投稿者: YamashitaKazuyoshi

Effects of internal heating sources on hydrogen-rich supernova light curves

Speaker: Tatsuya Matsumoto

Abstract:

Core-collapse supernovae (SNe) are caused by the death of massive stars, and their light curves provide a lot of information about the stellar evolution and physical processes of explosions. In particular, the light curves of hydrogen-rich SNe have a characteristic slowly-evolving phase, so-called the plateau phase, whose luminosity and duration are related to the SN parameters such as ejecta mass and energy. Recent observations revealed that some H-rich SNe exhibit evidence for a sustained energy source powering their light curves, resulting in a brighter and/or longer-lasting plateau phase.

We present a semi-analytic light curve model that accounts for the effects of an arbitrary internal heating source such as 56Ni/Co decay, a central engine (millisecond magnetar or accreting compact object), and shock interaction with a dense circumstellar disk.

While a sustained internal power source can boost the plateau luminosity commensurate with the magnitude of the power, the duration of the recombination plateau can typically be increased by at most a factor ∼2−3 compared to the zero-heating case. For a given ejecta mass and initial kinetic energy, the longest plateau duration is achieved for a constant heating rate at the highest magnitude that does not appreciably accelerate the ejecta. This finding has implications for the minimum ejecta mass required to explain particularly long-lasting supernovae, and for confidently identifying rare explosions of the most-massive hydrogen-rich (e.g. population III) stars.

Subaru/IRD high-resolution spectroscopy of a T-type brown dwarf and investigation of its atmospheric properties with high-resolution spectrum model ExoJAX

Speaker: Yui Kawashima

Abstract:

While brown dwarf atmospheres share composition and temperature with those of extrasolar gas giant planets, in general, brown dwarfs are observable with a higher signal-to-noise ratio when compared to exoplanets. Thus, the observation of brown dwarf atmospheres helps us establish our understanding of various processes in the atmospheres of such temperature and composition, including chemistry, thermal structure, dynamics, and cloud formation. Also, their high-resolution spectra serve as excellent templates for the observational validation of the molecular line lists at such high temperatures. The accuracy of molecular line lists holds the key to detecting chemical species in exoplanet atmospheres, which are often observed with a lower signal-to-noise ratio.

Recently, we observed the high-resolution spectrum of a T6.5-type brown dwarf Gl 229B with the InfraRed Doppler (IRD) spectrograph mounted on the Subaru Telescope. We have constrained its atmospheric properties, such as the molecular abundances and thermal structure, using an inverse-problem approach with our high-resolution spectrum model ExoJAX (Kawahara, Kawashima et al. 2022). We have also investigated the possibility of inferring the object mass using the embedded information on collision-induced absorption uniquely accessible by high-resolution spectroscopy. Furthermore, we have revealed that in some wavelength regions, specific molecular line lists do not match the observed absorption features.

Origin of high-ionization lines found in extremely metal poor galaxies.

Speaker: Shun Hatano

Abstract:

The extreme metal poor galaxies (EMPG) exhibit intense high-ionization emission lines, such as He II4686, unexplained by stellar synthesis models. Umeda et al. (2022) employed CLOUDY and MCMC to reproduce the observed spectrum, revealing an unidentified non-thermal radiation source. In this study, we introduce [Ne V]3426 emission (97.1 eV) and estimate spectral indices and luminosities for EMPGs in the 54.4-97.1 eV range. Confirming that non-thermal radiation dominates the 54.4-97.1 eV range for all the galaxies with [Ne V]3426 detections, we discuss the origin of the non-thermal radiation.

Synthesis of Sc, Ti, and V in core-collapse supernovae

Speaker: Ryota Hatami

Abstract:

A supernova explosion is an explosive phenomenon that occurs at the end of the life of a massive star. However, the explosion mechanism has not yet been clarified. As a clue to investigate the explosion mechanism, we focused on nucleosynthesis. Metal-poor stars reflect the result of explosive nucleosynthesis in supernova explosions of first stars, and reproducing the chemical abundances of metal-poor stars is one of the important issues in the nucleosynthetic calculation. Recently correlations among Sc, Ti, and V are observationally identified. Nevertheless, the abundances of Sc, Ti, and V in metal-poor stars have not been reproduced by nucleosynthesis calculations based on the results of hydrodynamical simulation. This is because one of the possible causes is that the explosion mechanism is not yet understood. Then, we attempted to constrain the explosion mechanism by (1) performing nucleosynthesis calculations with setting temperature, density, neutrino flux, etc. as parameters to find physical conditions which reproduce the observed chemical composition of metal-poor stars, and (2) examining the feasibility of these conditions by comparing them with 2D explosion simulations. In this talk, the progress of (1) and (2) will be discussed.

Estimating the characteristics of ejecta from magma ocean for water production on the protoplanet

Speaker: Akifumi Matsumura

Abstract:

How water is delivered to rocky planets during the planet-forming stage is a major issue in planetary science. While many previous studies considered water delivery by icy planetesimals, we consider water production by chemical interaction between the primordial atmosphere and the surface of the magma ocean of a rocky planet growing through planetesimal accretion. Previous studies based on this idea assumed that iron oxides in the magma ocean and atmospheric hydrogen are always in constant contact, which must be examined; namely, we need to consider properly how to bring the magma into contact with the atmosphere. In this study, we focus on the reaction between the atmospheric gas and the materials ejected from the magma ocean when planetesimals collide with the magma ocean surface during the growth phase of a planet. I am currently studying the scatter of magma upon the impact of planetesimals on the planet’s surface and its influence on the atmospheric composition. In this talk, I will describe our progress in the research to date and future research plans.

Carbon Isotope Fractionation of Complex Organic Molecules in Star-Forming Cores

Speaker: Ryota Ichimura

Abstract:

Recent high-resolution and sensitivity ALMA observations have unveiled the carbon isotope ratios (12C/13C) of Complex Organic Molecules (COMs) in a low-mass protostellar source. To understand the 12C/13C ratios of COMs, we investigated the carbon isotopic fractionation of COMs from prestellar cores to protostellar cores with a gas-grain chemical network model. We confirmed that in the prestellar phase, the 12C/13C ratios of small molecules are bimodal: CO and species formed from CO (e.g.,CH3OH) are slightly enriched in 13C compared to the local ISM (by ∼ 10 %), while those from C and C+ are depleted in 13C owing to isotope exchange reactions. COMs are formed from the simple species on grain surface, and thus basically inherit the bimodality of 12C/13C. In the protostellar phase, COMs are formed on the grain surface and in the hot gas (> 100 K) and have different 12C/13C from those in the prestellar phase. We additionally incorporate reactions between gaseous atomic C and H2O ice or CO ice on the grain surface to form H2CO ice or C2O ice suggested by recent laboratory studies. The direct C-atom addition reactions open pathways to form 13C-enriched COMs from atomic C and CO ice. We find that these direct C-atom addition reactions mitigate isotope fractionation, and the model with the direct C-atom addition reactions better reproduces the observations than our base model. Our calculations also show that cosmic-ray ionization rates affect the 12C/13C ratios of COMs.

Progenitors of ultra-long gamma-ray bursts: an ultra-long and ultra-slow developing story

Speaker: Bruce Gendre

Abstract:

Gamma-ray bursts are fantastic explosions seen at cosmological distances, and one of the most extreme high energy events of the Universe. Because of their distance, understanding the phenomenon at play is challenging. In this seminar, I will review the GRB phenomenon, what we already know about the progenitor of those events, focusing on the most unknown kind of event, the ultra-long ones, and how we use the current technology for improving our knowledge.

Ultraviolet Spectroscopy and Imaging in Solar System Science and Beyond

Speaker: Go Murakami

Abstract:

Ultraviolet spectroscopy technique is one of the most powerful tools for solar-terrestrial plasma physics, planetary science, and astronomy. For example, JAXA’s UV space telescope Hisaki performed long-term and continuous monitoring of Io plasma torus and revealed dynamic relations between Io’s volcanic activity and Jupiter’s magnetosphere. We also developed a UV spectrograph for planetary exploration probes such as BepiColombo, ESA-JAXA joint Mercury exploration mission. Now we are studying a concept and preliminary design of future UV spectroscopy mission LAPYUTA. Here I present overviews of our past UV observation heritages such as Kaguya, BepiColombo, and Hisaki, brief instrumentations, current developments, and future plans.

Chaotic Diffusion: Importance, approaches and consequences

Speaker: GUIMARÃES Gabriel

Abstract:

Regular motion in the dynamical systems might now be regarded as the odd phenomena instead of chaotic ones. That is because chaotic motion seems to take place more widely and commonly than periodic ones, and in Celestial Mechanics it could be no different.
Still, it is not uncommon to characterise orbits of asteroids and comets that are clearly stable as chaotic ones and vice versa. That is because of Chaotic Diffusion, which is responsible to drive dynamical systems from a regular state to a chaotic one.
Nonetheless, the onset of chaos — as well as the effective “chaoticity” of an orbit — might not be immediate nor evident, pronouncing themselves in distinct timescales, sometimes larger than the system’s own lifetime.
Such cases, those of “stable” or “weak” chaos, chaotic diffusion is thought to play a significant role in shaping and sculpting our Solar system and other extrasolar counterparts orbital architecture.
In this presentation, I will explain a bit about chaos, contextualize it within the realms of celestial mechanics and planet formation, present tools for quantification of chaotic diffusion and how to use them to estimate instability times that are comparable to observed/simulated ones without the need to intensive and extensively making use of computational resources nor sophisticated mathematical models.

The First Spatially-resolved Detection of 13CN in a Protoplanetary Disk and Evidence for Complex Carbon Isotope Fractionation

Speaker: Tomohiro Yoshida

Abstract:

Recent measurements of carbon isotope ratios in both protoplanetary disks and exoplanet atmospheres have suggested a possible transfer of significant carbon isotope fractionation from disks to planets. For a clearer understanding of the isotopic link between disks and planets, it is important to measure the carbon isotope ratios in various species. In this talk, we present a detection of the 13CN N = 2−1 hyperfine lines in the TW Hya disk with the Atacama Large Millimeter/submillimeter Array. This is the first spatially-resolved detection of 13CN in disks, which enables us to measure the spatially resolved 12CN/13CN ratio for the first time. We conducted non-local thermal equilibrium modeling of the 13CN lines in conjunction with previously observed 12CN lines to derive the kinetic temperature, H2 volume density, and column densities of 12CN and 13CN. The H2 volume density is found to range between (4 − 10) × 10^7 cm−3, suggesting that CN molecules mainly reside in the disk atmosphere. The 12CN/13CN ratio is measured to be ~70 at 30 < r < 80 au from the central star, which is similar to the 12C/13C ratio in the interstellar medium. However, this value differs from the previously reported values found for other carbon-bearing molecules (CO and HCN) in the TW Hya disk. This could be self-consistently explained by different emission layer heights for different molecules combined with preferential sequestration of 12C into the solid phase towards the disk midplane. This study reveals the complexity of the carbon isotope fractionation operating in disks.