Title & Abstract

Speaker:
Yasuda
Title:
Cosmic-ray acceleration on superbubble
Abstract:
It has been thought that Galactic cosmic-rays (GCRs) are produced at SNR shock through diffusive shock acceleration (DSA). From recent observational studies of young SNRs (e.g. MAGIC col.+2017), This becomes suspicious in terms of maximum accelerated energy, spectral index and so on. We therefore focus on the superbubble (SB), which is the big bubble structure (~100 pc) formed by many stellar winds and supernova shocks. In the SBs, The metal-rich environment is realized because of multiple supernova ejecta. However, It is not investigated that how the SBs can contribute the GCR flux, so we simulate the CR acceleration on SB with our developing code, CR-Hydro code. I will talk about the introduction of GCRs and problems of those, and my progress.

Speaker:
Kobashi
Title:
Towards a unified model of non-thermal radiations from young to middle-aged SNRs with CR-hydro code
Abstract:
Gamma ray spectra of different Supernova remnants (SNRs) show different shapes, and it seems depending on the ages of SNRs. To reproduce this trend, we are developing a numerical model that can reproduce the evolution of SNRs over all ages. Yasuda & Lee 2019 enabled us to calculate gamma ray spectra from SNRs from initial condition to Sedov phase (~5,000 yr) by coupling Diffusive Shock Acceleration (DSA) mechanism at shocks of SNRs and gamma ray radiation including pi0 decay and Inverse Compton scattering. However, the effects which dominate at lower temperature (~10^6 K) were not taken into account, such as heat conduction and radiative cooling. These effects may occur at gas just behind shocks of SNRs at Radiative phase (>~10,000 yr) because of decreasing of electron temperature due to adiabatic cooling. Now by adding these effects to CR-Hydro code developed in Yasuda & Lee 2019, we calculated up to Radiative phase. I will talk about my progress and future work.

Speaker:
Yamada
Title:
Revealing Torus Structure in Ultra/luminous Infrared Galaxies with Mid-infrared and Hard X-ray Observations
Abstract:
(1) We propose new diagnostics that utilize the [O IV] 25.89 um and nuclear 12 um luminosity ratio (which are radiated from the narrow line region and the torus, respectively), for identifying whether an AGN is deeply “buried” in their surrounding material. Applying the criteria for 23 local ultra\luminous infrared galaxies (U/LIRGs), we find that the fraction of “buried” AGNs increases with merging stage (Yamada+19). (2) Next, we examine the torus properties of 2 non-merging and 10 merging U/LIRGs with the hard X-ray (>10 keV) data, which is not affected by the star forming activities and reflects the emission from the AGN. By using the XCLUMPY model (Tanimoto+19), we analyze the broadband X-ray spectra with NuSTAR, XMM-Newton, Chandra, and Suzaku, and estimate the covering factors and Eddington ratios. The results indicate that AGN tori in non-merging LIRGs are not deeply buried, which may be explainable by the radiation pressure of the AGN outflow (e.g., Ricci et al. 2017, Nature). On the other hand, the comparison with the local Swift/BAT AGNs suggests that the AGNs in merging U/LIRGs have the large covering factors, and particularly the late-stage mergers have buried AGNs even with the high Eddington ratios.

Speaker:
Kimura
Title:
Thermal-viscous instability in tilted accretion disks: a possible application to IW And-type dwarf novae
Abstract:
IW And-type dwarf novae are characterized by repetitive light variations of the intermediate-brightness state with oscillations, which is terminated by brightening. Following the recent observations suggesting that some IW And stars seem to have tilted disks, we have investigated how the thermal-viscous instability works in tilted accretion disks in dwarf novae and whether it could reproduce the essential features of the light curves in IW And stars. By adopting various simplifying assumptions for tilted disks, we have performed time-dependent one-dimensional numerical simulations of a viscous disk by taking into account various mass supply patterns to the disk; that is, the gas stream from the secondary star flows not only to the outer edge of the disk but also to the inner portions of the disk. We find that the inner disk almost always stays in the hot state while the outer disk repeats outbursts. This phenomenon reproduces alternating mid-brightness interval sometimes with dips and brightening, which are quite reminiscent of the most characteristic observational light variations of IW And stars.

Speaker:
Robert
Title:
Behaviour of the post in-spiral common envelope ejecta: dynamics, thermodynamics and dust formation
Abstract:
We ran an hydrodynamics simulation of the common envelope interaction with the SPH code PHANTOM for a 0.88 Msun primary stars and a 0.88 Msun companion. The system has been evolved way past the end of the dynamic in-spiral phase to analyse the asymptotic behaviour of the unbound, expanding layers of the envelope. We find that, given enough time, the dynamics and thermodynamics of the gas can be approximated by a homologous expanding model. Additionally, by applying a dust formation model to our ejecta, we determine that at the densities and temperatures achieved during the expansion dust grains can form very efficiently. By coupling our results with those of stellar population synthesis codes, we estimate that the dust formed during common envelope events might be an important component of the ISM dust.

Speaker:
Hayakawa
Title:
X-ray emissions from a black hole forming supernova
Abstract:
To confirm the fate of stellar mass black holes (BHs) forming, we examine the X-ray emissions from a BH forming supernova (SN) with/without drastic explosion. By performing one-dimensional radiation hydro dynamics and estimating X-ray emissions by multiplying transparency in the ejecta and the central emitting spectra, we found the characteristic X-ray emissions from the accretion disk with optical counterpart. In this talk, we introduce our results and possibilities of detecting these events.

Speaker:
Ouchi
Title:
The effect of envelope stripping on the pulsational mass loss of a red supergiant
Abstract:
It is well known that the red supergiants are unstable to the radial pulsation. It has been proposed that the amplitude of such an pulsation can be quite large, which may lead to the "superwind", like AGB stars. Such a mass loss from the red supergiant, in turn, shapes the circumstellar environment around the progenitor of supernova, and affects its light curve and spectra. In spite of their importance, the quantitive estimation of the mass loss caused by the radial pulsation has been lacking, mainly due to its numerical difficulties. We have conducted the hydrodynamic simulation of the radial pulsation beyond the mass loss using the MESA code and estimated the ejected mass. Also, we have investigated how the different envelope stripping affects the mass loss. We have found that the mass loss becomes significant for the partially stripped stars. We also discuss the results in relation to the pre-supernova mass loss.

Speaker:
Taguchi
Title:
Radiative transfer calculation for classical novae
Abstract:
Classical novae are famous for many spectrum lines with P Cygni profiles and are regarded as well-studied phenomena. However, a recent spectroscopic observation reveals that in super-early stage there are no P Cygni profile but simply emission lines during brightening. In order to understand mechanism which cause the difference in spectrum lines between P Cygni profiles and emission lines, we execute a Non-LTE radiative transfer with wind in the spherical geometry by CMFGEN code (Hiller and Miller 1998, ApJ, 496, 407). This time, I talk the following four: 1. Introduction of classical novae, 2. details of radiative transfer equation, 3. calculated line fluxes and line profiles/shifts, and 4. "line-forming region" in Sobolev approximation.

Speaker:
Sasaki
Title:
Impact of Stellar Superflares on Planetary Habitability
Abstract:
High-energy radiation caused by exoplanetary space weather events from planet-hosting stars can play a crucial role in conditions promoting or destroying habitability in addition to the conventional factors. Recently we presented the first quantitative impact evaluation system of stellar flares on the habitability factors with an emphasis on the impact of stellar proton events. We derive the maximum flare energy from stellar star spot sizes and examine the impacts of flare-associated ionizing radiation on CO2, H2, and N2+ O2-rich atmospheres of a number of well-characterized terrestrial type exoplanets. Our simulations based on the Particle and Heavy Ion Transport code System suggest that the estimated ground-level dose for each planet in the case of terrestrial-level atmospheric pressure for each exoplanet does not exceed the critical dose for complex life to persist. However, large fluxes of coronal X-ray and ultraviolet radiation from active stars induce high atmospheric escape rates from close-in exoplanets, suggesting that the atmospheric depth can be substantially smaller than that on Earth. In a scenario with the atmospheric thickness of one-tenth of Earth's, the radiation dose from close-in planets reaches near fatal levels with annual frequency of flare occurrence from their host stars.

Speaker:
Ishizawa
Title:
Evolution of a vapor disk generated by a giant impact into proto-Uranus
Abstract:
A giant impact, which is a energetic collision between protoplanets at the stage of the planetary formation, could be both the origins of Uranus’s large axial tilt( ~ 98 degrees) and the regular satellites orbiting on the equatorial plane of Uranus. Ida et al. (submitted) modeled the impact-generated disk of a mixture of water vapor and H/He gas and showed that the Uranian satellite formation is regulated by the significant evolution of the disk until the disk cools down enough for ice condensation. We are ready to perform 1D simulation to investigate the evolution of the gas disk and the mass-orbit distribution of re-condensed ices/silicates. We would like to talk about it in this talk.

Speaker:
Yamanaka
Title:
Satellite formation around super-Jovian planets
Abstract:
Among known extrasolar planets, the number of known habitable planets is only 46 (ExoKyoto, Kopparapu+ 2013). Being a habitable world requires the body to be in the habitable zone, and be a terrestrial body. If an extrasolar satellites (exomoon), orbiting a gas giant at stellar habitable zone is large enough to have a substantial atmosphere, it could be habitable. Since satellite is heated by illumination and tide from the host planet in addition to stellar illumination, it is possible for an exomoon to be habitable even beyond stellar habitable zone. Using a common mass scaling law of gas giant planets (Canup & Ward 2006), it has been suggested that super-Jovian planets can have such massive satellites. But the formation of massive satellites around super-Jovian planets has not been examined precisely and the application of the mass scaling law remains questionable. I will talk about the introduction of habitability of exomoons and problems of their formation theory.

Speaker:
Sumida
Title:
Formation of the dwarf planet Haumea’s ring
Abstract:
A ring around the dwarf planet Haumea is located near the 3:1 resonance between the orbital motion of ring particles and the spin of Haumea (Ortiz et al. 2017). Based on the theory that the Haumea's two satellites were formed because of a rotational fission of Haumea (Ortiz et al. 2012), We have examined the formation process of the ring. First, we calculated the gravity field of Haumea, which has a triaxial ellipsoidal shape, and estimated the stable orbit region by using N-body simulations with the time-dependent gravity field. We found the unstable region locates just inside the 3:1 resonant orbit. Then, we calculated both analytically and numerically the Roche limit around a triaxial ellipsoidal body. Our results explain the present position of the ring.

Speaker:
Takeo
Title:
Super-Eddington accretion to black holes in the early Universe: effects of mechanical feedback
Abstract:
We investigate the properties of accretion flows exposed to both mechanical and radiative feedback from the central black hole (BH) with a mass of M_BH = 10Msun in a gas cloud with a density of n_infty in order to derive the necessary conditions for rapid accretion in the early Universe. Previous studies on rapid accretion have assumed that the gas accretion is regulated only by the radiative feedback such as photoionization heating and radiation pressure. However, the mechanical feedback from the central region also has the potential to control the BH accretion rates because outflows inject the positive momentum into the surrounding medium and shut off the gas infalling motion. In this study, we perform two-dimensional radiation hydrodynamical simulations with primordial chemical reaction networks considering the effects of both bipolar outflows and isotropic radiative feedback. We find that the flow structure consists of two distinct parts; (i) the bipolar outflowing region which is shock heated up to ~ 10^{6-7}K and (ii) the equatorial inflowing region where the ionized gas is mildly heated to ~ 10^5K due to the photoionization heating. We also find that the conditions for super-Eddington accretion are alleviated owing to outflows, compared to the cases without mechanical feedback. This is because (1) the solid angle covered by the equatorial inflowing region becomes smaller due to outflows around the polar axis, and (2) the BH accretion rate is reduced by the outflow-mass-loss. Because of above two effects, the radiative feedback becomes too weak to suppress the super-Eddington accretion. We also show that the super-Eddington accretion tends to be easier for larger outflow-opening-angle. Furthermore, we derive the critical outflow-velocity and mass-loss-rate below which the outflow effects are negligible.

Speaker:
Nacho
Title:
Large range SMBH simulation under super-Eddington inflow
Abstract:
This project intends to connect the galactic scale cosmological simulations with the high resolution black hole (BH) accretion simulations. And thus create a comprehensive tool to study realistic inflow and structure formation of super massive black holes (SMBH). With this we aim to reveal the origin of the super-Eddington accretion flow in a hands-free approach. For that we created a new simulation strategy to circumvent the hardware's limitations.

Speaker:
Tsuneto
Title:
Polarization imaging of M87 jets by general relativistic radiative transfer calculation based on GRMHD simulations
Abstract:
With polarimetry by the event horizon telescope (EHT) kept in mind, we perform general relativistic (GR) radiative transfer calculations of polarized light based on the GR magnetohydrodynamic (MHD) simulation data of accretion flow and outflow in M87, to obtain their linear and circular polarization images in the BH horizon-scale. We found that the linear polarization components originating from the jet base and inner accretion flow should experience Faraday rotation and depolarization when passing through magnetized plasmas around the BH, thus sensitively depending on the BH spin. Through the comparison with total intensity image at 1.3mm by the EHT and the polarization degree and the rotation measure (RM) measured at 1.3mm with the Submillimeter Array, the model with the spin parameter of a=0.9MBH (with MBH being the BH mass) is favored over other models with a = 0.5 MBH or 0.99 MBH, though we need further systematic studies for confirmation. We also find in low-temperature models clear ring-like image in the circular polarization map, which arises because of Faraday conversion of the linearly polarized synchrotron emission and is thus indicative of magnetic field direction. This occurs only when the emission region is threaded with well-ordered magnetic fields and hence no clear images are expected in high-temperature disk models, in which disk emission is appreciable. We will be able to elucidate the field configuration through the comparison between the simulated polarization images and future polarimetry with EHT and other VLBI observations.

Speaker:
Huruno
Title:
Fractal dimension analysis of outflow from super-Eddington accretion disk around a black holes
Abstract:
Super-Eddington accretion is one of the most important phenomena which is considered to relate with the formation of Super Massive Black Holes(SMBH) and Ultra Luminous X-ray sources(ULXs). Recently, three dimensional RHD simulatione revealed that there is outflow emerged from the accretion disk and the gas forms sheet-like structure. In our study, we analyzed the outflow gas structure by an approach referred to as "fractal dimension analysis". This anaysis showed that the dimension of outflow varies from 3 at near the center of BH to 1 at outer region, and we discussed these results.

Speaker:
Kawanaka
Title:
How to detect Galactic Black Holes
Abstract:
According to the inferred star formation rate and initial mass function, more than 10^8 black holes are supposed to reside in our Galaxy. However, only several dozens of black holes have been confirmed so far, and all of them are X-ray binaries (i.e. close binaries with stars). In this talk, I will discuss how to detect Galactic black holes regardless whether they are in binaries or not as many as possible.

Speaker:
Hosokawa
Title:
直接数値シミュレーションによる大質量初代星の連星形成
Abstract:
最近の重力波観測によって、数十太陽質量同士のブラックホール近接連星が宇宙にはたくさんあることが分かってきた。あり得る起源の一として、星風が効きづらい低金属環境下での大質量同士の近接連星が議論されている。我々は金属量ゼロの、いわゆる初代星形成の場合で、数十太陽質量同士の連星形成の様子をAMR法を用いた3D輻射流体計算で初めて追跡した。この成果を中心に最近の同分野の動向を紹介する。

Speaker:
Hori
Title:
Recent Development in Planet Formation Theory and Exoplanet Observations
Abstract:
Our understanding of exoplanets from Earth-sized planets to super-Earths, specifically their population and atmospheric compositions, are making rapid progress in the last 10 years. On top of that, toward exoplanet characterization and the search for biosignatures of life, space missions such as CHEOPS, followed by ARIEL and PLATO, are scheduled to be launched in the 2020s. In this talk, I would like to review recent development in planet formation theory and exoplanet observations, including studies in which I was involved, and discuss unresolved issues on exoplanet sciences.

Speaker:
Kawaguchi
Title:
Slowing Down of Cosmic Growth of Supermassive Black Holes
Abstract:
Although central supermassive black holes (SMBHs) are commonly found in massive galaxies even in the early Universe at z > 7, their origins (their seeds and the formation mechanisms) are still unclear. A direct solution for this issue is an observational measurement for the distribution of the Eddington ratio (in proportion to the luminosity over the SMBH mass of active galactic nuclei), which unfortunately turns out tohave large uncertainties, especially at high redshifts. The Soltan's argument also results in little constraints on ~< 10^8 Msun SMBHs, since the argument is based on the integration of the luminosity functions and the mass functions of SMBHs. We present our recent works on the growth history of SMBHs in the framework of a semi-analytical model for galaxy and black hole evolution (Shirakata et al. 2019a,b). We found that the growth rate of SMBHs at higher redshift more easily exceeds the Eddington limit and that a more rapid growth happens at higher redshift, because the typical gas fraction of the host galaxies is higher at higher redshift. These results indicate the "slowing down" of cosmic growth of SMBHs.

Speaker:
Suzuki
Title:
Radiation hydrodynamic simulations of supernova ejecta interacting with circum-stellar disks
Abstract:
Circum-stellar media (CSM) are believed to play important roles in various types of supernova (SN) explosions. The collision between the SN ejecta and the CSM sometimes gives rise to very bright thermal emission, which serves as the major power source for specific types of SNe. Type IIn SNe are among the most important class of such interacting SNe. In the extreme case of super-luminous type IIn SNe, CSMs as much as ~10 solar masses are around the progenitor star. The biggest question related to interacting SNe is when and how such massive CSM are produced. In addition, some type IIn SNe are known to exhibit unusual polarization and spectroscopic signatures indicating aspherical CSMs. Such aspherical geometry of CSMs may be a key to understanding the mechanism that massive stars shed their envelopes prior to the core-collapse explosion. Recently, I carried out some 2D radiation-hydrodynamic simulations of SN ejecta interacting with spherical and disk-like CSMs. In this presentation, I report some results of our simulations and discuss observational signatures of SNe interacting with aspherical CSMs.