Seminar Speaker

Dr. Fan Liu (Monash University, Australia)

Venue

B10A, Basement of Kane Science Building, UCC

Time/Date 

4pm / Monday, 23 Sept, 2024

Title

Stellar Chemical Signatures of Planetary Ingestion and Planet Formation

Abstract

Ingestion of planetary material and/or planet formation can imprint a distinct chemical signature into the host star’s photosphere. Detecting these ‘planet signatures’, however, is challenging due to unknown occurrence rate, small amplitudes of planet signals and heterogeneous star samples with large differences in stellar ages. Co-natal stars (e.g. binary stars and open clusters) offer a unique opportunity to detect stellar chemical signatures of planets thanks to their shared origin and identical initial chemical composition. Here we establish and report high-precision chemical abundances (~ 0.015 dex; 3%) for a large, homogeneous sample of 125 pairs of stars moving together (91 with shared origin, i.e., co-natal) with a well defined selection function using Gaia DR3. Our sample represents a ten-fold increase in sample size and a least five-fold increase in precision over traditional spectroscopic analysis of binary star systems. We identified at least 7 new instances of planetary ingestion, corresponding to an occurrence rate of about 8%. An independent Bayesian indicator was deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion. Our study thus provides clear evidence of planet signatures and facilitates a deeper understanding of the star–planet–chemistry connection by providing observational constraints on the mechanisms of planet engulfment, formation and evolution.

Seminar Speaker

Jerry Moloney, Arizona Center for Mathematical Sciences and Wyant College of Optical Sciences
University of Arizona

Venue

G7, Kane Science Building, UCC

Time

4pm / Monday, 12th Sept, 2024

Title

"Microscopic physics of ultrafast resonantly and non-resonantly driven 3D and 2D
semiconducting materials”

Abstract

Semiconductors, undergoing resonant or far from resonant interactions with ultrashort
laser pulses, exhibit fundamentally different nonlinear and nonequilibrium behavior.
Semiconductor disk lasers (SDLs), where light is extracted through the top surface, are
subject to very strong departures from quasi-equilibrium Fermi distributions, when
operating in pulsed mode. GHz repetition rate, multi-wavelength channel SDLs,
accommodate individual mode-locked pulse trains, exhibit extreme nonlinear and
nonequilbrium dynamics and extract photons from separate kinetic holes burned within
carrier reservoirs. By way of contrast, highly non-resonant strong field interactions with 3D
and 2D semiconductors, promote both direct interband and intraband currents driving high
harmonic generation and involve carrier transport across the full Brillouin zone. My talk will
begin by reviewing a broad class of experiments by our group, guided by microscopic manybody
physics. I will then discuss the application of the microscopic theory to resonant laser
operation and strong-field off-resonant driven 3D and 2D semiconducting materials.