Showing papers by "Takashi J. Moriya published in 2010"

Fallback Supernovae: A Possible Origin of Peculiar Supernovae with Extremely Low Explosion Energies

Abstract: We perform hydrodynamical calculations of core-collapse supernovae (SNe) with low explosion energies. These SNe do not have enough energy to eject the whole progenitor and most of the progenitor falls back to the central remnant. We show that such fallback SNe can have a variety of light curves (LCs) but their photospheric velocities can only have some limited values with lower limits. We also perform calculations of nucleosynthesis and LCs of several fallback SN models, and find that a fallback SN from the progenitor with a main-sequence mass of 13 M ? can account for the properties of the peculiar Type Ia supernova SN 2008ha. The kinetic energy and ejecta mass of the model are 1.2 ? 1048?erg and 0.074 M ?, respectively, and the ejected 56Ni mass is 0.003 M ?. Thus, SN 2008ha can be a core-collapse SN with a large amount of fallback. We also suggest that SN 2008ha could have been accompanied by long gamma-ray bursts, and long gamma-ray bursts without associated SNe may be accompanied by very faint SNe with significant amount of fallback, which are similar to SN 2008ha.

A Core-collapse Supernova Model for the Extremely Luminous Type Ic Supernova 2007bi: An Alternative to the Pair-instability Supernova Model

Abstract: We present a core-collapse supernova (SN) model for the extremely luminous Type Ic SN 2007bi. By performing numerical calculations of hydrodynamics, nucleosynthesis, and radiation transport, we find that SN 2007bi is consistent with the core-collapse SN explosion of a 43 M ☉ carbon and oxygen core obtained from the evolution of a progenitor star with a main-sequence mass of 100 M ☉ and metallicity of Z = Z ☉/200, from which its hydrogen and helium envelopes are artificially stripped. The ejecta mass and the ejecta kinetic energy of the models are 40 M ☉ and 3.6 × 1052 erg. The ejected 56Ni mass is as large as 6.1 M ☉, which results from the explosive nucleosynthesis with large explosion energy. We also confirm that SN 2007bi is consistent with a pair-instability SN model as has recently been claimed. We show that the earlier light-curve data can discriminate between the models for such luminous SNe.

Supernovae from Red Supergiants with Extensive Mass Loss

Abstract: We calculate multicolor light curves (LCs) of supernovae (SNe) from red supergiants (RSGs) exploded within dense circumstellar medium (CSM). Multicolor LCs are calculated by using a multi-group radiation hydrodynamics code STELLA. If CSM is dense enough, the shock breakout signal is delayed and smeared by CSM and kinetic energy of SN ejecta is efficiently converted to thermal energy which is eventually released as radiation. We find that explosions of RSGs are affected by CSM in early epochs when mass-loss rate just before the explosions is higher than 10^{-4} Msun/yr. Their characteristic features are that the LC has a luminous round peak followed by a flat LC, that multicolor LCs are simultaneously bright in ultraviolet and optical at the peak, and that photospheric velocity is very low at these epochs. We calculate LCs for various CSM conditions and explosion properties, i.e., mass-loss rates, radii of CSM, density slopes of CSM, explosion energies of SN ejecta, and SN progenitors inside, to see their influence on LCs. We compare our model LCs to those of ultraviolet-bright Type IIP SN 2009kf and show that the mass-loss rate of the progenitor of SN 2009kf just before the explosion is likely to be higher than 10^{-4} Msun/yr. Combined with the fact that SN 2009kf is likely to be an energetic explosion and has large 56Ni production, which implies that the progenitor of SN 2009kf is a massive RSG, our results indicate that there could be some mechanism to induce extensive mass loss in massive RSGs just before their explosions.

Multiple main sequence of globular clusters as a result of inhomogeneous big bang nucleosynthesis

Abstract: A new mechanism for enhancing the helium abundance in the blue main sequence stars of $\ensuremath{\omega}$ Centauri and NGC 2808 is investigated. We suggest that helium enhancement was caused by the inhomogeneous big bang nucleosynthesis. Regions with extremely high baryon-to-photon ratios are assumed to be caused by the baryogenesis. Its mass scale is also assumed to be ${10}^{6}{M}_{\ensuremath{\bigodot}}$. An example of the mechanisms to realize these two things was already proposed as the Affleck-Dine baryogenesis. As the baryon-to-photon ratio becomes larger, the primordial helium abundance is enhanced. We calculated the big bang nucleosynthesis and found that there exists a parameter region yielding enough helium to account for the split of the main sequence in the aforementioned globular clusters while keeping the abundance of other elements compatible with observations. Our mechanism predicts that heavy elements with the mass number of around 100 is enhanced in the blue main sequence stars. We estimate the time scales of diffusion of the enhanced helium and mass accretion in several stages after the nucleosynthesis to investigate whether these processes diminish the enhancement of helium. We found that the diffusion does not influence the helium content. A cloud with a sufficiently large baryon-to-photon ratio to account for the multiple main sequence collapsed immediately after the recombination. Subsequently, the cloud accreted the ambient matter with the normal helium content. If the star formation occurred both in the collapsed core and the accreted envelope, then the resultant star cluster has a double main sequence.

Observations of the Optical Transient in NGC 300 with AKARI/IRC: Possibilities of Asymmetric Dust Formation

Abstract: We present the results of near-infrared (NIR) multi-epoch observations of the optical transient in the nearby galaxy NGC 300 (NGC 300-OT) at 398 and 582 days after the discovery with the Infrared Camera (IRC) on board AKARI. NIR spectra (2-5 μm) of NGC 300-OT were obtained for the first time. They show no prominent emission nor absorption features, but are dominated by continuum thermal emission from the dust around NGC 300-OT. NIR images were taken in the 2.4, 3.2, and 4.1 μm bands. The spectral energy distributions (SEDs) of NGC 300-OT indicate the dust temperature of 810 ± 14 K at 398 days and 670 ± 12 K at 582 days. We attribute the observed NIR emission to the thermal emission from dust grains formed in the ejecta of NGC 300-OT. The multi-epoch observations enable us to estimate the dust optical depth as 12 at 398 days and 6 at 582 days at 2.4 μm by assuming an isothermal dust cloud. The observed NIR emission must be optically thick, unless the amount of dust grains increases with time. Little extinction at visible wavelengths reported in earlier observations suggests that the dust cloud around NGC 300-OT should be distributed inhomogeneously so as to not screen the radiation from the ejecta gas and the central star. The present results suggest the dust grains are not formed in a spherically symmetric geometry, but rather in a torus, a bipolar outflow, or clumpy cloudlets.

Observations of the Optical Transient in NGC 300 with AKARI/IRC: Possibilities of Asymmetric Dust Formation

Abstract: We present the results of near-infrared (NIR) multi-epoch observations of the optical transient in the nearby galaxy NGC300 (NGC300-OT) at 398 and 582 days after the discovery with the Infrared Camera (IRC) onboard AKARI. NIR spectra (2--5 um) of NGC300-OT were obtained for the first time. They show no prominent emission nor absorption features, but are dominated by continuum thermal emission from the dust around NGC300-OT. NIR images were taken in the 2.4, 3.2, and 4.1 um bands. The spectral energy distributions (SED) of NGC300-OT indicate the dust temperature of 810 (+-14) K at 398 days and 670 (+-12) K at 582 days. We attribute the observed NIR emission to the thermal emission from dust grains formed in the ejecta of NGC300-OT. The multi-epoch observations enable us to estimate the dust optical depth as larger than about 12 at 398 days and larger than about 6 at 582 days at 2.4 um, by assuming an isothermal dust cloud. The observed NIR emission must be optically thick, unless the amount of dust grains increases with time. Little extinction at visible wavelengths reported in earlier observations suggests that the dust cloud around NGC300-OT should be distributed inhomogeneously so as to not screen the radiation from the ejecta gas and the central star. The present results suggest the dust grains are not formed in spherically symmetric geometry, but rather in a torus, a bipolar outflow, or clumpy cloudlets.

GRB Nucleosynthesis in Dwarf Galaxies

Abstract: Recent observations with large telescopes have revealed that stars in nearby dwarf spheroidal galaxies (dSph stars) have elemental abundances distinct from metal poor stars in our galaxy [7, 8, 9]. This indicates that the chemical evolution of these dwarf galaxies was dominated by supernovae that have not mainly contributed to the chemical evolution of our galaxy. On the other hand, the identification of host galaxies of gamma‐ray bursts (GRBs) suggests that GRBs may preferentially occur in low luminosity metal‐poor galaxies [6]. Supernovae associated with GRBs might have exclusively imprinted their nucleosynthesis on the elemental abundances of stars in dwarf galaxies while these supernovae were too rare to contribute to the chemical evolution of our galaxy. To test this conjecture, we have planned to perform nucleosynthesis calculations in aspherical supernovae and investigate the elemental abundance patterns of stars inheriting the nucleosynthesis products by taking into account ejecta with different a...

Interaction‐Powered Supernovae as Probes of the High‐Redshift Universe

Abstract: A supernova (SN) becomes as bright as a galaxy and is a powerful tool for probing the high‐redshift universe. In particular, it has been suggested that extremely luminous SNe (MR 2, which is difficult for type Ia SNe. Some luminous SNe, such as type IIn SNe, are believed to be powered by the interaction of the SN ejecta with the circumstellar medium. One of the interesting features of interaction‐powered SNe is the fact that they are bright in UV. With their intrinsic brightness in UV, interaction‐powered SNe could unveil the properties of stars at high redshift and probe the primordial universe. We performed multigroup light curve calculations of interaction‐powered SNe using the STELLA code. Based on the synthetic multicolor light curves, we estimate the detectability of interaction‐powered SNe at high redshifts with several telescopes.

A Core-Collapse Supernova Model for the Extremely Luminous Type Ic Supernova 2007bi: An Alternative to the Pair-Instability Supernova Model

Abstract: We present a core-collapse supernova model for the extremely luminous Type Ic supernova 2007bi. By performing numerical calculations of hydrodynamics, nucleosynthesis, and radiation transport, we find that SN 2007bi is consistent with the core-collapse supernova explosion of a 43 Msun carbon and oxygen core obtained from the evolution of a progenitor star with a main sequence mass of 100 Msun and metallicity of Z = Zsun/200, from which its hydrogen and helium envelopes are artificially stripped. The ejecta mass and the ejecta kinetic energy of the models are 40 Msun and 3.6*10^{52} erg. The ejected 56Ni mass is as large as 6.1 Msun, which results from the explosive nucleosynthesis with large explosion energy. We also confirm that SN 2007bi is consistent with a pair-instability supernova model as has recently been claimed. We show that the earlier light curve data can discriminate between the models for such luminous supernovae.

Fallback Supernovae: A Possible Origin of Peculiar Supernovae with Extremely Low Explosion Energies

Abstract: We perform hydrodynamical calculations of core-collapse supernovae (SNe) with low explosion energies. These SNe do not have enough energy to eject the whole progenitor and most of the progenitor falls back to the central remnant. We show that such fallback SNe can have a variety of light curves (LCs) but their photospheric velocities can only have some limited values with lower limits. We also perform calculations of nucleosynthesis and LCs of several fallback SN model, and find that a fallback SN from the progenitor with a main-sequence mass of 13 Msun can account for the properties of the peculiar Type Ia supernova SN 2008ha. The kinetic energy and ejecta mass of the model are 1.2*10^{48} erg and 0.074 Msun, respectively, and the ejected 56Ni mass is 0.003 Msun. Thus, SN 2008ha can be a core-collapse SN with a large amount of fallback. We also suggest that SN 2008ha could have been accompanied with long gamma-ray bursts and long gamma-ray bursts without associated SNe may be accompanied with very faint SNe with significant amount of fallback which are similar to SN 2008ha.

Explosive Nucleosynthesis in Supernovae and Hypernovae

Abstract: We review the properties of supernovae (SNe) as a function of the progenitor’s mass M. (1) 8–10 M⊙ stars are super‐AGB stars and resultant electron capture SNe may be Faint supernovae like Type IIn SN 2008S. (2) 10–13 M⊙ stars undergo Fe‐core collapse to form neutron stars (NSs) and Faint supernovae. (3) 13 M⊙–MBN stars undergo Fe‐core collapse to form NSs and normal core‐collapse supernovae. (4) MBN–90 M⊙ stars undergo Fe‐core collapse to form Black Holes. Resultant supernovae are bifurcate into Hypernovae and Faint supernovae. (5) 90–140 M⊙ stars produce Luminous SNe, like SNe 2007 bi and 2006 gy (6) 140–300 M⊙ stars become pair‐instability supernovae which could be Luminous supernovae (SNe 2007 bi and 2006 gy). (7) Very massive stars with M≳300 M⊙ undergo core‐collapse to form intermediate mass black holes. Some SNe could be more Luminous supernovae (like SN 2006 gy).

Unusual Supernovae and Their Connections to First Stars and Gamma-Ray Bursts

Abstract: Recent observations have revealed remarkably large diversities of supernova properties. We present our challenge to explore the origin of unusual supernovae such as extremely faint and extremely luminous supernovae, and the extremely energetic explosions (hypernovae) associated with the Gamma‐Ray Bursts. In particular, we present a core‐collapse hypernova model for extremely luminous type Ic SN 2007bi as an alternative to the pair‐instability model. We discuss how nucle‐osynthetic properties resulted from unusual supernovae are connected with the unusual abundance patterns of extremely metal‐poor stars. Such connections may provide important constraints on the properties of first stars.

Explosive Nucleosynthesis in Luminous Hypernovae and Faint Supernovae

Abstract: The diversity in brightness and explosion energy of supernovae (SNe) that have recently been observed is remarkable. Determining the origin of unusual SNe, such as extremely faint or extremely luminous ones, or the very energetic explosions associated with GRBs (hypernovae), is very challenging. We present a core‐collapse hypernova model for the extremely luminous Type Ic SN 2007bi as an alternative to the pair‐instability model. We discuss how nucleosynthesis from a variety of SNe is connected to the abundance patterns of extremely metal‐poor stars. Such connections may impose important constraints on the properties of the first stars, such as their evolution with mass accretion, or the asphericity of their explosions.