CNO Bi-cycle Research Articles

A stripped helium star in the potential black hole binary LB-1

Context. The recently claimed discovery of a massive (MBH = 68−13+11 M⊙) black hole in the Galactic solar neighborhood has led to controversial discussions because it severely challenges our current view of stellar evolution. Aims. A crucial aspect for the determination of the mass of the unseen black hole is the precise nature of its visible companion, the B-type star LS V+22 25. Because stars of different mass can exhibit B-type spectra during the course of their evolution, it is essential to obtain a comprehensive picture of the star to unravel its nature and, thus, its mass. Methods. To this end, we study the spectral energy distribution of LS V+22 25 and perform a quantitative spectroscopic analysis that includes the determination of chemical abundances for He, C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe. Results. Our analysis clearly shows that LS V+22 25 is not an ordinary main sequence B-type star. The derived abundance pattern exhibits heavy imprints of the CNO bi-cycle of hydrogen burning, that is, He and N are strongly enriched at the expense of C and O. Moreover, the elements Mg, Al, Si, S, Ar, and Fe are systematically underabundant when compared to normal main-sequence B-type stars. We suggest that LS V+22 25 is a stripped helium star and discuss two possible formation scenarios. Combining our photometric and spectroscopic results with the Gaia parallax, we infer a stellar mass of 1.1 ± 0.5 M⊙. Based on the binary system’s mass function, this yields a minimum mass of 2–3 M⊙ for the compact companion, which implies that it may not necessarily be a black hole but a massive neutron- or main sequence star. Conclusions. The star LS V+22 25 has become famous for possibly having a very massive black hole companion. However, a closer look reveals that the star itself is a very intriguing object. Further investigations are necessary for complete characterization of this object.

AstrophysicalSfactor for theN15(p,γ)O16reaction

The $^{15}{\rm N}(p,\gamma)^{16}{\rm O}$ reaction provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong $J^{\pi}=1^{-}$ resonances at $E_{R}= 312$ and 962 keV and direct capture to the ground state. Recently, a new measurement of the astrophysical factor for the $^{15}{\rm N}(p,\gamma)^{16}{\rm O}$ reaction has been published [P. J. LeBlanc {\it et al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. The analysis has been done using the $R$-matrix approach with unconstrained variation of all parameters including the asymptotic normalization coefficient (ANC). The best fit has been obtained for the square of the ANC $C^{2}= 539.2$ fm${}^{-1}$, which exceeds the previously measured value by a factor of $\approx 3$. Here we present a new $R$-matrix analysis of the Notre Dame-LUNA data with the fixed within the experimental uncertainties square of the ANC $C^{2}=200.34$ fm${}^{-1}$. Rather than varying the ANC we add the contribution from a background resonance that effectively takes into account contributions from higher levels. Altogether we present 8 fits, five unconstrained and three constrained. In all the fits the ANC is fixed at the previously determined experimental value $C^{2}=200.34$ fm${}^{-1}$. For the unconstrained fit with the boundary condition $B_{c}=S_{c}(E_{2})$, where $E_{2}$ is the energy of the second level, we get $S(0)=39.0 \pm 1.1 $ keVb and normalized ${\tilde \chi}^{2}=1.84$, i.e. the result which is similar to [P. J. LeBlanc {\it et al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. From all our fits we get the range $33.1 \leq S(0) \leq 40.1$ keVb which overlaps with the result of [P. J. LeBlanc {\it et al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. We address also physical interpretation of the fitting parameters.

Asymptotic normalization coefficient and important astrophysical process 15N(p,γ)160

In this work we report the application of the ANC method for the determination of the non-resonant radiative capture amplitude for the important astrophysical CNO cycle reaction 15N(p, γ) 16O, which provides a leak from the CN cycle into the CNO bi-cycle and CNO tri-cycle. It is contributed by the resonance capture to the ground state through two strong 1− resonances and non-resonant capture to the ground state, which interferes with the resonant capture terms. To determine more accurately the contribution from the non-resonant capture we determined the proton ANCs for the ground and seven excited states of 16O by measuring the angular distributions of the peripheral 15N(3He, d)16O proton transfer reaction. Using these ANCs and proton and α resonance widths determined from an R-matrix fit to the data from the 15N(p, α)12C reaction, we calculated the astrophysical S factor for the 15N(p, γ)16O reaction. The results indicate that the direct capture contribution was previously overestimated. We find the astrophysical factor to be S(0) = 36.0 ± 6.0 keVb, which is about a factor of two lower than the presently accepted value. We conclude that for every 2200 ± 300 cycles of the main CN cycle one CN catalyst is lost due to this reaction.

New astrophysicalSfactor for theN15(p,γ)O16reaction via the asymptotic normalization coefficient (ANC) method

The ${}^{15}\mathrm{N}(p,\ensuremath{\gamma}){}^{16}\mathrm{O}$ reaction provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ resonances at ${E}_{R}=312$ and 962 keV and direct capture to the ground state. Asymptotic normalization coefficients (ANCs) for the ground and seven excited states in $^{16}\mathrm{O}$ were extracted from the comparison of experimental differential cross sections for the $^{15}\mathrm{N}$($^{3}\mathrm{He}$,$d)$$^{16}\mathrm{O}$ reaction with distorted-wave Born approximation calculations. Using these ANCs and proton and \ensuremath{\alpha} resonance widths determined from an $R$-matrix fit to the data from the ${}^{15}\mathrm{N}(p,\ensuremath{\alpha}){}^{12}\mathrm{C}$ reaction, we carried out an $R$-matrix calculation to obtain the astrophysical factor for the ${}^{15}\mathrm{N}(p,\ensuremath{\gamma}){}^{16}\mathrm{O}$ reaction. The results indicate that the direct capture contribution was previously overestimated. We find the astrophysical factor to be $S(0)=36.0\ifmmode\pm\else\textpm\fi{}6.0$ keV b, which is about a factor of 2 lower than the presently accepted value. We conclude that for every $2200\ifmmode\pm\else\textpm\fi{}300$ cycles of the main CN cycle one CN catalyst is lost due to this reaction.

Neon abundances in three Wolf-Rayet stars observed with the ISO Short Wavelength Spectrometer

We are motivated to study the Ne/He abundance ratio at the surfaces of Wolf-Rayet stars by evolutionary models, which have predicted enhancements by more than an order of magnitude over cosmic levels during the WC stage (e.g., Maeder 1991). This should occur early in the WC phase, as core-hydrogen is exhausted and the CNO bi-cycle gives way to the following chain of reactions for the Galactic stars: The latest evolutionary models, which include the effects of interior mixing due to stellar rotation, indicate that the enhancement may be somewhat more gradual, but that the Ne/He ratio is essentially unchanged in its peak value, coinciding with complete H-depletion (e.g., Meynet, these Proceedings).

Relativistic spaceflight and the catalytic nuclear ramjet

The interstellar ramjet concept allows us, at least hypothetically, to get around the mass-ratio limit inherent with relativistic fuel-carrying rockets. The required ramjet energy must be extracted from the nuclear reserves of the interstellar hydrogen (interstellar deuterium is too scarce). Unfortunately, the usual PPI chain for converting hydrogen to helium is hopelessly slow due to the minute weak interaction cross section of the reaction p + p → 2 D + e + + v at essentially any energy. It is shown here that this problem can be avoided, in principle, by exploiting a proton burning catalytic cycle. The best known catalytic cycle is the CNO Bi-Cycle occurring in sufficiently hot main sequence stars. The catalyst “fuel” may be carried on board the ship since it is not depleted, and the ultimate source of energy is the interstellar hydrogen. It is shown that with potentially realistic parameters the energy requirements for a ramjet accelerating at 1 g to near luminal velocities can be met with either the “hot” CNO Bi-Cycle or the Ne-Na cycle. Some of the formidable technological problems associated with a conventional heavy ion fusion reactor are briefly discussed. It is not absolutely necessary that a conventional plasma reactor model be used; for example a laser fusion reactor or a large scale Migma-type reactor (if technologically possible) might be employed. The problem of interstellar drag is considered and a model is suggested in which the incident proton's kinetic energy is stored in the electric field between charged grids and returned to the exhaust particles after the relevant nuclear reactions are completed. Such a combination of electric and magnetic fields would make less severe other suggested limitations to the ramjet's performance. The problem of ionizing the interstellar medium directly in front of the ramjet when operating in non-HII regions of space is also discussed. It is shown that laser ionization is energetically possible for interstellar number densities ≳10 cm −3; however, since the laser also tends to sweep the interstellar matter out of the ramjet's path, more quantitative study is necessary before the method can be considered feasible at any density. The possibility of using a thin stripper foil, placed over the intake cross section, to ionize the interstellar medium is suggested. This method has the advantage of efficiently ionizing the interstellar matter independent of density.

Molecular column densities in selected model atmospheres

From an examination of predicted column densities, the following conclusions were drawn: (1) The SiO ought to be visible in carbon stars which were generated from triple alpha burning, but absent from carbon stars generated from the CNO bi-cycle. (2) Variation in the observed relative strengths of TiO and ZrO is indicative of real differences in the ratio Ti/Zr. (3) The TiO/ZrO ratio shows a small variation as C/O and effective temperature is changed. (4) Column density of silicon dicarbide (SiC2) is sensitive to abundance, temperature, and gravity; hence all relationships between the strength of SiC2 and other stellar parameters will show appreciable scatter. There is however, a substantial luminosity effect present in the SiC2 column densities. (5) Unexpectedly, SiC2 is anti-correlated with C2. (6) The presence of SiC2 in a carbon star eliminates the possibility of these stars having temperatures greater than or equal to 3000 K, or being produced through the CNO bi-cycle.

Hot CNO-Ne Cycle Hydrogen Burning. Thermonuclear Evolution at Constant Temperature and Density

The relative concentrations of nuclei achieved in hydrogen burning on carbon, nitrogen, and oxygen at high temperatures are calculated as a function of time. Calculations have been performed for static burning conditions, for temperatures in the range 0.1 < T9 1 and densities 1 p < 10 g cm - 3. The Ne-Na cycle also operates under these high-temperature conditions. A network comprising 28 nuclei from 12C to 25Mg, related by 60 (p, y), (p, a), (a, y), (a, n), and positron decay reactions, has been used in this study. At higher temperatures the (p, y) and (p, a) thermonuclear reaction rates are typically much faster than the positron decay rates, quite in contrast to the situation existing under the usual CNO bi-cycle burning conditions in stellar cores. This distinguishing feature leads to nucleosynthesis which differs significantly from that calculated at lower temperatures. Specifically, large enhancements of nuclei of masses A = 15, 17, 18, 19, 21, and 22 are found to occur at various stages of the burning at constant temperature (the stable nuclei on these isobars being 15N, 170, O, 19F, 21Ne, and 22Ne). Under some conditions, 13C/12C ratios exceeding unity are achieved, in contrast to the ratio 13C/12C = 0.29 characteristic of equilibrium in the CNO bi-cycle at lower temperatures, T < 70 million degrees. The physical conditions determined to be most promising for nucleosynthesis provide insight as to possible sites for the formation of many of these lighter isotopes in astrophysical environments. Subject headings: interiors, stellar - massive stars - nuclear reactions - abundances

Carbon Stars and the CNO Bi-Cycle

view Abstract Citations (5) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Carbon Stars and the CNO Bi-Cycle Thompson, Rodger I. Abstract It is shown that in the context of present stellar evolutionary theory, carbon stars cannot be the result of mixing CNO bi-cycle products to the surface. This is because insufficient material is processed in the stellar interior to affect the 12C/18O ratio significantly at the surface of the star. A 9 M0 star from Iben's work is discussed as an example. Four speculative possibilities are listed for the origin of carbon stars. Publication: The Astrophysical Journal Pub Date: March 1972 DOI: 10.1086/151358 Bibcode: 1972ApJ...172..391T full text sources ADS |

Evidence for Hydrogen-To Rations in Accordance with the CNO Bi-Cycle in Several Carbon Stars

view Abstract Citations (15) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for Hydrogen-To-Carbon Rations in Accordance with the CNO Bi-Cycle in Several Carbon Stars Thompson, Rodger I. ; Schnopper, Herbert W. ; Rose, William K. Abstract Equivalent widths of a C2 and several CO infrared absorption bands are measured in four carbon stars (W Ori, X Cnc, U Hya, and 19 Psc). Line-of-sight abundances of C2 and CO are computed from the observed equivalent widths. Model-atmosphere calculations are then used to predict theoretical C2 and CO abundances for various H: C : N: 0 abundance ratios Two cases are considered: (1) a high carbon-to-hydrogen ratio which is indicative of either high initial carbon abundance or mixing of products of the triple- process and (2) a low carbon-to-hydrogen ratio which is indicative of a hydrogen-to-carbon ratio derived from the CNO hi-cycle. A comparison of the observed C2 and CO abundances with the best available theoretical models indicates agreement with the predicted CNO hi-cycle hydrogen-to-carbon ratio. Publication: The Astrophysical Journal Pub Date: February 1971 DOI: 10.1086/150797 Bibcode: 1971ApJ...163..533T full text sources ADS | data products SIMBAD (7)

Observations on the abundance of nitrogen in the primary cosmic radiation

New measurements of the intensity and spectrum of cosmic ray nitrogen nuclei made by instruments flown on balloons and on the Pioneer-8 space probe are reported. The nitrogen spectrum is found to be identical with that of the other medium nuclei, carbon and oxygen, over the range of measurement from 100 MeV/nuc to > 22 GeV/nuc. The ratio of N to all M nuclei is found to be =0.125, constant to within 10% over this energy range. This ratio is extrapolated to the cosmic-ray source using the most recently obtained abundances of oxygen and heavier nuclei and fragmentation parameters for the production of nitrogen from these nuclei. Taking an average material path length of 4 g/cm2 of hydrogen constant with energy, as required to make the abundance of L nuclei →0 at the cosmic-ray source, the resulting N/M source ratio is ≤0.03. In other words, to the same degree that the so-called L nuclei are absent in the cosmic-ray sources, N nuclei are also absent. This nitrogen abundance is therefore different from the estimated solar atmospheric abundance of ∼0.10 for the N/M ratio which is believed to represent the integrated effects of nucleo-synthesis in the galaxy at the time of the formation of the sun. Nevertheless under certain conditions in the CNO bi-cycle that operates for the production of nitrogen in stellar objects a negligible production of nitrogen might be expected. It is suggested that these conditions exist in the cosmic-ray sources. The C/O ratio of 0.9 deduced for cosmic-ray sources is compatible with the observed low nitrogen abundance arising in this CNO bi-cycle.

Spectrophotometry of a B-Type Star in the Globular Cluster M13

view Abstract Citations (37) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of a B-Type Star in the Globular Cluster M13 Stoeckly, Robert ; Greenstein, Jesse L. Abstract Barnard 29, a member of the cluster M13, is an e~rly B-type star lying 3 mag above the horizontal branch. Spectrograms of the blue region at 38 and 18 A mm1 show an extremely sparse line spectrum. A coarse analysis of the spectrum indicates an ionization temperature of 197000 ± 15000 K (O~ = 0.256), an effective surface gravity log ~ = 2.6, a radius of 3.4 ± 0 7 Ro, a luminosity of 2500 ± 1000 Lo, and a mass of 0.3 Mo, suggesting a highly evolved star. The He/H ratio seems close to that in Population I, unlike the surfaces of horizontal-branch stars. The logarithmic mean of the relative abundances of C, N, 0, Mg, and Si (using upper limits for three elements not detected) shows them to be less abundant than in `r Sco and the Sun by a factor of at least 20 The carbon abundance is very low, ruling out the possi- bility that this star is the exposed core of a highly evolved red giant. The likeliest interpretation is that it is an old star of initial mass near 1.4 Mo, in which no nuclear reactions beyond the CNO bi-cycle have operated and from which 80 per cent of the mass has somehow been removed to expose an only partially exhausted core. Photoelectric flux measurements show that the slope of the continuum is abnormally small compared with the Balmer jump, possibly indicating a double star containing a red subgiant companion. Seven measurements show variable radial velocity, also suggesting duplicity Publication: The Astrophysical Journal Pub Date: December 1968 DOI: 10.1086/149812 Bibcode: 1968ApJ...154..909S full text sources ADS | data products SIMBAD (1)

Approach to Equilibrium in the CNO Bi-Cycle

Differential equations of the CNO bi-cycle are solved to obtain the abundances of carbon, nitrogen, and oxygen nuclei as functions of protons consumed per initial nucleus for hydrogen burning in the temperature range 10-50 x 106 K. General features of the curves of abundance ratios for C12, C'3, N14, N'2, and 016 nuclei as functions of protons consumed are found to be insensitive to the temperature at which the reactions take place. The resonance at 65 keV in the O' (p, a) N'4 reaction is responsible for the temperature dependence of ratios involving O' nuclei. Analysis is made of the effect of convection with microscopic mixing on CN material passing through a hydrogen-burning zone. If a simple linear relationship or a sinusoidal relationship is assumed for the time dependence of temperature, the ratios of abundances attained at the surface in a given time are the same whether the time is spent in a single transit to the surface or in several transits back and forth from the bottom of the hydrogen-burning zone to the surface of the star. It is shown that the C"-C" ratio observed in typical carbon stars can be explained on the basis of the CNO bi-cycle if the time spent in the process is at least one-half the mean lifetime of C" for proton capture, but that, in order to explain the ratio of nitrogen to oxygen suggested by astronomers for these stars, it is necessary to assume that the time spent by the nuclei at the site of hydrogen burning must be no longer than the mean lifetime of C" for proton capture. In the Appendix a table is given of contributions of several resonant levels in the compound nuclei involved in the proton-capture reactions of C", C", and N'4. These contributions are presented in the form of equations for the temperature dependence of the mean lifetimes of the reactions.

Erratum: the Mean Lifetimes of Carbon, Nitrogen, and Oxygen Nuclei in the CNO Bicycle.

Erratum: the Mean Lifetimes of Carbon, Nitrogen, and Oxygen Nuclei in the CNO Bicycle.

The Mean Lifetimes of Carbon, Nitrogen, and Oxygen Nuclei in the CNO Bicycle.

The Mean Lifetimes of Carbon, Nitrogen, and Oxygen Nuclei in the CNO Bicycle.