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Journal Articles

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr cross section from the surrogate ratio method and its effect on $$s$$-process nucleosynthesis

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; Nishio, Katsuhisa; Lugaro, M.*; Karakas, A. I.*; Makii, Hiroyuki; Mohr, P.*; Su, J.*; Li, Y. J.*; et al.

Astrophysical Journal, 848(2), p.98_1 - 98_8, 2017/10

 Percentile:100(Astronomy & Astrophysics)

Journal Articles

Abundance profiling of extremely metal-poor stars and supernova properties in the early universe

Tominaga, Nozomu*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

Astrophysical Journal, 785(2), p.98_1 - 98_23, 2014/04

 Times Cited Count:54 Percentile:6.33(Astronomy & Astrophysics)

The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star and chemical evolution of the universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars is now being discovered. This allows us to statistically constrain properties of SNe of Pop III stars (Pop III SNe). We investigate the properties of Pop III SNe by comparing their nucleosynthetic yields with the abundance patterns of the EMP stars. We focus on the most metal-poor stars with [Fe/H] $$_sim^{<}$$ 3.5 and present Pop III SN models that reproduce well their individual abundance patterns. From these models we derive relations between abundance ratios and properties of Pop III SNe: [(C+N)/Fe] vs. an ejected Fe mass, and [(C+N)/Mg] vs. a remnant mass. Using fitting functions, distribution of the abundance ratios of EMP stars is converted to those of the properties of Pop III SNe, which can be compared with SNe in the present day.

Journal Articles

Supernova neutrino nucleosynthesis of the radioactive $$^{92}$$Nb observed in primitive meteorites

Hayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Iwamoto, Nobuyuki; Cheoun, M. K.*; Mathews, G. J.*

Astrophysical Journal Letters, 779(1), p.L9_1 - L9_5, 2013/12

 Times Cited Count:21 Percentile:32.63(Astronomy & Astrophysics)

Short-lived radioactivities are used as nuclearcosmochronometers for understanding the free decay time from the last nucleosynthesis episode until the time of solar system formation (SSF). $$^{92}$$Nb (half-life of 34.7 Myr) is one of a short-lived isotope existed at SSF. However, there is a controversy in that the inferred initial abundance ratios for $$^{92}$$Nb/$$^{93}$$Nb at the time of SSF cluster around two different values; one is near 10$$^{-3}$$, while the other is near 10$$^{-5}$$. Moreover, the astrophysical mechanism for the synthesis of $$^{92}$$Nb has remained an unsolved problem. Here we argue that conventional nucleosynthesis mechanisms cannot produce $$^{92}$$Nb and propose a new mechanism for the nucleosynthesis of this isotopebased upon neutrino induced reactions occurring during core-collapse supernova explosions.

Journal Articles

Cooling of compact stars with color superconducting phase in quark-hadron mixed phase

Noda, Tsuneo*; Hashimoto, Masaaki*; Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*; Fujimoto, Masayuki*

Astrophysical Journal, 765(1), p.1_1 - 1_5, 2013/03

 Times Cited Count:19 Percentile:35.83(Astronomy & Astrophysics)

Journal Articles

Production of the $$p$$-process nuclei in the carbon-deflagration model for type Ia supernovae

Kusakabe, Motohiko*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

Astrophysical Journal, 726(1), p.25_1 - 25_11, 2011/01

 Times Cited Count:37 Percentile:20.57(Astronomy & Astrophysics)

We calculate nucleosynthesis of proton-rich isotopes in the carbon deflagration model for Type Ia supernovae (SNe Ia). When the deflagration wave passes through the outer layer of the CO white dwarf, $$p$$-nuclei are produced by photodisintegration reactions on s-nuclei in a region with the peak temperature ranging from 1.9 to 3.6$$times$$10$$^{9}$$ K. We find that about 50% of $$p$$-nuclides are co-produced when normalized to their solar abundances in all adopted cases of seed distribution. Mo and Ru, which are largely underproduced in Type II supernovae (SNe II), are produced at a level similar to other $$p$$-nuclides. The ratios between $$p$$-nuclei and iron in the ejecta are larger than the solar ratios by a factor of 1.2. We also compare the yields of oxygen, iron, and $$p$$-nuclides in SNe Ia and SNe II, and suggest that SNe Ia could make a larger contribution than SNe II to the solar system content of $$p$$-nuclei.

Journal Articles

Neutron capture cross section to $$^{113}$$Cd isomer and $$_{s-}$$process contribution to rare $$_{p-}$$nuclide $$^{115}$$Sn

Hayakawa, Takehito; Shizuma, Toshiyuki; Chiba, Satoshi; Kajino, Toshitaka*; Hatsukawa, Yuichi; Iwamoto, Nobuyuki; Shinohara, Nobuo; Harada, Hideo

Astrophysical Journal, 707(2), p.859 - 865, 2009/12

 Times Cited Count:2 Percentile:88.94(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

Laboratory measurements of infrared absorption spectra of hydrogen-ordered ice; A Step to the exploration of ice XI in space

Arakawa, Masashi; Kagi, Hiroyuki; Fukazawa, Hiroshi

Astrophysical Journal; Supplement Series, 184(1), p.361 - 365, 2009/09

 Times Cited Count:16 Percentile:50.42(Astronomy & Astrophysics)

Infrared absorption spectra of ice were obtained at 4, 60, 100, 140, 160, and 240 K to make spectroscopic observations of hydrogen ordering at low temperatures. A broad peak observed at around 850 cm$$^{-1}$$ (11.7-181 $$mu$$m) was derived from libration of water molecules. The peak width was notably narrower at temperatures less than 140 K. A decrease in the peak width occurring in accordance with the formation of ice with ordered arrangements of hydrogen atoms was suggested from incoherent inelastic neutron-scattering studies. These results are consistent with ordering of hydrogen atoms. Existence of hydrogen-ordered ice in space is the subject of continuing astronomical debate. Our results demonstrate that the ordered ice in space is detectable using infrared telescopes and planetary exploration.

Journal Articles

Topological transition from accretion to ejection in a disk-jet system; Singular perturbation of the Hall effect in a weakly ionized plasma

Shiraishi, Junya; Yoshida, Zensho*; Furukawa, Masaru*

Astrophysical Journal, 697(1), p.100 - 105, 2009/03

 Times Cited Count:2 Percentile:88.94(Astronomy & Astrophysics)

A thin disk accompanied by spindle-like jet, created commonly near massive central objects, exhibits a topologically singular aspect when viewed from an ideal macroscopic theory. The accreting inflow and jet's outflow are "singular perturbation" on the ambient Keplerian rotation, which are generated by some non-ideal higher-order (in the order of derivatives) effect. The Hall effect can generate such a structure in a weakly ionized plasma of a protostellar disk. Numerical estimate of the characteristic length scale defined by the singular perturbation justifies the precedence of the Hall effect.

Journal Articles

Empirical abundance scaling laws and implications for the $$gamma$$ process in core-collapse supernovae

Hayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka*; Shizuma, Toshiyuki; Umeda, Hideyuki*; Nomoto, Kenichi*

Astrophysical Journal, 685(2), p.1089 - 1102, 2008/10

 Times Cited Count:20 Percentile:43.82(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

Neutrino-nucleus reaction cross sections for light element synthesis in supernova explosions

Yoshida, Takashi*; Suzuki, Toshio*; Chiba, Satoshi; Kajino, Toshitaka*; Yokomakura, Hidekazu*; Kimura, Keiichi*; Takamura, Akira*; Hartmann, D.*

Astrophysical Journal, 686(1), p.448 - 466, 2008/10

The neutrino-nucleus reaction cross sections of $$^4$$He and $$^{12}$$C are evaluated using new shell model Hamiltonians. Branching ratios of various decay channels are calculated to evaluate the yields of Li, Be, and B produced through the $$nu$$-process in supernova explosions. The new cross sections enhance the yields of $$^{7}$$Li and $$^{11}$$B produced during the supernova explosion of a 16.2 M$$_odot$$ star model compared to our previous study by factors of 1.3 and 1.2, respectively. On the other hand, the yield of $$^{10}$$B decreases by a factor of three. The yields of $$^{6}$$Li, $$^{9}$$Be, and the radioactive nucleus $$^{10}$$Be are found at a level of 10 to 11 M$$_odot$$. The temperature of $$nu mu, tau$$- and $$bar{nu} mu, tau$$-neutrinos inferred from the supernova contribution of $$^{11}$$B in Galactic chemical evolution models is constrained to be in the range 4.5 MeV to 6.4 MeV. The increase in the $$^{7}$$Li and $$^{11}$$B yields due to neutrino oscillations is demonstrated with the new cross sections.

Journal Articles

Neutrino-nucleus reaction cross sections for light element synthesis in supernova explosions

Yoshida, Takashi*; Suzuki, Toshio*; Chiba, Satoshi; Kajino, Toshitaka*; Yokomakura, Hidekazu*; Kimura, Keiichi*; Takamura, Akira*; Hartmann, D. H.*

Astrophysical Journal, 686(1), p.448 - 466, 2008/10

 Times Cited Count:75 Percentile:9.3(Astronomy & Astrophysics)

The neutrino-nucleus reaction cross sections of $$^4$$He and $$^{12}$$C are evaluated using new shell model Hamiltonians. The new cross sections enhance the yields of $$^7$$Li and $$^{11}$$B produced during the supernova explosion of a 16.2 $$M_odot$$ star model compared to the case using the conventional cross sections by about 10%. On the other hand, the yield of $$^{10}$$B decreases by a factor of two. The yields of $$^6$$Li, $$^9$$Be, and the radioactive nucleus $$^{10}$$Be are found at a level of $$sim 10^{-11} M_odot$$. The temperature of $$nu_{mu,tau}$$- and $$bar{nu}_{mu,tau}$$-neutrinos inferred from the supernova contribution of $$^{11}$$B in Galactic chemical evolution models is constrained to be in the range 4.3 MeV to 6.5 MeV. The increase in the $$^7$$Li and $$^{11}$$B yields due to neutrino oscillations is demonstrated with the new cross sections.

Journal Articles

Spectroscopic studies of extremely metal-poor stars with the subaru high-dispersion spectrograph, 4; The $$alpha$$-element-enhanced metal-poor star BS 16934-002

Aoki, Wako*; Honda, Satoshi*; Beers, T. C.*; Hidai, Masahide*; Iwamoto, Nobuyuki; Tominaga, Nozomu*; Umeda, Hideyuki*; Nomoto, Kenichi*; Norris, J. E.*; Ryan, S. G.*

Astrophysical Journal, 660(1, Part1), p.747 - 761, 2007/05

 Times Cited Count:39 Percentile:25.02(Astronomy & Astrophysics)

A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H] = -2.7) star BS 16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD 122563 indicates excesses of O, Na, Mg, Al, and Sc in BS 16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS 22949-037 and CS 29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the $$alpha$$ elements. No established nucleosynthesis model exists that explains the observed abundancepattern. A supernova model, including mixing and fallback, assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS 16934-002.

Journal Articles

The Connection between $$gamma$$-ray bursts and extremely metal-poor stars; Black hole-forming supernovae with relativistic jets

Tominaga, Nozomu*; Maeda, Keiichi*; Umeda, Hideyuki*; Nomoto, Kenichi*; Tanaka, Masaomi*; Iwamoto, Nobuyuki; Suzuki, Tomoharu*; Mazzali, P. A.*

Astrophysical Journal, 657(2, Part2), p.L77 - L80, 2007/03

 Times Cited Count:100 Percentile:6.48(Astronomy & Astrophysics)

Long-duration $$gamma$$-ray bursts (GRBs) are thought to be connected with luminous and energetic Type Ic supernovae [SNe, called hypernovae (HNe)] resulting from the black-hole (BH) forming collapse of massive stars. For GRBs 060505 and 060614, however, the expected SNe have not been detected. The upper limits to the SN brightness are about 100 times fainter than GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected $$^{56}$$Ni masses of $$M(^{56}$$Ni)$$sim 10^{-3}M_odot$$. SNe with a small amount of $$^{56}$$Ni ejection are observed as faint Type II SNe. HNe and faint SNe are thought to be responsible for the formaion of extremely metal-poor (EMP) stars. A relativistic jet-induced BH forming explosion of the 40$$M_odot$$ star is investigated and hydrodynamic and nucleosynthetic models are presented. These models can explain both GRB-HNe and GRBs without bright SNe in a unified manner. We suggest that GRBs without bright SNe are likely to synthesize $$M(^{56}$$Ni)$$sim 10^{-4}-10^{-3}M_odot$$ or $$sim 10^{-6}M_odot$$.

Journal Articles

Existence of ferroelectric ice in the universe

Fukazawa, Hiroshi; Hoshikawa, Akinori; Ishii, Yoshinobu; Chakoumakos, B. C.*; Fernandez-Baca, J. A.*

Astrophysical Journal, 652(1, Part2), p.L57 - L60, 2006/11

 Times Cited Count:34 Percentile:30.89(Astronomy & Astrophysics)

Whether ferroelectric ice, named ice XI, exists in a stable low-temperature phase attracts much interest. This question arose as a condensed-matter issue, and became of interest in astronomy (e.g., does ice XI exist on Pluto?) because astronomical observations identified the existence of crystalline ice in our solar system. From neutron diffraction experiments, we found the temperature conditions for the transformation of the largest fraction of ice into ice XI using the lowest level of impurity dopant. The finding of bulk crystal of ordered structure firmly supports that ice XI is stable. This suggests the existence of naturally occurring ice XI at a narrow temperature range (57-66 K) in our solar system.

Journal Articles

Principle of universality of $$gamma$$-process nucleosynthesis in core-collapse supernova explosions

Hayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka*; Shizuma, Toshiyuki; Umeda, Hideyuki*; Nomoto, Kenichi*

Astrophysical Journal, 648(1, Part2), p.L47 - L50, 2006/09

 Times Cited Count:17 Percentile:52.25(Astronomy & Astrophysics)

Using core-collapse supernova explosion models, we investigate the principle of the universality of the $$gamma$$-process that the s/p abundance ratios produced by individual nucleosynthesis are almost constant in the wide region of the atomic number. The universality originates from the weak $$s$$-process in pre-supernovae, the independence of the s/p abundance ratios of the nuclear reactions, and the shift of the $$gamma$$-process layers. Our calculations further suggest an extended universalitythat the s/p ratios in the $$gamma$$-process layers are not only constant but also centered around a specific value 3. To verify this, we propose an astronomical observation of Indium isotopic abundance fractions.

Journal Articles

Enrichment of very metal poor stars with both $$r$$-process and $$s$$-process elements from $$8-10M_odot$$ stars

Wanajo, Shinya*; Nomoto, Kenichi*; Iwamoto, Nobuyuki; Ishimaru, Yuri*; Beers, T. C.*

Astrophysical Journal, 636(2, Part1), p.842 - 847, 2006/01

 Times Cited Count:33 Percentile:31.76(Astronomy & Astrophysics)

Recent spectroscopic studies have revealed the presence of numerous carbon-enhanced, metal-poor stars with [Fe/H]$$<-2$$ that exhibit enhancements of $$s$$-process elements. These stars are believed to be the result of a binary mass-transfer episode from a former asymptotic giant-branch (AGB) companion that underwent $$s$$-process nucleosynthesis. However, several such stars exhibit significantly lower Ba/Eu ratios than solar $$s$$-process abundances. We propose a model in which the double enhancements of $$r$$- and $$s$$-process elements originate from a former $$8-10M_odot$$ companion in a wide binary system, which may undergo $$s$$-processing during an AGB phase, followed by $$r$$-processing during its subsequent supernova explosion. The mass of Eu captured by the secondary through the wind from the supernova is estimated. We find that the estimated mass is in good agreement with a constraint on the Eu yield per supernova event, when the initial orbital separation is taken to be $$sim$$ 1 year.

Journal Articles

Postbounce evolution of core-collapse supernovae; Long-term effects of the equation of state

Sumiyoshi, Kosuke*; Yamada, Shoichi*; Suzuki, Hideyuki*; Shen, H.*; Chiba, Satoshi; Toki, Hiroshi*

Astrophysical Journal, 629(2, Part1), p.922 - 932, 2005/08

 Times Cited Count:183 Percentile:2.63(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

New $$s$$-process path and its implications for a $$^{187}$$Re-$$^{187}$$Os nucleo-cosmochronometer

Hayakawa, Takehito; Shizuma, Toshiyuki; Kajino, Toshitaka*; Chiba, Satoshi; Shinohara, Nobuo; Nakagawa, Tsuneo; Arima, Taiko*

Astrophysical Journal, 628(1, Part1), p.533 - 540, 2005/07

 Times Cited Count:18 Percentile:49.62(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

Self-collimation and magnetic field generation of astrophysical jets

Honda, Mitsuru*; Honda, Yasuko*

Astrophysical Journal, 569(1, Part2), p.L39 - L42, 2002/04

 Times Cited Count:19 Percentile:48.16(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

Magnetic field effect on masses of atomic nuclei

Kondratyev, V. N.; Maruyama, Toshiki; Chiba, Satoshi

Astrophysical Journal, 546(2, Part1), p.1137 - 1147, 2001/01

 Times Cited Count:10 Percentile:64.95(Astronomy & Astrophysics)

no abstracts in English

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