Statistics of Young Visual Binary Stars: Implications for (Binary) Star Formation

Abstract

It is well known that most main sequence stars are members of binary and multiple systems (e.g. Abt 1983, Herczeg 1984). Recent survey work in nearby star forming regions (such as Taurus and Ophiuchus) has demonstrated that this is also the case for young low-mass pre-main-sequence stars (Zinnecker, Brandner, Reipurth 1992; Reipurth and Zinnecker 1993, Leinert et al. 1993, Ghez, Neugebauer, Matthews 1993, Simon et al. 1995). Therefore, it is fair to say that binary star formation is the rule in star formation, while single star formation (cf. Shu, Adams, and Lizano 1987) seems to be the exception. Statistical studies of pre-main-sequence binary stars are privileged over those of Main Sequence stars in that the former generally carry a closer memory of star formation and of binary formation mechanisms in particular. Also the memory of environmental influences on binary star formation (differences among young binaries born in T vs. OB associations or young star clusters) is not yet lost. We can also turn the question around and ask if there is something about Main Sequence binaries that we can use to learn about binary star formation without resorting to young pre-main-sequence objects. Indeed, the distribution of mass ratios might be such a property, provided mass ratios are frozen in since stellar birth. This is because on the Main Sequence there is a well-calibrated luminosity mass relation, while this relation is time-dependent for contracting pre-main-sequence objects; furthermore, accretion luminosity can contaminate the stellar luminosity in the case of actively accreting T Tauri stars, messing up any mass-luminosity relation.KeywordsStar FormationMain SequenceSemimajor AxisBinary StarBinary FrequencyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.