IvS Seminar: Adam Parkosidis (04/06/2026)

Adam Parkosidis - "Eccentricity as probe of mass-transfer physics" (IvS seminar 04/06/2026) Abstract: Binary star systems are common: at least half of solar-type stars and nearly all massive stars reside in binaries. Binary interactions such as mass transfer, tides, common-envelope phases, and mergers profoundly alter stellar evolution, producing various phenomena that single-star evolution cannot explain. Examples range from chemically peculiar stars and blue stragglers to supernovae, gamma-ray bursts, and gravitational-wave mergers. More recently, large surveys, such as Gaia and TESS, have revolutionized our census of binaries across the Galaxy, revealing that eccentricity in wide, evolved post-interaction systems is far more common than previously thought. This suggests a fundamental link between binary interactions and orbital eccentricity, yet the theoretical origin remains poorly understood and synthetic models still struggle to reproduce the observed orbital properties. In this colloquium, I will discuss our evolving understanding of eccentricity in the context of interacting binaries, review different eccentricity-pumping mechanisms and present the General Mass Transfer (GeMT) model, a new semianalytic framework for the secular orbital evolution of mass-transferring (MT) binaries. By comparing predictions to observations, I will demonstrate that nonzero eccentricity is a natural outcome of MT and depends directly on key MT parameters. Given the multitude of eccentric post-MT binaries with components ranging from low- to high-mass stars to compact objects, I will show that post-MT eccentricities offer a new window onto binary evolution, presenting a powerful tool to constrain uncertain MT parameters and formation histories across diverse populations.