Rosanne Di Stefano


Binaries Triples Supersoft
X-rays History
of Science
The reason that primordial binaries fascinate me is that many have small enough orbits for the component stars to interact. Interactions can change the fate of each star in dramatic fashion. A main sequence star that gains significant mass from its companion will burn nuclear fuel at a higher rate; its lifetime is shortened. Furthermore, any binary that interacts prior to the time when one of its components has become a stellar remnant, will undergo a second phase during which mass is accreted by the remnant. Interacting binaries are the progenitors of all Type Ia supernovae (through either the double-degenerate or single-degenerate channel), all gravitationally mergering black holes and neutron stars, and the majority of hydrogen-poor core collapse supernovae. As I will discuss in the section on triples, some of these interacting binaries may be part of triple-star-systems or even of higher-order multiples.

At this point in time it is particularly important to reliably compute the rates of energetic events spawned by binaries. A crucial element for this enterprise is a correct model for the population of primordial binaries. The model must incorporate a wide range of primary masses and mass ratios, as well as the full range of orbital properties. Until the past few years, astronomers conducting population synthesis calculations relied on toy models of primordial binaries. The dissertation research of Max Moe has changed this. We have created a model based on the full range of prior observations, and have filled in gaps by using data collected by the OGLE team. The result is realistic distribution of properties for binaries with primary mass n the range from $1\, M_\odot -20\, M_\odot$. The title of the paper which presents the full set of results includes the phrase ``mind your Ps and Qs'', because an important feature of the results is that the distribution of orbital periods (``Ps'') and mass ratios (``Qs'') are not independent. This contrasts sharply with the results of previous papers which used as input observations from systems with a limited range of parameter. In addition, it links well with studies of more massive stars. Any population synthesis which aims to model systems having WDs or NSs in their final states must start with our distribution.

Along the way we made an interesting discovery of yound star systems in which a massive star is already on the main sequence and its companion is a low mass star which has yet to fully contract. Max, who was about to become a father, refered to these as ``mismatched twins in a stellar nursery''.

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