CASSA

CASSA Colloquium 12: Between Stars and Planets
2025-12-18 14:30 - 16:00 UTC | CASSA, IUB Main Building Rooftop, Plot 16, Aftabuddin Ahmed Road, Block B, Bashundhara RA (Main Building Rooftop), Dhaka, 1229, Bangladesh
Title: Between Stars and Planets: Unveiling the Hidden World of Transiting Brown Dwarfs
Speaker: Md Redyan Ahmed, PhD candidate, Sydney Institute for Astronomy (SIfA), University of Sydney, Australia.
Abstract: Transiting brown dwarfs occupy the mass range between stars and planets, placing them in a unique regime where the physics of both worlds begin to overlap. Wide-field surveys have identified more than 1,000 isolated brown dwarfs in the Solar neighbourhood, yet only about 50 systems are known to transit their host stars. With the arrival of the TESS mission, this picture has begun to change: the sample of transiting brown dwarfs is growing steadily, providing more systems with precisely measured masses and radii and opening new opportunities to study how these objects form and evolve. In this talk, I will give a short introduction to transiting brown dwarfs, how they are detected, and how their known population has been expanding over time. I will then present TOI-2155 b, a newly characterised transiting brown dwarf lying right at the hydrogen-burning mass limit. With a mass of 81 $M_J$ (Jupiter mass), it contributes an important new data point to the growing population of transiting brown dwarfs and helps us probe the structure, cooling, and formation pathways of objects near the low-mass star boundary.

CASSA Colloquium 13: Modelling the Last Major Merger that Shaped the Milky Way
2026-01-27 14:30 - 16:00
Speaker (in person): Istiak Akib, PhD candidate, Laboratoire d’Instrumentation et de Recherche en Astrophysique (LIRA), Observatoire de Paris, Paris Sciences et Lettres University (PSL), France.
Abstract: The last major merger of the Milky Way (MW) occurred 9-10 Gyr ago with an incoming galaxy known as the Gaia-Sausage Enceladus (GSE). We present the first hydrodynamical modelling of this collision using GIZMO. Our simulation reproduces the observed kinematic signatures of GSE. Furthermore, the merger model successfully recovers key structural and dynamical properties of the present-day MW, such as, the bulge, disk, bar and its rotation, four spiral arms, surface mass density, rotation curve, gas fraction, and star formation history. The simulations also show evidence for the Galactic warp and flare.
