The Physics of Ultracompact Stellar Binaries

Coordinators: Lars Bildsten, Deepto Chakrabarty, Gijs Nelemans

February 1-2, 2003(Saturday/Sunday)
Kavli Institute for Theoretical Physics
Santa Barbara, California

This will be a two day informal workshop following the Globular Clusters Conference that ends on Friday. Our intent is to have a series of 20 minute talks on Saturday, followed by some talks and discussions on Sunday. We have invited a number of speakers for Saturday, and we are open to all participants.

If you are interested in speaking or attending, please REGISTER HERE. The registration deadline is December 6, and there is no registration fee. We advise you to make your hotel arrangements promptly -- see the registration form for details.

Scientific Organizing Committee:
Lars Bildsten(KITP/UCSB)(
Deepto Chakrabarty(MIT)(
Gijs Nelemans(IoA/Cambridge)( )

Invited speakers/participants:
Lars Bildsten(KITP), Deepto Chakrabarty(MIT), Paul Groot(Nijmegen), Lee Homer(Washington), Erik Kuulkers(ESTEC), Tom Marsh(Southampton), Gijs Nelemans(IoA), Joe Patterson(Columbia), Sterl Phinney(Caltech), Phillipp Podsiadlowski(Oxford), Gavin Ramsay(MSSL), Saul Rappaport(MIT), Jan-Erik Solheim(Tromso/Oslo), Danny Steeghs(CfA), Tod Strohmayer(*, GSFC), Brian Warner(Cape Town)

(*) = not confirmed yet

For a list of confirmed attendees, click here.



The dramatic increase in the number of known interacting binaries with orbital periods below an hour, and the growing advantages of bringing together three separate communities(AM CVn white dwarf binaries; neutron star low-mass X-ray binaries; and gravitational wave astrophysics/LISA), are the motivations for this workshop meeting. The most relevant developments:
  • Recent progress in the AM CVn community includes discoveries of many new systems that are filling in the period distribution, possible detection of a number of short period systems with direct impact, and sufficient statistics on double degenerate systems to begin to understand AM CVn populations.
  • In the neutron star systems, the progress has been triggered by the recent discovery of two new systems, both of which are X-ray transients harboring an accreting millisecond pulsar. In addition, Chandra X-ray spectroscopy of at least one system suggests a chemically fractionated white dwarf donor which was previously crystallized, raising a number of interesting questions about white dwarf cooling and the properties of the donors in ultracompact systems.
  • Both of these classes of system are natural targets for gravitational wave detection with LISA.

All of these systems share a number of open questions:
  • Evolution to make such a system. Frequency of double degenerates, stability at the onset of mass transfer.
  • Accretion disk properties. Thermal stability of He and C/O accretion disks, spectral lines. Origin and evolution during outbursts and properties in quiescence.
  • Accretion disk precession/superhumps in extreme-mass-ratio systems.
  • Gravitational wave emission: many of these are candidates for direct detection by LISA.
  • Properties of the low-mass He or C/O donor: the donor stars are probably not the cold white dwarfs encountered in standard textbooks.