投稿者: KatoRyo

How should we explore the origin of astrophysical high-energy neutrinos using multi-messenger data?

Speaker: Wataru Iwakiri (ICEHAP, Chiba University)

Abstract:

Astrophysical high-energy neutrinos (HENs) are valuable tools for tracing the origins of high-energy cosmic rays. In the 2010s, the IceCube Neutrino Observatory, which has 5160 PMT detectors buried in the 1450-2450 m depth of the South Pole, enabled us to detect HENs above 100 TeV, allowing us to observe this new messenger. So far, the IceCube team has identified three objects as HEN sources: the TeV blazar TXS 0506+056, the Seyfert II galaxy NGC 1068, and a galactic plane. However, the primary source of the diffuse flux of astrophysical HENs observed by IceCube remains unclear. Correlation analyses of several years of accumulated data indicate that observed gamma-ray blazars contribute to less than 20% of the diffuse flux at most. Furthermore, observed HENs show no significant correlation with gamma-ray bursts and account for less than 0.4% of the diffuse flux. In this talk, I will discuss potential candidates for astrophysical HEN sources and how to reveal them using multi-messenger approaches.

Toward Understanding the Evolution of Exoplanetary Systems: Occurrence Rate and Stellar Age

Speaker: Kento Masuda (Osaka University)

Abstract:

The orbits and physical properties of exoplanets may continue to evolve long after their formation. For instance, it has long been discussed that the shortest-period planets may have orbits unstable to tidal dissipation, ultimately causing them to spiral into their host stars. Additionally, recent transit observations of low-mass planets have uncovered evidence of atmospheric escape, which may shed light on their internal composition. Understanding these evolutionary processes is vital for interpreting the diversity of exoplanetary systems and situating our solar system within a broader context. In this talk, I will present our ongoing efforts to statistically probe these changes by analyzing the dependence of exoplanet occurrence rates on stellar age. Specifically, I will discuss our recent work on deriving the age-dependent occurrence rates of giant planets orbiting Sun-like stars using isochronal ages, and will also mention insights into the rotation-based age estimation method gained from high-resolution spectroscopy of Sun-like stars in twin binaries.

Stellar Genealogy: Rare Gems in the Milky Way as Probes of the Chemical Evolution of the Universe

Speaker: Vinicius Placco (NSF NOIRLab)

Abstract:

The lowest metallicity stars in the Milky Way Halo are the fossil records of the earliest star-forming environments in the Universe. Chemo-dynamical studies of such rare objects can address a myriad of open questions, ranging from primordial nucleosynthesis and the mass function of the first stars to the nature of the astrophysical r-process and the early merger history of the Milky Way. The detailed abundance patterns of these stellar relics, which can only be obtained from high-resolution spectroscopy, help us understand the pathways that led to the chemical complexity we observe today. In this talk, I will present the status of near-field cosmology in the era of large-scale surveys. I will also describe recent results on the spectroscopic validation of low-metallicity stars selected from narrow-band photometry and the discovery of chemically peculiar stars in the Milky Way, which present chemical abundance patterns that match the ones from the ejecta of a neutron-star merger event and zero-metallicity supernovae. Combined, these efforts are adding key pieces of information to help stellar archaeologists constrain the chemical evolution of the Universe and solve the intricate chemo-dynamical puzzle of the formation of the Milky Way.

Near-infrared Variability of (Ultra) luminous Infrared Galaxies

Speaker: Shun Hatano (NAOJ/SOKENDAI)

Abstract:

The origin of infrared emission in ULIRGs—starburst or AGN—remains uncertain. Compactness is key for differentiation, but infrared imaging is limited to resolutions of ~10–100 pc. In this study, we utilize NEOWISE time-domain data to examine near-infrared variability of ULRIGs. We identify multiple ULIRGs showing significant near-infrared variability, despite not being classified as AGN on the BPT diagram.

Gravitational waves from first star remnants

Speaker: Tomoya Kinugawa (Shinshu University)

Abstract:

We calculated binary evolutions of first stars (Pop III) and showed that the typical chirp mass of Pop III binary black holes is ∼30Msun with a total mass of ∼60Msun and the maximum mass of Pop III BBH is more massive than the limit mass of the pair-instability supernovae.
Our result, which predicted gravitational wave events like GW150914 and GW190521, can explain the origin of massive stellar binary black hole mergers.
In this talk, I will explain Pop III binary evolutions and the properties of Pop III binary black hole mergers.
There is a good chance to check indirectly the existence of Pop III massive stars by gravitational waves.

Numerical Challenges in Computational Astrochemistry

Speaker: Tommaso Grassi (Max Planck for Extraterrestrial Physics)

Abstract:

Astrophysical numerical models encounter substantial computational challenges when integrating complex, time-dependent chemistry with physical processes. To address these issues, I will present the use of autoencoders for the dimensionality reduction of chemical networks, enabling efficient solutions with standard ODE solvers while preserving key network features. Additionally, I will discuss the application of interpretable machine learning techniques to connect synthetic spectra with model parameters, facilitating the assessment of information retention in observational data.

The observer dependence of the Hubble parameter

Speaker: Jessica Santiago (LeCosPa)

Abstract:

Given the exponential growth on the upcoming supernovae data available, the possibilities of rigorously testing the cosmological principle becomes ever more real. One of the ways to do so is by measuring the multipole decomposition of the Hubble and deceleration parameters.

In this presentation, I will discuss the observational-theoretical approach, initially introduced by Kristian & Sachs, which allows for the interpretation of data in non-homogeneous and anisotropic universes. I will also explore the effects introduced by the relative motion between the observer and the matter frame, and show how the induced kinematic dipole can be disentangled from intrinsic anisotropies in the matter distributions. To conclude, I will show that the luminosity distance must be corrected depending on the chosen frame of the observer (z_cmb vs. z_hel).