arXiv subjects

Ken'ichi Nomoto

Publications and source records attributed to Ken'ichi Nomoto.

At least 127 records · Page 7Linked to original sources

arXiv2012

A Binary Progenitor for the Type IIb Supernova 2011dh in M51

We perform binary stellar evolutionary calculations following the simultaneous evolution of both stars in the system to study a potential progenitor system for the Type IIb supernova 2011dh. Pre-explosion photometry as well as light-curve modeling have provided constraints on the physical properties of the progenitor system. Here we present a close binary system that is compatible with such constraints. The system is formed by stars of solar composition with 16 Msun + 10 Msun on a circular orbit with an initial period of 125 days. The primary star ends its evolution as a yellow supergiant with a mass of ~4 Msun, a final hydrogen content of ~3-5E-03 Msun and with an effective temperature and luminosity in agreement with the HST pre-explosion observations of SN 2011dh. These results are nearly insensitive to the adopted accretion efficiency factor beta. At the time of explosion, the companion star has an effective temperature of 22 to 40 thousand Kelvin, depending on the value of beta, and lies near the zero age main sequence. Considering the uncertainties in the HST pre-SN photometry the secondary star is only marginally detectable in the bluest observed band. Close binary systems, as opposed to single stars, provide a natural frame to explain the properties of SN 2011dh.

astro-ph.SR↗

arXiv2012

A High-Resolution Spectroscopic Search for the Remaining Donor for Tycho's Supernova

In this paper, we report on our analysis using Hubble Space Telescope astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's supernova remnant (SN 1572). With these data, we measured the proper motions, radial velocities, rotational velocities, and chemical abundances of these objects. Regarding the chemical abundances, we do not confirm the unusu- ally high [Ni/Fe] ratio previously reported for Tycho-G. Rather, we find that for all metrics in all stars, none exhibit the characteristics expected from traditional SN Ia single-degenerate-scenario calculations. The only possible exception is Tycho-B, a rare, metal-poor A-type star; however, we are unable to find a suitable scenario for it. Thus, we suggest that SN 1572 cannot be explained by the standard single-degenerate model.

astro-ph.SR↗

arXiv2012

Light Curve Modeling of Superluminous Supernova 2006gy: Collision between Supernova Ejecta and Dense Circumstellar Medium

We show model light curves of superluminous supernova 2006gy on the assumption that the supernova is powered by the collision of supernova ejecta and its dense circumstellar medium. The initial conditions are constructed based on the shock breakout condition, assuming that the circumstellar medium is dense enough to cause the shock breakout within it. We perform a set of numerical light curve calculations by using a one-dimensional multigroup radiation hydrodynamics code STELLA. We succeeded in reproducing the overall features of the early light curve of SN 2006gy with the circumstellar medium whose mass is about 15 Msun (the average mass-loss rate ~ 0.1 Msun/yr). Thus, the progenitor of SN 2006gy is likely a very massive star. The density profile of the circumstellar medium is not well constrained by the light curve modeling only, but our modeling disfavors the circumstellar medium formed by steady mass loss. The ejecta mass is estimated to be comparable to or less than 15 Msun and the explosion energy is expected to be more than 4e51 erg. No 56Ni is required to explain the early light curve. We find that the multidimensional effect, e.g., the Rayleigh-Taylor instability, which is expected to take place in the cool dense shell between the supernova ejecta and the dense circumstellar medium, is important in understanding supernovae powered by the shock interaction. We also show the evolution of the optical and near-infrared model light curves of high-redshift superluminous supernovae. They can be potentially used to identify SN 2006gy-like superluminous supernovae in the future optical and near-infrared transient surveys.

astro-ph.HE↗

arXiv2012

Can the Growth of Dust Grains in Low-Metallicity Star-Forming Clouds Affect the Formation of Metal-Poor Low-Mass Stars?

The discovery of a low-mass star with such low metallicity as < 4.5x10^{-5} Z_sun reveals the critical role of dust in the formation of extremely metal-poor stars. In this paper we explore the effect of the growth of dust grains through accretion of gaseous refractory elements in very low-metallicity pre-stellar cores on the cloud fragmentation induced by the dust emission cooling. Employing a simple model of grain growth in a gravitationally collapsing gas, we show that Fe and Si grains can grow efficiently at hydrogen densities of ~10^{10}-10^{14} cm^{-3} in the clouds with metal abundances of -5 <~ [Fe, Si/H] <~ -3. The critical metal number abundances, above which the grain growth could induce the fragmentation of the gas clouds, are estimated to be A_{crit} ~ 10^{-9}-10^{-8}, unless the initial grain radius is too large (>~ 1 um) or the sticking probability is too small (<~ 0.01). We find that even if the initial dust-to-gas mass ratio is well below the minimum value required for the dust-induced fragmentation, the grain growth increases the dust mass high enough to cause the gas fragmentation into sub-solar mass clumps. We suggest that as long as the critical metal abundance is satisfied, the grain growth could play an important role in the formation of low-mass stars with metallicity as low as 10^{-5} Z_sun.

astro-ph.SR↗

arXiv2012

The Type IIb Supernova 2011dh from a Supergiant Progenitor

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star ---with R ~200 Rsun---, is needed to reproduce the early light curve of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the SN in deep pre-explosion images is the progenitor star. From the main peak of the bolometric light curve and expansion velocities we constrain the mass of the ejecta to be ~2 Msun, the explosion energy to be E= 6-10 x 10^50 erg, and the 56Ni mass to be approximately 0.06 Msun. The progenitor star was composed of a helium core of 3 to 4 Msun and a thin hydrogen-rich envelope of ~0.1 M_sun with a main sequence mass estimated to be in the range of 12--15 Msun. Our models rule out progenitors with helium-core masses larger than 8 Msun, which correspond to M_ZAMS > 25 Msun. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

astro-ph.HE↗

arXiv2012

Final Fates of Rotating White Dwarfs and Their Companions in the Single Degenerate Model of Type Ia Supernovae

Taking into account the rotation of mass-accreting white dwarfs (WDs) whose masses exceed the Chandrasekhar mass, we extend our new single degenerate model for the progenitors of Type Ia supernovae (SNe Ia), accounting for two types of binary systems, those with a main sequence companion and those with a red-giant (RG) companion. We present a mass distribution of WDs exploding as SNe Ia, where the WD mass ranges from 1.38 to 2.3 Msun. These progenitor models are assigned to various types of SNe Ia. A lower mass range of WDs (1.38 Msun < M_WD <~ 1.5 Msun), which are supported by rigid rotation, correspond to normal SNe Ia. A variety of spin-down time may lead to a variation of brightness. A higher mass range of WDs (M_WD >~ 1.5 Msun), which are supported by differential rotation, correspond to brighter SNe Ia such as SN 1991T. In this case, a variety of the WD mass may lead to a variation of brightness. We also show the evolutionary states of the companion stars at SN Ia explosions and pose constraints on the unseen companions. In the WD+RG systems, in particular, most of the RG companions have evolved to helium/carbon-oxygen WDs in the spin-down phase before the SN Ia explosions. In such a case, we do not expect any prominent signature of the companion immediately before and after the explosion. We also compare our new models with the recent stringent constraints on the unseen progenitors of SNe Ia such as SN 2011fe.

astro-ph.SR↗

arXiv2012

Super-Chandrasekhar-Mass Light Curve Models for the Highly Luminous Type Ia Supernova 2009dc

Several highly luminous Type Ia supernovae (SNe Ia) have been discovered. Their high luminosities are difficult to explain with the thermonuclear explosions of the Chandrasekhar-mass white dwarfs (WDs). In the present study, we estimate the progenitor mass of SN 2009dc, one of the extremely luminous SNe Ia, using the hydrodynamical models as follows. Explosion models of super-Chandrasekhar-mass (super-Ch-mass) WDs are constructed, and multi-color light curves (LCs) are calculated. The comparison between our calculations and the observations of SN 2009dc suggests that the exploding WD has a super-Ch mass of 2.2-2.4 solar masses, producing 1.2-1.4 solar masses of Ni-56, if the extinction by its host galaxy is negligible. If the extinction is significant, the exploding WD is as massive as \sim2.8 solar masses, and \sim1.8 solar masses of Ni-56 is necessary to account for the observations. Whether the host-galaxy extinction is significant or not, the progenitor WD must have a thick carbon-oxygen layer in the outermost zone (20-30% of the WD mass), which explains the observed low expansion velocity of the ejecta and the presence of carbon. Our estimate on the mass of the progenitor WD, especially for the extinction-corrected case, is challenging to the current scenarios of SNe Ia. Implications on the progenitor scenarios are also discussed.

astro-ph.HE↗

arXiv2012

Astrophysical Particle Simulations on Heterogeneous CPU-GPU Systems

A heterogeneous CPU-GPU node is getting popular in HPC clusters. We need to rethink algorithms and optimization techniques for such system depending on the relative performance of CPU vs. GPU. In this paper, we report a performance optimized particle simulation code "OTOO", that is based on the octree method, for heterogenous systems. Main applications of OTOO are astrophysical simulations such as N-body models and the evolution of a violent merger of stars. We propose optimal task split between CPU and GPU where GPU is only used to compute the calculation of the particle force. Also, we describe optimization techniques such as control of the force accuracy, vectorized tree walk, and work partitioning among multiple GPUs. We used OTOO for modeling a merger of two white dwarf stars and found that OTOO is powerful and practical to simulate the fate of the process.

astro-ph.IM↗

arXiv2012

Three-Dimensional Explosion Geometry of Stripped-Envelope Core-Collapse Supernovae. I. Spectropolarimetric Observations

We study the multi-dimensional geometry of supernova (SN) explosions by means of spectropolarimetric observations of stripped-envelope SNe, i.e., SNe without a H-rich layer. We perform spectropolarimetric observations of 2 stripped-envelope SNe, the Type Ib SN 2009jf and the Type Ic SN 2009mi. Both objects show non-zero polarization at the wavelength of the strong lines. They also show a loop in the Stokes Q-U diagram, which indicates a non-axisymmetric, three-dimensional ion distribution in the ejecta. We show that five out of six stripped-envelope SNe which have been observed spectropolarimetrically so far show such a loop. This implies that a three-dimensional geometry is common in stripped-envelope SNe. We find that stronger lines tend to show higher polarization. This effect is not related to the geometry, and must be corrected to compare the polarization of different lines or different objects. Even after the correction, however, there remains a dispersion of polarization degree among different objects. Such a dispersion might be caused by three-dimensional clumpy ion distributions viewed from different directions.

astro-ph.SR↗

arXiv2012

GRB 100418A: a Long GRB without a Bright Supernova in a High-Metallicity Host Galaxy

We present results of a search for a supernova (SN) component associated with GRB 100418A at the redshift of 0.624. The field of GRB 100418A was observed with FOCAS on Subaru 8.2m telescope under a photometric condition (seeing 0.3"-0.4") on 2010 May 14 (UT). The date corresponds to 25.6 days after the burst trigger (15.8 days in the restframe). We did imaging observations in V, Rc, and Ic bands, and two hours of spectrophotometric observations. We got the resolved host galaxy image which elongated 1.6" (= 11 kpc) from north to south. No point source was detected on the host galaxy. The time variation of Rc-band magnitude shows that the afterglow of GRB 100418A has faded to Rc \sim > 24 without SN like rebrightening, when we compare our measurement to the reports in GCN circulars. We could not identify any SN feature such as broad emission-lines or bumps in our spectrum. Assuming the SN is fainter than the 3σ noise spectrum of our observation, we estimate the upper limit on the SN absolute magnitude MIc,obs > -17.2 in observer frame Ic-band. This magnitude is comparable to the faintest type Ic SNe. We also estimate host galaxy properties from the spectrum. The host galaxy of GRB 100418A is relatively massive (log M_{star}/M_{sun} = 9.54) compared to typical long GRB host galaxies, and has 12+log(O/H) = 8.75.

astro-ph.HE↗

arXiv2012

Detectability of High-Redshift Superluminous Supernovae with Upcoming Optical and Near-Infrared Surveys

Observations of high-redshift supernovae (SNe) open a novel opportunity to study the massive star population in the early Universe. We study the detectability of superluminous SNe with upcoming optical and near-infrared (NIR) surveys. Our calculations are based on the cosmic star formation history, the SN occurence rate, the characteristic colour and the light curve of the SNe that are all calibrated by available observations. We show that 15-150 SNe up to z ~ 4 will be discovered by the proposed Subaru/Hyper Suprime-Cam deep survey: 30 deg^2 survey with 24.5 AB mag depth in z-band for 3 months. With its ultra-deep layer (3.5 deg^2 with 25.6 AB mag depth in z-band for 4 months), the highest redshift can be extended to z ~ 5. We further explore the detectability by upcoming NIR survey utilizing future satellites such as Euclid, WFIRST, and WISH. The wide-field NIR surveys are very efficient to detect high-redshift SNe. With a hypothetical deep NIR survey for 100 deg^2 with 26 AB mag depth at 1-4 um, at least ~ 50 SNe will be discovered at z>3 in half a year. The number of the detected SNe can place a strong constraint on the stellar initial mass function or its slope especially at the high-mass end. Superluminous SNe at high redshifts can be distinguished from other types of SNe by the long time-scale of their light curves in the observer's frame, the optical colours redder than other core-collapse SNe and the NIR colours redder than any other types of SNe.

astro-ph.CO↗

arXiv2011

Unburned Material in the Ejecta of Type Ia Supernovae

(Abridged) The presence of unburned material in the ejecta of normal Type Ia supernovae (SNeIa) is investigated using early-time spectroscopy obtained by the CSP. The tell-tale signature of pristine material from a C+O white dwarf progenitor star is the presence of carbon. The most prominent carbon lines in optical spectra of SNeIa are due to C II. We find that at least 30% of the objects in the sample show an absorption at ~6300 AA which is attributed to C II 6580. An association to H_alpha is considered to be unlikely. These findings imply a larger incidence of carbon in SNeIa ejecta than previously noted. We show how observational biases and physical conditions may hide these C II lines, and account for the scarcity of previous carbon detections. This relatively large frequency of carbon detections has crucial implications on our understanding of the explosive process. The observations indicate that carbon is present merely ~1000 km s^-1 above the bulk of Si II. Spectral modeling shows the detections are consistent with a mass of carbon of 10^-3--10^-2 M_sun. This would imply substantial mixing, which may be related to asymmetries of the flame propagation or clumps of unburned material along the line of sight. However, the uniformity of the relation between C II and Si II velocities is not consistent with the latter scenario. The observational properties of SNeIa with and without carbon signatures are compared. A trend toward bluer color and lower luminosity is found for objects with carbon.

astro-ph.CO↗

arXiv2011

A Single Degenerate Progenitor Model for Type Ia Supernovae Highly Exceeding the Chandrasekhar Mass Limit

Recent observations of Type Ia supernovae (SNe Ia) suggest that some of the progenitor white dwarfs (WDs) had masses up to 2.4-2.8 M_sun, highly exceeding the Chandrasekhar mass limit. We present a new single degenerate (SD) model for SN Ia progenitors, in which the WD mass possibly reaches 2.3-2.7 M_sun. Three binary evolution processes are incorporated; optically thick winds from mass-accreting WDs, mass-stripping from the binary companion star by the WD winds, and WDs being supported by differential rotation. The WD mass can increase by accretion up to 2.3 (2.7) M_sun from the initial value of 1.1 (1.2) M_sun, being consistent with high luminosity SNe Ia such as SN 2003fg, SN 2006gz, SN 2007if, and SN 2009dc. There are three characteristic mass ranges of exploding WDs. In an extreme massive case, differentially rotating WDs explode as an SN Ia soon after the WD mass exceeds 2.4 M_sun because of a secular instability at T/|W|\sim 0.14. For a mid mass range of M_WD=1.5-2.4 M_sun, it takes some time (spinning-down time) until carbon is ignited to induce an SN Ia explosion after the WD mass has reached maximum, because it needs a loss or redistribution of angular momentum. For a lower mass case of rigidly rotating WDs, M_WD=1.38-1.5 M_sun, the spinning-down time depends on the timescale of angular momentum loss from the WD. The difference in the spinning-down time may produce the "prompt" and "tardy" components. We also suggest the very bright super-Chandrasekhar mass SNe Ia are born in a low metallicity environment.

astro-ph.SR↗

arXiv2011

On the effects of microphysical grain properties on the yields of carbonaceous dust from type II SNe

We study the role of the unknown microphysical properties of carbonaceous dust particles in determining the amount and size distribution of carbonaceous dust condensed in type II supernova explosions. We parametrize the microphysical properties in terms of the shape factor of the grain and the sticking coefficient of gas-phase carbon atoms onto the grain surfaces. We find that the amount of dust formed is fairly independent of these properties, within the parameter range considered, though limited by the available amount of carbon atoms not locked in CO molecules. However, we find that the condensation times and size distributions of dust grains depend sensitively on the microphysical parameters, with the mass distributions being weighted toward larger effective radii for conditions considering grains with higher sticking coefficients and/or more aspherical shapes. We discuss that this leads to important consequences on the predicted extinction law of SN dust and on the survival rate of the formed grains as they pass through the reverse shock of the SN. We conclude that a more detailed understanding of the dust formation process and of the microphysical properties of each dust species needs to be achieved before robust prediction on the SN dust yields can be performed.

astro-ph.SR↗

arXiv2011

Formation of Dust in the Ejecta of Type Ia Supernovae

We investigate the formation of dust grains in the ejecta of Type Ia supernovae (SNe Ia), adopting the carbon-deflagration W7 model. In the calculations of dust formation, we apply the nucleation and grain growth theory and consider the two cases with and without formation of CO and SiO molecules. The results of the calculations show that for the sticking probability of alpha_j=1, C, silicate, Si, and FeS grains can condense at early times of ~100--300 days after the explosion, whereas Fe and SiC grains cannot form substantially. Due to the low gas density in SNe Ia with no H-envelope, the average radii of the newly formed grains are generally below 0.01 micron, being much smaller than those in Type II-P SNe. This supports our previous conclusion that the radius of dust formed in the ejecta is smaller in SNe with less massive envelopes. The total dust mass ranges from 3x10^{-4} M_sun to 0.2 M_sun for alpha_j=0.1--1, depending on whether or not CO and SiO molecules are formed. We also estimate the optical depths and thermal emission by the newly formed dust and compare to the relevant observations of SNe Ia. We find that the formation of C grains in SNe Ia is suppressed to be consistent with the observational constraints. This implies that energetic photons and electrons heavily depress the formation efficiency of C grains or that the outermost C-O layer of SNe Ia is almost fully burned. Finally, we perform the calculations of dust destruction in the SN remnants and find that dust grains formed in the ejecta of SNe Ia are almost completely destroyed in the shocked gas before being injected into the interstellar medium. This indicates that SNe Ia are unlikely to be the major sources of interstellar dust.

astro-ph.SR↗

arXiv2011

The Role of Dust in the Early Universe I : Protogalaxy Evolution

We develop one-zone galaxy formation models in the early Universe, taking into account dust formation and evolution by supernova (SN) explosions. Especially we focus on the time evolution of dust size distribution, because ${\rm H}_{2}$ formation on the dust surface plays a critical role in the star formation process in the early Universe. In the model we assume that star formation rate (SFR) is proportional to the total amount of ${\rm H}_{2}$. We consistently treat (i) the formation and size evolution of dust, (ii) the chemical reaction networks including ${\rm H}_{2}$ formation both on the surface of dust and in gas phase, and (iii) the SFR in the model. First, we find that, because of dust destruction due to both reverse and forward shocks driven by SNe, H$_{2}$ formation is more suppressed than that without dust destruction. At the galaxy age of $sim0.8 {\rm Gyr}$, for galaxy models with virial mass $M_{\rm vir}=10^{9} M_{\odot}$ and formation redshift $z_{\rm vir}=10$, the molecular fraction is 2.5 orders of magnitude less in the model with dust destruction by both shocks than that in the model without dust destruction. Second, we show that the H$_{2}$ formation rate strongly depends on the ISM density around SN progenitors. The SFR in higher ISM density is lower, since dust destruction by reverse shocks is more effective in higher ISM density. We conclude that not only the amount but also the size distribution of dust being related with the star formation activity strongly affects the evolution of galaxies in the early Universe.

astro-ph.GA↗

arXiv2010

Production of the p-Process Nuclei in the Carbon-Deflagration Model for Type Ia Supernovae

We calculate nucleosynthesis of proton-rich isotopes in the carbon-deflagration model for Type Ia supernovae (SNe Ia). The seed abundances are obtained by calculating the s-process nucleosynthesis that is expected to occur in the repeating helium shell flashes on the carbon-oxygen (CO) white dwarf (WD) during mass accretion from a binary companion. When the deflagration wave passes through the outer layer of the CO WD, p-nuclei are produced by photodisintegration reactions on s-nuclei in a region with the peak temperature ranging from 1.9 to 3.6 x10^9 K. We confirm the sensitivity of the p-process on the initial distribution of s-nuclei. We show that the initial C/O ratio in the WD does not much affect the yield of p-nuclei. On the other hand, the abundance of 22Ne left after the s-processing has a large influence on the p-process via 22Ne(alpha,n) reaction. 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 more than in SNe II although they are underproduced with respect to the yield levels of 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.

astro-ph.SR↗

arXiv2010

Supersoft X-ray Phase of Single Degenerate Type Ia Supernova Progenitors in Early Type Galaxies

In the single degenerate (SD) scenario for Type Ia supernova (SN Ia) progenitors, an accreting white dwarf (WD) is expected to undergo a supersoft X-ray source (SSS) phase. Recently, Gilfanov & Bogdan (2010, hereafter GB10) claimed that observed X-ray fluxes of early type galaxies would be too low to be consistent with the prediction of the SD scenario based on rather simple assumptions. We present realistic evolutionary models of SD systems and calculate durations of SSS phases. In most cases, accreting WDs spend a large fraction of time in the optically thick wind phase and the recurrent nova phase rather than the SSS phase. Thus the SSS phase lasts only for a few hundred thousand years. This is by a factor of ~10 shorter than those adopted by GB10 where the SN~Ia progenitor WD was assumed to spend most of its life as a SSS. The theoretical X-ray luminosity of the SSS has a large uncertainty because of the uncertain atmospheric model of mass-accreting WDs and absorption of soft X-rays by the companion star's cool wind material. We thus adopt an average of the observed fluxes of existing symbiotic SSSs, i.e., ~0.4 x 10^{36} erg s^{-1} for 0.3--0.7 keV. Using these SSS duration and soft X-ray luminosity, we show that the observed X-ray flux obtained by GB10 is rather consistent with our estimated flux in early type galaxies based on the SD scenario. This is a strong support for the SD scenario as a main-contributor of SNe Ia in early type galaxies.

astro-ph.HE↗