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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Common Occurrence of Explosive Hydrogen Burning in Type II Supernovae

In this paper, we report Mo isotopic data for 16 15 N-rich presolar SiC grains of type AB ( 14 N/ 15 N < solar, AB1) and their correlated Sr and Ba isotope ratios when available. Of the 16 AB1 grains, 8 show s-process Mo isotopic compositions, together with s-process Ba and/or Sr isotopic compositions. We found that a higher percentage of AB1 grains show anomalous isotopic compositions than that of AB2 grains ( 14 N/ 15 N > solar), thus providing further support to the division of the two AB subgroups recently proposed by Liu et al., who showed that AB1 grains most likely originated from Type II supernovae (SNe) with explosive H burning. Comparison of the Sr, Mo, and Ba isotopic compositions of the AB1 grains with SN model predictions indicates that the s-process isotopic compositions of AB1 grains resulted from neutron-capture processes occurring during the progenitor massive stars' pre-SN evolution rather than from an explosive neutron-capture process. Finally, in addition, the observations of (1) explosive H burning occurring in the C-rich regions of the progenitor SNe of X grains as suggested by the isotopic compositions of X grains, and (2) explosive H burning occurring both at the bottom of the He/C zone and at the top of the He/N zone as suggested by model simulations, imply that explosive H burning is a common phenomenon in outer SN zones.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Study of the Characteristics of Elementary Processes in a Chain Hydrogen Burning Reaction in Oxygen

The characteristics of possible chain explosive hydrogen burning reactions in an oxidizing medium are calculated on the potential energy surface. Specifically, reactions H{sub 2} + O{sub 2} → H{sub 2}O + O, H{sub 2} + O{sub 2} → HO{sub 2} + H, and H{sub 2} + O{sub 2} → OH + OH are considered. Special attention is devoted to the production of a pair of fast highly reactive OH radicals. Because of the high activation threshold, this reaction is often excluded from the known kinetic scheme of hydrogen burning. However, a spread in estimates of kinetic characteristics and a disagreement between theoretical predictions with experimental results suggest that the kinetic scheme should be refined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The Interior Angular Momentum of Core Hydrogen Burning Stars from Gravity-mode Oscillations

A major uncertainty in the theory of stellar evolution is the angular momentum distribution inside stars and its change during stellar life. We compose a sample of 67 stars in the core hydrogen burning phase with a log g value from high-resolution spectroscopy, as well as an asteroseismic estimate of the near-core rotation rate derived from gravity-mode oscillations detected in space photometry. This assembly includes 8 B-type stars and 59 AF-type stars, covering a mass range from 1.4 to 5 M {sub ⊙}, i.e., it concerns intermediate-mass stars born with a well-developed convective core. The sample covers projected surface rotation velocities vsin i∈[9,242] km s{sup −1} and core rotation rates up to 26 μHz, which corresponds to 50% of the critical rotation frequency. We find deviations from rigid rotation to be moderate in the single stars of this sample. We place the near-core rotation rates in an evolutionary context and find that the core rotation must drop drastically before or during the short phase between the end of the core hydrogen burning and the onset of core helium burning. We compute the spin parameter, which is the ratio of twice the rotation rate to the mode frequency (also known as the inverse Rossby number), for 1682 gravity modes and find the majority (95%) to occur in the sub-inertial regime. The 10 stars with Rossby modes have spin parameters between 14 and 30, while the gravito-inertial modes cover the range from 1 to 15.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Thermal instability of the hydrogen-burning shell in nondegenerate stars.

An investigation is made of thermal instability in the hydrogen-burning shell of stars of moderate to high mass evolving from the end of core hydrogen burning to the early stages of core helium burning, with the help of an approximate analytic criterion for thermal instability and full nonlinear numerical calculations of stellar evolution. Two different assumptions about the chemical evolution in the stars of highest mass are adopted. Thermal pulses are found to develop only in very massive stars having convective intermediate zones, when the hydrogen profile in the shell is sufficiently steep and the shell is still moderately thick.

Stothers, R.↗
NASA NTRS2021

Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit

We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup , and radii between 0.81 and 1.66 RJup . These targets have masses near the uncertain lower limit of hydrogen core fusion (~73-96 MJup ), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 ± 0.1 Gyr) and TOI-681 (0.17 ± 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smaller companion radii. With an effective temperature of 9800 ± 200 K, TOI-587 is the hottest known main-sequence star to host a transiting brown dwarf or very low-mass star. We found evidence of spin-orbit synchronization for TOI-148 and TOI-746 as well as tidal circularization for TOI-148. These companions add to the population of brown dwarfs and very low-mass stars with well measured parameters ideal to test formation models of these rare objects, the origin of the brown dwarf desert, and the distinction between brown dwarfs and hydrogen-burning main sequence stars.

Nolan Grieves↗
DOE OSTI2025

Solar fusion III: New data and theory for hydrogen-burning stars

In stars that lie on the main sequence in the Hertzsprung-Russell diagram, like our Sun, hydrogen is fused to helium in a number of nuclear reaction chains and series, such as the proton-proton chain and the carbon-nitrogen-oxygen cycles. Precisely determined thermonuclear rates of these reactions lie at the foundation of the standard solar model. This review, the third decadal evaluation of the nuclear physics of hydrogen-burning stars, is motivated by the great advances made in recent years by solar neutrino observatories, putting experimental knowledge of the proton-proton (𝑝⁢𝑝)-chain neutrino fluxes in the few-percent precision range. The basis of the review is a one-week community meeting held in July 2022 in Berkeley, California, and many subsequent digital meetings and exchanges. The relevant reactions of solar and stellar hydrogen burning are reviewed here from both theoretical and experimental perspectives. Recommendations for the state of the art of the astrophysical 𝑆 factor and its uncertainty are formulated for each of them. Furthermore, several other topics of paramount importance for the solar model are reviewed as well: recent and future neutrino experiments, electron screening, radiative opacities, and current and upcoming experimental facilities. In addition to reaction-specific recommendations, general recommendations are also formed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Direct measurement of the breakout reaction {sup 11}C({alpha},p){sup 14}N in explosive hydrogen-burning process

We determined the {sup 11}C({alpha},p){sup 14}N reaction rate relevant to the nucleosynthesis in explosive hydrogen-burning stars. The measurement was performed by means of the thick target method in inverse kinematics with {sup 11}C RI beams. We derived the excitation functions for the ground-state transition and excited-state transitions using time-of-flight information for the first time. The present reaction rate is compared to the previous one.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low-mass stars, BDs, and PMOs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

Thermal design and analysis of a hydrogen-burning wind tunnel model of an airframe-integrated scramjet

An aerodynamic model of a hydrogen burning, airframe integrated scramjet engine has been designed, fabricated, and instrumented. This model is to be tested in an electric arc heated wind tunnel at an altitude of 35.39 km (116,094 ft.) but with an inlet Mach number of 6 simulating precompression on an aircraft undersurface. The scramjet model is constructed from oxygen free, high conductivity copper and is a heat sink design except for water cooling in some critical locations. The model is instrumented for pressure, surface temperature, heat transfer rate, and thrust measurements. Calculated flow properties, heat transfer rates, and surface temperature distributions along the various engine components are included for the conditions stated above. For some components, estimates of thermal strain are presented which indicate significant reductions in plastic strain by selective cooling of the model. These results show that the 100 thermal cycle life of the engine was met with minimum distortion while staying within the 2669 N (600 lbf) engine weight limitation and while cooling the engine only in critical locations.

Guy, R. W.↗
NASA NTRS1979

Initial wind tunnel tests at Mach 4 and 7 of a hydrogen-burning, airframe-integrated scramjet

A research investigation of a new, fixed-geometry, hydrogen-burning scramjet engine concept, designed for total airframe integration, is currently in progress. Two heavily instrumented engine models incorporate inlet and combustor designs developed previously in component tests. Initial tests of these subscale engine models are being conducted in ground facilities at conditions simulating flight at Mach numbers 4 and 7. The scramjet test results which are presented include inlet performance, ignition/reaction aids, inlet-combustor interactions, and engine performance in terms of thrust balance measurements and internal pressure and heating rate distributions. The relationship of these results to flight engine performance is discussed.

Guy, R. W.↗
DOE OSTI2010

Properties of {sup 20}Na, {sup 24}Al, {sup 28}P, {sup 32}Cl, and {sup 36}K for studies of explosive hydrogen burning

The radiative proton-capture reactions {sup 19}Ne(p,{gamma}){sup 20}Na, {sup 23}Mg(p,{gamma}){sup 24}Al, {sup 27}Si(p,{gamma}){sup 28}P, {sup 31}S(p,{gamma}){sup 32}Cl, and {sup 35}Ar(p,{gamma}){sup 36}K potentially influence energy generation and/or nucleosynthesis during explosive hydrogen burning in classical novae and/or type I x-ray bursts. The thermonuclear rates of these reactions are dependent on resonance energies E{sub r}=E{sub x}-Q and strengths {omega}{gamma}. The {sup 20}Ne({sup 3}He,t){sup 20}Na, {sup 24}Mg({sup 3}He,t){sup 24}Al, {sup 28}Si({sup 3}He,t){sup 28}P, {sup 32}S({sup 3}He,t){sup 32}Cl, and {sup 36}Ar({sup 3}He,t){sup 36}K reactions have been measured using a 32-MeV, {sup 3}He{sup 2+} beam; ion-implanted carbon-foil targets developed at the University of Washington; and the Munich Q3D magnetic spectrograph. This experiment has already yielded precision mass measurements of {sup 20}Na, {sup 24}Al, {sup 28}P, and {sup 32}Cl [C. Wrede et al., Phys. Rev. C 81, 055503 (2010)], which are used presently to constrain the corresponding (p,{gamma}) reaction Q values. The new {sup 24}Al and {sup 28}P masses resolve a discrepancy in the energy of the lowest-energy resonance in the {sup 23}Mg(p,{gamma}){sup 24}Al reaction and better constrain a direct measurement of its strength. Excitation energies in {sup 32}Cl and {sup 36}K have also been measured. An important new proton-unbound level has been found at E{sub x}=2196.9(7) keV in {sup 36}K and the uncertainties in {sup 36}K excitation energies have been reduced by over an order of magnitude. Using the new data on {sup 36}K, the A=36, T=1 triplets have been reassigned. The thermonuclear {sup 35}Ar(p,{gamma}){sup 36}K reaction rate is found to be much higher than a commonly adopted rate and this could affect energy generation in type I x-ray bursts.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1976

Langley facility for tests at Mach 7 of subscale, hydrogen-burning, airframe-integratable, scramjet models

Modifications to a 20-megawatt arc-heated facility for testing a hydrogen-burning, airframe-integratable, subscale, scramjet model are described. Arc-heated flow is mixed with unheated air to furnish a test flow duplicating Mach 7 flight. (Stagnation temperature is 2220 K.) Modifications to the commercially available heater to improve survivability and smoothness are described. Pitot profiles show uniform flow and a slightly thinner nozzle boundary layer than predicted. Comparison of the tunnel boundary layer, which will be ingested by the engine model, with the boundary layer that a flight engine might ingest from its vehicle forebody shows a difference in the density distribution through the boundary layer. Calculations of wall heating and transient wall temperatures of the engine model show that for a 30-sec burn, the heat sink model requires cooling at selected locations to avoid thermal-stress, cycle-life problems. Model performance predictions show that fuel equivalence ratio and nozzle exit area both have large effects on thrust. Average inlet entrance Mach number (as affected by boundary-layer ingestion) has little effect on thrust.

Boatright, W. B.↗
DOE OSTI2020

TOI 694b and TIC 220568520b: Two Low-mass Companions near the Hydrogen-burning Mass Limit Orbiting Sun-like Stars

We report the discovery of TOI 694 b and TIC 220568520 b, two low-mass stellar companions in eccentric orbits around metal-rich Sun-like stars, first detected by the Transiting Exoplanet Survey Satellite (TESS). TOI 694 b has an orbital period of 48.05131 ± 0.00019 days and eccentricity of 0.51946 ± 0.00081, and we derive a mass of 89.0 ± 5.3 M{sub Jup} (0.0849 ± 0.0051 M{sub ⊙}) and radius of 1.111 ± 0.017 R{sub Jup} (0.1142 ± 0.0017 R{sub ⊙}). TIC 220568520 b has an orbital period of 18.55769 ± 0.00039 days and eccentricity of 0.0964 ± 0.0032, and we derive a mass of 107.2 ± 5.2 M{sub Jup} (0.1023 ± 0.0050 M{sub ⊙}) and radius of 1.248 ± 0.018 R{sub Jup} (0.1282 ± 0.0019 R{sub ⊙}). Both binary companions lie close to and above the hydrogen-burning mass threshold that separates brown dwarfs and the lowest-mass stars, with TOI 694 b being 2σ above the canonical mass threshold of 0.075 M{sub ⊙}. The relatively long periods of the systems mean that the magnetic fields of the low-mass companions are not expected to inhibit convection and inflate the radius, which according to one leading theory is common in similar objects residing in short-period tidally synchronized binary systems. Indeed we do not find radius inflation for these two objects when compared to theoretical isochrones. These two new objects add to the short but growing list of low-mass stars with well-measured masses and radii, and highlight the potential of the TESS mission for detecting such rare objects orbiting bright stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Production of 26 Al in stellar hydrogen-burning environments: Spectroscopic properties of states in 27 Si

Model predictions of the amount of the radioisotope Al-26 produced in hydrogen-burning environments require reliable estimates of the thermonuclear rates for the Al-26g(p,gamma) Si-27 and Al-26m(p,gamma)Si-27 reactions. These rates depend upon the spectroscopic properties of states in Si-27 within about 1 MeV of the Al-26g + p threshold (S-p = 7463 keV). We have studied the Si-28(He-3,alpha)Si-27 reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. For the first time with a transfer reaction, we have constrained J(pi) values for states in Si-27 over E-x = 7.0-8.1 MeV through angular distribution measurements. Aside from a few important cases, we generally confirm the energies and spin-parity assignments reported in a recent gamma-ray spectroscopy study. The magnitudes of neutron spectroscopic factors determined from shell-model calculations are in reasonable agreement with our experimental values extracted using this reaction.

Parikh, A.↗
NASA NTRS1964

Stellar evolution. ii. the hydrogen-burning phase of a star of 7.0 solar masses <sternentwicklung. ii. die wasserstoff- brennende phase eines sterns von 7.0 sonnenmassen<

With the computer program by Hofmeister, Kippenhahn, Weigert (1964, from now on referred to as ''I") the evolution of a population I star of 7.0 solar masses has been followed. The results presented here are based on a sequence of 119 models, the first of which represents the homogeneous main sequence state and has a convective core containing 26% of the mass. The following models describe the phase of depletion of hydrogen in the core, which is shrinking in mass until the convection around the centre disappears. After this the gradual development of a hydrogen burning shell source is shown. The models show the evolution into the red giant region, while the helium core is contracting until helium burning starts at the centre and a new convective core is built up. The luminousity is increased about 1 magnitude compared with the main sequence state. At the same time the outer convective region grows in mass and covers at the maxi­mum 71% of the total mass of the star. During the evolution to the red giant state, the evolutionary track crosses the region of the cepheids. Some aspects of the corresponding models are discussed.

STELLAR EVOLUTION↗
DOE OSTI2013

HYDROGEN BURNING ON ACCRETING WHITE DWARFS: STABILITY, RECURRENT NOVAE, AND THE POST-NOVA SUPERSOFT PHASE

We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the stable burning regime of accretion rates as modeled by time-dependent calculations done with Modules for Experiments in Stellar Astrophysics (MESA). We report the stability boundary for WDs of masses between 0.51 M{sub ☉} and 1.34 M{sub ☉} as found via time-dependent calculations. We also examine recurrent novae that are accreting at rates close to, but below, the stable burning limit and report their recurrence times. Our dense grid in accretion rates finds the expected minimum possible recurrence times as a function of the WD mass. This enables inferences to be made about the minimum WD mass possible to reach a specific recurrence time. We compare our computational models of post-outburst novae to the stably burning WDs and explicitly calculate the duration and effective temperature (T{sub eff}) of the post-nova WD in the supersoft phase. We agree with the measured turnoff time-T{sub eff} relation in M31 by Henze and collaborators, infer WD masses in the 1.0-1.3 M{sub ☉} range, and predict ejection masses consistent with those observed. We close by commenting on the importance of the hot helium layer generated by stable or unstable hydrogen burning for the short- and long-term evolution of accreting WDs.

79 ASTRONOMY AND ASTROPHYSICS↗