Special Session SS19  1 July 2022

Eccentric binaries with long, but too short, orbital periods

Aims and scope

The majority of stars are in binary systems and a non-negligible fraction of these will interact in some way, leading to various phenomena and types of stars. The interactions are more likely to take place when the primary star ascends the first or the asymptotic giant branch (AGB). In some cases, this will then lead in a common envelope (CE), with the orbit dramatically shrinking from several years to less than a few days, thereby leading to such important classes of objects as gravitational wave emitters, Type Ia and other supernovae, X-ray binaries, cataclysmic variables, and planetary nebulae, to name but a few. However, in many other cases, if a mass transfer does take place, such common envelope evolution is avoided. When dealing with low- and intermediate-mass stars, the outcome are binary systems containing a (pre-)white dwarf, but with orbital periods of hundreds to thousands of days and significant eccentricities. Such periods are too small to be the initial period of the system prior to the mass transfer (as an AGB star wouldn?t fit), but too long for the CE to have happened. Thus, these systems managed to shrink their orbits, but did so in a quite reasonable way, most likely by either stable or wind-Roche lobe overflow. Moreover, the fact that these systems show a non-zero eccentricity is also very puzzling. This is the case for many binary classes, all very important: post-AGB binaries, symbiotic stars, blue straggler stars, barium, CH and S stars, CEMP-s stars, etc. The reason why these systems managed to avoid CE, while still decreasing their orbital period, is still unknown and binary population synthesis studies mostly fail to reproduce the observed properties of these systems. With the advent of Gaia, as well as dedicated spectroscopic and interferometric surveys, we are now able to characterize more efficiently these families and provide constraints on theoretical models. Theoretical models and numerical simulations (whether in stellar evolution or hydrodynamical) are also becoming more and more sophisticated, and breakthroughs may be waiting for us on the corner. It is thus a right time to take stock of the available observational data and theories, and bring together all the scientists working in these adjacent fields to discuss these topics and lead progress in the field.

Programme

  • Post-AGB and binary planetary nebulae
  • Symbiotic stars
  • Barium, S stars, and their siblings
  • Blue and yellow stragglers, and other oddities in open clusters
  • Binary stellar evolution
  • Binary population synthesis
  • Mass transfer models

Invited speakers

  • David Jones (IAC)
  • Drisya Karinkuzhi (India)
  • Emily Leiner (Northwestern University, USA)
  • Holly Preece (MPA, Germany)

Scientific organisers

Henri M.J. Boffin (Chair), Maria José Rain, Ana Escorza, Alain Jorissen

Contact

hboffin @ eso.org

Updated on Sun Apr 03 13:59:06 CEST 2022