Galactic Nucleosynthesis Research Articles

Gamma-ray constraints on supernova nucleosynthesis

Gamma-ray spectroscopy holds great promise for probing nucleosynthesis in individual supernova explosions via short-lived radioactivity, and for measuring current global Galactic supernova nucleosynthesis with longer-lived radioactivity. It was somewhat surprising that the former case was realized first for a Type II supernova, when both Co-56 and Co-57 were detected in SN 1987A. These provide unprecedented constraints on models of Type II explosions and nucleosynthesis. Live Al-26 in the Galaxy might come from Type II supernovae, and if it is eventually shown to be so, can constrain massive star evolution, supernova nucleosynthesis, and the Galactic Type II supernova rate. Type Ia supernovae, thought to be thermonuclear explosions, have not yet been detected in gamma-rays. This is somewhat surprising given current models and recent Co-56 detection attempts. Ultimately, gamma-ray measurements can confirm their thermonuclear nature, probe the nuclear burning conditions, and help evaluate their contributions to Galactic nucleosynthesis. Type Ib/c supernovae are poorly understood. Whether they are core collapse or thermonuclear events might be ultimately settled by gamma-ray observations. Depending on details of the nuclear processing, any of these supernova types might contribute to a detectable diffuse glow of Fe-60 gamma-ray lines. Previous attempts at detection have come very close to expected emission levels. Remnants of any type of age less that a few centuries might be detectable as individual spots of Ti-44 gamma-ray line emission. It is in fact quite surprising that previous surveys have not discovered such spots, and the constraints on the combination of nucleosynthesis yields and supernova rates are very interesting. All of these interesting limits and possibilities mean that the next mission, International Gamma-Ray Astrophysics Laboratory (INTEGRAL), if it has sufficient sensitivity, is very likely to lead to the realization of much of the great potential of gamma-ray spectroscopy for understanding supernovae.

The chemical evolution of galaxies

The chemical evolution of galaxies is discussed starting with the simple box model. It is shown that this model with the additional assumption of metal-rich outflow provides a first useful insight into the chemical evolution of different stellar populations. More detailed models of galactic nucleosynthesis are then investigated which take into account galactic dynamics, noninstantaneous recycling and incomplete mixing. The implications of noninstantaneous recycling on the evolution of the element abundances in the galactic halo are discussed and constraints on the evolutionary time-scales of the halo are derived. Finally a model for the formation of the galactic halo is presented which takes into account local enrichment and incomplete mixing between different gas phases.

Diffuse galactic annihilation radiation and the present rate of galactic nucleosynthesis

Observations of positron annihilation radiation from the inner region of the Galaxy show that there are two components of the radiation: a steady, diffuse galactic disk component and a variable component from discrete, presumably compact sources. Here we focus on the observations of the diffuse galactic emission and their implications for the present galactic rate of iron nucleosynthesis. We discuss recent calculations of the nucleosynthetic yield and the survival of positrons in supernova ejecta, expected from current supernova models. These calculations show that positrons from the β + decay of nucleosynthetic 56Co→ 56Fe→, 44Sc→ 44→ 44 Ca, and 26Al → 26Mg, can easily account for the observed galactic annihilation radiation, and they suggest a present galactic rate of 56Fe nucleosynthesis of ≈(0.8 ± 0.5) M ⊙ per 100 yr.

Direct determination of the half-life of 187Re

We have determined the beta-decay half-life of 187Re to be (4.23 ± 0.13) · 1010 y, stated at the 95% confidence level. The method consisted of separating the daughter 187Os atoms from large sources of initially osmium-free rhenium. Yields were measured by the isotope dilution method using inductively coupled plasma mass spectrometry. Precision was gained through the use of two independent spike isotopes on each of five separate, large sources of rhenium. Because of the present lack of knowledge of other unrelated but equally important parameters, our value does not substantially narrow the range of uncertainty for the duration of galactic nucleosynthesis. However, the use of our half-life value to reinterpret the measurements of others on iron meteorites and chondrites suggests that iron meteorites might be 380 ± 160 million years younger than chondrites. Our half-life result may therefore have more profound implications for solar-system chronology than for galactic nucleosynthesis.

Topics in Gamma Ray Astronomy

Observations of gamma rays from solar flares, gamma ray bursts, the Galactic center, galactic nucleosynthesis, SS433, and Cygnus X-3, and their effects on astrophysical problems are discussed. It is observed that gamma ray spectra from solar flares are applicable to the study of particle acceleration and confinement and the determination of chemical abundances in the solar atmosphere. The gamma ray lines from the compact galactic object SS433 are utilized to examine the acceleration of jets, and analysis of the gamma ray lines of Cygnus X-3 reveal that particles can be accelerated in compact sources to ultrahigh energies.

Yields of Nucleosynthesis from massive and intermediate mass stars and constraints on their final evolution

Nucleosynthetic yields and production rates of helium and heavy elements are derived using new initial mass functions which take into account the recent revisions in O star counts and the stellar models of Maeder (1981a, b) which incorporate the effects of massloss on evolution. The current production rates are significantly higher than the earlier results due to Chiosi & Caimmi (1979) and Chiosi (1979), and a near-uniform birthrate operating over the history of the galactic disc explains the currently observed abundances. However, the yields are incompatibly high, and to obtain agreement it is necessary to assume that stars above a certain mass do not explode but proceed to total collapse. Further confirmation of this idea comes from the consideration of the specific yields and production rates of oxygen, carbon and iron and the constraints imposed by the observational enrichment history in the disc as discussed by Twarog & Wheeler (1982). Substantial amounts of4He and14C, amongst the primary synthesis species, are contributed by the intermediate mass stars in their wind phases. If substantial numbers of them exploded as Type I SN, their contribution to the yields of12C and56Fe would be far in excess of the requirements of galactic nucleosynthesis. Either efficient massloss precludes such catastrophic ends for these stars, or the current stellar models are sufficiently in error to leave room for substantial revisions in the specific yields. The proposed upward revision of the12C (α,γ)16O rate may produce the necessary changes in stellar yields to provide a solution to this problem. Stars that produce most of the metals in the Galaxy are the same ones that contribute most to the observed supernova rate.

Explosive nucleosynthesis and Type I supernovae

view Abstract Citations (71) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Explosive nucleosynthesis and Type I supernovae Nomoto, K. ; Thielemann, F. -K. ; Wheeler, J. C. Abstract The ejecta of a particular carbon deflagration model for Type I supernovae are combined with the ejecta of a massive star to show that Type I supernovae may be important contributors to galactic nucleosynthesis. Type I supernovae may help to fill in the paucity of oxygen-burning products from the massive stars. Problems with the overproduction of 16O from massive stars and 40Ca, 56Fe, and 54Fe from deflagration models of Type I supernovae are discussed. Publication: The Astrophysical Journal Pub Date: April 1984 DOI: 10.1086/184247 Bibcode: 1984ApJ...279L..23N Keywords: Nuclear Fusion; Supermassive Stars; Supernovae; Abundance; Carbon Stars; White Dwarf Stars; Astrophysics full text sources ADS | Related Materials (1) Erratum: 1984ApJ...283L..25N

Sm-Nd isotopic evolution of chondrites and achondrites, II

The 147Sm 143Nd and 146Sm 142Nd isotope systematics have been investigated in five chondrites and the achondrites Moama and Angra dos Reis (ADOR). The new chondrite data and those we have reported before are all consistent with our previously reported reference values for CHUR (“chondritic uniform reservoir”) of ( 143Nd/ 144Nd) CHUR 0 = 0.511847 and ( 147Sm/ 144Nd) CHUR 0 = 0.1967 . Most of the bulk chondrites analyzed have 143Nd/ 144Nd and 147Sm/ 144Nd within 0.5 ε-units and 0.15% of the CHUR values, respectively. This strongly suggests that the CHUR evolution is now known to within these error limits throughout the history of the solar system. The St. Severin chondrite yields an Sm Nd internal isochron age of T = 4.55 ± 0.33AE and an initial ε Nd = 0.11 ∓ 0.26 . Much larger variations in Sm/Nd ratios were measured in mineral separates of the Moama and ADOR achondrites. Thus, very precise ages of 4.46 ± 0.03AE and4.564 ± 0.037AE were obtained for these meteorites, respectively. The initial ε Nd values obtained for Moama and ADOR are 0.03 ∓ 0.25and0.14 ∓ 0.20, respectively. The values obtained on these meteorites are fully consistent with the CHUR evolution curve. Initial ε Nd data on terrestrial igneous and meta-igneous rocks demonstrates that positive initial ε Nd values occur throughout the past 4 AE. This confirms our earlier report that a light rare earth element-depleted layer has existed throughout most of the Earth history and is the source of present-day mid-ocean ridge basalts. The inferred shape of the ε Nd vs. age curve for the depleted mantle suggests profound changes in tectonic regimes with time; in particular, it suggests a much higher rate of recycling of continental materials into the mantle during the Archean as compared to later time periods. 146Sm 142Nd systematics of ADOR and Moama are supportive of the hypothesis that 146Sm was present in the early solar system and suggests a 146Sm/ 144Sm ratio of about 0.01 for the solar system ∼ 4.56 AE ago. This inferred high 146Sm abundance cannot be explained as a late injection from a supernova and must be due to galactic nucleo-synthesis.

Explosive helium burning in supernovae - A source of r-process elements

We have examined the results of shock heating of the helium zone in stars undergoing supernova explosions under a wide variety of temperatures and densities. We find that for peak temperatures near 4 x 10/sup 8/ K and peak densities near 10/sup 4/ g cm/sup -3/ the solar system r-process abundance curve can be reproduced. These conditions correspond to shock wave velocities of approximately 4000 km s/sup -1/ in the helium zone of an evolved star. The neutrons to drive the r-process are produced by /sup 13/C(..cap alpha.., n)/sup 16/O reactions. To produce a sufficient flux of neutrons over several seconds requires approximately 2% /sup 13/C by mass in the helium zone, and thus depends upon some type of mixing between the hydrogen-rich envelope and the helium zone prior to the supernova. We find that neither /sup 22/Ne nor /sup 18/O can provide a sufficient neutron flux in this type of environment. Our calculated fit to the solar system r-process curve is improved when the beta-decay rates of the heavy nuclei are increased by a factor of 5--10 over the rates using the gross theory, compatible with the recent results obtained by Klapdor et al. For reasonable mass ranges ofmore » supernova progenitors, a maximum of only 2.2 x 10/sup -5/ M/sub sun/ of r-process elements must be ejected per supernova to satisfy galactic nucleosynthesis requirements.« less

Diffuse galactic gamma-ray line emission from nucleosynthetic Fe-60, Al-26, and Na-22 - Preliminary limits from HEAO 3

Data obtained during a two-week period in the fall of 1979 with the HEAO 3 gamma-ray spectroscopy experiment have been searched for diffuse galactic plane gamma-ray line emission expected t4 result from the decay of nucleosynthetic Fe-60, Al-26, and Na-22. With the possible exception of the 1809 keV line from Al-26 decay, for which a 2.6-omicron cosmic excess of (6.0 + or - 2.3) x 0.0001 photons/sq cm per sec per rad was measured, no positive detection was made. However, new limits ranging from 1.8 to 11 times 0.0001 photons/sq cm per sec per rad, at the 3-omicron level of confidence, have been placed on diffuse emission in these lines from the vicinity of the galactic center (between -30 and 30 deg). These limits are lower than some theories predict and thus place new constraints on the yields of these radionuclides in explosive nucleosynthesis and on the present rate of galactic nucleosynthesis.

The geochemical coherence of Pu and Nd and the [formula omitted] ratio of the early solar system

Two very different sets of 244Pu 238U ratios have been reported for early solar system materials. One group of samples yields high (0.015–0.016) ratios (Podosek, 1970a, 1972; Drozd et al., 1977) and calculations based on another group of analyses yield low ratios (~0.004) (Marti et al., 1977). Recently measured partition coefficients for Pu and Sm are used to evaluate the data of Marti et al. and sol 244Pu 238U ratios from other sources are also considered. A low sol 244Pu 238U ratio (~0.005) is favored, and some implications of this low ratio to galactic nucleosynthesis and meteorite age dating are briefly discussed.

Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

view Abstract Citations (225) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M 92. Carbon, D. F. ; Langer, G. E. ; Butler, D. ; Kraft, R. P. ; Suntzeff, N. B. ; Kemper, E. ; Trefzger, C. F. ; Romanishin, W. Abstract The 169 low resolution image tube scanner spectra obtained at the Lick Observatory for 71 stars in the field of M92, covering the 3100-5200 A spectral interval, are matched with synthetically generated spectra to find the C and N abundances for a subset of 45 bright member giants. It is found that (1) stars side by side in the color-magnitude diagram show N and C abundance variations by factors of 10 and three, respectively, (2) the segregation of stars into small groups by effective temperature and log g shows no inversely proportional relationship between N and C abundance, and (3) the mean C abundance is 10 times smaller on the AGB than on the SGB. The C and N abundances of M92 therefore disagree with the predictions of classical evolutionary theory. Four different scenarios which have been suggested to account for the observations cited are discussed. In addition, primordial CNO abundances observed in, or deduced for, metal-poor field and cluster stars are compared with those deduced for M92, and then discussed in connection with the global galactic nucleosynthesis and cluster self-contamination process scenarios. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1982 DOI: 10.1086/190796 Bibcode: 1982ApJS...49..207C Keywords: Abundance; Giant Stars; Globular Clusters; Late Stars; Stellar Evolution; Stellar Spectra; Asymptotic Giant Branch Stars; Atomic Spectra; Carbon; Color-Magnitude Diagram; Hyperfine Structure; Image Dissector Tubes; Molecular Spectra; Nitrogen; Nuclear Fusion; Solar Spectra; Stellar Atmospheres; Stellar Models; Stellar Temperature; Ubv Spectra; Astrophysics full text sources ADS | data products SIMBAD (76)

The Masses and Origin of Carbon Stars

Carbon stars have always been amongst the most intriguing of stars which show grossly non-solar abundances. All such stars raise the questions:(a) at what stage of stellar evolution does this peculiar abundance phase occur?(b) do all stars pass through this stage?(c) is the phase significant in the overall picture of galactic nucleosynthesis?

Identification of the anomalous 26.131-MHz nitrogen line observed towards Cas A

Konovalenko and Sodin1 recently reported the detection of an absorption line at a frequency of 26.131 MHz towards Cassiopeia A and attributed the line to the 26.127 MHz F = 5/2 → 3/2 hyperfine transition of 14N. The difference in frequency corresponds to a radial velocity of –40 km s–1, which is compatible with the mean velocity of the Perseus arm H I absorption lines seen towards Cas A. However, to explain the strength of the line, Konovalenko and Sodin require (N/H) = 8 × 10–3 compared with the cosmic ratio of 1.2 × 10–4. An anomalous abundance of this magnitude would have substantial impact on ideas about galactic nucleosynthesis. We suggest here that the line is a 631α recombination line due to neutral atoms of heavy elements—either carbon atoms in the H I clouds or possibly heavier atoms (Mg, Ca, Fe) in hot (∼104 K) ionized gas along the line of sight to Cas A.

Os186,187,188(n,γ)cross sections and galactic nucleosynthesis

The $^{186,187,188}\mathrm{Os}(n,\ensuremath{\gamma})$ cross sections were measured over the incident neutron energy range 2.6-800 keV. Optimized statistical model fits to the average cross sections were made employing estimates of the $^{186}\mathrm{Os}$, $^{187}\mathrm{Os}$, and $^{188}\mathrm{Os}$ $p$-wave strength functions 0.29 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, 0.45 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, and 0.33 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, respectively, $d$-wave strength functions 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, 4.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, and 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, respectively, and gamma ray strength functions ($\frac{{\overline{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}}{{D}_{0}}$) 26.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, 176 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, and 20.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, respectively. A lower bound for the $^{187}\mathrm{Os}$ neutron inelastic cross section is estimated as 0.25(20) b at 30 keV. The Maxwellian-averaged capture cross sections are presented as a function of temperature. The ratio of 30 keV Maxwellian-averaged cross sections $\frac{〈{\ensuremath{\sigma}}_{\ensuremath{\gamma}}(186)〉}{〈{\ensuremath{\sigma}}_{\ensuremath{\gamma}}(187)〉}=0.504(17)$ is reported and the lack of agreement with earlier measurements of this ratio is discussed. The use of this cross section ratio in estimating, via the $^{187}\mathrm{Re}$-$^{187}\mathrm{Os}$ beta decay, the duration of galactic nucleosynthesis is discussed. The cross section ratio from this work yields an estimate of 10.4(25) \ifmmode\times\else\texttimes\fi{} ${10}^{9}$ yr for the duration of galactic nucleosynthesis, a result higher than but still consistent with the estimate 7(2) \ifmmode\times\else\texttimes\fi{} ${10}^{9}$ yr derived from U/Th decay.NUCLEAR REACTIONS Neutron capture, cross section, inelastic cross section, strength functions, nucleosynthesis, Maxwellian-averaged cross section.

Chemical evolution coefficients for the study of galactic evolution

A new evaluation of chemical evolution coefficients has been made using recent stellar evolution and nucleosynthesis data. The role of the low and intermediate mass stars in galactic nucleosynthesis has been emphasized. A significant amount of4He,12C and neutron-rich species is found to be contributed by these stars. Comparison with observed abundances suggests a primary origin of14N. The simple model of galactic evolution with the new coefficients has been used to derive the ratio of helium to heavy element enrichment in the Galaxy. The new stellar evolution data do not explain the large value of this ratio that has been determined observationally.

The oxygen abundance in metal-poor stars

Oxygen abundances in the atmospheres of a dozen unevolved stars of various metallicities (-2.3< or =(Fe/H)< or =+0.3) have been derived. In nearly all cases, the metal-poor stars exhibit an exhanced oxygen triplet at 7700 A. Substantial overabundances of oxygen are indicated for the program stars. This result is discussed in the light of current galactic nucleosynthesis theories.

Muon production of 92,94Nb in the Earth's crust

ACTIVITIES due to long-lived 92Nb (t1/2 ≃ 1.7×108 yr) and to 94Nb (t1/2 = 2.03×104 yr) in a refined bar of terrestrial niobium were discovered by Apt et al.1. They speculated that the 92Nb activity could have applications to chronologies of nucleosynthesis and to cosmogony. As an example, they calculated that their observed activity level would result if the isotopic ratio 4.7×109 yr ago were 92Nb/93Nb = 10−3 and if the halflife were 1.58×108 yr. More definite conclusions were difficult because the concentration expected today depends so strongly on the poorly known halflife, which they estimated to be 1.7×108 yr from a reactor irradiation. This sensitivity can be illustrated by noting that a 5% error in halflife corresponds after 4.7×109 yr to an error of a factor 2.74 in the anticipated activity. Quantitative calculations from galactic nucleosynthesis must therefore await a more precise measurement of the halflife. Implications of primordial 92Nb have recently been enlarged with the proposal2 to use enrichments δ(92Zr) in the isotopic composition of Zr due to extinct 92Nb to measure absolute time differences in the formation of meteorites and planets. If an initial 92Zr/94Zr ratio for each body can be obtained, differences between those initial values could be translated into time differences in the formation of the respective objects. We argue here that both projects are probably doomed to disappointment. It seems to us unlikely that the near equality in the two measured activities is a coincidence. They are respectively 0.058±0.035 d.p.m. per kg (Nb) for 92Nb and 0.32±0.03 d.p.m. per kg (Nb) for 94Nb. Such a result would be expected, for example, if both nuclei were created terrestrially over geologic time in the ratio of their activities, in this case in a production ratio p(92Nb)/p(94Nb) = 0.18±0.11. We suggest that nuclear reactions following the capture of stopped cosmic-ray muons is the likely source, and we will show that both the magnitude of the activities and their relative strengths are consistent with this idea. Similar ideas have been developed by others, most notably to explain Xe anomalies in Te ores3.

Dirac cosmology and the onset of galactic nucleosynthesis

Recently Browne and Berman determined the onset of nucleosynthesis of heavy elements in the galaxy to be about 18 billion years ago based on the weak decay of rhenium 187 to osmium 187. This age is appreciably larger than the 13 billion years determined from the uranium decay chains [2]. It is also larger than 16 billion year age of the Universe determined from the standard model by the latest values of the Hubble constant and decceleration parameter. This letter points out that this discrepancy is predicted by Dirac's cosmology and derives from a time- varying weak coupling constant.

Nucleosynthesis and Star Formation of the Galaxy and Magellanic Clouds

view Abstract Citations (7) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nucleosynthesis and Star Formation of the Galaxy and Magellanic Clouds Olson, Gordon L. ; Peña, Jose H. Abstract A simple model of galactic nucleosynthesis is presented and extended for an examination of the Magellanic Clouds. The Clouds are bluer than the Galaxy, thus indicating the presence of a larger fraction of massive stars. However, both Clouds are underabundant in heavier elements. To explain the observations we make the following conclusions: (a) The average stellar birthrate in the Magellanic Clouds has been nearly constant throughout their histories rather than being much higher in the past as is believed true for our own Galaxy. (b) Unless stars evolve differently in the Clouds, the initial mass function (IMF) for tar sformation in the Clouds must be significantly different from the Galaxy. In terms of a power law, the IMF must either have a much smaller lower mass limit or be significantly steeper than the IMF in the Galaxy. (c) To completely explain the colors of the Clouds when using a power-law IMF, it is necessary to postulate that the stellar birthrate is not a monotonically decreasing function of time but is interrupted by periods with higher than average star formation. Subject headings: galaxies: Magellanic Clouds - nucleosynthesis - stars: evolution - stars: formation Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154306 Bibcode: 1976ApJ...205..527O full text sources ADS | data products NED (2)