Title & Abstract

Speaker: Tatsuya Matsumoto

Title:  Random Thoughts about Delayed Radio Flares in Tidal Disruption Events

Abstract: Recent radio observation revealed that about 50% of optical tidal disruption flares are accompanied by radio flare ~1000 days after the optical detection. I will briefly review the observation again (I did in my previous lunch seminar) and talk about a simple model to explain some of these delayed radio flares.

Speaker: Kenta Taguchi

Title: 1-zone Approximation onto Spectra of the Classical Nova V1405 Cassiopeiae at the very Beginning

Abstract: TBD (I am thinking of briefly reviewing what I talked about in the Kayo seminar in July in the first ~ 10 minutes and showing some details on my formulating the emission line luminosity from the nova in the second).

Speaker: Shogo Yoshioka

Title: Jet and Wind Structure of Super-Eddington Flow around Super-Massive Black Holes

Abstract: Narrow Line Seyfert Galaxy (NLS1) is rapidly growing and has jets and strong disk winds, making it astronomically important for various aspects of black hole evolution and feedback. In some of the NLS1 jets, the collimation profile is found to be similar to that of jets in low-luminosity active galactic nuclei (LLAGN), with a parabolic shape. Why is the jet shape similar despite the significantly different mass accretion rates? To answer these fundamental questions, we performed general relativistic radiation magneto-hydrodynamic simulations under the large simulation box. As a result, it was found that the shape of the jet depends on the structure of the surrounding wind. In this talk we also discuss the dependence on the spin parameter of the jet shape as well as the acceleration mechanism.

Speaker: Yusuke Inoue

Title: Self-similar solutions for the SN-CSM interaction

Abstract: The interaction of a uniformly expanding gas with a stationary ambient medium is studied in the case where the expanding matter has a power-law density profile (ρ∝ r^-n), as well as the ambient medium (ρ∝r^-s). Self-similar solutions for the structure of the interaction region can be found provided that s<3 and n>5. Models for Type I Supernovae indicate that a p∝r^-n profile may occur in the outer part of the expanding star. The n = 7, s = 0 solution is applied to the remnant of Tycho’s supernova, and it is found to reproduce the basic dynamical and morphological properties of the remnant. The model may also explain the lack of strong Fe line emission in the X-ray spectrum. The solutions with s = 2 are applicable to Type II supernovae because the expanding supernova envelopes probably interact with regions of presupernova mass loss. The properties of the interaction region are important for the X-ray emission from Type II supernovae. (from Chevalier. 1982)

Speaker: Eleni Koutsiona

Title: Near and mid-infrared line emission analysis of starburst galaxy NGC7469

Abstract: Using James Webb Space Telescope observations obtained with integral field instruments to study the emission of hydrogen recombination lines and obtain spatially resolved maps of the dust attenuation towards star-forming regions in nearby luminous infrared galaxies.

Speaker: Takanori Sasaki

Title: With moons, or without moons, that is the question.

Abstract: Earth's Moon plays an important role in stabilizing axial tilt variations and promoting tidal pool formations—key factors in sustaining life. This study expands upon this concept to exoplanets. Despite numerous exoplanet discoveries, the existence of exomoons remains unconfirmed. First, I calculate habitable zones for exoplanets and analyze satellite orbital evolution. Then I explore constraints on moon presence around planets, focusing on Hill radii and Roche limit considerations, and apply these to known exoplanetary systems. The results suggest that a notable portion of these planets may not host moons. This insight not only contributes to our understanding of celestial bodies' capacity to support life but also poses significant implications for the search for habitable worlds beyond our solar system.

Speaker: Ryo Ikeda

Title: Formation of terrestrial planets in the solar system by ring-gap protoplanetary disk

Abstract:  By high-resolution ALMA observations, it is shown that the ubiquitous structures of protoplanetary disks are rings and gaps. These features suggest that in the existence of pressure bumps, pebbles have been trapped at specific locations and led to planetesimal formation. Pressure bumps are formed near the silicate sublimation line,  water and CO snow lines and gradually migrate inward over time. In our research, we conducted several N-body simulations, tracing the diffusion of rocky planetesimals associated with the movement of the silicate sublimation line. This process led to runaway and oligarchic growth, eventually culminating in the formation of terrestrial planets in the Solar System. The results of simulations are almost consistent with the current mass-orbital distribution of the inner planets.

Speaker: Haruya Maeda

Title: Planet formation and its atmosphere

Abstract: The origin of water, which brought the oceans to the Earth, is one of the most important topics in planetary science. In general, rocky planets experience protoplanets with hydrogen-rich primordial atmosphere derived from disk gases and magma ocean during their growth stage. The chemical exchange of materials between the atmosphere and the magma ocean on the surface of the planet is considered to have determined the present chemical composition of the planet. 

In this presentation, I will first introduce Young et al. (2023), which solved the chemical equilibria of protoplanets and suggested the process of determining the chemical composition of the Earth. As an extension of the paper, I will discuss my idea of applying the chemical equilibrium model to the growth process from protoplanets to planets. In particular, I will discuss in detail how the chemical composition of a planet is determined(At the presentation first, I will give a quick digest of former Tuesday seminar I presented before , and then give a new talk).

Speaker: Shin Mineshige

Title: Warm corona model for AGN soft excess 

Abstract: The soft (X-ray) excess in the spectra of active galactic nuclei is characterized by electron temperatures of 0.1 – 0.3 keV. It remains a puzzle why both values are not sensitive to the black hole mass nor accretion rate. Supposing that the scattering dominated surface layer of an accretion disk can act as a warm corona, we construct a vertically one-zone model to understand what determines its temperature. By solving the equations of

(1) the condition for the effective optical depth,

(2) the energy balance, and

(3) the dominance of the Compton cooling over the bound-free cooling,

we could reproduce the basic observational features of the soft excess, provided that anomalous heating dissipation) takes place in the warm corona.

Speaker: Kazuya Iwata

Title: Link between terrestrial and astrophysical detonation physics associated with the explosion mechanism of Type Ia supernovae

Abstract: Detonation wave, which is known to trigger Type Ia supernovae (SNe Ia), was originally discovered in the terrestrial combustion systems, associated with coal-mine explosive accidents. They have a close analogy such as their supersonic propagation speed, 3D bifurcated shock structure so-called 'cell', and many others of the burning physics. Terrestrial detonation has been extensively studied through experimental/numerical methodologies, for which fundamental understanding has already reached a mature level. However, efforts of collaboration or interdisciplinary research have been still limited, and the understanding of astrophysical detonation relies on roughly resolved numerical studies neglecting cellular dynamics, which is the most important to interpret terrestrial detonation. In the present talk, I am going to provide some interesting results on terrestrial/astrophysical detonations, which could be beneficial for understanding both phenomena and implications of the possibilities of the explosion mechanism of SNe Ia, which is still yet to be uncovered so far,  through the cellular dynamics and the theories/empirical rules for terrestrial detonation.

Speaker: Ryota Shimada

Title: Connection between Large and Small-Scale Dynamo in Solar Convection Zone

Abstract:  Dynamo as a magnetic field amplification mechanism by plasma flow is proposed by Larmor (1919). Most astrophysical objects possess magnetic fields, and the solar magnetic field is one of the most observationally constrained examples. To understand the mechanism to produce the solar periodic magnetic field(Large-Scale Dynamo), several global MHD simulations on the solar convection zone (CZ) are performed. However, the gap between the convective flow between observations and simulations was found by Hanasoge+ (2012), and this suggests that our understanding of CZ needs to be corrected. Recent high-resolution simulations(Hotta+2016, Hotta+2021) elucidate the possibility that efficient dynamo at small-scale (Small-Scale Dynamo: SSD) can fill the gap between them. In this talk, we are going to demonstrate how SSD affects large-scale structures(e.g. stratification) and how to model this effect. We further report our early results obtained by 3D simulation with this model.