投稿者: Yuko Matsushita

Planetesimal dynamics in the presence of a giant planet II – the dependence of outer planetesimal orbits on planet mass and eccentricity

speaker: Kangrou Guo

Abstract:

The presence of an existing planet embedded in the protoplanetary disk has mixed influence on the growth of other planetary embryos. Gravitational perturbation from the planet can increase the relative velocities of planetesimals at the mean motion resonances to very high values and impede accretion at those locations. However, it can also align the orbital pericenters of planetesimals in certain regions of the disk and thus make them dynamically quiet and “accretion-friendly” locations for planetary growth. Following the previous paper, where we investigated the effect of a Jupiter-like planet on an external planetesimal disk, we generalize our findings to extrasolar planetary systems by varying the planet parameters. In particular, we focus on the dependence of the planetesimal relative velocities on the mass and eccentricity of the existing planet. We found that the velocity dispersion of identical-mass particles increases monotonically with increasing planet mass. Meanwhile, the dependence of the relative velocity between different-mass planetesimals on their mass ratio becomes weaker as the planet mass increases. While the relative velocity generally increases with increasing planet eccentricity, the velocity dispersion of smaller-mass particles ($m \lesssim 10^{18}~\rm{g}$) is almost independent of planet eccentricity owing to their strong coupling to the nebula gas. The results suggest that in a protoplanetary disk with a massive planet ($\gtrsim M_{\rm{Jup}}$) in presence, subsequent planet formation can be challenging. Our results could provide some clues for the formation of Saturn’s core and the orbital features of extrasolar cold giant planets.

Modeling of accretion disks originating from disrupted planetary bodies around white dwarfs

speaker: Ayaka Okuya

Abstract:

From a quarter to a half of WDs have rock-forming elements in their atmospheres, and some of them show infrared excess from their circumstellar dusty disks. These are thought to be originated from the tidally disrupted minor planets. Therefore, the metals in the WD atmospheres would enable us to directly measure the elemental composition of exoplanetary bodies with unprecedented precision. Moreover, the dynamical arguments based on the delivery rate of minor planets to the Roche limit could provide unique insights into the planetary system architecture orbiting around WDs. 
In this study, as a first step to establishing the framework that can derive such information from observations, we develop the first accretion disk model that solves the coupled evolution of multiple materials. We find that the disks produced by the disrupted rocky bodies cannot reproduce the observed high accretion rate due to the rapid re-condensation of diffused-out vapor just outside the silicate sublimation line. In the case of icy body accretion, the volatile vapor can enhance the silicate accretion rate through gas drag to successfully achieve the observed high accretion rate. We find that, however, a high silicate accretion rate is always accompanied by a comparably high volatile accretion rate, resulting in the volatile-rich photospheric composition. This is inconsistent with the observed photospheric composition. No solution that reproduces observations implies that the existing disk models miss some physical processes and/or that the current data interpretation method might have some problems. I will finally discuss the future direction of this study.

Evolution and Activities of the Galactic Nucleus Sgr A*

speaker: Yuhei Iwata

Abstract:

The nucleus of our Galaxy, Sgr A, is one of the most convincing candidates for a supermassive black hole (SMBH). It shows short timescale variations of a few tens of minutes, which are suggested to be related to orbital motions in the vicinity of the SMBH. However, the truth and cause of these variations have remained controversial. Also, as for the formation process of SMBHs, a merger scenario between intermediate-mass black holes (IMBHs) has been proposed, but there are very few promising candidates for IMBHs, and it is insufficient to support this scenario. I have been researching time variations of Sgr A in the mm/sub-mm band and peculiar molecular clouds in the Galactic center having broad velocity widths to which IMBHs may be associated. I will introduce the short-timescale variability of Sgr A* obtained with ALMA and the latest observational results of the high-velocity compact clouds.

Seeding the second stars: enrichment from the first stars, dust evolution and cloud collapse

speaker: Gen Chiaki

Abstract:

I have investigated the process of chemical enrichment and evolution of stellar mass in the first billion years after the Big Bang. The first-generation of stars (Pop III stars) are born in chemically pristine, metal-free gas clouds. For the lack of cooling efficiency, the clouds collapse stably against fragmentation. Then, Pop III stars are believed to be massive (~100 Msun). After Pop III stars die with supernova (SN) explosions, metals and grains are dispersed to the interstellar medium. In clouds enriched with metals, the second-generation, metal-poor stars (Pop II stars) form. Due to additional cooling efficiency mainly from grains, the enriched clouds become unstable to fragment. Then, the first low-mass stars (~1 Msun) can form as metal-poor stars. The process of metal enrichment from Pop III stars is poorly known, because the distribution of ejecta is highly complex. Also, we do not have sufficient knowledge of the condition for cloud fragmentation. In this study, we carry out cosmological three-dimensional simulations from Pop III star to Pop II star formation, following the metal enrichment process. We find that Pop III SNe enrich the halos that host the Pop III stars. This indicates that the self-enrichment of the host halos is the main channel of metal enrichment from Pop III SNe. We also find that several enriched clouds fragment into low-mass clumps due to dust cooling. Since low-mass stars can survive for the Hubble time, the simulated low-mass Pop II stars can be observed in the present day as metal-poor stars in our vicinity.

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

Date	Speaker	Title	Time and direction
2022-4-6	All internal members	Self-introduction PDF	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Maria Dainotti)
2022-4-13	Gen Chiaki (NAOJ)	Seeding the second stars: enrichment from the first stars, dust evolution and cloud collapse Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Kenji Furuya)
2022-4-20	Yuhei Iwata (NAOJ)	Evolution and Activities of the Galactic Nucleus Sgr A* Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Moka Nishigaki)
2022-4-27	Ayaka Okuya (NAOJ)	Modeling of accretion disks originating from disrupted planetary bodies around white dwarfs Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Yuka Fujii)
2022-5-11	Student talks Fei Wang (D3), Kangrou Guo (D3)	Unveiling non-gray surface of cloudy exoplanets: the influence of wavelength-dependent surface albedo and cloud scattering properties on retrieval solutions (Fei-san) Abstract Planetesimal dynamics in the presence of a giant planet II – the dependence of outer planetesimal orbits on planet mass and eccentricity (Guo-san) Abstract	15:30- zoom DTA#1
2022-5-18	Jian Jiang (NAOJ)	Fast Transient Studies with Deep/High-cadence Time-domain Surveys Abstract	15:30- zoom DTA#1 (moderator: Yamazaki-san)
2022-5-25	Student talks Takemura Hideaki (D3)	Construction of dense core mass function with 3D MHD simulation data (Takemura-san) Abstract	15:30- zoom DTA#1 (moderator: Mizutani-san)
2022-6-1	Student talks Hoshino Haruka (D3)	Comparison of N-body simulations of Earth-like planets with observations (Hoshino-san) Abstract	15:30- zoom DTA#1 (moderator: Yuka Fujii)
2022-6-8	Di Li (NAOC)	From Arecibo to CRAFTS: Bridging the Centuries Abstract	15:30- zoom DTA#1 (moderator: Masato KOBAYASHI)
2022-6-15	Yuhiko Aoyama (Tsinghua University)	Hydrogen line emission from accreting gas-giant planets Abstract	15:30- zoom DTA#1 (moderator: Akimasa Kataoka)
2022-6-22	Chris Irwin (RESCEU)	Aspherical Shock Breakout Abstract	15:30- zoom DTA#1 /Rinko room (hybrid /moderator: Hiroki Nagakura)
2022-6-29	Student talks Ohmae Rikuto (D2), Yamazaki Yuta (D3)	Observability of magnetic field in lensing galaxies using broadband radio polarization data (Ohmae-san) Abstract The origin of the proton-rich and neutron-rich isotopes (Yamazaki-san) Abstract	15:30- zoom DTA#1 (moderator: Yuka Fujii)
2022-7-6	Student talks Kashiwagi Raiga (D2) Tashima Yuta (D2)	Numerical study on star formation process induced by collisions between filamentary molecular clouds (Kashiwagi-san) Abstract Pseudo-observation of spiral galaxies focusing on depolarization based on MHD simulation (Tashima-san) Abstract	15:30- zoom DTA#1 (moderator: Akimasa Kataoka)
2022-7-13	Student talks Seo Chanoul (D2) Kinoshita Shinichi (D2)	Atmospheres of sub-Neptune-sized exoplanets in contact with magma ocean (Seo-san) Abstract MHD simulation of cluster formation in clumps (Kinoshita-san) Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Gen Chiaki)
2022-7-20	Takanori Kodama (University of Tokyo)	Climates of terrestrial exoplanets with 3D GCM Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Yuka Fujii)
2022-7-27	Student talks Yoshida Yuki (D2) Huang Shuo (D2)	Molecular Dynamics Simulations Explore Dust Monomer Interactions: An Extension of the JKR Adhesion Model (Yoshida-san) Abstract Characterizing three serendipitously detected CO emitters (Huang-san) Abstract	15:30- zoom DTA#1 (moderator: Hiroki Nagakura)
2022-8-3	Ken Osato (Kyoto University)	Applications of Hydrodynamical Simulations for Clustering of Emission Line Galaxies Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Gen Chiaki)
2022-8-10	Tsutomu Takeuchi (Nagoya University)	High Dimensional Statistical Analysis of ALMA Map of NGC 253 Abstract	15:30- zoom DTA#1 /Instrument Development Bldg. 3 (hybrid /moderator: Ross Burns)

Planet growth from planetesimal rings

speaker: Mizutani Yohsuke

Abstract:

Ring like structures have been observed in protoplanetary disks in recent years. Such structures may cause the local formation of planetesimals and thus affect the growth of planets. I introduce the recent studies about this topic (Ueda et al. 2021, Cai et al. 2021) and then report my progress.

Time variation in mas accretion rate on protostars due to merging molecular cloud cores

speaker: Yano Yuta

Abstract:

According to the standard theory of star formation, a star forms from a molecular cloud core. It has also been assumed that the physical state of the core determines the evolution and formation of protostars that occur inside the core once it is formed. However, recent observational and theoretical studies suggest that the physical state of the core may be strongly affected  by surrounding influences such as accretion and merging/collisions(e.g., Shimajiri et al. 2019; Takemura et al. 2021). For example, hub filament structures may affect the core as global structures of the molecular clouds. If the accretion rate changes as external gas accretes to the hub’s core, it would also affect protostellar outflow. Thus, toward a full understanding of how stars form under realistic conditions, it is important to understand the effects of the core external environments. In this study, we investigate how the mass accretion rate to a central protostar changes when the stable core merges into the core with a protostar formed in the center from the outside. And we use 3D numerical simulations. The results show that core merging increases the mass accretion rate.

Evolution of galaxies in the large scale structure

Speaker: Agnieszka Pollo

Abstract:

Galaxies are objects known to evolve with time. This evolution depends on their environments, and even broader – on their position in the large-scale cosmic web. However, the old question – “nature or nurture” – i.e. to what extent this difference in evolutionary paths is driven by original properties of a galaxy and its host halo, and to what extent by interactions with the environment – remains open until this very day. In my talk, I plan to present a selection of results of our team aimed at solving this riddle, based on data from z~0.1 (like the GAMA survey), through z~1 (the VIPERS survey) up to z~3 (the VUDS survey). I will also discuss some prospects for the future.

Physical origin of extremely metal poor galaxies through statistical analysis

Speaker: Nishigaki Moka

Abstract:

Even in metal-emriched nearby universe, there exist extremely metal poor galaxies (EMPGs; Z < 0.1 Zsun). The physical origin of these galaxies is not yet known, so we conduct several statistical analyses to get closer to their physical origin. First, since EMPGs are faint and poorly observed, we have developed a new searching method using machine learning to enlarge the sample size enough for statistical analysis. We have so far succeeded in adding one additional EMPG. Then by using ~100 EMPGs identified in previous studies, we investigate the positions of these galaxies in the large-scale structure in relation to the sources that trigger star formation. Next, we calculate the cross-correlation functions to further quantify the clustering of EMPGs. Furthermore, by drawing the mass-metallicity relation and fundamental metallicity relation of EMPGs, we discuss whether they are close to equilibrium between inflows and outflows, comparing them with a simple chemical evolution model. Our analyses suggests that EMPGs are just beginning to experience metal enrichment by a burst of star formation.

Atmospheres of sub-Neptune-sized exoplanets in contact with magma ocean

speaker: Chanoul Seo

Abstract:

Previous observational studies revealed the bimodal distribution of the radius for the planets with R<4R_⊕. The larger size group, sub-Neptune, is likely to have a substantial atmosphere under which the rocky interior may be molten (i.e., “magma”) depending on the temperature. As the rocky core still dominates the mass, direct contact between the magma and the atmosphere implies that magma affects the atmospheric composition significantly. Intending to understand the relation between the final atmospheric composition and the origin of volatile, we study the effect of magma on the volatile distribution in the sub-Neptune-sized planets. Our model is based on the model of a former study, but we introduce a more realistic behavior of the fluids, new solubility laws, and carbon-bearing species simultaneously. Our calculation shows a much more reduced atmosphere than the former study with the same amount of accreted H2 at higher pressure (>2GPa), mainly due to the newly introduced pressure dependence of H2 solubility. The C-bearing species are mainly present as methane in the atmosphere because the role of the magma on the distribution of C-bearing species is limited. We show how H2O and CH4 mixing ratios in the atmospheric composition as well as mass and radius can help us constrain the atmospheric origin and the initial magma composition. Within the current framework, the small H2O/H2 ratio (<1) and carbon depleted atmosphere cannot be attained simultaneously, implying that the sub-Neptunes like K2-18b which show small water fractions require a carbon-enriched atmosphere or additional carbon-erasing mechanism.