List of Abstracts 


A questions for decades has been the potential production of heavy or superheavy elements in nature. Once the nuclear weapons tests showed that elements heavier than the Uranium were found in the debris, it was clear that a rapid neutron capture process followed by beta decay was creating heavier elements. The next question was the location of the r-process end? What other heavy elements are made? Did nature make the superheavy elements via the r-process too? The answer is yet to be found. There are many indications that it probably did but the definitive evidence is yet to surface. The laboratory experiments with neutron rich beams and neutron rich targets via cold and hot fusion reactions have created a number of new isotopes in addition to the elements that have completed the periodic table. Furthermore, the new superheavy element factory at the JINR in Dubna has now allowed the identification of over one hundred decay chains of the various isotopes of superheavy elements connecting to the main part of the chart of nuclides via decays. This is where we should look for the definitive evidence for the production of the superheavy elements in nature.


Explosive transients are among the primary engines of chemical evolution in the Universe. Our ability to use supernovae and kilonovae as laboratories for nucleosynthesis is now being transformed thanks to novel wide-field time-domain surveys, rapid multi-wavelength follow-up facilities, and new multi-messenger windows. These same advances are also revealing the tidal disruptions of stars and additional extreme accretion events around supermassive black holes, which are another main driver of galactic chemical and dynamical evolution. But what can we actually learn from light curves and spectra of such events? I will discuss what current datasets can (and can't) tell us, where key degeneracies remain, and review a few upcoming facilities that promise to further advance this time-domain revolution.


Late-stage nuclear processing in stars leaves observable imprints on their variability, surface composition, and mass loss. In this talk, I present results from a time-domain, population-level study of oxygen-rich asymptotic giant branch (AGB) stars in the Milky Way, aimed at constraining internal mixing processes such as third dredge-up and their dependence on stellar mass and environment. Using long-period variability information combined with multi-wavelength infrared data from large surveys, I analyze tens of thousands of evolved stars across the local foreground, Galactic disk, and bulge. I show that pulsation period distributions and infrared color–variability correlations differ systematically between these environments, revealing distinct evolutionary pathways. In particular, shorter-period and semi-regular variables in the foreground preferentially occupy regions of period–color space associated with technetium-rich stars, consistent with efficient third dredge-up in lower-mass AGB stars. By contrast, inner-Galaxy populations are dominated by long-period Miras with colors indicative of technetium-poor envelopes, pointing to either metallicity-dependent suppression of dredge-up or the onset of hot-bottom burning in more massive stars. These results demonstrate that time-domain variability, when interpreted alongside infrared diagnostics, provides a powerful observational probe of nucleosynthesis and internal mixing in evolved stars. I conclude by discussing how upcoming time-domain surveys and data-driven analysis methods will further sharpen these constraints and connect stellar variability directly to nucleosynthetic yields and Galactic chemical evolution.


Prior to their explosion, the neutrino emission from red supergiants (RSGs) is so large that a nearby RSG will become visible in terrestrial neutrino detectors. The rate of emission and the spectra of the pre-supernova (pre-SN) neutrinos from RSGs are sensitive to the temperature, density, and detailed isotopic composition of the core. During the last weeks of the star's life, these properties change considerably as the nuclear burning accelerates and deleptonization begins. There are several factors of stellar evolution -  such as mass loss and the treatment of convective overshooting - that alter the thermal conditions and composition of the RSG core as it approaches collapse, and thus one also expects a subsequent effect upon the pre-SN emission. We construct a grid of progenitor models using the stellar evolution code MESA with a large, 206-isotope nuclear network to study the effects of wind mass loss and convective overshooting on the structure and composition of a star.


Massive stars-- a majority of which occur in binaries-- are key drivers of chemical evolution within galaxies through interactions such as mass transfer, natal kicks, and stellar winds. Binaries give rise to some of the most energetic events in the Universe, including supernovae, gamma-ray bursts, and compact object mergers. Low-mass stars evolve relatively slowly on cosmological timescales, efficiently producing elements up to iron. In contrast, understanding how metallicity influences massive stars—and, in turn, binary systems—is essential for accurately modeling stellar evolution and formation. Metallicity directly affects stellar winds, which influence remnant mass and determine remnant type. These processes have broader implications for the initial populations of galaxies and for the abundance of compact object systems over cosmic time.Our research uses  Compact Object Synthesis and Monte Carlo Investigation Code ({COSMIC}) to produce astrophysically motivated cosmic rates of binary populations. We find a strong anti-correlation between metallicity and the fraction of binaries containing compact objects.  We find that the number of systems containing either a massive star–black hole binary or a binary black hole peaks at redshift z ~2, coincident with the peak of cosmic star formation, and declines toward higher redshifts.  Finally, we compare the convolved formation rates of the proposed progenitor systems, ∼ 10−9, {Mpc^−3, yr^−1}, to the observed volumetric rate of long gamma-ray bursts,∼ 10−9, {Mpc^−3, yr^−1} (Gehrels & M´esz´aros 2012). The close agreement between these rates supports low-metallicity environments as a critical frontier for identifying and characterizing massive stellar binaries and their explosive transients in upcoming surveys. These results have direct implications for long GRB progenitors which, in particular, are among the most powerful transient events used to study high-energy mechanisms that may contribute to the production of heavy elements.



Metallicity plays a crucial role in influencing the evolution of massive stars and the compact binaries they form. In this talk, I will use the detailed binary simulations suite, POSYDON, to show how metallicity affects the evolution of He star + NS binaries, the direct progenitors of binary neutron star (BNS) systems. I will discuss how it shapes the formation efficiency and delay time distribution of BNS mergers as a function of metallicity and redshift across cosmic time. Together, these results highlight key implications for gravitational wave sources and early r-process enrichment of galaxies.



Observations of GW170817 strongly suggest that binary neutron star mergers produce rapid neutron-capture nucleosynthesis (r-process) elements. However, it remains an open question whether these mergers can account for al the r-process element enrichment in the Milky Way's history. In particular, the neutron star merger-only enrichment scenario has been shown to be inconsistent with the observed r-process abundance trend of stars in the Galaxy. In this talk, I will show the constraints on the contributions of the neutron star merger channel using recent astrophysical neutron star observations, including gravitational waves, radio, X-ray, and gamma-ray observations. I will then present a Bayesian framework to consistently combine these lines of observations with r-process abundance data to quantify the contribution and uncertainties of single and multiple astrophysical enrichment sources.



Low-mass thermally pulsing asymptotic giant branch (TP-AGB) stars are the primary producers of heavy elements beyond the first s-process peak (Ba, La, Nd, Pb). Directly probing this phase is challenging given that it is short-lived (<1% of the total stellar lifetime), AGB stars are intrinsically difficult to observe, and surface abundance changes during this period obscure their initial metallicities. Barium, CH, and CEMP-s stars provide indirect constraints, as their anomalously high s-process and carbon enhancements are attributed to mass transfer from a former AGB companion. However, degeneracies in the chemical impact of progenitor mass, metallicity, neutron-source strength, and mixing limit their diagnostic power with respect to theoretical modelling. Globular clusters and their disrupted stellar streams offer controlled nucleosynthetic laboratories, with well-constrained ages and initial compositions. Using a recently discovered CH star in the 300S stream, we isolate the TP-AGB mass-transfer signature through differential abundances relative to its stellar twin. We construct a tailored grid of stellar evolution and nucleosynthesis models matched to the 300S abundance pattern and simulate binary mass transfer from a TP-AGB companion. Our models reproduce the full heavy-element abundance pattern of the 300S barium star, demonstrating that TP-AGB mass transfer alone explains its enrichment and placing tight constraints on neutron-source strengths and mixing during the TP-AGB phase. All models are computed with MESA, and we will release our inlists and analysis tools on publication to enable full reproducibility and application to large surveys.


The nature of the dominant neutron-capture element production channel in the early universe is still a mystery. Early neutron-capture nucleosynthesis is known to be a rare process, but whether this process is prompt or delayed remains unclear. To study the timescale of this process, here we present chemical abundances and kinematics of a large sample of extremely metal-poor stars (EMP; [Fe/H] ≤ −3) in the inner Milky Way (R_GC ≲ 6 kpc). With high-resolution Magellan/MIKE spectra, we determine chemical abundances for 19 elements, with particular emphasis on Sr and Ba, which are often the only neutron-capture elements that are measurable at low metallicities. Overall, this sample has a relatively high [Sr/Mg] (≳ −1) compared to [Ba/Mg] (≲ −1), and [Sr/Mg] appears to have a larger scatter than [Ba/Mg]. Our results suggest that Sr is likely produced in a rare and prompt channel, while Ba is likely produced in a rare but delayed channel. We also find that the stars with the highest Ba abundances are enhanced in Eu ([Eu/Fe ≳ 0.7]), suggesting that the main source of early Ba is the r-process. Studying the orbits of these stars, we find that ~40% of our stars have apocenters ≲ 5 kpc, with all stars confined within 15 kpc. This substantial sample of extremely metal-poor stars in the inner Galaxy, whether they are ancient proto-Milky Way stars or accreted halo interlopers, shows that neutron-capture elements are produced in multiple channels in the early universe.


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White dwarf mergers are thought to play an important role in producing thermonuclear supernovae, yet the nature of the resulting explosions and remnants remains poorly constrained. In this talk, I use three-dimensional magnetohydrodynamic simulations of mergers involving two white dwarfs to investigate how different progenitor configurations map onto distinct thermonuclear outcomes. I will present a grid of three-dimensional magnetohydrodynamic (3D MHD) simulations of mergers involving carbon–oxygen (CO) and Hybrid Helium-CO (HeCO) white dwarfs (WDs), aimed at exploring their potential as progenitors of faint thermonuclear transients. The results highlight a wide range of possible merger outcomes, from disk-forming remnants to weak thermonuclear explosions, underscoring the sensitivity of these events to relatively small changes in progenitor properties. In particular, helium-rich components appear to play an outsized role in promoting instabilities and triggering energetic transients, even in systems with modest total masses. Taken together, these findings point to multiple evolutionary pathways linking white dwarf interactions to faint and under-luminous transients, and suggest that hybrid progenitors may contribute significantly to the observed diversity of thermonuclear explosions. More broadly, this work illustrates how detailed multidimensional modeling can help bridge binary evolution theory with the growing zoo of observed stellar transients.



The protoplanetary nebulae (PPN) phase is a brief transitional stage in the evolution of low- and intermediate-mass stars during which material processed on the AGB is expelled. Oxygen-rich PPNe therefore provide a direct window for connecting stellar nucleosynthesis to isotopic compositions measured in circumstellar gas. We present millimeter/submillimeter observations of six O-rich PPNe (the Frosty Leo Nebula, IRAS 22036+5308, the Cotton Candy Nebula, M1-92, OH 231.8+4.2, and IRAS 18276-1431) targeting H2S (JKa,Kc = 11,0→10,1) and SiO (J=2→1, 3→2, 4→3, and 6→5), including the isotopologues H233S and H234S, 29SiO, and 30SiO. The data were obtained with the Arizona Radio Observatory 12m antenna and Submillimeter Telescope, as well as the IRAM 30m. Toward the Frosty Leo Nebula, we obtain 32S/33S = 21.6 ± 7.4 and 32S/34S = 6.6 ± 1.2 from H2S (Gold & Ziurys, ApJ, 2025), far below solar values (124.3 and 21.7), indicating heavy sulfur isotope enhancement. Across the remaining objects, measured ratios span 32S/33S = 4.7–26 and 32S/34S = 1.9–5.3. Silicon isotopic ratios also deviate from solar (28Si/29Si = 19.7; 28Si/30Si = 30.0), with 28Si/29Si as low as 3.5 and 28Si/30Si as low as 5.0. Optical depth effects do not drive these ratios. The observed heavy-isotope enhancements may indicate neutron capture on 32S, and possibly 28Si, during the TP-AGB, with 13C(α,n)16O as the primary neutron source. Current nucleosynthesis models (e.g., NuGrid, FRUITY, etc.) fail to reproduce the observed isotopic ratios, implying episodes of enhanced neutron density and/or non-standard mixing histories may play a significant role in these objects.



The astrophysical origin of the heaviest elements produced by the r-process remains an open question. While compact-object mergers are firmly established as prolific r-process sites, their typically long delay times may be difficult to reconcile with the early enrichment observed in metal-poor environments. Accretion disks formed in collapsars have therefore been proposed as a compelling alternative: they are the only known stellar-collapse environments capable of reaching densities comparable to those of post-merger disks, and they can enrich the interstellar medium on the short timescales set by the lifetimes of massive stars. Until recently, however, it was unclear whether neutron-rich outflows could emerge from collapsing stars, owing to the lack of large-scale neutrino-magnetohydrodynamic simulations of collapsars. In this talk, I will present results from the first simulations of this kind, which show that, contrary to previous expectations, collapsars do not produce neutron-rich ejecta. I will conclude by discussing the broader implications of this finding for r-process nucleosynthesis and for identifying the dominant astrophysical sources of the heaviest elements.



The chemical abundances of a galaxy encode information about nucleosynthesis and its astrophysical sites, but this information is confounded by the effects of star formation. Empirical constraints on supernova yields and their timing from abundances have therefore been very challenging. We introduce a galactic chemical evolution model DLEIY that uses an observed star formation history and metallicity distribution to reduce these confounding factors. Using a joint statistical model of the dwarf spheroidal galaxies Sculptor and Fornax, simultaneous constraints on population-averaged yields and galactic outflows are achieved with DLEIY without fixing the yield scale. The Fe yield from core collapse supernovae is consistent with existing theoretical yield models, while the measured Mg yield is a factor of 2-4 higher, corroborating previous suggestions that yield models may under-predict [Mg/Fe]. We also find that the rate of Type Ia supernovae is enhanced by about a factor of 5 relative to field galaxies, and the delay-time distribution goes as $\sim t^{-2}$, a much steeper relationship than that measured from supernova surveys ($\sim t^{-1.1}$). These findings may suggest a metallicity-dependence of the Type Ia rate and delay-time distribution.


The ancient stellar populations and relatively simple structure of dwarf spheroidal galaxies make them excellent laboratories for studying chemical evolution and star formation in the early universe. Leveraging the capabilities of medium-resolution, multi-object spectroscopy with Keck/DEIMOS, we assembled the largest homogeneous set of neutron-capture element abundances in dwarf spheroidals to date. In this talk, I will compare new one-zone galactic chemical evolution models, including s-process and r-process enrichment from multiple sources, to Sr, Y, Ba, and Eu abundances in Sculptor. Having both Ba and Eu abundances in many stars in Sculptor allows us to disentangle the contributions from the s- and r-process. In addition, the Ba and Eu measurements provide constraints on the minimum delay time of neutron star mergers at early times. The neutron star merger minimum delay time changes with the inclusion of a prompt r-process source in the models, such as magneto-rotational supernovae. The r-process Sr and Y abundances at low metallicities may place limits on the production of light r-process elements in neutron star mergers, which are difficult to predict from theory due to their strong dependence on accretion disk properties.


The relative enrichment of elements formed by different neutron capture processes is known to evolve with time, with the r-process dominating relative to the s-process at early cosmic times. Elements formed solely by the r-process are radioactive and can be used to constrain their production timescales. As such, studying the chemical composition of r-process enriched stars can provide a window into the enrichment history of the r-process itself. The initial relative abundance two co-produced r-process elements, in this case a radioactive r-process element and a stable r-process element, is known as the production ratio. Using observed abundances of r-process elements in stars with known ages in the Milky Way, the radioactive decay of thorium can be used to find the initial relative abundance of r-process present in the gas when the star first formed. However, observed abundances of stable r-process elements contain “contamination” from other processes and the initial abundance will not reflect the true production ratio. Moreover, the fraction of the element formed by contaminating processes has an unconstrained dependence on stellar age. In this work, we correct the stable r-process abundances for a sample of stars in the Milky Way disk to include only the fraction of the element produced by the r-process in order to obtain accurate r-process production ratios. Making joint use of statistical modeling and kinematic data, we find the temporal evolution of the r-process fraction for europium and neodymium in the Milky Way thin disk and corresponding functions for the time-dependent r-process production ratios. 


The astrophysical origin of the heaviest elements remains a mystery. While compact binary mergers are confirmed r-process sites, their delay-time distribution challenges their role as the dominant source of early enrichment. Massive collapsars, particularly those above the pair-instability gap, offer a compelling alternative, capable of producing neutron-rich outflows under extreme accretion conditions. We present results from 3D general relativistic magnetohydrodynamic (GRMHD) simulations with M1 neutrino transport, modeling the collapse of rapidly rotating, low-metallicity progenitors that form black holes with accretion disks. Our study quantifies how magnetic field strength and angular momentum configuration influence r-process yields and tracks black hole mass and spin evolution, which govern jet energetics and gamma-ray burst (GRB) signatures. These simulations provide self-consistent predictions of neutron-rich ejecta and their implications for kilonova emission.


Type II supernovae (SNe II) mark the terminal explosions of massive stars that retain their hydrogen envelopes, serving as key sites of nucleosynthesis, dust formation, and compact object production. However, direct constraints on the heart of these neutrino-driven explosions remain limited, aggravated by observations that have so far been largely limited to optical/NIR wavelengths. To date, two SNe II (2023ixf and 2024ggi) have been observed spectroscopically with JWST at >1 year post-explosion, and just one with a spectral resolution capable of robustly characterizing mid-IR emission line profiles necessary for a spatial mapping of nucleosynthetic yields. In this talk, I will present analysis on the IR emission lines of iron-group and intermediate-mass elements (e.g., Ni, Co, Fe, Ne, Mg, Ar) present in the nebular JWST spectra of SNe II 2023ixf and 2024ggi. I will discuss how spectral morphology across different species and ionization states can robustly map the velocity structure and composition within the inner core of SNe II. Furthermore, I will show evidence for a asymmetric Nickel distributions and efficient Ni-56 mixing during explosive nucleosynthesis and proceeding core collapse. Lastly, I will demonstrate how we can combining JWST data with state-of-the-art radiative-transfer and 3-D explosion simulations to constrain ejecta composition, species distribution, and the neutrino-driven explosion mechanism in SNe II.


I will present results from an ongoing search for Low Alpha Metal Poor Stars (LAMPS) selected from the Sloan Digital Sky Survey V. This selection was defined to identify stars from the lowest mass accreted dwarf galaxies, but it also picks out extreme abundance outliers. We have identified the lowest total metallicity star known, found evidence for unusual nucleosynthesis in massive stars, and seen many stars that appear to trace individual Type Ia supernova explosions. SDSS will have a major data release in Summer 2026.



Nucleosynthesis calculations performed to obtain astrophysical abundances employ theoretically evaluated neutron capture reaction rates. In this talk, I will discuss our work that finds that among the thousands of isotopes for which we rely on theory models, only 2 or 3 isotopes influence the production of each element in various weak r-process astrophysical conditions. The weak r-process conditions taken into consideration are two cold neutron star merger disk and a magnetorotational supernova each of which produce the first and second r-process peak elements. The uncertainties in neutron capture rates are however correlated due to correlations in Hauser-Feshbach inputs. I will discuss how one particular input, the optical model potential, makes neutron capture reactions correlated and further how these impact the elemental abundance-neutron capture rate correlations.

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All known Type Ia supernova models fail to reproduce the observed luminosity-width correlation The primary power source of optical emission in Type Ia supernovae is gamma-rays from the radioactive decay of 56Ni, synthesized during the explosion. As the ejecta expands, it becomes increasingly transparent, allowing gamma rays to escape. The gamma-ray escape time, t0, can be measured with high precision using an integral relation we derived, independent of the supernova distance. By combining t0 with the synthesized 56Ni mass (MNi56), we identified a strong correlation between t0 and MNi56. This observed relation is similar to the well-known Phillips relation, which links light curve width to peak luminosity. However, unlike the Phillips relation, comparing models to the t0-MNi56 relation bypasses radiation transfer calculations, as the ejecta properties directly determine t0. Accurately modeling thermonuclear supernovae requires solving hydrodynamic equations coupled with nuclear-burning networks involving hundreds of isotopes—currently infeasible in multidimensional full-star simulations. In particular, thermonuclear detonation waves (TNDWs), crucial to such explosions, remain unresolved. We developed a new numerical scheme that accelerates calculations by orders of magnitude while preserving accuracy. The scheme includes (1) a burning limiter that broadens the TNDW while maintaining internal structure and (2) an adaptive grouping of isotopes in quasi-nuclear-statistical equilibrium, optimizing burning calculations. Our method achieves percent-level accuracy in multidimensional simulations and enables, for the first time, reliable modeling of progenitor scenarios for thermonuclear supernovae. Applying our scheme, we found that all existing Type Ia supernova models fail to reproduce the observed t0-MNi56 relation. Urgent avenues for refinement will be discussed.


Unprecedented JWST observations of both normal type Ia supernovae (SN Ia) and a wide range of peculiar white-dwarf (WD) explosions are transforming our understanding of their progenitor systems and explosion physics. While optical spectra are dominated by blended lines of iron-group elements, mid-infrared (MIR) spectroscopy reveals more isolated lines from previously inaccessible ions, including important intermediate-mass elements. These features provide new, direct constraints on the distribution of nucleosynthetic products and the physical conditions in the ejecta. I will present JWST MIR observations of SN 2024gy that resolve distinctive late-time (nebular) emission-line profiles, enabling detailed tests of explosion physics. In SN 2024gy we find compelling evidence for a delayed-detonation transition (subsonic to supersonic burning) in a near-Chandrasekhar-mass white dwarf. These results illustrate how late-time MIR nebular emission lines in transients provide direct observational constraints on explosive nucleosynthesis, connecting time-domain data to the underlying nuclear burning processes.

Nuclear reaction networks are essential to understand the abundances and flow of reactions in dense matter environments such as neutron stars, binary mergers of neutron stars and supernovae. To speed up the calculation times and reduce the computational accuracy while preserving accuracy for sensitivity analyses, one can replace the solvers with surrogate models, also called emulators. To this end, we use a couple of methods to emulate the reaction networks for the CNO cycle, namely, dynamic mode decomposition[1-3] and Parametric matrix models[4]. In this talk I will present recent results towards emulating CNO cycle and r-process reaction networks using these methods.



The nucleosynthetic origin sites of elements are expected to affect their galactic spatial distributions, and these distributions in turn should determine the structure of stellar chemical abundance space. However, efforts to study the element-to-element variation in gas-phase abundances have thus far been limited due to both spatial resolution and difficulty in direct chemical abundance measurements. I will present a recent study that uses the integrated field unit data to produce maps of abundances of oxygen, nitrogen, and sulphur using the direct methods of two nearby dwarf galaxies and allowing detailed analysis of the spatial statistics of the three elements. We find strong observational evidence for differences and correlations in the elements’ spatial statistics. Our findings are quantitatively consistent with the prediction of nucleosynthetic models that nitrogen is injected by a 60/40 mix of non-explosive and supernova events, the latter of which are responsible for oxygen and sulphur enrichment. Despite these differences, the abundances of oxygen and sulphur are better correlated than nitrogen versus oxygen and nitrogen versus sulphur. The findings are qualitatively consistent with recent findings that stellar abundances in the Milky Way show very high element-to-element correlations. Our results suggest that such correlations originate in the highly-correlated spatial distributions of different elements in the interstellar medium.



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The rapid neutron capture process (r-process) is a key mechanism for synthesizing elements heavier than iron, and is entirely responsible for the natural production of the actinides. It has long been accepted that the r-process could occur in the unbinding of material during the inspiral and merger of a neutron star with either a black hole or another neutron star. Multimessenger observations of the binary neutron star merger event, GW170817, provided the first confirmation of lanthanide production in the merger ejecta. Despite this breakthrough in observational evidence of site-specific r-process production, constraining the full nucleosynthetic potential for binary neutron star mergers, and the role they play in chemically enriching the galaxy, remains a challenge. One of the major difficulties in addressing these challenges lies in reconciling models, measurements, and observations that operate on vastly different physical and temporal scales. In this talk, I will discuss the interplay between several different disciplines and their effects on predicting nucleosynthesis-related observables, including kilonova light curves and abundances of metal-poor stars.


Stellar abundances trace key astrophysical phenomena such as the chemical evolution of the Galaxy and the origin of the chemical elements. However, abundances are commonly affected by systematics and large uncertainties that can limit the precision with which we can constrain these processes. Differential abundance analysis, historically applied to small (<100) groups of twin stars, is the best way to achieve exceptionally high precision while minimizing unphysical systematic trends. We have constructed one of the largest differential abundance catalogs to date to place some of the highest precision constraints on the Solar neighborhood’s chemical evolution. Using high-resolution (60,000 > R > 120,000) spectra from the gr8stars catalog, we determine differential abundances for nearly 2,000 stars spanning -1.00 > [Fe/H] > 0.35 in up to 35 elements spanning C through Er. We work in narrow stellar parameter bins that are centered on well-characterized reference stars that span F, G, and K-type dwarfs. We achieve Teff precisions of 5 – 30 K, logg precisions of 0.01 – 0.1 dex, and [X/Fe] precisions between 0.005 and 0.05 dex for up to 35 elements. With this sample, we (1) quantify the intrinsic chemical dimensionality and scatter of the Solar neighborhood as a function of metallicity and age, and (2) compare our age-abundance trends to theoretical tracks from existing state-of-the-art galactic chemical evolution models. Finally, we examine yield adjustments required to match OMEGA+ galactic chemical evolution tracks to our observed trends. This work illustrates the power of differential abundances of small groups of twin stars to constrain Galactic chemical evolution and nucleosynthesis.


Magnesium isotope ratios provide a powerful constraint on nucleosynthesis in massive stars. The three stable Mg isotopes (^24Mg, ^25Mg, ^26Mg) are cycled within the Mg-Al chain, which operates during hot hydrogen burning, while the conversion of ^22Ne to ^25Mg via ^22Ne(a,n)^25Mg is the central neutron source for weak slow neutron capture nucleosynthesis in intermediate and massive stars. Multiple stellar populations in globular clusters challenge models of stellar evolution by exhibiting chemical variations that canonical nucleosynthetic frameworks cannot fully explain. Mg isotopic ratios offer particularly strong constraints on the origin of light-element abundance anticorrelations and provide a critical test of competing globular cluster formation scenarios. In this talk, I present a high-precision spectroscopic analysis of Mg isotope ratios in globular clusters. We identify a striking anomaly: although stars enhanced in N, Na, and Al show increased ^26Mg/^24Mg, we see no corresponding trend for ^25Mg/^24Mg. Further, Mg isotopic ratios do not differ between stars enhanced in slow neutron-capture elements and those without, suggesting that the dominant neutron source for the slow neutron-capture process in globular cluster members is the ^13C(a,n)^16O reaction, rather than ^22Ne(a,n)^25Mg. These results demonstrate that Mg isotopes encode the signatures of the typical nuclear reactions and temperatures responsible for the enrichment of globular cluster members, and provide a direct, isotopic-level probe of stellar nucleosynthesis.



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We investigate a sub-Chandrasekhar mass double detonation pathway for Type Ia supernovae arising from single degenerate helium accreting carbon-oxygen white dwarfs. Building on our previous one dimensional study of recurrent helium novae \citep{hillman2025}, we evolve a $0.7~\rm{M_\odot}$ white dwarf through steady accretion at $10^{-8}~\rm{M_\odot~yr^{-1}}$ until it reaches $1.1~\rm{M_\odot}$, yielding realistic, time evolved helium rich profiles. These profiles are mapped into FLASH simulations, incorporating nuclear burning for helium and carbon–oxygen detonation, in multi-dimensional hydrodynamic runs. A localized, modest temperature perturbation near the base of the helium shell robustly triggers an outward helium-shell detonation. The ensuing inward propagating shock converges in the carbon–oxygen core, igniting a secondary detonation that unbinds the star. We obtain a $^{56}$Ni yield of $\simeq 0.64 \rm{M}_\odot$, an intermediate-mass element (Si-Ca) mass of $\simeq 0.41 \rm{M}_\odot$, and maximum ejecta velocities approaching $\sim 22,000~\rm{km~s^{-1}}$ - values consistent with normal Type Ia supernovae. Our results demonstrate that recurrent helium accretors-typically quiescent over long timescales-can evolve under subtle, ``quiet" conditions to trigger robust double detonations, supporting their role as viable progenitors of sub-Chandrasekhar mass Type Ia supernovae. 


Our current understanding about the nucleosynthetic origin of majority of the elements and their abundance trends in the Milky Way come from the careful spectroscopic analysis of well characterised absorption lines in the optical spectra (e.g. Gaia-ESO, GALAH etc). However, there are several elements for which usable absorption lines are absent in the optical stellar spectra such as phosphorus, fluorine, ytterbium etc, and their origin and evolution are still under debate. Near-infrared (NIR) spectra of KM giants have been found to harbour several usable lines of these elements. In addition, NIR wavelength range is much less extinct by dust enabling observations along the Galactic plane where majority of the stars reside. With the advent of sensitive instruments and the possibility to efficiently record larger parts of the NIR spectrum simultaneously with instruments such as IGRINS (1.5 - 1.8 um, 2.05 - 2.4 um; R~45,000), it is now possible to explore the HK band spectra in detail. The high resolution IGRINS spectrum further ensures that the blends are disentangled better and the weak spectral features are well captured easing the line identification and abundance determination from them. In this talk, I will present the characterisation of the HK band absorption lines of phosphorus, fluorine, neutron-capture elements such as ytterbium and barium in the IGRINS spectra of KM giants in the solar neighbourhood. I will discuss the best stellar candidates or the range of stellar parameters for which these absorption lines are strong and unaffected by blends, ensuring reliable abundance determination. This opens up the possibility of using the existing (GIANO, CRIRES+), near-future (MOONS), and future high-resolution NIR spectrometers (ELT, TMT) to determine abundances of multitude of elements formed from a unique mixture of different nucleosynthetic networks, acting at vastly different timescales, for stellar populations in the dust-ridden regions of the Milky Way.


The lifetime of free neutrons was a long-standing puzzle: in the beam experiments it significantly exceeded the corresponding result from the trap experiments – far beyond the error margins. While the results of the trap experiments were based on counting neutrons, the results of the beam experiments were based on counting protons stemming from the 3-body decay of a neutron into a free proton and a free electron (plus antineutrino). It was well-known that there is a relatively small probability for the 2-body decay of a free neutron into a hydrogen atom (plus antineutrino). For explaining the above puzzle, the Branching Ratio (BR) for this 2-body decay (missed in the beam experiments) – compared to the usual 3-body decay – should have been ~ 1%. However, the theoretical BR for such 2-body decay was previously known to be 4x10-6. In our paper in New Astronomy 113 (2024) 102275, it was pointed out that after taking into account the second solution of the Dirac equation for hydrogen atoms (that becomes legitimate for the S-states after allowing for the experimental charge distribution inside protons), the theoretical BR for the 2-body decay of free neutrons (into hydrogen atoms and antineutrinos) got enhanced by a factor ~ 3000 to become ~ 1%. The existence of such atoms (abbreviated SFHA) is evidenced by several different types of atomic experiments and by astrophysical observation; due to the quantum selection rules for the S-states, they do not interact with the electromagnetic radiation: they remain dark. Thus, the neutron lifetime puzzle appeared solved completely. In our paper in Nuclear Phys. B 1014 (2025) 116879, we proposed conceptual designs of the experiments that will constitute both the first experimental detection of the two-body decay of free neutrons and the experimental confirmation that the two-body decay of free neutrons produces overwhelmingly the SFHA. Such experiments are in preparation at Los Alamos National Lab (USA) and at Forschungszentrum Jülich (Germany). In one of the above papers, we showed that via the enhanced 2-body decay of neutrons, old neutron stars could very slowly generate the new specific, described in detail baryonic Dark Matter (DM) in the form of the SFHA. Some old neutron stars would release it into their tiny atmospheres, while some other old neutron stars would release it into the interstellar medium. Besides, mergers of a neutron star with another neutron star or with a black hole, accompanied by the ejection of neutron-rich material, can also lead to the formation of SFHA as the ejecta cools down. This is another interesting aspect of the multi-messenger astronomy focused on studying these mergers through the gravitational waves they generate. There is observational evidence of the continuing generation of new baryonic DM by neutron stars via the enhanced 2-body decay of neutrons.


I will discuss how supernovae and stellar winds contribute to elemental abundance patterns in four FIRE simulations of Milky Way-mass galaxies. I will introduce a new method for tracking stellar enrichment in cosmological galaxy simulation that allows us to vary assumptions about enrichment and explore its effects entirely in postprocessing. I will discuss the relative contribution of white-dwarf supernovae, core-collapse supernovae, and stellar winds to metals stored in stars, examining trends as a function of age and position in the galaxy. I will then discuss how well each of the four galaxies retains their metals. I will show that metal retention depends on galactocentric radius, lookback time, and the channel through which metals were released, highlighting where my results reinforce or challenge the assumptions commonly made in closed-box models.



The slow neutron-capture process (s-process) and intermediate neutron-capture process (i-process) are important sources to elements heavier than iron, complementing the rapid neutron-capture process. The s-process, at neutron densities of ~10^8–10^12 cm^-3, occurs in He- and C-burning shells of massive stars and during thermal pulses in low- to intermediate-mass AGB stars, giving a crucial contribution to the solar abundances from Fe to Bi. Recent high-precision neutron-capture data and refined stellar models have improved constraints on its sites and yields. The i-process, operating at intermediate densities (~10^13–10^16 cm^-3), is activated by proton ingestion into hot convective He-layers, producing distinctive abundance signatures. It offers explanations for peculiar abundances in e.g., carbon-enhanced metal-poor stars, post-AGB stars and stars in some anomalous Open Clusters. Advances in multidimensional stellar simulations and nuclear inputs are required to clearly define the i-process astrophysics relevance. I will outline the current status of both processes, highlight key recent developments, and discuss open challenges including their roles in Galactic chemical evolution.



Accretion-induced collapse (AIC) of white dwarfs provides a promising astrophysical site for r-process nucleosynthesis and kilonova emission. Drawing on results from multidimensional GRMHD and radiative transfer simulations, my talk will explore the conditions that favor robust heavy element production and discuss the electromagnetic signature of these rare and intriguing events. 


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Kilonovae are the electromagnetic transients created by the radioactive decay of heavy elements synthesized in the ejecta from neutron star mergers (NSM). NSMs are thought to be the main source of half of the heavy elements in the universe. These elements are a result of rapid neutron capture (r-process) nucleosynthesis, a process that varies significantly due to local conditions. By better understanding how the local conditions in nucleosynthesis affect kilonovae, we can recover the quantities, like densities and temperatures, at which heavy elements (Au, U, Pu) are synthesized. Since the first kilonova discovery in 2017, much effort has been spent to create models that accurately represent observations. Previous models, however, do not include entropy as a parameter, though entropy is an essential aspect of r-process calculations. In order to solve such a complex problem, we used spherically symmetric models to allow greater variation in parameters. We modeled a grid that accurately accounts for the evolution of entropy as it interacts with other parameters outside of nuclear statistical equilibrium (NSE). These results expand on our current understanding of r-process nucleosynthesis.


The 2023 NSAC Long Range Plan for Nuclear Science posed the question, "what are the nuclear processes that drive the birth, life, and death of stars?" as one of the major open science questions in the present era. Neutron-capture reactions play a pivotal role in the synthesis of elements heavier than iron, and our understanding of heavy element nucleosynthesis relies on the interplay between experimental measurements, theoretical predictions, computational modeling, and observational data. Accurate measurements of neutron-capture cross sections and reaction rates provide crucial input for astrophysical models of neutron-capture processes such as the slow (s), intermediate (i), and rapid (r) processes. These measurements, however, prove challenging to perform directly due to the short-lived nature of the nuclei involved and the lack of a neutron target at present. Over the last decade, several indirect experimental techniques have been developed to provide constraints of neutron-capture reactions both near and far from stability. In this presentation, I will discuss the current state of experimental neutron-capture techniques and highlight recent nuclear astrophysics results.



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Actinides are the heaviest group of r-process elements and require special neutron-rich conditions to be formed. Over the past years, studies have shown that the most easily measured actinide element, thorium (Th), shows significant variations in metal-poor stars, with respect to lanthanide elements (e.g., Eu, Dy), hinting at variations in the underlying astrophysical conditions of the r-process events. However, these abundances have been measured by different studies using different atomic data. In this talk, I will present homogeneous Th abundances for 49 metal-poor stars, more than doubling the current literature sample in this regime. I will present the chemical evolution picture that is now emerging for actinides, and a refined estimate of actinide-to-lanthanide yield variations in r-process events. Finally, I will discuss the implications of these results for r-process sites and their astrophysical conditions.



Supernovae, the explosive endpoints of massive stars, are the universe’s cosmic alchemists, fundamentally responsible for forging and dispersing the heavy elements and dust that drive galactic chemical evolution. While the late-time enrichment of galaxies by stars is well-established, key uncertainties remain regarding the contribution of core-collapse supernovae (CCSNe) to the universe’s initial heavy element and dust inventory, placing limits on models of nucleosynthesis and chemical evolution. Leveraging the unprecedented infrared capabilities of the James Webb Space Telescope, our research is providing a transformative view of the processes governing nucleosynthesis and elemental dispersal in these stellar explosions. This presentation examines JWST’s groundbreaking observations of CCSNe, which trace the evolution from the initial formation of elemental dust precursors to the presence of substantial dust masses years after the explosion.

Key findings include direct constraints on the composition and mass of the supernova ejecta, which is a direct product of the star’s nuclear burning stages. By analyzing the observed molecular signatures (e.g., carbon monoxide and silicon monoxide) and the total dust mass, we can place new limits on the progenitor star's mass loss history and the total mass of elements expelled into the interstellar medium. These measurements are crucial for refining stellar evolution models and accurately quantifying the role of massive stars in the chemical enrichment of galaxies, thereby addressing key questions at the intersection of nuclear astrophysics and time domain astronomy. 


The CEJSN r-process site is one of the promising r-process sites for the early Universe and Galaxy. I argue that it is the most promising one. I will compare several theoretical r-process sites with observations and show that the CEJSN r-process site fulfills all observations. A very new result (unpublished yet) will be the usage of the scatter in the r-process abundance of metal-poor stars to deduce the presence of two populations, one that is best explained by the CEJSN r-process scenario.



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Explosive astrophysical environments, such as X-ray bursts, novae and supernovae govern nucleosynthesis on the proton-rich side of the valley of stability. In these sites, nucleosynthesis proceeds mainly through p- and α- induced reactions, as well as photodisintegration reactions that push the nuclear flux away from the valley of stability. Modeling these environments requires detailed knowledge of nuclear properties and reaction rates for the nuclei involved. To address this need, direct measurements in the astrophysically relevant Gamow window with radioactive beams are essential. In this talk, I will present two radioactive beam experiments for explosive nucleosynthesis. In the lighter-mass region, I will discuss one of the main breakout pathways from the hot CNO cycle towards explosive burning and the rp process, the 14O(a,p)17F reaction. At typical burst temperatures, this reaction proceeds predominantly through a 6.15 MeV resonant state in 18Ne, that can decay through p, α or possibly 2p emission. Using the Active Target and Time Projection Chamber (ACTAR TPC) at TRIUMF, the 6.15 MeV resonance was populated through inelastic proton scattering on a radioactive 17F beam. This measurement provides the first direct search for the two-proton decay of the 6.15 MeV resonance in 18Ne and aims to determine the branching ratios between the 2p, p, and α decay channels. Moving on towards the heavy elements and the astrophysical γ process, I will present the first measurement of the 73As(p,γ)74Se reaction, one of the main destruction mechanisms of the lightest p nucleus 74Se. The measurement was performed using a radioactive 73As beam with the Summing NaI (SuN) detector at the Facility for Rare Isotope Beams. Along with the total cross-section measurement, the impact of the extracted reaction rate in the production of 74Se in Type II supernovae will be presented.


Compact object binaries are central to nuclear astrophysics as sources of r-process elements and multi-messenger signals. We present a population synthesis study investigating the formation of circumbinary disks (CBDs) following common envelope evolution (CEE) between a neutron star (NS) or black hole (BH) and a giant companion and examine their impact on the evolution of double compact object (DCO) systems. We discovered that CBD formation is most common in systems expected to merge within Hubble time. Additionally, we observe that the CBD's interaction with the core and compact object post-CEE reduces DCO merger rates, regardless of binary dynamics. These effects have direct implications for gravitational-wave event rates and for the timing of r-process enrichment from NS-NS mergers. Our results highlight the importance of including post CEE CBDs in models connecting binary evolution, nucleosynthesis, and time-domain observations. 



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Neutrons are being produced in the highly dynamic environment of intershell mixing in low mass AGB stars and in the dying moment of massive red giant stars. So far the impact of neutron poisons on neutron production has been largely ignored, but will be highlighted in this presentation, which is based on the analysis of new nuclear reaction data.



The planetary nebula (PN) phase, which follows the Asymptotic Giant Branch (AGB), is the evolutionary ending for most stars. As the PN stage begins, nucleosynthesis ceases. Therefore, elemental and isotopic abundances of planetary nebulae should reflect those of the AGB/PN transition. Few studies, however, have been conducted of 12C/13C ratios in PNe. This ratio, in contrast, has been studied extensively in AGB envelopes with typical values of 12C/13C ~ 25–90 for shells with C >O and 12C/13C ~ 3-35 for the C < O case. Recently, we measured the 12C/13C ratio towards a sample of PNe using CO, HCN, HNC, CN, and other molecules, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The sample included well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440. The ratios found were unexpectedly low, lying in the range 12C/13C ~ 1.0 ± 0.7 to 13.2 ± 4.9, with an average value of 3.7 - drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Most of the PNe observed were clearly carbon-rich, eliminating Hot Bottom Burning as the explanation. New observations of other sources also show similar 13C enrichment. Furthermore, the lowest ratios have all been found in bipolar nebulae with N/O equal to or greater than 1, suggesting a correlation between 13C and nitrogen. New observations also suggest some 17O enrichment in such sources as well. The consistently low 12C/13C ratios observed, combined with their high N/O ratio and the bipolar morphology of all planetary nebulae observed, suggest that a rapid hot process, involving proton-capture, occurred at the AGB-PNe transition.