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Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars

We compile observations of early-type binaries identified via spectroscopy, eclipses, long-baseline interferometry, adaptive optics, common proper motion, etc. Each observational technique is sensitive to companions across a narrow parameter space of orbital periods P and mass ratios q. =. M-comp/M-1. After combining the samples from the various surveys and correcting for their respective selection effects, we find that the properties of companions to O-type and B-type main-sequence (MS) stars differ among three regimes. First, at short orbital periods P less than or similar to 20. days (separations a less than or similar to 0.4 au), the binaries have small eccentricities e... 0.4, favor modest mass ratios < q > less than or similar to 0.5, and exhibit a small excess of twins q. >. 0.95. Second, the companion frequency peaks at intermediate periods log P (days). approximate to. 3.5 (a approximate to 10 au), where the binaries have mass ratios weighted toward small values q. approximate to 0.2-0.3 and follow a Maxwellian " thermal" eccentricity distribution. Finally, companions with long orbital periods log P (days). approximate to 5.5-7.5 (a approximate to 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q. approximate to 0.1-1.0 that is nearly consistent with random pairings drawn from the initial mass function. We discuss these companion distributions and properties in the context of binary-star formation and evolution. We also reanalyze the binary statistics of solar-type MS primaries, taking into account that 30% +/-. 10% of single-lined spectroscopic binaries likely contain white dwarf companions instead of low-mass stellar secondaries. The mean frequency of stellar companions with q. >. 0.1 and log P (days). <. 8.0 per primary increases from 0.50. +/- 0.04 for solar-type MS primaries to 2.1. +/- 0.3 for O-type MS primaries. We fit joint probability density functions f (M-1, q, P, e) not equal f (M-1) f (q) f (P) f (e) to the corrected distributions, which can be incorporated into binary population synthesis studies.

Identiferoai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/624451
Date06 June 2017
CreatorsMoe, Maxwell, Di Stefano, Rosanne
ContributorsUniv Arizona, Steward Observ
PublisherIOP PUBLISHING LTD
Source SetsUniversity of Arizona
LanguageEnglish
Detected LanguageEnglish
TypeArticle
Rights© 2017. The American Astronomical Society. All rights reserved.
Relationhttp://stacks.iop.org/0067-0049/230/i=2/a=15?key=crossref.507df392cf615a9f3c6361791aa03cdc

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