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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Systematic Bayesian evaluation of resonance parameters in 19 Ne for the 15 O ⁡(𝛼, 𝛾)⁢ 19 Ne and 18 F ⁡(𝑝, 𝛼)⁢ 15 O reactions

Here, we present a comprehensive evaluation of the nuclear structure properties of 19 Ne using a novel and rigorous Bayesian statistical framework. Precise characterization of 19 Ne resonance parameters is critical for accurately determining reaction rates of the astrophysically significant 15 O ⁡(𝛼, 𝛾)⁢ 19 Ne and 18 F ⁡(𝑝, 𝛼)⁢ 15 O reactions, which govern breakout from the hot CNO cycle in x-ray bursts and influence 𝛾-ray emission in novae, respectively. By reconstructing likelihood functions from published experimental data—including asymmetric uncertainties and upper or lower limits—we derive posterior distributions for resonance energies, decay widths, and branching ratios. Our Bayesian approach systematically incorporates previously reported discrepancies among measurements, providing a statistically robust and consistent treatment of these uncertainties. The evaluated resonance parameters and associated uncertainties provide crucial input for stellar nucleosynthesis modeling, contributing to a refined understanding of explosive astrophysical phenomena.

Kim, Sohyun H. [Sungkyunkwan Univ., Suwon (Republi↗
DOE OSTI2020

The R -process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510

In this work, we report on the spectroscopic analysis of RAVE J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [Fe/H] = –3.57, this star has one of the lowest metallicities currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the solar system $\textit{r}$-process predictions suggests that there must have been a non-standard source of $\textit{r}$-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually high velocities in a neutron star merger event. We also explore the possibility that the neutron-capture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE J1830-4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Blanco DECam Bulge Survey (BDBS). VII. Multiple Populations in Globular Clusters of the Galactic Bulge

We present photometric evidence for multiple stellar populations (MPs) in 14 globular clusters (GCs) toward the southern Galactic bulge. The photometric data come as part of the Blanco DECam Bulge Survey, which is a deep, wide-field near-UV-near-IR (ugrizY) survey of the southern Galactic bulge. Here, we present the first systematic study of bulge GC multiple populations with deep photometry including the u band, which is a crucial indicator of the abundance of CNO-bearing molecules in stellar atmospheres. We identify cluster members using Gaia EDR3 proper motion measurements, and then isolate red giant branch stars using r versus u - r color–magnitude diagrams. We find evidence suggesting all 14 clusters host at least two populations, and NGC 6441, NGC 6626, and NGC 6656 appear to have at least three populations. Many of these clusters are not part of the Hubble Space Telescope (HST) surveys nor do they have comprehensive spectroscopic analyses so we are presenting the first evidence of MPs in several clusters. Not only do we find a strong anticorrelation between the fraction of first-generation stars and cluster absolute V magnitude, but the correlation coefficient and cluster-to-cluster scatter are similar to the results obtained from HST. Our ground-based data extend to much larger radial distances than similar HST observations, enabling a reliable estimate of the global fraction of first-generation stars in each cluster. This study demonstrates that ground-based u-band photometry as provided by DECam will prove powerful in the study of multiple populations in resolved GCs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Elemental and Isotopic Yields from T Coronae Borealis: Predictions and Uncertainties

T Coronae Borealis (T CrB) is a symbiotic recurrent nova system expected to undergo its next outburst within the next 2 yr. Recent hydrodynamic simulations have predicted the nucleosynthetic yields for both carbon–oxygen (CO) and oxygen–neon (ONe) white-dwarf models, but without accounting for thermonuclear reaction rate uncertainties. We perform detailed Monte Carlo postprocessing nucleosynthesis calculations based on updated thermonuclear reaction rates and uncertainties from the 2025 evaluation. We quantify the resulting abundance uncertainties and identify the key nuclear reactions that dominate them. Our results show that both the CO and ONe nova models robustly produce characteristic CNO isotopes. More pronounced abundance differences emerge for elements with A ≥ 20. Sulfur is the most robust observational discriminator between the CO and ONe nova models, with a model-to-model difference of a factor of ≈30 and minimal sensitivity to reaction rate uncertainties. Neon, silicon, and phosphorus exhibit even larger abundance differences (factors of ≈150–250), providing strong diagnostic potential. While their predicted yields are subject to larger uncertainties, these remain smaller than the model-to-model differences, allowing these elements to serve as useful, though less precise, tracers of white-dwarf composition. Chlorine, argon, and potassium also differ between models, but the 1σ-abundance ranges for the CO and ONe models overlap, reducing their present usefulness as composition tracers. We find that only nine nuclear reactions dominate the abundance uncertainties of the most diagnostically important isotopes, and their influence is largely independent of the underlying white-dwarf composition. These results provide guidance for future experimental efforts and for interpreting ejecta compositions in the next eruption of T CrB.

Chemical Abundances↗
DOE OSTI2026

High-spectral-resolution X-Ray Observations of the Evolved Supermassive Stellar Binary System η Carinae: Fe K α Band Profile Revealed with XRISM

The supermassive binary system, η Carinae, is experiencing enormous wind-driven mass loss at a rate unparalleled in the rest of the Galaxy. Their wind–wind collision (WWC) continuously produces shock heated, X-ray-emitting plasmas. The XRISM X-ray observatory observed the system in 2023 and 2024 when the X-ray emission began to increase toward periastron passage in 2025. This paper reports unprecedentedly high-resolution X-ray spectra in the Fe Kα band between 6.2 and 7.1 keV, obtained with the Resolve X-ray microcalorimeter. The hydrogen-like (Lyα) and helium-like (Heα) lines reveal three velocity components. Two of them are broadened with maximum velocities of 2000–3000 km s −1 , likely originating from the postshock companion wind. The other is relatively narrow, with a Gaussian broadening of only ∼290 km s −1 in 1σ, which may originate from the postshock companion wind at the WWC stagnation point or penetrating the primary wind. The Fe fluorescent lines exhibit a moderate blueshift and broadening with velocities at 100–200 km s −1 , consistent with the primary wind’s velocity field. The spectra also confirm a Compton shoulder of the Heα line complex for the first time. Both fluorescing and scattering spectral profiles indicate that the binary system is seen from the companion side during these observations. The flux ratio of the Compton-scattering emission to the fluorescent line suggests substantial hydrogen depletion of the primary wind, expected from CNO-cycled hydrogen nuclear fusion gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Stellar Neutrino Emission across the Mass–Metallicity Plane

We explore neutrino emission from nonrotating, single-star models across six initial metallicities and 70 initial masses from the zero-age main sequence to the final fate. Overall, across the mass spectrum, we find metal-poor stellar models tend to have denser, hotter, and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass–metallicity plane we identify the sequence (initial CNO → 14 N → 22 Ne → 25 Mg → 26 Al → 26 Mg → 30 P → 30 Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Antineutrino emission during C, Ne, and O burning shows a strong metallicity dependence with 22 Ne(α, n) 25 Mg providing much of the neutron excess available for inverse-β decays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5–1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and average β decay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Low-energy solar positrons.

Fluxes of solar particles, consistent with Kinsey's (1970) measurements and demodulated in a manner consistent with the cosmic-ray transport equations discussed by Gleeson and Axford (1967), are shown to be able to produce low-energy positrons in the solar atmosphere via unstable CNO beta-particle emitters. Computed positron fluxes are presented for various diffusion coefficient values and compared with measurements of Cline and Hones (1970).

Gregory, C. T.↗
NASA NTRS1972

Model atmospheres for cool supergiant stars.

The results of an exploratory grid of model atmospheres for cool giant stars are used to illustrate the effect of varying the chemical composition of the atmosphere. The effects of composition changes (depletion of C and O, enrichment of N, and increase in the ratio C/O), which might be expected from processing of the original material of a star through the CNO cycle of nuclear burning, are studied. The models also include the important CN opacity. They are illustrated by giving several representative T-P and T-tau diagrams, spectral energy curves, and column density tables of molecules.

Alexander, D. R.↗
NASA NTRS1973

Theory of interstellar abundances of the isotopes of carbon, nitrogen and oxygen.

It is shown that CNO hydrogen burning in stars with a mass of 3 to 8 solar masses can account for both the likely abundances of C-13, N-14, and O-17 in the interstellar medium and the observed ratios C-12/C-13 O-16/O-17 in the atmospheres of evolved stars. A model which gives these abundances is shown to be consistent also with previously suggested mechanisms for the production of He-3, N-15, and O-18.

Wollman, E. R.↗
NASA NTRS1973

Interstellar oxygen-17

Cases of line emission were observed from the molecular clouds associated with the Orion Nebula and the rho Ophiuchi complex. The emission is attributed to a certain rotational transition of CO consisting of the isotopes C-12 and O-17. This observation signifies the first detection of O-17 outside the solar system. It is pointed out that the relative abundance of O-17 is an important astrophysical quantity because of a possible enrichment during the hot CNO cycle.

Encrenaz, P. J.↗
NASA NTRS1974

Galactic heavy cosmic rays with 5 less than E less than 130 MeV/nucleon

With stacks of Lexan and cellulose triacetate exposed outside the lunar modules on Apollo 16 and 17, a study was made of the spectra and composition of low-energy particles in interplanetary space. For the period from Apr. 16 to 23, 1972 (Apollo 16), measurements were made of the spectra of the elements 6 less than or equal to Z less than or equal to 28 at energies 40 less than or equal to E less than or equal to 150 MeV/nucleon. For the period from Dec. 11 to 13, 1972 (Apollo 17), a study was made of CNO, NeMgSi, and elements with Z greater than 16 at energies 5 less than or equal to E less than or equal to 40 MeV/nucleon. Using the abundance of charges 17 less than or equal to Z less than or equal to 25 relative to iron as a tracer, it is found that the bulk of the heavy particles in interplanetary space at E greater than 10 MeV/nucleon are of galactic rather than solar origin. The relative abundances of the various charge groups are independent of energy from about 2 GeV/nucleon down to about 30 MeV/nucleon.

Price, P. B.↗
NASA NTRS1975

Novae, supernovae, and neutron sources

The evolution of thermonuclear runaways is examined in two models of white dwarfs with extreme enhancements of C-12 in their envelopes to test the predictions of Hoyle and Clayton (1974) that novae will result from such stars and a large neutron flux will be produced. In agreement with these predictions, it is assumed that the large amount of C-12 is due to the accretion of hydrogen-rich material from a disk surrounding a carbon-oxygen white dwarf. The evolution of the two models is described in detail, and the results suggest that accretion of hydrogen-rich material will always result in a thermonuclear runaway, although mass ejection will not occur unless CNO nuclei are enhanced. It is noted that one model produces a substantial neutron flux for a short time which is sufficient to drive an intermediate neutron-capture process.

Starrfield, S.↗
NASA NTRS1975

A grid of model atmospheres for metal-deficient giant stars. I

A grid of flux-constant model atmospheres for stars with effective temperatures between 3750 and 6000 K, log g between 0.75 and 3.0, and (A/H) between -3.0 and 0.0 has been constructed. The line absorption is approximated by opacity distribution functions. Metal lines and molecular lines, including those from the infrared bands of CO and CN, are taken into account. The variation of the structure of the models with metal abundance and microturbulence parameter is found to be quite regular and not very drastic. The surface cooling produced by CO is important for all the models with a maximum temperature of 5000 K, while CN mainly causes a backwarming effect but is not very important for solar CNO abundances. The effects of convection, estimated by using the mixing-length approximation, are important only for the coldest models. The models compare very well with models from overlapping regions of other grids. A solar model consistent with the grid models is found to agree satisfactorily with empirical solar model atmospheres. The careful use of scaled solar models for stars with (A/H) approximately equal to zero is justified.

Gustafsson, B.↗
NASA NTRS1975

Is a dwarf nova really a 'dwarf' nova

Since it is observed that the constituents of dwarf and common novae binary systems are similar, it has been commonly assumed that the mechanisms are the same varying only in the intensity of the outburst. The authors' published work shows that a thermonuclear runaway in the hydrogen-rich envelope of a carbon-oxygen white dwarf is responsible for the common nova outburst as long as the CNO nuclei are enhanced. We report here on less energetic thermonuclear runaways which ejects no material and produce a rapid luminosity rise that levels off on a short time scale. However, the luminosity increase is much too large for a dwarf nova. Several suggestions for reducing the luminosity peak are presented.

Sparks, W. M.↗
NASA NTRS1975

Accretion and the nova outburst

Evolutionary sequences of thermonuclear runaways in the hydrogen-rich envelopes of carbon-oxygen white dwarfs are presented which include the effects of accretion of infalling material, allow the initial envelope to be out of equilibrium, and reproduce the gross features of the nova outburst. The models show that massive infall rates produce strong shocks at the stellar surface, that material passing through the shocks reaches nuclear-ignition temperatures, and that the thermonuclear runaway proceeds with an extended envelope around the star in the most extreme cases. The major effect of accretion is found to be a reduction in the amount of material ejected for a given degree of CNO enhancement as compared with previous nonaccretion models. It is also found that all the heating that causes ejection occurs in the deeper layers and that the light curves produced by the present models are in closer agreement with observed nova light curves that the previous models.

Starrfield, S. G.↗
NASA NTRS1976

Ion and electron pulses observed in the magnetotail and rapid annihilation of magnetic field lines

Hydrogen, helium, and CNO ion and electron pulses were detected in the magnetotail, and in the upstream region from the earth's bow shock. It was found that, in the magnetotail, ions appeared more frequently in the dusk than in the dawn quarter whereas the electron population had a reversed asymmetry. This spatial distribution - a polarization in the same direction as the electric field in the neutral sheet - suggests that these particles are accelerated by the electric field induced by a rapid annihilation of magnetic field lines. From the observed particle energies, the annihilation speed was estimated and found to be as high as 0.2 times the Alfven speed.

Fan, C. Y.↗
NASA NTRS1976

A new interpretation of luminous blue stars

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, these exhibit a large 'bump' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes. Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. The stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures for O stars and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than about 20 solar masses. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars.

Stothers, R.↗
NASA NTRS1976

Theoretical models of Beta Cephei stars constructed with new radiative opacities

Equilibrium models for the main-sequence and early post-main-sequence phases of evolution are constructed for stars of 10.9 and 15 solar masses with two different initial hydrogen and metals abundances. Carson's (1976) radiative opacities are used in the calculations. It is found that the models which lie off the zero-age main sequence have cooler effective temperatures than corresponding models based on other opacities and cross the observed Beta Cephei strip in the H-R diagram only during the main phase of core hydrogen burning. The stability of radial and nonradial pulsations is studied by applying linear nonadiabatic perturbations to the models. The results show that all the modes examined are stable and that the margin of stability decreases with advancing evolution. It is suggested that the closeness of the periods of the two lowest nonradial quadrupole p-modes may be responsible for the 'beat' phenomenon observed in many Beta Cephei stars, if these modes are somehow excited. Possible instability mechanisms are evaluated, particularly the ultimate ionization of CNO elements.

Stothers, R.↗