No unstable solutions were identified beyond $n_\mathrm{pg} = 9$, in contrast to earlier studies reporting strange modes at $n_\mathrm{pg} = 10-12$. We quantified the duration of the instability crossing phase ($\tau_\mathrm{IS}$), the strange mode phase ($\tau_\mathrm{s}$), and their ratio $\mathcal{P}_\mathrm{s} = \tau_\mathrm{s} / \tau_\mathrm{IS}$. Toward higher masses, both $\tau_\mathrm{IS}$ and $\tau_\mathrm{s}$ decrease, yet their ratio shows no systematic trend with mass in models that include convective core overshoot. The absolute timescales for strange modes remain short, typically $\tau_\mathrm{s} \sim 10^{4.5}$-$10^{6}$ years, while $\tau_\mathrm{IS}$ is often an order of magnitude shorter, implying that these stars may spend a larger fraction of their life in the strange mode phase than in the instability strip itself. The extended duration of the strange mode phase may enhance the detectability of strange mode pulsators, provided that observational precision is sufficient to capture their low-amplitude variability. The predicted periods ($0.6-6.3$ days) are well covered by a single $27-$day TESS sector, making strange mode pulsators potentially detectable with current space-based photometry, although blending with nearby sources may pose challenges.

astro-ph.SR↗

arXiv2025

Search for millicharged particles in proton-proton collisions at $\sqrt{s} = 13.6$ TeV

We report on a search for elementary particles with charges much smaller than the electron charge using a data sample of proton-proton collisions provided by the CERN Large Hadron Collider in 2023--24, corresponding to an integrated luminosity of 124.7~fb$^{-1}$ at a center-of-mass energy of 13.6~TeV. The analysis presented uses the completed Run 3 milliQan bar detector to set the most stringent constraints to date for particles with charges $\leq0.24~\rm{e}$ and masses $\geq0.45~\rm{GeV}$.

hep-ex↗

arXiv2024

The Continuous Electron Beam Accelerator Facility at 12 GeV

This review paper describes the energy-upgraded CEBAF accelerator. This superconducting linac has achieved 12 GeV beam energy by adding 11 new high-performance cryomodules containing eighty-eight superconducting cavities that have operated CW at an average accelerating gradient of 20 MV/m. After reviewing the attributes and performance of the previous 6 GeV CEBAF accelerator, we discuss the upgraded CEBAF accelerator system in detail with particular attention paid to the new beam acceleration systems. In addition to doubling the acceleration in each linac, the upgrade included improving the beam recirculation magnets, adding more helium cooling capacity to allow the newly installed modules to run cold, adding a new experimental hall, and improving numerous other accelerator components. We review several of the techniques deployed to operate and analyze the accelerator performance, and document system operating experience and performance. In the final portion of the document, we present much of the current planning regarding projects to improve accelerator performance and enhance operating margins, and our plans for ensuring CEBAF operates reliably into the future. For the benefit of potential users of CEBAF, the performance and quality measures for beam delivered to each of the experimental halls is summarized in the appendix.

physics.acc-ph↗

arXiv2024

Barium stars as tracers of s-process nucleosynthesis in AGB stars III. Systematic deviations from the AGB models

Barium (Ba) stars help to verify asymptotic giant branch (AGB) star nucleosynthesis models since they experienced pollution from an AGB binary companion and thus their spectra carry the signatures of the slow neutron capture process (s process). For 180 Ba stars, we searched for AGB stellar models that match the observed abundance patterns. We employed three machine learning algorithms as classifiers: a Random Forest method, developed for this work, and the two classifiers used in our previous study. We studied the statistical behaviour of the s-process elements in the observational sample to investigate if the AGB models systematically under- or overpredict the abundances observed in the Ba stars and show the results in the form of violin plots of the residuals between spectroscopic abundances and model predictions. We find a significant trend in the residuals that implies an underproduction of the elements Nb, Mo, and Ru in the models relative to the observations. This may originate from a process (e.g. the intermediate neutron-capture process, i process) at the metallicity of the Ba stars not yet included in the AGB models. Correlations are found between the residuals of these elements, suggesting a common origin for the deviations. In addition, there is a weak metallicity dependence of their residuals. The s-process temperatures derived with the [Zr/Fe] - [Nb/Fe] thermometer have an unrealistic value for the majority of our stars. The most likely explanation is that at least a fraction of these elements are not produced in a steady-state s process, and instead may be due to processes not included in the AGB models. The mass distribution of the identified models confirms that our sample of Ba stars was polluted by low-mass AGB stars. Most of the matching AGB models require low accreted mass, but a few systems with high accreted mass are needed to explain the observations. (abridged)

astro-ph.SR↗

arXiv2023

Detailed asteroseismic modeling of RR Lyrae stars with non-radial modes

Photometric observations from the last decade have revealed additional low-amplitude periodicities in many classical pulsators that are likely due to pulsations in non-radial modes. One group of multi-mode RR Lyrae stars, the so-called 0.61 stars, is particularly interesting. In these stars, the radial first overtone is accompanied by additional signals with period ratios around 0.61. The most promising explanation for these signals is pulsation in non-radial modes of degrees 8 and 9. If the theory behind the additional signals in the 0.61 stars is substantiated, it would allow us to use non-radial modes to study classical pulsators. We aim to perform asteroseismic modeling of selected 0.61 stars with independently determined physical parameters to test whether this assumption behind the modeling leads to correct results. Namely, we test whether the additional signals are indeed due to non-radial modes of the proposed moderate degrees. We selected a number of and RR Lyrae stars that are also 0.61 stars and have good observational constraints on their other physical parameters. We assume that the nature of those modes is correctly explained with non-radial modes of degrees 8 or 9. Using this assumption and observational constraints on physical parameters, we performed asteroseismic modeling to test whether the observed periods and period ratios can be reproduced. For the majority of selected targets, we obtained a good match between observed and calculated periods and period ratios. For a few targets however, the results obtained are ambiguous and not straightforward to interpret.

astro-ph.SR↗

arXiv2023

A multi-wavelength analysis of BL Her stars: Models versus Observations

We present new theoretical period--luminosity (PL) and period--radius (PR) relations at multiple wavelengths (Johnson--Cousins--Glass and {\sl Gaia} passbands) for a fine grid of BL~Herculis models computed using {\sc mesa-rsp}. The non-linear models were computed for periods typical of BL~Her stars, i.e. $1\leq P ({\rm days}) \leq4$, covering a wide range of input parameters: metallicity ($-$2.0 dex $\leq$ [Fe/H] $\leq$ 0.0 dex), stellar mass (0.5--0.8 M$_{\odot}$), luminosity (50--300 L$_{\odot}$) and effective temperature (full extent of the instability strip; in steps of 50K). We investigate the impact of four sets of convection parameters on multi-wavelength properties. Most empirical relations match well with theoretical relations from the BL~Her models computed using the four sets of convection parameters. No significant metallicity effects are seen in the PR relations. Another important result from our grid of BL~Her models is that it supports combining PL relations of RR Lyrae and Type~II Cepheids together as an alternative to classical Cepheids for the extragalactic distance scale calibration.

astro-ph.SR↗

arXiv2021

Revised Best Estimates for the Age and Mass of the Methuselah Star HD 140283 using MESA and Interferometry and Implications for 1D Convection

In light of recently revised observational measurements of the radius and spectroscopic parameters of the extremely old and metal-poor Gaia benchmark star HD 140283 -- also known as the Methuselah star due to prior suggestions that its age is in tension with the age of the Universe -- we present new, best estimates for the star's mass and age from stellar modeling. These are derived using 1D stellar evolutionary tracks computed with MESA and the most up-to-date measurements from CHARA interferometry. Excluding modeling variance from the uncertainties, we report a mass of $0.809 \pm 0.001 M_{\odot}$ and an age of $12.01 \pm 0.05$ Gyr ($1 \sigma$). When dominant sources of modeling uncertainty are taken into account, we report $0.81 \pm 0.05 M_{\odot}$ and $12 \pm 0.5$ Gyr, respectively. These results are consistent with recent literature, and the best-fitting age is not in conflict with the currently accepted age of the universe ($13.5$ Gyr; arXiv:1303.5089 [astro-ph.CO]).

astro-ph.SR↗

arXiv2021

Test beam characterization of sensor prototypes for the CMS Barrel MIP Timing Detector

The MIP Timing Detector will provide additional timing capabilities for detection of minimum ionizing particles (MIPs) at CMS during the High Luminosity LHC era, improving event reconstruction and pileup rejection. The central portion of the detector, the Barrel Timing Layer (BTL), will be instrumented with LYSO:Ce crystals and Silicon Photomultipliers (SiPMs) providing a time resolution of about 30 ps at the beginning of operation, and degrading to 50-60 ps at the end of the detector lifetime as a result of radiation damage. In this work, we present the results obtained using a 120 GeV proton beam at the Fermilab Test Beam Facility to measure the time resolution of unirradiated sensors. A proof-of-concept of the sensor layout proposed for the barrel region of the MTD, consisting of elongated crystal bars with dimensions of about 3 x 3 x 57 mm$^3$ and with double-ended SiPM readout, is demonstrated. This design provides a robust time measurement independent of the impact point of the MIP along the crystal bar. We tested LYSO:Ce bars of different thickness (2, 3, 4 mm) with a geometry close to the reference design and coupled to SiPMs manufactured by Hamamatsu and Fondazione Bruno Kessler. The various aspects influencing the timing performance such as the crystal thickness, properties of the SiPMs (e.g. photon detection efficiency), and impact angle of the MIP are studied. A time resolution of about 28 ps is measured for MIPs crossing a 3 mm thick crystal bar, corresponding to an MPV energy deposition of 2.6 MeV, and of 22 ps for the 4.2 MeV MPV energy deposition expected in the BTL, matching the detector performance target for unirradiated devices.

physics.ins-det↗

arXiv2020

Testing dark matter halo properties using self-similarity

We use self-similarity in N-body simulations of scale-free models to test for resolution dependence in the mass function and two-point correlation functions of dark matter halos. We use 1024$^3$ particle simulations performed with ABACUS, and compare results obtained with two halo finders: friends-of-friends (FOF) and ROCKSTAR. The FOF mass functions show a systematic deviation from self-similarity which is explained by resolution dependence of the FOF mass assignment previously reported in the literature. Weak evidence for convergence is observed only starting from halos of several thousand particles, and mass functions are overestimated by at least as much as 20-25 percent for halos of 50 particles. The mass function of the default ROCKSTAR halo catalog (with bound virial spherical overdensity mass), on the other hand, shows good convergence from of order 50 to 100 particles per halo, with no detectable evidence at the few percent level of any systematic dependence for larger particle number. Tests show that the mass unbinding procedure in ROCKSTAR is the key factor in obtaining this much improved resolution. Applying the same analysis to the halo-halo two point correlation function, we find again strong evidence for convergence only for ROCKSTAR halos, at separations sufficiently large so that halos do not overlap. At these separations we can exclude dependence on resolution at the 5-10 percent level once halos have of order 50 to 100 particles. At smaller separations results are not converged even at significantly larger particle number, and bigger simulations would be required to establish the resolution required for convergence.

astro-ph.CO↗

arXiv2018

Classically and Asteroseismically constrained 1D Stellar Evolution Models of $\alpha$ Centauri A and B using Empirical Mixing Length Calibrations

The bright, nearby binary $\alpha$ Centauri provides an excellent laboratory for testing stellar evolution models, as it is one of the few stellar systems for which we have high-precision classical (mass, radius, luminosity) and asteroseismic ($p$-mode) observations. Stellar models are created and fit to the classical and seismic observations of both stars by allowing for the free variation of convective mixing length parameter $\alpha_{\text{MLT}}$. This system is modeled using five different sets of assumptions about the physics governing the stellar models. There are 31 pairs of tracks (out of ${\sim} 150,000$ generated) which fit the classical, binary, and seismic observational constraints of the system within $3\,\sigma$. Models with each tested choice of input physics are found to be viable, but the optimal mixing lengths for Cen A and Cen B remain the same regardless of the physical prescription. The optimal mixing lengths are $\alpha_{\text{MLT,A}} /\alpha_{\odot}= 0.932$ and $\alpha_{\text{MLT,B}}/\alpha_{\odot} = 1.095$. That Cen A and Cen B require sub- and super-solar mixing lengths, respectively, to fit the observations is a trend consistent with recent findings, such as in Kervella et al. (2017), Joyce and Chaboyer (2018), and Viani et al. (2018). The optimal models find an age for $\alpha$ Centauri of $5.3 \pm 0.3$ Gyr.

astro-ph.SR↗

arXiv2015

Investigating the Consistency of Stellar Evolution Models with Globular Cluster Observations via the Red Giant Branch Bump

Synthetic RGBB magnitudes are generated with the most recent theoretical stellar evolution models computed with the Dartmouth Stellar Evolution Program (DSEP) code. They are compared to the observational work of Nataf et al., who present RGBB magnitudes for 72 globular clusters. A DSEP model using a chemical composition with enhanced $\alpha$ capture [$\alpha$/Fe] $ =+0.4$ and an age of 13 Gyr shows agreement with observations over metallicities ranging from [Fe/H] = $0$ to [Fe/H] $\approx-1.5$, with discrepancy emerging at lower metallicities.

astro-ph.SR↗

arXiv2015

Angular momentum generation in cold gravitational collapse

During the violent relaxation of a self-gravitating system a significant fraction of its mass may be ejected. If the time varying gravitational field also breaks spherical symmetry this mass can potentially carry angular momentum. Thus starting initial configurations with zero angular momentum can in principle lead to a bound virialized system with non-zero angular momentum. We explore here, using numerical simulations, how much angular momentum can be generated in a virialized structure in this way, starting from configurations of cold particles which are very close to spherically symmetric. For initial configurations in which spherical symmetry is broken only by the Poissonian fluctuations associated with the finite particle number $N$, with $N$ in range $10^3$ to $10^5$, we find that the relaxed structures have standard "spin" parameters $\lambda \sim 10^{-3}$, and decreasing slowly with $N$. For slightly ellipsoidal initial conditions, in which the finite-$N$ fluctuations break the residual reflection symmetries, we observe values $\lambda \sim 10^{-2}$, of the same order of magnitude as those reported for elliptical galaxies. The net angular momentum vector is typically aligned close to normal to the major semi-axis of the triaxial relaxed structure, and also with that of the ejected mass. This simple mechanism may provide an alternative, or complement, to "tidal torque theory" for understanding the origin of angular momentum in astrophysical structures.

astro-ph.GA↗

arXiv2011

Muon and Cosmogenic Neutron Detection in Borexino

Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the efficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water-Cherenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are reviewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992% or better. Ad-hoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular distribution reflects the local overburden profile. The achieved angular resolution is 3-5 deg and the lateral resolution is 35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.

physics.ins-det↗

arXiv2010

Cold uniform spherical collapse revisited

We report results of a study of the Newtonian dynamics of N self-gravitating particles which start in a quasi-uniform spherical configuration, without initial velocities. These initial conditions would lead to a density singularity at the origin at a finite time when N \rightarrow \infty, but this singularity is regulated at any finite N (by the associated density fluctuations). While previous studies have focussed on the behaviour as a function of N of the minimal size reached during the contracting phase, we examine in particular the size and energy of the virialized halo which results. We find the unexpected result that the structure decreases in size as N increases, scaling in proportion to N^{-1/3}, a behaviour which is associated with an ejection of kinetic energy during violent relaxation which grows in proportion to N^{1/3}. This latter scaling may be qualitatively understood, and if it represents the asymptotic behaviour in N implies that this ejected energy is unbounded above. We discuss also tests we have performed which indicate that this ejection is a mean-field phenomenon (i.e. a result of collisionless dynamics).

astro-ph.CO↗

arXiv2009

Energy ejection in the collapse of a cold spherical self-gravitating cloud

When an open system of classical point particles interacting by Newtonian gravity collapses and relaxes violently, an arbitrary amount of energy may in principle be carried away by particles which escape to infinity. We investigate here, using numerical simulations, how this released energy and other related quantities (notably the binding energy and size of the virialized structure) depends on the initial conditions, for the one parameter family of starting configurations given by randomly distributing N cold particles in a spherical volume. Previous studies have established that the minimal size reached by the system scales approximately as N^{-1/3}, a behaviour which follows trivially when the growth of perturbations (which regularize the singularity of the cold collapse in the infinite N limit) are assumed to be unaffected by the boundaries. Our study shows that the energy ejected grows approximately in proportion to N^{1/3}, while the fraction of the initial mass ejected grows only very slowly with N, approximately logarithmically, in the range of N simulated. We examine in detail the mechanism of this mass and energy ejection, showing explicitly that it arises from the interplay of the growth of perturbations with the finite size of the system. A net lag of particles compared to their uniform spherical collapse trajectories develops first at the boundaries and then propagates into the volume during the collapse. Particles in the outer shells are then ejected as they scatter through the time dependent potential of an already re-expanding central core. Using modified initial configurations we explore the importance of fluctuations at different scales, and discreteness (i.e. non-Vlasov) effects in the dynamics.

astro-ph↗

arXiv2009

Dynamics of finite and infinite self-gravitating systems with cold quasi-uniform initial conditions

Purely self-gravitating systems of point particles have been extensively studied in astrophysics and cosmology, mainly through numerical simulations, but understanding of their dynamics still remains extremely limited. We describe here results of a detailed study of a simple class of cold quasi-uniform initial conditions, for both finite open systems and infinite systems. These examples illustrate well the qualitative features of the quite different dynamics observed in each case, and also clarify the relation between them. In the finite case our study highlights the potential importance of energy and mass ejection prior to virialization, a phenomenon which has been previously overlooked. We discuss in both cases the validity of a mean-field Vlasov-Poisson description of the dynamics observed, and specifically the question of how particle number should be extrapolated to test for it.

cond-mat.stat-mech↗

arXiv2006

Gravitational Dynamics of an Infinite Shuffled Lattice: Particle Coarse-grainings, Non-linear Clustering and the Continuum Limit

We study the evolution under their self-gravity of infinite ``shuffled lattice'' particle distributions, focussing specifically on the comparison of this evolution with that of ``daughter'' particle distributions, defined by a simple coarse-graining procedure. We consider both the case that such coarse-grainings are performed (i) on the initial conditions, and (ii) at a finite time with a specific additional prescription. In numerical simulations we observe that, to a first approximation, these coarse-grainings represent well the evolution of the two-point correlation properties over a significant range of scales. We note, in particular, that the form of the two-point correlation function in the original system, when it is evolving in the asymptotic ``self-similar'' regime, may be reproduced well in a daughter coarse-grained system in which the dynamics are still dominated by two-body (nearest neighbor) interactions. Using analytical results on the early time evolution of these systems, however, we show that small observed differences between the evolved system and its coarse-grainings at the initial time will in fact diverge as the ratio of the coarse-graining scale to the original inter-particle distance increases. The second coarse-graining studied, performed at a finite time in a specified manner, circumvents this problem. It also makes more physically transparent why gravitational dynamics from these initial conditions tends toward a ``self-similar'' evolution. We finally discuss the precise definition of a limit in which a continuum (specifically Vlasov-like) description of the observed linear and non-linear evolution should be applicable.

cond-mat.stat-mech↗