投稿者: KatoRyo

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).