Astronomy Tea Talk
Speaker 1: Corey Bradshaw (PhD Candidate; University of Hamburg)
Title: Big Pulsations in Small Stars: The Remarkable Population of Large-Amplitude Hot-Subdwarf Pulsators
Abstract: B-type hot subdwarfs (sdBs) are a rare class of evolved stars occupying a sparsely populated region of the Hertzsprung–Russell diagram. Their existence is not readily explained by standard single-star evolutionary channels, indicating that binary interactions play a key role in their formation. In recent years, several classes of sdB-like stars have been found to exhibit remarkably large-amplitude, short-period pulsations dominated by low-order radial modes. These include radial-mode sdB variables (rm-sdBVs) and blue large-amplitude pulsators (BLAPs). The most extreme examples, the BLAPs, undergo dramatic changes in radial velocity, effective temperature, and surface acceleration as their radii vary drastically over short pulsation cycles of less than an hour. These pulsations can even be violent enough to generate shocks in the stellar atmosphere during phases of extreme compression. Despite their extraordinary behavior, the evolutionary origins of these objects remain largely unconstrained. Proposed formation pathways include envelope stripping by a binary companion, white-dwarf mergers, and even the surviving companions of Type Ia supernovae. These scenarios predict different stellar mass ranges and evolutionary states, making detailed spectroscopic observations essential for measuring their properties and distinguishing among their proposed origins. In this talk, I will present results from recent observational studies of large-amplitude hot-subdwarf pulsators. I will examine the observational and physical distinctions between the rm-sdBV and BLAP classes, characterize their extreme pulsation dynamics, and discuss how measurements of their physical properties can constrain the evolutionary pathways responsible for their formation.
Speaker 2: Andrew Boyle (PhD Candidate; University of North Carolina at Chapel Hill)
Title: The Fraction of Bound Stars as a Function of Age within 500 pc
Abstract: Open clusters are gifts to the curious astronomer looking to study how stars and planets evolve, providing populations with shared ages and birth environments. However, the timescale over which clusters disperse and populate the Galactic field remains poorly constrained, leaving open questions about how long these benchmarks survive, whether they represent typical birth environments, and where to find nearby young stars. In this talk, I will present a new study measuring the fraction of nearby stars in gravitationally bound clusters as a function of age. We find that only 20% of stars reside in bound clusters at 10 Myr, falling below 5% by 50 Myr. We also assess how well current observations connect young stars to recognizable stellar groups: by 20 Myr, most young stars cannot be assigned to a known association given current data. Many young unbound stars nevertheless remain concentrated around stellar groups before dispersing more broadly into the field. These results show that long-lived gravitational binding is a minority outcome for nearby stars. As the Galactic field grows, a shrinking population of surviving clusters remains to anchor studies of stellar and planetary evolution.