談話会 | 2026年度
定例の場合
・金曜日午後4時～5時（毎週行なうわけではありません）
・理学研究科4号館 5階 504号室（宇宙物理学教室講義室）
という時刻・場所で行なっています。 談話会でのトークを考えていらっしゃる方は、どの教室スタッフにでも良いので、コンタクトをお願いします。
世話人 Host: Herman Lee (email: herman_at_kusastro.kyoto-u.ac.jp)
第673回
Speaker: Giulia Cinquegrana (Swinburne University of Technology)
Date: 9/24 Thursday
Time: 10:00 – 11:30
Place: Room 504 seminar room, building 4
Language: English
Title: Tracing the Chemical Fingerprint of AGB Mass Transfer in 300S Using Stellar Siblings
Abstract: Low-mass thermally pulsing asymptotic giant branch (TP-AGB) stars are the dominant site of slow neutron-capture (s-process) nucleosynthesis, producing most of the heavy elements along the s-process path beyond the first peak (Ba, La, Nd, Pb). Directly probing this phase is challenging: it is short-lived in comparison to the total stellar lifetime, AGB stars are difficult to observe, and surface abundance changes obscure their initial composition. Chemically peculiar stars (Ba, CH, and CEMP-s stars) provide indirect constraints on TP-AGB nucleosynthesis, as their anomalous carbon and s-process enhancements are attributed to mass transfer from a former, more massive AGB companion. However, field systems provide limited constraints on AGB nucleosynthesis models. The observed abundance pattern reflects impacts of progenitor mass, metallicity, neutron-source strength, and internal mixing, ultimately compounded by the accretor’s usually unknown pre-enrichment composition.
Disrupted stellar streams offer a way around this degeneracy: their chemically homogeneous populations allow a polluted star’s pre-enrichment abundance pattern to be reconstructed empirically. Using a recently discovered CH star in the 300S stream, we isolate its TP-AGB mass-transfer signature through a differential abundance analysis relative to five chemically normal stellar siblings sharing its birth composition. We constructed a tailored grid of TP-AGB stellar evolution and nucleosynthesis models matched to the 300S metallicity. By comparing predicted and observed neutron-capture patterns across the first and second s-process peaks, we identify a 2.6Msun donor with a lifetime of ~418 Myr as the best-fitting progenitor. We will discuss the implications for the formation and dynamical history of 300S, extend our predictions to heavier, as-yet-unobserved elements out to Pb, and highlight disrupted stellar streams as well-suited laboratories for testing AGB nucleosynthesis more broadly.
第672回
Speaker: Adam Burgasser (UC San Diego), Genevive Bjorn (Higher Learning Lab)
Date: 9/17 Thursday
Time: 16:00 – 17:30
Place: Room 504 seminar room, building 4
Language: English
Title: Improve your Scientific Research Literacy with the CERIC Method
Abstract: Critical reading of the scientific literature is an essential skill for all researchers, yet is rarely taught as an evidence-based practice. The CERIC Method is a research-validated approach to reading scientific articles through five key elements: Claim, Evidence, Reasoning, Implications, and Context. CERIC gives readers an efficient and systematic framework for understanding and evaluating the core arguments of a scientific research article. Join authors Dr. Genevive Bjorn (Director, Higher Learning Lab) and Dr. Adam Burgasser (Professor, UC San Diego Astronomy & Astrophysics) in a 90-minute workshop on how to use the CERIC Method for literature reviews, journal discussions, and peer review.
第671回
Speaker: Shuji Matsuura (Kansei Gakuin Univ.)
Date: 8/4 Tuesday
Time: 15:30 – 17:00
Place: Room 504 seminar room, building 4
Language: Japanese
Title: 光赤外域の宇宙背景放射の観測計画を展望する
Abstract: 私たちは、観測ロケットやスペース望遠鏡を用いて近赤外域における宇宙背景放射を観測することで、個別の銀河観測では検出できない未知の低輝度天体や拡散放射が存在することを明らかにした。
その正体を明らかにするためには、赤外観測の高感度化だけでなく、可視光への観測波長の拡大や、惑星間空間へ望遠鏡を投入することが必要であると考えている。宇宙背景放射観測のこれまでとこれからを、将来計画を紹介しつつ展望する。
第670回
Speaker: Maria Camisassa (Polytechnic University of Catalonia Barcelonatech)
Date: 6/24 Wednesday
Time: 10:30 – 12:00
Place: Room 504 seminar room, building 4
Language: English
Title: White Dwarfs in the Big Data Era
Abstract: White dwarf stars are the most common endpoint of stellar evolution. Therefore, these numerous, old and compact objects provide valuable information on the late stages of stellar evolution, the physics of dense plasma and the structure and evolution of our Galaxy. The ESA Gaia space mission has revolutionized this research field, providing parallaxes and multi-band photometry for nearly 360.000 white dwarfs. Furthermore, this data, combined with spectroscopical and spectropolarimetric observations, have provided new information on their chemical abundances and magnetic fields. This large data set has raised new questions on the nature of white dwarfs, demanding a thorough understanding of the physics that governs their evolution and a proper statistical analysis of their collective properties. In this talk, I will summarize these questions and I will describe possible explanations for them, on the basis of detailed theoretical models and population synthesis studies.
第669回
Speaker: Jonay I. Gonzalez Hernandez (Instituto de Astrofísica de Canarias)
Date: 6/9 Tuesday
Time: 13:30 – 15:00
Place: Room 504 seminar room, building 4
Language: English
Title: The Spanish contribution to ANDES for the ELT
Abstract: ANDES (ArmazoNes high Dispersion Echelle Spectrograph) is a high-resolution ultra-stable spectrograph that will be installed at 39m-ELT located at Cerro Armazones (ESO, Chile). ANDES will join the effort of about 35 institutions of 13 countries. ANDES consists of three (four) fibre-fed UBV, RIZ, YJH (K) spectrographs providing a wavelength coverage of 0.4–1.8 microns (goal 0.35–2.4 microns) at a spectral resolution of ~100,000. ANDES will operate in both seeing- and diffraction-limited modes. The ANDES Project is currently finalizing the preliminary design phase.
ANDES will address a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. The top science cases are detecting biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, testing the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration.
During the last decades, the Instituto de Astrofísica de Canarias (IAC) has significantly contributed to the development of high-resolution ultra-stable spectrographs, such as ESPRESSO at 8.2m-VLT, considered a precursor to the ANDES spectrograph. ESPRESSO, with a radial velocity precision of 10 cm/s, is already exploring new frontiers in science such as the search for rocky planets and the variation of fundamental constants, thus encouraging new studies with future facilities such as ANDES@ELT.
In this talk I will describe the main characteristics and the expected scientific achievements of ANDES.
第668回
Speaker: Erik Petigura (UCLA)
Date: 5/22 Friday
Time: 16:00 – 17:00
Place: Room 504 seminar room, building 4
Language: English
Title: Emerging boundaries in the planet formation process
Abstract: The eight planets in the solar system fall neatly into three main categories: rocky terrestrials, hydrogen-dominated Jovians, and ice giants. These planet classes reflect different formation environments, processes, and timescales. Extrasolar planets, in contrast, span a continuum of sizes, masses, and orbit. They demand a richer taxonomy. Recently, large studies of the orbital eccentricities of transiting exoplanets have revealed new dividing lines in the planet formation process. Close-in planets larger than Neptune form according to very different pathways compared to their smaller counterparts. At the same time, new synergies involving RVs, direct imaging, and astrometry are beginning to illuminate the boundaries between the most massive planets (formed by core accretion) and the least massive brown dwarfs (formed by direct collapse). Surprisingly, this empirical boundary occurs well below the deuterium burning limit. Studies like this offer a preview of the types of insights we can look forward to with the upcoming release of Gaia DR4 in December of this year, which will dramatically expand our census of giant planets and brown dwarfs.
第667回
Speaker: Raphael Hirschi (Keele University)
Date: 4/13 Monday
Time: 9:30 – 10:30
Place: Science Seminar house
Language: English
Title: Predicting the evolution and fate of massive stars in 1 and 3D
Abstract: In this colloquium, I will start by briefly reviewing the importance of stars in the Universe. I will then discuss how we can re-create stars on computers using a range of simulations using a few hours on a laptop to months on supercomputers. I will explain how these simulations help us understand and predict the structure, fate and impact of massive stars. In particular, I will present recent work studying how mass and rotation affect their fate across cosmic times and compare the predicted black-hole mass distribution to the latest gravitational waves detections from the LVK collaboration. I will then introduce the 321D (3 to 1-dimension) loop, a framework to improve 1D stellar evolution models using very detailed 3D hydrodynamic simulations.
第666回
Speaker: Vera Delfavero (Canadian Institute for Theoretical Astrophysics, University of Toronto)
Date: 4/2 Thursday
Time: 16:00 – 17:00
Place: Room 504 seminar room, building 4
Language: English
Title: Simulating Compact Binary Mergers and Gravitational Wave Detections from a Synthetic Universe
Abstract: For the past decade, the LIGO/Virgo/KAGRA (LVK) instruments have detected gravitational waves from merging black holes and neutron stars out to cosmological distances. Population synthesis approaches have simulated the formation channels for such events from isolated binary evolution and various dynamical environments. In this talk I discuss the methods I use to combine different population synthesis codes in order to construct compact binary populations on an observer’s light cone, treating the evolution of star formation and galaxy populations consistently between simulations representing different astrophysical assumptions.