投稿者: Yuko Matsushita

Observational signatures and physical effects of cosmic rays in and around galaxies

speaker: Ellis Owen

Abstract:

Cosmic rays go hand-in-hand with violent and energetic astrophysical conditions, and can produce observable signatures across the electromagnetic spectrum. They also play a role as an active agent in shaping the evolution of their local environment, and their effects in modifying astrophysical processes over a broad range of length-scales can be substantial. In this talk, I will present an overview of some of my recent work on modeling the effects and signatures of cosmic rays in different environments – from star-forming cores in our cosmic backyard, to circum-galactic structures and populations in the furthest reaches of the observable Universe. I will outline the impacts that cosmic rays can have on the evolution and dynamics their host system, how their astrophysical effects can manifest themselves on sub-galactic, galactic, and super-galactic scales, and how the microphysics of cosmic ray feedback may operate within interstellar and circum-galactic settings. 

The possibility to find a clue of nucleosynthesis in super-massive stars’ explosion

speaker: Yuta Yamazaki

Abstract:

The origin of the heavy elements in the universe is not completely clear. Elements heavier than iron are mainly produced by neutron capture processes, among which neutron-rich stable nuclei are produced by the rapid neutron capture processes (r-process). In particular, neutron-rich stable nuclei are produced by the r-process. The r-process occurs in physical environments with extremely high neutron density, however the specific astrophysical site are still not fully understood. Some stable nuclei cannot be theoretically produced by the neutron capture processes, although they exist in small amounts. These neutron-deficient nuclei (p-nuclei) are thought to be produced in proton-rich environments. The explosion of a supermassive star is thought to be the site of the r-process, as well as the site where p-nuclei are produced in the vp-process, a nucleosynthetic process induced by neutrinos. In this talk, I will discuss the possibility to find a clue of nucleosynthesis in supermassive stars by applying the latest nucleosynthesis calculation results to galactic chemical evolution.

Dust N-body simulations and their implications to formation of small Solar System bodies

speaker: Misako Tatsuuma

Abstract:

Small bodies in the Solar System, such as comets and asteroids, are thought to be leftover planetesimals or rubble piles, which are accumulations of collisional debris of planetesimals. However, the formation process of these small bodies is not fully understood. To constrain it by using the bulk densities of observed small bodies in the Solar System, we measured compressive strength of dust aggregates by using dust adhesion N-body simulation, calculated their diameters and bulk densities, which are determined by balancing the compressive strength with the self-gravity, and compared them with observation results of small bodies. We found that comets can be explained by direct coagulation in terms of internal density, but it requires fragile material. On the other hand, we found that asteroids are too dense to be explained by direct coagulation. To explain the bulk densities of asteroids, we need compression in large parent bodies, which implies that asteroids are rubble piles.

Seven eyes on the sky: the eROSITA X-ray telescope onboard the Spektr-RG observatory

speaker: Manami Sasaki

Abstract:

Two years ago, the new eROSITA X-ray telescope, which was developed by a German consortium, was launched successfully onboard the Russian Spektr-RG observatory. eROSITA is carrying out the first all-sky survey in the X-rays up to 10 keV with a much better resolution and higher sensitivity than what was available before in the soft X-ray band. It will thus provide us with a new map of the hot, energetic universe with more than one million extragalactic and Galactic objects. I will talk about the telescope and its mission and present the first results which we have obtained so far.

Simulating dust monomer collisions: The JKR theory revisited

speaker: Yuki Yoshida

Abstract:

Planet formation proceeds in protoplanetary disks, which are composed of dust and gas. Dust is the material of planetary bodies, and it is considered that the minimum building block of the dust is dust monomers whose size is sub-micrometer. Dust monomers grow by collisional sticking and form dust aggregates. The JKR theory is widely adopted in the numerical simulation of collisions of dust monomers/aggregates. The JKR theory describes the interaction of two spherical bodies of elastic solids. The properties of dust aggregates are important in determining the distribution of the dust and its growth rate, which are related to the planetesimal formation. Laboratory experiments and numerical simulation have been carried out to reveal the growth of dust monomers and aggregates. However, the results of the experiments and the simulations based on the JKR theory are still inconsistent. For example, the threshold velocity for sticking in the experiment is larger than that with the JKR theory (e.g., Poppe et al. 2020; Gundlach and Blum 2015). Krijt et al. (2013) considered that the energy dissipation due to the viscoelasticity is important, which is not included in the JKR theory. Tanaka et al. (2015) performed the molecular dynamics (MD) simulation of the monomer collisions, and found energy dissipation during monomer collisions, which is not included in the JKR theory. However, Tanaka et al. (2015) considered only the perfect lattice model, and didn’t systematically investigate the monomer collision.
We are preparing a systematic survey of monomer collisions by MD simulations to understand the more realistic monomer interactions. In this talk, we introduce our purpose of this study, and show the results of test simulations following Tanaka et al. (2015).

Stellar mass dependence of the habitable zone planetary systems formed by giant impacts

speaker: Haruka Hoshino

Abstract:

Recent exoplanet surveys revealed that for solar-type stars close-in super-Earths are ubiquitous and many of them are in multi-planet systems. These systems are more compact than the solar system’s terrestrial planets. Ongoing and future exoplanet observations will find more planets around low-mass stars. However, there are not many theoretical studies on the formation of such planets around low-mass stars. Now is the time to clarify the dependence of the stellar mass on planet formation. 
We investigate the effect of the stellar mass on the architecture of planetary systems. We perform N-body simulations of the giant impact stage around different stellar masses. Using the minimum-mass extrasolar nebula model, we set the isolation mass of protoplanets and distribute them around habitable zone. We follow the evolution for 200 million orbital periods of the habitable zone inner edge. We find that the eccentricity and inclination of orbits and the orbital separation of adjacent planets increase with the stellar mass. The results can be used to predict the number of planets in the habitable zone from the orbital separation.

The most extreme climates in the Universe

speaker: David Ehrenreich

Abstract:

Planets around other stars ―exoplanets― showcase an amazing diversity. This diversity offers many opportunities to study phenomena that do not occur on our Solar System planets, but which may have occured in the past, or could occur in the future. Ultrahot gas giants offer such an opportunity: these are exoplanets so close to their hot stars that they receive thousands of time the insolation of Earth. As such, they are extreme laboratories to study atmospheric physics, chemistry, and climates. They are also well amenable to remote sensing by space-borne and ground-based observations. Trying to learn more about the most extreme climates in the Universe, we could measure stellar dayside temperatures, metallic rains on the nightsides, and atmospheric escape so strong that it may sculpt the whole population of close-in planets. We have also been using these outstanding exoplanets as trojan horses to benchmark characterization techniques that could eventually be applied to smaller, milder planets. I will discuss some of the recent results my group has obtained exploiting data from a range of space-borne and ground-based instruments.

Depolarization effects of the magnetic fields in a spiral galaxy obtained from 3D MHD simulation

speaker: Yuta Tashima

Abstract:

I would like to talk about an observational visualization of a spiral galaxy based on MHD simulation. Radio observations have shown that the average magnetic field strength of spiral galaxies is about a few micro G, but the structure of the global field is still unknown. Since observables are integral values on the line of sight, it is not possible to directly obtain a three-dimensional structure. So it is necessary to compare observables with simulated observables using numerical MHD simulations. We focus on the Faraday rotation and depolarization effects in the meter wavelength. Since the Faraday rotation amount is very large in meter wave length observation, the depolarization effect is very important. I will report the effect of depolarization on radio observations.

Due to the COVID-19 situation, the colloquium is running online for this semester.

Date	Speaker	Title	Time and direction
2021-04-07	All internal members	Self-introduction PDF	15:30- zoom DTA#1
2021-04-14	Kotomi Taniguchi(NAOJ)	Chemistry in High-Mass Star-Forming Regions Abstract	15:30- zoom DTA#1
2021-04-21	Takayuki Ohgami (NAOJ)	ElectroMagnetic follow-up observation for gravitational wave event with Subaru/HSC Abstract	15:30- zoom DTA#1
2021-04-28	Taichi Uyama (NAOJ)	High-contrast imaging observations of planet-formation laboratories Abstract	15:30- zoom DTA#1
2021-05-12	Salvatore Capozziello (University of Naples)	Cosmography as a tool to discriminate among cosmological models Abstract	15:30- zoom DTA#1
2021-05-19	Student talks Yuta Tashima (new member, D1) Rikuto Omae (new member, D1)	Depolarization effects of the magnetic fields in a spiral galaxy obtained from 3D MHD simulation (Tashima-san) Abstract Effects of Depolarizing Intervening Galaxies on Background Radio Emission (Omae-san) Abstract	15:30- zoom DTA#1
2021-05-26	Yosuke Mizuno (Shanghai Jiao Tong University)	The Shadow of the Supermassive Black Hole in M87: EHT observations and theoretical modeling Abstract	15:30- zoom DTA#1
2021-06-02	Haruka Sakemi (NAOJ)	Cosmic-ray Particle Acceleration by Galactic Microquasar Jets Abstract	15:30- zoom DTA#1
2021-06-09	Sebastian Marino (Jesus College Cambridge)	Studying ExoKuiper belts through ALMA observations Abstract	15:30- zoom DTA#1
2021-06-16	Student talks Huang Shuo (D1) Yudong Luo (D3)	Dust-to-stellar mass ratio in 162 dusty star-forming galaxies (Huang-san) Abstract Funny story about the big-bang nucleosynthesis constraints on the primordial black holes (Yudong-san) Abstract	15:30- zoom DTA#1
2021-06-23	David Ehrenreich (Université de Genève)	The most extreme climates in the Universe Abstract	15:30- zoom DTA#1
2021-06-30	Yuichi Ito (new member PD)	Mineral Atmosphere of Hot Rocky Exoplanet Abstract	15:30- zoom DTA#1
2021-07-07	Student talks Haruka Hoshino (D2) Yuki Yoshida (D1)	Stellar mass dependence of the habitable zone planetary systems formed by giant impacts (Hoshino-san) Abstract Simulating dust monomer collisions: The JKR theory revisited (Yoshida-san) Abstract	15:30- zoom DTA#1
2021-07-14	Student talks Xingqun Yao (D1) Kangrou Guo (D2)	Supernova Nucleosynthesis: Radioactive Nuclear Reactions and Neutrino-Mass Hierarchy (Yao-san) Abstract Planetesimal dynamics in the presence of a giant planet (Guo-san) Abstract	15:30- zoom DTA#1
2021-07-21	Michiko Fujii (The University of Tokyo)	Dynamical structures of the Milky-Way disk Abstract	15:30- zoom DTA#1
2021-07-28	Manami Sasaki (Friedrich-Alexander-University Erlangen-Nürnberg)	Seven eyes on the sky: the eROSITA X-ray telescope onboard the Spektr-RG observatory Abstract	15:30- zoom DTA#1
2021-08-04	Professor Malgorzata Bogdan	Statistical methods for the analysis of large dimensional data Abstract	15:30- zoom DTA#1
2021-08-11	(break?)	TBD	15:30- zoom DTA#1

Title: Chemistry in High-Mass Star-Forming Regions

speaker: Kotomi Taniguchi

Abstract:

The chemical composition is a useful diagnostic tool to investigate the physical conditions and the star formation processes.In this talk, I will talk about our recent studies about the chemical diversity around massive young stellar objects (MYSOs) and about the NGC 2264 cluster.Carbon-chain species, which were considered to be deficient around MYSOs, can be abundant around some MYSOs, using single-dish radio telescopes.I will show our latest ALMA data toward the NGC2264-D cluster-forming clump in Cycle 7.In addition, I will briefly mention my future research plan.